Some basic lens info

[KmH]

The field of view of whichever lens you choose to use has a big influence on the perspective in whatever scene you photograph. In other words, the perspective of the focal length you choose to use can have a powerful impact on the overall composition of your photo.

To that end lens focal lengths tend to be used for fairly specific kinds of photographs.

Note: Field of view means after taking an image sensor crop factor into account. So for 1.5 crop factor image sensor, a lens with or set to a 13 mm focal length has the field of view a 19.5 mm lens would have on a full frame image sensor. On a 1.6 crop factor image sensor, a 13 mm lens has a field of view a 20.8 mm lens would have on a full frame image sensor.

• less than 20 mm - ultra wide angle - architecture.
• 20 mm to 35 mm - wide angle - landscapes.
• 35 mm to 70 mm - normal - candid, documentary, street
• 70mm to 135 mm - telephoto - portraiture
• 135 mm and up - long telephoto - sports, wild animals, birds

~The field of view of whichever lens you choose to use has a big influence on the perspective in whatever scene you photograph. In other words, the perspective of the focal length you choose to use can have a powerful impact on the overall composition of your photo.

To that end lens focal lengths tend to be used for fairly specific kinds of photographs.

Note: Field of view means after taking an image sensor crop factor into account. So for 1.5 crop factor image sensor, a lens with or set to a 13 mm focal length has the field of view a 19.5 mm lens would have on a full frame image sensor. On a 1.6 crop factor image sensor, a 13 mm lens has a field of view a 20.8 mm lens would have on a full frame image sensor.
less than 20 mm - ultra wide angle - architecture.
20 mm to 35 mm - wide angle - landscapes.
35 mm to 70 mm - normal - candid, documentary, street
70mm to 135 mm - telephoto - portraiture
135 mm and up - long telephoto - sports, wild animals, birds

 

[D-B-J]

Great post Keith

 

[Ron Evers]

Note: Effective focal length means after taking an image sensor crop factor into account. So for 1.5 crop factor image sensor, a lens with or set to a 13 mm focal length has an effective focal length of 19.5 mm. On a 1.6 crop factor image sensor, a 13 mm lens has an effective focal length of 20.8 mm.

Sorry, but this is not so. The focal length is not affected by the crop factor, only the field of view is. A wide lens, say a 24mm will make the subject look farther away than the eye sees on any camera, a 50mm lens will make the subject look close to what the eye sees on any camera & a 135mm lens will make the subject look closer than the eye sees on any camera regardless of crop factor.

The crop factor only affects how much of the scene is recorded - the higher the crop factor the less of the scene is recorded. Look through a toilet paper roll & then a soda straw, that is crop factor.

 

[KmH]

I was careful to use the term effective, and not affected.

 

[Helen B]

Effective Focal Length already has a meaning in photographic optics (the distance between a principal plane and its respective focal point), so giving it another meaning is risky. How about something like Equivalent 35 mm focal length even though it isn't great?

Best,
Helen

 

[KmH]

I edited the OP to say 'field of view' so there is no ambiguity.

 

[Ron Evers]

I was careful to use the term effective, and not affected.

Perhaps so Kieth but the impression given by what you posted as well as many other folk, leads folks to think that they are getting more magnification from a lens on a crop body than they are. Far to often, we see folk being told that a 35mm lens is the new "normal" lens on a crop body & it is NOT. It still makes things look further away than the eye sees, whereas a 50mm still looks like what the eye sees even on a crop body like mine @ crop 2x. I just wish folks would not be confused by what the crop factor really is.

 

[Tomasko]

I agree with Ron on this. When I started with taking pictures, I found exactly the same info Ron is warning about - 35 on crop is something like 50 on ff, etc. It can confuse newbies quite nicely I understand some people like to do the math, but statements like these are just false. You can't put 100mm on a crop body and expect it to magically gain extra zoom thanks to smaller sensor. That's just bull.....
Btw Keith, contents of your first post are somewhat doubled. Something probably went wrong during editing.

 

[scorpion_tyr]

The crop factor only affects how much of the scene is recorded - the higher the crop factor the less of the scene is recorded. Look through a toilet paper roll & then a soda straw, that is crop factor.

That's a better way to show an example of how focal length affects the angle of view, not the cropped sensor. There is a magnification factor with cropped sensors. The size of the subject as it passes through the lens and even when it's projected onto the image sensor does not change, but since the image sensor is smaller, when you take that picture and make it the same size as the exact same picture taken with full frame you'll see the subject is now bigger.

 

[Ron Evers]

That is only because you enlarged the image to print.

Here is a link I found that demonstrates crop factor.

http://www.digital-photography-school.com/crop-factor-explained

 

[Dao]

For beginners, I do not think the crop factor really means too much unless you are coming from 35mm film, full frame sensor digital body.
My first SLR camera is a digital Rebel which is 1.6x crop. What does that mean? Well, in the beginning, it means nothing to me. I looked through the viewfinder with a 50mm lens mounted. That's the view I saw. I had nothing to compare. I did not used to any other type of light recording medium before. So 1.6x means nothing to me.

I think the crop factor is only good if you are used to the field of view of a 35mm film or full frame sensor digital body. So when you switch the body, you know what to expect when the lens is mounted as far as field of view concern. Therefore, for beginners who just pick up the cropped body DSLR, do not worry about the crop factor too much. All you need to care is whether the view is wide or narrow enough for you when you look through the viewfinder. That's all.

If that will make you happy, jumper from a medium format film to cropped Canon body, that is 2.5x cropped. Does this 2.5x mean anything to you? humm .. I doubt it.

 

[scorpion_tyr]

Unless you're looking at a picture the same size as the sensor it was taken on (or smaller), it's always enlarged. I understand where you're coming from, but if you take a 35mm camera, or a full frame DSLR, and you take a picture with oh say a fixed 50mm lens, and then you use the same lens on a DSLR with a cropped sensor in the exact same position, the pictures you get will be different. And if you take both cards out of the camera, go right to a printer and print both at a 4x6, the subject will be bigger in the picture taken by the cropped sensor.

I do see what you're saying that the image itself is not going to be magnified, but as most of us view it on a computer, or printed, it will be since it's always going to be enlarged to the same size. Even when you look through a viewfinder, the subject is magnified on the cropped sensor. To see the subjects as the same size when taken by a full frame vs. a cropped sensor the images themselves would have to be different sizes.