Tutorial: Should I Use a High ISO or a Long Exposure?
When you should use a high ISO and when should you use a long exposure?
I first started wondering if I was going down the right photographic path when I started bringing books along to read while shooting. For about two years now I’ve pretty exclusively done night photography, with my camera firmly bolted onto a tripod and making exposures measured in minutes.
And what do you do when you’re standing in a park with nothing to do for the next four to eight minutes? Bring a book!
But long exposures bring with them noisy images. I’ve made 30 minute exposures with a P45+ and the files, well, the files mostly hold up just fine. With the newer DSLRs I’ve been wondering: is it better to make a 8 minute exposure at ISO 100 or a 15 second exposure at ISO 3200? How can I best minimize the noise in my image when I’m shooting in very, very, very low lit environments?
Let’s find out! Thus far I’ve conducted this test with the Nikon D800. I’ll do it again soon with some of the newer crop of Canon’s.
Here’s the test shot, with the crop detail we’ll be zooming in on:
My methodology is pretty simple:
- I’m shooting with the Nikon D800 and Nikon’s AF 35mm f/2 lens, with compressed 14-bit RAW files. Noise reduction is set to “normal” on the camera.
- Using Lightroom 4, I’ve tweaked the white balance a tiny bit, the exposure by +.50, and have cropped in on a detail. I have NOT adjusted anything else — no noise reduction, no sharpening, etc.
So! Let’s look at the results. Each image includes the metadata, but I’ve arranged these from shortest exposure (at the highest ISO) to long exposure (at the lowest ISO and smallest aperture).
1. This means that we start with a very, very noisy image at ISO 25,600, aka “H2.0″. This is warp 9, all systems maximum, I’m-not-sure-she’ll-hold-together-captain territory. Is this noisy? Yes! But given how tight the crop is, I’m still pretty impressed by how much detail the D800 holds at this ISO, especially given how many megapixels Nikon’s crammed onto this sensor!
2. Things get better at ISO 12800 but not appreciably so. Nikon calls this “H1.0″, implying that they consider this “pushing the limits”.
3. We still get plenty of noise at ISO 6400, but the color at this point is pretty much spot on and we’re already seeing considerable detail. And, as with most newer DSLRs, the noise looks more like manageable grain than nasty pixellation.
4. This is getting better, but the sharpness will get better yet.
5. We’re beyond a 100% crop and you’ll be hard-pressed to find a significant difference in detail or noise in the next five or six images. The silver letters on Brian Ulrich’s Is This Place Great or What are already sharp enough to see the fiber of the binding beneath the embossed letters.
6. I mean, do you see much of a difference here?
7. This, I think, is probably the sharpest image, but I’m not sure I can really see a difference between ISO 800, 400, 200, or 100…
8. Take a moment and scroll back up to the top to see how much less noise we have at ISO 200 compared to the monster ISO of 25,600.
9. The D800 goes down to an ISO of 50, but Nikon calls it “L1.0″ meaning “low ISO 1.0″ I guess. ISO 100 is the lowest that we will go.
10. We’ll be at ISO 100 the rest of this series, but climbing both doubling both our aperture and our shutter speed.
11. So, this image should be sharper. f/5.6 is likely one of the sharpest apertures on Nikons 35mm f/2, but not when you bump the camera and cause motion blur. With long exposures “camera discipline” often ends up being a more important factor than any setting on your camera. Use a tripod. Use a remote shutter release. Don’t shoot next to passing trains or in strong wind. Really, honestly, be like 10 feet from the camera using a radio trigger and a two second delay. And then hold your breath during the exposure.
12. I think we’re still getting a little camera shake here, which is my bad. We’re also getting the first “hot pixels”: single bright pixels that are literally getting too warm from the long exposures. See that little green dot in the “S” of “Andreas” (on the orange spine)? That’s a hot pixel. We don’t like hot pixels, but like dust on a negative you can get rid of them if you have enough patience.
13. Is this reciprocity failure — which should only apply to film and never digital? Or is this the one minute difference between 15 minutes and 16 minutes? I imagine it is the latter: reciprocity failure refers to film’s diminishing sensitivity to light over very long exposures. It shouldn’t happen with digital and yet…
14. OK, I messed up here. I forgot to change the aperture, so we’re still at f/11. It was like two in the morning, OK!? But let’s look at this image closely, because it is pretty impressive. I’ve never seen a camera — medium format digital, film, DSLR, any camera — make this flawless of a 30 minute exposure. There are plenty of hot pixels, but about 15 minutes in photoshop can clone-stamp or heal them out.
15. One. Hour. We’ve got hot pixels and we’ve got a little noise, but we’ve still got color fidelity. The noise from these long exposures looks more like “old school” noise. What feels like grain at ISO 3200 feels more like splotchiness and a slight lack of detail here in our one hour exposure. That said, this image is stunning. STUNNING I tell you!
Wow. I really am stunned, just in case you still don’t believe me. I’ve been a Nikon shooter since the D80. A one minute exposure from the D80 would look worse than the ISO 25,600 image up top from the D800. And with the D80 I would never be able to do a one hour exposure, anyway–because the battery would die first. I wouldn’t trust my D7000, my current baby, above five or six minutes. Even the Phase One P45+, a medium format digital back with a sensor that specifically features the ability to do long exposures, can’t compare. Not even a little. (The P45+ is almost five years old, in its defense.)
This means that we have a $3,000 36-megapixel camera that can essentially take any length exposure you need. Rare is the photographer, unless you’re in charge of Hubble maybe, that needs an exposure anywhere near an hour long. Not only do the images hold up, by the way, but the battery life does as well: after taking all of the images above — a total of two hours or so of leaving the shutter open — the camera still claimed to have 80% of the battery left.
The sole caveat here is that the camera’s meter can’t be trusted in situations this dark. Use the high ISOs to your advantage for metering: take a few test shots at a high ISO, look at your histogram, and then do the math to figure out the proper exposure at the right ISO.
Stay tuned for similar tests from other cameras!
What’s the longest exposure you’ve made?
I realize most of us will never need to make an hour long exposure (although you should! they can be fun!). What’s the longest exposure you’ve ever made?