Reasonable Expectations

[brenski]

Equipment: ♦ Zwo ASI 183MC Pro (cooled), ♦ Skywatcher Evostar 72ED DS-Pro ♦ Skywatcher Star Adventurer Pro 2i Wifi ♦ Optolong UHC Light Pollution Filter 2" ♦ Stellamira Field Flattener / 0.8 Reducer

With the above setup I can successfully track unguided for between 30-35s. I'm in a bortle 6 location.

So, some questions:

♦ What would be reasonable expectations for image quality?
♦ What Gain settings should I be using for [say] Andromeda, Pleiades, Horsehead, Orion?
♦ What other Sharpcap settings should I be using?

As you can see, image ain't great
any help appreciated,

[admin]

Hi,

given your observing conditions and equipment, the sky background calculator at https://tools.sharpcap.co.uk/ estimates a light pollution level of about 2 electrons per pixel per second.

The rule of thumb for minimum exposure length for deep sky is 10 * (read noise squared) / (light pollution rate in e/pix/s).

So, suppose you pick gain 150, the read noise for your camera is 2e, so the calculation above comes out at 20s, so you will be comfortable doing your 30s exposures for good tracking - no need to go longer. These settings will be a decent starting point for most targets.

Looking at your image, the first thing that I notice is that the stars seem a bit big. While this can be a side-effect of the image stretch used to bring out the faint detail, I think the focus isn't quite spot on, and if that is the case, getting the focus perfect will be the biggest improvement you can make.

cheers,

Robin

[brenski]

Hi Robin

thanks for the (as ever) helpful reply. My Bahtinov pattern indicates that focus is pretty much "on".
so if exp=30s / gain =150 are good settings to apply, would there be anything else in Sharpcap to change for the better?

I'm thinking change to .fits instead of .tif files? - if yes, would Raw16 still be the way to go?
Anything other things to adjust? - White Balance, Gamma, Brightness ??

[oopfan]

I agree with Robin that your focus looks soft.

In the past I've tried Bahtinov masks but I never liked that I needed a bright star. I had to slew a distance away to find one and then return to my target. Also since I have a mono camera I'm always changing filters, and the focal point changes between filters.

Now, believe or not, I focus by eye. I select the smallest ROI to achieve the fastest frame update rate, increase the gain a bit, reduce the exposure to 1/2 sec or so, and then use SharpCap's Zoom from 400% to 800%. I stand at the focus knob and rotate it briskly forward then backward and back again to find the best focus. This method works quit well. I can routinely achieve results like the following:

M13_2022-04-18_R-600x6s_G-600x6s_B-R-0.1_ST-0.00045_BA-0.01875_HL-0_SAT-0.22_TH-0.0_SH-1.5_PRO-5.jpg (421.24 KiB) Viewed 1280 times

Brian

[turfpit]

For focus, I use a Bahtinov Mask with the Display Histogram Stretch turned on and the Zoom > 100%. Works well for me.

focus.JPG (47.16 KiB) Viewed 1277 times

I can get results like this in Bortle 6 skies with a 183C sensor and 60s exposures (unguided):

M31_Altair183C_100x60s.JPG (70.87 KiB) Viewed 1277 times

With 30s exposures, stacking more frames will beneficial.

FITS with RAW16 is the way to go for deep sky imaging.

The objects you mentioned are Andromeda, Pleiades, Horsehead, Orion. Orion (M42) is a bright object, so shorter exposures will suffice. Horsehead is a fainter object which will need longer exposures than 30s to achieve decent results. Although the Pleiades stars are bright, the nebulosity is faint and again longer exposures are needed for decent results.

At the end of the day, don't be afraid to experiment. Over time, with experience, you will learn what results are possible imaging different objects with your equipment.

Dave

[brenski]

thanks Dave, Brian & Robin.

So 60s (unguided) is possible out of my setup? interesting, maybe worth a shot at that

[turfpit]

60s (unguided) is possible out of my setup?

You will have to try it to find out. A good polar alignment will be needed coupled with a careful star alignment.

Dave

[brenski]

60s (unguided) is possible out of my setup?

You will have to try it to find out. A good polar alignment will be needed coupled with a careful star alignment.

Dave

star alignment on the Star Adventurer Pro 2i Wifi ?

[turfpit]

Read the manual, looks like polar align only.

Dave

[brenski]

Read the manual, looks like polar align only.

Dave

Hi Dave, I was following up your suggestion of Star Alignment, with a question - because as far as I was aware that the 2i cannot do Star Alignment