Wallet full of $100 bills

[neuroanatomist]

Thanks, Guys!


I thought there was a flaw in my logic - obvious once you pointed out the effect of cropping on noise.


Despite my hopes to the contrary, the elegant yet occasionally frustrating laws of physics have reduced this to a simple choice of the most appropriate focal length for my needs - and that's 35mm.


Merry Christmas to All!


--John

[Daniel Browning]

[quote user="neuroanatomist"]


- am I better off shooting with the 24mm at f/1.4 and cropping to get the desired framing?


[/quote]


Definitely not. If you think about it, it

[Daniel Browning]

the elegant yet occasionally frustrating laws of physics

Love it!

[Jon Ruyle]

the only time that cropping (or using a smaller sensor) is going to give you a real benefit in DOF is when bellows factor is significant, and it isn't in these circumstances.

Interestingly (to me, anyway), even taking bellows factor into account, cropping gives no DOF advantage. The "effective crop factor" changes as you get close up, but with a given DOF, you still get the same amount of noise. The same is true of diffraction: with a given DOF, you get the same amount of diffraction no matter how much or little you crop.


You can't win. (But on the upside, you can't lose). The elegant laws of physics do not favor one sensor size over another- if you have the right lens, you never need to crop.

[Daniel Browning]

even taking bellows factor into account, cropping gives no DOF advantage.

Am I calculating it wrong? Here is what I get:


78.9mm DOF for 28.8x36mm sensor size, 0.0287mmCoC, 1.36m focus distance,50mm lens, f/2.08 (effective), 1.038 bellows factor


38.6mm DOF for194x245mm sensor size (8x10 view camera),0.195mm CoC, 1.36m focus distance, 340mm lens, f/14.67 (effective), 1.333 bellows factor.






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[Jon Ruyle]

Am I calculating it wrong?

I'm not sure- by bellows factor, do you mean 1 + n, and by f (effective) do you mean f * bellows factor? If so, these two lenses have different apertures.


My point was that if aperture is the same, subject distance is the same, and framing is the same, then DOF, exposure speed (or amount of noise with a given exposure time), and diffraction will be the same. There is no advantage in using a larger or smaller sensor, and thus no need to crop to get more DOF.

[HDNitehawk]

Thanks, Guys!


I thought there was a flaw in my logic - obvious once you pointed out the effect of cropping on noise.


Despite my hopes to the contrary, the elegant yet occasionally frustrating laws of physics have reduced this to a simple choice of the most appropriate focal length for my needs - and that's 35mm.


Merry Christmas to All!


--John

John


I decided to shoot our christmas gathering today with both lens. First half with the 24mm and the second half with the 35mm. After it was all said and done I have to say with this type of shooting (tight quarters, low light, front living room) I would grab the 35mm first for sure now. A couple of reasons.


I shot both at ISO 1600, with apertures between 1.4 and 2.2, I tried to keep the shutter speeds at about 1/100 to 1/125. Both using the 5D Mark II.


First the framing of a people event close quarters, the 35mm was obviously better. Less distracting back ground. But this focal length is the obvious, but not the real thing that bothered me.


The other thing I have noticed and I didn't expect this. After downloading and going through the images. The 24mm are noisier. (without any croping or anything else done to it) The 35mm looked a lot more acceptable to me in this particular situation at the higher ISO.


Rick

[neuroanatomist]

Thanks, Rick! That's very helpful information, and definitely supports my decision to go with the 35L. I also did some shooting on Christmas Eve with the the 16-35mm f/2.8L II set to either 24mm or 35mm, and found the 35mm focal length to be preferable.


Odd about the noise - I can't see focal length per se making a difference. Perhaps the extra background included with the wider angle of view led to more dark areas - that would make the same amount of noise look more noticeable.

[HDNitehawk]

Odd about the noise - I can't see focal length per se making a difference. Perhaps the extra background included with the wider angle of view led to more dark areas - that would make the same amount of noise look more noticeable.

Thats possible and was my thinking as well. More area letting light in, less light on each specific subject maybe? I have lenses mounted on two different 5D's. Both cameras shooting at the same time with the same light were metering exactly the same way. It comes up with the same shutter speed at the same aperture on both. The 24mm takes a 77mm filter and the 35mm takes a 72mm maybe that has some thing to do with it.


I suppose it could have been the difference in the 5D's but I really doubt it, I checked all the settings and both were identical. I doubt it is the case because my main 5D was on the 24mm. If one performs better than the other I would say it does.


I might run a few tests for myself later tonight just to confirm this for future reference, so I will know for sure which one to grab if I have a low light place to shoot.


Have fun with the new 35mm when you get it.





Rick

[Daniel Browning]

I'm not sure- by bellows factor, do you mean 1 + n, and by f (effective) do you mean f * bellows factor? If so, these two lenses have different apertures.

Yes, that's what I meant, and now I see what you're saying. But even if the apertures are the same and the DOF is the same, doesn't bellows factor mean the larger sensor will get less light (and therefore have more noise for the same DOF)?