Sunday, September 30, 2012

The Design: Primary Mirror - Part 1

Quick Recap

In my last new telescope related post, I finalized my decision to build a telescope rather than buy.  Towards the end of that post, I did some thinking about my budget.  After some quick calculations, it became pretty clear that the mirror has a huge impact on the cost. 

It seems that no matter what size mirror I buy, the rest of the scope is going to be pretty much the same price.  A couple of parts, namely the primary cell and secondary, vary a bit with the size of the mirror, but everything else remains constant.  I'm estimating this 'base price' for the telescope, sans mirror, at about $1500.

The Long List

After looking around for a bit online, here is my long list of 17 potential telescope mirrors.  They are ordered by name of the company that produces them:

CompanyMaterialSizef-ratioHeightXT8 MultPriceLink
HubblePyrex / Sandwich1457231775link
Waite ResearchSUPREMAX 3314.54603.32650link
Waite ResearchSUPREMAX 3315461.53.52800link
Waite ResearchSUPREMAX 331646543000link
ZambutoSUPREMAX 3314.54.5673.32650link
ZambutoSUPREMAX 3315461.53.53360link
ZambutoSUPREMAX 331646543924link

*XT8 Mult is how many times more area this new mirror would be than my current 8" mirror

Two obvious points, there are a lot of options (this may not even be a complete list), and they vary quite a bit in price.  If I choose the least expensive option, the mirror will make up 50% of the $3000 cost of the telescope.  If I choose the most expensive, the mirror will make up 73% of the $5500 cost.

So this is the decision that seems to have the most impact on the cost, and probably quality, of my new telescope.  A telescope I hope will last a long time.  I'm beginning to dread this decision.

A Disappointing Realization

When I was thinking about the size of my new telescope a while back, I felt that something in the 14-16" f4.5 range met my criteria for portability, and for flat footed observing.  Along with price and overall aperture these are two of my most important considerations.  After a recent experience at the Pacific Astronomy and Telescope Show, I think my allowable size range might be a little off.

Me and a LightBridge 16" f4.5 Telescope
You can pretty much see in the photo above, that my eye is NOWHERE NEAR the eyepiece...

In order to observe with my feet on the ground, without a ladder, step-stool, box, or the like, I have to be able to reach the eyepiece through most of the range of motion of my new telescope.  Observing with the telescope straight up is somewhat awkward, so I'm willing to forego a bit of sky close to 90 degrees, but I am really committed to a flat foot telescope.  This means that the eyepiece height has to be at or below 62", which is the distance my eyes are from the ground, for the vast majority of angles.

The main factor in how high the eyepiece of a dobsonian telescope is from the ground is the focal length of the telescope, which is determined by the size of the mirror and it's Focal Ratio.  The focal ratio (or f-ratio) of a telescope is the relationship between the size of the mirror and the distance away from that mirror the converging light beam reaches focus.  In short, the higher the f-ratio the longer a telescope will be for a given size mirror.  There are some other design issues that can raise or lower the eyepiece a few inches, but really it's the focal length of the scope.

In retrospect, it should have been obvious to me that a 16" f4.5 scope, with an eyepiece height at zenith (pointed straight up) of somewhere around 73" would be no good.  I was hopeful that my rough calculations of eyepiece height might be off.  After all, eyepiece height is not exactly the focal length of the scope since the light path is turned at a right angle and the mirror is not sitting on the ground.  I also figured that even if the height at zenith was too much, that pointing the scope down just a bit would get the eyepiece and my eye better aligned.  

Seeing a 16" f/4.5 scope in person, standing next to it, moving it to various altitudes, really showed me just how wrong I was.  It was not until lower than 70 degrees that the eyepiece got to a height I could actually view through.  This means I would give up the upper 40-50 degree patch  of the sky, which is pretty much the darkest and most awesome part.  

So I am ruling out any mirror that will produce an eyepiece height greater than 65".  Even at 65" I could not use the scope straight up, but it would let me get close.  I think this height would be comfortable for me, and the area of the sky that would be inaccessible would be pretty small.  

Cut #1 - Eyepiece Height

All of that long winded explanation means I have to go with something more like a 16" f/4, or a smaller f/4.5 mirror.  This limits my options a bit, which is good, because too many options are proven to make people anxious and less satisfied with their decisions.  Sadly, 16" f/4.5 is a very common size, and common tends to equal less expensive.  Here is the slightly shorter list, now with 13 options:

CompanyMaterialSizef-ratioHeightxt8 MultPriceLink
Waite ResearchSUPREMAX 3314.54603.32650link
Waite ResearchSUPREMAX 3315461.53.52800link
Waite ResearchSUPREMAX 331646543000link
ZambutoSUPREMAX 3315461.53.53360link
ZambutoSUPREMAX 331646543924link

Cut #2 - Price

I could theoretically save up money for as long as I need to get the most expensive mirror on the list above, but every month I save is another month I don't get to use my new telescope.  That's why I set a goal of one year; I'd love to have the telescope ready to go for the summer star party season 2013.  Spending more than $4000 on this project is probably unrealistic if I want to meet my goal.  So I'm going to have to spend less than $2500 on the mirror to make it work.  That brings us down to these 4 options:

CompanyMaterialSizef-ratioHeightxt8 MultPriceLink

I still think those are a lot of good options, based on some of the tests and opinions I have found so far.  Ultimately, there is only room for one primary mirror in my new telescope, so I'm going to have to figure out some way to evaluate these mirrors.

The Short List

Now that I have a manageable list, I need to figure out what I need to do to convince myself to buy one.  All things being equal, I want the most bang for my buck.  A good first way to compare these options is dollars per inch of area.  Here is the same list, with dollars per inch replacing links, and sorted by the same:

CompanyMaterialSizef-ratioHeightxt8 MultPrice$/Inch

Now this is a list I can do some thinking about!  It's reasonably short and ordered by value.

I'm hoping to decide in the next week or two and see if I can place an order.  Here are my thoughts on each of these options, and what I want to look into:

Discovery 15" f/4.2: There is a virtue in being the least expensive.  The money saved could potentially go for a nicer focuser, or perhaps a nice fan system.  I have not read any information about their quality, so I'll definitely need to do a bit more digging

Pegasus 14.5" f/4.3: About 7% smaller than the 15", but this does not sound like much.  I've heard generally good things about Pegasus mirrors, but is the extra quality worth less aperture and more cost?

O.W.L 15" f/4: Almost $800 more than the Discovery, but slightly lower f-ratio for a shorter scope.  In fact, I'd be able to use this one straight up!  Not sure how the quality compares to the Discovery mirror. This is another company I've not heard much about, so I'll have to try to find some reviews.

LightHolder 14.5" f/4.1: The most expensive inches of aperture of the bunch, but LightHolder is supposed to be very good.  Again, will I notice?  Is it $340 better than the Pegasus?

So my next step is to try to learn about mirror quality, and how much difference it makes at the eyepiece.  I'm sure that there are differences in quality that can be measured with various machinery, but are these differences perceptible?

Another consideration is lead time.  Since most of these companies make mirrors to order, I'm going to email each one to see what their current wait/lead time is.  I'll let you know in a future post what sort of responses I get.

A Eulogy for the 16"

I'd like to pause here for a second to mourn the passing of the 16" options.  There is just something nice, round and magical, with the idea of upgrading to a telescope that offers 4x the light gathering of my existing telescope.  16" offers 21% more aperture than the 14.5", and 13% more than the 15" mirrors.  If I was able to go with an f/4.5 and still reach the eyepiece, 16" would be within my grasp!  Curse my shortness!

I'm very much tempted to open up my budget a little bit to get to the 16" mark.  I'd have to go at least $2900 to get there.  That's $1100 more than the Discovery 15" above!  I'm just not sure it's worth it for 13% more light gathering.

One very interesting option that I dropped due to price was the Pegasus 16" f/3.5.  For $3100 it would have given my the LOWEST eyepiece height out of any of the options, a mere 57" off the ground!  That complete telescope would cost roughly $4700, about 46% more than a 15" based on the Discovery mirror.

What do you think?

I'm going to do some research on manufacturing methods, reputation, and test reports, but ultimately, How much difference does the quality of a mirror make to the visual observer?  Have you had any relevant experience?  Do you know, or have you heard, anything about the mirrors on my short list?  Are there any I missed?

Also, if I'm going to have this telescope for a long time, will I end up disappointed if I don't spend 50% more and get a 16" scope?  That fast 16" Pegasus is tempting!  I'd love to hear what you think.

Wednesday, September 26, 2012

PATS 2012 - Good Products, Great Fun, and Sad Realizations

A Tale of Two Shows

Last Sunday I made some time to visit the Pacific Astronomy and Telescope Show in Pasadena.  It's a yearly exposition of astronomy related vendors and clubs which claims to be "the largest and most exciting astronomy show on the west coast".  This was the second time I've checked it out, and can't say that it's either the largest, or most exciting astronomy show on the west coast, but it's a nice way to spend and afternoon and maybe find a deal or two from one of the vendors.

The show runs Saturday and Sunday; tickets at the door are $20.  I think last year I purchased in advance and received some discount. There is an exhibit hall with booths setup and a series of presentations in adjacent rooms.  The Pasadena convention center is pretty sizable, and the PATS is not really large enough to fill the entire space.  This year it was sharing the main exhibition hall with the Bride World Bride Expo. 

As I was walking towards the hall after purchasing my ticket, it was pretty easy to guess who was attending which event.  The people walking around with the Sky and Telescope bags, or with arms full of astro gear were here for the PATS.  Everyone else had copies of Bridal World or flowers.  Lots of flowers.

PATS was sharing with the Bridal Expo... the line is for the Expo.  There was no line to enter the PATS exhibits.

The Exhibition Hall

Everybody attending the show got a free issue of Sky and Telescope and a program upon entry.  I briefly glanced at the program schedule and did not see anything to interest me, so I headed straight to the exhibits.  This was only my second year, and I remember it being pretty small, but this year seemed even smaller.  According to the program there were 44 vendors, and they were arranged in four rows.

I did an initial walk through of the exhibit in about 15 minutes or so and even though it was not a huge show, it was very nice to be surrounded by like minded folks.  The booths ranged from the large and professional, to the small and volunteer.  It was not very crowded, which meant the venders were available to chat and spend some actual time with the attendees.

There was not really any specific thing I was looking for.  I thought that it would be nice to see some of the newer gear, talk to some of the organizations and clubs, and maybe find something for my telescope project.  If nothing else I figured it was a nice way to spend a Sunday afternoon.

The Big Names

As one would expect the three heavyweights in telescopes and accessories were on hand.  Meade had a large booth, spaciously appointed with selections of their current line.  They had mounts, SCT's and one 16" LightBridge to round things out.  This was the first time I had seen their convertible Alt-Az/GEM mount.  It seemed pretty solid and was presented in the Alt/Az dual scope configuration.  Pretty neat.

Meade Instruments

Right across the way was the smaller, but still impressive, Celestron booth.  They had a nice selection of their SCTs on GEMs, along with eyepieces and some educational items, such as microscopes and a very small/cheap newtonian.  You can see the little guy at the screen right end of the table in the pictures below.

Celestron.  Notice the little guy at the far end of the table.  A Newtonian Finder?

The FirstScope is a 76mm f4 reflector with a spherical mirror.  Immediately upon seeing it's diminutive size, I was launched into a several minute daydream of using it as a finder.  I suspect it would work, but it would be difficult to get the image into the 'correct' orientation.  Some people have no issue with the mental gymnastics required for non-correct image finders.  I, however, prefer to use finders that orient the sky the same as my un-aided eyes, so this dream was dashed.  

Around the corner, Tele Vue had a large, but sparse booth.  They only have so many telescopes in their line, and eyepieces don't take up much space.  It is pretty impressive to see a full set of Ethos, Nagler or Delos eyepieces though.  Speaking of which, there is still time to enter the the International Dark Skies Association Dark Sky Giveaway for a chance to win an entire set of Ethos eyepieces!

TeleVue - Home of the Eyepiece!

On the right side of the picture above you can see a gentleman pointing to a black case.  He's probably explaining to the other gentleman that you can use one telescope to collimate another!  This was the most interesting thing in the booth as far as I was concerned.  There was an artificial star stuck in the diagonal of one telescope, which was then pointed at and rigidly joined to a second you wanted to collimate.  The optics of the first scope made the star appear like it was very far away, far enough to use it to collimate or star test.  It was a clever idea and an interesting experiment in optics.

The Up and Comers

Aside from the bigger names, there were a few other telescope manufacturers.  PlaneWave and Williams Optics were there, showing two different approaches to astrophotography.  PlaneWave produces very well corrected, large aperture, exotic telescope designs mainly for non-visual use.

PlaneWave Instruments

Williams Optics sells smaller aperture refractors, also geared more towards astrophotography.  They produce very high-quality versions of a tried and true design with some higher tech innovations.  Both booths really showcased the quality of manufacturing from these smaller run shops.  Not to say that Meade or Celestron don't produce quality scopes, but the fit and finish from these two are difficult to beat.

Williams Optics


I spent a fair amount of time talking to the guy at the Thirty Meter Telescope (TMT) booth.  Observing is a part of the hobby I enjoy quite a bit, but I also have an interest in the science and technology of astronomy and this project has it all.  When complete, this will be the largest telescope ever produced.  Well, it might actually end up being the second largest, as the Europeans are working on a 39 meter scope.

The Thirty Meter Telescope Outreach Booth
It was fascinating to hear about the design of the scope, but also about some of the long term issues such a large telescope faces.  Many amateur astronomers are aware that the reflective coatings on mirrors degrade with time.  Often, mirrors are sent out for re-coating to restore their reflectivity.  To maintain the highest level of performance continuously, so that the massive investment can be best utilized, the TMT will be swapping out several mirror segments weekly for re-coating.  This will allow them to re-coat each of the 492 segments every two years.

After the first few minutes I was ready to donate to help the cause.  Turns out, they are not looking for donations, just doing general outreach.  Very cool.  If you love telescopes, the website is an interesting read.

The Vendors

Theoretically, all the booths were vendors, but there were only a few booths you could actually buy things from and take them home.  The two largest were Woodland Hills Camera & Telescope and Oceanside Photo & Telescope.  Both had nice booths with a wide selection of things to tempt the crowd.

Woodland Hills Camera & Telescope
OPT - Oceanside Photo & Telescope
Both offer special pricing, and no sales tax, at the show.  This makes almost everything at least 20% cheaper, so it's a nice time to buy.  If you don't feel comfortable deciding on your feet, they will honor the same deal if you call or visit their websites a few days after the show and mention PATS.  I found both crews to be very friendly and knowledgeable.

Among the vendors actually selling product was Howie Glatter.  He's an ex-hippie who now spends his time inventing and patenting useful things for telescopes, mainly in the area of collimation.  It was great fun to talk to him about his design and manufacturing process, and the merits of various types of collimation equipment and techniques.  He's very friendly and very knowledgable.  All his products were wonderfully machined, solid and well designed.

Howie Glatter, Inventor / Collimator
One of his products I had never seen before were nebula filters designed to fit over the eye lens of binoculars.  As soon as I saw this I was struck by the cleverness of the idea and his implementation.  Compared to the objective lens, the eye lens has much less area to cover, reducing price and weight.  To protect the delicate filter from eye gunk, he sandwiches it between two pieces of optical glass.  This allows you to clean them without worrying about scratching the coating.

Eye Lens Binocular Nebula Filters - Very cool idea
To affix the filters to the binoculars, he mounts them in a metal ring of various sizes.  By ordering a size the correct diameter for your binos, it can be held in place by the rubber eye guard.  You roll the cup down, place the filters over the eye lens and roll the eye guard back up holding the metal ring in place.  It's tricky to describe in words, but simple and easy when you see it in person.  If I were not planning on buying a new pair of binoculars in the semi-near future, I'd think about buying a set.

The Truth About 16" Scopes

As I was heading out, I saw that the Meade both was relatively empty and decided that I should really see what a 16" scope would be like to use.  I'm leaning towards this size, and I was hoping it would allow me to observe without a ladder or stool.  Sadly, I'm not so sure this would be the case.  

Me and a 16" LightBridge.  Notice they Eyepiece Height
One of the Meade reps was kind enough to take my photo next to the LightBridge pointed at Zenith.  I'm about 5' 6" tall, a bit under average for a male human, and there was a pretty wide gulf between my eye and the eyepiece.  There was another show attendee, slightly taller than average, who could walk right up to the scope and peer into the eyepiece... sigh.  I did not measure exactly, but I figure anything over 70 degrees would be a stretch for me on this 16" f4.5 scope.

So... what does this mean for my plans?  It means I have to think about them.  Observing at the zenith is uncomfortable anyway, so maybe it's not bad?  Perhaps a small box would not be too cumbersome?  Can I find an f4 mirror at a reasonable price?  Is a 15" a better size?  Would another structure offer a significantly lower eyepiece?  Are elevator shoes expensive?  There are a lot of questions to consider.  I'd love to hear your thoughts on the questions above, or about aperture vs. eyepiece height, or any experiences you have had observing with feet on, or off, the ground.  

The PATS Bounty

So I left the show with a lot of questions about my telescope design, but I also carried out some other things.  Before leaving I gave into the tempting opportunity to purchase a new finder scope.  I knew I wanted something larger than 50mm for my new scope and I was leaning towards an Orion ST 80, then I saw this great StellarVue 80mm finder.  

The StellarVue is an 80mm f3.75 achromat that comes complete with an erecting prism, helical focuser, and 23mm eyepiece with reticle.  It's roughly the same price as the 80mm f5 Orion with an erect image prism and 32mm plossl, both of which would provide about the same 3.9 deg TFOV.  

After some quick cell phone research and a few calculations I choose the StellarVue for two reasons.  First, it's shorter focal length means I can get an even wider 5.2 deg field of view with a 32mm plossl if I decide to upgrade it.  Second, it's just a bit over 50% of the weight of the Orion, which will help with any potential balance issues.

My Haul from the Show
You can see the finder, with mounting rings, in the picture above.  I thought the 50mm finder was large when I first got it, the 80mm is more like a small scope than a large finder.  It looks almost comical on the Orion XT8, but I think it will be much more proportional on my new scope.  The comical nature won't stop me from using it in the meantime though.

The extra aperture will be nice to hunt down some of the NGC objects and dimmer Messiers as I progress onto dimmer and more difficult objects.  The scope/finder should also provide nice views of the wide field objects like the Double Cluster, or the Coathanger.  I'm looking forward to sweeping it over the Milky Way under a dark sky!  As soon as I have a chance to try it out, I'll write up a review here.  That new moon can't come soon enough.

If you are in the Los Angeles area next year in September, I would suggest checking out PATS.  At the very least it's something to do between observing sessions!

Monday, September 24, 2012

Build Vs. Buy: Build for the Win!

My work has been a bit crazy lately, but I was fortunate enough to get some needed time off and spend several nights observing in Joshua Tree last weekend around the new moon.  The observing at night was great, once I get my photo's together and have a few free moments, I'll post a report.  During the day I had some time to compare some options and think a lot about my next telescope, and I've decided...

I'm going to build

Ever since the idea for this project really solidified in my head, I always imagined building the telescope I want;  Not from scratch, but by assembling the parts I hand picked.  However, I wanted to take a look at what's out there and make sure I could not get a better deal with a commercially available telescope.  Something already built that would fit my requirements.

To help make my decision, I took a look at all the parts that make up a telescope, so I could look at the commercial options out there compared with what I could buy.  It helped a bit to solidify what I was looking for in a telescope, and ruled out several commercial options (for more detailed look at each of these commercial options, check out this post from 10MinuteAstronomy):

  • Orion XTxx Scopes: There are several goto, and push to, scopes in 14 and 16" size from Orion.  Across the board they are just too heavy, and I don't really need the extra cost and complexity of the Goto/Push to.
  • Hubble Optics 16" ultralight dob: Price seems good, very portable, but the reviews indicate mechanical issues.  If I have to make a lot of modifications to make it smooth and stable, I might as well get something more solid right off the bat.
  • Meade LightBridge 16": Price is very good, but they are pretty heavy.  There have also been mixed reports regarding the motion and overall build/design.  It seems like with a bit of work these can turn out to be nice scopes, but they are still larger and heavier than I think are needed.
  • T-Scope, Obsession, StarStructure, et. al.: All very nice options, and they all seem like they could be configured to meet my needs, but I'm pretty sure I can assemble a scope just about a nice, and make some more specific decisions along the way, for less money.  

Additionally, I do like to work with my hands, and I'm sure I'd enjoy at least some parts of assembling my own telescope.

Assembly Budget

Part of evaluating commercial scopes, particularly the high end ones that seem to meet my requirements, was figuring out if they were more or less I would spend to build.  Armed with my broad list of parts, I fleshed out a rough budget.

None of these numbers are very specific, they represent average costs for the components I would need.  As I have time, I'll research each of these components and figure out which specific ones will work best for me and my budget.

16" Primary Mirror$1400Based on JMI Primary/Secondary Kit
Secondary Mirror$0Included Above
Mirror Cell$250Multi Point Flotation Type Cell
Structure$700Based on Dob Stuff 13"-16" Kit

This assumes a 16" scope, which may not be the size I choose based on a recent experience at the Pacific Astronomy and Telescope Show (more on that later), but the pricing for every component except the mirror and mirror cell is valid for anything roughly 13-16".  In figuring out an ballpark price for each part, it was pretty clear that the mirror is both the most expensive, and the most variable component.

You can buy $500+ dollar focusers, and that would be two or three times the cost I budgeted, but the change to the overall budget would be only 11% or so.  Conversely, I might be able to save a bit of money if I build my structure from scratch, rather than buying the DobStuff kit, but it would not be much compared to the overall budget and I'm not sure it would be a good investment of my time.

The Mirror, however, is the big variable.  In looking around, the JMI option listed above was the least expensive option I found; The costs can easily go to double that price.  If the mirror were $2800, that would increase the overall budget by a whopping 52%!

Next Step: Mirror

If I'm going to try to meet my one year timeline, I'll need to eventually start purchasing stuff, and the mirror seems like the first decision to be made.  It's the largest component, cost wise, and it's size, weight and mounting will influence other decisions.  So I figured it's the component I should research and decide on first.

I've put together a preliminary list of manufacturers, but they are a bit hard to find and I expect my list is incomplete.  Please leave a comment if you are aware of, or have seen reviews for, any mirror manufacturers or suppliers in the 14-16" range.  I'd love to hear what you think.

Saturday, September 8, 2012

My Current Eyepieces - A Lesson About Investing

A few weeks back I did a post about My Current Scopes.  I wanted to take stock of the two telescopes I have, share a bit about how and why I decided to buy them, and to ruminate about what each has to offer.  My goal was to help me get a better idea of what's important to me in a telescope by really thinking about my experiences to date, and to see if there was anything I wanted to sell or salvage in pursuit of my new telescope.

It seemed popular and elicited some useful feedback, so here is another somewhat rambling look at another part of my current observing kit; eyepieces.  I realized pretty quickly that eyepieces were a huge part of the observing experience.  Like most parts of a telescope, they can work well and disappear into the experience, or they can work poorly and remind you of their frustrating presence all too often.

Before I dive into my eyepiece experiences,  I'll warn its a bit long and can be technical in parts.  This blog is aimed mainly at people who have been observing for a while, so I'm going to assume a bit of eyepiece jargon knowledge.  If you'd like to get up to speed, or need a refresher, you might want to check out Astronomical Telescope Eyepieces: A Discussion for the Beginner.

My Eyepiece Menagerie with the XT8

BrandTypeMMAfovReliefX PupMagTfov
OrionEpic ED 212.555202.11960.57
OrionEpic ED 27.555201.271600.34
TeleviewNagler 61382122.20920.89

If you are looking at the chart above and thinking "This seems a little haphazard" you are right.  They are listed in the order I acquired them and they seem to show an almost studied disregard for planning.  There is a story, and I've learned something from it.

The Story

The first telescope I purchased as an adult was my Orion XT8 dob and it came with the 25mm plossl eyepiece.  I used it for several observing sessions, enjoying the views and getting oriented in they sky again after a long absence.  The 25mm plossl gave pleasing views and was comfortable to use, but it was not long before I felt like I needed some options.  Particularly some higher magnifications for globulars, planetary nebula, and the occasional peek at one our solar system neighbors.

Orion Epic ED2s

After doing a very little bit of research and seeing some positive reviews of the relatively inexpensive ( < $100 ) Orion Epic ED2 eyepieces, I jumped in and purchased two; a 12.5mm and 7.5mm.  These gave me basically 2x and 3.3x times the magnification of the included 25mm plossl with a little more apparent field of view and eye relief.

I debated getting a 2x barlow instead of the 12.5 as it would give me the same magnification as the 12.5mm, and I'm not really sure in retrospect why I did not.  It might be because of the terrible barlow I had when I was a kid.  It really seemed to degrade the view, and with the added inconvenience of another set screw to work in the dark, I just never really seemed to use it.  Every time I purchase a new eyepiece, I think about a barlow, or powermate, instead.  Maybe next time....

The Epic ED2's did provide more options when I was observing, and I did enjoy the higher magnification on globulars and planetary nebula.  Looking back through my observing logs, the 12.5mm seemed to get a bit of use, but I seldom used the 7.5mm.  This is somewhat because I often view extended objects and through my 8" scope they can get pretty dim at high magnification, but I think it was mostly because both were uncomfortable to use, particularly the 7.5mm.

A few online reviews mentioned some issues with 'kidney beaning', darkening of portions of the field if your eye was not in the perfect position relative to the eye lens, but I blithely ignored them.  I had never really seen the effect before, the 25mm plossl was easy to view through, and it did not really sound so bad.  "Okay, so I just look through the eyepiece dead center, no problem at all".

Sadly, this was not as easy as I thought and it was just distracting enough that I found myself avoiding the eyepieces, even when an object probably would have benefited from some more magnification.  I'm not an optical engineer, so I can't really say why one eyepiece with 20mm of eye relief  would exhibit this issue, when another with the same eye relief would not, but these eyepieces seemed positively vexing to view through.  The 12.5mm seemed better in this regard, so it got more use than it's brethren, but even at their comparatively low price point, I felt I was not really getting my money's worth.

Enter Televue

Disenchanted by my experiments at the high end of magnification, I decided to expand my eyepiece collection in the other direction.  There are some great objects, or collections of objects,  that are over the 1 degree field my 25mm plossl provided.  I had also recently purchased my Celestron C6 and, with a longer focal length than my XT8, I wanted something that would provide a wider field.

The C6 has a 1.25" visual back, and I want to be able to share eyepieces as much as possible, so I started looking into the widest true field of view (tfov) 1.25" eyepiece I could get.  After some reading and math, A 32mm plossl seemed like the way to go.  There were some exotic designs that could squeeze a little more tfov out of 1.25", but they were pricey and it seemed like a lot of additional money, complexity, and optical surfaces, to get a very fractional increase.  Besides, I did enjoy the view through my 25mm plossl, and I was a little shy about more exotic designs based on my experience with the ED2's.

I'd read just about everywhere that Televue is the cadillac of eyepiece manufacturers.  Reviews of Ethos' or Naglers abound with tales of life altering views and hefty price tags.  So when I started looking at 32mm plossls I was surprised to see them among the results.  Amazon had them for a bit over $100, and I just happened to have a gift card, so I made the leap.

The eyepiece arrived a few days later and as soon as I opened it I felt good about my purchase.  It was well packaged in a substantial box, and it has the feel of fine craftsmanship.  The knurling was distinct, clean and even, and the text was crisp and easy to read.  These are small touches, but they added up the impression of a long lasting piece of kit.

When I took it out under the stars, the view was great.  It was a very comfortable eyepiece to use, had high contrast and a view as sharp as I had seen through my telescopes.  In short order it became my favorite eyepiece to use in both scopes and the double cluster with the XT8 and the 32mm became one of my favorite targets.

Eyepieces as Investments

My experience with the Televue 32mm plossl on the one hand, and the Orion Epic ED2's on the other, showed me how important an eyepiece is to my overall observing experience.  Since they can be used with any telescope I might own, and can last a lifetime with proper care, I decided I was going to invest in them.  I figured it would take longer for me to fill out my eyepiece case, but I hoped I'd be happy with each and not regret my purchases.

It was about this time that I wished I had more observing friends, or that I was part of an astro-club.  I could only scour reviews and go with my limited experience to decide on which eyepieces I wanted to save up for and purchase.  Looking through a variety of eyepieces owned by other people would have been a wonderful decision making tool.  I've still not joined a local club... something that I need to rectify sometime soon.

Nagler Type 6 13mm

A few months later I had saved up enough money to purchase a Televue Nagler Type 6 13mm.  It seemed like a good next step in magnification, providing a slightly smaller tfov than my 25mm plossl, but with almost double the magnification.  It's also small and light, which I really like.  No balance issues and it's easy to handle in the dark.

The Nagler 13mm has proven to be a spectacular eyepiece.  I really can't say anything negative about it, save for the price.  It seemed high when I purchased it, but it's become a staple of my observing and I never feel it get in the way of what I am viewing.  If there is an object that can take some additional magnification, I never hesitate to switch eyepieces now.  I do wish it was parfocal with the 32mm plossl, and I'm tempted to try some parfocalizing rings to make switching magnifications even easier.

Delos 6mm

To round out my eyepiece set I wanted something about double the magnification of the 13mm Nagler.  My first thought was a 7mm Nagler.  I was really pleased with the 13mm and the small size was attractive compared to other short focal length premium eyepieces.  As I was saving up and contemplating my purchase Televue released their first round of Delos eyepieces.

The Delos are designed for 72 degree, 20 mm eye relief at every focal length.  Early reviews were very good, comparing them very favorably to the legendary Ethos eyepieces, only with a smaller apparent field of view (afov).  As time went on, people posted head to head comparisons with similar focal length Naglers and it was pretty much universal that the Delos offered a better experience for a small (~12%) extra cost.

When I was ready, I spent the extra money and purchased the Delos.  I don't have a similar Nagler to compare it with, but I do find the sharpness and color rendition superior to my 13mm, which is absolutely no slouch!  It's incredibly comfortable to use, and my only issue is the size and weight.

Size Comparison: Delos 6mm, Nagler 13mm, Plossl 32mm
As you can see, it's somewhat of a beast.  Not the largest, or heaviest, eyepiece out there, but compared to the Nagler and Plossl, it's very large.  In the diagonal of my C6 it's almost comical.  Fortunately, I only have balance issues in my dob if I'm observing lower in the sky, and engaging the friction springs on the XT8 generally holds the scope in place.  I'd really like to do a side by side with a 7mm or 5mm Nagler someday just to see if the extra size is worth it.

The Lesson

I've been very happy with my more recent eyepiece purchases.  To me, and my observing experience, they were completely worth the extra money.  It was a learning experience, and I want to apply my lesson to my better telescope project.

My intention is to buy or build a telescope which will last me a long time.  Both in durability, and  usefulness.  I want to be frugal, but ultimately if I don't enjoy the observing experience, it will be a false frugality as I'll just end up purchasing another scope, or replacing cheap parts.

I've already been saving money for a while, and I expect that I'll be saving for a while to come before I can invest in my new telescope.  I'm planning to use that time exploring my options and thinking hard about where the quality/price sweet spot is for each component.  At least when I buy my new telescope, I'll already have some fine eyepieces to use!

Since I've narrowed my better scope down to something in the 14-16" range, I thought it might be interesting to plug a hypothetical 16" f4.5 scope into my eyepiece/telescope spreadsheet to see what I could expect.

My Current Eyepiece Collection with a hypothetical 16" f4.5

BrandTypeMMAfovReliefX PupMagTfov
TeleviewNagler 61382122.201400.58

Not bad, but eventually I expect to purchase some sort of wide field 2" eyepiece to get me back to a 1+ degree field, and perhaps add a bit more magnification to take advantage of the increased light collection and resolution a 3-4x jump in aperture might afford.

I'd be interested to hear what anyone has to say about their own experiences trying to balance cost and quality.  With plenty of time ahead to think about the issue, I'm sure there is plenty to learn.

Clear Skies!  I'm hoping to get out of the city to take advantage of the new moon.  I hope you can as well.

Monday, September 3, 2012

Build Vs. Buy: The sum of the parts

To those of you in the U.S. Happy Labor Day.  For me it's a great day to spend some time researching my new telescope.

I've now done some thinking about the size of my better scope, and I've decided on something in the 14-16" range.   Large enough to be a big step up from my current scope that can fill my observing needs for long time to come, but small enough to be manageable and affordable.  As I continue to try to scrape together some pennies, I'm left wondering what my options are.

Since I started this project,  I've been leaning heavily towards building my own scope.  Not from scratch, but more by assembling the parts I wanted.  In my mind this seems like a good way for me to control all the various trade offs between price/performance and get just the scope I want, but it also seems that it could end up being a boondoggle of sorts.  I could end up spending more than a commercial scope and getting less.  The tagline on my blog is a joke of sorts, Saving one penny at the cost of two, but I don't want it to be an omen...

To help put my mind at ease, and to get some ideas for the design of my telescope, I've been surveying what is available commercially over the last few weeks.  As luck would have it Matt Wedel, of 10 Minute Astronomy fame, just posted a great overview of telescopes available in the size range I was looking at.  He shares some of my concerns about price and portability, so his pros and cons are instructive for me as well.

With such a wide range of options, and a similarly wide range of prices, how can I go about really knowing which decision, Build Vs. Buy is right?  If I decide to buy, how do I go about choosing which one?  If I decide to build, how can I figure out how much I need to spend?

I think the answer to all of these questions is to look at which basic parts make up a telescope, try to judge their impact on the overall telescope experience and figure out which features are important to me.

Sum of the Parts

I've been around telescopes for a while, and if you are reading this, I bet you have too.  In my observing experiences with my own telescopes and others, each telescope has a different feel... some are easy to use and seem to disappear into the observing experience.  Others assert themselves with distracting issues that interrupt the zen-like flow of observing.

These experiences often center around one or other piece of the scope which is not working as well as I'd like.  I've thought about them in the moment, but never taken an inventory of each part and what I would like to see from them.  This will come in handy as I evaluate commercial scopes and put together a budget and parts list for building a better scope.

Most of these will warrant a post to themselves as I try to figure out the key measures of quality for each and evaluate different options and suppliers.  Here are my main areas of consideration in no particular order:

Size is king, but there are also considerations such as focal length, thermal properties of the material, weight vs. deformation and shape (conical vs. flat).   Each manufacturer seems to have different standards of, and reputations for, quality.  In my experience the mirror is probably the largest factor in the overall experience of a telescope and I've already spent some time trying to figure out where the value/dollar sweet spot is.

Mass produced, or machine produced, mirrors are less expensive but quality can be hit and miss.  Most commercial scopes will have some sort of mass produced mirror.  Hand figured mirrors are usually higher quality, since some person spent time testing and fine tuning them, but can be pretty expensive.

Unless I am lucky enough to have a full set of parfocal eyepieces some day, I'm going to need to refocus my telescope.  A cheap, sticky, sloppy or overly fast focuser can be a big annoyance over a night of observing.  With faster focal ratios, the critical focus plane gets thinner and thinner, so a good quality focuser is a must.  A very nice focuser can run upwards of $250 and this is an area I've seen some commercial scopes cut corners.

This is not really a part, per se, but it's directly dependent on the design and quality of the moving parts of the mount.  It's the feeling one has when pushing the telescope around the sky.  Is it easy to move?  Does it require the same amount of force to move in altitude as it does in azimuth?  Can it be knocked off target by a stray bump of the eyepiece?

I've already decided on a dobsonian style scope, so the basic design will be the same no matter if I build or buy, but there are a lot of different ways to implement the same design.  This is an area where the details matter.  The sizes of the various surfaces that rub against each other, the materials they are made of, and the weight and balance of the overall telescope are all critical to the motion of the scope.

Aside from a few, very high end, commercial scopes, it seems like this is always the first area people try to modify when they purchase one.  I've done a fair amount of tweaking on my XT8 to improve the motion, with some success, but I want my next telescope to be a real joy to use, without a lot of modifications.

Since I'm not a fan of goto or push-to systems, I spend a lot of time with my finders.  Locating deep sky objects can be a fun challenge, but working with a bad finder is a major frustration.  Aside from the mirror, the is probably the next most important aspect for me.  I like having a unit (non-magnified red dot or reticle) finder for getting the scope in the right part of the sky, and a magnified correct image finder for fainter star hopping.

From what I have seen so far, commercial scopes either come with a unit finder (if you are lucky) or some sort of terribly small straight through finder.  I'm figuring that regardless of my build/buy decision, I'll be purchasing a new finder, so it's sort of a wash.

The spider is the structure that holds the secondary mirror near the top of the telescope.  It is not a component I really think about, until it comes time to collimate my telescopes.  Having to re-align the secondary is infrequent, so this is not a huge concern, but there are some options that impact the appearance of bright objects.  Since the arms of the  spider are in the light path, they will diffract light and cause scattering and other noticeable optical effects.

I don't think a particular spider design is going to make or break my build vs. buy decision, but some people are passionate about it, so I don't want to ignore this subtlety in a scope I hope to have for a long time.

Mirror Cell
With my largest telescope being 8" I've never had to think about the mirror cell.  It's the thing that holds the mirror and joins it with the rest of the telescope.  At a minimum, it has to keep the mirror from falling out and have some way to adjust it's tilt to get the telescope properly collimated.

An 8" mirror does not require anything that special for support.  The mirror is going to be pretty light, and since it's somewhat small it's not going to flex much under it's own weight.  As mirror size and weight increase, supporting it without changing it's shape becomes a trickier task.  14-16" is where this component starts to matter.  What good is a wonderfully figured mirror if it is deformed under it's own weight as the telescope it moved around the sky?

The mirror cell is not going to be like a bad focuser, reminding you of it's presence all the time, but stability, adjustment, protection, and air flow are all important issues to think about.  They will all affect the overall performance of the scope, and in ways that might not be immediately obvious like a bad focuser.  I've not checked into the commercial scopes I might consider, so I'm not sure how they handle these issues.  If I choose to build, I think this is going to be one of the more difficult parts to research and source.

The Structure is the skeleton of the scope... the stuff that holds all the other stuff together and keeps it aligned correctly.  It holds everything off the ground and lets the mirrors be pointed at various parts of the sky.  Ideally, it keeps everything aligned perfectly as the direction of gravity changes.  The larger and heavier the mirrors and other components, the more difficult building a good structure becomes.

With smaller scopes, like my XT8, the structure is a solid tube with the mirrors, spider, focuser, finders, etc, all bolted on.  A solid tube is strong, and stiff, but with larger telescopes they can be heavy and overly long.  Larger scopes need something a bit more clever.  There are a lot of different solutions to this, each with their own weight/size/stiffness tradeoffs.

I've seen commercial scopes with very different designs, and even more variety of home built telescopes.  Since size and weight are important considerations for me, and I want a telescope that will last a long time and move well, the structure of the scope will be nearly as important as what it's holding together.

Those are some of my thoughts on the criteria I can use to evaluate different commercial options, and to think about the parts I might need to build one of my own.  I'd love to hear any thoughts you might have on how important you've found each of these, or if I've overlooked some pieces of the puzzle.