Re: [APML] Coma corrected SCT

[Duncan Munro <dmunro@sfu.ca>]

Just to follow up on this. I did some test images with the CC  and my 
NEG. Unfortunately, we've had a maddening spell of cloudy/thin cloud 
weather, so only the brighter stars show up. Coma at the extreme edge of 
a 10" f6.3 35mm frame is better but still not acceptable. Guide stars 
are much improved, however, so this combo does yield results. I would 
speculate that the Lumicon CC and NEG will work quite well with an F10 
SCT. I'll try that when the weather permits.

I'm going to try a Baader MPCC next. with my 10" F6.3. By all reports 
the MPCC is quite superior to the Lumicon CC, but it is less convenient 
as the MPCC must be placed directly in front of the camera to achieve 
the correct, 55mm, spacing. I'm already spoilt by the tighter, coma 
corrected, stars that the NEG/CC combo produces so placing the MPCC 
after the guiding prism is disapointing. My Meade 208xt seems to work 
well in standalone mode with the NEG/CC combo but I'm not so sure how 
well it will do without the CC in place. I may have to switch to my 
Mx516/Star 2000 rig but this will mean adding  a laptop into the mix.

cheers

Duncan



Duncan Munro wrote:

> I tried out my Lumicon Coma Corrector tonight. I'm using it with a NEG 
> and a 10" F6.3 SCT OTA. I can say that visually, the CC does work with 
> an SCT as the off axis stars in the guider prism are much tighter and 
> do not exhibit the typical coma flare. The on axis sharpness does not 
> appear to be affected. I did some test expoures on Fuji 400 with my 
> Nikon F2. I should have some rough results tomorrow.  If this set up 
> works I should have a nice rig for film. In theory it should also work 
> with an f10 OTA as well. The CC will not help the field curvature but 
> the F6.3 OTA has a flatter field than an F10 setup.
>
> I am still working the kinks out of my autoguider setup as my 208xt 
> requires about .8 mm more in-travel than the NEG will permit. Time for 
> a trip to the machine shop... It's kind of frustrating as I'm waiting 
> for a Star2000 module to arrive in the mail so I can use my MX516 an 
> an autoguider as I know it will focus with the NEG.
>
>
> cheers
>
> Duncan
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