How Determine if a New PowerShot has a Non Adjustable Aperture?

waterwingz

12139

Re: How Determine if a New PowerShot has a Non Adjustable Aperture?

« Reply #10 on: 30 / July / 2014, 13:01:17 »

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Quote from: blackhole on 30 / July / 2014, 11:45:24

Hmm, that's not true. The best performance will be in the middle range of aperture or perhaps for one stop more.

That may be generally true for a "normal " 50mm lens from a DSLR but does not always apply for the little lenses used in P&S cameras. You have no idea what the minimum and maximum iris opening is relative to the actual lens geometry so it's not possible to make such a statement.

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Anyway camera with adjustable iris diaphragm is always better than one that has a fixed aperture and uses only the ND filter.

Again, that is only true because cameras with adjustable diaphragms tend to be more expensive than those without and therefore better made. The is no law of physics that says one has to be better than the other.

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blackhole

940
A590IS 101b

Re: How Determine if a New PowerShot has a Non Adjustable Aperture?

« Reply #11 on: 30 / July / 2014, 13:45:33 »

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That may be generally true for a "normal " 50mm lens from a DSLR but does not always apply for the little lenses used in P&S cameras. You have no idea what the minimum and maximum iris opening is relative to the actual lens geometry so it's not possible to make such a statement.

Take a camera with adjustable diaphragm in AV mode in hands and at night shoot a image of a lamp in the neighborhood at f2.8 and F8.0, and tell which the image is sharper.

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Again, that is only true because cameras with adjustable diaphragms tend to be more expensive than those without and therefore better made. The is no law of physics that says one has to be better than the other.

Adjustable diaphragm gives you more creative abilities, if you know how to properly use it. The theory here is not important, look what you get in the practical work.

« Last Edit: 30 / July / 2014, 13:50:01 by blackhole »

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fabri22

208

Re: How Determine if a New PowerShot has a Non Adjustable Aperture?

« Reply #12 on: 30 / July / 2014, 13:50:13 »

Quote from: blackhole on 30 / July / 2014, 11:45:24

Hmm, that's not true. The best performance will be in the middle range of aperture or perhaps for one stop more. The biggest aperture (smallest f-number) will always give a more diffuse picture than smaller aperture (larger f-number). If you use the 'Diffraction Limited Aperture Estimator' from this link, you will see that the diffraction can occur only at a middle value of aperture or smaller aperture(larger f-number), which the manufacturer offers to use. If you use a larger f-number, diffraction spikes will begin to appear only on point sources of light, the usual scenes will be sharper than at the larger aperture and other forms of diffraction will not be visible. Anyway camera with adjustable iris diaphragm is always better than one that has a fixed aperture and uses only the ND filter.
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Thanks for this very intresting link.
It seems to comfirm exactly what i know about diffraction, lens aperture and compact cameras small sensors.

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blackhole

940
A590IS 101b

Re: How Determine if a New PowerShot has a Non Adjustable Aperture?

« Reply #13 on: 30 / July / 2014, 14:16:24 »

Sharpness falls on extremely small aperture, on the compact cameras in the worst case occurring spikes.
Look for this part of the text on the link at the end of my post:
"This should not lead you to think that "larger apertures are better," even though very small apertures create a soft image; most lenses are also quite soft when used wide open (at the largest aperture available). Camera systems typically have an optimal aperture in between the largest and smallest settings; with most lenses, optimal sharpness is often close to the diffraction limit, but with some lenses this may even occur prior to the diffraction limit. These calculations only show when diffraction becomes significant, not necessarily the location of optimum sharpness (see camera lens quality: MTF, resolution & contrast for more on this)."

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fabri22

208

Re: How Determine if a New PowerShot has a Non Adjustable Aperture?

« Reply #14 on: 30 / July / 2014, 15:27:10 »

Quote from: blackhole on 30 / July / 2014, 14:16:24

Sharpness falls on extremely small aperture, on the compact cameras in the worst case occurring spikes.
Look for this part of the text on the link at the end of my post:
"This should not lead you to think that "larger apertures are better," even though very small apertures create a soft image; most lenses are also quite soft when used wide open (at the largest aperture available). Camera systems typically have an optimal aperture in between the largest and smallest settings; with most lenses, optimal sharpness is often close to the diffraction limit, but with some lenses this may even occur prior to the diffraction limit. These calculations only show when diffraction becomes significant, not necessarily the location of optimum sharpness (see camera lens quality: MTF, resolution & contrast for more on this)."

Didn't notice the link in your signature. Very nice astro pictures, Boris

I fully agree with your comments about lenses and their "sweet spots", but only for dslr systems with bigger sensors.
MTF, resolution, optical aberrations, diffraction, etc have influenced my purchases of cameras and lenses for a lot of years ... drying out my pocket