15 inch dob project

Hi,

I want to build a telescope and I've finally settled on a 15". Originally I had kicked around a 18"-20" but that was just too big for my current living arangment and vehicle. So I've settled on a 15". 15" seems to be a good blance of photon guzzling power and portability.

I'm seeking a bit of advice about the focal ratio and who should make it.

I'm split between f/4.5 and f/5. An f/5 mirror would make me use a step stool at zenith but would have less coma and make using a 2.6" diagonal for more feasable. An f/4.5 mirror would requite no step stoll but thye coma would increase and that 2.6" diagonal would more than likely have to become a 3.1" diagonal which makes the central obstruction larger.

I'm thinking of getting my mirror from either R.F. Royce or Steve Swayze. It would more than likely be 2" thick, because I'm using the Kriege book as my guide and 2" seems to be the rule. Though I might change my mind.

Also why I'm at it here's the rest of my ideas as to what I would put into this dream dob.

-Protostar secondary mirror and diagonal mount.
-Cable sling like the ones that Stellar Cat sells.
-Feathertouch focuser.
-Obsession aluminum side bearings.

I'm still not sure on which clamp system I will use for the trusses but they probably won't be wood. Wood is far to moisture sensitive for my tastes. Obsession, Moonlite and Aurora Precison all sell interesting units.

Thanks in advance.

Eric

Hi Eric,
I have had a 15" f/4.9 Swayze and now the 14.3" Zambuto in a Starmaster.
Really, I miss the clarity of the 15" f/4.9. My wife says the images were sharper because stars were more pinpoint. I can say with the Paracorr the 14.5" is quite sharp, probably the same, but that takes it to f/4.945 so it is about the same focal ratio anyway. The 14.5" f/4.3 is shorter and more convenient for the wife to get to the EP, though a step is required at Zenith. The 15" required 2-3 steps for her and one for me.
The 15" is a great size and will bring in just about anything a larger scope will, just not as bright is all. Aperture rules in that category.
Both of these scopes used a 2.6" secondary and it seems to work well in both scopes.
The 2" mirror is heavier and requires more cool down time, but it acts as a counter weight and makes balance easier on some scopes, but other designs would then be tail heavy.
Protostar makes a good secondary but so does Antares. I have had both and the Antares does offer a better PV if you want it.
Astrosystems makes a great spider and holder too.
Feathertouch is a given.
Aluminum side bearings are nice.
Slings are good, but not better.
Royce or Swayze, hmmm, hard choice.
Moonlite ball and socket attachments quite nice, no wood.
That is my $.02 worth.