Old C8 reflection

[Sunfish]

Finally aligned the old fork within 10- 30 min. of the pole and got one 50 sec test shot that worked at 400 somewhere near Centaur with the f6.3 reducer . I thought at first this was an object but on reflection I think it is a reflection or refraction . Look at that bright star.

Any ideas what causes this?

[PKay]

Hi Ray.

Not for me to give advice, but I can guess.

I had an old Celestron (for a few weeks) and it was totally buggered.
You may have a collimation issue &/or the gears are worn.

Useless for astro photography, but OK for visual.

You might try shorter exposures of less than 30sec.

Having said that you made a start so well done!

[bojan]

Internal reflection... possibly caused by reducer?
Or reflection from glass covering camera sensor.

[Sunfish]

Thanks for the comments.

The scope is in good condition as it was owned by a scientist friend and the clock drive works fine except for PE. I have the collimation sorted out and alignment less than 5 min. off the pole now .

I will try without the reducer and think about modifying my second camera.

I have had more luck with an old 800 f8 ed lense and GPS astrotracer up to 40 sec. or wide field. However the field rotation and GPS is a pain so I would like to try it on the scope with old school hand correction until I can build a new arduino hand control with guiding. I think if it can be done on film by hand you should be able to do it with a DSLR. Learning a lot before throwing money at a new eq mount and small ed scope.

[raymo]

Your focus looks to be off in both shots.
raymo

[multiweb]

That's a Schmidt ghost, the reflection of a bright star in focus off the CCD surface back to the glass of the corrector plate and then back to the CCD.
Here's a bit of reading about internal reflections.
http://iopscience.iop.org/article/10.1086/648457.
In your case a large amount of dithering and stacking will reject these.

[Sunfish]

Correct. I think the Orion shot was before I made a Bahtinov and locked down the focus at full live zoom.

A harder problem that causes slight double stars in both shots is probably vibration , mirror slap and the aluminium fork added to slight trailing Which seem harder to fix.

[Sunfish]

Thanks Marc. I hoped someone would reply with that knowledge. Enjoying the World Cup ?

[multiweb]

:lol: In my case it was always a win-win situation. :)

[Sunfish]

Thanks to all who commented regarding reflections. Busted the Schmidt Ghost. Tried stacking a few shots with mean stack mode but the single still looks better. The NASA image is blue so I went a little that way.

I will keep the reducer to fit the moon.

Marc's reference should be recommended reading. Even with a dedicated astro camera and filters, reflections are a thorny issue. Good information. A 20sec exposure without the reducer of a bright object with no bright stars. Helps. Also pulled the drive base and fork arms apart and tightened and greased all the loose parts. Then had to realign as everything changed. So if anyone wants to know what the inside of a worm block for a Power Star 4 (or Ultima) from 1990 looks like I have the photos. According to Sky and Telescope from 1990 I can improve the PE further with some adjustment and manually guide . That is a challenge for another day when Orion is up.