Of resolution and P-mpix

Started Mar 7, 2013 | Discussions thread
qianp2k
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Re: another read
In reply to MAC, Mar 11, 2013

MAC wrote:

qianp2k wrote:

MAC wrote:

Steen Bay wrote:

Mako2011 wrote:

qianp2k wrote:

Mako2011 wrote:

qianp2k wrote:

Mako2011 wrote:

A sharper lens will always resolve more detail, regardless of the pixel count, and a sensor with more pixels will always resolve more detail, regardless of the lens.

True but you didn't mention the crop factor (sensor size) that is a far more dominant factor than pixel amount for example.

I guess you missed it

"Two photos taken from the same position will have the same perspective regardless of the focal length or sensor size regardless of the FL (focal length) of the lens used."

We should add,

Regardless what lenses, larger sensor with the same lens always outresolves smaller sensor with the same pixel mount, and likely larger sensor still will outresolve with less pixel amount than more pixels in smaller sensor.

You missed it again

Equivalence

  • The photos all have the same AOV (diagonal angle of view) and aperture (entrance pupil) diameter: 50mm / 2 = 62.5mm / 2.5 = 67mm / 2.7 = 100mm / 4 = 25mm.

  • The photos all have the same DOF (as well as diffraction softening) when they have same perspective (subject-camera distance), AOV, aperture diameter, and display size.

  • The photos all have the same motion blur and the same total amount of light falls on the sensor when the aperture diameter and shutter speed are the same (e.g. ISO 100 on mFT, ISO 160 on APS-C, and ISO 400 on FF).

  • The photos all have the same same noise when the same total amount of light falls on the sensor if the sensors are equally efficient (less noise if the sensor is more efficient, more noise if the sensor is less efficient).

  • Other elements of IQ, such as resolution, bokeh, flare resistance, etc., as well as elements of operation, such as AF speed/accuracy, size, weight, etc., are not covered in this use of the term "equivalent".

Crop factor, Crop factor, Crop factor that you simply cannot ignore.

Unrelated when we have Equivalence and thus can actually compare.

What equivalence you are talking about? I don't shoot under any bible of equivalence such as rubbish to shoot in the same DOF. I am talking about the same AOV equivalence in this thread that a fair comparison must be taken.

That would mean you didn't read the article I linked that explained how to better understand the things that affect resolution. Go ahead and read it and you'll see that you are perhaps mixing a few oranges in with your apples. Hard to discuss resolution when you see things from a different perspective regards definitions. Your "same AOV equivalence" point means you didn't notice how photos all have the same DOF (as well as diffraction softening) when they have same perspective (subject-camera distance), AOV, aperture diameter, and display size. Given that, I can understand your confusion.

Though, if shooting a flat/2D subject like a resolution test chart, then it doesn't really matter whether the shooting distance is the same. What's important is that the framing of the test chart is the same. The shooting distance will necessarily vary, depending on the equivalent FL.

and moving closer in distance is logically unfair -- by virtue of being closer, more detail can be seen

You cannot move closer in portraiture, studio, wedding, street, building...? Or let's look from another perspective, I use 85mm lens for 85mm purpose on 5D. With 60D you'd have to retreat to shoot half body. Do you have space to move backward in your small apartment room?

one can always move around, but we're talking equivalence, not optimizing focal length on the fly for a particular format over many seconds in time.

I use 50 mm f1.4

The lens also designed for FF for whole body or 2/3 body portrait.  50/1.4 on FF also has better background rendering, more separation of your model and background when you frame your model into the same AOV between 5D and 7D.  So 5D will have more pleasing result.  You use 85mm for half body portrait and 135mm for shoulder above portrait.  All these prime lenses are designed and optimized for FF not for APS-C.

The issue you mention is an issue for crop for different reason ---- canon hasn't developed the same level of portrait lenses in the portrait range for APC-s that they have for EF. - with those right focal lengths that they have for EF over many decades. But Sigma may change that with the development of their 30 mm F1.4 Art lens for crop and more. We'll see. I may buy the 30 f1.4 art. Also if they update their 50 f1.4 to the art -- I may buy that one as well.

Definitely.  Yes Canon APS-C shooters need more EF-S prime lenses (so far EF-S 60/2.8 macro is the only one).  Nevertheless 5D with Sigma 50/1.4 should still outresovle 7D/60D with Sigma 30/1.4 art, wait and see DXOMark test.

moving feet -- is not always possible.

True but possible in portrait, studio, wedding, and most street, events and even landscape.

Keeping the sensors the same distance from the subject is the fairest way to compare -- to answer the instant in time comparison scenario -- and to keep distance between the sensor and the subject the same.

The fair test is having the same AOV either by adjusting distance or by using different focus length.

These sensors are not magnifying devices -- they are sensors to be fair they need to sense what is the same distance away -- to do a fair comparison between formats

We need to test on the same AOV or scene otherwise you're testing on two different photos. DXOMark just confirms a common fact that you cannot have operation/convenience and IQ at the same time.   The reason you could use 100mm lens instead of 160mm lens on 1.6x crop is thru 1.6x crop magnification.  By doing so you win operation and convenience advantages but sacrificing IQ.  Nothing wrong that depends on your priority.

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