When is 50mm *not* 50mm? I have a question about focal lengths and crop factors. If a lens is made for FF, then a focal length of 50 will *be* a focal length of 50, right? If that same...

Bloke Loc: Waynesboro, Pennsylvania

I have a question about focal lengths and crop factors.

If a lens is made for FF, then a focal length of 50 will *be* a focal length of 50, right? If that same lens is used on a crop camera, it will be equivalent to 80mm, or thereabouts.

So, if a lens I made *specifically* for crop cameras, would that 50mm be still labeled 50, meaning equivalency, or would they label it as an 80mm.

I guess what I am asking is, can I assume that *any* lens which fits the crop camera would have the 1.5x 'conversion factor'?

Never really been interested enough before, with the SX50 and it's built-in lens. But now, with my nice new (to me) T4i, I'm curious.

Linda From Maine Loc: Yakima, Washington

I thought I had this all figured out 'til someone pointed out it's an "angle of view" thing not magnification :)

Here's an interesting article:

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

Wellhiem Loc: Sunny England.

It will be a 35mm equivalent. If you look at your exif data it will say something like "lens 50mm. equivalent 80mm".

jeep_daddy Loc: Prescott AZ

Bloke wrote:

I have a question about focal lengths and crop fac... (show quote)

50mm is 50mm no matter how you spell it or explain it. The crop factor is what you are asking about and has nothing to do with the physical properties of the lens itself. Canon full frame cameras won't allow lenses that are designed for their APS-C bodies so the issue is moot. With Nikon, their DX or APS-C lenses fit their full frame bodies but will only take advantage of that area of the sensor contained in a APS-C sensor.

Take a look at UHH FAQ pages and one will explain sensors better than I can.

lightchime Loc: Somewhere Over The Rainbow

In addition to what everyone else said, it depends on the sensor size whether the conversion factor is 1.5X or somewhat different.

traveler90712 Loc: Lake Worth, Fl.

Bloke wrote:

I have a question about focal lengths and crop fac... (show quote)

I don't know if this will help or not. Anyway it is a good piece of information to hold on to.

http://static.nikonusa.com/Lens-Simulator/simulator.htm

Bloke Loc: Waynesboro, Pennsylvania

Linda From Maine wrote:

I thought I had this all figured out 'til someone pointed out it's an "angle of view" thing not magnification :)

Here's an interesting article:

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

I *know* that it is the angle, and not magnification, but for all practical purposes, that lens with that camera will *appear to* magnify the image.

Thanks for the link, but I pulled this out of their page:

Quote:

Be warned that both of these terms can be somewhat misleading. The lens focal length does not change just because a lens is used on a different sized sensor just its angle of view. A 50 mm lens is always a 50 mm lens, regardless of the sensor type. At the same time, "crop factor" may not be appropriate to describe very small sensors because the image is not necessarily cropped out (when using lenses designed for that sensor).

That last bit is really what I am trying to find out. Canon make EF and EFS lenses, one of which (can't remember which) is for crop cameras only. I have an EFS 55-250, and an EF 75-300. So, will my camera give the same magnification/angle/carbon footprint at, say, 200mm with these 2 lenses.

It is a simple question (in my head!), but because of all this terminology stuff, I don't think most people are reading what I wrote - or what I *intended* to write, anyway. Probably wasn't worded precisely enough, but that is my fault. Maybe this iteration is clearer...

Bloke Loc: Waynesboro, Pennsylvania

lightchime wrote:

In addition to what everyone else said, it depends on the sensor size whether the conversion factor is 1.5X or somewhat different.

Yeah, another short-cut I took. I believe mine is 1.6, but I have seen mention of crop factors of 2.0. I wouldn't want to *think* what it is on my SX50!

GoofyNewfie Loc: Kansas City

Bloke wrote:

Yeah, another short-cut I took. I believe mine is 1.6, but I have seen mention of crop factors of 2.0. I wouldn't want to *think* what it is on my SX50!

I was curious.
Someone else says it's a factor of 5.58.
This being the internet it must be true!
(Just look through you camera and shoot what you see)

Dave_TX

Others have addressed the angle of view difference between a full frame and a crop frame sensor and lens combination. However, there are other factors at play, too. A lens designed for a full frame sensor or 35mm film frame is designed to form an image on a disk (image circle) large enough to encompass the whole frame. The crop body cameras can use lenses that are designed with a smaller image circle that encompasses the smaller APS-C sensor. The lenses designed specifically for smaller sensor cameras can be cheaper to build and sell for a lower price.
Yet another issue: I don't know about other lenses but if I mount my Canon 10-22mm EFS wide angle zoom lens on a full frame camera the back element will interfere with the mirror when the lens is set at the wide end of its range. That can be rough on the mirror.

Samuraiz Loc: Central Florida

As Linda stated, possibly the question is about angle of view.

Focal Length is Focal Length:

http://en.wikipedia.org/wiki/Focal_length

This question would also crop up at times during film days when a "standard" prime focal length on 35mm was a wide angle focal length on a medium format camera.

Linda From Maine Loc: Yakima, Washington

I think I get your question though the part of the quote that says "very small sensors" wouldn't apply to the T4i. Let's ponder this some more and figure out a way to re-word the question or figure out if someone has already answered. I'm with you in that after I read two sentences of somewhat technical language, I'm lost :)

Dave_TX

Bloke wrote:

I have an EFS 55-250, and an EF 75-300. So, will my camera give the same magnification/angle/carbon footprint at, say, 200mm with these 2 lenses....

Yes, 200mm is 200mm. The two zoom lenses will form the same size image on your T4i's APS-C sensor when they are set to the same focal length. The image quality may be different due to differences between the optics and coatings on the two lenses but the image size will be the same.

Bloke Loc: Waynesboro, Pennsylvania

Dave_TX wrote:

Yes, 200mm is 200mm. The two zoom lenses will form the same size image on your T4i's APS-C sensor when they are set to the same focal length. The image quality may be different due to differences between the optics and coatings on the two lenses but the image size will be the same.

Thanks, I think that was what I was asking.

dgkli

Just sticking my $.02 in to avoid a long cross-talking conversation. I'm pretty sure OP's question was NOT a request for explaining crop factors, angle of view, etc. I think OP understands all that.

I think the question is simply one of labeling. The question, I think, is if a lens for an APS-C sensor camera is labeled 50mm, does that mean it's really a 50mm, or does that mean that it's a FF equivalent 50mm (i.e. really 35mm or whatever). I think the question has been answered, correctly, is that it's really 50mm, not "50mm equivalent."