DSO Imaging Problem

Discussion of using SharpCap for Deep Sky Imaging
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brenski
Posts: 82
Joined: Mon Aug 10, 2020 4:01 pm

DSO Imaging Problem

#1

Post by brenski »

Really hoping someone can advise here.
First real attempt at Pleiades with new equipment and there appears to be a couple of issues.

Equipment:
♦ Star Adv Pro mount
♦ Skywatcher Evostar 72-ED DS Pro
♦ Zwo ASI 193 Pro C

Before I begin, I'd need to say that daytime focus is fine - I've set the scope targeted at some trees around 1mile away and the branches are nicely in focus.
The problem I'm having is image quality/focus? (see 1st attachment).
I've tried every combination of the adapters with the Zwo camera - both with/without the 90°
and until I added those extra two adapters (2nd attachment) I couldn't get even remotely close to focus - the focusing knob being almost completely closed. The two adapters currently attached provide the 55mm backfocus, but the focus is still slightly off.

I've been capturing Raw16 tif format and pasting these into Deep Sky Stacker to produce an autosave.tif for later processing in PS.


Ideally, I'd like to get some nice crisp stars M45 in colour and be able to stretch the levels and curves. Sharpcap Capture settings are below.

thanks for any help/advice.


++++++++++++++++++++++++++++++++++++++++++++++

[ZWO ASI183MC Pro]
Debayer Preview=On
Pan=0
Tilt=0
Output Format=TIFF files (*.tif)
Binning=1
Capture Area=5496x3672
Colour Space=RAW16
Hardware Binning=Off
High Speed Mode=Off
Turbo USB=100
Flip=Both
Frame Rate Limit=Maximum
Gain=170
Exposure=13.020474
Timestamp Frames=Off
White Bal (B)=57
White Bal (R)=59
Brightness=25
Temperature=6
Cooler Power=74
Target Temperature=-28
Cooler=On
Auto Exp Max Gain=66
Auto Exp Max Exp M S=1969
Auto Exp Target Brightness=73
Mono Bin=Off
Banding Threshold=19.424778761062
Banding Suppression=2
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
Notes=
TimeStamp=2022-01-20T07:47:31.9342172Z
SharpCapVersion=3.2.6480.0
Attachments
Untitled-2 copy.jpg
Untitled-2 copy.jpg (138.25 KiB) Viewed 2249 times
Untitled-3.jpg
Untitled-3.jpg (366.58 KiB) Viewed 2251 times
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oopfan
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Re: DSO Imaging Problem

#2

Post by oopfan »

Hi,

I think your focus looks fine although I would recommend losing the 90 degree diagonal. It's just another optical element that robs you of image quality. I recommend taking measurements and then purchasing a single extension tube that places focus in the middle of the focuser's travel. Be sure to measure the amount of travel.

M45 contains some very bright stars that easily saturate with a 13-second exposure, so never judge focus quality on saturated stars. Look at the faint, unsaturated stars. Your faint stars look good although there is some star elongation which is most likely due to tracking errors.

I am not familiar with your mount. Are you sure it is beefy enough to swing your scope? Also, check the balance. From your middle photo it looks nose heavy. If it is in balance, then you will need some sort of counterweight near the objective lens when you switch over to using a straight extension tube since it will place the CG farther forward.

Brian
Last edited by oopfan on Thu Jan 20, 2022 3:39 pm, edited 1 time in total.
brenski
Posts: 82
Joined: Mon Aug 10, 2020 4:01 pm

Re: DSO Imaging Problem

#3

Post by brenski »

Hi Brian

thanks for the advice - I'll make some tweaks tonight if things are clear.

I've ordered one of these: https://www.amazon.co.uk/dp/B084VJ99SC/ ... 81_TE_item
Hopefully it may help.
I'll removed the diagonal too.

The scope/camera weight are well within the tolerances of the Star Adventurer Pro so that shouldn't be a problem.

what would you recommend as maximum exposure time for M45?
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oopfan
Posts: 1321
Joined: Sat Jul 08, 2017 2:37 pm
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Re: DSO Imaging Problem

#4

Post by oopfan »

Re: "what would you recommend as maximum exposure time for M45?"

Well, I think it depends on what you are pursuing. Most people want to capture the nebula, even if that means that the bright stars grossly saturate. That exposure should be determined by the "The Brain". However don't attempt it when the Moon is nearby. You need dark skies. Right now, the Moon is nearly full. Here is a website that I built that visually shows the current Moon phase and also for each day going forward for a month:
https://u235-astro-library.vercel.app/

If you just want to show stars with little to no nebula, a short exposure will suffice, something like 2 seconds. You'll get the roundest stars that way, and you can image while the Moon is out.

Brian
brenski
Posts: 82
Joined: Mon Aug 10, 2020 4:01 pm

Re: DSO Imaging Problem

#5

Post by brenski »

Hi Brian

yes, it'd be nebula in this case - so you think the stars look normal(ish) for a nebula grab?

another question if you don't mind:
Image Capture format - to get best colour images for editing levels/curves in PS:

Raw16 / Raw 8 / RGB24 ?
png / tif / fits ?

thanks
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oopfan
Posts: 1321
Joined: Sat Jul 08, 2017 2:37 pm
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Re: DSO Imaging Problem

#6

Post by oopfan »

I do RAW16 FITS.
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