Newtonian 12" Reflector Options - Advice Needed

[Gary Shaw]

Hi All:

I need to upgrade my current  8" TS Optics UNC to a 12" aperture to enhance my capabilities for Exoplanet Transit Imaging. I'm currently using an iOptron CEM70G mount and would like to be able to use this mount with the larger telescope. I'm hopeful that some of you may have some recommendations on telescope 'options'. I am looking for a high quality, amateur grade, instrument -I hope this somewhat vague descriptor helps. Currently I am considering the following 12" options:

- Orion UK 12 AG F4

- TS Optics UNC F4

- TS Optics ONTC F4

- Other suggestions please ...

As you see, I'm partial to traditional F4 Newtonians but I'm also intrigued with some of the truss-type Newtonians as well as the Dall Kirkhams.

I've been quite happy with the TS UNC but would prefer a higher grade instrument. the TS ONTC seems to have a better primary mirror cell ans other quality advantages but the OTA length is, perhaps, too long for my micro-observatory enclosure. The Orion UK AG12 seems nearly perfect but I've heard of QC and Customer Service problems in the past so I'm particularly interested to know if those issues still persist.  Anyway, I'd very much appreciate your input on the choices above and, especially, on any alternative ideas for a quality scope.

Cheers!

Gary

[StarryEyed]

Gary. 

A lot of views no replies

I tried searching for those scopes here on SGL

Some previous threads came up so you might try replying to them to resurrect those threads and see where that leads you. 

or

Tweak the title to 12" f4 astrographs for exoplanet hunting" or something. That might draw the right people in. 

 

[Mr Spock]

There probably aren't many people using f4 scopes. 

There is this one https://www.firstlightoptics.com/skywatcher-quattro-f4/skywatcher-quattro-12s-f4-imaging-newtonian.html I don't know how it performs though.

[iantaylor2uk]

I had a f/4 Orion Optics DX300 which I sold last year - I think the equivalent nowadays would be the VX300 f/4. The nice thing about the OO scope is that it was quite light (as these things go) at around 14 kg, whereas many other scopes of this size from other manufacturers would be much heavier. I used it with a G11 on a losmandy heavy duty tripod and it was solid and I managed to autoguide it at less than 1" RMS, although the size of the scope meant it was sensitive to the wind (I don't have an observatory). An OO Newtonian should be OK, the problem with Orion Optics is that it is quite a small manufacturer and there is a lot of demand, so you are probably looking at a 6 month or greater wait for a new scope. If you can find one second hand that would be good, but they don't come up that often. 

[rl]

Hi Gary

I have an AG12 and a few comments might be in order. 

First, I'm surprised there is nothing on the US market  this category. I would have thought this sort of scope would have been available from some of the smaller high quality manufacturers. If you import from Europe or UK you might well have problems with the guarantee. 

I've had the AG12 since 2017 as a background project to be completed when I retire; the opportunity to acquire one secondhand at reasonable cost came up at a a time when I has some spare cash. 

• Orion Optics mirrors have a good reputation in the UK. That might not be relevant if all you need is a light bucket for a specific photometry project, or even prime focus imaging, but they're actually quite good planetary scopes when collimated and cooled in spite of the massive secondary.  It's not quite the full 12"; the mirror is 298mm and the AG12 has a knife-edge circular mask that takes a couple of mm off this figure. The 1/10 wave figure is slightly misleading since its measured in red light at 632 nm but the mirrors are still very good. Zambuto good? Probably not but certainly more than good enough for most of us who don't demand the absolute best. I've had several from OO and never been disappointed since they got the Zygo rig. 
• For photometry you might be better off with a lower quality but bigger mirror. The photon statistics might be one of your most important design criteria for looking a planetary transits. Subject to mount limitations of course..
• The general build quality is very good, but it's not in the same league for metalwork as some of the top-notch US companies.
• The spider is really solid, being milled out of aluminium plate which helps keep the collimation. Because the vanes are relatively thick (2mm?), diffraction spikes will be theoretically a bit worse than scopes with very thin vanes but I can't say I've noticed in practise.
• The carbon fibre tube is very rigid but scratches quite easily.
• The primary cell is 9-point floating and solidly made, works very well. 
• Collimation is difficult since the focuser is 3". You will need an adapter for 2" tools. But it does hold collimation well. 
• The Wynne corrector expects the focal plane to be about 79mm from the back face which allows plenty of space for accessories. It has an 82mm thread; you may well need some adapters specially made to suit your camera / filter gear. OO will do this for you but you will have to specify the dimensions yourself. I've had one done to suit the big Celestron OAG, which suits my camera but limits the diameter of the imaging circle (potentially 60mm). You need to plan this..Do you have a friend with a lathe?
• The AG12 is intended as a pure astrograph. If you want to use it visually you will need an adapter made to put the eyepiece focal plane at the right place, and you will need the manual focuser option. I've tried mine with a 10mm Ethos and it makes a superb mid-power mid-field combo. Or consider the CT12 with standard 2" accessories. Quite a lot of the cost goes into the 3" Wynne corrector. 
• There are no feet on the tube; stood upright the OTA stands on the collimation screws. Not a problem if it lives permanently on the mount. It's easy to fit some feet using the existing holes but on a scope of this cost maybe you should'nt have to. Just a pet hate of mine..
• It really needs an EQ8 class mount. 
• Mine has the FLI Atlas focuser option which is excellent, but the travel is quite small. Coarse focus is by locking screws on to the Wynne corrector which leave marks. I added some thin copper shim to avoid further scratching. This may have been improved on the latest models. 
• The tube rings are really nice. You can buy extra to support the focuser if you feel the need. 
• Personally I like the 12" f/4 format; it's a serious scope that is compact enough to manageable if you have to move it around. But I suspect most AG12s don''t see much grab-and-go action in view of the mount requirements. But I've had 12" f/4 dobs and they have worked very well for me. 

Difficult decision. They are very good scopes but not perfect. Would I pony up the new cost? Probably not..but they're like hen's teeth secondhand because people get them as scopes for life. If you find you don't like it then the depreciation is brutal..

OO really ought to provide as standard some 3" to 2" adapters.

Hope this helps..RL

Edited February 20, 2022 by rl
factual error

[Gary Shaw]

RL - Thank you very much for the helpful and thorough response. I share your feelings about standing the OTA on the collimation knobs - my TS Unc has the same poor design. I've had a few responses to my query but none so far that have steered me onto a new path with new options to consider. So, I'll have to decide between the OO and 6 months of waiting or the TS UNC and 6 months of waiting. I would lean towards the UNC given the mixed reviews I've received whenever I inquire about OO.  The uncertainty regarding quality makes me reluctant to invest 2.5x the cost of the TS scope. My 8" TS UNC has performed very well and TS is very good with customer service.

Thanks again and cheers...

Gary