Hi ! Question for MarkS - Focal Reducer Problem

[RobertM]

Because the image is heavily stretched it's difficult to tell precisely but it does look like your collimation is a bit out.

[Mac]

Because the image is heavily stretched it's difficult to tell precisely but it does look like your collimation is a bit out.

CCD Inspector agrees.



Yes i know the image is huge but its a small file.

[hgg]

Hi,

Is the CCD Inspector result from the first image???
How about the second one?

George.
p.s. Robert I am very curious about your results, since the collimation was dead on.
      If I image without the reducer, the coma is minimal.

[Mac]

Yup that was the first image,
I'll try the second image now.

[Mac]

second image.


Mac

[hgg]

So, what is the verdict?   
Looks like the second one with a distance of 105mm has less curvature?   
It has a big offset from center.   Do we trust CCDInspector?

[RobertM]

Ccd inspector can be trusted but it's better with a more even star fields like open clusters. Just one exposure of M44 would do.  A globular coulsewnew the calculations though I think it's probably correct.

Robert

[hgg]

Hi,

I am not sure what to make of the results.  I think I will use the spacing that was measured
by projecting the moon on a surface.  For my reducer that was 75mm (205mm focal length).

Thank you very much for your help!
George.

[RobertM]

The centre of curvature looks quite a way out to me and also seems to coincide with the center of the distortions you're experiencing.  Was the star you collimated on in the dead centre of the eyepiece?  If so then I would check the secondary hasn't moved - use a ruler from the tube edge to give you some idea.  I also found collimation to be quite critical on my C9.25, even 1/16th of a turn on the screws was quite noticable in a star test.

Good luck sorting your problem out George.

Robert

[hgg]

Robert,

The star was indeed in the center when I was collimating.
I don't know..  I will try again to check the collimation, although a star test
I did recently was successful.

Thank you very much for your help.
George.

[RobertM]

Just a thought - any sag caused by the weight of the imaging equipment is also worth investigating.

[hgg]

Hello, its me again...   

Robert, I think you might be correct.  Below its a recent picture of M92 cluster with perfect
star collimation.  The coma is smaller.  It seems that the weight of the camera depending on
the elevation places stress on the small Visual Back to CCD adapter.  If the target is straight
up, the comma is less, if the elevation is lower then its more.  I think I have to find a different
and stronger adapter!

Is it possible to double check the image with CCD Inspector?



Thank you!.
George.

[RobertM]

Hi George,

The collimation is still well out but in a different direction, I think you have found your problem...

Regards
Robert

PS. That's a very good image even with the collimation problem !

[hgg]

Thank you Robert.

I think I have to start looking for a good quality adapter...

Regards,
George

[Mac]

As reguested.