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"Can you come up with a counter example where DOF doesn't change in this direction?" I gave three examples above. I can elaborate: DoF changes depending on how

"Can you come up with a counter example where DOF doesn't change in this direction?" I gave three examples above. I can elaborate: DoF changes depending on how you strangle the light by contracting the diaphragm the lights passes through (thus preventing light from dispersing), not from having a higher ƒ value. A really dark lens is a good example of this. Some can have a light throughput that begins at ƒ/6.3, or even ƒ/8.0, yet at wide-open aperture they produce as narrow DoF as f.e. my Nikkor 50mm ƒ/1.4 does, which is 5 exposure steps brighter - or, as you reason, 5 aperture steps more open. Why? Because their apertures are wide-open in both cases.

lutorm 15y ago
Sorry, but you are wrong about this. Look at http://en.wikipedia.org/wiki/F-number http://en.wikipedia.org/wiki/F-number You seem to be thinking of something similar to what the Wikipedia article calls "T-stops", a calibration of the absolute transmission of different lenses. That's something different from the f/ratio.
- hackermom 15y ago
  Are you nitpicking? You can point to aperture stop theory and the history of the f-numbers etc. indefinitely, but ƒ is and will remain synonymous with light transmission (or "T" as you keenly insist; thank you, I am familiar with it) in every single practical situation of photography, no matter how much you try to balance the needle on its tip.
  - ghshephard 15y ago
    hackermom, I mean this with earnest sincerity - so please take it in that nature; In fifteen years of photography, photography classes, photography magazines, and photography books - I have never, ever, had anyone suggest that ƒ is synonymous with light transmission. It is possible, that I, and every photographer, photography magazine, photography book, photography instructor, technical reference, manufacturer, and Wiki-Page, has been using the term incorrectly all this time - but could you stop for a second and possibly consider that perhaps you might be the one using it somewhat differently than everyone else? At the very least - look at a camera, and note that when you set the "F-Stop" to, or read it to be, say, F/3.5, it does precisely the same thing to the camera if you are in a completely pitch-dark room or outside on a very sunny day. That alone should suggest that F-Stop is not a measure of light, but instead of something else, and, perhaps also consider that it is, as I have suggested numerous times on this thread, the ratio of the focal length to aperture diameter.
ghshephard 15y ago
You can't adjust your F-Stop with dark lenses. F-Stop is not a measure of light coming in, it's a measure of the focal length to the aperture. Light conditions prior to hitting the aperture (Either by flashes, sunlight, or dark lens) are entirely separate from the concept of F-Stop. For a given focal length on a subject in focus at a reasonable distance (not at infinity), increasing the F-Stop will always increase the DOF.

lutorm 15y ago

Sorry, but you are wrong about this. Look at http://en.wikipedia.org/wiki/F-number http://en.wikipedia.org/wiki/F-number You seem to be thinking of something similar to what the Wikipedia article calls "T-stops", a calibration of the absolute transmission of different lenses. That's something different from the f/ratio.

hackermom 15y ago
Are you nitpicking? You can point to aperture stop theory and the history of the f-numbers etc. indefinitely, but ƒ is and will remain synonymous with light transmission (or "T" as you keenly insist; thank you, I am familiar with it) in every single practical situation of photography, no matter how much you try to balance the needle on its tip.
- ghshephard 15y ago
  hackermom, I mean this with earnest sincerity - so please take it in that nature; In fifteen years of photography, photography classes, photography magazines, and photography books - I have never, ever, had anyone suggest that ƒ is synonymous with light transmission. It is possible, that I, and every photographer, photography magazine, photography book, photography instructor, technical reference, manufacturer, and Wiki-Page, has been using the term incorrectly all this time - but could you stop for a second and possibly consider that perhaps you might be the one using it somewhat differently than everyone else? At the very least - look at a camera, and note that when you set the "F-Stop" to, or read it to be, say, F/3.5, it does precisely the same thing to the camera if you are in a completely pitch-dark room or outside on a very sunny day. That alone should suggest that F-Stop is not a measure of light, but instead of something else, and, perhaps also consider that it is, as I have suggested numerous times on this thread, the ratio of the focal length to aperture diameter.

ghshephard 15y ago

You can't adjust your F-Stop with dark lenses. F-Stop is not a measure of light coming in, it's a measure of the focal length to the aperture. Light conditions prior to hitting the aperture (Either by flashes, sunlight, or dark lens) are entirely separate from the concept of F-Stop. For a given focal length on a subject in focus at a reasonable distance (not at infinity), increasing the F-Stop will always increase the DOF.