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'f stop' versus 'aperture value'

Posted 30/05/2015 - 06:40 Link
Looking at the exif of some photos, can anyone explain what 'aperture value' is ?
Posted 30/05/2015 - 07:08 Link
Something that I don't get either, like tattoos, people carriers or owning a dog when you're not a sheep farmer.
Best wishes,


"These places mean something and it's the job of a photographer to figure-out what the hell it is."
Robert Adams
"The camera doesn't make a bit of difference.  All of them can record what you are seeing.  But, you have to SEE."
Ernst Hass
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Posted 30/05/2015 - 08:49 Link
I've asked various people to explain this and never got a straight answer. So, my best guess is that, given we have lenses with variable apertures, the f stop is what we set and the aperture value is the actual open aperture value at that setting. One does seem to relate to the potential largest aperture at the focal length selected.

It's a bit irrelevant really, and the EXIF on ePHOTOzine just shows the aperture. As the team cure the EXIF anomalies on PU no doubt that will be simplified.
Best regards, John
Posted 30/05/2015 - 10:23 Link
And just to confuse the issue a bit more - t-stops.


Some people call me 'strange'.
I prefer 'unconventional'.
But I'm willing to compromise and accept 'eccentric'.
Posted 30/05/2015 - 10:26 Link
The T stop was widely used at one time as uncoated lenses lose a lot of light due to internal reflections. A four element lens can lose 35% of the light in this way, meaning the f stop is accurate only for depth of field but not for exposure. With modern lenses and multi coating this is no longer necessary.

T stops continued to be used in cinematography, but rarely get a mention in still photography.
Best regards, John
Posted 30/05/2015 - 16:41 Link
Lenses used in cinematography such as multi coated Carl Zeiss Distagons still have both T and F indices. T for aperture and F for calculating depth of field. However in real terms the physical difference between the two, especially on wide angle lenses, is miniscule; I've never believed there would be any noticeable difference and given the vagaries of the various methods used in the production of depth of field tables the whole thing becomes very subjective indeed.
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -

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