extra long exposures (split from: Hardcore modding on a A530, thanks to CHDK!

  • 183 Replies
  • 43034 Views
Advertisements
Here's my 10 minute exposure, as you can see it doesn't look too bad. The amp glow can easily be subtracted or cropped at this level. I'd be interested to see one of your longest exposures.

I'm working on a project to calibrate sensors to enable long term exposures, so for now it's a research interest, but when I'm finished, I can take some calibrated pics to show you.

I've also discovered that 'hot pixels' do work when it's colder. I think most analysts just assume they're dead, but they can work perfectly.

"Theoretically, the longer the exposure the fainter you can detect, however light pollution limits the total time." (quoting myself) - I wasn't clear, what I mean is that light pollution limits the total exposure time of each frame, for example where I live, 6 minutes creates a bright white sky at night.

As far as those articles, I know they are recommending stacks of 5 minutes, but their point is to optimize the efficiency of your imaging time. Things change subtly in my case, I'm thinking of photos where efficiency is not important, only sensitivity. I would have to read the article more carefully though. Clearly if you're at the point of waiting for photons to hit, you need a long exposure. I'm testing those limits.

As to the noise, I'm chilling my camera in the freezer and it works no problem, and the noise noticeably goes down.

Anyhow, my point was to not artificially limit programs, as you never know what your users will do. If extending my limit requires extra programming, I don't expect anyone to do that, and for my experiments I can just try my other camera. Do you know the exposure limits with the SX50 or SX60?
« Last Edit: 27 / January / 2018, 23:30:28 by jmac698 »

And here's a closeup of a RAW showing some stuck pixels. It's been brightened a lot to show the amp glow. I'm still confused as to why the amp glow is reduced in the mask area; maybe, being an electric field, it's shielded by the metal mask.

Ignore the jpg artefacts, they show as undulations around the dots.

*

Offline reyalp

  • ******
  • 11487
Clearly if you're at the point of waiting for photons to hit, you need a long exposure.
You need a longer total exposure, but the photons don't care how many times you read out the sensor in between their respective arrival times. Astronomy routinely gets deeper by adding images collected over many separate exposures (e.g. http://xdf.ucolick.org/)

On the subject of stacking with low end sensors, this may be of interest https://research.googleblog.com/2017/04/experimental-nighttime-photography-with.html (also the SeeInTheDark presentation linked from there)

Quote
I'm still confused as to why the amp glow is reduced in the mask area; maybe, being an electric field, it's shielded by the metal mask.
It may be that the area outside the mask is artificially brightened by the camera (related to https://chdk.setepontos.com/index.php?topic=12926.msg130133#msg130133)

Quote
Anyhow, my point was to not artificially limit programs, as you never know what your users will do.
I agree completely. All else being equal, CHDK should let user push things as far as they want.
Quote
If extending my limit requires extra programming, I don't expect anyone to do that
I'm not averse to extra programming, but I'm more likely to be motivated if I see a clear real-world use case. 

In the case of cameras that natively support 1000 seconds vs implementing exp_drive (up to 2000) there's a trade of effort to implement, maintenance and RAM that would otherwise be available for other things. If someone shows me a real case where using a single 30 minute exposure makes the difference compared to a few shorter exposures, I'd support implementing it on those cameras.
Quote
Do you know the exposure limits with the SX50 or SX60?
Both have code to support up to 2000 seconds. Whether something else fails before that as on your sd1200 I don't know.
Don't forget what the H stands for.

Just as an aside, does anyone have any experience with amp glow at long exposures in the A810 or A1300 cameras? Both were released in 2012.

Thanks for any tips, best, Lee


 

Related Topics