How fast is the focus in SLR vs. P&S

[rainmanone]

and why is that ?

[Motorsports Photo]

rainmanone wrote:
and why is that ?

Many have found out the dreaded shutter lag in P&S cameras. I think its from the slow focus. WHY? There is only so much room in most P&S to put fast circuitry and mechanisms.

-Pete

[JMSetzler]

The speed of the autofocus is generally a function of the lens itself, especially on an SLR camera. The speed of the motors in those lenses determine how fast the camera will find correct focus. It's another one of those situations where more money gets you more speed :)

[slin100]

The speed of the motors is, indeed, the prime factor, but I believe the body also plays a role. I've heard that the Canon 1V has amazing AF speed.

Shutter lag is indeed a major problem with P&S. You can generally eliminate the focus time by half-depressing the shutter button.

[RichardtheSane]

I don't know exactly how it works, but I am certain that the shutter lag in a P & S can also be partly attrubuted the the lack of a shutter.
Slow focus motors on the lens is another problem with a point and shoot.
Canon USM on the EF series will not be matched by P & S focus for many years to come.

[Yance]

I don't know exactly how it works, but I am certain that the shutter lag in a P & S can also be partly attrubuted the the lack of a shutter.


No, it is really a matter of crappy AF sensors. With most high end EOS systems and a USM lens, you can get very responsive AF. I have learned how to get the best response time out of my G1 but it is still hit or miss. Mostly it is miss with poor focus or the shutter doesn't want to expose when I am ready. It is great for still life shots but very bad for any type of action.

[psk4363]

Having come from the Powershot series (G1, G2 and G5) to the 10D I can confidently say that focussing in the 10D is much faster than in the Powershot cameras.

Hope this helps,
Barry

[Cordell]

Focus on an SLR is not only a matter of being an SLR. Trust me, it's lens compatability too. Some SLR lens are much slower on one camera, but fast on another.

Many P&S are very good these days. I'm not talking about the G1 of yesteryear either. We have to look at the advancements of products today to make a true comaparison. Just because you had a P&S a couple of years ago and it was slow then, does not have anything to do with today's model.

With all that being said, I truely beleive there are no (or at least in my limited experience) P&S digicams that can keep up with SLRs when it comes to focus speed.

As far as lag on the P&S is concerned, I think it is a great matter of getting to know your camera and realizing what you are shooting. I shot girls basketball with a Nikon 990 and it worked out pretty darn good using the half press method. However, grain was horrible at the highest ISO do to having the slower lens.

[cole]

Some P&S can focus pretty fast, but their continuous focus tracking, if available, is generally quite bad. Also it's sometimes hard to tell from the LCD or viewfinder whether the focus is right, whereas it's much better on an SLR.

[rainmanone]

any one knows how the SLR "fast" Autofocus works ?

if it's like in P&S based on a window in the CCD and software running on the main camera processor (which in case of Canon DSLRs and Canon G3/5 and S45/50, is the same processor), then the only reason it's faster on SLRs is faster motor response.

I just don't understand why SLRs focusing faster, it doesn't make sense that it's only a software difference, cause then it would have been implemented in P&S as well.

[RichardtheSane]

The AF is a totally seperate system to the CCD/CMOS processing that goes on.

[Cordell]

Rainmanone,

Are you planning to build your own digital camera or something?

[dtrayers]

In a contrast focus system like P&S cameras have, the CPU in the camera 'looks' at the image and the contrast of the image under the autofocus points. It adjusts the focus until the image is at maximum contrast under the AF point(s).

It's easier to explain how phase-detection AF works in pictures:

Here's a link to how a Minolta AF works. I'd expect Canon's to be similar:

http://www.mir.com.my/rb/photography/hardwares/classics/maxxum7k/AF.htm

Here's one by Scientific American:

http://www.sciam.com/article.cfm?articleID=000E3DD0-F20E-1C73-9B81809EC588EF21

[rainmanone]

I'ts briliant !!!!!
Why can't Canon implement this in a P&S camera ?
After all, they build the lens module in the P&S.

it will be the ultimate P&S...

And I did build some cameras in my life... I worked for a company that makes processors for DigiCams

[dtrayers]

rainmanone wrote:
I'ts briliant !!!!!
Why can't Canon implement this in a P&S camera ?


One of the necessary items in the SLR AF system is the secondary mirror behind the main reflex mirror. The secondary mirror is what directs the image to the AF sensors. P&S cameras don't have a reflex mirror.

You'd need a pellicle mirror like on the Olympus E-10/20. Added bulk and cost and reduced light transmission to the image sensor.

[Mashuri]

Put it this way, by the time you keep building up your P&S to match an SLR in quality and speed, you'll have a camera the size and cost of an SLR or more.

[CyberDyneSystems]

Mashuri wrote:
Put it this way, by the time you keep building up your P&S to match an SLR in quality and speed, you'll have a camera the size and cost of an SLR or more.

Exactly,

There is no one factor that would need to be changed but many,

1. An actual Shutter like a DSLR,
2. A VERY expensive HSM focus motor (look how much a 35mm lens with an HSM motor costs compared to a P&S digital... this stuff aint cheap)
3. More sofisticated AF sensors
4. Faster auto-exposure

etc... too many things go into making a fast AF and the real goal,. faster AF and capture combined.. As Mashuri says,. getting all this to work will take money and size.

The result is a large DSLR body.