What's causing these blurs ?

[LandyJon]

I've just finished setting up the back focus for the reducer/corrector on my Nexstar 6SE and I can't seem to get a decent image out of it.  I'm getting a strange smudge on stars at the top of my image seeming to radiate out from towards the bottom of the frame.  The lower left and right corners the smudge is near horizontal towards the edge and the upper corners it smudges at 45 deg toward the corners.

Is it collimation ? or does it look like a problem with the back focus, or something I haven't considered ?

Thanks for looking ...

Edit: Added unprocessed tif ... should be easier to view ... jpg added.

 

M 82_00009.fits Autosave.tif

Edited March 17, 2021 by LandyJon

[michael8554]

The stars radiating out at the top of frame indicate the FR is too close to the camera sensor.

However, the radial blurring of the stars at the bottom of frame indicate the FR is too far away from the camera sensor.

In other words, the FR spacing is correct, but there is tilt in the image train.

Michael

[LandyJon]

Thanks Michael, that does make sense, I'll have a look but I'm sure it's all screwed in properly, there must be something either in the corrector itself or the camera.

Can't get the image to display in that op ... does it need to be jpg to display it or is there a different way of attaching it to have it display ?

[michael8554]

For this sort of problem converting a sub, not a stacked image, to a 1000 pixel wide JPEG will suffice.

choose files below the text window.

Once they've loaded, hit the + in the small icon to post in the text where your cursor is already positioned.

Michael

[LandyJon]

Ok, I have a 1000 px wide jpg.

Ahh that works thanks,

 

Had a look at the image train and can't figure how it's out of alignment.  Could it be the corrector lens is tilted inside its housing, or the sensor misaligned in the camera ?  Any way to tell which is more likely ? both were 2nd hand, the camera from Daz on here and the corrector came with the scope from a local marketplace on facebook, it has a couple marks on the lens and theres a securing ring holding the lens in, is it worth trying to remove it and see if theres anything stopping it seating correctly ... it would be miniscule as it 'appears' well seated against the lip.

[LandyJon]

Am I correct in thinking it's the corrector or sensor, could it be the other side, inside the OTA ? could it still be either of the mirrors misaligned ?

[michael8554]

What camera?

An astro-modded DSLR may well have had it's sensor reinstalled with tilt.

Michael

[LandyJon]

44 minutes ago, michael8554 said:

What camera?

An astro-modded DSLR may well have had it's sensor reinstalled with tilt.

Michael

No, its a ZWO ASI183C Pro