Dealing with vignetting

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Re: Dealing with vignetting

Post by BlackWikkett » Sat Feb 02, 2019 7:04 pm

I'm making a couple of assumptions here (we all know what that can lead too.) You have not provided your exposure and gain settings but i'm assuming you're using a relatively short exposure being that you are using Hyperstar. I notice your brightness setting is at 5, for short exposure this is too low. Try turning this up by 5 and seeing if the histogram shape in live stack is off the left edge. Keep adjusting until you get the histogram shape you want but don't over do it with brightness. If you go too far with brightness you'll start getting some ugly vignetting with the 294.

Don and I both broadcast on NSN and we have come up with different process to get the results we're after. We've been testing various different methods for creating flats for the 294. This camera is very color sensitive and you'll find it can be frustrating to get this right for live stacking but it can be done.

My process for flats:

Exposure: 200 - 375 ms (this depends on use of filters, reducers and anything in the image train, will also vary with your flat panel or other light source)
Gain: 300
Brightness: 0
WB Red: 50
WB Blue: 50

--- Flats tools settings---
- enable subtract bias frame
- create monochrome flat
- for exposure and gain - for my RC6 I've provided the gain and exp settings that work for me. in setting the exp and gain adjust until the histogram is almost clipping the left side. I usually stay about 95% with the left most edge of the highest color curve, in my case green channel. I average 50 frames and that's the master flat for the night.

Once you start live stacking and you have two frames stacked the histogram will become live and you'll notice the color are way out of alignment. Don't be alarmed! apply an auto stretch and auto white balance in live stacking. You may notice red channel gets a severe boost just give this a slight nudge and it we bring it down. Now watching the Display histogram adjust your red, green and blue channels to get alignment. From hear on I try to make all stretching adjustments to the Display histogram leaving the Live stack histogram alone except for minor tweaks and adjustments to taste.

Hope this helps

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Joined: Tue Feb 14, 2017 9:04 pm

Re: Dealing with vignetting

Post by saguaro » Sat Feb 02, 2019 9:25 pm


Thanks for the great tips. You and Don have been very helpful in sharing how to get the best results with 294 flats. Anyone who's using a 294 with Hyperstar and SC live stacking will especially benefit from this info.

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Location: Charlotte, NC USA

Re: Dealing with vignetting

Post by descott12 » Sun Feb 03, 2019 1:43 am

Hi Robin,
Hmmm...Beginners luck for sure! I know I created a mono flat withOUT the bias checkbox checked. I think it is not checked by default.
Brightness was set to 12. I adjusted the exposure to get the flat's histogram centered around 50%. I can't remember where it was but it was in the ms range. Gain was very low - somewhere around unity which I think is around a 100 for the 294?? Or maybe I had it even lower as I think the SC manual recommended that.
The only thing that stands out as different is the bias checkbox. I am out of town right now but I will try again next clear night and record exactly what I did. Also, SC usually creates a text log of the settings so I will see if I can find that.

Posts: 45
Joined: Mon Dec 17, 2018 2:32 am
Location: Charlotte, NC USA

Re: Dealing with vignetting

Post by descott12 » Mon Feb 04, 2019 2:19 am

saguaro wrote:
Sat Feb 02, 2019 3:38 pm

But it seems like you got good results with whatever settings you used to create your flats, so I'd be interested to learn about the settings you used. Thanks.
Hi Robin,
I made some new flats tonight and they worked well just like last time. Here is a screenshot of all the settings.
Definitely had the bias checkbox Unchecked. I hope this helps.
Screenshot2.png (794.98 KiB) Viewed 681 times

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