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long lenses & 2/3 chips, I see a long thread coming.....
Old 04-24-2005, 09:14 PM   #1 (permalink)
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OK techies, here's the premise based on a conversation I was having last night. Most of us know the unique "look" you get when you shoot a 3/4 shot of a model with a 300mm f2.8 lens wide open on a standard 35mm camera. The question is, is it possible to get the same "look" on a digital camera with a 2/3 chip (that means most of the digi cameras we're using - not the Canon 1Ds M2)?

Think about this for a sec. If we use a 300mm lens on a 2/3 chip camera, the model has to move 50% farther away from the camera in order to get her framed exactly the same, which increases the depth of field around her (by virture of us having to focus farther back, thus increasing DOF). If we use a 200mm lens (wider lens, to get a "300mm" lens cropping with the 1.5x factor), we're not really getting the same depth of field falloff as the 300mm, since we can't be any closer to the model to reduce the DOF. Add to that the "compression" factor of the 300mm, and I don't think you can do it. Am I missing something here, is this possible to replicate, or are we SOL?

(Shann Johnson with a 300mm lens, 35mm film camera F100)


Regards,
Andy Pearlman
Andy Pearlman Studio
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-24-2005, 09:48 PM   #2 (permalink)
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I suppose we are not allowed to play with the photo in Photoshop? If we can, then we can get almost the same effect.
Cheers,
rfs
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-24-2005, 10:52 PM   #3 (permalink)
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Yeah, you can do it, just use the 300mm F2.2! [img]/ubbthreads/images/graemlins/shocked.gif[/img]
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-24-2005, 11:25 PM   #4 (permalink)
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Here's another way to look at it that may simplify things a bit. You're sitting on a stool that is a fixed distance from the model. You get the same crop with a film camera/300mm lens combo as you do with a digital SLR/200mm lens combo. With a digital camera, only a lens' apparent angle of view changes (because you're cropping to the sweet spot of the lens). The other physical properties, such as minimum focusing distance and DOF remain the same. The DOF for any given aperture on the 200mm lens is greater than the DOF of the 300mm lens at the same aperture. The only way (the laws of physics are immutable) to achieve the same DOF is to open up the aperture. If you're already wide open, you're SOL.

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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-24-2005, 11:29 PM   #5 (permalink)
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That's why I'm thinking what you're thinking...

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Andy Pearlman
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-24-2005, 11:43 PM   #6 (permalink)
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So I guess it's a IDs 2 and 300 2.8 for you Andy... [img]/ubbthreads/images/graemlins/grin.gif[/img]

Ian
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-25-2005, 06:31 AM   #7 (permalink)
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Aren't we splitting hairs to a ridiculous degree here? So you move your model 50% further away. At 300mm F2.8 you're increasing your DoF by what? A meter, maybe two? Sure, in the studio that's a lot, but if you're shooting 3/4 shots in the studio with a 300mm lens you should be able to afford a full frame sensor camera. If you're outside and the background is further away than 6 feet, why worry? I just looked at the DoF meter on an old 200mm lens, 6 feet added DoF is easily an overestimate even at 30 meters. Theoretically you're right, not the same image, practically I don't think you could tell a crop pic from a full frame if they were side by side under most shooting circumstances when you would use a 300mm lens. Nikon people, Sheesh! [img]/ubbthreads/images/graemlins/grin.gif[/img] I kid, I kid!
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-25-2005, 07:04 AM   #8 (permalink)
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It may or may not be trivial, depending on what you're trying to throw out of focus. Six feet, to use your example, may make all the difference in the world if the model is only 4 feet from the background. With the 300mm it's out of focus, with the 200mm it's in focus.

I use selective focus all the time. Below is a shot where I wanted only two things in focus, her eyes and the earring. I had to shoot wide open to achieve the effect I was looking for. DOF was something like 2 inches, so greater DOF would have changed everything.



-Chip
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-25-2005, 08:42 AM   #9 (permalink)
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Just curious. It's a lovely image, but how do you get focus on the the eye and earring, while the ear is soft, when the eyelashes are further from the viewer than the ear? Is this a view camera image?
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Re: long lenses & 2/3 chips, I see a long thread coming.....
Old 04-25-2005, 09:26 AM   #10 (permalink)
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What is the shortest extension tube you can get? If it is short enough and with increased f-stops you could get the same result.

If it was possible to adhust the back element a mm or two you would be there [img]/ubbthreads/images/graemlins/smile.gif[/img]



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