Alley in Pisa, Italy

by Lars Kotthoff

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Ok, maybe I'm crazy, but I'm curious what will happen when I combine a ND400 filter (9 stops) with a zone plate or zone sieve "lens."

If I'm shooting a sunset, it I might get a 30 second exposure with the zone sieve in place. (I have two, they are about f50 and f100). So if I tape the ND400 in front of it, do I multiply the 30 seconds by 512? (2 to the 9 is 512). This will yield about a 4 hour exposure.

With a 4 hour exposure, what can go wrong? I expect some overheating on the sensor, but how bad will it be?

And yes, I know I need to experiment but at hours per shot, a bit of advance planning will go a long way.

(Note, I have a power adapter for the camera, so I could use a car battery and an inverter to give me 4 hours of power in the field.)

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The people who probably know the most about this kind of stuff are the extreme astrophotographers with tracking or the guys doing star trails. –  rfusca May 21 '12 at 14:37
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Super long exposures are an area where I know film is still used sometimes also. No power issues, no overheating, and no thermal noise. –  rfusca May 21 '12 at 14:38
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I want to know where you're going to find a 4-hour sunset to shoot. :) –  Flimzy May 21 '12 at 14:43
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I'm not. I'm going to start 4 hours before sunset and get the line of the sun coming down. A star trail, only brighter... –  Paul Cezanne May 21 '12 at 18:06
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4 hours...nothing... - petapixel.com/2012/03/16/… ;) –  rfusca May 23 '12 at 19:00

1 Answer 1

up vote 3 down vote accepted

I really like the idea but in my opinion anything can go wrong with a 4 hour exposure.

Firstly, you may be right about the sensor. It might overheat, although opinions are divided on this issue. CMOS sensors are really energy efficient and I've never experienced sensor overheating while taking pictures or recording videos. However, my longest exposures were 3 consecutive 30min exposures, captured with a Nikon D7000. Some people claim that the reason why you can only capture 20min videos on most DSLR cameras relates to sensor overheating. I personally believe that this isn't really a problem. Most advanced DSLR cameras are probably equipped with a thermal cut-off system that simply turns the sensor off when it reaches critical temperatures (please don't quote me on that). Besides, overheating also depends on a variety of outside factors like the weather.

Secondly, with a 4 hour exposure it would be difficult to determine the light conditions and calculate other settings such as ISO and aperture. I realise that you want to use the zone sieve so the aperture is already determined. However, with such 'extreme' setup, your built-in light meter will become inaccurate or even unusable. Therefore, if you are wrong with your calculations, your pictures can be either overexposed or underexposed. I personally think that a 4 hour exposure is just like a stab in the dark. You never know what to expect as the light conditions can drastically change in 4 hours.

Next, the images may be completely unusable due to the amount of noise. My experience is limited to APS-C sensors but I can tell you that a 30min exposure I took was very noisy. It took me a long time and effort to reduce the noise and the image quality wasn't great.

Finally, you have to think about image stabilisation. Like I said, anything can happen during 4 hours so you have to stabilise your tripod and protect it from outside influences such as a strong wind or even rain.

I hope I managed to answer your question and I'm looking forward to seeing your 4 hour exposure soon.

Best Greg

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Nice tip on the tripod stabilization, I had actually forgotten about that! As for the light changing, well yeah, it is going to change, a lot. Starting 4 hours before sunrise, well, it is pretty darn bright, and sunset is pretty dark. So it certainly is a crap shoot. I expect I'll need to do this several times, but I'd like to take care of as many gotchas as possible. Thanks! –  Paul Cezanne May 21 '12 at 18:26
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I don't think that the sensor itself will actually overheat, or any other component for that matter, but you might have components close to the sensor that will get hot enough to affect the sensor. This would typically show up as slightly lighter areas around the edge of the image, similar to clouding on an LCD display. –  Guffa May 22 '12 at 8:14

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