test shot of Southern Pleiades using Baader fringe killer

[h0ughy]

i tested this out the other night, with really bright stars i was getting a "blue" fringe on stars. well it does work on them, but it creates a problem with internal reflections?

[renormalised]

Are you getting any reflections without the filter??

[DavidU]

Dave if you are getting blue halo's on the 127 the stars are not in focus.

From about 1/2 way down.
http://www.iceinspace.com.au/forum/showthread.php?t=56696&highlight=blue+stars+focus&page=5

[h0ughy]

this is a shot i did with the same scope ( without the fringe killer), processing not quite the same but you see the fringing around the stars

[h0ughy]

quite the contrary David the stars are in focus, but i will take note of the experiment

[DavidU]

Your image shows it is very well focused in red & green. Not in the blue/violet.

[h0ughy]

try looking at this crop

[gbeal]

What's the camera Huff?
I tried a camera lens recently, with the SX M25C and got bloated stars.
Needed a UV/IR. Not saying this is your problem, just wondering.
Gary

[h0ughy]

cooled modded 40d, with the modded uvir filter from yun

[gbeal]

OK, that's that idea down the gurgler then. Good luck. I'd be interested to see the same camera with a reflector then.
The "colour" can only be from the objective.A reflector "should" give colour-free images.
The reflections you may be able tame or eliminate by varying the position of the MV filter, much like others have found with the front filter on the likes of the QHY8.
Good luck,
Gary

[DavidU]

Dave, I have done some searching for you.Indeed the triplet APO lens in your case is well corrected in red & green however the blue is out a little regarding longitudinal aberration.
Here is an exaggerated plot showing how the overall focus is within 1/2mm but the blue is out.
A bit of a search found this
http://deepspaceplace.com/ed127.php

Indeed, refractors of any sought are a different beast regarding focus compared to a reflector.