Why Do DSLRs not have shutter lag?

[ozziworld]

Hello photographers!

Thought I would post this question that has been bugging for awhile.

Is there something inherent in the design of DSLRs that make them much faster handling than Point and Shoots? Focusing and subsequent tripping of shutter is just so much faster. What makes point and shoots burdened by shutter lag?

Would appreciate if someone could help shed some light on this.

 

[mikerault]

Because instead of going directly to flash memory (the card) which is very slow for writes, they use a DDR memory buffer (fast memory like in the main memory of a computer) to hold the data from the sensor and they write that out when they aren't busy. A DDR write is on the order of microseconds (15 or so) while some flash can be milliseconds.

Mike
Oracle Guru
Texas Memory Systems makers of the RamSan, the fastest computer storage in the World.

 

[Codiak]

Mike does a good job explaining the why they are faster at storing the results.
Physically storing the image is only part of the issue otherwise the same laggy camera would also lag with video capture, which isn't always the case. So you can't ignore the the time required to do compression which in low end, older cameras plays a part in lag.

Typically SLRs,
larger sensors
wider lenses
faster focusing
better light sensitivity
larger and faster cache memory
Faster cache to memory card data paths
Faster compression engine(s)
More user options
etc

That all assist in lower latency times... IE Less Lag..

Note, it's less, not ZERO.

Some of the more current point and shoot have gotten much better at reducing shutter lag.
Digital Camera Reviews and News: Digital Photography Review: Forums, Glossary, FAQ

 

[Gombessa]

DSLRs from the beginning (and I'm just going to go back to the NC2k/D1 era) have always been engineered for fast shooting, in part because the film SLRs on which they were originally based were as well. Because of that, DSLRs borrowed such systems for metering, focusing, etc. that were very fast, and the cameras themselves were larger and more expensive because of it.

Compact point-and-shoot cameras, on the other hand, were primarily focused on size and cost, and because of that they sacrificed a lot of the speed-centric features of the DSLRs. Things like retractable lenses, contrast detection focus and electronically-controlled zoom certainly didn't help here either.

Another big difference that shouldn't be discounted is acclimated behavior. People shooting DSLRs are pretty well used to half-shutter, focuslock/exposurelock, compose, and then shoot. However, for P&S cams, many people still compose through the display/viewfinder without focus or exposure lock, and just mash the shutter when they're ready, requiring the camera to focus/meter/shoot all in one go. Even older P&S cameras have pretty marginal shutter lag, and if you focus/compose first, the lag isn't all that bad (though usually still nowhere close to that of a DSLR).

 

[davelew]

Hello photographers!
Is there something inherent in the design of DSLRs that make them much faster handling than Point and Shoots? Focusing and subsequent tripping of shutter is just so much faster. What makes point and shoots burdened by shutter lag?

DSLRs usually have a half-silvered mirror in them, so that some light goes to the viewfinder, some light goes to a dedicated focus sensor, and some light goes to an exposure sensor. When you take the picture, a mirror moves and the light goes to the main sensor, which doesn't have to do anything other than capture the image. Because the focus sensor is dedicated to focusing, it can use some neat tricks like phase-detect autofocus which can't be done in a camera without a dedicated path of light for autofocus.

Phase detect autofocus used in most DSLRs will tell the camera "You are out of focus by exactly this much" and give the camera number, and the camera can move to the correct focus. The contrast detection autofocus systems used in most P&S cameras will just tell the camera, "You are out of focus, try focusing differently and I'll tell you if focus gets better or worse". Contrast detect autofocus involves a long conversation between the sensor and the focus motor, and typically some hunting around and trial&error to get the best focus.

As camera technology improves, the difference between P&S cameras and DSLRs is getting smaller. For example, the Panasonic GF1 uses contrast-detection autofocus that works in about 0.3sec, which I would consider acceptable for a DSLR with phase-detect AF.

 

[Puffer Fish]

Well they do, just not very much.. and compared to the typical P&S... they are fast.

Keep in mind the camera "only" has to be faster or as fast as a human.. after that, we don't notice it.

Today, most of the lag time, with new P&S's is due to focus and any preflash...DSLR's typically don't use preflash (this is also changing).

If you look here at the time to take an image with the latest Panasonic...if you half depress the shutter (removing all the focus and lens movement).. and the time is around the same as a DSLR (faster than some)

Panasonic Lumix DMC-ZS7 Digital Camera Performance - Review - The Imaging Resource!

I shoot a lot of fish pictures using that method to avoid lag.

 

[TomR1]

Correct. The only thing you can't do is snap of a shot of a moving subject at exactly the point you want if the movement is causing the focus point to change. Shooting a macro shot with a good dslr, the photographer will set the single focus point on the eye. When the critter is in the proper location he will depress the shutter and the camera will focus, pre-flash if necessary and fire. The P$S shooter will set the focus on the body, prefocus and shoot. In both cases the shot will be in focus. However, the shot with the eye ultra sharp and the exact position of the critter (mouth open for example) means a slightly better shot. That why we pay the big bucks (;

 

[eelnoraa]

Just to clarify one thing above. DSLR, at least with Canon and Nikon, when use their automatics flash system, they all use pre-flash. they call it TTL flash metering has been around forever. So preflash is NOT the reason P&S are slow, not at all.

2 major reasons:

1) AF system, DSLR has dedicated AF sensor and use phase detect AF. P&S use contrast detect of the image sensor itself. It needs to search around to detect the highest constrast scene seen by the sensor. And how the sensor know it has the highest contrast? By doing some contrast calculation of the live view image. This method is inherent slower than the phase detect AF, but also more accurate.

2) Metering system. DSLR has dedicated metering sensor, so the exposure is being determine before the light ever hits the sensor. In P&S, metering is also done by image sensor. When use half press, P&S calculate exposure base on what the sensor see. Then the sensor need to be "reset" before it can capture the real picture with the exposure value it calculated before.

To test this yourself, use a newer DSLR with live view, and try to take a picture in auto mode in live view. The lag is not any better than a P&S, or maybe even worse because DSLR's shallow DOF, it requires a lot finner search step for contrast detect AF.