[stevebrot]

So when my APS-c K-3 image pulls 2700 lw/ph out of an area that on my K-1 would produce 2100 lw/ph, is the FF sensor wasting 600 lw/ph? You can look at this both ways.

Yes...as a matter of fact, it is...by wasting all that space with FAT pixels!


Steve

(...or is it pitifully skinny pixels...I am so confused... )

[Pentaxxoid]

Out of curiosity, does this thread have anything to do with your other thread regarding possible purchase of the DA 55-300/4.5-6.3 over your existing FA 100-300/4.7-5.8? My take is that if you are not happy with the FA 100-300, it is probably that lens for your subjects rather than that lens on APS-C.

Yes, right, the FA100-300 made me thinking of this long time ago, but today I was thinking of FA 35/2 vs. DA 35/2.4. I am no optics engineer, but I think a good approximation for the resolution of the optical system would be the sum of inverses (analogous to the total resistance of resistors in parallel; this is why we cannot directly compare resolution of lenses tested on different sensors - now we have two variables in one equation: Lens Pixels and Sensor Pixels). If we use a smaller fraction of the circle projected by the lens, then Lens Pixels gets smaller. Hence, Total (Mega)Pixels get smaller as well.

Footnote 1: I am aware that light flux is not made of pixels... but I think you would agree that we could define a pair of pixels as an inverse of the spatial frequency where contrast drops to 50% of its low frequency value (I did not invent this; this is how Line Pairs per Picture Height is determined).

Footnote 2: Did you notice you also lose light flux as well when using an FF-lens on a cropped sensor? Full-frame FA 35/2.0 performs as a 53/3.0 lens on the APS-C sensor. Yeah, a full stop of light is literally wasted illuminating the throat of the camera. Those "pixels" are wasted bouncing off the walls of the camera and pentaprism I wonder where they go (perhaps, this is how hot pixels are born!).

[DeadJohn]

...What is your real-life experience of using FF-lenses on APS-C camera vs using an APS-C lens?...

A good FF lens is a good lens, regardless of whether I'm using FF or APS-C sensors. Resolution is not a limiting factor for the vast majority of photos with typical viewing distances on a home TV, computer monitor, or printing 16x20 and sometimes larger.

[Thagomizer]

What are "lens pixels" and how are they counted?

[Pentaxxoid]

What are "lens pixels" and how are they counted?

The same way MTF is measured. In the simplest form, two "lens pixels" correspond to 1 lp/ph. In reality, 1lp/ph is more like 3-4 pixels, but that does not matter when you compare lenses to each other. Here is how you measure MTF.

A lot of people seem to be hang on "lens pixels". Let's use lp/ph as a measure of len's resolving power, if it makes people more comfortable. The concept of the "pixel" is just more familiar to most people than modulation transfer function. I just had to use some term to describe spacial resolving power of the lens.

[stevebrot]

Footnote 1: I am aware that light flux is not made of pixels... but I think you would agree that we could define a pair of pixels as an inverse of the spatial frequency where contrast drops to 50% of its low frequency value (I did not invent this; this is how Line Pairs per Picture Height is determined).

Part of my background is as a software engineer and I can assure you that pixels are abstractions used to describe raster data for digital images and nothing more. They truly don't exist outside of coded instructions and stored data.

Footnote 2: Did you notice you also lose light flux as well when using an FF-lens on a cropped sensor? Full-frame FA 35/2.0 performs as a 53/3.0 lens on the APS-C sensor.

No, I never noticed that. TTL light measurements of a calibrated source through a given lens are the same on my K-3 as on my FF bodies. I am not sure, but I believe this conversation is drifting into the realm of "Total Light Dogma" a rabbit hole I have zero interest entering. Good luck with your lens and camera improvements. Be prepared to be amazed by your K-70 or KP when you get it.


Steve

[rod_grant]

I am aware that light flux is not made of pixels

If light flux is not made of pixels, why keep talking about pixels in/from the lens?
The pixels of the sensor are collecting the light that falls upon the sensor.
Extraneous light is just not needed or used.
Nothing is "wasted"

[tduell]

Y Full-frame FA 35/2.0 performs as a 53/3.0 lens on the APS-C sensor.

That's interesting. Is there a reference to the source of that info?

Cheers,
Terry

[Pentaxxoid]

That's interesting. Is there a reference to the source of that info?

Here is a super-popular explanation.

[clickclick]

yummy

[Benedict Michael]

What is your real-life experience of using FF-lenses on APS-C camera vs using an APS-C lens?

Pretty good, paid for all of them. And really handy with a K1-II!

[MarkJerling]

Or no sensor at all The lens has no idea what sensor is behind the lens ... why should the performance be affected??

Because of fewer pixels making it onto the print (or monitor).

I'm sorry, you're just dead wrong. How can there possibly be "less pixels making it onto the print (or monitor)"?

And it's not even 1st of April yet!

[MarkJerling]

Here is a super-popular explanation.

Do you really believe that video from Tony and Chelsea explains it?

[StiffLegged]

Do you really believe that video from Tony and Chelsea explains it?

I always find Professor Northrup (and his fine colleague) explain things so well - unfortunately it all goes straight over my head, so it’s rather wasted. The best lenses I have and use are actually old FF A-series glass from before they worked in pixels: nothing wasted when they deliver sharp clear aps-c images like they were bought for.

[mikesbike]

Here is a super-popular explanation.

F/2 with a FF body is really not the "same" as f/3 on APS-C, except in the matter of DOF regarding the degree of background blur with a given lens. But a correct exposure setting of f/2 under the same lighting with a lens capable of f/2 will still be the same whether with FF use or with APS-C use.