I am considering adding a TV Paracorr to my main rig to increase my focal length for higher resolution shots and also, the shorter barrel length would avoid the front end protruding into the light as the current SW CC (GPU) does much to my chagrin. One thing I still not clear with is what do you need to connect the business end of the Paracorr to the camera end (via Tilt unit and Filter drawer) as they are all M48 threaded and apparently the Paracorr isn't (some kind of weird thread in there). I can't think the Tunable Top is the way or is it? Plus, any tips on how best to use and what cons there might be in use or things to look out for.
Cheers,
Andrea
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One of the downsides of the Paracorr IMO.
I had to use mine in the 2" compression fitting of my focuser. Other folks that I know who use it did the same thing. The tunable top is only for visual. It's a pretty substantial downside IMO, and if you don't lock down the compression fitting evenly you can introduce tilt. I also had a bigger issue with my GSO newt, the focal plane was too far above the tube and I had to actually shim my Paracorr into the compression fitting with 3D printed parts to achieve focus. Other folks who use the TS Optics ONTCs (adjustable primary mirror) were able to avoid this issue by simply shifting their primary back further in the tube. The paracorr is a great corrector, but the implementation is kinda poor for imaging.
For connecting to the camera, you'll need to buy the Paracorr adapter, here is the link. It's available in M54, which I used... and also M48
https://agenaastro.com/tele-vue-m54-camera-adapter-for-2-4-imaging-system-m54-1073.html |
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Here's an old image of when I first put it together. The adapter adds 6.6mm of backfocus. M54 worked for me because QHY's ecosystem runs M54 native.
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Thanks for the advice, Brian. The only thing I could find that "might" work is this Tele Vue 48mm Filter Adapter for 2.4" # AFT-1105 (agenaastro.com) but I don't even know if someone is selling it over here (UK) 'cause so far I haven't seen any on sale. I dread to think the length I'd have to go to import it from the US.
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andrea tasselli:
Thanks for the advice, Brian. The only thing I could find that "might" work is this Tele Vue 48mm Filter Adapter for 2.4" # AFT-1105 (agenaastro.com) but I don't even know if someone is selling it over here (UK) 'cause so far I haven't seen any on sale. I dread to think the length I'd have to go to import it from the US.
I can't say for sure but it looks like it should work.
TS Optics has it
https://www.teleskop-express.de/en/adaptors-10/adapter-to-other-threads-123/televue-aft1105-2-filter-adapter-for-imaging-system-1739 |
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You need the proprietary TeleVue thread adapter to do anything with the corrector, i have both an M48 one and an M54 one (TS sells them). Both say they have "6mm optical length" but this is not at all true. The threads kind of go behind the last lens of the corrector, where the backfocal distance calculations are counted from so that 6mm is never really being eaten up.
The real length these take is i would estimate somewhere around 1-3mm. I cant give you a more accurate number than that, because i am not sure what that is, i just found the best distance by trial and error with spacers. A much better way of calculating the backfocus is to measure 58mm from the back of the flange, this way you can ignore much of the confusion and get very close to the best backfocus without too much trial and error.
By the way this means that you dont really have the full 55mm to work with since a few millimeters are eaten up by the mandatory nonsense thread adapter. You may want to check that your other kit is narrow enough to fit the shorter than 55mm available space.
What camera are you planning on using the Paracorr with? And for that matter, what focal length is your newt? The Paracorr stands for Parabola corrector which is all it does, it does not flatten the field at all like your GPU does. TeleVue claims on their site that with less than 1200mm focal length there may be some field curvature on large chips, and i can confirm this is the case with mine. My scope is roughly 885mm focal length without the Paracorr and 1018mm with and coupled with my APS-C means either a) my sensor is a bit too large or b) the scope does not have quite enough focal length for the corrector or c) both. If yours is also less than 1m focal length and the camera you use has a large chip, you may not actually get the resolution increase you were wishing for, so some food for thought.
One more thing, the Paracorr shifts focus outwards by 40mm. Double check that you actually have enough focuser travel for this.
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Oskari Nikkinen:
You need the proprietary TeleVue thread adapter to do anything with the corrector, i have both an M48 one and an M54 one (TS sells them). Both say they have "6mm optical length" but this is not at all true. The threads kind of go behind the last lens of the corrector, where the backfocal distance calculations are counted from so that 6mm is never really being eaten up.
The real length these take is i would estimate somewhere around 1-3mm. I cant give you a more accurate number than that, because i am not sure what that is, i just found the best distance by trial and error with spacers. A much better way of calculating the backfocus is to measure 58mm from the back of the flange, this way you can ignore much of the confusion and get very close to the best backfocus without too much trial and error.
By the way this means that you dont really have the full 55mm to work with since a few millimeters are eaten up by the mandatory nonsense thread adapter. You may want to check that your other kit is narrow enough to fit the shorter than 55mm available space.
What camera are you planning on using the Paracorr with? And for that matter, what focal length is your newt? The Paracorr stands for Parabola corrector which is all it does, it does not flatten the field at all like your GPU does. TeleVue claims on their site that with less than 1200mm focal length there may be some field curvature on large chips, and i can confirm this is the case with mine. My scope is roughly 885mm focal length without the Paracorr and 1018mm with and coupled with my APS-C means either a) my sensor is a bit too large or b) the scope does not have quite enough focal length for the corrector or c) both. If yours is also less than 1m focal length and the camera you use has a large chip, you may not actually get the resolution increase you were wishing for, so some food for thought.
One more thing, the Paracorr shifts focus outwards by 40mm. Double check that you actually have enough focuser travel for this.
Thanks for sharing your experience. The newton it would need to go on is 1200 mm in FL and using an ASI294MC so it might sit in the grey area there. The fact it doesn't flatten the field is a bummer though as I plan to move up one day. Also, I'm not sure I have these extra 40 mm which is kind of surprising as the TV site claims just 14 instead! When all said and done I might not go with it as it seems cheaper to get/swap with another camera (I also have an IMX533-based camera).
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andrea tasselli:
Oskari Nikkinen:
You need the proprietary TeleVue thread adapter to do anything with the corrector, i have both an M48 one and an M54 one (TS sells them). Both say they have "6mm optical length" but this is not at all true. The threads kind of go behind the last lens of the corrector, where the backfocal distance calculations are counted from so that 6mm is never really being eaten up.
The real length these take is i would estimate somewhere around 1-3mm. I cant give you a more accurate number than that, because i am not sure what that is, i just found the best distance by trial and error with spacers. A much better way of calculating the backfocus is to measure 58mm from the back of the flange, this way you can ignore much of the confusion and get very close to the best backfocus without too much trial and error.
By the way this means that you dont really have the full 55mm to work with since a few millimeters are eaten up by the mandatory nonsense thread adapter. You may want to check that your other kit is narrow enough to fit the shorter than 55mm available space.
What camera are you planning on using the Paracorr with? And for that matter, what focal length is your newt? The Paracorr stands for Parabola corrector which is all it does, it does not flatten the field at all like your GPU does. TeleVue claims on their site that with less than 1200mm focal length there may be some field curvature on large chips, and i can confirm this is the case with mine. My scope is roughly 885mm focal length without the Paracorr and 1018mm with and coupled with my APS-C means either a) my sensor is a bit too large or b) the scope does not have quite enough focal length for the corrector or c) both. If yours is also less than 1m focal length and the camera you use has a large chip, you may not actually get the resolution increase you were wishing for, so some food for thought.
One more thing, the Paracorr shifts focus outwards by 40mm. Double check that you actually have enough focuser travel for this.
Thanks for sharing your experience. The newton it would need to go on is 1200 mm in FL and using an ASI294MC so it might sit in the grey area there. The fact it doesn't flatten the field is a bummer though as I plan to move up one day. Also, I'm not sure I have these extra 40 mm which is kind of surprising as the TV site claims just 14 instead! When all said and done I might not go with it as it seems cheaper to get/swap with another camera (I also have an IMX533-based camera).
*I think youll be fine with that setup. There is a big difference in field curvature right around that 1m mark, and your chip is 7mm smaller than mine so better in both cases.
With mine its fixable with BlurXT, but that outer edge of field is kind of dodgy in mine without BXT. Coma correction is perfect i should say, so not a bad corrector even with a suboptimal scope.
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I ran mine on APS-C and didn't have any crazy issues with flat field. Admittedly, I wasn't very good at backfocus at the time, it was my first scope. 40mm sounds about right tho. If you look at my above Pic, you can see the tape where I marked the barrel. That's how far out I was protuding. I made some adjustments later on to bring it in more, but I still had a solid 20mm beyond the compression fitting. That's where my 3D printed shim came in.
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What is your focuser? I used a moonlite with a paracorr and used this adapter https://www.teleskop-express.de/en/adaptors-10/adapter-m68-205/ts-optics-m68-system-connection-adapter-for-vip-2010-paracorr-to-m68-5014
There may be other similar adapters.
Hope you can get it to work. It's a big step up from the GPU and I didn't mind the skight Barlow effect.
I also considered the wynne corrector, but didn't have a full frame camera at the time.
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Thanks everyone. To answer some of the queries: 40mm backfocus could be the deal breaker as I'm not sure I have that much (but I'm going to find out soon) and seems quite a lot for tilt avoidance. My focuser is a 2" Moonlite of 2004 vintage so I have to stick with 2" correctors.
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So it turns out I have 36mm past focus before bottoming out. Doable with parafocal rings but hardly ideal.
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I use a type 2 Paracorr with my ONTC. I am fortunate that the scope comes with the ability to position the primary mirror correctly for the Paracorr.
As others have mentioned - the tunable top can be removed. Here is the optical diagram with that removed:
https://www.televue.com/engine/TV3b_page.asp?id=61&Tab=_phot
You have 56 mm of backfocus from the lens.
You can use a Televue made T thread adapter like this one, that'll screw on to the business end. It'll eat up ~1 mm of backfocus.
https://www.telescope.com/Tele-Vue-Standard-T-Ring-Adapter/p/8395.uts
A few notes:
- I use it with a 2" Feathertouch focuser. Yes, if you are not careful, the compression fitting will introduce tilt. But, over time, I've found this is not a huge limitation with a sensor the size of the 294MM or smaller (to my standards, anway). The trick is to apply downward pressure ((i.e, towards the focuser) on the camera while tightening the fitting. A threaded connection would be better, but I have no idea how to concoct one.
- For collimation, I use a Tublug for primary axial error. Since it has 2" diameter, you can actually use the Tunable Top (unthread and remove camera equipment), place the Tublug and laser in that. The advantage is that you can now do the (PAE) collimation accounting for any tilt caused by the optics of the Paracorr. The barlow effect caused by the Paracorr simply adds on to that in the Tublug and the collimation can be perfomed normally.
- Focuser axial error correction is through a catsye autocollimator (off set pupil), without the Paracorr. Note, since the Paracorr pushes the focal point out, you have to use an autocoliimator with a 1" extension (Catseye makes one) to make sure you are doing the FAE closer to the actual focal point with the unit in place.
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