Help With Astro-Tech 8" Ritchie Creighton Scope & 1600MM-Pro

[TheButcher]

Hey all,

I just got my Astro-Tech RC 8" telescope today and have a some questions about setting up my imaging train.
FL= 1600mm
Aperture = 200mm

The back of the telescope has 3 removable solid rings (1) 2". (2) 1" attached, then the focuser screws into them. I can take anyone of them or all off as seen in the photos below post.

Now I will be using the following:

ZWO 1600mm-Pro (with a the 11" spacer and the 21" one with an adapter connecting them together, the EFW takes replaces the 16.5mm one)
ZWO EFW 8 Position Filter wheel
Hotech Field Flattener (Do I need the field flattner?)

Skywatcher EQ6-R Pro Mount

Also what is the correct view of this scope (is it off Vertically or Horizontally or both?)

I will eventually get a reducer but for now I will image with it at F8. Now will also be ok with my "Orion 50mm Deluxe w/ Helical focuser Guidescope with a ZWO290mm"
I read that It says it is good for up to 1500mm FL but would this be pushing it or okay since I am using a 290mm guide camera.

Thanks All

With 3 Spacers on before focuser


Without Spacers

[JayTee]

Because it's an RC you shouldn't (theoretically) need an FF. As to the spacing, with my 6" RC and the same spacers, I just inserted them experimentally till I found the right spacing. Then wrote it down so I wouldn't forget. Because I'm using a DSLR my spacing will be different than yours.

Cheers,
JT

[yobbo89]

My Newtonian scope listed 180mm focus point from the crayford mounting plate, which was pretty accurate + - 5 to10mm. My understanding is that an rc mirror is fixed with adjustment bolts like a regular newt, unlike a sct where the whole mirror moves, so the rc should have a fixed focus position. You might be able to find some specs about its focus point online and then measure it from the back of the scope. Most manufacturers skimp out on this info, it's pretty handy to have if you're doing a focuser upgrade prior getting to the field

[TheButcher]

Thanks J-Tee and Yobbo,

I will look it up, I am sure it is around somewhere for the focus point. I think I will start with three spacer rings like shown in the photo with the 2" one closest to the mirror. Then the 2 1"ers toward the camera. Also I will eliminate the FF. The three rings on there supplies about 76mm/3" of back focus 3" Now for for the spacing tubes that the ZWO camera supplies, I guess I got to play around with them if I need them. I also have 2" extension tubes, a 35mm and 2" orion extension tube that extend out of the focuser if needed and maybe do away with the ZWO spacer rings and hook the camera/filter wheel directly in the Focuser. I feel like this is some sort a puzzle game/brain teaser lol

So I guess it comes down to Flexture, I have enough spacing tubes/rings but what combo to produce the least amount of flex in the Focuser/optical train, it is just what combo to choose. Anyway I will report back of what I did. Tonight is supposed to be a clear night and then the next few days crappy with snow and such.

Thanks again both of you

[STEVE333]

Here is some information I found for your telescope regarding the Field Flattener.

Optional field flattener: For even more impressive coma-free imaging with the AT10RCF, consider adding the Astro-Tech AT2FF field flattener. While not specifically designed to work with Ritchey-Chrétien astrographs, images taken with the field flattener by Astro-Tech R-C owners have shown that the Astro-Tech 2" field flattener works remarkably well with these advanced coma-free reflectors as well as with refractors. This modestly-priced imaging accessory essentially eliminates the residual field curvature inherent in all reflector telescope designs, so that the coma-free star images remain point-like all across the field. An optical analysis and ray tracing of the field flattener was done in ZEMAX and applied to the R-Cs by Roger Ceragioli, the noted optical designer who did the final optimization of the Astro-Tech Ritchey-Chrétien optics. Here is what he had to say about the #AT2FF, "My conclusion, which seems supported by what users are saying, is that you don't need any other field flattener. This one performs well over a 40mm image circle in all three small RCs (6", 8", and 10")."

Still not sure if you need it for your ASI1600mm Pro, but, thought it might be of interest.

Cheers,
Steve

[TheButcher]

Thanks Steve

Yeah I will see how the images come out tonight, I also found the correct amount a spacing I took photos that I will upload here tomorrow. I do I have a Hotech Field Flatenner but heard the Astro Tech is better. I may sell mine and get that, I could use it for my refractor as well. Thanks for the share Steve and Good Luck with your new Camera you will love it And I can't wait to see what you can do with it!

[JayTee]

I own both, the AstroTech AT2FF is better than the Hotech.

Cheers,
JT

[TheButcher]

I own both, the AstroTech AT2FF is better than the Hotech.

Cheers,
JT

Thanks JT, Yeah I remember you saying that. I will get that soon as I get more funds. \
Also I figured out the spacing with trial and error. You need to use the big 2" spacer ring and 2 of the 1" ones for the 1600mm-P. Overall last night went well. I am taking darks today so won't.

One thing I got to work out is my guide camera. It sits towards the left side of the scope and makes the weight unbalanced. I never had an issue with my refractor, but then again this is up much higher now rather then sitting low. There is another place for another finder scope (2 Holes but no bracket, but I have one from my Dob I will throw on), So I may just put my finderscope on that side and add some weight to it to balance it out.

[JayTee]

I installed a "v" rail on top of mine and that's where I affix my guide scope that has a "v bar" foot bolted to it so I don't use any rings.

JT