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Uranium235

Imaging with the Samyang 135mm f2

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On 18/09/2020 at 14:29, mAnKiNd said:

Finished another project with this gem of a lens :)

Full details in the link: https://www.astrobin.com/g569tc/?nc=user

Cheers,

Minos

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Minos, that's simply fantastic! Superb image, and great work! I spent a few minutes contemplating the details you captured, and like you I was surprised at these dark areas. Fascinating!

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Thanks to @mAnKiNd I've changed the mounting arrangement of my Samyang by using the WO tube ring - it is soooo much better. I find that the CEM25-EC allows me to image without guiding up to 180s which is also the sky limit around here.

This is 10 x Ha, 20 x SII and 30 x OIII (all 180s) stacked in APP and processed in PI with a little bit of noise reduction (Dfine2) in Affinity.

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The new setup.

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Adrian

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25 minutes ago, Dinglem said:

where did you get the pulley/belt for your EAF from?

MotionCo - they provide a very comprehensive supply of pulley wheels and belts.

I bought an additional belt to cut and stick to the lens itself to help with registration.

HTH

Adrian

Edited by Adreneline
Clarification
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I thought I would combine H, O and S in the linear state and then stretch, so this is 10 x 180s of Ha, OIII and SII mapped as SHO. At least this approach ensures all channels are equally stretched (as advocated with RGB) but results in a rather pastel look.

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More data would be good but surprising what you can get with 90 minutes and a Samyang 135mm.

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10 minutes ago, Adreneline said:

I thought I would combine H, O and S in the linear state and then stretch, so this is 10 x 180s of Ha, OIII and SII mapped as SHO. At least this approach ensures all channels are equally stretched (as advocated with RGB) but results in a rather pastel look.

Stretching color can make it turn pastel as it changes the RGB ratios for non linear stretch.

Try following approach:

- create artificial luminance (just add all three linear channels with pixel math for starters - that will create usable luminance) and stretch that to your liking

- do what you already did - make linear combination of RGB (SHO)

- paste stretched luminace as new layer on top of linear rgb and set its blend mode to luminance (LAB color model - Gimp does this, not sure if PS has that option, it should).

This will make color transfer keeping RGB ratios (I hope).

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2 minutes ago, vlaiv said:

Try following approach

Thanks Vlad - I'll give it a go and see how I get on.

P.S. The GSO is boxed up for moving to darker skies - It might be a few weeks before it see the light of night again.

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Currently just playing with this excellent lens using a modded 550D but eventually intend to switch to my ZWO ASI1600MM-Cool + x7 31mm EFW.

Just wondering if 31mm filters will be large enough for this fast lens or will I need to go bigger (36mm) to avoid vignetting at say f2.8 or faster?

Graham

 

 

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11 hours ago, groberts said:

Currently just playing with this excellent lens using a modded 550D but eventually intend to switch to my ZWO ASI1600MM-Cool + x7 31mm EFW.

Just wondering if 31mm filters will be large enough for this fast lens or will I need to go bigger (36mm) to avoid vignetting at say f2.8 or faster?

Graham

 

 

Easy, go bigger for anything not just the lens, you will know that you will be in safe side always, i didn't process my image yet to see if i can see much bad vignetting, but i don't have Samyang 135mm lens actually.

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OK I get that but for those using the ZWO1600 what size filters are you using and do they work OK? 

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1 hour ago, groberts said:

those using the ZWO1600 what size filters are you using and do they work OK?

I use the Samyang 135mm (at f2.8) with the ZWO EFW (8 position), filled with 1.25" Baader LRGBC and Astronomik Ha, OIII, SII filters with the EFW attached directly to the ASI1600MM-Pro (set up as in photographs above). I find there are no problems with vignetting that flats cannot sort. FLO sell the ASI1600 packaged with either the 1.25" or 31mm filters so I guess that is some sort of endoresement that the pairing works.  I am very happy with the results that I get but then I am not as discerning as some.

Adrian

Edited by Adreneline
Clarification

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Thanks Adrian that's reassuring.  It's just that I haven't used my ASI1600 with the Samyang yet and am considering upgrading my filters to Chroma / Astrodon and wanted to make sure the 31mm would still be OK.  As a matter of interest  what bandwidth do you use 3 / 5 / 7nm & what sort of exposure times do you need?

Graham

Edited by groberts

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22 minutes ago, groberts said:

As a matter of interest  what bandwidth do you use 3 / 5 / 7nm?

Haha! 6mm! Trust Astonomik to be different.

I'm afraid Astrodon and Chroma would require me to dig far deeper than the bottom of my pocket! I also have the Baader NB filters but was never happy with the 8mm OIII, hence the change to Astronomik. I rarely image in LRGB because the light pollution round here is so high.

Again I stress I am not that discerning - I can live with the dodgy stars in the corners and the minimal vignetting - at the end of the day I usually crop them out as part of the alignment process in PI. I try to put what I am imaging in the middle of the frame and if others are more interested in the corners of my images (as some clearly are) then that's their problem and not mine.

Just as an aside I have also used my Canon 200mm f2.8 lens with the same setup and get just the same amount of vignetting and dodgy stars in the corners. I am confident I've got the spacing right - it's just the way it is.

HTH in your deliberations.

Adrian

Edited by Adreneline
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This lens is the best astrophotography purchase I've ever made. Pictures taken with Samyang 135mm, a modified Canon 60D and SW Star Adventurer.

 

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