The part where ‘you collect light from a larger area’ is incorrect. This is what the Greta Bustard guy is confusing and his 'amount of light' concept is totally flawed.
It’s actually exactly the opposite.
I'm giving you credit for approaching the discussion in good faith, rather than just an excuse for argumentation. So read the material. When you do you will understand what the discussion is about. You may still disagree, but your points will at least become pertinent to what is being discussed.
http://forums.dpreview.com/forums/read.asp?forum=1032&message=21221392
I usually use this one now. It's all the same shot, just cropped differently.
Replace "blunt" with "simultaneously stupid and insulting", and you'll be closer to the mark. Cheers.
No, it is entirely correct. If you frame wider, you collect light from a larger area of the scene. If you don't understand that, it would explain a lot.
I said before that you should take care with that attitude. It's a classic case of "people who think they know everything can really annoy those of us that do."
It is one of the factors, and I have said, several times , that the scenarios you present, without further qualification, are meaningless.
No, it isn't -- mattr is quite correct. The light from the scene to the aperture is not focused, thus the ISL applies. The light from the aperture to the sensor is focused, so the ISL does not apply.
You're completely, and totally, wrong. Good luck with that.
Sorry but you are the one who's confused. Consider asking for a second opinion.
Since you suggest it:
I see two actions: one is croping, another is resizing to get the same image size. Which of those is responsible for softness change?
Rephrased: "When you use a smaller image sensor (a so-called "cropped" sensor) to record an image of a given field of view, then enlarge the sensor image to the same size as one of the same field of view made with a larger sensor, the resulting image will have less depth of field than the one made with he larger sensor, when both are view from the same distance and with the same visual acuity."
X-vision, Great Bustard has established his credibility through many years and many incarnations in this forum. His viewpoints and writings can be thought-provoking and may require one to look at what we already know (or think we know) in a different way, but they ultimately withstand scrutiny. You obviously know a lot of stuff, but you don't understand all the implications of what you know. I recommend that you take his invitation to examine what you know in a different light by studying his link.
Both, together. Just cropping without resizing doesn't change anything, you will just see a smaller portion of the image.
There are 3 parameters : viewing size, enlargement and visual acuity. All three have been melted into one, the CoC. Of course, to do that some assumptions are made on the viewing distance and on the average visual acuity. When in some situation one of the 3 parameters differs significantly from the assumption (e.g. viewer is blind as a bat) the CoC would need to be changed accordingly (in this example, increased, because a person with poor eyesight will not notice a much larger degree of softness in the picture).
The enlargement. You have to do it to keep the image size the same because DOF is measured at a reference size (assuming a reference distance, etc.)
Maybe he lacks a bit of visibility due to the reincarnation process
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I can say the same - but I am not an optical engineer, just a boring mathematician.
It's caused by the different enlargement ratios of the differently-cropped images. I guess you could say that's the resizing.Only one question. Difference in dof is caused by cropping or following resizing which is applied to get required same size of the images.
If you're not comparing the same FOV and the same final image size, you're comparing different images. Thus, I don't think that's really valid.
In general to understand why 4.000$ 50/f1 on the crop behave like 400$ 85/f1.8 on FF.
There's a lot of processes going on simultaneously while comparing different systems at the same perspective, framing and print/display dimension. To isolate them and find which one is responsible for what we change requirements to nullify their affects.
