DOF and Cropping take 2

Started Feb 11, 2014 | Discussions thread
moving_comfort Veteran Member • Posts: 8,238
Re: What it is vs. what it is thought to be

Great Bustard wrote:

moving_comfort wrote:

Great Bustard wrote:

The point of photography is making photos. As such, one doesn't choose the particular system to get images which are equivalent to another system. A person chooses a particular system for the best balance of the factors that matter to the them, such as price, size, weight, IQ, DOF range, available lenses, and/or operation. By understanding which settings on which system create equivalent images, the difference in their capabilities is more easily understood.

One of the main sources of resistance to equivalence seems to stem from an aversion to it based on the false assumption that it exists to 'prove' one format is better than the other. Folks who have this aversion hear 'equivalence' and immediately go on the defensive, start refuting things that should be self-evident. Almost always, they're protesting what they think equivalence is, not what it actually is.

There are those, of course, and they are numerous. However, there are also those who can only think in terms of relative aperture (f-ratio) and ISO, and cannot understand, or simple refuse to understand, that, in terms of the visual properties of the recorded photo, it's about the virtual aperture (entrance pupil) and the total amount of light that falls on the sensor.

Interestingly, these two paradigms can be reconciled with the equivalence ratio (crop factor), but due to a complete and total misunderstanding of aperture, exposure, and total light, they absolutely refuse to apply this to the f-ratio, and only apply to the focal length.

I've recently tried introducing the jarring sudden image of a P&S  into a thread to try bring home why it's important to apply it to both.  (Thx also for helping to keep terms concise, it's easy to fall into the lazy habit of adopting 'aperture' to follow someone's lead in a thread when what you meant to write was 'f-ratio'.)


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