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first123
Photographer
MC Grain
Posts: 1,647
New York, New York, US


Leggy Mountbatten wrote:

Leggy Mountbatten wrote:
To the AF system, an 85mm f/1.2 is an 85mm f/2.8, or f/4 or f/5.6, depending on the design of the sensor in question

No, he and I were talking about the sensitivity of the autofocus sensors. An autofocus sensor that is optimized for f/2.8 lenses will see the same thing, in terms of the amount of light it has to work with or the precision of the focus, from either an f/2.8 lens or an f/1.2 lens. The lens itself isn't losing anything. People have the mistaken perception that an f/1.4 lens give the AF sensor more light, and therefore will be easier for the AF system to focus.

Image format has nothing to do with this.

Really?

I thought all lenses focus at their maximum aperture when you use AF.

I see a huge difference between my 24-70's ability to focus in low light and my fast primes' ability in the same light.

I'm talking about hunting not speed.

Nov 19 12 10:23 am  Link  Quote 
Photographer
MC Grain
Posts: 1,647
New York, New York, US


Leggy Mountbatten wrote:

Leggy Mountbatten wrote:
To the AF system, an 85mm f/1.2 is an 85mm f/2.8, or f/4 or f/5.6, depending on the design of the sensor in question

No, he and I were talking about the sensitivity of the autofocus sensors. An autofocus sensor that is optimized for f/2.8 lenses will see the same thing, in terms of the amount of light it has to work with or the precision of the focus, from either an f/2.8 lens or an f/1.2 lens. The lens itself isn't losing anything. People have the mistaken perception that an f/1.4 lens give the AF sensor more light, and therefore will be easier for the AF system to focus.

Image format has nothing to do with this.

Really?

I thought all lenses focus at their maximum aperture when you use AF.

I see a huge difference between my 24-70's ability to focus in low light and my fast primes' ability in the same light.

I'm talking about hunting not speed.

Nov 19 12 10:23 am  Link  Quote 
Photographer
MC Grain
Posts: 1,647
New York, New York, US


Leggy Mountbatten wrote:

Leggy Mountbatten wrote:
To the AF system, an 85mm f/1.2 is an 85mm f/2.8, or f/4 or f/5.6, depending on the design of the sensor in question

No, he and I were talking about the sensitivity of the autofocus sensors. An autofocus sensor that is optimized for f/2.8 lenses will see the same thing, in terms of the amount of light it has to work with or the precision of the focus, from either an f/2.8 lens or an f/1.2 lens. The lens itself isn't losing anything. People have the mistaken perception that an f/1.4 lens give the AF sensor more light, and therefore will be easier for the AF system to focus.

Image format has nothing to do with this.

Really?

I thought all lenses focus at their maximum aperture when you use AF.

I see a huge difference between my 24-70's ability to focus in low light and my fast primes' ability in the same light.

I'm talking about hunting not speed.

Nov 19 12 10:23 am  Link  Quote 
Photographer
MC Grain
Posts: 1,647
New York, New York, US


Leggy Mountbatten wrote:

Leggy Mountbatten wrote:
To the AF system, an 85mm f/1.2 is an 85mm f/2.8, or f/4 or f/5.6, depending on the design of the sensor in question

No, he and I were talking about the sensitivity of the autofocus sensors. An autofocus sensor that is optimized for f/2.8 lenses will see the same thing, in terms of the amount of light it has to work with or the precision of the focus, from either an f/2.8 lens or an f/1.2 lens. The lens itself isn't losing anything. People have the mistaken perception that an f/1.4 lens give the AF sensor more light, and therefore will be easier for the AF system to focus.

Image format has nothing to do with this.

Really?

I thought all lenses focus at their maximum aperture when you use AF.

I see a huge difference between my 24-70's ability to focus in low light and my fast primes' ability in the same light.

I'm talking about hunting not speed.

Nov 19 12 10:23 am  Link  Quote 
Photographer
Leggy Mountbatten
Posts: 12,560
Kansas City, Missouri, US


Leggy Mountbatten wrote:
Well the 1.3 body didn't sell in near the quantities of the APS format bodies, and I would suggest that the majority of these went to sports shooters who were not constrained by the limitations in not having format-specific lenses available.
MC Grain wrote:
Which is my point. What percentage of the 20Ds were sold to people who'd pay for a pro lens designed for APS-C? I'm sure more 20Ds overall, but the market within 20D owners would have been small.

And really you're taking about 20D owners who would consider an L inadequate because it wasn't designed for the crop.

The 20D was a $1,600 camera when it came out (still have my receipt). It was the best-selling camera in its class for years, and a significant percentage of the owners were professional photographers. They could have sold an awful lot of pro grade lenses designed for the format, especially considering that the only FF option at the time was $8,000.

Hell, Sigma and Tokina managed to produce some competent fast lenses designed for the format way before Canon did. Sigma was first, with their 18-50 f/2.8, which came out long before Canon's 17-55. They also produced the first normal designed for the format.

Why couldn't Canon have done at least that much? They owned the dSLR market at the time, hands down.

Nov 19 12 11:20 am  Link  Quote 
Photographer
Leggy Mountbatten
Posts: 12,560
Kansas City, Missouri, US


MC Grain wrote:
Really?

I thought all lenses focus at their maximum aperture when you use AF.

Of course they do. But that doesn't mean the AF system sees any more light.

MC Grain wrote:
I see a huge difference between my 24-70's ability to focus in low light and my fast primes' ability in the same light.

A lot of that will be because of the design of the individual lens as much as anything. A major issue is the location of the exit pupil. Did you see Canon's list of what lenses work with the f/2.8 crosspoint AF sensors for the Mk III and 1Dx? The 24-70 only works with the center point at f/2.8. That has to do with the location of the exit pupil, and therefore what the other f/2.8 sensors can see.

I suspect that has something to do with the old 24-70's "backward" zooming. I'll bet the new model will work better. 

MC Grain wrote:
I'm talking about hunting not speed.

Yeah, I know what you mean. It's when you're near the threshold where it won't AF at all.

Nov 19 12 11:29 am  Link  Quote 
Photographer
Marin Photography NYC
Posts: 6,748
New York, New York, US


I have both but I always find myself using my 50d. All my lenses fit the 50d but not the 5d.  I do have the new 5d mkIII one the way!!! Can't wait....
Nov 19 12 11:50 am  Link  Quote 
Photographer
MC Photo
Posts: 4,144
New York, New York, US


Leggy Mountbatten wrote:

MC Grain wrote:
Really?

I thought all lenses focus at their maximum aperture when you use AF.

Of course they do. But that doesn't mean the AF system sees any more light.

MC Grain wrote:
I see a huge difference between my 24-70's ability to focus in low light and my fast primes' ability in the same light.

A lot of that will be because of the design of the individual lens as much as anything. A major issue is the location of the exit pupil. Did you see Canon's list of what lenses work with the f/2.8 crosspoint AF sensors for the Mk III and 1Dx? The 24-70 only works with the center point at f/2.8. That has to do with the location of the exit pupil, and therefore what the other f/2.8 sensors can see.

I suspect that has something to do with the old 24-70's "backward" zooming. I'll bet the new model will work better. 


Yeah, I know what you mean. It's when you're near the threshold where it won't AF at all.

I can only remember using the 24-70 once with my 5D3 and it was terrible, but it was so long ago I can't recall if I'd been using the center AF point or not.

I'm not sure I follow what you're saying with the AF sensor.

Are you saying that a wider aperture will allow more light in and the AF sensor will receive more light, but that it's sensitivity is such that there's no difference if it receives more light?

I'm not sure that makes sense, since more light is more light.

Nov 19 12 11:50 am  Link  Quote 
Photographer
Leggy Mountbatten
Posts: 12,560
Kansas City, Missouri, US


MC Photo wrote:
I'm not sure I follow what you're saying with the AF sensor.

Are you saying that a wider aperture will allow more light in and the AF sensor will receive more light, but that it's sensitivity is such that there's no difference if it receives more light?

I'm not sure that makes sense, since more light is more light.

No, that's not what I'm saying at all. Imagine looking at the back of a lens (or get one out). The circle you're seeing is the "exit pupil."

Individual AF sensors are set up in offset pairs. One designed for f/5.6 precision has them set at a 10 degree angle to each other, looking at opposite edges of the exit pupil of an f/5.6 lens. One designed for f/2.8 precision has the pairs offset at a 20 degree angle. A lens with a maximum aperture of, say, f/4 doesn't have an exit pupil that the f/2.8 AF points can see at all, because they're aimed outside the maximum size of the lens' exit pupil.

Likewise, the area of an f/1.4 lens that is outside the f/2.8 exit pupil aren't "seen" by the AF points either, because they're offset to a 20 degree angle, aimed at the f/2.8 exit pupil.

This also explains why some lenses you'd expect to work with the f/2.8 precision sensors don't. A good example of this is a macro lens, whose exit pupil moves farther away from the sensor as it focuses. The exit pupil gets smaller, from the AF system's point of view, so the high precision sensors don't receive any light.

Nov 19 12 12:22 pm  Link  Quote 
Photographer
Leighthenubian
Posts: 2,748
Toronto, Ontario, Canada


London Fog wrote:
So, are there NO pros at all who use Canon crop cameras?

By Pro, I mean a photographer who actually earns his living with whatever camera he has at hand, and has been published and paid for his work or both? This includes wedding photographers of course!

Dunno if your being sarcastic....

Many pros use crop bodies. I'm one. Still had my 20D and 1D classic up to a few years back.

And being published says nothing about whether you are pro or used a pro camera.

Nov 19 12 12:33 pm  Link  Quote 
Photographer
Steve Crossan
Posts: 114
Letchworth, England, United Kingdom


Hi all, after reading most of the replies, I'd understand if someone thought I was a clever Nikon http://lh5.googleusercontent.com/-iw5TaUpM1OI/AAAAAAAAAAI/AAAAAAAAABg/oWjr6XtVW8o/s120-c/photo.jpg. But anyway!

I've decided to go for a 50D. Sorry 5D lovers.

As an advantage over the 450D/XSi, for me it's a case of:

- It's beefier and I've got big hands (I'm 5'18")
- Faster more accurate cross-type sensors (kids aren't great at staying still)
- ISO ... the 450D goes to 1600, which is a bit meh, LR4 works miracles on it, but the advantage of the 50D will be welcome

Stuff like the weather sealing, burst rate. 1/250 flash sync are nice too.

When I consider I can flog my 450D for £200-£300, and get a 50D for £350 it seems silly not to. It's a lot of camera for the money, and I'm surprised it's so cheap.

The only selling point of the 5D is the FF sensor. I would prefer a FF sensor like most people, but I think a lot of my love for it was purely perceived. There are too many incredible crop sensor shots in the wild, and I have too much to learn about photography, and I think it's naive to think a bigger sensor would make me a better photographer. I actually take a lot of pleasure it getting more out of less, because it's forces you to digger deeper in terms of skill and effort.

As for lenses, I also don't get the argument about having less variety. If people want to label 85mm a portrait lens, then fine. I don't understand why such a convention exists. If someone can't take a decent portrait without having some herd-following-to-the-millimeter-lens, then I think that says more about their skills as a photographer. Plus there's the EF 50/1.4 and the 85/1.8 - both incredible "portrait" lenses. If you can't take good portraits with those on a crop, then seriously, photography probably isn't for you, full frame or otherwise.

Cheers peeps.
Nov 19 12 01:31 pm  Link  Quote 
Photographer
MC Photo
Posts: 4,144
New York, New York, US


Leggy Mountbatten wrote:

No, that's not what I'm saying at all. Imagine looking at the back of a lens (or get one out). The circle you're seeing is the "exit pupil."

Individual AF sensors are set up in offset pairs. One designed for f/5.6 precision has them set at a 10 degree angle to each other, looking at opposite edges of the exit pupil of an f/5.6 lens. One designed for f/2.8 precision has the pairs offset at a 20 degree angle. A lens with a maximum aperture of, say, f/4 doesn't have an exit pupil that the f/2.8 AF points can see at all, because they're aimed outside the maximum size of the lens' exit pupil.

Likewise, the area of an f/1.4 lens that is outside the f/2.8 exit pupil aren't "seen" by the AF points either, because they're offset to a 20 degree angle, aimed at the f/2.8 exit pupil.

This also explains why some lenses you'd expect to work with the f/2.8 precision sensors don't. A good example of this is a macro lens, whose exit pupil moves farther away from the sensor as it focuses. The exit pupil gets smaller, from the AF system's point of view, so the high precision sensors don't receive any light.

So it's a location thing.

It seems to me that AF works better with more light. It may be that the contrast is changing as the light decreases, but I'm not clear why the additional volume of light coming in through the larger aperture doesn't make a difference.

Nov 19 12 01:31 pm  Link  Quote 
Photographer
Kaouthia
Posts: 3,152
Lancaster, England, United Kingdom


Steve Crossan wrote:
I'm 5'18"

6'6" then? smile

Nov 19 12 01:37 pm  Link  Quote 
Photographer
B R U N E S C I
Posts: 25,319
Bath, England, United Kingdom


Nov 19 12 01:38 pm  Link  Quote 
Photographer
Steve Crossan
Posts: 114
Letchworth, England, United Kingdom


Kaouthia wrote:

6'6" then? smile

No, I shrunk. Down to 4'30" now. sad

Nov 19 12 01:40 pm  Link  Quote 
Photographer
London Fog
Posts: 6,625
London, England, United Kingdom


Illuminate wrote:
Dunno if your being sarcastic....

Many pros use crop bodies. I'm one. Still had my 20D and 1D classic up to a few years back.

And being published says nothing about whether you are pro or used a pro camera.

No, I wasn't being sarcastic, my point is just what you said, that there are plenty of pros using crops. The camera matters little if the person behind it has no idea what to do with it.

I love my crops, I feed them regularly! One likes Sandisk, the other prefers Lexar!

Nov 19 12 01:46 pm  Link  Quote 
Photographer
Leggy Mountbatten
Posts: 12,560
Kansas City, Missouri, US


MC Photo wrote:
So it's a location thing.

That's a way of looking at it.

MC Photo wrote:
It seems to me that AF works better with more light. It may be that the contrast is changing as the light decreases, but I'm not clear why the additional volume of light coming in through the larger aperture doesn't make a difference.

Ever wonder why most cameras won't AF with lenses with maximum apertures smaller than f/5.6, regardless of the amount of light? Noon on a sunny beach in Mexico, and your f/4.5 lens with a 2x TC won't AF. And yet even lenses with moderate maximum apertures will AF in fairly low levels of light.

Nov 19 12 02:53 pm  Link  Quote 
Photographer
Raoul Isidro Images
Posts: 5,974
Sydney, New South Wales, Australia


Steve Crossan wrote:
I'm surprised it's so cheap.

I am trying hard to think of a DSLR that has retained 70% of it's value after 5 years.

Maybe there is.

Maybe not. (someone will find out...)

.

Nov 19 12 03:20 pm  Link  Quote 
Photographer
Wild Image Media
Posts: 173
Canberra, Australian Capital Territory, Australia


Raoul Isidro Images wrote:
I am trying hard to think of a DSLR that has retained 70% of it's value after 5 years.

Maybe there is.

Maybe not. (someone will find out...)

.

Your pretty right there Raoul - that's why I'm not an early adopter and stand off 2-3 years/one model back - which I find is well up to task. Savings usually around 50%.

Lenses dont devalue so I dont wait as long there.

Nov 19 12 10:53 pm  Link  Quote 
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