Did I choose an ISO too high?

[pipnina]

last night I found the timer settings in my D3200. it only lets me take 9 shots at a time but until my intervelometer arrives it'll have to do.

So i got all 37 of my shots in DSS, stacked it and it looked like this:

http://i.imgur.com/fAJI8C3.png

http://i.imgur.com/DTyZHEp.jpg

The hot pixels are having a party in there!

Does this mean 3200ISO is just a *little* too much? I would have used 1600 but if I open my lenses aperture to lower than F/8 it gets some serious coma leading to effects just as undesireable once stacked. I needed the light!

Also, is there any way to get rid of them or am i done for?

(p.s. that's plymouth's LP, just over 20 miles away, someone loves their lights!)

[ronin]

Not sure what the details are like exposure length and possibly other things.

Have a look at this just posted:

http://stargazerslounge.com/topic/242186-milky-way-from-devon/

Seem to have used ISO 3200 but it is a single exposure of 25 seconds, forgot to read the aperture.

I assume therefore no tracking and the camera is just on a fixed tripod, or fixed something.

You should be able to replicate that just by manually setting Exposure length, ISO, Aperture and setting it off (use the timer to reduce shake).

Maybe turn the noise reduction feature on and allow the camera to do it's own noise reduction.

Suspect that you will get better results at a single exposure of 20 and 25 seconds, then move on to stacking when the timer arrives.

[lensman57]

last night I found the timer settings in my D3200. it only lets me take 9 shots at a time but until my intervelometer arrives it'll have to do.

So i got all 37 of my shots in DSS, stacked it and it looked like this:

http://i.imgur.com/fAJI8C3.png

http://i.imgur.com/DTyZHEp.jpg

The hot pixels are having a party in there!

Does this mean 3200ISO is just a *little* too much? I would have used 1600 but if I open my lenses aperture to lower than F/8 it gets some serious coma leading to effects just as undesireable once stacked. I needed the light!

Also, is there any way to get rid of them or am i done for?

(p.s. that's plymouth's LP, just over 20 miles away, someone loves their lights!)

Increasing the ISO in a DSLR camera has no effect on the sensitivity of the sensor. The sensor has a fixed sensitivity value ( QE )  but changing the ISO  only alters the gain of the amplifiers so you get a brighter representation of the captured data. Your camera works best between 400 and 1600 and the higher the ISO the more nasties appear on the image such as hot pixels. Next time try ISO 800 and compare. The best way of getting rid of hot pixels besides cooling the sensor to around -20C ( which is not possible with your camera ) is to use a large number of  Dithered Subs in the Stack, about 25 should do, and then apply a Sigma Clipping routine alongside Cosmetic Correction to get rid of the hot pixels and the inevitable cosmic hit spots, even DSS has these facilities and you should learn to make use of them.

A.G

PS: if you think that you have LP problems try my neck of the woods in Manchester. every thing up to 50 degrees of elevation is just an orange blob.

[pipnina]

Increasing the ISO in a DSLR camera has no effect on the sensitivity of the sensor. The sensor has a fixed sensitivity value ( QE )  but changing the ISO  only alters the gain of the amplifiers so you get a brighter representation of the captured data. Your camera works best between 400 and 1600 and the higher the ISO the more nasties appear on the image such as hot pixels. Next time try ISO 800 and compare. The best way of getting rid of hot pixels besides cooling the sensor to around -20C ( which is not possible with your camera ) is to use a large number of  Dithered Subs in the Stack, about 25 should do, and then apply a Sigma Clipping routine alongside Cosmetic Correction to get rid of the hot pixels and the inevitable cosmic hit spots, even DSS has these facilities and you should learn to make use of them.

A.G

PS: if you think that you have LP problems try my neck of the woods in Manchester. every thing up to 50 degrees of elevation is just an orange blob.

LP is the universal problem for us peeps down on the ground. Even the grand canyon sees the glow of Las Vegas and that's out in the sticks. LP was better there than any other place i've been, though. But I can't justify spending nearly an hour to get there again.

I'll try 800 next time, If it won't make a difference to how much light I'm getting then there's no problems.

I guess this is why lower ISOs tend to have better dynamic ranges.

[lensman57]

LP is the universal problem for us peeps down on the ground. Even the grand canyon sees the glow of Las Vegas and that's out in the sticks. LP was better there than any other place i've been, though. But I can't justify spending nearly an hour to get there again.

I'll try 800 next time, If it won't make a difference to how much light I'm getting then there's no problems.

I guess this is why lower ISOs tend to have better dynamic ranges.

What you want is an ISO value to bring you close to Unity Gain. For Canons it is around ISO1000 and I use either 800 or 1600 with my modded 1100d but I don't know this value for Nikons, shame on me as I was a Nikon guy for a long time. I really ought to find out as I have got a Mono modded d5100 which is still waiting to be put to serious test. It is also important to use a good LP filter if one could be found to fit a Nikon internally.

A.G

[dph1nm]

You could try subtracting darks or biases. That should help remove the hot pixels.

NigelM

[pipnina]

You could try subtracting darks or biases. That should help remove the hot pixels.

NigelM

I'm guessing this won't work now that the camera's cooled down... It's meant to be heat that causes this effect right? or are "hot pixels" just dead/a consistant defect?

[Cath]

What you want is an ISO value to bring you close to Unity Gain. For Canons it is around ISO1000 and I use either 800 or 1600 with my modded 1100d

mmmmm, a very useful / very formative / nice thing to learn about an ever so useful gain setting !

Thank you lensman

[lensman57]

mmmmm, a very useful / very formative / nice thing to learn about an ever so useful gain setting !

Thank you lensman

You are welcome, if you have not already then you can have a read of this. http://forum.luminous-landscape.com/index.php?topic=76446.0

Regards,

A.G

[pipnina]

It worked! I took 30 darks (not especially good ones, you could see the camera getting hotter throughout them). And the hot pixels are DEAD!

I managed to get way more stars out of it than I expected! Thousands of them!

http://i.imgur.com/QGFvGBZ.jpg

It's still a shame about the LP, though. I seriously thought I'd have gotten away from it after 20 miles. Either I'm missing a trick or people like Olly live in some remote areas :/

[sharkmelley]

The ISO for unity gain varies incredibly from camera to camera e.g. around ISO 200 for the Nikon 7000 and around ISO 4000 on the Sony A7S.  It can also vary considerably within one manufacturer's range of cameras e.g. Canon.  It is a function of bit depth and number of electrons for saturation. 

There is an easy way to determine unity ISO for your camera, assuming it appears in the list at http://www.sensorgen.info/ and assuming the accuracy of those figures.

For a 12 bit camera the unity gain occurs at the ISO whose saturation is nearest 4096

For a 14 bit camera the unity gain occurs at the ISO whose saturation is nearest 16384

For a 16 bit camera (do they exist?)  the unity gain occurs at the ISO whose saturation is nearest 65536

Mark

[glowingturnip]

The ISO for unity gain varies incredibly from camera to camera e.g. around ISO 200 for the Nikon 7000 and around ISO 4000 on the Sony A7S.  It can also vary considerably within one manufacturer's range of cameras e.g. Canon.  It is a function of bit depth and number of electrons for saturation. 

There is an easy way to determine unity ISO for your camera, assuming it appears in the list at http://www.sensorgen.info/ and assuming the accuracy of those figures.

For a 12 bit camera the unity gain occurs at the ISO whose saturation is nearest 4096

For a 14 bit camera the unity gain occurs at the ISO whose saturation is nearest 16384

For a 16 bit camera (do they exist?)  the unity gain occurs at the ISO whose saturation is nearest 65536

Mark

does that mean that the Canon 1100D has a unity gain at only ISO200 ?  Seems very low

[sharkmelley]

Yes. It would have unity gain around ISO 200. But best to image faint objects at a higher ISO to escape the high read noise of ISO 200.

Mark

[glowingturnip]

indeed, interesting to note the read noise declining with increasing ISO in the first graph, up to about ISO800/1600.  Not sure what the other two graphs are showing me though.

Also checked the graph for my old Nikon D80, shocking how much worse the read noise is !