Short/medium telephoto lens primarily for action, advice please!

[Daniel Browning]

I agree with John. (But wait... which John? Tee hee.)

But those two factors are not causally related.

No, but both noise and DOF are causally related to iris diameter. But only under certain circumstances/assumptions, and I think you two are assuming slightly different circumstances (e.g. whether exposure duration is the same or not), which I think may explain the disagreement. I'll try laying things out in the way I think of it:


For a given DOF, focus distance, and bellows factor, the only way to get thinner DOF is to increase iris diameter. That increase in diameter is going to reduce image noise by one of two ways: increasing the light intensity over the same amount of sensor area, or increasing sensor area exposed to the same amount of light intensity.


If both sensors have the same sensor technology (e.g. QE, or Quantum Efficiency), are exposed for the same duration, to the same scene (e.g. same flash power), and are intended to achieve the same image brightness, then noise will scale with DOF. Photon shot noise for certain, and often times read noise as well.


So why talk about DOF when the real cause is iris diameter? Because many photographers don't tend to care that much about iris diameter, but they do care about DOF, so explaining in terms of something that is an important factor in composition is more immediately useful. The reason it's possible is because DOF scales linearly with iris diameter when all formats are assumed to have the same AOV, focus distance, and bellows factor.

Take the statement, "Asuming you have the same sensor technology, the thinner the DOF the better the noise regardless of sensor size," let's assume you have exactly the same sensor - are you saying that a shot at f/2 would have less noise than a shot at f/5.6?

I don't know about John, but I would say yes. The reason you may disagree is because you may be assuming a context where it's possible to adjust exposure duration, flash, or ND filters to achieve the same brightness. In cases where that is true, DOF does not scale with noise.


But when duration and other factors are kept the same, then the f/5.6 shot will require either +2 EC in post or two stops higher ISO to have the same brightness as the f/2 shot.

In your example, you're comparing different sized sensors - and you seem to be saying that if one shoots with an aperture 1.33 stops faster on the 7D, that the noise will be equal to that of a 5DII. That's certainly not the case.

For the circumstances explained above, I think it is the case. At least for photon shot noise and the random part of the read noise. (The 7D and 5D2 do differ a bit in pattern noise, with my preference leaning toward the 7D, but a lot of photographers wouldn't ever go that high anyway.) For example, I think these two shots would have the same noise:


1. 7D, 125mm, f/2.8, 1/500, ISO 640


2. 5D2, 200mm, f/4.5, 1/500, ISO 1600

[neuroanatomist]

Thanks for your informative response, Daniel!

I think you two are assuming slightly different circumstances (e.g. whether exposure duration is the same or not), which I think may explain the disagreement.

Makes sense - my assumption was that our assumptions were assuming a significant role in the disagreement.

For the circumstances explained above, I think it is the case. At least for photon shot noise and the random part of the read noise. (The 7D and 5D2 do differ a bit in pattern noise, with my preference leaning toward the 7D, but a lot of photographers wouldn't ever go that high anyway.) For example, I think these two shots would have the same noise:


1. 7D, 125mm, f/2.8, 1/500, ISO 640


2. 5D2, 200mm, f/4.5, 1/500, ISO 1600

Makes perfect sense. However, I suspect that many photographers would instead shoot:





1. 7D, 125mm, f/2.8, 1/500, ISO 640


2. 5D2, 200mm, f/4.5, 1/200, ISO 640


...in which case the noise would be less with the 5DII. Of course, that assumes that 1/200 s would be adequate to stop whatever subject motion was present. But, in Av mode with Auto ISO set, on a 5DII at 200mm, the camera would lower the shutter speed to 1/200 s before it started raising the ISO.

[Fast Glass]

I just went to DOF master and it takes almost exactly (for practical perposes) 1 1/3 stops of aperture to get the same DOF for the 5D II than the 7D, having equivalent FOV.


I was assuming; a higher ISO, different focal length and faster aperture. Hope that makes sense.


Cheers,


John.

[Daniel Browning]

Makes perfect sense. However, I suspect that many photographers would instead shoot:


1. 7D, 125mm, f/2.8, 1/500, ISO 640


2. 5D2, 200mm, f/4.5, 1/200, ISO 640


...in which case the noise would be less with the 5DII.

Agreed.

[erno james]

If I could chime in, I really like the 135 f/2. It's fast and what's really nice is that it's fairly light in the bag and small around the neck. I've taken it to an NBA game and out in the woods too, so it is verstatile. I shoot a 7D and like it's reach for sports photography. Hope this help. -Erno


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[cls]

Let us know how it goes! And if you end up with the 135, tell me so I can be green with envy.
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The path to my decision was far from straight. Finally I came to the conclusion that for indoor sports I will stick with my 85/1.8 and, when the lighting is good, I can pair it with the 70-200 f/4. I've been to a couple of arenas with good lighting where I've used 1/500 - ISO3200 - f/4. I'm also positively surprised by the high ISO noise of the 7D. Even at ISO6400 it is quite usable (as I mentioned this is helped by lots of white background in hockey arenas).


If it was only for the indoor sports part I should have either replaced the 70-200 f/4 witha 70-200 f/2.8 or added the 135 f/2. These two are lenses I really desire but they will have to wait because my desire for the EF 100 f/2.8 L IS Macro was even worse. That's what I ended up with, and after a week of getting to know it I am really beginning to like it. So far I don't reallyhave any shots that qualify for sharing but there may be some uploads in the future. (Most photos I've taken so far are extremely detailed close-ups of meaningless subjects that may possibly be considered as optics po*rn - this lens is amazing.)

[thekingb]

Congrats, and enjoy shooting all the bugs, flowers and little things of the world!