Noise reduction with 10 stop ND filter.

[NigelC]

I've ordered a 10 stop ND filter, which may well involve exposures of up to 45 minutes in extreme cases. I was wondering whether its advisable to have in-camera noise reduction enabled (5D original) - if this works by taking another exposure would be sort of unmanageable, and bettre to deal with noise post capture?

[feppe]

I'm pretty sure 5D works the way other Canon's do, by taking a second black frame capture with the shutter closed - so it would double the exposure time.

I do quite a bit of low-light photography, and have never bothered with black frames. Apparently the new Lightroom 3 has excellent noise reduction, and there's a front-page LL article about Topaz. I choose to bracket and blend exposures with Tufuse to kill noise.

[BobFisher]

Yes, the Long Exp NR is a dark frame subtraction.

What you could do, if you plan to do a lot of long exposure work with the filter, is take a series of shots with the lens cap on at different exposure times.  Keep those on your hard drive then use them in post to do the dark frame subtraction there.  Dark frame current is not random so having a 'stock' dark frame shot or series of them is all that's necessary.  It'd take some time to do the shots but once you have them, you're good to go.  Where this will be less than ideal is if the temperatures are different in your shooting conditions from when you made the dark frame shots.  Temperature can affect dark frame current.  But the 'stock dark frame' method will certainly be better than nothing and will definitely shorten your shooting time in the field, not to mention lengthen battery life in the field.

[jasonrandolph]

It will double your exposure time, but my experience with my Nikon D300 is that NR in post gives me better results than the in-camera NR.  For faster shots, it's not that big of a deal, but I can't imagine doing a 45-minute exposure and then waiting another 45 minutes to even compose the next shot (since the mirror is up at that point), but I suggest you experiment with it and see which gives you better results, and whether it's worth the extra time.

[walter.sk]

I've been wondering the same, although my exposures do not approach times as long.  I use a 1DMkii for night-time HDR, usually with 5 exposures at least 1 EV apart.  I have been driven crazy by the extra time for dark-frame noise reduction in the camera, as a typical sequence might start with a 1-minute exposure, followed by 2, 4, 8 and 16 minutes, each doubled by the NR.

I have not had a chance to experiment, but the idea of preparing a "stock" of lens-capped exposures to use later sounds doable if not ideal.  I wonder if anybody here has tried the 1Dii on long exposures without the NR?

[Luis Argerich]

I like to mix astrophotography with landscape photography.
In many cases you can improve noise in a very long exposure by taking a series of shorter exposures.

You just have to stack the exposures afterwards, and that's easy in PS, Gimp or any other editing software.

For star trails for example 60 1 minute exposures work as well as a 1 hour exposure, the advantages are
less noise as thermal noise is eliminated,  less chances of something ruining the whole shot, less chances
of the battery dying in the middle of the exposure, etc.

Hope it helps, not sure if it applies in your scenario.

[feppe]

I've been wondering the same, although my exposures do not approach times as long.  I use a 1DMkii for night-time HDR, usually with 5 exposures at least 1 EV apart.  I have been driven crazy by the extra time for dark-frame noise reduction in the camera, as a typical sequence might start with a 1-minute exposure, followed by 2, 4, 8 and 16 minutes, each doubled by the NR.

I have not had a chance to experiment, but the idea of preparing a "stock" of lens-capped exposures to use later sounds doable if not ideal.  I wonder if anybody here has tried the 1Dii on long exposures without the NR?

Not sure what your goal is, but exposures 1 EV apart is overkill. There's a good article on this forum somewhere from Guillermo Luijk (search for zero noise technique), and he came to the conclusion that all you need is two exposures in most real-world cases: properly ETTRd shot, and 4 stops overexposed.

I used to shoot nighttime cityscapes with multiple exposures ranging from 0.5 to 90 seconds. Based on Guillermo's resarch I've gone down to three exposures, ~0.5 secs (to capture neon lights), ETTR and +4 EV. I save 30-60 minutes of time per panorama by cutting down on exposures. This gives very good, noise-free results (sample Hong Kong cityscape). You have to of course blend the exposures together in post.

If you're tonemapping for HDR you might need more exposures, though - I haven't done much "proper" HDR so can't really comment.

[BobFisher]

Feppe, that's a different issue.  What Walter is doing is HDR.  That's why the bracketed exposures.  

Walter, for what it's worth, I don't have LE NR turned on when I do night HDR work.  Especially for HDR timelapse projects it wouldn't be at all practical.  

Luis, I haven't tested it myself but have a question for you.  I fully appreciate the stacking of multiple shots and have played with at a bit myself.  But in terms of thermal noise (i.e., noise resulting from increasing temperatures inside the camera), my guess is that doing a series of shorter shots wouldn't be significantly different because the camera is still working for nearly the same amount of continuous time.  Heat wouldn't be able to dissipate substantially between shots so would still build over the total time, wouldn't it?

[feppe]

Feppe, that's a different issue.  What Walter is doing is HDR.  That's why the bracketed exposures.

I was responding to Luis, not Walter. But I'm done hijacking Nigel's thread.

[BobFisher]

Sorry.  My mistake.  I assumed you were responding to Walter since you quoted his remarks.  Carry on then.

[feppe]

Sorry.  My mistake.  I assumed you were responding to Walter since you quoted his remarks.  Carry on then.

No, just checked, you were right, I'm clueless. I blame the Monday.

[Luis Argerich]

Luis, I haven't tested it myself but have a question for you.  I fully appreciate the stacking of multiple shots and have played with at a bit myself.  But in terms of thermal noise (i.e., noise resulting from increasing temperatures inside the camera), my guess is that doing a series of shorter shots wouldn't be significantly different because the camera is still working for nearly the same amount of continuous time.  Heat wouldn't be able to dissipate substantially between shots so would still build over the total time, wouldn't it?

I'm not sure how much noise disippates from shot to shot. If the sensor is able to disipate heat very quickly then it's probable that several short exposures will have significantly less thermal noise than a large one.
While not sure of the amount I think we can conclude that the N disipations together in between the shorter exposures will reduce noise if compared to a long one where the sensor is only heating more and more as time advances.

[walter.sk]

No, just checked, you were right, I'm clueless. I blame the Monday.

Not to worry.

Anyway, my night HDR shooting requires long exposures because I shoot at low ISO.  The shortest exposure is that which correctly exposes the brightest part of the scene, often streetlights or lights on bridges.  The longest exposure is what is required to get the darkest areas of the scene exposed well enough to bring out detail in the shadows.  I think I will disable the in-camera NR, though, and remove hot pixels or other noise later on.

[BobFisher]

Feppe, no worries.  Not a fan of Mondays either.

Luis, logically that makes sense.  Will have to do some practical experimenting and see how it ends up.