Why digital P&Ss suffer from shutter lag?

October 21, 2005 11:21 AM

Why do digital SLRs have no shutter lag and digital P&Ss (even expensive ones) have a bad case of it? What's the technical reason I mean (I am not an engineer)? In fact, most people who still don't like digital mention shutter lag as a major problem of digital photography. Thanks.
posted by PenguinBukkake to sports, hobbies, & recreation (9 comments total)

I would assume it has something to do with switching the CCD from the mode that provides video to the screen, and to the whitebalance and light level evaluators, to the mode that actually captures a high-quality shot.

Digital SLRs don't have to use the CCD to calculate light levels and white balance, they have other sensors to do this, and use the CCD strictly for capturing the real picture when the mirror flips up.

Of course, IANAEE either.
posted by odinsdream at 11:25 AM on October 21, 2005

... don't have to use the CCD to calculate light levels, white balance, and provide real-time video*
posted by odinsdream at 11:26 AM on October 21, 2005

The explanation I've heard is metering, focus, white balance, as you posit. And while I am an (unlicensed) engineer, I don't design cameras for a living, so that's just hearsay.
posted by GuyZero at 11:27 AM on October 21, 2005

A couple reasons:

1) Focusing and metering on SLRs are done with separate sensors from the imaging sensor, and focusing in particular is way faster using the phase detection system on an SLR than the camcorder-style contrast detection system most digicams use. In SLRs, performance is a solved problem -- when the automatic SLRs came out, nobody would have bought one that was slower than the manual ones, so they did the engineering back then.

2) Only recently have market pressures begun to induce manufacturers to work on fixing this in the low-end cameras. Until the last year or two, basically any digital camera owner was a nerd or a pro (or at least a semi-pro) and they were willing to deal with some limitations just to get the job done. But now mom and pop are buying digicams and they will return them if they don't get the shots they want. From the other end, the Canon Digital Rebel served as notice to those who were making $900-$1000 digicams that they would have to match SLR performance or lose the market. Who would bay $900 for a Sony CyberShot F828 when you could get a Rebel for the same price?

Things are beginning to improve... over the next couple years, faster digicams will start trickling down.
posted by kindall at 11:29 AM on October 21, 2005

Here's some useful information.

Most shutter lag can be minimized by pre-focusing.
posted by selfnoise at 11:30 AM on October 21, 2005

It does seem like there's a market for small P&S cameras with fast shutters and focus. One issue for small cameras is the smaller the lens and aperture, the less light for the autofocus system to operate. Big 35mm SLRs have a distinct geometric advantage here. But I think the bigger issue is that P&S cameras don't have the fancy autofocus systems of SLRs. That's fixable, with money.
posted by Nelson at 12:39 PM on October 21, 2005

I actually bitched about this in a post here earlier this year. Since then I've studied the issue and done some practical experiments.

Prefocusing helps, yes- but there is a perceptible lag between reality and what you see in an electronic viewfinder. That, coupled with your reaction time leads to less than optimum photos.

Try this experiment- open both eyes while looking through an electronic viewfinder- You'll see immediately the lag and also notice one other thing- the refresh rate of the viewfinder will cause motion to appear jerky in the viewfinder. When you look through the viewfinder with one eye closed, your brain tends to paper over the discontinuities between frames. It's sort of surprising to see how much is lost in the translation to video.

EVF's (electronic viewfinders) are an engineered solution to the perceived problems of optical rangefinders in cameras- you don't see what the lens is seeing. Unfortunately, you also lose perhaps 50 to 60 percent of the data that you get through an optical view.

What this means in practical terms, is that if you are trying to capture a specific moment in time, a cheap rangefinder camera will do a better job than the most expensive EVF camera.

When I wrote the previous post, I was just starting to get interested in digital photography- the last new camera I had bought was a Minolta SRT-201 circa 1977. I used it almost exclusively until the lack of the special mercury batteries and the rising costs of film and processing killed it for me. It's still on the shelf above my head, because I'm sentimentally attached to it, but I'll probably never take a picture with it again.

I'm currently usuing, for budget reasons, a Fujufilm S5100. The EVF has all the faults I list above, but, of course, I have to experience all these for myself. I'm currently saving my pennies for a Nikon D50.

There is no practical substitute for an SLR, unless it's a really good rangefinder. And really good rangefinders were last seen on Leica film cameras, imnsho.
posted by pjern at 12:44 PM on October 21, 2005

I sold cameras for a year at a high-end optics store.

When I first started, Minolta's top-end camera at the time was a point and shoot called the A2. A 'psudo-slr' is what I called it. Anyhow, It was *extremely* fast with focus, metering, etc.

Then they came out with their SLR, the 7D. Suddenly the A2 was replaced with the A200... and guess what. That lag time? Shot up bigtime.

In other words, some of it has to do with the manufacturers unselling you to an slr by crippling their point/shoot lines.

Other reasons above also apply.
posted by mmdei at 3:56 PM on October 21, 2005

lots of great answers, thanks everybody, I'd mark all as best answer but then the thread would look all funky

and mmdei's answer was good and scary, too
posted by PenguinBukkake at 8:38 AM on October 22, 2005