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Old Feb 18, 2007, 3:45 AM   #1
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When people ask DSLR-owners why the should upgrade from P&S to DSLR, one of the main arguments are often AF speed and accuracy.
AF system is lightning fast and superior those on the P&S's.
The phase detection is much more efficient than regular contrast detection, its easy to understand for anyone that reads something about it.

BUT, it seems when you put your gear together it doesn't help if the camera body is lightning fast at finding focus, cause the lens also affects it.
Buy a cheap long telezoom and everyone complains how slow (and sometimes unreliable) the AF system is, and if your unlucky it seems the MF are somewhat useless on some lenses too.

So, since I'm mainly into telezoom-shooting (like up to at least around the 35mm equiv of 400mm), this could be a serious issue for me if I consider going from my P&S bridge cam up to a DSLR.
So I wonder if anyone can explain to me what slow means on a DSLR.
When people write reviews of their somewhat cheap Sigmas or Canons that go from like 100-300 or 75-300 or therearound and complain that they have slow AF....
....how slow are they really?

My S3 locks at full tele (432mm) in about 0.5 sec if I'm lucky, and if it has to hunt somewhat maybe around 1 sec. How's that compared to a DSLR with a cheaper telezoom, that in total costs more than double of my S3?

Thanks for some feedback
Hard to find detailed reviews about these kind of things, with performance and timings. It just says "The AF is very slow, but thats ok since the lens is so cheap" and similar, but I dont have a clue what slow means in the DSLR-world.
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Old Feb 18, 2007, 2:51 PM   #2
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I think you're going to have a hard time finding a concrete answer. I've never seen anything anywhere that shows scientific timing of focus speed. So, the best you get is relative answers.

Focus speed of a lens is going to be driven by several factors: max aperture (camera always focuses at max aperture regardless of what aperture you're using for the exposure - it simply stops down the aperture when the picture is taken), sharpness and focus motor are the 3 biggest components.

So, in general a 300mm 2.8 lens will focus faster than a 300mm 5.6 lens because it lets in more light. A canon lens with USM will focus faster than one without USM and a sharper lens will focus better because the camera gets a sharper image to find it's contrast (which is part of the focus algorithms).

Any USM lens is going to do better than your S3 though. If you want a film equiv of 400mm though that means 250mm lens on a 1.6 crop camera. I don't know of many lenses 250mm so you'd have to jump to a 300mm lens. Lots of good 300mm lenses:

Canon 300mm 2.8

Canon 400mm 4.0

Sigma 120-300 2.8

Sigma 100-300 4.0

Canon 70-300 5.6

are probably the top of the list. Any of them are a quantum leap from your S3.
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Old Feb 19, 2007, 3:31 AM   #3
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JohnG wrote:
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I think you're going to have a hard time finding a concrete answer. I've never seen anything anywhere that shows scientific timing of focus speed. So, the best you get is relative answers.

Focus speed of a lens is going to be driven by several factors: max aperture (camera always focuses at max aperture regardless of what aperture you're using for the exposure - it simply stops down the aperture when the picture is taken), sharpness and focus motor are the 3 biggest components.

So, in general a 300mm 2.8 lens will focus faster than a 300mm 5.6 lens because it lets in more light. A canon lens with USM will focus faster than one without USM and a sharper lens will focus better because the camera gets a sharper image to find it's contrast (which is part of the focus algorithms).

Any USM lens is going to do better than your S3 though. If you want a film equiv of 400mm though that means 250mm lens on a 1.6 crop camera. I don't know of many lenses 250mm so you'd have to jump to a 300mm lens. Lots of good 300mm lenses:

Canon 300mm 2.8

Canon 400mm 4.0

Sigma 120-300 2.8

Sigma 100-300 4.0

Canon 70-300 5.6

are probably the top of the list. Any of them are a quantum leap from your S3.
Ok, thanks for the feedback
This really seems like a nice forum, I'm glad I registered

So that explains why the cheap Sigma telezooms (hitting 300mm at the long end) are said to have slow AF. They are slow, they are unsharp wide open, and they probably have cheap motors too.

Those you listed sound pretty cool, but I guess they cost a fortune (or weigh like a car....they often go hand in hand so probably both at the same time lol).

So, what would be really interresting for me is if anyone could explain/compare to me how one of the cheaper telezooms (hitting around 300mm) behaves at full tele. Is it maybe even slower than my S3? What do you DSLR-guys mean when you complain AF is slow and unreliable?

I guess most guys just think "of course its better than a P&S, its a DSLR for gods sake, of course its better". Thats not the kind of answers I'd like though, I'm not at all sure it absolutely has to be better, P&S bridgecams are very much worth their price indeed.
So, anyone out there that has experience with both a bit cheaper long telezoom (or superzoom) AND a newer bridge cam like the S2/S3/FZ7/H5....?

EDIT: Oh yes, those two Sigmas were extremely expensive, and heavy. Didn't even dare check the Canons you listed.
I knew it!!!
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Old Feb 19, 2007, 10:08 AM   #4
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ASBR wrote:
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My S3 locks at full tele (432mm) in about 0.5 sec if I'm lucky, and if it has to hunt somewhat maybe around 1 sec. How's that compared to a DSLR with a cheaper telezoom, that in total costs more than double of my S3?
In general a dSLR is faster, but you'll see the same issue there... :idea:

Again this has to do with the conditions you're shooting in: In bright daylight you'll be hard pressed to not notice that even a 'slow' cheap Sigma is faster than an S3.
Now in less than ideal condition even a fast (i.e. f/2.8 or less) lens will hunt - It'll all depend on how dark, but this is when the camera will dither back and forth to lock focus on a subject (made a little bit harder if this target was actually moving in the dark)
-> So a cheap Sigma that is only fractionally slower in daylight because of a slow motor can be quite noticeable when it has to 'hunt' in the dark because this fraction of a second get multiply by as many times as the camera commands the lens to move back and forth when it tries to focus - An ultrasonic USM (Sigma HSM) direct drive just does it a little bit faster because each rotation is that much faster to start with.

Now to the weight issue - P/S and 'bridge' camera have little sensor which do not neccesitate large lens. DSLRs on the other hand have a much larger sensor so they start with bigger lens already to cover a larger area, but now when you add a 'faster' lens (i.e. larger aperture) the lens to the mix this is becoming even larger because the aperture is a ratio of a lens opening over its focal lenght... You also want a very long focal lenght of 300mm which means larger optics still -> which means larger glass -> which mean you'll need some kind of metal to hold the whole thing together: It's just heavier! :O
Plastic/composite lenses are quite light, but their apertures are also smaller which is why they are lighter as well - You'll notice that the lenses with this type of construction will usually droop when pointed downward as they tend to loosen up after long usage...

There's also another aspect to the overall speed that you have not touched: the shutter release.
In a dSLR a shutter release can be programmed in servo mode so the shutter has priority over AF in order that the shutter can be released while a lens is still tracking focus - You'll see a big difference here with the S3 (or bridge cameras) where a shutter just won't fire at all... until the AF has locked.
IMO you'll have to just go to a store and try them out (in the same lighting conditions). There are just too many variable to generalize here :roll:
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Old Feb 19, 2007, 11:16 AM   #5
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Thanks
Yeah its probably best to try one out myself, if possible, I dont know.

I just thought since when talking P&S's everyone knows stuff about AF, which camera is 1/10 of a second faster or slower than the other, and reviewers always (almost) measure it (as well as they can) and compare to the competing models.
I just thought maybe someone would know how a cheap telezoom hitting around 300mm would compare. I dont have a clue if it'll be way faster than lets say my S3, about the same, or maybe even much much slower. Not a clue

Maybe DSLR's are best at normal focal lengths, or wide. For tele it seems if you dont have a fortune to spend, and strength like superman, its better with a good ultrazoom bridge-cam. They are very compact, fast, and bring sharp nice results for very little money. And for macros it seems (from what I've heard) that the incredibly short DOF makes it extremely hard to shoot with a DSLR, making you need both bright sun, flash, and tripod, at the same time. A good P&S has a bit of the edge there too it seems like. Oh well, I dont know...
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Old Feb 19, 2007, 1:48 PM   #6
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ASBR wrote:
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For tele it seems if you dont have a fortune to spend, and strength like superman, its better with a good ultrazoom bridge-cam. ...
It all depends on what you mean by 'a fortune'. As mentioned, the S3 will not compete favorably with the Canon 70-300 ($550). It doesn't have the same optical quality. And, again, your focus on the S3 WILL be slower. Not to mention things like frame rate, focus tracking (servo focus)and, if you need faster apertures you need them - with the bridge cameras you have absolutely no option. But it all depends on what you shoot. If you're using telephoto to shoot wildlife or sports then the s3 just isn't in the same league as a DSLR even with a consumer grade lens like the Canon 70-300. And, of course, ISO performance. DSLRs have ISO 1600 performance like the ISO 200 performance of the S3. That's a 3 stop advantage.

This is why it's detrimental to only look at one aspect - focus speed. Yes it's important, but there are so many other factors at play too.

Having said that - if $550 is 'a fortune' for you to spend on a lens then yes, the DSLR world might not be for you - especially if you like telephoto shots.

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Old Feb 19, 2007, 4:53 PM   #7
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JohnG wrote:
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ASBR wrote:
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For tele it seems if you dont have a fortune to spend, and strength like superman, its better with a good ultrazoom bridge-cam. ...
It all depends on what you mean by 'a fortune'. As mentioned, the S3 will not compete favorably with the Canon 70-300 ($550). It doesn't have the same optical quality. And, again, your focus on the S3 WILL be slower. Not to mention things like frame rate, focus tracking (servo focus)and, if you need faster apertures you need them - with the bridge cameras you have absolutely no option. But it all depends on what you shoot. If you're using telephoto to shoot wildlife or sports then the s3 just isn't in the same league as a DSLR even with a consumer grade lens like the Canon 70-300. And, of course, ISO performance. DSLRs have ISO 1600 performance like the ISO 200 performance of the S3. That's a 3 stop advantage.

This is why it's detrimental to only look at one aspect - focus speed. Yes it's important, but there are so many other factors at play too.

Having said that - if $550 is 'a fortune' for you to spend on a lens then yes, the DSLR world might not be for you - especially if you like telephoto shots.
Have you used such a lens (or similar) and also used a Canon S3 or similar modern ultrazoom bridge-cam? Would be nice to know, some people just assume or guess, while others really know what they talk about.

Anyway, yes, that Canon IS-lens is pretty good I guess, but sure, just the lens costs a bit more than a complete S3, I could almost have a Panasonic FZ50 with Leica optics for the money of just that lens.
Its pricy, I cant see it any other way.

And regarding higher ISO's on a DSLR, I dont really see it as just something positive, its more of a necessary thing since all zoom tele lenses are so extremely slow.

Please talk some more guys if you want, I find it very interresting
There should be more DSLR vs P&S reviews, I mean serious reviews, comparing AF-speed and resolution and CA and DOF and bokéh and everything, just to get a hint of how they compare and how prices compares for a few budget setups.
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Old Feb 19, 2007, 6:21 PM   #8
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ASBR wrote:
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Have you used such a lens (or similar) and also used a Canon S3 or similar modern ultrazoom bridge-cam? Would be nice to know, some people just assume or guess, while others really know what they talk about.
I've used an Fz-7. But again you miss my point. I've seen quite a few DSLR photos and some S3 photos. Again, based upon the only thing that counts - picture quality, the s3 doesn't compete.

As far as knowing what I'm talking about. Unlike a number of people I readily display my photos on this forum. I shoot quite a lot of sports and spend a lot of time with telephoto lenses. I can assure you from what I've seen the S3 doesn't come close to what a DSLR can produce. But again, you have to spend the money. It's a question of how important that quality is to you. If it's not important it's not worth spending the money. If it is then you'll find a way to save your pennies.

Again, it also depends on what you want - want a nice blurred background? won't get that with the FZ50:







Besides the subject isolation, good luck getting the focus tracking to track a moving subject like the DSLRs can. Again, these other attributes whick help produce quality photos may not be important to you. This may just be an academic discussion. And you just may be looking for someone to lie to you and say the bridge cameras are just as good as the DSLRs.

Good luck in your hunt!!


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Old Feb 19, 2007, 10:38 PM   #9
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ASBR wrote:
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... And for macros it seems (from what I've heard) that the incredibly short DOF makes it extremely hard to shoot with a DSLR, making you need both bright sun, flash, and tripod, at the same time. A good P&S has a bit of the edge there too it seems like. Oh well, I dont know...
Just the required flash for macros... The brief flash burts will freeze any movement (from the subject or the photographer) - i.e. No tripod needed:
http://www.stevesforums.com/forums/v...amp;forum_id=7
http://www.stevesforums.com/forums/v...amp;forum_id=7

-> IMO you'll have a much harder time with a P/S since flash control is practically non-existent on a P/S (or most 'bridge' camera)...

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Old Feb 20, 2007, 3:15 AM   #10
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Ok, thanks you guys

I wouldn't say though that the only thing that counts is image quality. I would say usability and performance is at least as important, since with a slow hardworked camera you'll miss most of the shots, and better to have lots of good shots and lots of fun than one or two incredible ones.

I just dont know about image quality either. From what I've read a bridge cam often gives better IQ than a DSLR with a cheaper kit-lens or cheap telezoom. I'm afraid if I buy something "cheap" the pictures will just turn out worse than my S3, and maybe even some of the performance/usability will be worse.

I'll have to get my hands on a DSLR sometime....any of you guys want to lend me yours, just ship it to Sweden
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