First a disclaimer: I don't believe this works with Canon cameras, but not being a Canonista, I can't try it to find out. Perhaps one of my readers can test it and post a comment here.
As a second disclaimer, I've only tested this on the Nikon D600 but I have been informed that Auto-ISO has been available since the D200. Again, if someone has a D200, D7000, etc., perhaps they might try it and let us all know.
Now a little background.
The 'accepted' way of doing HDR's is to bracket a number of exposures around what you choose as the nominal value, and blend them using one of a variety of programs, including Nik HDR Efex Pro (my favourite), Photomatix Pro, or HDR Pro inside Photoshop (CS4/5/6).
We are told that the camera should be on aperture priority (or manual, Nikon changes the shutter speed in manual, not the aperture) because when you blend images taken with different apertures, you introduce a lot of chromatic aberration and create difficulties aligning all elements of the image because of the changing depth of field. That doesn't mean you can't or shouldn't use a fixed shutter speed and vary the aperture: after all you're free to experiment however you wish and of course rules are made to be broken.
Here's the problem. Suppose you're shooting a scene handheld in aperture priority with a 200mm lens and you've chosen f/8 for maximum sharpness, and a nominal ISO of 400. On a given day, the nominal shutter speed might be 1/250 sec, let's say. That means that all other things being equal, your -2EV exposure will be at 1/1000 sec but your +2EV exposure will be at 1/60 sec. Your +2EV shot is going to exhibit camera shake, even if you have VR (Canon IS). So you can't really use those settings, you're going to have to bump the ISO up a couple of stops, or open the aperture.
But then you'll be bumping up against the fast limit of your shutter speed (1/2000? Varies from camera to camera).
This occurred to me while I was experimenting with auto-ISO, shooting a 400mm lens. I KNOW I can't shoot sharp pictures with that lens under 1/500 sec and fiddling with aperture under varying conditions was a pain, I really wanted to set that depth of field. So I thought, "change the ISO". It works.
With earlier cameras, there's a limit of how high you can go (ISO) without introducing unacceptable noise. Well, that's true on all cameras, but the D600 seems to handle it better and I've even had acceptable shots in certain conditions at ISO 6400! So I set about trying it and sure enough, it worked.
So why not try it when shooting bracketed for HDR?
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This is an HDR generated in Nik HDR Efex Pro 2 from 3 exposures. They were all at f/6.3, 1/160 sec, focal length 70mm. The 3 shots were at ISO 400, 1400 and 6400. The sky was still featureless, so I brought it into CS6 and used Topaz Adjust 5 to further tone the image. |
In this image, I achieved the effect I was going for. Yes, there's noise in the sky, mostly introduced by Topaz when I tried to get some detail in it. I did balance some sharpening and noise reduction in Lightroom 4 in the normal course of post processing it.
Here's another image:
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This restaurant was across the street from the abandoned paddle shop above. In this case, the 3 exposures were 1/160@ f/8, ISO 1100, 1/250 at f/8 ISO 400 and 1/160 at f/8, ISO 4500. Why did the middle one (the -2EV shot) jump to 1/250 sec? I have no idea. Post-processing was much the same as the previous image, except I added a vignette in Lightroom. |
Another feature in the D600, and again I'm not sure about other models, is the ability to set the minimum shutter speed when you turn auto-ISO on. You can also set that to "Auto", which keys the minimum shutter speed to the focal length of the lens (you can shoot slower with a shorter lens without introducing visible camera shake).
I've read here and there, that you shouldn't use high ISO when doing HDR blends. Probably true, but sometimes it's better to trade off high noise for increased depth of field and a faster shutter speed. It's your call.
Do I feel as though I'm using too many auto settings? Am I going back to being an amateur snapshooter? Not at all. If the Gods (I mean Nikon) didn't want high end shooters to have these capabilities, they wouldn't have built them into the D600. Furthermore, I'm making all the decisions: in this case I just want to limit the shutter speed and let the camera make changes to other settings on the fly, without having to worry about bumping up against traditional limits. I'll do more of these. Count on it.
