Full frame EF lens on a crop sensor camera question:

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Paul B - UK Regular Member • Posts: 243
Full frame EF lens on a crop sensor camera question:

I want to buy a Full frame Canon EF 75-300 mm f/4.0-5.6 USM III Telephoto Zoom Lens. My camera is a Canon 800D which has a crop sensor. I'm trying to figure out what the equivalent effect putting that full frame lens on crop sensor camera would produce.

I don't know too much about lenses but I've been doing some research. I'm a little bit unsure, but so far have concluded the following, but i'd appreciate it if you could tell me if I've understood things correctly or not:

1) because a crop sensor only sees the middle of the full frame lens it doesn't see all of the scene that a full frame sensor would see using the same lens/focal length. So the outer part of the scene is not recorded or in other words 'cropped'. This gives you an extra magnification. To work out an equivalent focal length for a full frame lens on a crop sensor camera you have to multiply the lens's focal length by 1.6, so the EF 75-300 mm effectively becomes a 120-480 mm lens on a crop sensor.

Now this is the part I'm unsure about but i think I'm right (please correct me if I'm wrong as i want to know for sure):

2) the widest aperture of the lens allows the same exposure whether attached to crop sensor or full frame, i.e there's no loss of exposure putting a full frame lens on a crop sensor? So for example, using that lens at f4 on a full frame or crop sensor camera both gives you the same exposure settings to use.

3) however, the depth of field is affected and you have to times that by 1.6 too, so the full frame EF 75-300 mm f/4.0-5.6 len's depth of field on a crop sensor would be like using a f/6.4-8.9 EF-S lens? Have i got that the right way around?

Have i understood that all correctly, or have i got it wrong (probably the latter knowing me, lol)


Canon EOS Rebel T7i / EOS 800D / Kiss X9i
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