Society for Popular Astronomy

Widefield Imaging with DSLR Problem
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Author:  gfletcher [ Sun Apr 17, 2016 9:20 am ]
Post subject:  Widefield Imaging with DSLR Problem

Hi Guys
I attempted imaging through my 1000D fitted with CLS Clip I Filter and Canon EF 28-135mm lens last night.
I was using 28mm focal length at f4 and at ISO 800 in Manual Mode and was shooting in RAW.
I took:
10 Lights each 120secs
5 Darks each 120 secs
10 Flats (In AV mode)
Looking at the Lights in DDP they all had a blueish tinge (as to be expected due to he CLS filter), they looked pretty good to me. Stars seemed quite tight.
I put it all through DSS and arrived at the resultant TIFF image.
When I post processed in Photoshop CS6 the right hand 1/3 of the image developed a colour cast which was obviously different to the rest of the image. I could not find any way of getting rid of this .
Any of you guys got any ideas as to the cause of this and a way of getting rid of it to produce an even image?
Attached are sample of one of the lights (prior to putting through DSS), the resultant flat and dark (after processing in DSS).
I have also attached Autosave 01 (after DSS processing)

_MG_5425a.jpg [ 187.58 KiB | Viewed 2331 times ]
_MG_5414a.jpg [ 209.97 KiB | Viewed 2331 times ]
_MG_5404_2a.jpg [ 243.35 KiB | Viewed 2331 times ]

Author:  gfletcher [ Sun Apr 17, 2016 9:23 am ]
Post subject:  Re: Widefield Imaging with DSLR Problem

Dss resultant TIFF and post processed in CS6

After CS6a.jpg
After CS6a.jpg [ 224.8 KiB | Viewed 2330 times ]
Autosave_1.jpg [ 213.64 KiB | Viewed 2330 times ]

Author:  David Frydman [ Sun Apr 17, 2016 2:59 pm ]
Post subject:  Re: Widefield Imaging with DSLR Problem

Hi Graham,
The star images are not really symmetrical on the left and right side.
Left a bit of coma, right something else.
I suspect that the lens is not quite centred.

However, this should not result in uneven brightness.

If it was a film camera I would suspect light leakage from a not tight door.
But with a DSLR, I don't know.
Can the sensor have some light leakage?

Do you have a wide angle prime lens to see if you get the same result?

It could be that there is a slight tilt of the sensor to the lens axis.
Do you have another DSLR body to try with the same lens?


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