Flats - Darks - Fits - PNG - Live Stack

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turfpit
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Re: Flats - Darks - Fits - PNG - Live Stack

#41

Post by turfpit »

Tim

A decent histogram shape for a DSO - slight gap at the left (5735), rising steeply, tailing off gently. The 2 humps (bimodal histogram) come from the colour camera - this is normal. You might want to take single frames for 45s, 50, 55s and make a judgement re the right hand side of the histogram. M67 is an open cluster so won't be subject to burning out. Whichever exposure you decide try for at least an hour of capture. If that works, try 2 hours. The benefits of stacking more can be seen here viewtopic.php?f=18&t=1808 .

The histogram below resulted in this https://www.astrobin.com/1graw1/?nc=user. 60x60s with an Altair 183C.

M27-single-frame.JPG
M27-single-frame.JPG (73.32 KiB) Viewed 2229 times


It takes time to get used to the object not being visible is actually a good setting. Use the Display Histogram Stretch (bottom right of images below) to brighten the image.


M27-no-display-stretch.JPG
M27-no-display-stretch.JPG (94.26 KiB) Viewed 2229 times

M27-display-stretch.JPG
M27-display-stretch.JPG (116.76 KiB) Viewed 2229 times

Dave
tmyers
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Re: Flats - Darks - Fits - PNG - Live Stack

#42

Post by tmyers »

All great information, hoping to get out early tomorrow morning, use some of my new information
Tim

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tmyers
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Re: Flats - Darks - Fits - PNG - Live Stack

#43

Post by tmyers »

My last reply was on the 9th, and I have been out imaging twice since then. I think I am starting to get it, and the 60s exposure at Unity gain 141 is working. Dave, as you said I need to be patient and gather more data. My imaging last night included 100 - 60s frames of M51, M63, and M65, or 300 total minutes plus time to get Darks, flats, Dark Flats, and Bias frames. So overall a good session. Too bad I had to get up after a couple hours sleep and work from home, otherwise I would have probably went through daylight.

The technology of all this has been kinda like taking a drink from a fire hose. It is the simple revelations that floor me. A lot of my frustration was that in my mind, I could only stack the images from the image sequence file I shot for that evening. It wasn't till about 3 nights ago that I realized I could use DSS to bring multiple nights into one large stack of data.

That one fact removes a lot of pressure on my decision making.

My guide scope arrived and though I might not really need it, I from time to time see some oblong start if I go above 60s. I am waiting for some mounting hardware to arrive to mount it and get it out into the night sky.

I also spend a good deal of time fussing over the focus. I am sure an electronic focuser purchase is on the horizon.
Tim

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turfpit
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Re: Flats - Darks - Fits - PNG - Live Stack

#44

Post by turfpit »

Tim

Glad it is starting to make sense.

For deep sky, I use a Bahtinov Mask on a refractor. These cost about £20 and it takes a couple of minutes to achieve good focus. I use Zoom, the Display Stretch and an Exposure of around 2s (medium brightness star near to the object of interest). Once I think I have focus I increase the exposure to ~15s. If the 3 parallel lines can be seen, then focus has been achieved. Trying to focus using a bright star does not work as well (for me). For example: M51 use Alkaid, M3 use Denebola, M13 use Alpheratz, M42 use Alnitak …...

bahtinov-mask.JPG
bahtinov-mask.JPG (66.63 KiB) Viewed 2195 times


For lunar/planetary I use a JMI motorised focuser on a Celestron C8. This helps very much with lunar focusing, which with atmospheric turbulence is a bit of a 'best estimate' anyway.

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Re: Flats - Darks - Fits - PNG - Live Stack

#45

Post by BlackWikkett »

I've had really good luck using the focusing tools in SharpCap. There's some fiddling with settings to get it working but once you have this dialed in they work great. Initially started with manual focuser then switched to powered Moonlite. Keep in mind to allow the system to settle a few seconds after making a focus change. The tools are more accurate than the mk1 eyeball.
https://docs.sharpcap.co.uk/3.2/#Focusing

-Chris
tmyers
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Re: Flats - Darks - Fits - PNG - Live Stack

#46

Post by tmyers »

I have used SC focusing tools with varying success. Focusing by hand can be a challenge because you have to ignore a couple image cycles because due to movement in the scope train from touching the focus knob.

Interesting story about the Bahtinov mask though, my step son has a 3d printer and I have sent the file to him for a mask for my 100ED. He responds yes but some personal issues are getting in the way. I kind of have to give him an opportunity to make the thing before purchasing one for family political reasons, if you get my drift. Being the industrious type, I found a site where you can print out a Bahtinov mask to fit your scope. Glued four layers of manila folder, and the printed mask together, then cut it out. Was a royal PITA and took about a hour to do. Not perfect but it works.

Unfortunately when trying to use the Bahtinov Focus tool, SC doesn't like my mask and comments that my slits are not parallel and not of uniform width. I know this is probably true, it was tough to cut out and I know there are some miss cuts in the process. I chuckled when I read it. I have found that I can use it to focus, just not able to use the SC tool for that.

All of this is leading to eventually purchasing a mask after the step son has had time to print or not print.

Also leading to the purchase of an electronic focuser so improve the process
Tim

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tmyers
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Re: Flats - Darks - Fits - PNG - Live Stack

#47

Post by tmyers »

Another question regarding flats. DSS alerts me if my Darks, Flats, Dark Flats, or Bias frames are not taken at the same gain as the Lights.

I did observe this parameter a few nights ago and after completing taking my Lights, as follows:

Stood the scope up to zenith, turned off tracking, installed the Scope Cap, and used the same Gain and Exposure for Darks scope since they need the same gain and exposure as the Lights

Then Flats by removing the Scope Cap, using a t-shirt and white screen on my tablet, and adjusted exposure for the 50% range on the histogram

Removed the tablet, shirt, and reinstalled the cap on the scope for my Dark Flats with same settings as the Flats

Lastly, took my bias frames. Have read some comments that say with the ASI1600 to try to keep the Bias Exposure around .3s

Everything had the same gain

I did notice improvements on my stacked image in DSS

Thoughts?
Tim

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Re: Flats - Darks - Fits - PNG - Live Stack

#48

Post by Timothy S »

Is this the correct way to capture and use flats for Livestack (and for postprocessing) with a ZWO OSC camera ? Choose Capture Flats. Set exposure so histogram is in correct range. Cover end of telescope and capture a series of darks. Save to use as Master Dark for Flats. Go back and capture Flats with Bias not checked and using the Master Dark for Flats in the Preprocessing / Subtract Dark. Use that as your Master Flat. Master Dark will of course depend on the exposure length of Lights.
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