Does a 1:1 Macro Lens Remain 1:1 on a Cropped Sensor?

[Chello]

I am a bit confused. If lens is marked as Macro (1:1) for a full 35mm frame format camera, does it make it still 1:1 on cropped camera or less?

Chello

[McQ]

Yes. Cropping a digital camera sensor does not shrink or enlarge the image projected from the lens. An object which is 10mm in real life therefore remains 10mm when projected onto the sensor, regardless of whether it is a full frame or a cropped sensor.

On the other hand, the cropped sensor will of course have an improved depth of field and will have more of its frame filled with this 10mm object...

[Chello]

It does not shrink or enlarge the image, but if it is projected the same and then cropped for the sensor then does not it make the image larger? As I thought of it, it seems that if a third party lens is marked 1:1 on 35mm camera and then only adapted to the other formats then should not it become 1.6:1 on Canon 40D and 2:1 on Olympus?

Chello

[McQ]

1:1 in a macro lens refers to the absolute size in real life relative to the size this object becomes when projected onto the sensor. As a result, a cropped sensor just means that you cannot fit objects as large within the sensor. A cropped sensor just trims off the edges of the objects; the absolute size of everything remains exactly the same on the sensor.

On the other hand, in order to make a print of a given size, then of course a cropped sensor will be enlarged more. For a 10MP cropped sensor and another 10MP full frame sensor, the cropped sensor would therefore be enlarging objects more than the full frame sensor. In this sense the cropped sensor is providing more magnifying power, but only because it has been enlarged more, and not because the lens itself if providing any more magnification than it would on a full frame sensor.

[Henry Peach]

It does not shrink or enlarge the image, but if it is projected the same and then cropped for the sensor then does not it make the image larger?

1:1 means the subject is life size at the sensor or film. Life size stays the same whatever camera you are using. A life size dime fills the frame of an APS format camera, and leaves a lot of empty space in the frame of a 4x5 camera, but if you made contact prints the dime on the film/sensor would be the same size as a real dime. If you enlarged both to 8x10, then the dime in the print from the APS sensor would be much larger because you are using a much greater enlargement ratio than if making an 8x10 print from 4x5. If you used the same degree of enlargement on the 4x5 you'd end up with a print much larger than 8x10, but the dimes would be the same size.