Sensors & Lenses

[mevakesh]

How are lenses affected by full frame and croped sensors?

 

[bratkinson]

How are lenses affected by full frame and croped sensors?

Lenses themselves are NOT affected in any way, regardless of what compatible body they are mounted on. They do not "magically" become longer focal lengths when mounted on a crop body or anything like that.

What DOES change, however, is the portion of the projected image projected that is 'received' or 'sensed'. A full-frame sensor 'reads' the same size image as if 35mm film were being used. With a crop sensor, only a smaller portion of the image is 'read', which results in a 'narrower view', aka a 'cropped image'. This reduced angle of view is comparable to the narrower angle of view of a lens with a slightly longer focal length. But in no way is the focal length of the lens altered when mounted on a crop body.

Perhaps one of the more confusing issues with crop bodies is it "appears" that a slightly longer (eg, telephoto) focal length lens was used. This "magical zoom effect" occurs when the resultant image is viewed on your computer. It looks 'zoomed in', ie, everything is slightly larger than if the same lens was used on a full-frame body. But this is only the image seen on your monitor, or when printed, NOT what was recorded in your camera. This is due to the cropped image (the smaller portion of the image that hit the sensor) is enlarged as needed to fill your screen. Because there is more image area recorded by a full-frame camera, there is less 'enlargement' ("zoom in")needed to fill your screen.

For a complete discussion of crop sensors, see APS-C - Wikipedia, the free encyclopedia

 

[table1349]

How are lenses affected by full frame and croped sensors?

There not.

 

[480sparky41 40]

How are lenses affected by full frame and croped sensors?

Lenses don't give a darn about 'full frame' or 'cropped' sensors. Heck, they don't even mind if there's film back there.

 

[KmH]

 

[480sparky41 40]

My version:

 

[mevakesh]

A full-frame sensor 'reads' the same size image as if 35mm film were being used.

Does a full frame capture the entire scene as seen in the viewfinder?

Great Answers, Thanks everyone!

 

[480sparky41 40]

...........Does a full frame capture the entire scene as seen in the viewfinder?.........

Yes, as does every camera.

Although, in a technical sense, it's not always exactly what-you-see-is-what-you-get. In many cameras, the viewfinder isn't 100% accurate. You may see only 98% of what the camera records. But that's a minor issue in most cases.

 

[mevakesh]

There not.

So why do people say for example that a 35mm lens would be a 50mm on a cropped lens?

 

[bratkinson]

So why do people say for example that a 35mm lens would be a 50mm on a cropped lens?

A 35mm lens on a crop body such as a Canon 60D with it's 1.6 crop factor would approximate a 56mm lens (35 x 1.6) in that the angle of view of the 35mm gets "cropped down" from it's normal 54 degrees x 38 degrees to about 35 degrees x 25 degrees. (a 50mm 1.8 angle of view is 40 x 27 degrees, so I estimated a little 'tighter' angle) It's akin to taking the 'full picture' on a full-frame body and then chopping a bit off the sides and top/bottom...eg, cropping it.

 

[Theninjaseal]

A smaller sensor requires a shorter lens for the same picture than a larger sensor.
At ten feet with a large sensor (full frame) you might use 75mm for a headshot.
At ten feet with a smaller sensor (crop sensor) you may only need 45mm for the same "zoom" amount.
If you were at ten feet with a small sensor and used 75mm, the picture would be way too zoomed in - you may only get half the face or just an eye.

Think this way - a big sensor needs a big lens. A small sensor doesn't need so big a lens, so the first lens from the large sensor is proportionally bigger. So it "zooms" in more.

I take the lens on my FT3 (full frame) and adjust the zoom so that the moon fills the center third of the picture. If I then took the lens and put it on my GH2 (crop sensor), the moon would fill up most of the frame. This is because the sensor on my GH2 is only as big as the center third of the FT3's film. Nothing has changed in the lens, but the image appears zoomed in more for a given focal length (mm). For the moon to fill up all of the FT3's picture, I might need almost double the focal length. that's because I have to make the projected image bigger, because the film plane is bigger. Does that make sense?

35mm photography is a standard. Just about everyone (by that I mean the bigwigs that decide these sorts of things) that's been in the photography biz for a while owns a 35mm SLR. So most people have a feel for the "zoom" you get at different focal lengths on a 35mm SLR. When you change the sensor size (or film size), the apparent zoom is different for a given focal length. But the difference is linear, so 42mm on a m4/3 sensor will always be just as "zoomed in" as 74mm on a full-frame camera. Thus it is the "equivalent."


If you will, think of your lens as a projector. Focusing aside, image you have several different sized bedsheets with which to watch a movie, and one projector. If you have a very large sheet, it will have to be further away from the projector for the correct size image to be projected. A smaller sheet (crop sensor) can be closer to the projector. The image is smaller, but so is the sheet.

 

[Solarflare]

There not.

So why do people say for example that a 35mm lens would be a 50mm on a cropped lens?

Thats short for: you get the same angle of view from a 35mm (more like 32mm) lens on a 1.5 crop sensor than from a 50mm lens on a full frame (non-crop, 1.0 crop) sensor.