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Thursday, December 28, 2006

Anti-Shake Pt. II, or, Shake Reduction as Virtual Tripod for Nature Work

By Carl Weese

Most references to anti-shake technology talk about using long lenses at shutter speeds normally useful only with normal lenses, or about working in very low light conditions for reportorial-style shooting with short or normal lenses wide open at shutter speeds that were not possible to hand-hold in the past. The rule of thumb with 35mm cameras is that you can, with practice, expect a good success rate at about the reciprocal of the focal length, i.e., 1/60th second with a normal 50mm lens, 1/30th with a 35mm or a 28mm, 1/250th with a 180mm. For a DSLR with a 1.5 factor relative to 35mm you'd up those rule of thumb speeds by the same 1.5 so a 40mm/60mm-equivalent should need 1/60th sec.

I've been thinking about another potential use. The light in a forest during a soft rain can be magical, though in winter it can be pretty uncomfortable to work with. I've done a lot of large format pictures in this light, but it's arduous work with many traps to ruin pictures, ranging from tripod legs sinking into soft ground to large pieces of film buckling during long exposures because they've absorbed too much humidity. Working in wet conditions with a small camera on a tripod isn't a whole lot more expedient.

When I first got a good DSLR several years ago, which had weather-resistance as a key feature, I went out to shoot rain in the forest, both on tripod and in a freewheeling, walkabout manner. The weatherproofing worked fine, though it was hard to keep water drops off the lens, especially handling the camera on a tripod. With the small sensor and short lenses of digital capture, a few drops that would have no meaningful effect on an 8x10 camera's results show huge soft blobs in the DSLR picture because of the enormous depth of field. But I also found that, despite that relatively deep focus, I didn't like my results with the lenses wide open, which they had to be to work in the dim light handheld. A really shallow plane of focus and wildly out of focus backgrounds—the "selective focus" technique—just isn't what the woods look like to me. Not that I need Group ƒ.64 universal focus, but considerable depth and a fair amount of definition even in the out-of-focus background seems necessary. So when the day after Christmas offered soft and beautiful light with on and off gentle, but chilly, rain, I headed to my favorite nearby forest reservation for an experiment.

First, a digression about hand-holding slow shutter speeds, or speeds that are slow in relation to a long lens. Any marksman knows that no matter how steady and accurate your aim may be, if you flinch the release of an arrow or jerk a firearm's trigger instead of squeezing it skillfully, you simply will not hit what you aimed at. In fact, a steady aim isn't especially important at all. What counts is being able to have the aim perfect at the exact instant of an equally perfect release. Watching photographers over the years, including plenty of pros, I'm convinced that far more hand-held pictures are ruined by lousy shutter release technique than by shaky hands. Any marksman can also tell you how to get better at this. It's the same way musicians get to Carnegie Hall—practice, Dude, practice! End digression.

What I wanted to find out was whether the SR function of the Pentax K10D would let me stop down to apertures that gave the depth of field I wanted and deliver good results at the resulting shutter speeds, which could not reasonably be expected to work without anti-shake technology (I was thinking of, say, 50/50 success instead of one out of ten). This way I could walk around with the camera cradled in my hands, lens pointed down out of the drips and drops, and lift it only to make exposures of interesting subjects. In the woods, I set the K10D to one of its two Aperture Priority functions, set the ISO to Auto with range limited to 100–400, with the aperture for the 21mm/32mm-equivalent lens at ƒ/8, and of course, the Shake Reduction function switched on. The first thing I looked at...

Persistent Leaves, Hidden Valley

...came in at 1/8th sec. exposure, and while the background of this close framing is certainly not in focus, I think it works fine whereas with the lens wide open barely a single leaf would be sharp and the background would have turned to mush instead of reading as forest floor. The texture of the leaves is wonderfully detailed in all five exposures I made (this is simply the prettiest), but that won't be terribly apparent in small web repro. So SR passed its first test as a virtual tripod for this sort of shooting. Here is a shot done from considerably greater distance at 1/6th sec....

Two Trees and the Shepaug, Hidden Valley

...the bark of the two trees crackles with detail in the original file and the laurel leaves in front are in quite good focus. While the focus is not universal from front to back, I like it much better than I would a sharp zone of a foot or less, which is what it would be with the lens wide open, which is what it would have to be for a rational unassisted shutter speed of 1/30 sec. I did a lot of captures over an hour or so. I shot each idea two or three times. When ƒ/8 pulled the shutter below 1/4 sec. I opened to ƒ/5.6. There are some captures that look soft at 100% view but few that wouldn't look fine (at least for resolution) sized for a small print. The amazing thing is that a large percentage of them look OK even at 100% and so could easily be interpolated up well beyond the native (13-inch wide) resolution of the K10D. If you'd like to see more of these captures, just to think about the sorts of pictures this technique lends itself to—you can't judge resolution from the web-prepared files—pop over to my web log to see a few others in the posting for 12/28/06.

Posted by: CARL WEESE

Part I is here.

7 Comments:

Blogger christer3805 said...

Carl,

what lens did you use?

Happy New Year!

Chris

9:39 AM  
Blogger Ernest Theisen said...

Excellent article Carl. I going for a walk in the woods. Ernie

11:44 AM  
Blogger FN said...

If I'm reading it right, Carl used the SMC Pentax-DA 21mm F3.2 AL. I just got mine in the mail yesterday, and went out on the street today with my K100D. I have to say, it's about as perfect a walkabout lens as can be.

Now I need to get to the woods!

2:32 PM  
Blogger Jeff Kott said...

Carl, I'm not sure about this comment:
"For a DSLR with a 1.5 factor relative to 35mm you'd up those rule of thumb speeds by the same 1.5 so a 40mm/60mm-equivalent should need 1/60th sec."

A 40mm lens is a 40mm lens on both a FF and 1.5 cropped DSLR. It's just that on the cropped sensor the 40mm view is cropped to a 60mm view. But a hand held shot that is sharp with the 40mm view would still be sharp if cropped - right?

5:21 PM  
Blogger Carl said...

Hi Jeff,

No, the reason the 1.5 factor applies to shutter speed requirements is that the sensor is in fact physically smaller. That means that the original optical image projected by the lens onto the (was film, now sensor) is smaller, and so must be enlarged 1.5 times as much. That means, when you make a print from an APS-C sensor instead of 35mm film, any degradation from movement of the lens during the exposure will be enlarged 1.5 times as much as if you'd used it on a 24x36 format and made the same size final print. So shutter safety keeps pace with field-of-view, not focal length. You could think of it this way: the 40 is serving as a 60, so requires that shutter speed. By the same logic, if I used a 90mm lens on a 6x9cm format, I'd expect to get away with shutter speeds much lower than 1/90th. The use of the term "crop" is fraught with difficulties like this. An APS-C sensor--or a 4/3s sensor, or a piece of 8x10-inch film--isn't a "crop" of anything, each is just one of the dozens of formats photographers have worked with over the years. Pentax has enough of a handle on it that the viewfinder features a "SHAKE" warning that kicks in when the shutter speed drops below 1.5X the traditional 35 reciprocal of focal length.

fn, you read it correctly on the lens I used.

Ernie, having seen some shots on your blog, your walk in the woods is going to have some astoundingly different things to show. Hawaii and New England turn out to be quite different.

5:54 PM  
Blogger eolake said...

Yes, great article, thanks.
This is also important for general indoors photography, flash-free. Four out of five times, you like to get some DoF.

This is also the reason high-ISO noise is important. An extra stop noise-free is an extra stop penalty-free. For example ISO 1000 is noise-free on the Canon 5D.
Sadly Canon does not (yet) have IS in-body, so you need an IS lens like the quite expensive 24mm-105mm. But if you have that, you'll have a fantastically sharp lens, and IS for the kind of work you talk about.

6:55 PM  
Blogger Max said...

What Carl said about sensor size and lens focal length is very interesting. We all think of longer lenses and shake reduction technologies, while the other variable that will seriously profit from it are larger sensors. What doesn't show in a regular print from a 35mm piece of film or sensor of comparable size will show up when we get more sensor resolution and expect to make a proportionally larger print. There's a limit to resolution in hand held shots, unless these technologies really work.
This is painfully obvious when you feel tempted to use a 6x9 camera handheld at 35mm speeds, and the shots might look great on a light table, but in terms of resolution after a good scan it becomes obvious that you aren't getting all you would expect from a neg that is 7 times larger.
Really, if anti-shake can push this limit in larger formats, in a future of higher resolution sensors it will be of extreme importance to have it.
This might not be so extreme to all of us, but for those shooting landscapes, for example, it's an incredible bonus: Higher USABLE resolution + higher freedom in composing (no tripod) + less gear to carry around.

10:43 AM  

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