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Old Jan 27, 2009, 9:48 PM   #11
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John,

First, thanks for the reply. I do appreciate it very much.

As for the math, I just plugged in the numbers on the website

http://www.dofmaster.com/dofjs.html

I haven't vaguest idea how that math works, but it asks me for distance, focal length, fstop and then it does some voodoo and spits out an answer. I just wrote the answer down, then posted it here.

So now the big question, based on your experience, would you go with the math or does your experience tell you that the 50mm is the better answer because I'd have to crop the 70-200 (shot at 70) to get the framing to match the 50mm. And when I crop it, I'll forfeit the sharpness?

That sound reasonable to me. But like I said, I'm the idiot in this conversation.:?


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Old Jan 27, 2009, 11:33 PM   #12
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FaithfulPastor wrote:
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So now the big question, based on your experience, would you go with the math or does your experience tell you that the 50mm is the better answer because I'd have to crop the 70-200 (shot at 70) to get the framing to match the 50mm. And when I crop it, I'll forfeit the sharpness?
IMO you got it backward: you have to cropped the 50mm to get to the framing of a 70mm!

This is what JohnG tried to tell you... to get the framing of the 50mm @ 15ft you have to step back to ~20ft with a 70mm hence what you input to the DOF calculator is incorrect (i.e. the DOF of a 70mm should be computed with a distance of 20ft instead for the same view/composition - which put it at a larger DOF @ 2.66ft for everything in focus) but then you might run into a different set of issue as your flash may not have enough power :shock:

-> On the other hand with a 30mm the same framing only requires about 10ft, and with this reduced distance by 1/2, the flash will have to work much less (leaving headroom for it to bounce if needed...)
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Old Jan 28, 2009, 10:29 AM   #13
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Okay, I think I getting a better handle on this.

In an earlier post, the distance of 15 feet was mentioned. I did not assume that 15 feet was a variable, I thought it was a constant across both lenses.

Told you I wasn't the sharpest tool in the shed.
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Old Jan 28, 2009, 10:29 AM   #14
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Okay, I think I getting a better handle on this.

In an earlier post, the distance of 15 feet was mentioned. I did not assume that 15 feet was a variable, I thought it was a constant across both lenses.

Told you I wasn't the sharpest tool in the shed.
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