ic2602 from the doghouse (dodging clouds)5 april 2010

[h0ughy (David)]

i took this below par image tonight from the doghouse - the evening started clear then the cloud marched in. its only 19 minutes worth but it shows i still have some problems with the OTA - i think the optics are pinched? now would it be the secondary or the primary mirrors? if you haven't noticed i have triangular stars.......
stacked in DSS then imported into Pixinsight for processing

re-sized in photoshop , the first image was just re-sized but the second one i adjusted the levels slightly

the scope was the vixen R200SS with a baader coma corrector - cooled canon 350D iso 400 2 minute shots (except the last one LOL)

[RB (Andrew)]

Dave it does look like the optics are pinched.
Shame the clouds ruined the evening for you though.

For 19 min, the blue star colour is beautiful.
Imagine getting a few hours on this.

[Paul Haese]

Dave, not a bad image all up. Check your secondary first. It might be the collimation screws being too tight. Loosen the screws off a bit and collimate again. Then check your primary if that does not sort the problem.

Good star colour.

[multiweb (Marc)]

Looks great David. You have a tiny bit of tilt in your field so the corrector is not doing its job 100%. Once you have that fixed you'll be cooking.

[telecasterguru (Frank)]

David,

I think the image is pretty good.

Frank

[Garyh]

Know what it`s like dodging the clouds! been that way up here too!
Doesn`t look to bad up close but like Marc says, maybe something is quiet not square on? Also could be the secondary being pinched or Astigmatism..
Gary

[h0ughy (David)]

Originally Posted by Paul Haese

Dave, not a bad image all up. Check your secondary first. It might be the collimation screws being too tight. Loosen the screws off a bit and collimate again. Then check your primary if that does not sort the problem.

Good star colour.

i will try that soon - raining now

[h0ughy (David)]

Originally Posted by multiweb

Looks great David. You have a tiny bit of tilt in your field so the corrector is not doing its job 100%. Once you have that fixed you'll be cooking.

i also agree - it is a pity the hotech adapter doesnt come on the MPCC that would centralise everything better

[strongmanmike (Michael)]

Great shot Dave, the astigmatisim is mild and at that display size hard to see. This brings back memories of the ASA but my triangles were much more obvious .

You need to look at the primary and secondary for stressed optics, in the case of my ASA it was the secondary mounting glue that was pinching the secondary

MIke

[gregbradley]

I had a Vixen R200SS once. I fpound collimation VERY touchy.

It was easy though when I used one of those cheapish laser collimators that reflect back onto a bullseye.

Also the coma corrector probably has a specific metal back distance.
All correctors do. Perhaps your spacing is wrong because you are getting coma and the corrector should handle that. I think there are examples on the net of the R200SS and DSLRs so it should be able to be done.

For example my AP140 and its 155TCC corrector requires an exact distance with a tolerance of +/- 1mm! If it is say 4mm off you can see +the coma in the corners a bit like your image. Typical correctors have more tolerant margins of perhaps +/- 5mm.

Probably the faster the optics the more exact the spacing needs to be for the corrector to work. That plus collimation is probably your problem. But that is clearly primarily coma in your image.

I'd say your metal back distance is considerably off for that much coma.

Greg.

[h0ughy (David)]

Originally Posted by gregbradley

I had a Vixen R200SS once. I fpound collimation VERY touchy.

It was easy though when I used one of those cheapish laser collimators that reflect back onto a bullseye.

Also the coma corrector probably has a specific metal back distance.
All correctors do. Perhaps your spacing is wrong because you are getting coma and the corrector should handle that. I think there are examples on the net of the R200SS and DSLRs so it should be able to be done.

For example my AP140 and its 155TCC corrector requires an exact distance with a tolerance of +/- 1mm! If it is say 4mm off you can see +the coma in the corners a bit like your image. Typical correctors have more tolerant margins of perhaps +/- 5mm.

Probably the faster the optics the more exact the spacing needs to be for the corrector to work. That plus collimation is probably your problem. But that is clearly primarily coma in your image.

I'd say your metal back distance is considerably off for that much coma.

Greg.

thanks Greg for the view, any ideas on how i can address that when the tring is fixed and the mpcc is fixed( i am a bit thick)? is there a way to adjust? How and what do i measure?

Looks like i have two problems - it has sidonioitis as well . so do i start at the secondary or look at the primary Mike?