35 mm Equivalance ...meaning

[480sparky]

The closest comparison I could find on Nikons website is the DX 17-55 and FX 17-35.

The DX 17-35 has, according to Nikon, a FOV of 79° at 17mm. The FX 17-35 FOV at 17mm is.........79°, but when in DX mode. In FX, it's 104.

But both lenses will 'see' the same scene at 17mm. It's just what the sensor will record.

 

[Big Mike]

I don't really understand all of Nikon's mumblings....but as I understand it; A lens only has one FOV angle for a given focal length. It's just physics. So if the 17-35mm is capable of a FOV of 104 degrees at 17mm.....then that is it's actual FOV at that focal length.

If you use that lens on a DX sensor camera, the final/recorded FOV is 79 degrees...the extra is being cropped off but the lens itself, still has a FOV of 104.

 

[480sparky]

I guess maybe I should clarify what I'm trying to say.

A 50mm FX lens and a 50mm DX lens will project a subject or object in a scene on the sensor, and if you were able to measure the projected subject at the sensor, they will be the same size.

Let's say you have an FX body with a 50mm lens right next to a DX body, also with a 50mm lens. They are both aimed at the same scene.... let's say a playground across the street. The child on the swingset will be the same size when projected by both lenses on to the respective sensors. However, since the DX sensor is smaller, the result will be the child taking up a larger portion of the frame.

By analogy, think of putting a negative in an enlarger and raising the head up to the top of the rail. Put an 8x10 sheet of photo paper under the enlarger and make a print. Now put a 4x5 paper under it. The optics of the lens has not changed. The size of the subject projected by the enlarger has not changed. All that has changed is the size of the paper. Any subject in the either print will be the same size. But a subject in the 4x5 print will take up a larger portion of the print as compared to the 8x10.

The 4x6 print can be compared to a cropped sensor, while the 8x10 can be compared to a full-frame sensor.

Or, take the 8x10 and use a pair of scissors to cut it down to 4x5. This is equivalent to what happens when you go from full-frame to cropped sensors.

 

[Big Mike]

I would agree with all of that. I knew you had the right idea, but I was just pointing out that in a couple previous posts, you had worded it poorly or incorrectly....which could cause confusion with people who don't have the principle clear in their mind.

On this whole crop factor issue...I think that is the greatest problem. There is so much misinformation, and/or poorly worded explanations out there...that people pick up the wrong ideas about it. That's why I'm such a stickler (jerk) when it comes to the details on this issue.

 

[KmH]

Maybe this will help:

 

[480sparky]

Maybe this will help:

Is that YOUR photo?

 

[Infinite_Day]

I understand it now. For some reason my mind just didn't want to reverse process that statement this morning. Thanks for clearing the cobwebs.

 

[KmH]

Of course that's my photo!

I took that in eastern Nebraska from the Amtrack California Zepher.

That was back a couple of months ago when the Missouri river was flooding.

 

[niranjan]

thax all of you guys .... the explanation was quite lucid ..

i guess one who has never worked with 35mm camera / FX sensor , shouldn't be looking for the comparison at all

 

[fortinw]

It is 'tech jargon' you DO need to concern yourself with.... if you want to make an intelligent lens purchase.

I disagree. I'd be willing to bet that the vast majority of people think more along the lines of "I need a WIDER / LONGER lens", I doubt that the difference in field of view even enters the mind of non-geek shooters.

 

[480sparky]

It is 'tech jargon' you DO need to concern yourself with.... if you want to make an intelligent lens purchase.

I disagree. I'd be willing to bet that the vast majority of people think more along the lines of "I need a WIDER / LONGER lens", I doubt that the difference in field of view even enters the mind of non-geek shooters.

To some degree, true.... the average 'snapshotter' won't be concerned all that much with FOV. But someday they'll likely graduate from PhD cameras. When comparing a full-frame compared to a crop sensor, would not 'crop factor' be an issue when it comes time to purchasing one or the other?

Joe has a full-frame sensor, Fred owns a crop sensor. Joe own the Nikkor 14-24 lens, Fred owns the Tokina 11-24.... quick.... who has the wider FOV?

 

[radiorickm]

A different idea.

All of the technical reasons of why and how are really great, and need to be understood. But here is a little bit different idea of why they do it.

Poor ol' Rick here, has been shooting 35mm for going on 30 years now. Even at a thousand pics a year, well thats a lot of pictures. But the thing is, during that time I have "LEARNED" what a 50mm lens does, and what a 28mm lens does to the image. I can choose which one I need, based on years of looking through them. In other words, when I decide to "MAKE" a photo, I can generally get the right lens out to begin with. I don't need to put on a 135mm, then say oops, i need less, get the 50mm out, and then say oops again, needed the 28mm.

The problem comes in when I put a 28mm lens on a "crop" sensor, it no longer acts (for all of the technical reasons in all of the above posts) like a 28mm lens. Insted, it acts more like a 50mm lens would have. So I, as an old time shooter, say what to heck....I wanted a 28m lens.

So the lens people put up a comparison for us old time shooters to know that if I want to see the same thing on a crop body as I would have on a 35mm, well then I probably need the 18mm lens (35mm equilivent of 28mm on my 1.6cf Canon). Then, I know more what to expect from the lens.

Of course, for all the newbies, if you have never shot 35mm, well then you will just simply "learn" what a 28mm looks like on your camera and go from there, 'cuz it really doen't matter to you.

Good luck in all your shooting

 

[fortinw]

It is 'tech jargon' you DO need to concern yourself with.... if you want to make an intelligent lens purchase.

I disagree. I'd be willing to bet that the vast majority of people think more along the lines of "I need a WIDER / LONGER lens", I doubt that the difference in field of view even enters the mind of non-geek shooters.

To some degree, true.... the average 'snapshotter' won't be concerned all that much with FOV. But someday they'll likely graduate from PhD cameras. When comparing a full-frame compared to a crop sensor, would not 'crop factor' be an issue when it comes time to purchasing one or the other?

Joe has a full-frame sensor, Fred owns a crop sensor. Joe own the Nikkor 14-24 lens, Fred owns the Tokina 11-24.... quick.... who has the wider FOV?

Quick, tell me which one worried about the different FOV they'd get from different formats, and I'll tell you which one is the biggest geek! When YOU buy a lens, unless you need to take exactly the same shot, from exactly the same position using both a FF and a "cropped" sensor, does it really matter? Basic understanding of focal length tells you all you need to know for MOST people.

 

[480sparky]

Quick, tell me which one worried about the different FOV they'd get from different formats, and I'll tell you which one is the biggest geek! When YOU buy a lens, unless you need to take exactly the same shot, from exactly the same position using both a FF and a "cropped" sensor, does it really matter? Basic understanding of focal length tells you all you need to know for MOST people.

Just because it's of no consequence to you doesn't mean the rest of us should ignore the fact that there's a difference. It's called learning, and it's something most here want to do.

 

[jake337]

It's important to let people who are just starting out know the difference. We don't want them thinking they're new 50mm f1.8G is an 85mm lens(79mm or whatever). Also that they may think they are getting more "reach" at 300mm on a crop body vs a 35mm frame.