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View Full Version : 4/3 rd's CROP FACTOR. What I'm a missing?



insanityfw
11-14-2009, 12:42 PM
OK. I'm baffled. I don't know much about anything, but I thought I had it figured out how to handle things when it comes to adding non 4/3 lenses to the GH1.

I dropped and crunched part of my kit lens. Still seems to work, but I'm not trusting it entirely so I've ordered a few different lenses and a Nikon to GH1 adapter to use.

I thought that adding still lenses to the GH1 would magnify by a factor of 2 (or something like that). So, my thinking was that a 50mm Nikon AI would become similar to 100mm focal-length with the kit lens....but I must be missing something.

I have a Tokina 11-16 and a Sigma 24-70. When I frame something on the kit lens and then swap to one of these lenses, I end up with similar focal length. Definitely not 2x's magnified.

So, what am I missing? :)

Sorry, if this is a really bonehead thing, but I can't figure this out. Must be missing something very simple.

Thanks,

Jason

Jason Ramsey
11-14-2009, 01:24 PM
what nikon glass did you get? is it dx glass or full frame?

Later,
Jason

ydgmdlu
11-14-2009, 01:59 PM
OK, here's what you're not understanding. Focal length only has practical meaning on any given image format.

A 50mm lens on Micro Four-Thirds will look the same as any 50mm lens, whether it's made for full frame or not. The crop factor is only relevant when comparing to some other image format such as full frame.

If you apply the crop factor principle to the kit lens, then the 35mm equivalent would be 28-280mm. That's how crop factor works.

When you get a 50mm lens, there's no frame of reference until you specify or until you mount it on a camera. A 50mm lens on Micro Four-Thirds will give you the same field of view as a 100mm lens on a full-frame camera.

But it will not give you 100mm on Micro Four-Thirds.

ydgmdlu
11-14-2009, 02:01 PM
what nikon glass did you get? is it dx glass or full frame?

Later,
Jason
BTW, Jason, Nikon AI and AI-S lenses are old manual lenses... So they're for "full frame."

insanityfw
11-14-2009, 02:20 PM
Thanks. I think I'm understanding a bit more.

I was comparing full-frame sensor to what I have. I thought that a 50mm full-frame would give the equivalent of 100mm....on my camera. But that's not the case then?

Basically, I've been over-thinking it and mixing up cropping and sensors and focal lengths. Again. I think.

So, in review the focal lengths are going to be similar on my camera lens to lens...if I don't factor the....errrr...crop-factor??

Thanks again for straightening me out.

Best,

Jason

JASON-Yes, the Nikon's are AI's, the Tokina is the DX and I believer the Sigma is DG (???)

Park Edwards
11-14-2009, 02:25 PM
Thanks. I think I'm understanding a bit more.

I was comparing full-frame sensor to what I have. I thought that a 50mm full-frame would give the equivalent of 100mm....on my camera. But that's not the case then?

Basically, I've been over-thinking it and mixing up cropping and sensors and focal lengths. Again. I think.

So, in review the focal lengths are going to be similar on my camera lens to lens...if I don't factor the....errrr...crop-factor??

Thanks again for straightening me out.

Best,

Jason

JASON-Yes, the Nikon's are AI's, the Tokina is the DX and I believer the Sigma is DG (???)


equivalent field of view. not focal length.

focal length will always stay the same, but your field of view will not. it's like taking your hands and creating a rectangle out of them. putting it in front of your eyes doesn't change your focal length, but, the further or closer you move them it changes your field of view.

http://en.wikipedia.org/wiki/Focal_length
http://en.wikipedia.org/wiki/Angle_of_view (http://en.wikipedia.org/wiki/Field_of_view)

Barry_Green
11-14-2009, 02:52 PM
On any given format, 50mm = 50mm = 50mm. Doesn't matter whether the lens you're talking about was originally a c-mount lens, or a cinema lens, or a still-camera lens. A millimeter is a millimeter.

And this is why I think the whole "crop factor" thing is just more confusing than it actually does any good.

If you put the 50mm lens on a full-frame camera, and then on a cinema camera, and then on a GH1, you'll see a different field of view on each of them. But if you took a 50mm lens from a full-frame SLR, and one from a cinema camera, and the GH1 kit lens zoomed to 50mm, they'll all look identical.

If you want a wider-than-kit lens, you'd have to find something with less than 14mm.

msorrels
11-14-2009, 03:07 PM
If you set the kit zoom lens to 50mm, the view you get will be the same as a Nikkon 50mm lens using an adapter. All 50mm lenses will produce the same field of view on the GH1.

The crop factor only comes in when talking about what those lens will look like on another camera. Specifically a full frame camera(where you will get a wider view than the GH1 with the same lens).

What this means is that if you don't have nor have ever worked with a full frame camera you don't need to care.

You want a wider view that the kit lens at 14mm, you need to find a lens smaller than 14mm. It's that simple.

msorrels
11-14-2009, 03:10 PM
I swear Barry's post wasn't there when I hit post. :)

Jason Ramsey
11-14-2009, 03:14 PM
BTW, Jason, Nikon AI and AI-S lenses are old manual lenses... So they're for "full frame."

that's what I get for not reading the entire post :) didn't see that part in his post.

insanityfw
11-14-2009, 03:29 PM
that's what I get for not reading the entire post :) didn't see that part in his post.

I would read everything from me anyway, because it's usually gibberish :)

insanityfw
11-14-2009, 03:31 PM
I swear Barry's post wasn't there when I hit post. :)

That's OK, we all get to see how two different people say the same thing ;)

Car3o....thanks for the links.

Ben_B
11-14-2009, 03:55 PM
what nikon glass did you get? is it dx glass or full frame?

Later,
Jason

Crop factor will affect those in the same way....