October 23, 2014, 05:08:55 AM

Author Topic: 17-40mm advice please!  (Read 8194 times)

3kramd5

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Re: 17-40mm advice please!
« Reply #30 on: March 14, 2013, 03:18:53 PM »
Although the 17-55mm F2.8 IS is the full frame equivalent of 27-88mm F4 IS

The 17-40mm is 27-64mm F4 on crop

Just to avoid some confusion:
The 17-55mm f/2.8 IS is the full frame equivalent of 27-88mm f/4.5 IS.
The 17-40mm f/4 is equivalent to 27-64mm f/6.4 on crop.  ;)

You don't lose a stop and a half by cropping. You must mean 'as it pertains to DOF'. Just to avoid confusion.
« Last Edit: March 14, 2013, 03:25:28 PM by 3kramd5 »
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Re: 17-40mm advice please!
« Reply #30 on: March 14, 2013, 03:18:53 PM »

tomscott

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Re: 17-40mm advice please!
« Reply #31 on: March 14, 2013, 03:25:57 PM »
No what he means is the depth of field, not that you loose a stop and a half of light.
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astevenscr

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Re: 17-40mm advice please!
« Reply #32 on: March 14, 2013, 04:17:36 PM »
Although the 17-55mm F2.8 IS is the full frame equivalent of 27-88mm F4 IS

The 17-40mm is 27-64mm F4 on crop

Just to avoid some confusion:
The 17-55mm f/2.8 IS is the full frame equivalent of 27-88mm f/4.5 IS.
The 17-40mm f/4 is equivalent to 27-64mm f/6.4 on crop.  ;)

You don't lose a stop and a half by cropping. You must mean 'as it pertains to DOF'. Just to avoid confusion.

Furthermore, I think this example can't be quite right for even DOF. Note that the o.p. says:
The 17-55 is the full frame equivalent of 27-88 f/4.5 IS; AND
the 17-40 f/4 is equivalent to 27-64mm f/6.4 on crop

but how can the equivalent f/stop for DOF purposes increase both when you move to full frame and when you move to crop? Or am I missing something?
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marinien

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Re: 17-40mm advice please!
« Reply #33 on: March 14, 2013, 04:41:44 PM »
Although the 17-55mm F2.8 IS is the full frame equivalent of 27-88mm F4 IS

The 17-40mm is 27-64mm F4 on crop

Just to avoid some confusion:
The 17-55mm f/2.8 IS is the full frame equivalent of 27-88mm f/4.5 IS.
The 17-40mm f/4 is equivalent to 27-64mm f/6.4 on crop.  ;)

You don't lose a stop and a half by cropping. You must mean 'as it pertains to DOF'. Just to avoid confusion.

Furthermore, I think this example can't be quite right for even DOF. Note that the o.p. says:
The 17-55 is the full frame equivalent of 27-88 f/4.5 IS; AND
the 17-40 f/4 is equivalent to 27-64mm f/6.4 on crop

but how can the equivalent f/stop for DOF purposes increase both when you move to full frame and when you move to crop? Or am I missing something?

Oh sorry! I wanted to use the same words as tomscott. He certainly understands the conversion, I think he had juste typed too fast  ;). A longer statement would be:
The 17-55mm f/2.8 IS is the full frame equivalent of 27-88mm f/4.5 IS on crop (I ignored the "on crop" in the previous post because the 17-55mm is a lens for crop bodies).
The 17-40mm f/4 is the full frame equivalent to 27-64mm f/6.4 on crop. 

@3kramd5: thanks for the added detail, yes, I meant DoF equivalent.
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Re: 17-40mm advice please!
« Reply #33 on: March 14, 2013, 04:41:44 PM »