[UncleVanya]

I’ll wade in.

The pixels of most apsc sensors are smaller than the ff the lens is measured on. Bear in mind that even if the lens has a finite maximum resolution that resolution is likely higher than it was measure as. We have seen that places that do lens measurements find that every time sensor resolution goes up their measured lens resolution also goes up - not necessarily in a direct proportion however.

What this means is that you can’t simple assume that the detail available at ff is the most the lens can provide. Think of it as if you had two coloring programs. One with 3mmx3mm blocks that was 2.25 times the area of another with 2mmx2mm blocks. Each block does not map directly to another even in the central portion. In a 6mm x 6mm area 4 blocks becomes 9. This change is why a lens may resolve better on apsc than ff unless the ff sensor is very high resolution (A7rIV for example).

Note that this is not always this way. It is well known that some larger format lenses were/areless perfect than they needed to be if used on smaller formats. Large format lenses shot on 35mm cameras sometimes struggled to meet the expected performance due to the size of the negatives relative to the prints made. Smaller lenses often have to be more carefully engineered as tiny imperfections will show. But the delta in image size is typically much larger than 1:2.25 area. Put an 8x10 lens on a q7 and the high density of pixels might reveal flaws. But in more practical terms it isn’t seen in practice much. The main penalty for using ff gear on apsc is weight/size.

[angerdan]

Let's say a full-frame lens has a resolution of 2000 lp/ph. On an APS-C sensor that would become 1333 lp/ph. That's in linear dimension. Over the area of the sensor, that would be a 2.25-fold decrease in resolution. That's enough to turn and awesome lens into trash. I understand that lens "resolution" is not the same as resolution of the lens+camera, but a 2.25-fold decrease in resolution of one part of the system is going to have a dramatic effect on the final image.

Surprisingly for me it seems you're right.

If compared the results of the Nikon AF-S 58mm f1.4 on a FF and a APS-C camera, the APS-C camera got significant Lower lp/ph with the same lens than the FF camera.
Nikkor AF-S 58mm f/1.4 G (DX) - Review / Test Report - Analysis
Nikkor AF-S 58mm f/1.4 G (FX) - Review / Test Report - Analysis

DX
f1.4
Center 2627
Border 2082
Extreme 1994

FX
f1.4
Center 3095
Border 2775
Extreme 2705

[AstroDave]

The total number of "pixels" that the lens projects onto an APS-C sensor is going to be 1.5 times less

Ah, but the number of pixels depends on the camera, too. For a real-world example, compare a K-3 and a K-1, both exposed with the same full-frame lens. If the K-1 is used in its crop sensor mode, you get about 15 megapixels in the output image, whereas a K-3 has its 24 megapixels in the same footprint and outputs those in its image. So, if the lens is up to snuff, you get a better image - number of pixels, which appears to be your criterion - from the APSC camera with the full-frame lens.

And, as noted above by others, that full-frame lens is probably doing its best at the center of the frame.

[stevebrot]

If compared the results of the Nikon AF-S 58mm f1.4 on a FF and a APS-C camera, the APS-C camera got significant Lower lp/ph with the same lens than the FF camera.

As noted by Klaus at optical limits...never cross compare between formats or sensors.


Steve

[PJ1]

If compared the results of the Nikon AF-S 58mm f1.4 on a FF and a APS-C camera, the APS-C camera got significant Lower lp/ph with the same lens than the FF camera.

This is why many (most?) lens testing sites warn that comparisons should not be made between systems.

But to get to the OP's concern that

a full-frame lens has a resolution of 2000 lp/ph. On an APS-C sensor that would become 1333 lp/ph

, in my view a better assessment of lens "sharpness" is lines per millimetre (lpm). To get 2000 lp/ph on APS-C a lens would need a sharpness that gives over 3000 lp/ph on FF. Think Zeiss Otus at Zeiss Otus prices. There are diminishing returns in seeking infinite sharpness. And there are reasons why larger sensors perform better - if that is what the user requires.

that

[swanlefitte]

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

Yet using an apsc lens on a apsc camera has that same issue. Your argument is about FF vs crop. Regardless of what lens I use this issue is present. Thus the "wasted" part doesn't matter. Price difference, weight, form factor, and use for more than one camera, are all that matter

[pepperberry farm]

yet, again, I continue to remind the masses that I was told there would be no math....

[normhead]

Yet using an apsc lens on a apsc camera has that same issue. Your argument is about FF vs crop. Regardless of what lens I use this issue is present. Thus the "wasted" part doesn't matter. Price difference, weight, form factor, and use for more than one camera, are all that matter

The APS-c K-3 puts 24 MP in the area of the it's crop sensor, the K-1 puts 15 MP in the area of the crop sensor. THERE IS NOHING YOU CAN DO TO DO AN ACCURATE COMPARISON. remember, the sharpest part of the lens is the centre. Resolution falls off at the edges. So cropping off the edges doesn't cut the lw/ph in half.

The lw/ph of the 16 MP K-5 with a Sigma 70 macro is about 2100 lw/ph. That should be about the same as the cropped K-1.
Pentax K-5 Review - Image Quality

The K-3 tops out at about 2700 lw/ph using the same lens. That's about a 30% increase in resolution in the crop area over the k-5, using the same lens, but different APS_c camera and pixel density. This illustrates the problem with this kind of comparison. The 16 MP sensor doesn't capture all the resolution of the lens. This is critical.
Pentax K-5 Review - Image Quality

The K-1 tops out at 3450 lw/ph with pixel shift. 3350 without.

Now the interesting part.

The K-1 sensor is double the size, but even looking at the k-5, at 2100, that's a 60% increase. More than double the number of pixels, double the area, but only 60% more resolution. With the same lens you can't just cut the resolution in half. Half of the K-1 resolution is 1675 as compared to the measured 2100.

But the K-3 is 2700 lwph, so even though you're doubling the sensor size using the K-1 you are only increasing the lw/ph by 25%

My point is this is way to complicated for such simple explanations.

When you factor in different sensors etc. Canon tends to get more lw/ph out of their smaller MP sensors than those using Sony sensors of the same MP, and there is a host of other factors as well, like noise. By the time you clean up the images, you may have reduced your resolution to make your image acceptable to a level that is way below the measured lw/ph. So the only way to do a comparison that has any meaning in the real world is to normalize the noise in both images.

Bottom line, it's too complicated to think about, to complicated to understand. Look at your images and decide if they re good enough. If not look for something you might find more pleasing. But whether that will a one inch sensor, micro 4/3, APS-c or FF, you won't figure it out with math. To many variables and too much personal preference. But all those sensors can produce images in the 2600-4000 range. That is good enough for 26 x __ inch print at 100 distinct lines per inch or more, which is darn good.

And also darn near indistinguishable looking at the print if you have more than that.
So it comes down to not the math, but if you like how the camera renders.

I bought my ZS100 because it could render at about the same resolution as a K-3 at the same resolution. But I much prefer the way my K-3 renders. Or to be less wordy, I like K-3 image more than I like ZS100 images. The ZS100 come a niche camera for when I'm not planning to shoot, so I don't want to bring a camera bag, but I might have time to wander around and snap a few images, s something that fits in my pocket is appropriate.

There's nothin wrong with this ZS100 image.


But I prefer k-3 images


Or K-1 images


But if I preferred the ZS1000 images, there' be absolutely nothing wrong with that, from a lw/ph perspective. It's not about the size of the sensor, it's about the image processing the manufacturer uses to process its images, and whether I like what comes out of the whole process. I don't dislike the ZS100 images, I like them, but I like the images for my k-3 and K-1 more.

I find my ZS100 images tend to be a little gaudier than I like and sometime look over sharpened, but I have absolutely no doubt that some people prefer ZS100 images. And those people would be wasting their money on more expensive gear, regardless of the sensor size comparisons.

[swanlefitte]

My point is this is way to complicated for such simple explanations.

A lot of good stuff. Reading it made me think more of what is being compared and how to put this in a logic test. The true/falss of this conclusion is implied by the OP's logic. "If I have a full frame 200mm lens on my K1 and I decide to use my K1 in crop mode I should switch out the lens for an apsc 200mm lens so I am not wasting image circle."
I think to answer true is at best laughable. Though it will minimize the waste of image circle, it is just silly.

[pschlute]

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

I would ask you what your real-life experience of photography is ?

You do not get reduced resolution using a FF lens on aps-c.

And lenses transmit light, not pixels.

[RICHARD L.]

The total number of "pixels" that the lens projects

1) A lens does not "project pixels", it focuses electro-magnetic radiation, resulting from a Hydrogen to Helium fusion process in a Star located 93 million miles (150 million Km) from Earth, known as "visible light" on a plane (film or digital sensor).

2) I use a Pentax 645Z having a sensor measuring 33 X 44 mm, thus requiring an illuminated field of at least 55 mm (the diagonal) to cover the photogram.

3) I started using the 12 Pentax 6X7 lenses I possess on my 645Z. P67 lenses must cover a 55 X 70 mm photogram, thus covering a 90 mm minimum diameter illuminated field.

4) The P67 45 mm f/4, 90 mm f/2.8 and 165 mm f/2.8 lenses were "average performers" on film with my Pentax 67 II, honest but "only average".

5) On the 645Z digital, these same 3 lenses produce "stellar results", exploiting only the sharpest central part of the aerial image.

P67 45 mm f/4

P67 90 mm f/2.8

P67 165 mm f/2.8

6) Other P67 lenses that were stellar on 6X7 are still "stellar" on the 645 digital sensor.

P67 M*300 mm f/4


Regards

[stevebrot]

I see that SMC-FA 35mm f/2 has glowing reviews. How would it do on an APS-C camera relative to SMC DA 35mm F2.4?

I own the FA 35/2 and it does very well on APS-C and 24x36mm FF and am a bit of a fan boy. The DA 35/2.4's optical design was derived* from that of the FA 35/2 and is also competent on APS-C and has garnered a high degree of owner loyalty. Based on what I have seen from the DA 35/2.4, I don't disparage ownership or owners. Based on what I know of the FA 35/2, I continue to recommend it or the HD version to any who ask, particularly if they want the option of shooting 24x36mm FF. In my opinion the K-mount competition for the HD FA 35/2 is the Sigma 35/1.4, not the DA 35/2.4, but what can I say me being a fan boy and all.

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.


Steve

* Similar optical formula, though otherwise different (e.g. element diameters, image circle and off-axis performance, minimum focus distance, and such)

[normhead]

I think to answer true is at best laughable. Though it will minimize the waste of image circle, it is just silly.

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.

[Alex645]

We can use full-frame lenses on APS-C cameras, but that sounds like an awful idea, since only the center of the lens would be used. The total number of "pixels" that the lens projects onto an APS-C sensor is going to be 1.5 times less. That's enough to turn and awesome lens into trash.

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

I see that SMC-FA 35mm f/2 has glowing reviews. How would it do on an APS-C camera relative to SMC DA 35mm F2.4?

I'm afraid you are wrong - The capture with an APS-C sensor just records the "best" i.e. center portion of the image projected by the lens.

The only downside of using an FF lens with an APS-C sensor is size and cost. And as others have said, the resulting image would be equal or better than a lens designed for APS-C because of the crop of the edges and corners.

The SMC-FA 35mm f/2 at, for example f/2.8, will have better overall IQ than a SMC DA 35mm f/2.4 at f.2.8 or any equivalent aperture.

I say all this not just from theory but from real-life experience. The flaw in the original logic was that a measured lens resolution is affected by the size of the sensor. It's a good question and questions like this are what a good forum can unfold.

[normhead]

The SMC-FA 35mm f/2 at, for example f/2.8, will have better overall IQ than a SMC DA 35mm f/2.4 at f.2.8 or any equivalent aperture.

You can't make a direct comparison at Optical limits because the 35 2.4 is tested at 16 MP and the 25 2 at 10 MP, but looking a the graphs, the 35 2.4 looks like it would be better based on the level of the bar as it relates to"perfection" at the top.




Usually images test worse on a higher density sensor.

I'd love to see some indicaion you are right, but this is all I can find at the moment and it suggests the design of the lens is more important than APS-c or FF and there certainly is little reason for thinking an ƒ2.8 lens at ƒ4 would be sharper than an ƒ4 lens at ƒ4.

That is not an advantage of faster glass. That's an advantage of better lens design.