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Sometimes when I see a photo such as this one, I wonder why the photographer chose such a high ISO (640), despite using a tripod with a static subject.

As far as I know, a lower ISO means less noise, and vice versa. When shooting in low light with a tripod, it should be possible to just increase the shutter time. I believe the photo can be taken at a lower ISO without any major problems. So is there any other reason?

[EDIT]: For those who can not open the link, here is the photo: Image Equipment and settings: Canon EOS 5D, 24-105mm, 1/6sec at f/22, ISO 640, tripod, ND grad filter

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The other question to ask is why they're using f/22. Perhaps the answer is that you can still make great photos even if you don't do what is technically best. –  Philip Kendall Jul 23 '14 at 13:53
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Such a high ISO and 640 do not belong in the same sentence on modern cameras. That's a mid range ISO bordering on low, that said, the question is still valid as to why not to use a slower shutter speed, even if noise is not a real issue at ISO 640. –  AJ Henderson Jul 23 '14 at 15:00
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@PhilipKendall I guess because they read classical photography books and f22 on large format cameras is used quite often for landscapes. –  Andrew Jul 24 '14 at 7:31
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I really think you're reading too much into the settings. This may be something as simple as that he had the camera set to ISO 640 for something else and just didn't change it. –  Mike Jul 24 '14 at 7:40
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Include the photo inline please? The link is down. –  Phil Jul 24 '14 at 16:43

11 Answers 11

The mountain and the valley obviously are static -- even more from that distance. The clouds, however, move. If you chose a low ISO value, e.g., in the range of 50 to 100, the exposure time might be enough to get washy/faded/blurred clouds.

If I calculated it correctly, an ISO value of 100 with the other settings (exluding shutter speed) staying the same would result in a shutter speed of 2 seconds.

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Plus, of course, using a tripod always helps with sharpness. –  Andy Blankertz Jul 23 '14 at 15:07
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Yes, as anyone who has shot such scenes with these type of clouds can attest, they usually move rather quickly. Multi-shot HDR is out of the question unless you mask it and only use the sky from one of the multiple exposures. –  Michael Clark Jul 25 '14 at 3:00

I can't think of any technical reason for this to be the case. Even assuming that he used the lens at 105mm, if he was more than 387 ft from the closest object in the frame, he could have focused at 750 feet and had everything in focus even at f/5.6, so f/22 was completely unnecessary unless intending to get the shutter speed longer. A faster shutter speed or lower ISO could have easily been achieved. That said, my best guess is that the photographer may have been shooting in aperture priority mode and had the aperture cranked to max to help deal with the amount of light coming in from sunlight or possibly from a misunderstanding of how depth of field works.

This really demonstrates that taking decent photos is far more about the ability to recognize and take a good photo than it is about technical competency. It is helpful to have both, but you are far better off to be artistically skilled and technically bordering on illiterate than technically proficient but having no idea what makes a good artistic shot.

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The photographer chose a slightly higher ISO to compensate for using f/22 aperture (small opening = less light). You may ask, so why not make the shutter speed longer? The shutter speed was set to 1/6th of a second, rather than say 10 seconds, so that the image is nice and sharp, it may have been windy and might have shaken the tripod even just a little bit.

Judging from the colors of the clouds it might also have been dawn/dusk. It may not look like it in the picture but that's exactly why the ISO was bumped up.

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I'd have thought that 1/6 second is not going to help at all with a shaky tripod (whether vibration or wind). –  thomasrutter Jul 25 '14 at 2:20
    
It depends how sturdy the photographer's tripod is. 1/6th will avoid little shakes and vibrations compared to using say 10 seconds of shutter speed. –  Jeff B Jul 25 '14 at 5:36

I can't buy the clouds moving being an issue here. However, I can think of one reason that would be invisible: There are mobile objects near the photographer that sometimes get in the frame. He shot quickly to avoid them. He might have shot several, this is just the one that actually worked.

I do think it's more likely an oops, though.

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Disclaimer: this answer is highly dependent on equipment, firmware, etc. and may actually be conjecture.

Another possibility is that the digital camera is not optimized for the lowest ISO values. If you look at the internals of a camera some sensors do not support "50 ISO" and instead the camera firmware shoots at about 160 - 200 and pulls the exposure down with either amplifiers or software.

I remember hearing, anecdotally, that some earlier Canon sensors behaved this way and the lowest noise was achieved at ISO 160 - or multiples of 160. The in-between values are either amped up or pulled down in software providing less than perfect results. e.g.

100 is 160 pulled down 200 is 160 amped up 320 is truly captured at the sensor

Think of it as the opposite of the "HIGH" ISO modes that offer 25,600 ISO, etc. The high modes are actually shooting at 6400 and then amplifying the signal in a chip or software to give you the crazy values - but quality suffers.

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A very narrow aperture such as f22, which allows for an almost infinite Depth of Field, lets in very little light. ISO 640 may have been required to ensure the shutter speed stayed at a reasonable level, if the photographer didn't want to risk camera shake from wind or cloud blur.

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But f/22 also causes diffraction effects, reducing sharpness. –  David Richerby Jul 26 '14 at 8:30
    
And those diffraction effects are almost universally overstated for general photography. There is a huge amount of absolute crap based on test targets that's floated around as Photographic Truth that has very little bearing on real photography. –  user28116 Aug 4 '14 at 13:45

F/22 suggests to me that the photographer first took some pictures with nearby objects in the foreground and then forgot (or didn't bother) to increase the aperture for this particular shot. The ISO setting of 640 is then quite appropriate, you can go lower with a longer exposue time, but as the other answerers point out that can cause problems if the clouds move visibly (they become unsharp). Also, even if the motion of the clouds is not visible directly, this can still cause fluctuations in the illuminaion of the landscape. The shadows that the clouds cast can move accross the landscape by a large amount in a few seconds causing parts of the image to get under or overexposed.

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The only technical reason I can see in this particular case is that there might be some traffic on that road that you don't want in your shot. Thus the faster shutter speed was required to catch it between vehicles.

Not that I think this was actually the reason, since the timeframe for ISO 100 is still pretty short.

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I don't think that really applies, because any car would be tiny in the photo, even at quite a large print size. Furthermore, I suspect that an exposure of 1/6s would actually make any traffic look worse. A car travelling at 30mph covers about 2m in 1/6s, which is going to give horrible blur; in a second, though, it would travel about 13m, i.e., about three times its own length. That might not even be visible, if the car was a dull colour and had no lights on. –  David Richerby Jul 23 '14 at 20:50

It could have been very windy. =0)

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One (remote) possibility, based on a different camera...

My Fujifilm X-Pro1 has a "dynamic range" setting that lets me choose between 100%, 200%, and 400%. Higher settings are supposed to extract more shadow and highlight detail (almost like a simulated HDR) in the out of camera JPEgs.

BUT the 200 and 400 settings are only available at higher than minimum ISO settings. DR 200 becomes available at ISO 400, and DR 400 becomes available somewhere higher than that.

Maybe this guy's camera has a similar feature (or some other feature) that's only enabled at higher ISOs?

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I'm not aware of any such feature on the Canon 5D. Most people who own a camera at that end of the scale are working with RAW files and don't care what's in the JPEG. –  David Richerby Jul 24 '14 at 7:21
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@DavidRicherby Highlight Tone Priority is almost exactly the equivalent of the DR settings on the Fuji - but that only bumps the minimum ISO to 200. In general, I'd agree with you about RAW, but this photo was taken at f/22 :-) –  Philip Kendall Jul 25 '14 at 7:40

1) Be simple. (s)he forgot to switch to the lower ISO. ). For example, (s)he wanted to catch a bird before.

2) But I heard one story from an older photographer (?) about the long exposure (sensor reheating during the long exposure): sometimes it's better using short high ISO shot vs. long exposure shot to avoid noise.

The best solution to make two shorts and to compare results... :)

So, I think - 1)

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