200pds optics &baader mk3 cc spacing m48

[bottletopburly]

So on my 200pds i have been tweaking the optics to refine the optics to give better stars so apeture mask fitted to primary ,drawtube trimmed so not to protrude into ota now as far as i can tell primary and secondary are collimated tweaked the primary last night using barlowed laser and secondary used concentre now the baader cc mk3 now has a spacing of approx 57.6 ,using the m48 fitting ,so 46.5mm sensor distance ,T-ring to cc shoulder 9.1mm and a friend made me a delrin washer 2mm which i fitted under cc lenses to push further away from sensor to give 57.6 ,attached a 10 sec sub of arcturus now stars seem to show coma pulling to 5 oclock which i think may be down to PA so if more experienced members in the fine art of tweaking cc does this look like i'm there abouts ,do you think the star shape is down to PA or does spacing need further tweak .  Raw files attached a 6 sec and two 10 sec and a screen shot 

@alacant

https://www.dropbox.com/s/3uqyyqahnvzx0cr/Single__0084_ISO1600_6s__NA.NEF?dl=0

https://www.dropbox.com/s/bt19xehlt39i8t6/Single__0085_ISO1600_10s__NA.NEF?dl=0

https://www.dropbox.com/s/px058pgrzcivbl2/Single__0086_ISO1600_10s__NA.NEF?dl=0

[alacant]

Hi

The Baader needs at least 58mm so maybe try an extra washer or -better- an 11mm eos t-ring [1]. Bottom left is astigmatism. the extra mm may help with that too.

To retain collimation during and between sessions, my advice would be to lose the aperture mask, remove the mirror clips and fix the mirror with three small patches of neutral silicone sealant, fit stronger springs (1.4mm wire), a longer losmandy dovetail and a rigid box section to tie the top of the rings. An oag and shower cap help too.

But TBH, that's one of the best frames I've seen with the Baader cc. In the end, if you want small stars corner to corner over aps-c, you're gonna have to go with the gpu or ES cc.

Cheers and HTH

 

[1] **EDIT. Ooops, sorry. Just realised it was a Nikon. But you'll get the idea...

       

Edited May 30, 2021 by alacant

[bottletopburly]

23 minutes ago, alacant said:

Hi

The Baader needs at least 58mm so maybe try an extra washer or -better- an 11mm eos t-ring [1]. Bottom left is astigmatism. the extra mm may help with that too.

To retain collimation during and between sessions, my advice would be to lose the aperture mask, remove the mirror clips and fix the mirror with three small patches of neutral silicone sealant, fit stronger springs (1.4mm wire), a longer losmandy dovetail and a rigid box section to tie the top of the rings. An oag and shower cap help too.

But TBH, that's one of the best frames I've seen with the Baader cc. In the end, if you want small stars corner to corner over aps-c, you're gonna have to go with the gpu or ES cc.

Cheers and HTH

 

[1] **EDIT. Ooops, sorry. Just realised it was a Nikon. But you'll get the idea...

       

Cheers Steve I did order a 3mm m48 extension they sent an m42 version😡 

I will look at springs , I have a losmondy bar and rings bridged 👍 I will look at shimming 1mm more