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Going from full frame to APS-C

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I do wish that people would keep "brightness" or "light gathering" out of it.  It only leads to confusion.

 

Even if  a lens designed for a larger format is capable of transmitting more light (energy) in total due to its larger diameter, the amount of light projected per square surface unit will be exactly the same with the same aperture number, regardless of sensor format.

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Too bad for the so-called "equivalence" between 35/1.4 on APS-C and 50/2 on FF. Thank you for that.

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Too bad for the so-called "equivalence" between 35/1.4 on APS-C and 50/2 on FF. Thank you for that.

What Jaap said about light grasp and irradiance is completely accurate but says nothing about equivalence.

 

Equivalence does not claim that a 35mm 1.4 lens on APSC has the same irradiance as a 50mm f/2 on full frame for a given exposure. Rather, it claims that for a given shutter speed the depth of field is the same, the field of view is the same, and the the signal-to-noise ratio is the same.

 

Obviously, you need to set the gain higher on the full frame camera to match exposures since the irradiance levels are different. Irradiance (light per unit area per unit time) is determined by focal ratio alone. That’s WHY equivalence says the signal to noise ratio is the same—the full frame camera with a slower lens would need a higher ISO to reach the same exposure if you hold shutter speed constant.

 

I absolutely believe in equivalence, but it is often mis characterized. It does not claim that all formats produce identicalresults. For starters, that would be ignoring the fact that theee often aren’t “equivalent” lenses. Or the fact that wheee “equivalent” lenses exist, they are often bulky enough that you are giving up the advantages of a smaller format. Or that megapixel counts, and thus resolution, are generally higher with larger formats. It just speaks to field of view, depth of field, and signal-to-noise. Equivalence is not a “threat” to larger formats.

 

All that being said, the quality and resolution of everything from iPhone sensors to the latest Phase One backs is so good these days that there are lots of photographers who could make an APSC camera such as the CL their primary camera and never notice a drop off in technical image quality in their photographs.Seriously.

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I beg to differ but i seem to recall that we've discussed about this already. 35/1.4 on APS-C may be considered equivalent to 50/1.4 on FF but not to 50/2. Different beasts. When i need f/1.4 in dim light i take an f/1.4 lens be it a 50 on FF or a 35 on APS-C. YMMV.

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There are many articles about equivalence. Its a simple mathematical concept to compare sensor sizes. I can not understand why facts are not accepted. There are simple mathematical formulas behind. Nothing magic.

 

But the whole concept can be fully ignored when taking photographs with an APS-C cam. When you have lenses with f/1.4 on an APS-C lens then this is f/1.4. No doubt. Maybe you just calculate this f/1.4 (which represents a mathematical formula). 50mm/1.4 or 35mm/1.4. The result is different. It is a number in mm. Is this accepted at least?

Edited by Alex U.

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What Jaap said about light grasp and irradiance is completely accurate but says nothing about equivalence.

 

Equivalence does not claim that a 35mm 1.4 lens on APSC has the same irradiance as a 50mm f/2 on full frame for a given exposure. Rather, it claims that for a given shutter speed the depth of field is the same, the field of view is the same, and the the signal-to-noise ratio is the same.

 

Obviously, you need to set the gain higher on the full frame camera to match exposures since the irradiance levels are different. Irradiance (light per unit area per unit time) is determined by focal ratio alone. That’s WHY equivalence says the signal to noise ratio is the same—the full frame camera with a slower lens would need a higher ISO to reach the same exposure if you hold shutter speed constant.

 

I absolutely believe in equivalence, but it is often mis characterized. It does not claim that all formats produce identicalresults. For starters, that would be ignoring the fact that theee often aren’t “equivalent” lenses. Or the fact that wheee “equivalent” lenses exist, they are often bulky enough that you are giving up the advantages of a smaller format. Or that megapixel counts, and thus resolution, are generally higher with larger formats. It just speaks to field of view, depth of field, and signal-to-noise. Equivalence is not a “threat” to larger formats.

 

All that being said, the quality and resolution of everything from iPhone sensors to the latest Phase One backs is so good these days that there are lots of photographers who could make an APSC camera such as the CL their primary camera and never notice a drop off in technical image quality in their photographs.Seriously.

But you are basically introducing concepts like pixel count and pixel density here - without mentioning them. Starting from the fact that, given the same aperture, the light intensity, i.e. energy per square mm is the same; if you have the the same MP count on the sensor, the energy per sensel will be less, giving more noise. To have the sensor perform identically, you need to reduce the pixel count  on the smaller sensor. With changing sensor size the noise/resolution ratio shifts.

Basically a 24 MP APS-C sensor behaves like a crop of a 48 MP FF sensor.

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Gods, you all seem to want to make this as complicated as possible.

 

"Given that you're used to shooting with a Leica M and the three lenses 28, 35 and 50 mm, and usually shoot at f/8, to get the same FoV and DoF on the CL as any one of them just drop down a focal length (to 18, 24 and 35 mm) and open the lens to f/5.6."

 

That's really all you need to know in practice. The rest is easy to figure out by looking through the camera...

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I do wish that people would keep "brightness" or "light gathering" out of it.  It only leads to confusion.

 

 

 

Exactly!

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I do wish that people would keep "brightness" or "light gathering" out of it.  It only leads to confusion.

Exactly!

 

You said it

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But you are basically introducing concepts like pixel count and pixel density here - without mentioning them. Starting from the fact that, given the same aperture, the light intensity, i.e. energy per square mm is the same; if you have the the same MP count on the sensor, the energy per sensel will be less, giving more noise. To have the sensor perform identically, you need to reduce the pixel count on the smaller sensor. With changing sensor size the noise/resolution ratio shifts.

Basically a 24 MP APS-C sensor behaves like a crop of a 48 MP FF sensor.

I absolutely agree. That’s one reason why a faster lens on an APSC format camera is required to get the same signal to noise ratio as a slower, “equivalent” lens on full frame. Higher pixel density for the smaller chip equals worse SNR. A 24 megapixel crop sensor should, in fact, behave like a cropped 48 megapixel full frame because that’s what it is.

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I beg to differ but i seem to recall that we've discussed about this already. 35/1.4 on APS-C may be considered equivalent to 50/1.4 on FF but not to 50/2. Different beasts. When i need f/1.4 in dim light i take an f/1.4 lens be it a 50 on FF or a 35 on APS-C. YMMV.

Yes, I believe we have had this discussion before, And we continue to misunderstand each other. If you need 1.4 in dim light by all means use a fast lens. I’m not suggesting for a second that focal ratios change when you change formats. I’m suggesting—as Jaap pointed out—that noise characteristics change when pixel density increases with smaller chips. So your f/1.4 lens at, say, ISO 200 on a crop sensor camera will give you the same level of noise as an f/2 ISO 400 exposure on full frame. Isn’t f/1.4 ISO 200 the same as f/2 ISO 400? Same EV for a given shutter speed?

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I absolutely agree. That’s one reason why a faster lens on an APSC format camera is required to get the same signal to noise ratio as a slower, “equivalent” lens on full frame. Higher pixel density for the smaller chip equals worse SNR. A 24 megapixel crop sensor should, in fact, behave like a cropped 48 megapixel full frame because that’s what it is.

But, always assuming the same sensor architecture

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Yes, I believe we have had this discussion before, And we continue to misunderstand each other. If you need 1.4 in dim light by all means use a fast lens. I’m not suggesting for a second that focal ratios change when you change formats. I’m suggesting—as Jaap pointed out—that noise characteristics change when pixel density increases with smaller chips. So your f/1.4 lens at, say, ISO 200 on a crop sensor camera will give you the same level of noise as an f/2 ISO 400 exposure on full frame. Isn’t f/1.4 ISO 200 the same as f/2 ISO 400? Same EV for a given shutter speed?

 

Why taking examples at isos that low? Because differences are less visible then? None of my f/1.4 lenses at 3200 iso will give me the same rendering as an f/2 lens at 6400 iso, let alone when comparing 6400 to 12800 iso. And this on all my digital cameras including my cleaner Sony A7s mod. 

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6400 is pretty clean on the CL... Provided one exposes correctly.

Once again you are conflating aperture with sensor size. Not.

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Why taking examples at isos that low? Because differences are less visible then? None of my f/1.4 lenses at 3200 iso will give me the same rendering as an f/2 lens at 6400 iso, let alone when comparing 6400 to 12800 iso. And this on all my digital cameras including my cleaner Sony A7s mod. 

 

No particular reason.  It should work no matter the ISO (assuming, as Jaap pointed out, the architecture of the chips is the same).  

 

Why would an f/1.4 lens on an APS-C camera at ISO 3200 not give you the same result as an f/2 lens at ISO 6400 on full frame?  Are you saying the CL is cleaner at ISO 3200 than the A7S at ISO 6400?  Or the other way around?  

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Now we are into apples and oranges. Different senors, different designs. I suspect that the Sony sensor of the CL is technologically ahead of the A7S, which is a generation behind, at least in time.

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By way of an apology for those here who tried to help me to understand equivalency. Having now seen the realities of what the image looks like when you mount a FF 50mm lens on an APSC camera instead of the TL35mm lens I can see I was barking up the wrong tree backwards. Apologies if I barked a little loudly. I've got it now...I think.

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[...] Why would an f/1.4 lens on an APS-C camera at ISO 3200 not give you the same result as an f/2 lens at ISO 6400 on full frame?  Are you saying the CL is cleaner at ISO 3200 than the A7S at ISO 6400?  Or the other way around?  

 

I can add very little to the example i took when we discussed about this ( http://www.l-camera-forum.com/topic/281150-apeture-affecte-from-fulframe-too-apsc/page-5?do=findComment&comment=3450949 ). In my modest practice at least, the so-called equivalence between 35/1.4 on APS-C and 50/2 on FF is only relevant for DoF. 

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