Big DSLR sensors are stitched together

[Canadian Roger]

Will this affect the full frame Nikon astrophotography camera - the D810a?

There was a review of this camera in the American magazine Sky and Telescope.  I haven't read the article yet, but I know a couple of people who have Nikon cameras are very much interested in the D180a.  They claim to feel "unclean" if they use a Canon camera.

Canadian Roger
Freezing in Canada

[MarkS]

I definitely want to know the answer to this.  I plan to outline a step by step methodology to show the problem, that anyone can use.  The problem can then be "crowd solved" by owners of various cameras.  I'll post a request on Cloudy Nights, DPReview, SGL and hopefully we can get some momentum on this problem.

Mark

[MarkS]

I've now written up the methodology for investigating the issue on other cameras on the Cloudy Nights thread:
http://www.cloudynights.com/topic/519941-sony-a7s-split-sensor-and-banding/?p=6993007

Mark

[Carole]

I've been thinking that not every-one who has one of these cameras seems to suffer with the banding, it seems some do some don't. 

So could be be just bad luck, or maybe those who say the don't just think they don't have a banding problem and perhaps don't analyse their images or stretch them sufficiently to notice.

Also I have had an idea.  It's not ideal but might overcome the worst of the problem, and certainly is not a solution, but just might get you out of a frustrating hole sometimes.  This will only work if you image both sides of the meridian.
If you took some of the data from a meridian flip, some of the areas with the banding you might be able to do a layer and use the flipped data on those areas as this will be using the other wise of the chip. 

It would be very annoying to have to resort to this, but if you are doing a meridian flip anyway.

Carole

[Mike]

Wouldn't that just move the banding to the opposite corner?

[Carole]

Wouldn't that just move the banding to the opposite corner?

It would Mike, but I was thinking if he took twice as much data, he could use the good side on each side of the Meridian i.e:

Basically take a normal image a), then take some more b), stack and process both.  flip b) and place a) over the top, and rub out the offending areas revealing the better data below.

Long winded but might help if the banding really spoils an image.

Carole

[MarkS]

Hi Carole,

That idea would definitely work - it would reduce the overall effect of the banding.  I'm also working on another idea which I need to think some more about.

Mark

[The Thing]

Wouldn't that just move the banding to the opposite corner?

It would Mike, but I was thinking if he took twice as much data, he could use the good side on each side of the Meridian i.e:

Basically take a normal image a), then take some more b), stack and process both.  flip b) and place a) over the top, and rub out the offending areas revealing the better data below.

Long winded but might help if the banding really spoils an image.

Carole

Or simply invert the camera halfway through the imaging run...

[RobertM]

What about isolating the banding by subtracting a flat from a camera where the problem is not showing so much ?  In exactly the same conditions you should be able to do that successfully.

It might be a bit more challenging to process but you could then apply a negative of the banding.  I'm not quite sure how much the banding depends on flux levels; that would be the limiting factor.

Robert

[MarkS]

What about isolating the banding by subtracting a flat from a camera where the problem is not showing so much ?  In exactly the same conditions you should be able to do that successfully.

It might be a bit more challenging to process but you could then apply a negative of the banding.  I'm not quite sure how much the banding depends on flux levels; that would be the limiting factor.

That's why I did those experiments at different exposure levels - to test out how stable the banding is:
https://drive.google.com/file/d/0B3Ky5pyZvsINTTQwNllXTXFpWm8/view?usp=sharing

Unfortunately the banding shifts quite a lot with exposure level i.e. with the level of sky fog.  So it won't work - it's too difficult to match the banding to the image frames.

I'm now thinking of using a set of 30sec exposures to render the brighter stars properly (without star eating) mixed with a set of long exposures.  With the long exposures the banding is less prominent and the very faint stars are "protected" from the star eater by the sky fog noise.

Some good news is that Sony engineers are actually looking seriously at the star eater problem.  Personally I don't think they will come out with a firmware fix for existing cameras but it might mean future cameras may have the option to disable it.

Mark