FF... Crop? does it change the F number?

AshleyKent

AshleyKent

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Ashley
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so say you have 100mm f4 on a FF censor?

would it change the F on a crop to...

160mm f6.4 EQUIV?

just thinking about it today and didnt know the answer??
 
It'll change how the depth of field appears, compared to if a FF camera was composed in the same way at the same aperture, but not the amount of light that's hitting the sensor.

I think!
 
F4 is F4, regardless.

Chris is right; on FF the DoF appears shallower because it is effectively a wider view, the real view of what the image 'sees'. On DX the DoF appears to be deeper (even though it's the same) because you're using a smaller section of the image circle.

It's only the effective focal length that changes going from FF through the different crop factors (1.3x/1.5x/1.6x/2x crops).
 
specialman said:
F4 is F4, regardless.

Chris is right; on FF the DoF appears shallower because it is effectively a wider view, the real view of what the image 'sees'. On DX the DoF appears to be deeper (even though it's the same) because you're using a smaller section of the image circle.

It's only the effective focal length that changes going from FF through the different crop factors (1.3x/1.5x/1.6x/2x crops).
Click to expand...

u answered my question :thumbs:

thanks was curious. people ive spoken too said the DoF of FF is so much better
 
F/number doesn't change with the crop factor, say 1.6x or whatever, because the focal length doesn't change. The DoF changes though, because of the different magnification involved in enlarging a smaller image up to a given viewing size.

The f/number does change if you use an extender/teleconverter, 1.4x or 2x etc, because that is a real change of focal length, not just a change in field of view. And DoF with it of course.

Edit: the change in DoF between crop format and full frame is not night and day, but you do get less DoF with full frame, if the subject is framed the same (ie you change focal length to compensate) and at the same f/number. The difference is about one and a quarter stops, calculated as f/number x crop factor.
 
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An easy way to think about it, is to imagine a crop camera has a magnifying glass attached to the mount, nothing else is altered, just that things are closer. DOF will be different as others have said.
 
The DoF only changes if you compose the image the same on the two different sensors - that is, move closer to the subject with the full frame or use a different focal length so it fills the image just as it did on the crop. The change in depth of field comes from the closer subject distance that the full frame allows you to get as it has a bigger sensor. If you can't/don't want to get closer, you will get exactly the same DoF if you take a picture at 10m with a 50mm lens at f2 on a crop and full frame sensor, just you will get a wider view on the full frame.

This is sooo much easier to understand it you think of field of view. A full frame sensor has a wider field of view at a given focal length than the crop sensor. This allows you to compose your pictures in a different way (get closer/use different focal lengths for the same picture). Nothing more, nothing less...
 
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arad85 said:
The DoF only changes if you compose the image the same on the two different sensors - that is, move closer to the subject with the full frame or use a different focal length so it fills the image just as it did on the crop. The change in depth of field comes from the closer subject distance that the full frame allows you to get as it has a bigger sensor. If you can't/don't want to get closer, you will get exactly the same DoF if you take a picture at 10m with a 50mm lens at f2 on a crop and full frame sensor, just you will get a wider view on the full frame.

This is sooo much easier to understand it you think of field of view. A full frame sensor has a wider field of view at a given focal length than the crop sensor. This allows you to compose your pictures in a different way (get closer/use different focal lengths for the same picture). Nothing more, nothing less...
Click to expand...

they all do make sence now... many different explinations... i noticed that today with my camera that i can get so close at 17mm and still fit loads in with the FF camera... but then i think im losing the reach abit :(
 
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