# Thread: reading on lenses, how to use?

1. ## reading on lenses, how to use?

as per the portion circled in red, how do i make use of this reading? i believe this has something to do with aperture. i also noticed a red dot below the right side "4". what does this mean? TIA!!

2. It has to do with depth of field, I believe.

The numbers are showing the aperture values (f/4, 11, and 22) and the respective DOF (from front to back).

3. ## Re: reading on lenses, how to use?

The distance range within the markings (for f4, f11 or f22) would be in the dof.

Can read this too.
http://www.fineart-photography.com/dofScale.html

4. ## Re: reading on lenses, how to use?

The red dot is called the infrared index mark, it is for focusing when doing infrared photography.

Look under the heading "Focusing Infrared"
http://en.wikipedia.org/wiki/Infrare...using_infrared

5. ## Re: reading on lenses, how to use?

It is the depth of field markers..

http://www.cambridgeincolour.com/tut...h-of-field.htm

it is especially helpful if you do landscape or scale focusing..

http://www.normankoren.com/Tutorials/MTF6.html

if you see the second link, there is a picture of a lens with this marking, at the marking you can see the infinity distance is directly above the 16 mark, it means that at f/16, all from ~2.5m to infinity will be in focus.. the hyperfocal distance is 5m..

that lens is set at f/5.6, and reading from the markers, those from ~4m to ~9m are acceptably sharp.. (the marker for f/5.6 is between the 4 and 8, space constrain makes this omitted)..

for your lens as per picture, if you set the aperture at f/22, all from ~0.47m to ~0.9m will be in focus.. at f/11, from ~0.5m to ~0.7m will be focused.. and so on..

I am not sure about the red dot, though, i have not ventured into IR yet..

hope you are clearer about this now.. it was quite confusing at first, but once you get it, it is easy.. just for example, my F1 pics in my flickr are taken with 50mm manual focus lens that i pre-focus using this technique.. so once you get it, it opens up a lot more opportunity.. but this technique is difficult to use with zoom lens, you need to know the hyperfocal distance instead of using the markers..

P.S. any expert please correct me if there is any mistake in the concept..

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