Any thoughts on a 12inch ota

xelasnave · #1 11-04-2007, 08:49 AM

Having seen Mike place a 12 inch on an eq6 and so far it has not complained I started thinking of maybe building a new 12 inch OTA as light as possible, no secondary just a astro cam and minimal focuser, a light frame with black silk…all in an effort to reduce the weight and maybe be able to have a go at 12inch photos.

Does anyone know the weight of the 12inch mirror set up?

I was thinking if the polar align is good (as it should be in a permanent pos.) I should be able to get short runs and maybe leave a guide scope off.

A truss set up with just a ring to hold the mirror and a ring to support the spider for the cam, two poles and wire ..I dont know how much weight would have to go or even if it would be enough as even a light 12inch may be too much?.

Or any comment as to being able to trim a 12 inch to go on an eq6 for relatively short exposures on deep sky objects. Or simply forget the idea it will never work?
Alex
.

iceman (Mike) · #2 11-04-2007, 08:57 AM

Paul Mayo uses a 12" GSO on a G-11 and does fantastic deep sky stuff with it.

I don't know that putting it on an EQ6 would be such a good idea for deep sky work, it might be too heavy for the accurate tracking required.

My 12" OTA weighs about 21kg.

davewaldo · #3 11-04-2007, 09:00 AM

I remember having a conversation with Striker "imaging guru" about big scopes for imaging. His main issue with a setup like this was flexure rather than wieght. It sounds like a two/wire setup might have too much flex/movment through its travel.

I'm no expert on this but I have heard that flex can be a huge problem....

Dave.

xelasnave · #4 11-04-2007, 09:26 AM

Quote:

Originally Posted by iceman

Paul Mayo uses a 12" GSO on a G-11 and does fantastic deep sky stuff with it.

I don't know that putting it on an EQ6 would be such a good idea for deep sky work, it might be too heavy for the accurate tracking required.

My 12" OTA weighs about 21kg.

Yes Mike I have followed Paul’s work

in fact it was seeing his images

that I thought about the idea in the first place

,
and seeing those images inspired me to design a mount to carry a 12 inch that I could build

..
You could say he started me thinking in the first place

.

Thanks for the weight figure.
Alex

duncan · #5 11-04-2007, 09:37 AM

Hi all,
I don't know much about the subject of tracking but considering DSO's are usually millions of times further away than Jupiter one has to assume tracking would have to be extremely fine. With that in mind what sort of weight can an EQ6 mount handle? Secondly i've been reading a few complaints here about the EQ6. Mike how does yours perform and does it handle the 12" newt well?
Cheers,
Duncan

gbeal · #6 11-04-2007, 09:37 AM

Alex. Why 12"? If imaging is all it will be used for, then something smaller will certainly suffice. Depending on what your targets are anything from the humble 80mm up is feasible. I use the 10" newt on an EM200, and it is in a homebrew Carbon Fibre tube. It is as big as I would want to go right now. At the native 1250mm focal length, guiding/tracking/seeing/focus all are as grouchy as I can handle. The shorter/smaller the better I reckon. Hence the E130.
Lunar/planetary? Now thats a different kettle 'o fish.
You are thinking of mounting the camera at the prime focus? I suggest this is a good concept with something like the MX7C that Gerlad has for sale, or similar, as they are 2" OD, and actually about the same profile as the secondary on the 10" I have. You would have to provide a means of moving the whole camera fore and aft to focus, but Takahashi do it with their bigger Mewlons, so it is a great concept.
If it were me, I would be looking to do all this with an 8" or maybe a 10". Assuming DSO imaging is what you are considering.

xelasnave · #7 11-04-2007, 09:40 AM

Quote:

Originally Posted by davewaldo

I remember having a conversation with Striker "imaging guru" about big scopes for imaging. His main issue with a setup like this was flexure rather than wieght. It sounds like a two/wire setup might have too much flex/movment through its travel.

I'm no expert on this but I have heard that flex can be a huge problem....

Dave.

You are right expert or not everything in this game is about zero movement

.

I need to be reminded

but then I think heck it must be doable and you get pulled into building one that wont flex but is light weight

...
Looking at Ed's excellent design with the 24 inch I think such would be a way to do it

.
Solid better centre of gravity so even a five inch secondary would change length and take away little light gathering power.. well a lot of light gathering power but there is a lot left over

..think of the area relationships five inches must only be about 25 to 30 %.

Its the old build a better mouse trap happening I think

.
I will do some drawings of different approaches ..that will keep me occupied happily for a while

.
alex

xelasnave · #8 11-04-2007, 09:57 AM

Quote:

Originally Posted by gbeal

Alex. Why 12"? If imaging is all it will be used for, then something smaller will certainly suffice. Depending on what your targets are anything from the humble 80mm up is feasible. I use the 10" newt on an EM200, and it is in a homebrew Carbon Fibre tube. It is as big as I would want to go right now. At the native 1250mm focal length, guiding/tracking/seeing/focus all are as grouchy as I can handle. The shorter/smaller the better I reckon. Hence the E130.
Lunar/planetary? Now thats a different kettle 'o fish.
You are thinking of mounting the camera at the prime focus? I suggest this is a good concept with something like the MX7C that Gerlad has for sale, or similar, as they are 2" OD, and actually about the same profile as the secondary on the 10" I have. You would have to provide a means of moving the whole camera fore and aft to focus, but Takahashi do it with their bigger Mewlons, so it is a great concept.
If it were me, I would be looking to do all this with an 8" or maybe a 10". Assuming DSO imaging is what you are considering.

My short term long term plan is a very good triplet 80mm which with the guide scope on the eq6 figured would be as good as I could comfortably invest. I figured less weight more mount and I may have a chance

..

Not to go big but get the best gear I could afford ...the eq 6 is as far as I can go mount wise for a while and maybe a 80mm triplet..maybe a 400d or next step up after that...even that is a long way off

.
But as I said I think it was seeing what Paul turned out with his 12 inch that got me thinking

..
I cant be the only person around here who comes up with another "scope" idea

.
But thinking more a lot of problems can be fixed with a massive focal reducer.. so the first problem is what can we reduce the 12 inch effective f/l to?

alex

gbeal · #9 11-04-2007, 10:53 AM

Quote:

Originally Posted by xelasnave

But thinking more a lot of problems can be fixed with a massive focal reducer.. so the first problem is what can we reduce the 12 inch effective f/l to?

alex

Forget ti, at f4 - f5 it is as "short" as you can go without major headaches. The Epsilons are f3.3 (in my case) or the latest are f2.8, but they employ a humungous corrector/reducer system to correct the optical problems.

Phil · #10 11-04-2007, 05:08 PM

Not to put you off but i would start smaller with the telescope. If you are going to be imaging then you will have alot more fun with a smaller telescope wielder field of view fast F/. The bigger you go the more problem you are going to have and seeing will play a big role in the imaging platform at 12" smaller not so bad. Thats just one problem out of a heap that can go wrong when imaging. If it where just from shoting planets i would go bigger but if you are going to shot deep sky images i would go smaller. Just my two cents worth Alex. At the end of the day you need to happy with what you have.
Phil