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05-06-2018, 11:44 AM - 2 Likes   #16
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....and if I made add a couple points:
a) When using your FF lenses on your APS-C sensor, you are cropping the corners and borders where you typically will have less resolution and more issues like chromatic aberration and vignetting. So this gives you a bit larger or bigger range of a "sweet spot" than if you were shooting FF.

b) f/stop is simply a measure of the focal length divided by the diameter of the aperture of the lens. The size of the sensor or film is not part of the equation. There are nuances mentioned above and ultimately if you are seeking "perfection", cinema lenses that use T-stops (actual transmission of light thru that specific optic) would be the ideal standard.

05-06-2018, 06:12 PM - 2 Likes   #17
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I agree with the sentiment that if you have never or will never shoot a 135 format camera (or medium format) just do not think about "crop factor". It is a marketing quip used to confuse and detract.

Crop factor has nothing to do with focal length. Focal length is designed into the lens, changing the sensor size (i.e. crop factor) does not change the physical characteristics of the lens. What changes is the field of view - for that lens at from the same place - that's it. One of these days I will have to draw a picture to show this.

Suppose you are shooting a cube that on a given lens will project a 10mm tall image of said cube onto the sensor of a camera body A.

Shoot that with a 135 format camera (camera A) (so - called "Full Frame" --- 135 is the nomenclature used by the film manufactures to designate 35mm film) and it will produce a 10mm image on the sensor. (film or digital)
Change the body (camera B), using the same lens, from the same position and the image projected onto the sensor is ------ wait for it ------ 10mm.

It does not matter what body you put it the lens on. It is the lens that determines the focal length not crop factor.

The same number of photons will hit the sensor at a given exposure, regardless of the size of the sensor. Remember that the number of photons are measured at the photo site, not the entire sensor.

Last edited by PDL; 05-06-2018 at 10:32 PM. Reason: Got rid of a quote I mis read
05-06-2018, 11:24 PM   #18
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QuoteOriginally posted by UncleVanya Quote
The diffraction effects are tied to pixel size which is related to sensor size. .
I'd actually leave that line out for a beginner ... the pixels in a K-1 are the same size as the ones in a K-50, for instance. And in a Canon 5DSR, they're smaller.
05-07-2018, 05:48 AM   #19
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QuoteOriginally posted by UncleVanya Quote
However... The diffraction effects are tied to pixel size which is related to sensor size. So a lens that has peak performance on the k-1 at f11 might peak at f8 on the KP since diffraction onset is earlier the smaller the pixel sites are.
Initially I thought this was a really interesting point (and even "liked" it).

But is it true? Let's say you measure lens center sharpness with the KP and determine that f/8 is sharper than f/11 because the KP's pixels are small enough to see the difference in diffraction effects. Next, if you measure lens center sharpness with the K-1, you may not notice f/8 being much sharper than f/11 because f/8 is out-resolving the K-1's sensor. But that doesn't mean the ranking of f-stops would invert and f/11 would look sharper than f/8 on the K-1.

Sensor pixel size would affect the broadness of the peak in sharpness but not it's location. A big-pixel sensor camera (e.g., K-1) would have a broader sweet spot with many apertures essentially out-resolving the lens. A smaller-pixel sensor camera (e.g., KP or Q) would have a sharper peak with fewer if any f-stops out-resolving the lens.

05-07-2018, 07:00 AM   #20
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QuoteOriginally posted by CarlJF Quote
It's because they mix up noise and exposure. All other things being equal, for a same exposure, a larger sensor will give you less noise. But in the real world, all other things are never equal and sensor technology now plays a major part in how noise is handled, often trumping sensor size
Not only that, according to Pentax, the K-p and K-70 with the accelerator chip are equivalent to the K-1 in high ISO noise, so even with two models selling at the same time, the whole noise thing, which was always a bunch of non-sense is completely exposed.
05-07-2018, 08:25 AM   #21
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The simple way to think about it is this:
The same lens takes the same image regardless of the format it is mounted on. Everything is identical, light transfer, DoF, FoV, sharpness, everything. It is the lens that creates the image, the body only records it.

An APS-C body then simply crops the centre ~2/3 of the image and discards (never records) the rest. FF records it all. The only time that matters is if you were trying to capture the same image on two formats, which you aren't and won't ever unless you're very dull or seriously bored.
05-07-2018, 08:56 AM   #22
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QuoteOriginally posted by victormeldrew Quote
The simple way to think about it is this:
The same lens takes the same image regardless of the format it is mounted on. Everything is identical, light transfer, DoF, FoV, sharpness, everything. It is the lens that creates the image, the body only records it.

An APS-C body then simply crops the centre ~2/3 of the image and discards (never records) the rest. FF records it all. The only time that matters is if you were trying to capture the same image on two formats, which you aren't and won't ever unless you're very dull or seriously bored.
Pullease.
That is a silly way to think about it.

To counter that thinking think of it his way.

Using the same APS-c lens the APS-c camera will correctly display the whole image produced by the lens, whereas the FF camera will be heavily vignetted on the corners and much of the image will be wasted.

This is just as true as what is stated above.

QuoteQuote:
The only time that matters is if you were trying to capture the same image on two formats, which you aren't and won't ever unless you're very dull or seriously bored.
OK, now that is just straight up wrong. You go to a scene, you see picture, you have APS-c and FF cameras, the question is how do I reproduce that scene in the most positive way. You are capturing the same scene, what sensor you use is unimportant. Your ability to frame the scene with the FoV you want is important and it is all that's important. It's the notion that the APS-c is a smaller sensor that's important is completely wrong. It doesn't matter to the final outcome.

This is a K-1 image.


This is a K-3 image


And if I took the image with my Q it would still be the same image. That the APS-c image is just part of the FF is utter nonsense. Please stop repeating it. What no one does is frame their image on FF so it's different and a wider FoV than their APS-c image.

The other difference being that if I shoot with my 18-135 at 135mm, I need a 200mm lens on my K-1 to get the same image. There will be practically no difference except that the K-1 package will be more than twice the weight.

Last edited by normhead; 05-07-2018 at 09:08 AM.
05-07-2018, 09:17 AM   #23
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QuoteOriginally posted by clackers Quote
I'd actually leave that line out for a beginner ... the pixels in a K-1 are the same size as the ones in a K-50, for instance. And in a Canon 5DSR, they're smaller.
Perhaps - but I was not limiting myself to those sensor sizes. This really starts to be a bigger deal as the size of the sensor drops. My point is that pixel sizes are related to (but there is overlap) the sensor size and these determine when diffraction starts to diminish the sharpness enhancing that stopping down can supply.

@Normhead - your dog is remarkably well trained!

---------- Post added 05-07-18 at 12:22 PM ----------

QuoteOriginally posted by photoptimist Quote
Initially I thought this was a really interesting point (and even "liked" it).

But is it true? Let's say you measure lens center sharpness with the KP and determine that f/8 is sharper than f/11 because the KP's pixels are small enough to see the difference in diffraction effects. Next, if you measure lens center sharpness with the K-1, you may not notice f/8 being much sharper than f/11 because f/8 is out-resolving the K-1's sensor. But that doesn't mean the ranking of f-stops would invert and f/11 would look sharper than f/8 on the K-1.

Sensor pixel size would affect the broadness of the peak in sharpness but not it's location. A big-pixel sensor camera (e.g., K-1) would have a broader sweet spot with many apertures essentially out-resolving the lens. A smaller-pixel sensor camera (e.g., KP or Q) would have a sharper peak with fewer if any f-stops out-resolving the lens.
I think you are focused on APSC vs. FF here which is fair given the topic of the original post. But my statement isn't limited to those formats. There are small sensor formats where the first f stop is already into diffraction so the peak performance is wide open. My point is made to illustrate that a given lens may have an optical peak at different places on different sensors if diffraction comes earlier on one vs. the other. This isn't as simple as knowing where the lens peaks - but where the lens peaks on a given sensor. But as @normhead pointed out - sometimes the loss of absolute sharpness isn't as important as the other factors. I have shot many macro shots past the point of diffraction trying to eek out a little more DOF for example.

05-07-2018, 10:40 AM   #24
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I think it is very telling that in DXOmark's somewhat outdated sensor tests that MF and FF fill the top 33 spots before the first APS-C:

Camera Database - DxOMark

In a 72 ppi, sRGB color space comparison, the difference is going to be minimal to insignificant as normhead and Jesse have shown us. But at 300-600 dpi, AbobeRGB color space, printed 13x19" or larger, the differences become more apparent, especially in higher contrast scenes, higher ISOs, etc.

As I've said before, ultimately the lens is going to be the biggest asset or liability to the image, but if all things are equal, size matters (yes, yes, with the understanding that the 'focal length is the focal length') not only in the sensor but also in the viewing of the screen or print and the viewer's distance from the media.
05-07-2018, 11:12 AM   #25
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QuoteOriginally posted by Alex645 Quote
I think it is very telling that in DXOmark's somewhat outdated sensor tests that MF and FF fill the top 33 spots before the first APS-C:

Camera Database - DxOMark

In a 72 ppi, sRGB color space comparison, the difference is going to be minimal to insignificant as normhead and Jesse have shown us. But at 300-600 dpi, AbobeRGB color space, printed 13x19" or larger, the differences become more apparent, especially in higher contrast scenes, higher ISOs, etc.

As I've said before, ultimately the lens is going to be the biggest asset or liability to the image, but if all things are equal, size matters (yes, yes, with the understanding that the 'focal length is the focal length') not only in the sensor but also in the viewing of the screen or print and the viewer's distance from the media.
Only past the point of oversampling. At 300 DPI, which is still a lot for most purposes, a 19 inch print needs 5700 pixels, so a K-1 and even a K-3 oversample the images. Any body K-3 or higher is an oversample of the required resolution. I've never seen evidence to suggest a higher degree of over sample leads to more resolution or abetter image especially at 100 ISO.

I have 16x20 prints of my window ice crystals shot with my K-3 and my K-1, and I've forgotten which image was taken with which camera and can't tell the difference. So, it is conceivable that at some point it makes a difference, but I'd prefer to here that from someone who has actual prints that show when that difference becomes apparent.

Without such references, and with concepts like an image that is larger is going to be viewed from further away if it's bigger I am reluctant to make such judgements.

Photography tends to be dependant on double and half type differences. A K-5 is 5000 pixels wide a K-1 is 7400 pixels wide. Folks will argue that makes a difference, yet on my biggest viewing surface. my 4k 55" TV, a K-1 and K-5 image are virtually identical. On a 4k TV which has become my favourite method of looking at large "prints" even a K-5 is an oversample.

So, in short, follow such logic at your own peril. You may not get what you think you are going to get. And I'm not going to believe it's true until I see some definitive proof, not pixel peeping, but evaluating the whole printed image. I already know it makes no difference on my 4k TV. And I also know it makes difference for the largest prints I do.

And with modern vector based enlarging software, enlarging an image can often clean up the mess left by too much resolution and the capture of irrelevant and messy looking detail.

Most of us don't care if there's a little more detail on dogs wisker. It amay be there, but the difference is not within the range of human perception. I don't examine prints with a loupe.

Of all the people who've claimed you'd see a better result at larger sizes no one has ever produced a print comparison to show that's true. The only person who tried, compared a K-5 to D800, and in blind test, the test participant couldn't makeup their mind which they preferred. That's the only evidence I have to date, and it doesn't point to a resolution increase of even 100% leading to increased enjoyment of a print.

I've waited over 5 years now for the counter point, and it simply hasn't been forthcoming. At some point (like 5 years ago for me) you have to decide it isn't there because no one has done it, leading us to suspect it can't be done. Yet people go on as if this were a proven fact.

What it is is commonly stated unproven assumption that through repetition has come to be accepted as fact, with absolutely no evidence beyond people saying its what "should" be true.

Last edited by normhead; 05-07-2018 at 11:28 AM.
05-07-2018, 11:56 AM - 1 Like   #26
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QuoteOriginally posted by normhead Quote
So, it is conceivable that at some point it makes a difference, but I'd prefer to here that from someone who has actual prints that show when that difference becomes apparent.
Without such references, and with concepts like an image that is larger is going to be viewed from further away if it's bigger I am reluctant to make such judgements.
And I'm not going to believe it's true until I see some definitive proof, not pixel peeping, but evaluating the whole printed image.
Most of us don't care if there's a little more detail on dogs wisker. It amay be there, but the difference is not within the range of human perception.
Of all the people who've claimed you'd see a better result at larger sizes no one has ever produced a print comparison to show that's true.
I've waited over 5 years now for the counter point, and it simply hasn't been forthcoming. At some point (like 5 years ago for me) you have to decide it isn't there because no one has done it, leading us to suspect it can't be done. Yet people go on as if this were a proven fact.
What it is is commonly stated unproven assumption that through repetition has come to be accepted as fact, with absolutely no evidence beyond people saying its what "should" be true.
If you're ever on Oahu, send me a PM and I'd love to meet up to show you my enlargements from 645, FF, APS-C, and even an iPhone. I'm not posting replies based on theory; it comes from observation and the theory is just one interpretation of the results. My shooting my prints and then downsizing for web viewing on a monitor is not going to prove much, as I've tried that and lose the details I can see in the prints. I've run tests printing 300 dpi and 600 dpi (large format 44" roll paper), and on first glance, they look the same; but they aren't and if I can get the detail on the dog's whiskers, it's better than no detail.

In this video with Christopher Burkett, at the 2:00 mark, he talks about the 8x10 transparency, good technique, combined with enormous Ilfochrome prints as creating a "super-realism"; something more than what the human eye would usually see or resolved at.


For the web, my iPhone does holds it's own until I want different focal lengths, various shutter speeds, manual focus control, etc, and then I agree with you that a DSLR APS-C is more than sufficient. In my age, I should be wearing glasses more often, and when I do, I'm reminded of the detail I'm missing without them. But it's somewhat offensive to state that someone posting a comment is an unproven assumption simply because you have not seen evidence.

Dewitt Jones is truly wise when he states, "it's not you'll believe it when you see it, but you'll see it when you believe it."
05-16-2018, 10:45 PM   #27
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I tried to read all this thread but couldn't keep up with all that was said 😕
Please help me out on a couple of issues.
#1: If you use a lens that has a max f-stop of f:2.8 on a aps-c it will not act the same as if it was used on a FF (exposure & DOF)
#1 A: Would it act about 1/2 stop slower than if it was mounted on a FF? (exposure)
#1 B: DOF would be similar to 3.5 on a FF? (so on a aps-c body you would need to have around f:2 to achieve the same bokeh as the f:2.8 on a FF)?

#2: If I use a light meter and it tells me to shoot @ 1/200 & f:4. Would I get the same exposure using the same lens mounted on the FF and then moved to the aps-c body (using the exact same setting)?

My understanding is when you use a lens on an aps-c body you gain in the focus length but lose in the aperture. Is this not true?

Thanks for you input 😀 but keep it simple for my little brain 😵😵😵😵😵
05-16-2018, 10:52 PM - 1 Like   #28
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QuoteOriginally posted by Photobill Quote
I tried to read all this thread but couldn't keep up with all that was said 😕
Please help me out on a couple of issues.
#1: If you use a lens that has a max f-stop of f:2.8 on a aps-c it will not act the same as if it was used on a FF (exposure & DOF)
#1 A: Would it act about 1/2 stop slower than if it was mounted on a FF? (exposure)
#1 B: DOF would be similar to 3.5 on a FF? (so on a aps-c body you would need to have around f:2 to achieve the same bokeh as the f:2.8 on a FF)?

#2: If I use a light meter and it tells me to shoot @ 1/200 & f:4. Would I get the same exposure using the same lens mounted on the FF and then moved to the aps-c body (using the exact same setting)?

My understanding is when you use a lens on an aps-c body you gain in the focus length but lose in the aperture. Is this not true?

Thanks for you input 😀 but keep it simple for my little brain 😵😵😵😵😵
Bill, there's a beginners article at The Crop Factor Unmasked - Articles and Tips | PentaxForums.com
05-17-2018, 05:09 AM - 1 Like   #29
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Bill exposure is exposure. There can be subtle differences in lens designs that have the same f stop (but different T stops) and cameras don't always rate their sensor iso precisely (Nikon!) But assuming those factors are the same the full frame lens set to the same exposure will give the same basic exposure on a crop body and a full frame. Also an equivalently fast crop lens will do likewise.

The advantage in low light that you see in full frame isn't based on a different exposure response - it is based on the inherently better performance of the sensor at a higher ISO which allows higher ido to be used with less noise.

Depth of field and equivalence get really contentious. But read the article linked in the previous post for more details.

Last edited by UncleVanya; 05-17-2018 at 09:54 AM.
05-17-2018, 09:30 AM   #30
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