Recent content by Helen B

  1. Helen B

    Anybody know of a calculator or simulator for size of bokeh balls?

    Not quite - the magnification changes with the distance from the rear nodal point to the image plane (just like normal focus breathing). The significance of the change in magnification compared to the circle of confusion will vary with f-number and it will also depend on the position of the exit...
  2. Helen B

    Anybody know of a calculator or simulator for size of bokeh balls?

    This forum laughs at the notion of a "right" answer. Ha ha ha. Just like that. (The nearest thing to a correct answer has already been given, I think - by photoguy99. )
  3. Helen B

    Anybody know of a calculator or simulator for size of bokeh balls?

    Yes it's quite delicious. Hollis Frampton called his collection of essays 'Circles of Confusion'. I like that book.
  4. Helen B

    Anybody know of a calculator or simulator for size of bokeh balls?

    Unless you know enough about the lens to be able to calculate the point spread function, the formulae given in that Wikipedia article are about as good as you'll get and they give the best estimate of the size of the 'bokeh ball', as you call it, is the circle of confusion (when there is no...
  5. Helen B

    Can i balance my elinchrom model light to daylight temp?

    Gelling tungsten to match daylight loses a couple of stops. It's easier to gel daylight Kinos to tungsten (because you only lose about 2/3 stop going that way) or, much better, switch out the Kino daylight-balanced tubes for tungsten-balanced tubes. The latter would be the common way to do it...
  6. Helen B

    Continuous v strobe lighting for product photos

    I prefer continuous light for product photography (that's the majority of my paid work these days), as long as I don't need a short exposure; need to use large format film (shooting typically at f/32 or f/45, ISO 100 or 160) or have to balance the output from, say, a lantern or flashlight (UK...
  7. Helen B

    What Does The "f" in f/x.x stand For?

    I know a lot of formulae that use the f-number without decomposing it into focal length and entrance pupil diameter. F-number has been found to be a useful combination, in something of the same way that Reynold's number, kinematic viscosity, the Prandtl number, the Grashof number and many others...
  8. Helen B

    What Does The "f" in f/x.x stand For?

    ... but not if you try using the focal ratio or f-number in a formula. It's defined for a good reason. (I wasn't confused, I was just trying to remove your confusion by suggesting that you check elsewhere because you had no reason to believe me.)
  9. Helen B

    What Does The "f" in f/x.x stand For?

    Could you give a reliable reference for it being aperture diameter divided by focal length rather than the other way round? I'm curious.
  10. Helen B

    What Does The "f" in f/x.x stand For?

    Don't you mean 'thus has a focal ratio of 10' rather that 1:10?
  11. Helen B

    What Does The "f" in f/x.x stand For?

    The number itself (ie 2.8 in your example) is called the f-number. It is defined by the ISO (for general photographic usage) as the focal length divided by the diameter of the entrance pupil.
  12. Helen B

    Crop factor - misleading

    To the OP, Reflex: have you any way of testing the angle of view on a full frame camera? (The focal length is measured from the rear nodal point to the image plane. The lens (and only the lens) may be rotated about the rear nodal point without the image of objects at infinity moving.)
  13. Helen B

    Crop factor - misleading

    The focal length of a photographic lens is defined at infinity focus. It's not the manufacturer's choice.
  14. Helen B

    What is shutter-speed, and what is blender?

    Ask someone who is bilingual in English or a German - Nordic language and they will spot the mistranslation / mixup straight away. Blende is German for aperture.
  15. Helen B

    Depth of Field Calculator Question

    Think about this. If you crop in printing isn't it more like using a smaller sensor than switching lenses? In the example you give it would be wrong to increase the focal length but right to decrease the format size (and implicitly the MACC - maximum acceptable circle of confusion) used in the...
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