Wednesday, October 17, 2012

The Design: Primary Mirror - Part 2

Work has been a bit hectic for me lately, long hours and such, so I've not had a lot of time to post anything here.  Even as busy as it's been, I've found time to daydream about my new telescope.  In my last post I narrowed my list of potential mirrors down to four candidates:

CompanyMaterialSizef-ratioHeightxt8 MultPrice$/Inch

It was a nice tidy list, and I contacted each of the manufactures to double check pricing and see about delivery times and such.  The pricing was accurate, and lead times were all around three months, which is pretty reasonable considering the work involved in a mirror like this.  Everybody I've contacted was helpful and responsive, which goes to show the passion they seem to share.

All of the emails did not bring me any closer to a decision, so I decided to try and get some additional input.  There are a lot of helpful and knowledgeable people on Cloudy Nights so it's usually my go-to place for questions I might have.  I started a thread titled 'Mirror Choice for 14-16" Dob Project' and laid out my plans and the current short list.

Quality vs. Price

In no time at all I was getting some insightful comments.  The entire thread is an interesting read, but the most useful posts were not about any specific mirror I had on the list, but were the more philosophical posts and the posts that added perspective.  Two things stood out to me; The first is summed up by these two quotes:
What you are paying extra for is the comfort and re-assurance that your mirror will be excellent. [...] On nights of excellent seeing you can certainly tell an excellent mirror apart from a good one. These nights aren't all that common but it's worth it when the air is good and knowing what you have doesn't get better. - John Bambury 
The thrill and satisfaction of quality is remembered long after the sting of high price. If you intend this to be a "lifetime" telescope take the pain now. [...] Forget the price for now. Aperture, length, and availability is what you need. - Jeff Morgan
A few of my questions boiled down to,  'How good is good enough?' and 'What is the extra money for a premium mirror really buying?'.  These two posts, along with others, sort of put things in perspective for me.

If I purchase a great mirror, from someone with a reputation for quality, there is a good chance that I will be happy for the lifetime of the telescope.  Aperture fever may kick in again, but I will never wonder 'What if I had paid a little extra?'.  Additionally, if I ever do succumb to aperture fever and want to sell my scope, the resale value will probably be higher.

Size Vs. Price

The second thing I realized in reading through the posts was closely related to the first.  Basically, if I was going to spend the money for a 'lifetime' scope, I should be happy with the end product.  Even though a 16" has only 14% more area than a 15" mirror, I know myself, and I'm pretty sure I'd be often wondering what that 14% would be like.

When I had to rule out the 16" mirrors due to price constraints, I was disappointed.  From the start I imagined this as a 16" scope project, even though I was open to a smaller scope if my design constraints (Eyepiece Height, Overall Size, Budget) meant 16" would not be possible.  I was tempted to go beyond my $2500 budget for a mirror and just make it happen....

Wisdom of the Crowd

I spent a fair amount of time trying to find mirror vendors, but I am not at all surprised that I missed a couple.  Two new manufacturers were suggested, Steven Swayze, who I had somehow missed but was very well respected and Terry Ostahowski, who also has a great reputation for quality optics.  I contacted both of them asking for pricing on a 15" or 16" f/4 mirror.

Both of them were responsive and informative.  I even got three different options from Steven Swayze, which was appreciated.  Here is the table with the new possibilities added, again sorted by $/inch.

CompanyMaterialSizef-ratioHeightxt8 MultPrice$/Inch

The Decision

So many great options, and I was really excited to have 16" mirrors back into the mix, even if they blew my budget by 8% or so.  I was leaning heavily towards the 16.25" cellular mirror Steven Swayze suggested.  It's larger, and lighter, than a 16" mirror and would probably have superior cooling and stiffness.  Ultimately, I decided a 16" is more standard, and would make replacing (if I did something foolish to damage it) or selling the mirror (if something else terrible happend) easier in the future.

Looking at the price per square inch, and doing some research about the acknowledged quality, finally made my choice clear.  Today I put down a deposit on a 16" f/4 mirror from Terry Ostahowski.  Delivery is estimated sometime in March of next year... that's going to seem like long time, I'm sure!

Unlike the larger 80mm finder I bought a while back at P.A.T.S. this is the first, scarily big, step towards my new telescope.  Since the dimensions and focal length of the mirror sort of anchor the design, I can pretty much finalize all the other options I have to consider.  I can figure out what size secondary to use, find a spider to hold it, double check my decision on a structure, and think about focusers and other accessories.

It's exciting to think that I could have a working telescope as soon as April or May, 2013.  Seems like a long time from now, but I have a lot of things to consider, and observing to do with my current XT8 in the meantime!

Here's hoping for clear skies to keep me occupied...