What's happening?

[JohnSadlerAstro]

Hi everyone,

This evening was my 1st attempt at a DSO imaging run, using the Canon EOS 1000d and 55-200mm lens that I was given for Xmas. I wanted to take image the Andromeda Galaxy, M31, and I planned for 50 subs of 2 minutes each. Then the cloud descended and when I went out to check on the setup, the sky was completely covered. So, I had 1 good image, and several 'dud' ones. I wasn't too bothered, as being my 1st run, I wasn't expecting anything amazing. I then converted the Canon RAW, .cr2 format to a 24bit .bmp image, using a free program called CR2 CONVERTER. However, when I viewed the bmp, the image was completely changed, and the histogram looked like nothing I've ever seen, shifted over to the right. Could I just be adding sky brightness, or is the program dud?  Does anyone know what's going on? I've attached the M31 'before and after images', along with a grab of the histogram in gimp. 

Could I sort this out by imaging in standard .jpeg, or would this make the problem even worse?

BEFORE COVERSION:

AFTER CONVERSION:

IMG_5965.bmp

THE RESULT'S HISTOGRAM:

John

[Leveye]

Have you tried using DPP that comes with canon cameras? You can edit and convert the RAW file to other formats quite easily.

[wxsatuser]

See you have LP.

May be 2minutes over exposed, histogram to the right.

Check where the histogram is on the back of the camera.

To gauge the correct exposure for your sky brightness, expose so the peak of the histogram is around 20>40%

[Garethr]

John,

Its worth using the software canon supply with the camera (it can also be downloaded from the web free if you enter the serial number of your camera)

Digital photo professional is a good start and will allow you to make basic changes in curves and such.

Then using DSS also free you can save into various formats.

Also agree with wxsatuser 2 mins is probably a bit to long your getting trailing starting on the stars.

Try 30 seconds then check if all good try 45 seconds and so on till you get the maximum exposure without egg shaped stars.

Stack in DSS and away you go  

Hope that helps

Gareth

[Eri]

there's a bit of detail in there but really 2mins is too long as you're getting star trailing, I'd prob suggest 30sec to 1min subs and stack in DSS or similar, don't convert the CR2's as DSS will read them fine you can then save the stacked image as tif and process in photoshop or pixinsight or whatever image program you prefer.

[JohnSadlerAstro]

Thanks for the advice guys! I

had a think about it after I had posted, and I reckoned I probably was overexposing, like you say. The star trailing business is odd, because if you look at the stars zoomed in loads, the trails, instead of being lines, are 3 dots. The mount was unbalanced, as my counterweight is too heavy to balance the camera, (I was imaging without the scope) so I went without it. This meant that the mount was heavier on the western side of the mount, the direction I was tracking in. So the mount may have 'walked ahead' of the drive, and then bumped to a stop against the next cog tooth, and so on.

John

[JohnSadlerAstro]

Oh, and just a crazy idea, why couldn't I sample the light pollution the same as with hot pixels, etc. I could take different exposure lengths, and create a library of Pollution frames. these could then be subtracted from the subs the same as darks. Does anyone think it would work?   :grin:   (not expecting it too!!!) 

John

[Pompey Monkey]

Oh, and just a crazy idea, why couldn't I sample the light pollution the same as with hot pixels, etc. I could take different exposure lengths, and create a library of Pollution frames. these could then be subtracted from the subs the same as darks. Does anyone think it would work?   :grin:   (not expecting it too!!!) 

John

Not quite the method that you're thinking of, but stacking many images and software like the Gradient exterminator plugin for Photoshop or DBE in Pixinsight can help you reduce the effects of light pollution very effectively.

The drawback is that it takes a lot more exposures in a light polluted location than in a dark site to achieve a comparable signal to noise ratio.