Help with processing Pleiades

[smr]

Hi,

The other night I set about imaging Pleiades. I took around 3-4 hours worth of images with my Canon 80D, ISO 200, mostly 1m subs, but I'm having trouble processing the image. I took lights only - no darks or flats, no flats because I can use the lens profile correction in my raw converter, the lens is a 55-250 EFS f5.6.

I apply a small crop around the image first of all, then align the RGB channels - Blue and Green are already aligned but red is slightly out so I bring that back in. Then I use gradient xterminator, and apply some curve stretching, I can then start to see some nebulosity showing through but if I stretch the image more with curves adjustment I start to see distorted colours on one or both sides of the image, and run into a grey, washed out image. I was wondering if anyone here could lend some advice. Maybe I've stretched out as much nebulosity as I can? I don't know. I've uploaded the original TIFF, and here's where I get to:

 

 

Pleiades profile correction only.tif

[wimvb]

You have a nice result already, with some nebulosity showing.

I may have a go at your data later.

Just an early remark: lens correcting software can, imo, never be an alternative to calibration frames. Not if you really want to make every photon count.

With a dslr, you should at least take bias and flats. Darks can be replaced by sigma clipping and cosmetic correction, if you can't make them to match your lights.

[happy-kat]

and Dark Flats are very easy to take.

[PaulR1]

Here is my rendition from your file , crop, mode change to 16 bit. gradient exterminator , couple of stretches and a bit of vibrance in photoshop.

I'm still quite noobish at this , others may have more success

 

[happy-kat]

I opened the file in DSS first to save it to a version I could work with, then opened in StarTools and reversed the stretch. Binned 50% then cropped and manual develop. Then wipe and vignetting gradient removal. Then in PaintShopPro to adjust the histogram and then a level tweak. Nice data but needs flats and dark flats.

 

 

[wimvb]

Here's mine. Processed in PixInsight.

• Crop
• DBE x 2 to remove the sky light gradient (subtraction) and the vignetting (division)
• Colour calibration (background neutralisation, colour calibration)
• TGVDenoise on Luminance
• MMT denoise on chrominance
• Arcsinh stretch
• Colour saturation adjustments and several histogram tweaks

[smr]

These are all superb, well done guys. At the moment I only really have Photoshop and Lightroom for processing, so a lot of these terms are alien to me. Presumably the methods in Pixinsight can be done in PS but I wouldn't know what they're called or how to do them. 

I'll take flats and bias frames now, anyway - I have just bought my first refractor so I'll have to !

 

[happy-kat]

Dark flats, take your flats once done stick the lens cap on change nothing but take more images.

I might try again tomorrow just using paintshoppro and gradient exterminator.

[smr]

22 minutes ago, happy-kat said:

Dark flats, take your flats once done stick the lens cap on change nothing but take more images.

I might try again tomorrow just using paintshoppro and gradient exterminator.

Thanks, if I take lights at differing exposure lengths, say some are 1 minute, some are 30 seconds, should I also take dark frames for the same lengths, and how many? I do really need to find my MEPC book.

[happy-kat]

I personally try to take 25-30 but you need the same zoom and focus and ISO and aperture as the lights they are to go with.

Exposure length for flats is not about the length but more about what is needed for an even light distribution. Some use AV mode for flats.

[wimvb]

2 hours ago, smr said:

Presumably the methods in Pixinsight can be done in PS but I wouldn't know what they're called or how to do them. 

The main difference between PixInsight and PS is that in PS you have to stretch the image first. PixInsight has a so called screen transfer function (STF) that shows the image stretched on you screen, but it doesn't apply that stretch to the data.

PS also has a plugin for the arcsinh stretch. It was developed some time ago by SGL member Mark Shelley (@sharkmelley). You can find the original thread in his profile.

Histogram transformation in PI is the same as levels in PS, and curves transformation is (no surprise) curves in PS.

As for darks with a DSLR, some people use them, and some can't get them to work properly. The problem is that DSLR cameras aren't cooled, and dark current is very much temperature dependent. If you can't get your darks to match the lights, darks may do more harm than good. The only way to find out is to experiment, and stack your subs once with darks, and once without darks (but with bias frames). Then compare the results.

[happy-kat]

That's why with my DSLR I do flats and dark flats, I don't do darks.

[PaulR1]

I stopped doing darks a while back , dithering seems better for me

[michael.h.f.wilkinson]

I loaded the TIFF in APP, applied LP removal, applied one of the standard stretch profiles, and tweaked curves in GIMP

The background could be better. Flats could sort that out partially. The lens profile correction doesn't take variations in pixel sensitivity into account. I also find using darks makes the background much less noisy

[asset189]

On 06/12/2018 at 14:32, happy-kat said:

I opened the file in DSS first to save it to a version I could work with, then opened in StarTools and reversed the stretch. Binned 50% then cropped and manual develop. Then wipe and vignetting gradient removal. Then in PaintShopPro to adjust the histogram and then a level tweak. Nice data but needs flats and dark flats.

 

 

Great to see someone else with Paintshop pro , I can't afford Photoshop but have found PSP a good less costly alternative