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Pete Watkins
23-May-2009, 13:09
I've just read in a magazine that on a digital camera (I know nothing about digital cameras by the way) a lens changes it's "effective" focal length depending on the size of the sensor. The example given is that "four thirds cameras from Olympus and Panasonic use a small sensor which creates a focal-length magnification of 2x. Therefore, a 50mm lens on a four thirds format sensor covers an "effective" focal length of 100mm". What the heck is this all about? If I stick my 15" Ilex on my Wista and use my 6x7 roll film holder it's a 15" lens, when I put it on the front of my 11x14 it's still a 15" lens. Whats so different about the size of digital sensors compared to L.F. camera backs?
Help,
Pete.

Arne Croell
23-May-2009, 13:22
There is no difference. They are talking about how the angle of view changes when your sensor (digital or film) size changes. A 15" lens always stays a 15" lens, digital or not. In the LF world we have always been used to this. In the world of 35mm, before digital, a focal length signified a certain angle of view, and this designation has been kept for digital sensors; often lens focal lengths are designated as "35mm equivalent" focal lengths since nobody wants to use the angle in degrees as a measure but all the different sensor sizes give different focal lengths for the same angle of view.

John T
23-May-2009, 13:26
If your 11x14 camera the same distance from the subject as your Wista with the 6x7 back and you have the same 15" lens on the cameras, what happens to the images on the film? Are they exactly the same? No. If you place the 6x7 negative on top of the 11x14 negative, it will be exactly the same and the 11x14 will contain a lot more information around the 6x7 neg. That is the "crop factor".

John T
23-May-2009, 13:28
Oops forgot to finish my post.

We call it a "format change" or something similar.

jb7
23-May-2009, 14:40
A 300mm lens on a 35mm or 'full frame' camera is said to have a crop factor of 1.
On a smaller APS sensor, such as the Nikon D300, the same lens has a crop factor of 1.5, making its equivalent focal length on full frame 450mm.

On 8x10, that 300mm has a crop factor of 0.12, making it the equivalent of 36mm.
Or thereabouts.
At infinity.
Compared to 35mm.

What bugs me most, are the 'experts' who tell people that their 300mm is a 450mm.

As if things aren't confusing enough already.

Marko
23-May-2009, 16:58
What I don't understand is why would a bunch of large format shooters obsess or worse, be confused or bothered, about something that happens in 35mm and smaller formats? Or the other way, for that matter...

Whatever helps the target audience get a better grasp on the subject should be just fine.

Archphoto
23-May-2009, 17:37
We have the same whether you like it or not.
Just we are used to it.
A 150mm lens on 4x5 and a 300mm lens on 8x10 give us the same picture, just on a diferent format.

I have seen this kind of question here a number of times, but then it was about lenses for 6x7cm, 4x5 inch, 5x7 and 8x10 inch and how to interpret their forcal lengh.

In digital you call it crop-factor because the sensor is smaller than a 35mm negative, but at the end all depends on you reference point.

Peter

Pete Watkins
23-May-2009, 22:55
Many thanks for all your help. Marko, I'm not obsessing about anything. I read the article, didn't understand what the hell they were going on about and decided that the best place to get an explaination was on this forum. Now it's been explained to me I see it as another reason to avoid the world of digital imaging.
Thanks again,
Pete.

Marko
24-May-2009, 12:22
Many thanks for all your help. Marko, I'm not obsessing about anything. I read the article, didn't understand what the hell they were going on about and decided that the best place to get an explaination was on this forum. Now it's been explained to me I see it as another reason to avoid the world of digital imaging.
Thanks again,
Pete.

No problem, Pete. After I had it "explained" to me so many times on this board how irrelevant DSLRs really are to the average LFers, I just thought it curious that someone would ask a DSLR question on this board and even outside of The Lounge.

Besides, as great a resource for Large Format as this board is, I would reasonably think that places such as DPreview or LL would be much more natural to look for and get a good answer to a small format "digital" question.

But I agree with you - if different way to explain the same concept is a good enough reason for you to avoid it, then by all means, both you and digital imaging can only benefit from it. :D