Levenhuk Ra Carbon Fiber 8" RC
Posted 12 October 2013 - 10:30 AM
I have been debating whether to get the 8" RC or the 8" imaging newtonian. Now that you have the RC, are you still glad you started with the faster newt first?
Posted 14 October 2013 - 03:42 PM
I have a very similar setup as you:
AT8RC carbon fiber
Canon T2i camera
AP CCDT67 reducer
I was having some flexure problems in certain mount orientations, so I switched to off-axis guiding (TS-OAG9 guider + SX Lodestar guiding camera) and am now getting better results. I was originally using a long 2" nose piece in between the CCDT67 & the camera for an effective focal ratio of about 5.34 (lower than yours), but I found this to cause too much vignetting on the APS-C sized chip for my tastes, so now I have the CCDT67 screwed directly into the TS-OAG9 body and use the CCDT67 as the nose piece. This gives me an effective focal ratio of about 6.09, and way less vignetting.
I am jealous of the color in your test images - unfortunately I am still using an un-modded camera, which requires a LOT of stretching to tease the H-Alpha out of the background. I gotta get me a T3/1100D & get it modded like you, which will be my very next AP purchase.
One more thing I did for my 8" RC CF: Mine seems to go out of collimation frequently, and I disliked using the Allen wrenches to tweak the collimation (which I check every time I move the scope by doing a star test in camera "live view" in BackyardEOS), so I added Bob's Knobs screws for the secondary adjustment. For me, it is now about 5x easier to collimate with the BK knobs.
In your write up, you said you have imaged with an f/4 Newt. How would you compare imaging with the Newt with imaging with the RC (other than exposure time and field of view) - advantages/disatvantages? I am thinking of getting one of the 8" f/4 imaging Newts (which would also be guided with the OAG) because of the fast f/r.
Posted 17 October 2013 - 02:08 PM
I havent yet needed to touch the collimation of the RC since the initial adjustment. The newt needs to be collimated every time it is used and can sometimes be a pain. If I were starting out with one of these two I believe I would choose the RC, but only with the Astro Physics Telecompressor. The fast optics of the f/4 newt is very nice but the difference isnt all that bad when using the Telecompressor with the RC. I think the stars look a bit nicer with the RC.
As for the camera, the Canon T3 does a nice job when its cool out but the Summer/early Fall heat has been awful. If the outside temp is above 80 degrees the noise is just terrible. Its best when its below 60 and this is why I am now looking into getting a cooled monochrome CCD camera. Since the weather has cooled off I'll be fine with it for a few more months but plan to get a new CCD before next Summer. If I knew then what I know now I dont think I would have spent money to get the camera modified. I probably would just buy something like the QHY8L one shot color. Even after I get my monochrome and filter wheel/filters I'll probably buy some sort of cooled OSC camera.
I just received the Levenhuk Ra 80mm triplet with FPL-53 optics on Friday, the 11th, and its been cloudy and/or raining everyday since. Today it finally cleared so I'm hoping to at least get to view some stars with it this evening. As bad as I hate to, if it performs well I may sell my AT65EDQ and keep to 80mm. It has been a fantastic scope for imaging and I recommend it all the time for beginners. I just cant justify keeping them both and feel the 80mm will be more versatile.
I'll keep an eye on this thread now so just ask if you have anymore questions and I'll be glad to help if I can.
Posted 19 October 2013 - 01:10 AM
I looked at your astrobin site, very nice images with both the RC and the newt.
You mentioned the RC does holds its collimation much better than the newt. Do you find the fact the camera is behind the primary rather than off the side makes it much easier to use for imaging? Or that the CF tube and quartz mirror made that much difference in maintaining focus?
If I were to get the 8" RC and and a CCDT67 for long focal length imaging, do you think a 6" imaging newt would be a better complementing scope than the 8" newt for wide field?
Posted 19 October 2013 - 07:49 AM
The CF tube does make a huge difference in maintaining focus. I love it and now would like to sell my AT8IN and get the Levenhuk CF newt. They are quite a bit lighter also.
Regarding the 6" or 8" newt, yes I think if those would be your only 2 then a 6" newt would probably be the better compliment. I also have a small refractor for wide field so I tried to get a 400/800/1200/1600 spacing with my focal lengths.