how to found out F.stop on a lense?

[Lee_Maryland]

I have purchased a used canon zoom lense from a flea market, and the lense reads 17-85mm with macro. How do I found out the F. stop on the lense?

 

[480sparky]

Look around the front element.

 

[TheBiles]

Look at the front of the lens for the info.

Sent from my HTC Glacier

 

[AUG19]

f4 that one I think.

 

[Lee_Maryland]

got it. Thanks. Its F4-5.6

You guys think I can take a picture with a blurred background, if I set it to F4.0 and aperture priority? Or I am better off buying a prime lense with a lower F stop?

 

[AUG19]

Take a picture of something quite close-up, with some seperation between it and the background. Should work.

 

[fokker]

If you want a blurred background chances are you'd be better off using it at the long end (85mm), even though that necessitates using f/5.6. The key is to have a large distance between the subject and background, relative to the camera to subject distance.

 

[flyin-lowe]

A lot of it depends on what you are shooting and distances. Here is a picture I took with a crappy 75-300 lens at f5. The pic is not great but you can see what the background looks like.

 

[fokker]

Yeah you can blur a background very easily with telephoto lenses, and in particular at macro distances.

This photo was taken at 100mm and f/16, yet the depth of field is still so small that the behind legs are still quite blurry. This is because the lens was only a couple of centimeters from the subject, so anything more than a couple of centimetres behind it starts to get pretty blurry (to grossly oversimplify the maths).