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hello Redcat71 users, are you happy with your stars? Are your stars round all over the field , or are they elongated at the corners of the field when observed at high magnification? I have tried different cameras and back focuses, from 55 to 60 mm, but the problem persists. Maybe an optical issue or maybe a flattener issue. Have you had a similar experience?
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I am ecstatic with my stars. The Redcat 71 was a game changer with me because I don't have to worry about back focus, as long as I can find focus. I've not had any issue with stars distorting at all. You can look at my recent images for examples but I usually do 5 minute subs using a filter wheel and an ASI294MM Pro and love the results. I don't use any spacers in my setup. It's scope -> filter -> camera. Jeremy |
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My Redcat 71 gives me the best stars of any of my scopes using an APS-C size sensor. I didn't have to make any adjustments for tilt either. And there really isn't a back focus distance as it's a Petzval design. You just have to bring it to focus. If you are adding spacers, then when you refocus you just counteracted the spacers that were added.
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For me round all over the field. I don't do any back focus spacers like the 55mm when the camera (ASI294MC Pro) was attached to my C8. Just focus for the Redcat and it works. I don't know the reason why, perhaps someone more knowledgable will explain.
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When I first got my Redcat 71, it was obvious from my first imaging session that the OTA sent to me had pinched optics. The stars were all elongated in one direction. I went on Cloudy Nights and discovered one or two other users had the same issue. The seller, Ganymedes in the Netherlands, sent the scope back to Taiwan for decollimation. I got it back after a little under three months, but the collimation, as far as I can tell, was corrected perfectly and I've had round stars out the edges ever since. I think these are outstanding OTAs and I'm very happy with mine, but I'm at least the third person I know of who has had pinched optics at the start. Worth checking into, and if WO needs to fix it, it takes a little time, but they will do it well. Good luck! –Doug |
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 Here is 1 5min shot off the RedCat71 using the full frame ZWO ASI2400, flats take care of the vignetting but stars can look a little strange in those areas. BlurX will fix those stars with strange spikes along with TVGDenoise if using PixInsight |
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Below is an AberrationInspector image of a sub of M45 using an ASI2600MC Pro APS-C camera. The stars around the edges are out of round somewhat. I guess I could have asked for a replacement but it was quite a while before I got to use the telescope due to weather. Its the luck of the draw. Thank heaven for BXT.  |
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I'm like the others here - very happy with my stars all the way to the edges of my APS-C sized sensor. I really love the RedCat 71!
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Roberto Testi: Yes, my stars are round to the corners. Redcat 71 is Petzval design so yours is not a problem of back focus, but, in my opinion, of some tilt of the optical axis. Did you check it? |
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I agree, the problem is probably optical, but I have no idea of how to check it or fix it. I am waiting for some reply from the vendor on how to proceed. I bought it new two years ago and used it 3 times.
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There is a tilter on the back before the M48 thread. Try using it
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ok I will try. Thankyou!
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Round corner to corner. Most of my Redcat 71 shots on my page here have very little cropping to this point. You can see they are round. You can DM me and I can send you a link with plenty of fit files for you to review.
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I use a 55mm backfocus with my ZWO camera, a 2400MC-PRO. Your issue may be a slight tracking problem. Also, with the 71, I find it unnecessary to use a flattener. If you go to my Astrobin Page, look at the veil nebula I shot. These were 1st light images with my new 71. Hope this helps Patrick Graham |
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For me round all over the field. I don't do any back focus spacers like the 55mm when the camera (ASI294MC Pro) was attached to my C8. Just focus for the Redcat and it works. I don't know the reason why, perhaps someone more knowledgable will explain. You do NOT need a field flattener for C8, they are talking about refractor telescope, a different aminal  As to my Meade 80 triplet -I use Orion field flattener, I used to have precise 55 mm distance between the flattener and the camera ( I also have ASI 294 MM and ASI 1600), but lately changed to almost 64mm -better stars, some people report the similar-recommended backfocus is not a hard rule, may vary.
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Yes indeed....I have a William Optics RedCat 71 and had issues with the stars and also eccentricity gradient in the optics. I got with my vendor, and I shot some star fields and he studied them and eventually William Optics got involved. As far as the stars, W.O. thought these might be due to stress on the front lens of the scope or in other words "Pinched Optics". This stress could be from not using a dew heater and so they wanted me to shoot with one attached which I did. This did not help the wonky looking stars. The next option W.O. suggested was to relieve the stress by unscrewing the screws (4 at 90 degrees) one revolution holding the front lens and then retightening this screw until it just touches the lens. Then proceed with the other 3 screws in procession by rotating the scope in the T-Ring saddle 90 degrees to reach each screw. I did this and still the stars were funky looking. My stars were oblong in the corners too but as you all know Russ Croman's BXT can fix these easily. But I would rather not have a collimation issue, so the scope is going back to W.O.  |
