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Old 19-03-2011, 09:32 AM
garymck (Gary)
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Baader Rowe Coma Corrector and matching Off Axis Guider

Hi,
just received a new Baader RCC1 Rowe Coma Corrector and Baader Off Axis Guider to use on my 8" f4 GSO Newt. Decided to get these to hopefully cure differential flex problems I had been having on very long exposures.

The coma corrector appears nicely made and the entrance lens is quite large - around 46mm or so. The Off Axis guider came in a Baader box, but is labeled as a Celestron Radial Guider, and appears to be exactly that, but without the SCT connection bits. No instructions were provided with either unit.

Will post pics and test results as soon as the sky clears enough to try some test pics, as I'm sure I'm not the only one interested in this combo - especially since it allows a filter wheel to go after the guider, or the use of a DSLR with coma corrector/off axis guider due to its long (91.5) mm spacing. The guider is 36.5mm thick, so allows an extra 55mm to put a t-ringed DSLR at optimum spacing, or a CCD camera + filter wheel up to that thickness. Purchased from Alpine Astro in the US, with usual excellent service....

cheers
Gary

Last edited by garymck; 30-03-2011 at 10:23 AM.
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Old 20-03-2011, 02:04 AM
garymck (Gary)
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First trials were limited tonight. The Baader RCC1 coma corrector came to focus in my 8 inch f4 GSO Newt without having to shift any mirrors etc. There have been reports of people having to move their primary so that the RCC1 could focus, however most of them appear to not have been using the correct spacing. Tonights test indicates that used per spec, (91.5 mm between coma corrector and camera chip) the corrector focuses without any need to mod a scope. The Baader off axis guider would not focus with a QHY5, it requires a couple of mm more in focus. This necessitated an 11.00 pm visit to a friends engineering business for a bit of late night lathe work to turn down a 1 1/4" to t adapter so that the QHY5 could get some extra room to focus. Once reassembled both the Main camera (QHY8) and the QHY5 were able to achieve simultaneous focus. At this point the combined effects of a full moon and almost zero transparency meant calling it quits.....

Gary
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Old 30-03-2011, 10:22 AM
garymck (Gary)
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Hi,
after having to wait well over a week for a clear night where I was not working, I finally managed to test this combination on my 8" f4 GSO Newtonian. At this point I am unable to recommend the Rowe Coma corrector. It is incredibly (excessively?) sensitive to collimation. Prior to use I collimated the scope using a set of Catseye tools to get what I thought was perfect collimation. This level of collimation is sufficient that with the Baader MPCC I already owned, I get perfect stars in all four corners of a QHY8 frame. At no point was I able to achieve this with the Rowe corrector. At first I wondered if the extra length was causing focuser sag that was changing the effective collimation, so I tried imaging first on one side of the meridian, and then the other. However there was no change in the star shapes between frames indicating that the focuser was not shifting appreciably. At this point, I believe the only way to salvage my whole imaging system is to buy a set of the new dual hole Catseye tools to see if their increased accuracy cures the imaging problems. Not sure yet whether to do that as it may be good money after bad. Imaging with cheap newts seems very problematical, and I guess you get what you pay for..... Imaging with refractors is sooooo much easier and more relaxing.

The Off Axis Guider was much easier to use than I expected. I managed to get a guide star everywhere I pointed the scope using 3 second exposures on a QHY5 - not the most sensitive of guide cams. I was able to get round stars (in the center of field of course!) with a 30 minute exposure, so that at least works.

I haven't posted copies of images since there is nothing to really show off..... Buyer beware.

cheers
Gary
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Old 30-03-2011, 11:16 AM
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multiweb (Marc)
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Quote:
Originally Posted by garymck View Post
At this point, I believe the only way to salvage my whole imaging system is to buy a set of the new dual hole Catseye tools to see if their increased accuracy cures the imaging problems.
Sorry to hear about you misadventure with the latest Baader Coma Corrector. IMHO I don't think the latest double pupil A/C will help in your case. It sounds like you may still have the spacing wrong. Flaring will be exacerbated by misalignement but it's more forgiving when the spacing is right, so in my view it is and indication your corrector is still too far or too close. Make sure you measure your spacing from the glass surface closest to the secondary. Don't give up yet.
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Old 30-03-2011, 11:28 AM
garymck (Gary)
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Hi,
spacing is bang on spec at 91.5mm. I use a special adapter made by Peter Tan in Hong Kong to get my spacing bang on. I probably was not clear enough in saying that the 4 corners of the image are different - indicating collimation...Its not flare as such. It's not huge, but the misshapen stars are there nevertheless!! Because of the difference in each corner, I believe it is collimation. The long back spacing (91.5 for the Rowe versus 55mm for the MPCC) as well as the extra air spaced element in the corrector, must make collimation MUCH harder!!! At least more so than I expected....
cheers
Gary
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Old 30-03-2011, 11:44 AM
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tlgerdes (Trevor)
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Did you collimate with the corrector in? The catseye collimation is sensitive to spacing as well and with the extra length of the CC you will need to collimate with it in place.
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Old 30-03-2011, 11:49 AM
garymck (Gary)
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Nope, collimated without corrector in - will see if I can rig something up to do so adapter wise...

will report back after trying it out...

cheers
Gary
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Old 30-03-2011, 12:02 PM
bratislav (Bratislav)
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It could be that CORRECTOR is miscollimated (lenses decentered/tilted). I've seen it in much more expensive "pedigree" units (TeleVue Paracorr) so it wouldn't be the first ...
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Old 30-03-2011, 04:15 PM
garymck (Gary)
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Couldn't collimate with the corrector in place, so stacked every extension tube I had to get out to where the corrector would focus. There is a very slight collimation difference out there as opposed to where I originally collimated. This may be due to the extension tubes not locking down square, or may be a real collimation difference. Will have to try next clear night and see if this fixes things...
cheers
Gary
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Old 13-04-2011, 12:26 AM
Chris.baron (Chris Baron)
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Quote:
Originally Posted by garymck View Post
Couldn't collimate with the corrector in place, so stacked every extension tube I had to get out to where the corrector would focus. There is a very slight collimation difference out there as opposed to where I originally collimated. This may be due to the extension tubes not locking down square, or may be a real collimation difference. Will have to try next clear night and see if this fixes things...
cheers
Gary
Any joy Gary? I'm interested in the RCC1 myself. I have a customised R200ss (carbon fibre and a feathertouch focuser) and am finding that whilst my 50mm finder scope guiding solution works, it isn't perfect. I'm therefore hoping to get my Lumicon OAG into service to see how that turns out. I was able to finally achieve the correct spacing with my MPCC so that's at least a positive thing, but given I am relegated to narrowband imaging longer exposures are a necessity. Fat stars are somewhat sub-optimal.

So all of that said, I'm hoping you're able to achieve proper collimation/focus/whathaveyou with your combo so that I can feel comfortable with trying it out myself. I've bought too many items brand new only to find they don't cut it and then have to take a bath on reselling them. The CFO has not been amused.

Cheers,
Chris

Last edited by Chris.baron; 13-04-2011 at 12:41 AM. Reason: proper formatting
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Old 13-04-2011, 07:44 AM
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peeb61 (Paul)
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Hi Gary,
Can you post an image showing these errors? I too had problems with stars on one side close to focus and stars on the other showing coma with stars in the middle being close to perfect and this is just with the Baader Coma Corrector in the imaging train until I used the extension tube that came with my scope and all is well with focus.

I bought the Bintel 8" f/4 and I am completely happy with it.

Paul
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