Comparing 3 approaches to calibrate lights using an OSC camera

[umasscrew39]

This is more of a note on a quick and dirty experiment I did using 3 different approaches to calibrate my lights from a ZWO ASI2600MC Pro (100 gain/50 brightness) on the Needle Galaxy. I posted 2 images (only about 2.3 hours of total data) in the gallery but unfortunately not being able to display the full resolution images, I think, makes a big difference in their appearance on the screen to demonstrate the point to its full extent. Given the debates I have read on multiple sites about whether it is ok or bad to use darks and flats created from one program in another program to calibrate your lights, I was curious to see if it really matters- at least in my case for this one example. Some background info: Bortle 6 skies; lights taken over 2 nights under average seeing on C11" EdgeHD @ f/7 using 120s guided subs with dithering captured in SharpCap; ASI2600 MC Pro has a built in UV/IR filter and I added a L-Pro LP filter. Flats were taken using the t-shirt method during early morning hours with the scope pointed to the blue sky opposite the sun with 50 captures at around 200ms (peak in middle of histogram). Twenty darks taken at 120s at -10.

Three approaches:
1. Used SC generated master flat and dark in PixInsight and manually calibrated the lights for post-processing in PI
2. Generated master flat and dark in PI and manually calibrated the lights for post-processing in PI
3. Generated master flat and dark in PI and used the new PI Weighted Batch Prep-Processing script (WBPP) to calibrate the lights for post-processing in PI

My initial conclusion:
The visual differences were not dramatic but I do believe, as a few others both here and on another astronomy forum believe, that the image from approach 2 was better than approach 1 in that the galaxy was brighter, but more importantly, the background sky and DSO had a more natural looking appearance. Of course, my post-processing steps which were identical in all instances could have varied slightly to contribute to some of this effect but I believe it goes beyond that. Finally, when I tried approach 3, the results were very similar to approach 2 despite the fact that several algorithms are built into the WBPP script to supposedly enhance the quality of the image as well as being fully automated. It definitely generated a less noisy image but that can also be dealt with in PP.

[oopfan]

Hi Bruce,

Is it possible to crop your images down like this? I'd love to see the difference.

umasscrew master calibration comparison mockup.jpg (21.55 KiB) Viewed 2131 times

Thanks,
Brian

[BlackWikkett]

Hi Team,

Disclaimer: I'm not an employee of or compensated by flickr.

Easiest / most cost effective way to share images I've found is via https://www.flickr.com You can get a free account that allows posting of up to 1000 images. When you share via a forum like SharpCap forum you can link via BB code for an example look at one of my posts in the gallery. Flickr host full resolution images that you can view online or download.

Thanks for the info and I'd really like to see the pictures!

-Chris

[BlackWikkett]

fbbcode1.jpg (345.5 KiB) Viewed 2094 times

In your flickr account go to the image you want to share then click the share photo button

fbbcode2.jpg (24.69 KiB) Viewed 2094 times

In the share photo dialog that pops up choose BBCode (1) then Select all the text and copy (2)

In the SharpCap forum (or any other forum that supports BBCode) past the copied text into the body of the forum message. To check results just click preview to see the result. let me know if you have any other questions.

-Chris

[umasscrew39]

Thanks for your help with Flickr, Chris.

Here are the 3 images per each method/approach as stated above. If I strain my eyes, I think maybe #2 looks the best but both #2 & #3 clearly look better than the first method. The WBPP has some clear advantages over the manual process but doing it manually helps one to understand what is going on and how to address error messages. I am sure to get better with the WBPP as I keep playing with it.

Needle Galaxy_Method 1 by Bruce Donzanti, on Flickr

Needle Galaxy_Method 2 by Bruce Donzanti, on Flickr

Needle Galaxy_Method 3 by Bruce Donzanti, on Flickr

[oopfan]

Super!

The clear loser is Method 1 although I can't see much difference between Methods 2 and 3.

Just so I am straight:

Method 1: You used SC's master calibration files to calibrate light frames in PixInsight.
Method 2: You used PixInsight to create masters from the individual dark and flat frames captured in SC.
Method 3: Same as Method 2 but you used an enhanced processing script in PixInsight.

This seems to support the argument for not using SC's masters in other programs.

Now, there needs to be a Method 4:
Method 4: Everything done within SC. No need for PixInsight.

Brian

[umasscrew39]

Thanks and agree about Method 1 being the loser.

You are correct in your assumptions of the 3 approaches and I agree with your conclusion based on this one experiment. I think any slight difference between method 2 and 3 can be chalked up to slight differences in my PP abilities.

I think a Method 4 would be a great idea.

[BlackWikkett]

I agree with 2 and 3 being clear winner with 3 having a slight advantage in the galaxy detail.

I'm a total method 4 guy. I've been using SharpCap exclusively for over a year via master dark, flat and Live Stacking. The images I capture on the fly are all pretty good. I'm usually broadcasting on NSN and everyone seems to like the live images. Depending on how long I go, usually 6+ hours I can get about 8-12 objects in an evening. The next day I spend 5-10 minuets per image in Photoshop and have a result I'm happy with sharing.

I've been on the fence going mono with LRGB / narrow band. I feel like I'm getting 80%-90% of what's possible with the gear and skies I have. The struggle of doing 80% + more work to get at most a 20% improvement. The whole diminishing returns thing. I'm sure I'll give it a shot eventually just to have the fun (?) of learning it.

-Chris

[umasscrew39]

Well, you are lucky to be a method 4 guy- I was that when I lived in California but not now in Florida. Funny you mention NSN. After starting out doing visual astronomy and some lunar images with film (remember that?) when my kids were tiny tots years ago, I wanted to get back into astronomy. A few years ago, I heard about live viewing and then met a now good friend who would broadcast on the NSN, Don Rudny. Don taught me live viewing and stacking. I could look at Arp's peculiar and interacting galaxies by living stacking off of my California deck. Even did narrowband color palettes. It was a lot of fun. Unfortunately, it is a different story in Florida. I built a nice observatory on top of my 4 car garage but the sky is not as nice as in California. So, being a method 4 guy now will not work; thus, I had no choice but to learn a lot of new things over the past 2+ years.