Weird artefacts on stars

[Tom123]

Hello,

Recently, I've started noticing a weird artefact on stars in my photos. It looks like a silhouette of a finger, except it's repeated on most of bright stars at about 4 o'clock.

ArtefactM101.tif

I've looked at the optical train and there doesn't seem to be anything in the way and clean. Three ideas:

1) It might be some sort of diffraction peak from the Baader UHC filter. I've been doing more AP from my back garden recently, which living in the city and filters off LP

2) I have also only recently modded so I wondered whether it's from that (I've only started noticing since I had it modded)

3) Alternatively, it might be a collimation issue with the scope.

The optical train is 120ED, Baader UHC filter (2"), Skywatcher 0.85x Reducer, Canon 1100D.

Does anyone have any thoughts on what it might be (and how to get rid)?

Many thanks in advance

Tom

ArtefactM101.tif

[cp255]

It may be internal reflections. Since I got my Nikon D300 modified I have had them too. I never had reflections before the modification. Look at the rings around the brighter stars in these images.

http://www.rawastrodata.com/images/photos/openclusters/m45/m45.jpg

http://www.rawastrodata.com/images/photos/nebulae/ic434/horse2.jpg

[Tom123]

Hmm... possibly. Any ideas on how to fix it?

I've attached another photo, which is a better example of the problem at hand. This one is processed but as you can see in the brightest star at the top, there's a horrible black line sticking right out of the star.

[ollypenrice]

This looks rather like an effect which the SXVH36 CCD camera produces if you try to use it in Bin 2. It may be something to do with the gain settitngs according to Terry Platt. I don't know much about this stuff but if this is the case then turning down the ISO setting might help.

I have to say that I've seen worse artefacts afflicting bright stars. If you can't fix it at the capture stage then I'd write a one click Photoshop action for it, saved to a function key for speed.

Select star with magic wand then record this;

Select-modify-expand by (trial and error. Maybe 4.)

Select-feather by about a third of the value above.

Filter-Blur-Radial Blur set to Spin and Best Quality.

Deselect.

Stop recording.

Olly

[cp255]

Your reflections look different from mine. Your problem may be infrared bloat cause by the fact that you are using a refractor. Your new filter may be letting in too much out of focus infrared light. Maybe try a filter such as the Baader UV/IR cut filter.

[Tom123]

Thanks guys.

Some things to think about.

I'll see about the baader filter. Having to cut back on my astronomical spending for the time being

But I'll try adjusting the ISO and the PS magic wand might be an easier trick

cheers