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Old Apr 13, 2007, 10:02 AM   #1
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I know that in order to get 35 mm equivalents you multiply the focal length of an olympus lens by 2. So, a 150 mm lens is 300 mm equivalent.

However, I was told by someone that it's not the same in terms of focusing power just the angle of the shot or something like that.

So, if I had a 300 mm 35mm lens and a 150mm Olympus lens and took a shot of a duck that was far away, would I actually get the same shot in terms of size of subject in the picture?

I apologize if this question has been asked before.
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Old Apr 13, 2007, 10:14 AM   #2
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it is the same field of view (FoV)
300mm on full frame (FF) same as 150mm on 4/3
this because the crop factor is 1.96, almost so 2x
what will differ is the depth of field when compared with a full frame 35mm
but for general purposes i wouldnt give a damn about that

Riley

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Old Apr 13, 2007, 10:25 AM   #3
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So, other than the DoF, the two lenses would give equivalent shots of my duck ceteris parabis?

How is the DoF different?
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Old Apr 13, 2007, 10:49 AM   #4
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yes they would

on DoF
usualy an effect you try to exploit is to have a sharp focus on the subject and a blurred background
to get the same amount of blurred background, a 4/3 camera needs to be 2 stops lower than a full frame
if the FF guy shoots at F4, you need to shoot at F2
but if he can get a lower stop, say 2.8
you might be able to see that, eventually you run out of stops, you cant go lower

you also need to match the selected stop with an apropriate shutter speed
metering will tell you what you are shooting at but,
hand held for your 150mm there is a lowest speed
to calculate this
it is one over the equivalent focal length (EFL), which is 150 x 2x
or 1/300, 1/300th of a second
this may also limit your range of stops

i hope that helps

Riley


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Old Apr 13, 2007, 11:27 AM   #5
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Yup. You can figure out the DOF differrence by applying the crop factor also to th f-stop.

So a 35mm f3.5 will look the same as a 70mm f7.0 on full frame. You would have to of course use a faster shutter or lower ISO for the same exposure. To compare to ASP-C sized, divide the crop factors, for example for Canon, 2/1.6=1.25.

So a 35mm f3.5 is the same as about 44mm f4.4 would be on a digital Rebel. The added depth of field could be a small benefit in macro shooting, where the more common problem is needing more DOF. It could be a disadvantage in trying to do portraiture, for example, with that same 35mm lens, as a that point you might wish for a bit less DOF at f3.5. On the other hand, with a large apperture, say with a 30mm f1.4, it might be a benefit in some cases, as the larger appertures needed for low light shooting can be difficult to use when DOF gets too narrow.

You also should be aware that this affect when diffraction kicks in softening a lens. So in a situation where you might stop down to f22 on full frame, you would only want to go to f11. You'll get the same DOF there, but you wouldn't want to go much past that as diffraction is already starting to soften things. It would be the same as it would with the same lens at f13.75 on a Rebel.

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Old Apr 13, 2007, 2:34 PM   #6
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You guys rock. I think I'm finally 'getting it' with this 4/3 lens differences.



Thanks for the insightful and prompt replies.
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Old Apr 25, 2007, 7:33 PM   #7
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Wow, I was reading a bit about this and really didn't let it sink in until you guys started discussing it (oh, uh, hi. 4 year lurker 1st time poster)

I was very VERY convinced I should go with a 510, I've been working up a $$ explanation for the wife for a few weeks now. I used to shoot Nikon film but sold all my Nikon gear when my kid was born about a half dozen years ago. I've made due with a c2100 since (and it's really an awsome little camera!)

But the DSL world's been calling my name and the only thing that kept me from going with something like the 550uz was lenses and being able to shoot OVER f11, something I desperately needed with my Nikon gear. That and I nabbed my wife a fe170 for Xmas w/out researching it and it's got a 'yuck' factor of 170:angry:

But now, between this discussion and some samples of extreme diffraction at small fstops I'm wondering if I'm out thinking myself I'm sure those incredibly sweet lenses they kit with the 510 are sharp, but advanced digis are faster, even if the noise isn't as well contained at higher ISOs. Then again, blurring a background in photoshop after the fact isn't really much of a task. My main desire for the 510 was being able to shoot at f16 or higher, but it sounds like that's not really as desireable as it was for landscape shooting with film.

Does anyone actually expose their CCDs at anything beyond f11 anymore?


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