100% crop and macro???

[jimsolt]

Two terms that just as I think I know what they mean, I see something that confuses me.

Please, a simple definition of 100% crop ---

And the same for macro -- I don't understand how a telephoto lens can have a "macro" function AND I'm really confused when I see "life size" and 2 to 1 or some other ratios when it relates to the macro capabilities of a lens.

Thanks,
Jim

[nitsch]

Let me try to explain, no doubt someone else will come along and explain far more eloquently than I ever could but here goes!

First the 100% crop.

If you open a photo in any photo editing software you have the option to zoom in and out so I'm sure you are familiar with the concept of looking at an image at 100% so you can see all of the detail. OK, now imagine you wanted to show someone on the web this level of detail without posting the whole full size image? You would crop out a small section of this image viewed at 100% so that they could see the same level of detail albeit within just a small area. This is what is referred to as a 100% crop.

Macro lenses. The important figure here is the maximum magnification of a lens. With macro lenses this is normally in the region of 1:2 or 1:1. A 1:1 (or lifesize) lens will (at max magnification) produce an image on the sensor which is the same size as the subject in real life. A 1:2 lens will produce an image on the sensor which is half the size of the subject in real life. Confused? OK, my sensor on the 300D is 22mm wide and 15mm high, say for arguments sake I take a picture of a large bee which is 22mm long with the 1:1 lens it will completely fill the shot. With the 1:2 lens it will fill half of the image.

Hope this makes sense! :)

[jimsolt]

I'm sure you gave a good explanation of the 100% crop, but you lose me when you explain about the portion of the image (I understand that part) at 100% magnification -- that's the part I'm not clear on. Say I select the portion in question. Do I use the crop tool to isolate that portion, then select (say in PS) the magnification that says 100% and then post that for comments? I guess in other words, who/what desribes 100%?

RE: Macro. It will take some digesting, but can I assume it only applies to small objects (my original understanding) and the ratio is as in relation to my sensor? If so, the macro capabilities of my telephoto lens have to do more with being able to focus up close than the more obvious magnification features of the lens?

In other words, if the lens can fill the screen with and focus on an object the same size or smaller than the sensor then it is a Macro lens?

Thanks. Other wording may help some, but this is a good start -- I think.
Jim

[alfa1six4]

If you use the crop tool in PS, leave the width/hight/resolution fields blank and it will make a "100% crop" without changing any pixel information in the cropped area. All pixels outside of the selection will be discarded.

[Jon]

You're correct, a real macro lens should be able to produce an image (on the sensor, forget about enlargements here) of at least 1/2 life-size. Many lenses, where the marketroids have gotten hold of them, will claim "macro" if they can focus on something within, say, 6-10x the focal length, but they're not really macro.

[jimsolt]

If you use the crop tool in PS, leave the width/hight/resolution fields blank and it will make a "100% crop" without changing any pixel information in the cropped area. All pixels outside of the selection will be discarded.
Aha! So, the magnification at which I'm looking at it doesn't matter, it's 100% crop if I don't make any size or dimension changes within the crop? Right?
Jim

[nitsch]

Exactly! I guess I confused you with my woeful explanation, I was trying to put across a visual idea of looking at an image on the screen at 100% into words. I knew someone would come along with a better way of explaining it! :)

[alfa1six4]

Aha! So, the magnification at which I'm looking at it doesn't matter, it's 100% crop if I don't make any size or dimension changes within the crop? Right?
Jim

You got it now! Just like clipping out a coupon from the newspaper. All you're left with is the coupon and it's size hasn't changed.

[nitsch]

Just like clipping out a coupon from the newspaper. All you're left with is the coupon and it's size hasn't changed.

What a fantastic analogy! :)

[jimsolt]

I agree.

Thanks to all for your help.

Jim

[chris clements]

..but what if it's a "10% off" coupon??

[Jon]

..but what if it's a "10% off" coupon??

Then you're supposed to cut inside the lines, not right on them . . .