M45 Pleiades - Failure

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

M45 Pleiades - Failure

Post by brenski »

Equipment: ♦ Bresser AR90S – 90/500 F/5.5 ♦ Skywatcher Star Adventurer Pro ♦ Zwo ASI 183MC Pro (cooled)

I attempted to grab some images of the Pleiades last evening, but have no idea what I've done wrong.
On first setup, the Bresser has nice pin-sharp images of the stars in the eyepiece. Then, after attaching the Zwo I adjusted Sharpcap settings to match those of other images found online: RGB24, Gain 120, Exposure 60s.
Nothing even faintly recognisable appeared onscreen. I then tried slight adjustments up/down for both gain and exp - all I ever get is a completely black or very pale image.

The camera is definitely working - as I tested it yesterday afternoon and images of tree branches some distance away were nice and clear.
I'm clearly missing something obvious here, but can't see what.
any help appreciated.
Skywatcher 130p Alt-AZ (Starsense for skywatcher) ♦ Bresser AR90S 90/500 ♦ Bresser 70/350 ♦ Zwo ASI183MC Pro (cooled) ♦ SVBony SV205 ♦ Canon 200d ♦ Samyang 14mm F/2.8, ♦ Samyang 85mm F/1.4 ♦ Omegon Minitrack LX2 ♦ Skywatcher Star Adv Pro ♦ Fiji WS1 3D
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turfpit
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Re: M45 Pleiades - Failure

Post by turfpit »

the Bresser has nice pin-sharp images of the stars in the eyepiece. Then, after attaching the Zwo I adjusted Sharpcap setting
Swapping the eyepiece for the camera can result in a shift of the image and potentially being off-target. I used to work that way but consider following the steps below. The example shows an Altair 183C and how a 90s exposure of M45 would look when captured as a FITS image.

session-start.JPG
session-start.JPG (63.65 KiB) Viewed 185 times


The tower is about 1 mile away. The setup is carried out as the sun sets (for safety). These are my steps:
  • Using the eyepiece, find the land based object and focus.
  • Align the finder scope/red dot finder to point to some feature (in this example the top of the tower).
  • Swap the eyepiece for the camera.
  • Start SharpCap, connect the camera and turn on the reticule. At this point, the focus will be close but the object may have shifted.
  • Centralise the object with the reticule and adjust the focus.
  • Check/adjust the finder scope/red dot finder to align with the centre of the image.
At this point, the telescope and finder scope are pointing at the same place - any mount alignment will be accurate and the object is more likely to be in the field of view when slewed to. Also the focus will be 'near enough' for the stars (accurate focus can be obtained using a Bahtinov Mask). For focus, use a star (not too bright) which is close to the object of interest - Hamal would be suitable.

focus-with-bahtinov-mask.JPG
focus-with-bahtinov-mask.JPG (63.92 KiB) Viewed 185 times


This is an actual capture of M45.

M45-90s-exposure.JPG
M45-90s-exposure.JPG (79.45 KiB) Viewed 185 times
M45-setttings.JPG
M45-setttings.JPG (63.7 KiB) Viewed 185 times


The nebulosity of M45 will not be visible on a single frame. Some techniques to help check that the object is in the field of view:
  • Turn up the gain to more than 50% to check the object.
  • Use the Display Histogram Stretch to brighten the onscreen image (see the focus image above).
I always take test images and evaluate by stretching in FITS Liberator before committing to an imaging run.

The above process leads to me reliably finding objects, especially with the wide field of the 183C.

Dave
brenski
Posts: 19
Joined: Mon Aug 10, 2020 4:01 pm

Re: M45 Pleiades - Failure

Post by brenski »

thanks Dave. really helpful stuff.
will give it a go next time the skies clear.
Skywatcher 130p Alt-AZ (Starsense for skywatcher) ♦ Bresser AR90S 90/500 ♦ Bresser 70/350 ♦ Zwo ASI183MC Pro (cooled) ♦ SVBony SV205 ♦ Canon 200d ♦ Samyang 14mm F/2.8, ♦ Samyang 85mm F/1.4 ♦ Omegon Minitrack LX2 ♦ Skywatcher Star Adv Pro ♦ Fiji WS1 3D
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turfpit
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Re: M45 Pleiades - Failure

Post by turfpit »

Let us know how you get on. Your query is fairly common.

This was my last M45 (heavily cropped), a 66mm refractor under Bortle 6 skies.

M45_70x90s.jpg
M45_70x90s.jpg (353.35 KiB) Viewed 176 times



Dave
brenski
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Joined: Mon Aug 10, 2020 4:01 pm

Re: M45 Pleiades - Failure

Post by brenski »

well the forecast here is overcast for the next few days. a real pity as the Mars/Pleiades conjunction occurs Weds & Thurs.
Skywatcher 130p Alt-AZ (Starsense for skywatcher) ♦ Bresser AR90S 90/500 ♦ Bresser 70/350 ♦ Zwo ASI183MC Pro (cooled) ♦ SVBony SV205 ♦ Canon 200d ♦ Samyang 14mm F/2.8, ♦ Samyang 85mm F/1.4 ♦ Omegon Minitrack LX2 ♦ Skywatcher Star Adv Pro ♦ Fiji WS1 3D
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Menno555
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Re: M45 Pleiades - Failure

Post by Menno555 »

@ Brenski
Maybe stupid question but what you see, is that when you use SharpCap and make a 1 captures or a bunch of captures and then stack them?
If it is 1 capture, then you will only see (faint) stars. You can "enhance" that view by clicking the AutoStretch button on the right side (the little button with a lightning symbol at the little histogram. This will brighten the view as a kind of temporary brightness boost but on screen only.

Menno
brenski
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Joined: Mon Aug 10, 2020 4:01 pm

Re: M45 Pleiades - Failure

Post by brenski »

@Menno thanks for the reply.
definitely nothing visible. with gain/exp slider adjusted significantly.

I've used sharpcap in the past for timelapse allsky stuff and it always worked fine - so I (kind of) know where gain/exposure-wise stars should start to appear. odd that nothing did with this.
Skywatcher 130p Alt-AZ (Starsense for skywatcher) ♦ Bresser AR90S 90/500 ♦ Bresser 70/350 ♦ Zwo ASI183MC Pro (cooled) ♦ SVBony SV205 ♦ Canon 200d ♦ Samyang 14mm F/2.8, ♦ Samyang 85mm F/1.4 ♦ Omegon Minitrack LX2 ♦ Skywatcher Star Adv Pro ♦ Fiji WS1 3D
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