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Thread started 10 May 2009 (Sunday) 20:17
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How about a camera with only f/2.8 and f/2 AF sensors?

 
joe ­ mama
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May 10, 2009 20:17 |  #1
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Since a decent number of people have only f/2.8 and faster lenses, why not a variant of some existing models with f/2 and f/2.8 AF sensors instead of the f/2.8 and f/5.6 AF sensors currently used?

I'd like to say f/1.4 and f/2.8 AF sensors instead (2 stops apart, just like the f/2.8 and f/5.6 AF sensors currently used), but then the 85 / 1.8, 100 / 2, and 135 / 2 woudn't see any benefit, and going f/1.4 and f/2 AF sensors would exclude all the macro lenses, as well as many of the popular fast zooms.

Would such a move be unprofitable? That is, we have no choice but to get the bodies with the current AF sensors, so what's the incentive to go to the effort to give us a choice? Or might it not improve the AF speed/accuracy enough to maybe convince at least enough of the people Canon has lost to Nikon to come back and be a profitable move?


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EOS_JD
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May 10, 2009 20:47 |  #2

Not sure I understand this. The sensors work for ANY lens faster than f2.8/f5.6 - so they will work fine with the f2 lenses. the problem arises when the lens has a smaller aperture than f2.8 for the centre and f5.6 for the other sensors.....

So feel happy the sensors are active for your fast primes :)


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joe ­ mama
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May 10, 2009 20:54 |  #3
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EOS_JD wrote in post #7895851 (external link)
Not sure I understand this. The sensors work for ANY lens faster than f2.8/f5.6 - so they will work fine with the f2 lenses. the problem arises when the lens has a smaller aperture than f2.8 for the centre and f5.6 for the other sensors.....

So feel happy the sensors are active for your fast primes :)

The point is that with f/2 + f/2.8 AF sensors instead of f/2.8 + f/5.6 AF sensors, one "should" get more accurate/faster AF with all your lenses, no? The downside being, of course, that you wouldn't be able to use any lens slower than f/2.8, which, unsurprisingly enough, is not a concern I have. : )


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EOS_JD
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May 10, 2009 21:32 |  #4

No. You would only get the faster AF with lenses that can open to f2 or f2.8. Only your primes can open up to f2. So all with zooms would not be able to get the faster AF.

Currently we get the faster AF woth f2.8/f5.6 lenses. Making an f2 sensitivity wouldn't make these any faster as they already get the use of the faster AF points.

The 1D series AF points are sensitive up to f8 (now that would be better for all)


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midnight_rider
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May 10, 2009 21:39 |  #5

joe mama wrote in post #7895899 (external link)
The point is that with f/2 + f/2.8 AF sensors instead of f/2.8 + f/5.6 AF sensors, one "should" get more accurate/faster AF with all your lenses, no? The downside being, of course, that you wouldn't be able to use any lens slower than f/2.8, which, unsurprisingly enough, is not a concern I have. : )

Dont bird much do you?
I would have to be the poor guy that has to lug around the 600mm 2.8.
Currently any lens 2.8 or faster can utilize the cross points on the AF system. So your 1.4 prime does benefit from this.


I never, Not once claimed to read your post...

  
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joe ­ mama
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May 10, 2009 21:51 |  #6
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EOS_JD wrote:
No. You would only get the faster AF with lenses that can open to f2 or f2.8. Only your primes can open up to f2.


That was kinda my point.

So all with zooms would not be able to get the faster AF.


Why not? The AF sensors that were previously f/5.6 would now be f/2.8.

Currently we get the faster AF with f2.8/f5.6 lenses. Making an f2 sensitivity wouldn't make these any faster as they already get the use of the faster AF points.


I don't know what that means. An lens slower than f/2.8 will not be able to utilize an f/2.8 AF sensor.

The 1D series AF points are sensitive up to f8 (now that would be better for all)


It's "better" for those that don't shoot entirely at f/2.8 and below, which was the point of my post.

midnight_rider worte:
Dont bird much do you?


Not unless you count eating chicken and turkey as "birding". : )

I would have to be the poor guy that has to lug around the 600mm 2.8. Currently any lens 2.8 or faster can utilize the cross points on the AF system. So your 1.4 prime does benefit from this.


My f/1.4 prime can also utilize an f/5.6 AF sensor, too, but I wouldn't say it "benefits" from this. It seems that the point of my initial post is being missed by one and all -- I'm not saying for *all* DSLRs to have f/2.8 and f/2 AF sensors only, I'm saying if *some* DSLRs had *variants* that had such AF sensors. For example, a 5DIIX. Would there be enough of an advantage to the faster AF sensors that *some* people would want the *variant*, and would there be enough people purchasing said variant to make it a profitible move on the part of Canon?

I'll take a stab in the dark and guess your answer would be a resounding "no". : )


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midnight_rider
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May 10, 2009 22:27 as a reply to  @ joe mama's post |  #7

So if you wanted to shoot birds with this special market camera you would need one of these?
Click here (external link)

I see what you are saying but to be honest I think it is the most profitable to a company to never limit a camera this way. If a person were to ever want a UWA or a fisheye or a super tele they would have to get a different body.
Cool thought but AF is assisted by the amount of light a lens lets through. So by using a 1.2 lens you are getting better light to the AF system and the only thing slowing you down at that point is the lens AF system.
The 50mm f/1.2 and 85mm 1.2 for example are by nature slow in the Af department. However you will be hard presses to find a prime to be more consistently accurate than them. By forcing these lenses to focus faster you would most likely make the accuracy decrease.


I never, Not once claimed to read your post...

  
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Panopeeper
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May 10, 2009 23:05 |  #8

The AF speed has nothing to do with the max aperture diameter. The accuracy is higher with the larger aperture.

However, it is not necessary to increase the aperture. The 1Dxxx models prove, that the electronics can be more elaborate: the high accuracy (phase detection) focusing works already with f/4.


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joe ­ mama
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May 10, 2009 23:10 |  #9
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midnight_rider wrote in post #7896443 (external link)
So if you wanted to shoot birds with this special market camera you would need one of these?
Click here (external link)

Not at all. If you wanted to shoot birds, you'd either get closer and use a 400 / 2.8L IS, or not get one of these bodies with the faster AF sensors. Not unlike if you wanted 10 fps, you wouldn't get a 5DII.

I see what you are saying but to be honest I think it is the most profitable to a company to never limit a camera this way. If a person were to ever want a UWA or a fisheye or a super tele they would have to get a different body.

I am not talking about "limiting a camera". I am talking about creating another *version* of a camara, not unlike Canon did with s special version of one of the 1.6x bodies for IR work.

As for a fisheye, well, maybe some won't work, but the 15 / 2.8 FE and 10 / 2.8 FE (for 1.6x) would.

Cool thought but AF is assisted by the amount of light a lens lets through. So by using a 1.2 lens you are getting better light to the AF system and the only thing slowing you down at that point is the lens AF system.

This isn't the case. It's not the amount of light, but rather the geometry specified by the minimum f-ratio of the lens.

The 50mm f/1.2 and 85mm 1.2 for example are by nature slow in the Af department. However you will be hard presses to find a prime to be more consistently accurate than them. By forcing these lenses to focus faster you would most likely make the accuracy decrease.

100 / 2, 70 / 2.8 macro, 200 / 2.8L -- I know, I own those three plus the 50 / 1.2L.


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cdifoto
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May 10, 2009 23:17 |  #10

I don't think you're really understanding the concept of the sensor "rating" Joe. No offense intended of course. However, the "f/2.8 or faster" means a lens that's f/2.8 or faster wide open will benefit with a faster and more accurate autofocus than anything with a smaller maximum aperture. If it's an "f/2 or faster" sensor, it'll be worse.


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joe ­ mama
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May 11, 2009 00:19 |  #11
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cdifoto wrote in post #7896753 (external link)
I don't think you're really understanding the concept of the sensor "rating" Joe. No offense intended of course. However, the "f/2.8 or faster" means a lens that's f/2.8 or faster wide open will benefit with a faster and more accurate autofocus than anything with a smaller maximum aperture. If it's an "f/2 or faster" sensor, it'll be worse.

Could you elaborate? Are you saying that an f/5.6 AF sensor is faster and more accurate than an f/2.8 sensor, for example? In other words, an f/2 AF sensor would be slower and less accurate than a slower AF sensor since it would require a faster lens to operate? Thus, slower AF sensors are better than faster AF sensors in speed and accuracy? If so, why does Canon advertise f/2.8 AF sensors? For stupid people like me? : )


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cdifoto
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May 11, 2009 00:34 |  #12

joe mama wrote in post #7897087 (external link)
Could you elaborate? Are you saying that an f/5.6 AF sensor is faster and more accurate than an f/2.8 sensor, for example? In other words, an f/2 AF sensor would be slower and less accurate than a slower AF sensor since it would require a faster lens to operate? Thus, slower AF sensors are better than faster AF sensors in speed and accuracy? If so, why does Canon advertise f/2.8 AF sensors? For stupid people like me? : )

I don't know of any sensors advertised as f/5.6 or faster. However, if there were such a thing, it would (in theory) be better than an f/2.8 or faster sensor if an f/4 or f/5.6 lens was used, assuming everything else was equal (but when is it ever? ;)), because it would be sensitive "sooner" - ie on a cheaper, slower aperture lens. It probably wouldn't be much better with an f/2.8 lens or faster though.

They advertise f/2.8 sensors to sell you f/2.8 and faster lenses. Advertising an f/5.6 sensor would neither sound impressive and nor give anyone other than a photographer who needs the shutter speeds an incentive to ditch the kit lens in favor of something expensive.


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joe ­ mama
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May 11, 2009 00:41 |  #13
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cdifoto wrote in post #7897166 (external link)
I don't know of any sensors advertised as f/5.6 or faster. However, if there were such a thing, it would (in theory) be better than an f/2.8 or faster sensor if an f/4 or f/5.6 lens was used, assuming everything else was equal (but when is it ever? ;)), because it would be sensitive "sooner" - ie on a cheaper, slower aperture lens. It probably wouldn't be much better with an f/2.8 lens or faster though.

They advertise f/2.8 sensors to sell you f/2.8 and faster lenses. Advertising an f/5.6 sensor wouldn't be impressive and wouldn't give anyone other than a photographer who needs the shutter speeds an incentive to ditch the kit lens.

Excuse me for being a bit slow. Let me rephase my question. Consider a 100 / 2 (one of the fastest and most accurate lenses I know of). If it were used on three different hypothetical bodies that were otherwise identical, except one had only f/2 AF sensors, another only f/2.8 AF sensors, and a third with only f/5.6 AF sensors, on which body would the focus be the fastest and most accurate, and by how much?


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Panopeeper
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May 11, 2009 00:42 |  #14

cdifoto wrote in post #7897166 (external link)
They advertise f/2.8 sensors to sell you f/2.8 and faster lenses

The limitation is not arbitrary but technical. The role of the maximum aperture is, that the image projected by the two halves of the lens shows greater difference with larger apertures; the aim of the focusing is to achieve equal image in the two halves. This is the same principle as the split focusing screen.


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cdifoto
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May 11, 2009 00:51 |  #15

joe mama wrote in post #7897201 (external link)
Excuse me for being a bit slow. Let me rephase my question. Consider a 100 / 2 (one of the fastest and most accurate lenses I know of). If it were used on three different hypothetical bodies that were otherwise identical, except one had only f/2 AF sensors, another only f/2.8 AF sensors, and a third with only f/5.6 AF sensors, on which body would the focus be the fastest and most accurate, and by how much?

I doubt there'd be any difference. You're talking about a fast lens that maxes out all three bodies spec-wise. In a way it's like asking whether a BMW, M-B, or Ford would be better in stop-and-go traffic. All three meet the minimum requirement - a brake pedal and 5mph capability. Pick the one with the best AC and radio.


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