HELP! Coma on stars at Edge of field STILL

[alacant]

On 16/10/2017 at 08:11, Gerry Casa Christiana said:

still not got this sorted.

Still too close to the sensor. Add a spacer cut from e.g. a water bottle before you screw the cc home. Assuming you have the Baader cc, remember the m48 spacing is 57.5mm, not 55mm. HTH.

[Gerry Casa Christiana]

Hi there. 

I'm not using the M48 but I'll try adding more spacing. I thought it would be enough!  My first picture is below before I added 1mm to compare if that helps .

I hope that is all it is because this happened after I modified my camera but it wouldn't make sense to be that because it's in all the corners. 

Ill try adding more space then. So in your opinion it's not the primary mirror being pinched?

Thanks Gerry 

[Spaced Out]

I’m a newby but I’ve had similar experiences with the MPCC, you can see the thread I started on the Baader CC here, it covers a bit on T rings and spacing, maybe going over old ground but something might be helpful...

https://stargazerslounge.com/topic/291046-baader-mpcc-mkiii-connection/

In my case I’ve settled for a spacing that produces slightly ‘eggy’ stars around the edge, it is just as close as I seem able to get it and it left me wondering f I was just expecting too much from the MPCC and a DSLR. Maybe it can be better and I should revisit it sometime ?    

[Gerry Casa Christiana]

Oh yes I understand those things but yes it's good to go over the basics and see what's wrong. That's why I dismantled my secondary mirror to align my focuser but it wasn't that either.

All part of the fun 

 

Gerry

[Adam J]

On 10/16/2017 at 09:02, Gerry Casa Christiana said:

Hi there. 

I'm not using the M48 but I'll try adding more spacing. I thought it would be enough!  My first picture is below before I added 1mm to compare if that helps .

I hope that is all it is because this happened after I modified my camera but it wouldn't make sense to be that because it's in all the corners. 

Ill try adding more space then. So in your opinion it's not the primary mirror being pinched?

Thanks Gerry 

Exactly what filters did yo add and remove from the camera, also what camera is it?

[Gerry Casa Christiana]

11 hours ago, Adam J said:

Exactly what filters did yo add and remove from the camera, also what camera is it?

Hello there 

Yes it's a Canon 550d so I did the full spectrum mod with a replacement clear glass. So I have to use a clip in filter now to cut the ir otherwise I could have bloated stars. I think I may be finding the solution with the spacing of coma corrector I've moved it out a couple of mm and the pictures are better not perfect but definitely better. 

Id still like to hear your thoughts though. 

Gerry

[Adam J]

I did a conversion of a 550D but altered the sensor spacing in the camera instead of using the clear glass replacement, not easy to do as you have to laser align the sensor afterwards. I added about 3mm in total.

2 mm to the sensor and a 1 mm shim between the T-ring and the Coma Corrector. If you did the clear glass replacement though you should not need a shim...