focal length clarifications...

J

Jonathan12uiz

Well-known member
Ok so I'm working around the fact that I use a m4/3 sensor which is a 2x crop sensor compared to full frame.

Since everything optics wise is kinda based of 35mm and full frame in dslrs, here is my question.

Ok so 50mm is what your eyes see right...

So 50mm on a full frame dslr or 35mm slr gives you what you see...

To get the same FOV on the 2x crop sensor you have to use a 25mm lens, so this also affects distortion too right...

Since 25mm is wider than the 'normal' look of the 50mm that the eye is use to, if used close up on faces then you will get that wide look right?

And the same thing goes for if I use a 50mm FD on my GH1, since it is equivalent to 100mm FOV, does the picture contain a 100mm Full Frame look or a 50mm full frame look...

You might be confused on what I'm talking about, but let me explain it like this...

the wider your lenses are the more distortion you get, but your picture doesn't look to flat(in terms of depth)

but the more telephoto the lenses are... the flatter the image looks. (hence a pic of several rooftops looks like the houses are close together, but they really arent.)

So does my 50mm give me the same flat look as a 100mm? Or will depth look natural. I'm asking because I don't have a 50mm and a FF dslr or slr.
 
Jonathan12uiz said:
To get the same FOV on the 2x crop sensor you have to use a 25mm lens,
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Yes.

so this also affects distortion too right...
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NO. Distortion is a property of how close you are to the subject, not what focal length lens you are using.

Since 25mm is wider than the 'normal' look of the 50mm that the eye is use to, if used close up on faces then you will get that wide look right?
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Absolutely not. Use a 25mm lens on m43, and a 50mm lens on a "full frame" camera, and stand side by side and shoot the exact same subject at the exact same distance and the results will look exactly the same.

And the same thing goes for if I use a 50mm FD on my GH1, since it is equivalent to 100mm FOV, does the picture contain a 100mm Full Frame look or a 50mm full frame look...
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It would have the field of view of a 100mm lens on a "full frame" camera.

the wider your lenses are the more distortion you get, but your picture doesn't look to flat(in terms of depth)
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Not true. The closer you are to your subject the more distortion you get. And the wider your lens, the closer people tend to stand to their subjects. But think about it, have you ever used a 1/3" video camera? On that, you'd be using a 6mm lens for a "normal" field of view, and there's no hyper-wide-angle distortion happening there!

So does my 50mm give me the same flat look as a 100mm?
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If you frame up the shot so that it looks exactly the same as on the full frame camera, it will have the exact same flat look.

Simply put -- there isn't a problem. Nothing to worry about. Where you would have used a 50mm on a full-frame, use the 25mm for the same look and the same effect on the GH1. Where you would have used a 100mm on the full frame, use the 50mm on the GH1 for the exact same field of view and same "look" and the same "effect".
 
Barry_Green said:
Yes.


NO. Distortion is a property of how close you are to the subject, not what focal length lens you are using.


Absolutely not. Use a 25mm lens on m43, and a 50mm lens on a "full frame" camera, and stand side by side and shoot the exact same subject at the exact same distance and the results will look exactly the same.


It would have the field of view of a 100mm lens on a "full frame" camera.


Not true. The closer you are to your subject the more distortion you get. And the wider your lens, the closer people tend to stand to their subjects. But think about it, have you ever used a 1/3" video camera? On that, you'd be using a 6mm lens for a "normal" field of view, and there's no hyper-wide-angle distortion happening there!


If you frame up the shot so that it looks exactly the same as on the full frame camera, it will have the exact same flat look.

Simply put -- there isn't a problem. Nothing to worry about. Where you would have used a 50mm on a full-frame, use the 25mm for the same look and the same effect on the GH1. Where you would have used a 100mm on the full frame, use the 50mm on the GH1 for the exact same field of view and same "look" and the same "effect".
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Ok so to get the "normal" look that they eyes see of what the camera is looking @, I do have to invest in a lens close to 25mm then. Prolly be looking into the FD 28 or 24mm. Do you have any ideo how much more mm the adapters apply to the focal length, example... i uses a 50mm f1.4 on the gh1, but with the adapter does it turn into something more telephoto like a 55mm or something like that?
 
Barry_Green said:
The adapter doesn't change anything. I think you might be interested to look at the chart I did for the AF100, on relative field of view and angle of view, perhaps it will make it more clear to you. This was done for the AF100, which has a slightly different field of view, but it's pretty close...
http://www.dvxuser.com/V6/showthread.php?227826-Relative-Focal-Length-Angle-of-View-and-CCF-Chart
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ok thanks barry... you really are badass. I always thought the adapter added mm to the focal length, kinda like a extender or something.

the reason this all came about was because I was looking through the viewfinder of a 7d with a 50mm ef prime on it and i could open my other eye and It was like "3d" everything was exactly how It looked compared to my eye.

I tried the same thing with my 50mm prime on my gh1 and Its looking all telephotoish on my eye that is on the cameras viewfinder.
 
Well, there is a bit of a crop difference between the GH1 and the 7D, so they shouldn't look exactly the same. The 50mm should look a bit telephoto on the GH1, as compared to the 7D. Not tremendously telephoto, but about 20%.
 
Hey Barry just wanted to clear one thing up for me. I knew everything you stated about FOV and the 2x crop factor but I was wondering (and would rather write the next story than shoot tests, haha) but if I use say a 25mm lens I get the 50mm FOV, but I wouldn't have the same DOF properties I would have on a Full Frame camera would I? Maybe a better example would be a 40mm on a GH2 vs. 85mm on a 5D, to get the same exact DOF I would have to be using the same lens correct? Or am I way off?
 
seanmcleod said:
Hey Barry just wanted to clear one thing up for me. I knew everything you stated about FOV and the 2x crop factor but I was wondering (and would rather write the next story than shoot tests, haha) but if I use say a 25mm lens I get the 50mm FOV, but I wouldn't have the same DOF properties I would have on a Full Frame camera would I? Maybe a better example would be a 40mm on a GH2 vs. 85mm on a 5D, to get the same exact DOF I would have to be using the same lens correct? Or am I way off?
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You're spot-on. The FOV and perspective would be the same, but the DOF would be different, because you'd have two different focal lengths in play. To get the exact same DOF you would have to open up the iris on the GH2.

To determine the iris difference, you have to divide the FF camera's iris by the GH's crop factor (we'll use a crop factor of 2.0 to make it simple). You'd then have to compensate for the exposure difference by using an appropriate ND filter on the GH, or by lowering the ISO.

If you used a 5D at 400 ISO, with a 50mm lens, at f/4... and a GH1 at 100 ISO with a 25mm lens, at f/2... both shot from the exact same place... you should have identical pictures (in terms of FOV, DOF, and perspective).
 
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Barry_Green said:
You're spot-on. The FOV and perspective would be the same, but the DOF would be different, because you'd have two different focal lengths in play. To get the exact same DOF you would have to open up the iris on the GH2.

To determine the iris difference, you have to divide the FF camera's iris by the GH's crop factor (we'll use a crop factor of 2.0 to make it simple). You'd then have to compensate for the exposure difference by using an appropriate ND filter on the GH, or by lowering the ISO.

If you used a 5D at 400 ISO, with a 50mm lens, at f/4... and a GH1 at 100 ISO with a 25mm lens, at f/2... both shot from the exact same place... you should have identical pictures (in terms of FOV, DOF, and perspective).
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great info... this makes the V.95 more desirable right now.
 
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