What unicorn scope?

Hi Sean, 

Could you tell a but more about your current setup and the targets that you’re looking to shoot. 
I am sure you’ll get a lot of help, but some background might help.

Thanks,
Deepan

I maybe biased but i have an RC 8 and love it!!! For the money you can`t beat it when it comes to focal length. I actually like diffraction spikes, like i said i`m biased lol

If you don't want diffraction spikes and want similar focal length / price / aperture, then a C8 with a focal reducer would be the closest.

I have a 102 F7 scope and would like to double-ish my focal length, and be fast enough to image dso’s in my lifetime.   While I’m not a fan of diffraction spikes, I also don’t want an SC.  
A refractor in that focal range is either really slow and big, or really really big and really really expensive. A mak cass is awfully slow and I’m not sure about the contrast as I stopped looking when I saw f14.  I’m bortle 8 so I need more integration time (yes?) so a slow scope will make this less fun. I’d love an esprit 100, but it doesn’t solve this issue. Even a 150mm f/7 refractor is too short. 

So we return to the original question…. Does that only leave me with an RC?

Well…. Too slow native, combined with an expensive reducer and contrast that isn’t the best.  Honestly if I lived in a darker area I’d probably consider one, but it’s not cheap when you add it all up including adding autofocus.  What would a reduced edge8 HD get me over an rc8 or rc10 other than a lack of diffraction spikes?  To be honest I can’t afford the cost or weight of a c9.25 or 11 or 14 and those are the sct that have an image quality that I’d be ok with.

Your pics with the c11 look pretty good!  Sadly I’m in canada so buying from the US isn’t easy or cheap. I took a look around here on facebook and kijiji and people seem to think that the $2000 scope they bought 15 years ago is worth the same as a brand new one after covid increases. If i could get a c11 for $1100 I’d probably do it.

Sean Mc:
I have a 102 F7 scope and would like to double-ish my focal length, and be fast enough to image dso’s in my lifetime.   While I’m not a fan of diffraction spikes, I also don’t want an SC.  
A refractor in that focal range is either really slow and big, or really really big and really really expensive. A mak cass is awfully slow and I’m not sure about the contrast as I stopped looking when I saw f14.  I’m bortle 8 so I need more integration time (yes?) so a slow scope will make this less fun. I’d love an esprit 100, but it doesn’t solve this issue. Even a 150mm f/7 refractor is too short. 

So we return to the original question…. Does that only leave me with an RC?

Got it. didn't know that you already had a 4-inch refractor.

If you're considering RC's and SCT's just be aware of the thermal acclimatization required for it to work well. Also the Collimation.
Also factor in the central obstruction, which could possibly affect the contrast of the image. 
Mass produced RCs have Crayford focusers, which might not be the best for photography. But there are cheap alternatives available.
The Celestron SCT's might suffer mirror flops (Except Edge 9.25, 11, 14 that has the lock). 

Also, personal opinion, 150 F/7 refractor would put up a tough fight with long FL SCTs or RCs.
I experimented with SCTs, RC's and finally settled with Esprit 150. 

Hope it helps.

Thanks,
Deepan

Actually the dew/pollen is a good point. Dew seems to be a big problem in southern ontario. Also lately there’s been tiny droplets of something coating my refractor and cars lately. It’s almost like sap. Alcohol won’t take it off, I need to use soap and water and scrub it. Can’t imagine having to deal with that with an RC or a newt. 

dammit. I want something that’s f/4, 1500-3000mm, small, light, has perfect stars, and is inexpensive.

Sean Mc:
Actually the dew/pollen is a good point. Dew seems to be a big problem in southern ontario. Also lately there’s been tiny droplets of something coating my refractor and cars lately. It’s almost like sap. Alcohol won’t take it off, I need to use soap and water and scrub it. Can’t imagine having to deal with that with an RC or a newt. 

dammit. I want something that’s f/4, 1500-3000mm, small, light, has perfect stars, and is inexpensive.

Sharpstar SCA260 is F/5 and 1300 FL. Somewhat close to what you say you want.

Hi Sean,

I own a Esprit 100 f5.5, Hypergraph 8 f3.2 , and GSO RC 8 f8 and operate all with a full frame sensor.

I enjoy Bortle 2 skies, but lousy 4arcsec seeing.  Its been a lot of fun taking images will all, but now I almost exclusively use the RC.  Indeed, I have ordered an RC10 as my next telescope upgrade.   So I can be considered a fan of the RC design. [In my professional astronomy career I also used - almost exclusively - an RC telescope for my work.  A little bigger than my current one.] 

Why do I use the RC?  Ease of use, aperture and price point.  Do I care that the focal length is not matched to my seeing.  Not really, since I can easily resample to any "effective" image scale I want in processing.  [I can also bin my FF CMOS sensor - although I don't gain as much in RN as I would with a CMOS - but I am rarely RN limited even for NB]. 

Of course, the real limitation with such a "long" focal length is f.o.v. not speed.  Indeed, my primary motivation for moving to a RC10 is actually having a system that can accommodate a reducer/corrector which will give me good images over a FF sensor.  Currently my corrector gives me good images over an APSC sized area, but not beyond.  Even so, currently I have a field-of-view over 30arcmin in size - large enough for most DSO (and certainly galaxies - excluding LMC/SMC).

If you do go with an RC8, also get a corrector (the field is curved).  I couldn't find any reducer/correctors for the RC8, so I use a 2inch TS 1.0x  field flattener specifically built for the RC8, and live withthe 1600mm focal length.  [Which great for the moon]

It would also pay to invest in good collimation equipment.  The RC does hold collimation well [particularly if permanently mounted] and I found collimation a lot easier than for a fast Newtonian.  There is lots of advice on RC collimation out there.  Some of which I am a little skeptical of.  I use a Takahashi collimator - essentially a telescope within a telescope to ensure all those reflections line up.  Takes about 15mins every month during daylight.  [But it was a bit of a journey to get there - going up too many blind alleys, courtesy of thise internet "experts"] 

CS Brian

Ian McIntyre:

Brian Boyle:
Hi Sean,

...

CS Brian

*Hi Brian,

I have follow-up questions for you as someone who feels like giving up on the GSO RC8:

1. Is this the collimator you are referring to? https://landseaskyco.com/products/tak-collimating-scope-b-4-5?variant=40935533936812&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&_vsrefdom=adwords&gclid=CjwKCAjwyNSoBhA9EiwA5aYlb6NN3BLG58p6SySFZcw7aFG4_XQuL6ecfRayXRyLVOY4bR4knJpkiBoC7vgQAvD_BwE
1a. Is there other collimating tools that are required in conjuction with the Takahashi?
2. How do you deal with secondary fogging? Well, and primary for that matter.
3. Have you had to clean the mirrors? If so, what is your process?
4. Are you still using the stock focuser?
4a. Do you use an electronic focuser? I bought the ioptron focuser (it's the GSO marketed by ioptron) and will not maintain position. Which do you use?

Sorry I'm piggy backing onto the OPs thread here. But the help of someone who seems to have the opposite experience with this scope would be very helpful.

Hi Ian

All good questions

1) Yes.  The biggest hassle for me is getting my arm past the 2ary when I reach inside to unscrew the 1ary baffle [which you have to do in order to see all the reflections]
1a) No.  I have used a Cheshire to do a "sanity check" but you just see the same thing - just less magnified - than the Takahashi. 
2) With a heating pad stuck onto the back of the 2ary cell designed for the RC8 bought from TS.    Need to carefully lead the wires back across the spider vane to avoid mucking up the diffraction spikes.   
1ary not really needed, but I put an astrozap belt around it just in case.
3) Yes.  I wash them with water and let it drain through the hole in the middle.  [Essentially how we cleaned the primary for the 3.9m Anglo-Australian telescope mirror. 
Except we also scrubbed off the aluminium coating with brushes and re-aluminised in a tank.  [I don't do that for my RC8]
4) Yes.
4a) Yes.  I use the ZWO EAF with the 3D-printed shim needed to fit the curved plate of the GSO stock focuser.  It works fine, and I am hanging 3.5kg off the back of it. Occasionally I do have to check everything is tight, as it can slip near to the zenith if things are tightened up properly. 
I would agree that the stock focuser is a weak part of the system [true of many scopes]
and is one of the reasons I am upgrading, since the RC8 doesn't take a larger focuser.

This sound like a fair bit extra to the "simple and cheap" RC8 setup.  But I don't think any telescope is immune from similar necessary tweaks out of the box.

For me, the RC wins over a Newtonian for stability of collimation and ease of use.  It is so much easier to use a telescope where the gear is hung off the back than dangling at the top of the tube.  YMMV. And that's fine too.

Sean Mc:
You take the mirror out or leave it in the scope to wash it?

Hi Sean 

I leave it in.  I acknowledge that I am probably causing a number of sharp intakes of breath across the AB community for my abusive treatment of a delicate optical instrument.  And reducing my chances of anyone buying my RC8 when I sell it on the 2nd hand market. :-)   

For those that are aghast at my treatment, I do pour the water in  slowly with the telescope mounted close to horizontal and then have a tour of the sky programmed into my ZWO ASiAir  to mimic the gentle swirling of fine wine in a glass.  Aaah the aroma.... 

The 1ary baffle prevents the water going down the hole until I take it out.  The mirror drains and I leave it to air dry naturally.  Appears to the job.  


CS Brian