Baader RCC vs Skywatcher GPU

[Lognic04]

Hi all,:hi:
Out of the Baader RCC1 and the Skywatcher GPU correctors, for an f4 scope, Which would perform best?:shrug:
And yes i know, the paracorr would win, but the paracorr is quite expensive :(
:question::thanx::thumbsup:

[Camelopardalis]

From what I've read, the GPU corrector is better corrected over a larger field for f/4. The Paracorr may be better visually, but not for imaging. Take with a pinch of salt, I'm just regurgitating, no first-hand evidence.

[bratislav]

Paracorr-2 is a gold standard coma correcting device. Imaging AND visual. Second to none, including Keller's and Riccardi's Wynne variants.
GPU is a good choice, so is RCC1. It really depends on how much BFL you need, and how big chip do you want to cover. I would give GPU (the tiniest) edge, because Dave Rowes' design will vignette a tad more at f/4.
Another option to consider may be Harrie Rutten designed Explore Scientific HR coma corrector. All 3 of those will be similar in performance at f/4, but not in the same class as Paracorr-2, Riccardi's or Keller's Wynne variants.

[billdan]

This list may help - only the cheapies shown

Skywatcher - F4 to F6 - 55mm distance to chip - decreases FL by 0.9
Baader MPCC MkIII - F3.5 to F6 - 55mm dist to chip - no change to FL
Baader RCC1 - F3.5 to F6 - 92mm dist to chip - no change to FL
GSO - F3 to F6 - 70mm dist to chip - increases FL by 1.1
Quattro - F3.5 to F6 - 70mm dist to chip - no change to Focal Length

All of the above guarantee a 44mm corrected field

Cheers
Bill

EDIT: The Quattro should read 55mm distance to the chip

[Camelopardalis]

That's interesting...what's your source? I have the GPU corrector and TS claim distances in the 50s mm :shrug:

https://www.teleskop-express.de/shop/product_info.php/info/p5836_GPU-Designed-Aplanatic-Newtonian-Coma-Corrector-4-element.html

(incidentally, my test images with a Quattro are miserable at ~55mm)

[billdan]

Just had a look at OPT-corp pricelist and your right Dunk it is 55mm, I did my spreadsheet 3 years ago, so either I misread the specs or it has changed in that time.

Sorry its not working for you at 55mm, collimation has to be more precise with coma correctors.
I have the Baader MPCC MKIII and it works OK at 55mm but it does make the stars fatter than without it.

Interesting comparison here between the Quattro and MPCC MKIII, the MPCC does not compare very favorably.

https://www.cloudynights.com/topic/554686-coma-corrector-compariosn/

[Camelopardalis]

Ah bugger, I was hoping TS were wrong and that the extra spacing would solve my problems :lol:

I guess it only serves to highlight getting a good corrector :thumbsup:

[rbronca]

This is the best comparison I have seen. http://www.astrofotoblog.eu/?p=856#more-856
I had the MPCIII and have now moved to the GPU. The stars are now way better, but it is far less forgiving with tilt.

[glend]

I have used the Baader MPCC Mk3 for years, on both my 10" f5 carbon strut imaging newt and a 8" F5 GSO, and never had any problems. Spacing is correct at 55mm but be careful with DSLRs because Nikon and Canon actualky have different sensor setback spacings. TS make different thickness bayonet adaptors for thise DSLRs. Stars can appear more bloated when imaged through newts, compared to say a well corrected triplet APO, but this can often be due to a tendancy to over expose using fast newts, the quality of glass used in the coma corrector, and the lower contrast levels due to central obstruction effects and the lack of internal tube baffling on most production newts (Mak-Newts are different in my experience as they don't need external correction, have smaller secondaries, and are heavily baffled internally).

And Dunk, don't worry about coma correction until you have collimation sorted.

[billdan]

Thanks for that Rbronca, it was a good read and interesting results that was achieved.

There must be two versions of the Quattro going round, as this blog implies it needs 70mm distance to the chip.

" On the other hand TS quarto CC performs very badly. I would say that the stars are more deformed than in case without the corrector. The comets are flying outwards the center. One could say that it’s not coma corrector, but coma creator 🙂 And yes, I didn’t forget to use 15 mm spacer between the camera and the corrector, because back focal distance is 70 mm and not 55 mm as for every other CC. "


Bill