Continuation: Sensor Size, Present & Possibilities

Started Apr 10, 2013 | Discussions thread
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Re: On DOF
In reply to EinsteinsGhost, Apr 11, 2013

EinsteinsGhost wrote:

joejack951 wrote:

EinsteinsGhost wrote: Now, why do you think an f/1 would be necessary on an APS-C for the same?

It's simple optical math. For the same "view" as my 35mm on a FF camera, you'd need approximately a 24mm lens on APS-C. At f/1.4, the aperture size on my lens is 25mm. So to equal the aperture size and get the same "look" in your image (as well as getting similar noise by allowing you a 1-stop lower ISO), you'd need f/1 (24mm aperture).

The point being, the need is utterly irrelevant. You opted to shoot something wide open disregarding the fact that the DoF is too shallow. Your priority was clearly to over come limited lighting situation rather than go for a full fledged blur that includes parts of your subject (rather than to properly isolate your subject).

It's funny that you are telling me what I wanted in the shot and what is "proper isolation", as if that were a quantifiable thing. I'm perfectly happy with the DOF in the shot. That you have a problem with her hair being out of focus is far from relevant to me. I didn't want to shoot it at f/2 or f/2.8. I didn't want a 50mm FOV like your shot (which compressed the background far more than mine). I took other shots that night at f/2 (at up to ISO 25600) so, no, my choice of f/1.4 had nothing to do with overcoming limited lighting.

You are confused. I can take pictures identical (save for being lower MP) images to APS-C cameras with my D3S by using the APS-C crop mode. Shooting with the full sensor, I can have the same subject framing with the same lens but at a closer distance yielding less DOF.

I can't blame you for not being able to keep up with my post, but I've mentioned that a couple of times (crop mode in FF cameras). In fact, it was one of three cases I've presented.

Here's what you presented:

1- Exposing all of an APS-C sensor

2- Exposing part of a full frame sensor (FF in APS-C mode)

3- Digital cropping

Now I'm not totally clear on what you were trying to show as distinctions between these three. As far as the final image is concerned, the only difference between 2 and 3 is that the camera will be metering the full scene versus only the APS-C crop. There is no difference at all (again, save for the number of MP in the final image) between 1 and 2.

It depends on what you value as a "final image". Do you not care about resolution? Do you not care about carrying a lens with longer reach since you can always crop the image anyway? Should pros sitting by the sidelines at an NBA game simply stick with a 50mm or so lens, and simply crop their way to producing the same effect optical reach provides?

I've stated several times that cropping a larger sensor down to the size of a smaller one reduces resolution, but that is the only difference between the two images and that's assuming that the FF camera didn't have such a high MP advantage already that the outputs would drastically different. For example, a D800 in APS-C crop mode still outputs a 15MP file or thereabouts. There are only a few APS-C cameras on the market that can top that resolution by a significant amount (most match or only slightly exceed it). The rest of your point here is arguing about something that I've never suggested.

There is no difference other than the MP of the captured image. You are confusing simple cropping with the "digital zoom" feature some cameras have which extrapolates the cropped images back to the original number of MP.

You're confused. The argument is between getting results optically (using a 400mm lens for 400mm FoV) versus cropping a 100mm lens to achieve 400mm FoV in post processing.

If we're talking APS-C and full frame, it's a 1.5X crop factor, not 4. Regardless, the only difference between using an actual crop sensor and cropping a larger sensor to the smaller sensor size in post is the metering and the number of MP in the final image. Doing the cropping in the camera at the time of capture eliminates the metering difference.

Yes, I'm well aware of the crop factor. But, if 1.5x applies, why won't 4x? Are you losing something by cropping?

Quit arguing points that I've never brought up. We're comparing a 1X crop camera to a 1.5X crop camera and what the final image looks like in terms of DOF. I've admitted that MP differ after cropping (an obvious statement). That's all that differs though assuming a crop mode was used in camera (to give the same/similar metering).

Is this a serious question?

Yes. What would you use 50mm f/1.4 on FF for a similar situation? Would it be to lessen the isolation effect, or to improve it? For that matter, do you always shoot wide open?

This has been answered by others. No, I don't always shoot wide open but I do sometimes shoot wide open, especially with zoom lenses.

At f/1.4? That is where we were at.

I'm illustrating another advantage of full frame lenses where your argument about "who needs such shallow DOF" falls apart.

You illustrated with an example where you should have increased the DoF a little (same mistake that Eric made below).

That's your opinion. My opinion is that the DOF is just fine.

There are times when wide open at f/1,4 on full frame (or wide open at f/2.8 or f/4 depending on the lens) that I wish I had less DOF, or am happy with the amount I have. Using an APS-C camera would then mean that I'd have more DOF than I desired.

Give me an example.

I like the DOF in the image posted above.

It is good, but it could use a slightly deeper DoF for better isolation unless you wanted a part of the subject to blend into the background. Was that the idea?

The subject isn't blending into the background. She goes slightly out of focus (her hair) but that allows for everything behind her to be thrown that much more out of focus. To get more of her in focus and still get the background that out of focus, I'd have to use a longer lens which would cut down on my angle of view, and I wanted the wider angle of view.

That was the idea here:

You have a fairly flat subject. You could have used just about any aperture and had almost all of it in focus. I did just notice that the edges of the hat are going out of focus. Was that intentional or not?

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