RC scopes: Do I need a FF and FR lens?

[Star Hunter]

I'm contemplating getting a 12" or larger GSO RC OTA from Andrews Comms.

Are these scopes up to par with other RC's? I know you get what you pay for, but aren't GSO scopes ideal for a DSLR or CCD camera?

Also, if imaging with a chip smaller than 24x36mm on a RC, do I need a Field Flattener and or Focal Reducer? Who makes them?

In re the FR, what is best for an RC and what focal ratio and AoI (Area of Illumination) will I reach?

Thanks,

James

[RickS]

James,

You'll only need a FR if you want to image at a shorter focal length than the native length of the scope. It does make the scope more versatile and gives you the option of a faster focal ratio. I have used an Astro-Physics TV27PH focal reducer with my RC10 and it works well. Other have used the CCDT67, also from A-P, and appear to like it.

I find the RC10 is OK without a flattener using a KAF8300 sized chip (17.96mm H x 13.52mm). There definitely is some field curvature but it's not horrid. I think if you went any bigger you would want a flattener. I tried using my STL11K camera (KAI11000M full frame 35mm size sensor) and it was awful in the corners. The vignetting was severe too.

Cheers,
Rick.

[allan gould]

I've had exactly the same experience with the 10" GSO RC scope and AP67 reducer. Works really well with qsi583 and Qhy 10 cameras.

[Paul Haese]

Jimbo, I have a 12" RC and am using a STL11,000 from SBIG on it. The following image was taken with it and without a focal reducer or flattener.

NGC253 (http://paulhaese.net/NGC253.html)

You can use an AP or Tak reducer or flattener with them and they work really well.

Yes they are not an RC from some of the more expensive brands and the construction is not as solid but the scopes do the job. I need to dedicate some time to writing up a review of the 12". Bang for buck these are great, but you will need a good focusor and a dew strap on the front of the scope.

[Star Hunter]

Paulie,

Mate, thanks for the tip. I think it would be great if you did a review of that 12" RC GSO you have. You mentioned a dew heater up front? and bigger focuser? Why's that, mate? BTW the shot of 253 is bloody awesome! Since I'll be using a FF DSLR with a mod. sensor on that 16"GSO RC, I don't think I'll need a FF or reducer or will I?
BTW, give my regards to Bill Jenkins and Joe Grida of the SAAS

cheers mate,

Jimbo (ex SEQAS member)

[swannies1983]

Not sure how much the aperture effects curvature etc, but I took this image (http://www.flickr.com/photos/47268787@N05/8383721676/sizes/l/in/photostream/) with my RC8 using a modded Canon 30D. No FF or FR was used. Only slightly cropped due to stacking artifacts.

[Paul Haese]

Jim, the dew heater is needed to keep the dew of the secondary. Without it the dew builds up. Using a better focusor than the stock one will mean you will not get flexure issues that the stock one presents.

You will get some field curvature but it is minor, and you can always crop. I do with the shots taken on the RC12.

Its Rob or Bob Jenkins and we are ASSA.;) Rob is the current president, I am VP and Joe is a lifer now. I will pass on your regards.:)

Feel free to ask me anymore questions. I have included a few more images taken with the GSO RC's.

Horse Head (http://paulhaese.net/HorseheadLRGB.html)

Thors Helmet (http://paulhaese.net/ThorsHelmetHaRGB.html)

M83 (http://paulhaese.net/m83closeup.html)

[nobbygon]

Hi James,

I've just done a fair bit of research on this for my GSO RC8. I want a shorter FL and faster FR so I can fit a bit more in my images, not to mention shorter exposures for narrow band.

The only reducer/flattener I could find that works well with RCs was the televue TRF2008. I'm yet to get one due to its price ($400) and the fact that I got a moonlite focuser for the scope (also a must it you want good images).

Hope this helps.