Fast lenses are useless on a big sensor ?

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Rambow Senior Member • Posts: 2,259
Fast lenses are useless on a big sensor ?
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After many years i have recently acquired two apsc dslrs with the kit lens and a 50mm f1.8 lens.

Having never used f1.8 on a large sensor before, i was a bit surprised to see how shallow the depth of field is with the 50mm lens attached. So much so, that for me it's almost useless, especially since the AF speed is not really impressive on this particular lens.

I experimented a bit and realised that in order to make use of the 50mm lens i'd have to use f5.6, otherwise the subject(flower, pet, person etc), would be out of focus basically.

Maybe the f1.8 would be more practical on a shorter lens, but as it is i never use it, the DoF is way too shallow.

Small sensor cameras don't have this issue and it makes me believe that since the rise of the 1 inch sensor cameras and improvements in noise output not much has been lost in terms of image quality after i quit using larger cameras.

However i will say this, even at f5.6 the apsc sensor produces much better blurring of the background than a compact camera at f1.8-f2.8.

That doesn't explain why people buy these very fast lenses, what is the real use of f1.8 on a large sensor, since using it on a portrait basically means only the nose or the eyes of the person will be in focus? Shouldn't the entire face be in focus?

"Bokeh" can be too much of a good thing.

What do you think?

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