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Advice on widefield (capture and processing) pls....? o.O


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Hi,

As there are many talented imagers here, and i'm struggling with the unfamiliar techniques involved It was suggested I post a thread and hope that anyone can help with the issues I seem to be at a loss on.

Apart from inexpensive lenses, the coma and CA I seem to be getting not only vignetting in the corners but a kind of almost 'dirty' area in the middle like vignetting but with a strange colour to it like the whole middle area is not quite stacking right, or its during capture that the problem starts.

Also, processing so many stars is overwhelming either the software or me or both, although i'm sort of sure the data is saveable but the processing ive tried so far just seems to make it more messy.

Apologies in advance for the bad explanations and babbling, pls be patient with the text in this post. :p

post-18772-0-72268500-1379714358_thumb.j this is double cluster area, the big reddish blotch like a severe vignette - it looks to me like it stacked badly and the centre looks thin and flattened.

post-18772-0-70783100-1379714957_thumb.j this looks like gravely snow which got trampled by muddy footprints with ill-defined dark lanes or something. again with the reddish murky look where the 'tracks' are. Sorry for weird analogies but the technical terms escape me. :p

post-18772-0-59013700-1379715256_thumb.j some more vignette type issue. reddish muddy look and the appearance of uneven stacking also in the middle bit.  I tried flats but not sure they were done right and the images with flats dont seem any better.

These aren't the only problems but i'm not really certain what i'm doing right or wrong to be honest, i'm hoping you folks can shed some light on it. :p

Any help appreciated, and many thanks for looking.

Regards

Aenima

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Thanks. :) EDIT: sorry I took ages to answer - I was uploading an image that 'stuck' halfway and was watching the busy icon going round :\

My equipment is just piggy backing a nikon d3100 onto the 200p/EQ5 for tracking, and either a 55-200mm nikkor zoom, or the kit 18-55mm and one or two (pleiades shot now in my gallery) a 135mm prime soligor from ebay (ok for a tenner).

I usually set ISO at 1600 or 3200 with added exposure comp. +2.0 or thereabouts. Expose for 2mins and stack the subs in DSS - I usually get between 4 and 13 subs, unfortunately Darks are less common and flats give me grief due to the ease with which focus is nudged out while covering the lens with t-shirt :p

When the stacking is done I use layer based editors for levels and curves even though its very unfamiliar territory.

The lens is cheap I know but still I could use it for practice which I do need lots of :)

Regards

Aenima

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Did you calibrate your data? (dark/flat/bias)

That will go a long way to cleaning it up by removing uneven illumination and vignetting (but not gradients or cloud damage). Once calibrated and stacked,  noels actions does a good job in removing any excess colour (soft colour gradient removal / colour blotch remove / deep space noise reduction) - but they have to be used carefully because sometimes they can suck the colour right out of the thing youre trying to image!

You should also give HLVG a go (its free!), however Ive been unable to find a download link for some time as the original host is no longer available. It does a great job in zapping any green in your photos.

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I really should make more of an effort when it comes to calibration frames, and learn to do them properly in case they add to the problem rather than help.

Space and computer processing speed is a problem there, as the d3100 produces files twice the size of my old 300D and takng 3x the number of images gives my poor laptop much grief when processing it all.

I was hoping to learn a few tips or techniques regarding capture and processing widefield stuff in general as it seems quite different to DSO imaging with a telescope which I recently started trying to get the hang of. Maybe there is a good tutorial or link that someone can recommend?

Thanks to the above posters for the comments and advice,

Regards

Aenima

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