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Teleconverter and DOF
Old 09-13-2005, 05:59 PM   #1 (permalink)
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This may be an obvious question but I'm trying to figure out the effect of a teleconverter on DOF. I notice that Rolando often shoots with a 50mm with a 1.4x converter. I know that you lose light but do you retain the DOF of the original lense at a given f-stop?
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Re: Teleconverter and DOF
Old 09-13-2005, 07:04 PM   #2 (permalink)
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I'm gonna go out on a limb here and say that DOF should remain fairly constant over the apeture range in spite of the teleconverter. I would think it would be just as shallow on the wide open end and just as broad on the stopped down end. Just my two cents, feel free to correct me.
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Re: Teleconverter and DOF
Old 09-13-2005, 09:28 PM   #3 (permalink)
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Except for minimum focusing difference, there's no free lunch with a teleconverter. It's all about the physics. Every other physical aspect of the lens is affected by the multiplication factor including DOF, which is divided by said factor. Thus, DOF is either ~.71 (1.4x) or 1/2 (2x) of what you had before at the same aperture setting.

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Re: Teleconverter and DOF
Old 09-13-2005, 11:11 PM   #4 (permalink)
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[ QUOTE ]
Except for minimum focusing difference

[/ QUOTE ]

That should read "minimum focusing DISTANCE", not "difference".

-Chip
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Re: Teleconverter and DOF
Old 09-14-2005, 12:24 AM   #5 (permalink)
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[ QUOTE ]
This may be an obvious question but I'm trying to figure out the effect of a teleconverter on DOF. I notice that Rolando often shoots with a 50mm with a 1.4x converter. I know that you lose light but do you retain the DOF of the original lense at a given f-stop?

[/ QUOTE ]

[img]/ubbthreads/images/graemlins/confused.gif[/img] I don't understand why he'd do that..

For one,...you lose image integrity with the use of teleconverters,....unless it is his goal to diminish the look of the image for some sort of special effect,.... As far as increasing depth of field,... hmmm....you've got me there.. I honestly don't believe that it does,...because you have also increased the focal length of the lens.

This was taken with a Canon 400mm f2.8 MKII L with a Canon 2.0 teleconverter.. which came out to 800mm f5.6,....which I hand held believe it or not.. Camera was the EOS 1n in AI servo, Film was Fuji 800 SuperHG
I have a 20x30 of this shot on the wall of my studio:
 
 
Re: Teleconverter and DOF
Old 09-14-2005, 10:11 AM   #6 (permalink)
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You get less depth of field with a teleconverter.

As for light loss, yes you lose a stop with a 1.4, and 2 stops with a 2.0. but that is in comparison to the lens without the convertor....in other words, if you put a 2.x converter on a 2.8 lens, you are taking away 2 stops worth of light (compared to without, so you will need a longer shutter time) but the lens is still open to 2.8 so you still get the aperature "effect" of the 2.8, it's just that it takes more light to expose the same scene with the 2.x on compared to off. You would need the same amount of light "as if" you were shooting at 5.6, but you are in fact at 2.8.

So a 50 1.4 with a 1.4 teleconverter would need a stop more of light for a proper exposure in comparison to without, but it's still open to 1.4. so you get the aperature effect of 1.4 but an even shallower depth of field.

Mark
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