Continuation: Sensor Size, Present & Possibilities

Started Apr 10, 2013 | Discussions thread
Contributing MemberPosts: 874
Re: On DOF
In reply to EinsteinsGhost, Apr 10, 2013

EinsteinsGhost wrote:

olliess wrote:

Supposing you really want to argue about this, do you think that no light shines on the FF sensor outside of the APS-C frame when DX crop mode is activated? Even allowing for a dedicated DX lens?

Image circle needs to be larger than the sensor. But that is completely irrelevant to the issue. If you want to consider the entire circle, you could but what do you expect out of it?

So why are you arguing about this?

Two obvious cases come to mind: 1) you don't have a longer lens with you, and 2) you get to make the final decision later.

You can do this anyway, and as addressing a need. Obviously you realize that it isn't ideal. No?

You asked why anybody would use "digital" cropping instead of what you call "optical" cropping (either in the lens or at the sensor). I asked what's the difference, and rather than answering, you moved on to the question of why anybody would use digital cropping instead of just using a longer FL lens. I answered that too, and now you're telling me it isn't ideal. Ideal for what?

Objective analysis requires a demonstration of facts. By claiming "you need larger aperture you are able to increase subject isolation" isn't that but simply theoretical (and worse, only a part of it). You can see it for yourself by asking self a very simple question: "Do I get the best isolation at all times by keeping aperture wide open?"

A fast-aperture lens can allow you to achieve a greater subject-background isolation than a narrower aperture, given a fixed subject-background distance. A fast-aperture lens also allows more light to reach the sensor when shutter speed is held fixed. As a side benefit, the fast aperture lens may give some advantage in low-light focusing. These are pretty well-known basics facts about wider vs. narrower apertures; is a "demonstration" really needed in these forums?

You will realize that the answer is not as cut and dry. You may end up making a part of the subject blend with the surroundings (too shallow DoF). Recognizing that aspect is being objective.

I gave a list of objective things that could be accomplished using a faster aperture, without any subjective judgment about whether it is "best" or not to use the faster aperture in any given case.

It is true that you can go one way but not the other. The issue I've pointed at, however, has to do with the practical side of it. I can see an insignificant advantage but larger cost and size of going with larger aperture, but if that is the thread you want to hang your hat on, for FF sensor, well, you have that choice.

But even this is not always the case. The Sony 35mm f/1.8 E-mount lens is about 6mm shorter than the Nikon 50mm f/1.8G, but sells for more than twice the price, despite the fact that the Nikkor provides more than 1 stop advantage in light gathering and DOF control.

I don't see a point to it. Or, perhaps you can show me what is it about these yet shallower DoF at wide angles that is dictating the need to spend several times more.

The classic use for fast wide angles is, to my knowledge, to get the low-light advantages. I can't imagine most people choosing a 24/1.4 to get isolation (although I'm sure there are exceptions).

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