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Requesting the resources of the collective wisdom of this forum ???


3 Mar 2014 5:19PM
I was asked: "Why is the minimum aperture on compact zoom cameras often only f8 as, one would normally want to use f16 or f22 for landscapes or other subjects requiring a large depth of field" ?

As the person who asked me was not convinced by the answer he was given by others, I thought best to consult this group and see if a consensus can be achieved.

Thanks:
Niknut Plus
11 3.0k 82 United Kingdom
3 Mar 2014 5:31PM
Bear in mind that compact cameras have very short focal lengths, say 4.5mm at the wide end !!.....such short f/l provide
masses of depth of field for a landscape, even when they're wide open !!.....just imagine how tiny the aperture would be
at anything smaller than f8 (from f11 to f22)....with image quality deteriorating too......

Very small apertures are only necessary to achieve lots of DoF as the focal length increases, say from 50mm upwards maybe ?

It depends on the subject matter, & what one is trying to achieve in the final image !
lemmy 14 2.9k United Kingdom
4 Mar 2014 2:00PM

Quote:I was asked: "Why is the minimum aperture on compact zoom cameras often only f8 as, one would normally want to use f16 or f22 for landscapes or other subjects requiring a large depth of field" ?


When light passes through a very small hole it is diffracted. At f16, a 50mm lens has the light passing through an aperture 50/16mm, roughly 3mm across. A 25mm lens with the same angle of view on an MFT camera will therefore have an aperture of half that, 1.5mm.

When light passes through such a small aperture on an MFT camera, it is already noticeably diffracted and performance is degraded. With a point and shoot having a lens focal length of a fraction of that, diffraction effects become so large that the image is unusably fuzzy below f8 or so.

For example, a Canon Ixus has a lens at the short end of 4.5mm focal length. At f22 that would give an aperture diameter of 4.5/22 = less than 0.2mm. Such an tiny hole would probably act as a pinhole lens on its own without any glass in it!
petebfrance 9 3.1k France
4 Mar 2014 4:47PM
To experiment with the effects of:
sensor size, focal length f number and distance on depth of field have a go at this 'calculator':
http://www.cambridgeincolour.com/tutorials/dof-calculator.htm
and the effects of sensor size and f number on diffraction, try this calculator - you need to scroll down the page a bit to get to it:
http://www.cambridgeincolour.com/tutorials/diffraction-photography-2.htm

Hopefully they will help to 'demonstrate' the information in the above two responses....
5 Mar 2014 11:47PM
Thanks everyone, much appreciated
Gundog 8 629 Scotland
6 Mar 2014 3:02PM
....and some compacts don't even have variable apertures. The lens is always at maximum aperture and the manufacturer (e.g. Fuji) say they achieve smaller "aperture" values by using an ND filter (although, I suspect it is some electronic compensation rather than a physical filter).

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