Long exposure with A200, A300, A350 and NR off goes bad

[Hawk]

Recently my friend sold his a200 and bought a700. When I asked "why?" he told me his night shots were completly unusable due to lots and lots of hot pixels and some flares in upper corners. He asked me and some other people owning a Sony Alpha cameras to do simple test: 30 sec exposure with all in-camera NR off, and lens cap on. Below are the results from my copy of a200. One is out-of-camera image, second has +4.00 on middle levels applied to reveal hot pixels and other things.

As we found a200, a300 and a350 are affected by this issue, a700 is not. Don't know about a100 or a900. Turning in-camera NR on gets rid of flares and most of hot pixels but of course destroys some sharpness and messes up some light flares on night images. I don't really care about that problem, just wanted other people to know what they can run into when taking 30sec+ night exposures.

Oh, and it seems that various copies had more or less bigger flares, sometimes they're round, sometimes they got vertical stipes, sometimes they're blue, sometimes purple. Samples from my camera seems to have quite small flares comparing to other I saw.

Out of camera jpeg

DSC03502_orig.JPG (5.42 KiB) Viewed 2744 times

After applying +4.00 on mid levels

p.s. I don't know why first one didn't get resized and thumbnailed in post, seems its bug in forum attachement handling

[Vidgamer]

I have read about this on another forum. The A100 also suffers from the flares in the corners. Mine has a small one at the top-middle too.



That image has been cropped slightly, taking off the worst of the flaring. I have turned on NR, but it did not seem to lock up for 20 min. like I would have expected it to for a dark frame, so it must not do that when at the Bulb setting. Does that sound right?

I have not noticed the streaks or banding in my recent star trail tests.

For exposures of 30 sec., if the NR setting causes a dark frame subtraction, then I guess I'm still not too worried about it. I can see where you might want to use a different camera for astrophotography, although it's also common to take shorter exposures and stack them. Not sure how that factors into this discussion, but perhaps it will help.

I'd like to try astrophotography again... I have not done so with my A100. And between the mosquitos when it's warm and the cold weather when it's cold, and then just the time required, it's hard to work up the motivation.

[Hawk]

I have turned on NR, but it did not seem to lock up for 20 min. like I would have expected it to for a dark frame, so it must not do that when at the Bulb setting. Does that sound right?

The longer exposure the bigger flares thus NR can't get rid of them. Also it may be that NR removed flares on my tests because image was simply black. When actual colors or objects are involved NR algorithm may think that flares are part of exposure/sky/object/whatever and doesn't try to reduce them.

[Vidgamer]

...
The longer exposure the bigger flares thus NR can't get rid of them. Also it may be that NR removed flares on my tests because image was simply black. When actual colors or objects are involved NR algorithm may think that flares are part of exposure/sky/object/whatever and doesn't try to reduce them.

On the A100, I thought that turning NR on should result in a dark-frame subtraction. It shouldn't analyze what is in the dark frame. Conventional NR probably won't do anything for the flares.

I tried some 10" and 30" exposures, and I don't see any flares in the LCD when reviewing.... or on the computer. (I even tried pulling up the shadows with curves, but there's nothing...) I seem to have a few stuck pixels, and the dark-frame subtraction that I expected to kick in isn't happening -- the NR setting doesn't seem to affect this. How frustrating!

When I did astrophotography before, I did both shorter exposures and longer ones. Looks like with the A100, it might be ok with shorter exposures. I'll have to try it one day. I've purchased the adapters, I just need to do it.

[Vidgamer]

I went back and tried again, and I could get curves to show the flares. Yup they are there, but at such a low level you don't even notice it unless you really push the background noise. I mean, it seems like something that would be extremely abnormal, to push the exposure this much. If you're doing 20 min. exposures, like you can see, it'll be brought up to the visible range, but with these shorter exposures, it shouldn't be noticeable.

What I haven't done, but that I thought about when I was doing the star trails and looking at the noise, is taking a number of short exposures, and stack them to simulate the star trail effect. I'm not sure how to automate this, but maybe I can do so with the wired remote.

[PhotoTraveler]

30 seconds is not long, and should not cause many issues. I could go maybe 3 minutes with a 7D without much issue. But when you try doing long exposure stuff, 5, 10, 30 minutes, and hours, all heck breaks loose with the CCD cameras.

That's where the A700, A900 come in. They can do the very long shots without much issue.

Long exposure is the main reason why I won't have a CCD based camera again.