Lens question

A recent post elsewhere had me wondering since a digital sensor is smaller than a negative, then wouldn't it also affect the macro capability of a lens?

For example, if you say a lens gives you 1:4 on a film body, wouldn't it give you something like 1:3.(something) on a digital sensor?

Seeing as how the sensor crops the image when using a non-digital lens it seems logical, just wondering if anyone has any definite answer.

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Originally Posted by payn817

A recent post elsewhere had me wondering since a digital sensor is smaller than a negative, then wouldn't it also affect the macro capability of a lens?

For example, if you say a lens gives you 1:4 on a film body, wouldn't it give you something like 1:3.(something) on a digital sensor?

Seeing as how the sensor crops the image when using a non-digital lens it seems logical, just wondering if anyone has any definite answer.

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Yes and no. I think Michael Fanelli answered this post a while back when I had a similar query. Physically, no, the image size that transfers to the sensor is still whatever it would be whatever it is for full frame, but the net effect of the crop on the viewable image shows a greater than rated macro capture had you shot full frame or on film. In terms of being able compensate for the crop to get the correct non cropped image requires a little bit of math and a macro lens that has the required markings on the barrel to allow you manually focus to get the correct image ratio on the actual viewable image. All this mumbo jumbo is only critical if there is an actual ratio that is required for capture in the viewable image (as in AACD accreditation photos if you're a dentist trying for immortality in the AACD hierarchy of demigods).
Hope that helped. I'm not good at explaining. Sorry.:o

The lens does the same thing it always does - the image it focuses onto the sensor or a piece of film is still the same size. If you have a DSLR with a smaller sensor, then you're just seeing less of the same thing because of the crop factor. The best analogy I can come up with is taking an 8x12 print from a 35mm negative or slide and cutting the edges off. Same image, same magnification, same perspective - you just see less of it.

...which when you print back to 8x12 gives you a larger image of the parts of the subject, no?

I think you get what I'm trying to figure out Chunk. Thanks everyone for taking your time to answer.

hmmm. maybe it wasn't michael who answered this in another post awhile back. Was it you?

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Originally Posted by Chunk

...which when you print back to 8x12 gives you a larger image of the parts of the subject, no?

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Yes, it does - but so would making a 20x30 print. With macro magnification factors, the thing we were looking at was how big the object was recorded on a piece of film. In other words, using 35mm film (about 1" x 1-1/2" per frame), a one-to-one or life-size ratio would have given us an image of a quarter (US 25 cents which is about 1" diameter) that would completely cover the height of the negative (not the width obviously).

You could then take that 35mm negative and blow it up as big as you wanted and control the size of the quarter that way. You could also have a less than 1:1 magnification, blow up and crop the print too for the same result. It's just a matter of how big the image is on the film versus how big it is in real life. Of course if you wanted to make a big poster of a picture of a quarter, you'd want to start with the biggest negative that you could so you'd want to use that 1:1 magnification ratio (not getting into larger film formats here...!).

The same 1:1 ratio on a DSLR with a 1.3x crop factor would give us slightly less than the whole quarter; we wouldn't see the edges. With a 1.5x we'd see a little less than that; with a 1.6x we'd see even less, etc. I'm not sure if it's still really defined the same way with digital, but I don't see why it wouldn't (or shouldn't) be.

How big is a sensor on a 1.5x DSLR? I don't know off hand, but I'd guess it would work out to about .67" (.67" x 1.5 = ~1"). So - try it with something that's .67" in size, which would be about the diameter of a US Dime (10 cents). You'll need less magnification (at least based on 35mm standards) to do it.

Quote:

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Originally Posted by payn817

A recent post elsewhere had me wondering since a digital sensor is smaller than a negative, then wouldn't it also affect the macro capability of a lens?

For example, if you say a lens gives you 1:4 on a film body, wouldn't it give you something like 1:3.(something) on a digital sensor?

Seeing as how the sensor crops the image when using a non-digital lens it seems logical, just wondering if anyone has any definite answer.

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No the images on the sensor are still the same size ratio 1:4. The only thing is the image is croped. 35mm film is 35mm wide so with a 1.5 crop factor the sensor size is 23mm, and other way of looking at it is: 50mm lense on a camera with a 1.5 crop factor is equivalant to a 75mm lense with the same field of veiw that you would get if you installed a 75mm lense on a 35mm film camera like a Nifon F series or any other brand of 35mm film camera.