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1st DSO - M27

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My 1st real effort at a DSO. Also a first light for guiding and the Celestron reducer

M27 taken with an unmodified Canon 400D, Celestron C6 and f6.3 reducer on a CG-5. Guided with a Skywatcher ST80 and an unmodified webcam.

Had to chuck a couple of subs away due to guiding errors - need the webcam modified, it was so tricky to find a guide star!

Processed in CS3. Are the elogated stars towards the corners down to the reducer and are flats meant to solve that? My flats probably weren't all that great.

- 11 x 2 mins

- 5 x darks

- 10 x flats

Advice and criticism welcome...

Thanks Jordan


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Hi Jordan,

Pretty good for a first DSO.

The elongated stars in the corners are due to the curved focal plane that the scope produces, the only way to eliminate these is to use a field flattener. I deal with them by cropping the image.

Well done.



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Thanks for the comments Chris.

I think the Celestron f6.3 reducer is a combined reducer/corrector but doesn't produce a flat field with a DSLR sized chip? Not sure though. Might be a spacing issue as well.

Cropping sounds like the best solution. Do most of the imagers here crop?


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Fora first light and first autoguiding session, this is a pretty fair image. The centre field star shapes are good and there is plenty of colour in the planetary. My only suggestion is that the overall colour balance is a little too red - if you adjust the colour balance away from red and towards cyan, the background becomes more 'natural' and the reflection nebulosity of the nebula becomes more pronounced.

Well taken!

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Hello Jordan.

That's a fine image for a first go.

Good focus...the detail is fine in the Ha regions of the nebula, and the stars are tight.

I agree with Steve re. colour, but you aren't far off at all.

You're asking a lot of your optics to get a flat field with a SCT and focal reducer on a big DSLR chip....you can spend a fortune chasing that pot of gold, and many have :)

Flats won't sort out stuff like elongated stars. What they do is take an image of the optical train against a flat background. This shows up any vignetting, dust etc etc and allows this to be subtracted from the image.

To get a flat to work correctly though, you must take bias frames and apply these to both the image and the flat when you calibrate the image, otherwise rather odd things can happen, such as the flat overcompensating, and giving a dark centre.

The flats you applied to this don't seem to have worked that well....how did you get them and what program are you using to calibrate your images?



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Thanks Rob...

I'll have to read up on on bias frames as I'm not really sure how to do them. :)

For the flats I just left the camera in the exact same position in the scope (didn't touch it) when I packed up and the day after I put a sheet of printer paper in front of the SCT and shone a lamp through!!! I'll attach an example only a jpg. the RAW files are too big.

I was using Deep Sky Stacker for image calibration then Photoshop CS3 for tweeking. My second less redish version is attached as well. Any better? I think I prefer it.

Thanks for the advice all.




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