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Post by Deleted on Jul 20, 2014 8:47:29 GMT
I was testing my all sky cam last night in preparation for the forthcoming Perseids meteor shower in August and I found something I don't understand. So I need a bit of help understanding how my VA cam works. Here is a view from last. Adjusted in Miloslick to get the best contrast. Shutter=OFF DSS=x8 AGC=X12 This is what I woke up to. A white out, as expected. The confusion began when I turned the tv monitor on and had a much darker image on screen. Now normally I would just change the cam settings to get a nice daylight pic on screen again, but something didn't seem right. So, as a pic is worth a thousand words, here is he confusing bit. I turned AGC and DSS off and got this. Not too bad but a bit dark. So I adjust shutter to 1/100,000sec. Then to 1/10,000sec. Then 1/50sec . It was about now that I saw something I could not understand. It is my understanding that 1/50sec is the slowest/longest shutter speed, and when AGC and DSS is off, this is the longest exposure obtainable. So in order to get longer exposures we use the DSS settings and these settings are multiples of 1/50sec. Then we can use AGC to increase sensitivity and brighten the image further. So just for fun I set the cam for its max of 10secs and AGC 60db, but got this. So the question is................Why is this 10sec exposure not completely white and overexposed. Also, why am I not getting 10sec exposures. The tv screen just looks like normal video.
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Post by davy on Jul 20, 2014 9:42:07 GMT
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Post by Deleted on Jul 20, 2014 10:20:17 GMT
Read it Davy, but could find no answer to my questions.
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Post by davy on Jul 20, 2014 10:41:51 GMT
are you using an auto iris lens
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Post by Deleted on Jul 20, 2014 11:47:24 GMT
Seems weird. Question… 'AE SETUP' … that wouldn't happen to be auto exposure possibly? Cause it kinda looks like thats whats happening... picking the exposure for you. And clearly its not exposing for 10 secs.
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Post by Deleted on Jul 20, 2014 13:31:40 GMT
Davy, I'm using a manual fixed lens. Another odd thing. If I switch to DC lens I do get a white out, and the only way to get a properly expose image is to use the shutter settings.
Chris, the AE SETUP is the only menu that gives the exposure controls.
I'm kinda thinking there is an inbuilt Automatic exposure control (AES) that is working to stop the image overexposing in daylight. More testing in the dark needed. I am running the cam with shutter, AGC, and DSS off, and it almost seems like its on AUTO. I'll keep it running until it gets dark and see if it self adjusts.
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Post by davy on Jul 20, 2014 14:01:43 GMT
Has ir filter been removed from camera
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Post by Deleted on Jul 20, 2014 16:47:33 GMT
It is Auto exposure. I have a camera that works just like this, Setting DSS to x512 is just setting the MAX value AE can use. Some cameras under the shutter setting allow fixed DSS modes, but some don't. When you set a value under shutter such as 1/1000, you are overriding the AE. When you turn shutter off you are turning AE on.
This is why its important to know if a camera has these fixed modes before using for VA. But for an allsky cam I think auto exposure is a good thing.
Hemmi
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Post by Deleted on Jul 20, 2014 17:24:54 GMT
Davy, IR filter is still in place. It moves over when it gets dark.
Hemmi, I think you are right. My Sammy 4000 has fixed shutter settings as well as normal shutter settings., so I can control the exposure manually. For the purpose of an all sky cam, the way this cam works will probably be ok. I'll wait till its dark and see if this AES only works in daylight. It would be nice if I could get the cam to do a 10sec integration. For meteor capture this may be better than normal video mode. If all else fails, I will put the DMK41 into meteor catching duty for a while.
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Post by johnno on Jul 20, 2014 20:37:22 GMT
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Post by Deleted on Jul 20, 2014 22:10:58 GMT
Your right Johnno, 512 is way over the top. With even a hint of cloud the image looks like daylight. With a setting of x8 I can see stars to mag 2.7 and better on a clear night, so that should be ok for bright meteors. Time will tell. 3 weeks to go for Perseids.
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