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FORUMS General Gear Talk Changing Camera Brands 
Thread started 07 Apr 2019 (Sunday) 18:51
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I just switched to Fuji

 
Two ­ Hot ­ Shoes
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Apr 19, 2019 19:27 |  #76

cug wrote in post #18847678 (external link)
Yep. That's forums (and humanity in general).

It's the same thing as people saying "f/2.8 is f/2.8 and it let's in the same amount of light no matter the sensor size". That's like saying a full two seater car transports as many people as a full four seater, just because every available seat has exactly the same number of people in it.

But but but…
My 18-55 T/2.9 let’s in the exact same amount of light as my 50-135 T/2.9 whether on X, A or MFT.


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Apr 19, 2019 22:10 as a reply to  @ Two Hot Shoes's post |  #77

Argl ... where's the filter function when you need it ...




  
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Apr 20, 2019 02:16 |  #78

Just behind your eyes


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Apr 20, 2019 14:27 as a reply to  @ cug's post |  #79

My mind is open to your reasoning and understanding on this; "f/2.8 is f/2.8 and it let's in the same amount of light no matter the sensor size"

Could you elaborate...


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Apr 20, 2019 19:29 as a reply to  @ Two Hot Shoes's post |  #80

Simple: a lens properly illuminating an APS-C sized sensor puts the same amount of photons per square millimeter but about 2.3x less overall light than an f/2.8 lens that illuminates a FF sensor. Exposure is the same per square millimeter but the total amount of light for the (different sized) sensor is different. That's why the whole "equivalence equation" is more complex than just comparing one piece of the whole system.

If you want to understand how to create the overall "same" picture, you need to:

- Account for focal length equivalence
- Amount of total light and size of entrance pupil

This means a 33/1.3 on a 1.5x crop APS-C sensor puts the same amount of light on the overall sensor as a 50mm f/2 on FF would. Now, given that the amount of light per square millimeter is different on these lenses at max aperture, we need to adjust the "gain", meaning selecting a lower ISO value for the APS-C sensor. If we picked ISO 200 on FF, we'd need to use ISO 89 on APS-C.

At this point we basically have equivalence - in photons per sensor cell (if we go with same pixel counts on both) as well as in DoF rendering. The problem now becomes when the APS-C (or even smaller sensors) can't go to very low native ISO values, because their buffers overflow. It's interesting that it's actually harder to achieve equivalency with low ISO values, which also explains why a larger sensor with larger photo cells can achieve higher dynamic range at base ISO. At higher ISO values read out noise becomes a factor, that's where smaller photo sites actually help, plus the effect that if you have more pixels, de-noise is more efficient.

Now, what that overall means is that you can typically use one stop smaller lenses on a FF sensor compared to the APS-C sized sensor and achieve the same overall sensor illumination (total amount of photons recorded by the respective sensor). That's why comparing a f/2.8 lens on for example a Sony A7 III with a f/2.8 lens on a Fuji X-H1 (I picked the older camera only to account for same pixel count) is incorrect as you're ignoring the more than double amount of photons let in by the FF lens to the FF sensor – which you don't need if you want the same overall sensor readout. It's perfectly fine to use a f/4 lens on the A7 III.

Therefore, the whole argument for APS-C lenses being so much smaller for the same f-stop, while technically correct, is not an argument for the same illumination of the sensor and therefore not an argument if you want to actually use a camera with that lens. The factors of f-stop, entrance pupil, sensor size, ISO (gain) defines the whole system. Ignoring one when we talk about different system just shows ignorance, nothing else.

Now, whether this matters in the real world is a different question. I have a FF system (EOS R) and an APS-C system here (Fuji X). Both have their respective places in my kit, but at least I understand the actual differences and where they come and when I have an advantage using one or the other or why APS-C lenses at same aperture can be smaller than the ones on FF. It plain is because the sensor is smaller and they let in less than half the light.

That's why I said: saying f/2.8 on APS-C is the same as f/2.8 on FF is the same as saying a two seater car is the same as a four seater car, since every car has exactly one person per seat. The issue is that the four seater still transports twice as many people, but this is happily ignored in the photo world. And don't get me wrong: I'm perfectly fine if people say "it's irrelevant for me, I never need more than two people in the car" – nobody can ever say it's not, because that part is personal. What I'm not fine with is people saying "It's irrelevant for me therefore it has to be irrelevant for you" or "I ignore part of the system and just quote a fact out of context and still expect it to be the only defining factor".




  
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bobbyz
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Apr 20, 2019 23:08 |  #81

Now, whether this matters in the real world is a different question.

Sorry I didn't read everything. I am happy with my little cropper and bigger cropper. I don't need FF.:)


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Apr 20, 2019 23:56 |  #82

cug wrote in post #18848855 (external link)
Simple: a lens properly illuminating an APS-C sized sensor puts the same amount of photons per square millimeter but about 2.3x less overall light than an f/2.8 lens that illuminates a FF sensor. Exposure is the same per square millimeter but the total amount of light for the (different sized) sensor is different. That's why the whole "equivalence equation" is more complex than just comparing one piece of the whole system.

If you want to understand how to create the overall "same" picture, you need to:

- Account for focal length equivalence
- Amount of total light and size of entrance pupil

This means a 33/1.3 on a 1.5x crop APS-C sensor puts the same amount of light on the overall sensor as a 50mm f/2 on FF would. Now, given that the amount of light per square millimeter is different on these lenses at max aperture, we need to adjust the "gain", meaning selecting a lower ISO value for the APS-C sensor. If we picked ISO 200 on FF, we'd need to use ISO 89 on APS-C.

At this point we basically have equivalence - in photons per sensor cell (if we go with same pixel counts on both) as well as in DoF rendering. The problem now becomes when the APS-C (or even smaller sensors) can't go to very low native ISO values, because their buffers overflow. It's interesting that it's actually harder to achieve equivalency with low ISO values, which also explains why a larger sensor with larger photo cells can achieve higher dynamic range at base ISO. At higher ISO values read out noise becomes a factor, that's where smaller photo sites actually help, plus the effect that if you have more pixels, de-noise is more efficient.

Now, what that overall means is that you can typically use one stop smaller lenses on a FF sensor compared to the APS-C sized sensor and achieve the same overall sensor illumination (total amount of photons recorded by the respective sensor). That's why comparing a f/2.8 lens on for example a Sony A7 III with a f/2.8 lens on a Fuji X-H1 (I picked the older camera only to account for same pixel count) is incorrect as you're ignoring the more than double amount of photons let in by the FF lens to the FF sensor – which you don't need if you want the same overall sensor readout. It's perfectly fine to use a f/4 lens on the A7 III.

Therefore, the whole argument for APS-C lenses being so much smaller for the same f-stop, while technically correct, is not an argument for the same illumination of the sensor and therefore not an argument if you want to actually use a camera with that lens. The factors of f-stop, entrance pupil, sensor size, ISO (gain) defines the whole system. Ignoring one when we talk about different system just shows ignorance, nothing else.

Now, whether this matters in the real world is a different question. I have a FF system (EOS R) and an APS-C system here (Fuji X). Both have their respective places in my kit, but at least I understand the actual differences and where they come and when I have an advantage using one or the other or why APS-C lenses at same aperture can be smaller than the ones on FF. It plain is because the sensor is smaller and they let in less than half the light.

That's why I said: saying f/2.8 on APS-C is the same as f/2.8 on FF is the same as saying a two seater car is the same as a four seater car, since every car has exactly one person per seat. The issue is that the four seater still transports twice as many people, but this is happily ignored in the photo world. And don't get me wrong: I'm perfectly fine if people say "it's irrelevant for me, I never need more than two people in the car" – nobody can ever say it's not, because that part is personal. What I'm not fine with is people saying "It's irrelevant for me therefore it has to be irrelevant for you" or "I ignore part of the system and just quote a fact out of context and still expect it to be the only defining factor".

I get what you're saying and I've read this before, but it also seems irrelevant... it has absolutely no effect on how you adjust for exposure.

An f2 lens on a 135mm sensor will expose exactly the same as an f2 lens on an APS-C sensor... so why even fret about it? I get that technically there is more light going through an FF lens to cover that larger image circle, but if that light is straight up not needed for the APS-C sensor, isn't it a pointless consideration? If you were to compare that f4 FF lens to an f2.8 lens on APS-C then the APS-C lens would expose the image a full stop brighter, even if they technically transmit the same amount of light.

I guess I'm having trouble understanding your point. Hopefully I'm still worthy of a response and you don't just view me as a "moron", I'm genuinely curious :lol:

I can certainly understand/appreciate the argument in terms of how the crop factor effects DOF and FOV, but the argument about light transmission doesn't really seem to matter in any practical sense unless I'm missing something.


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Post edited 6 months ago by Two Hot Shoes. (3 edits in all)
     
Apr 21, 2019 04:17 |  #83

I always find this interesting as it is simple but a concept that seems difficult probably due to the internet and the many 'experts' who post their opinions on it. My understanding is:

Lenses: a lens will always transmit the same light no matter what sensor size you put behind it (assuming it's mountable correctly). If I put something like a Sigma 85/1.4 Art lens on a EOS R or an D500 or a X1D, all the settings should be more or less the same [Should be the same but there are other things that go into making the image with a digital camera]. So if the transmission value of that lens is, say, T/1.8. then that is the same no matter what the sensor size is. Of course there is the whole vignette thing also, wide open there is darkening in the corners on a 135mm and 44x33 sensor.The lens projection is not full covering those sensors but the exposure is the same. Now let's say we mounted something like a Zeiss super prime (that cover the 65mm LF sensor size so really big image circle) that has the same t-stop of 1.8. No more darkening in the corners, yet the same settings on each camera for the given exposure. Sensor size is irrelevant when talking about light transmission in lenses.

F stops are the physical relation of focal length to aperture, so a 24mm F/2.8 and a 300mm f/2.8 have very different size apertures at f/2.8 [almost 100mm wider] yet let in the same amounts of light, more or less.

Sensor size: as mentioned above the amount of light is constant from any given lens. It projects an image circle, so as long as the sensor is within that it will read the light. If I were to tape over part of my 135mm camera sensor so as to make it the same as the crop, the same camera/lens settings will give the same exposure regardless of the taping of the sensor. Kinda like putting a 6x7 film back on a 4x5 view camera, smaller area but same settings to expose the film, as the light intensity is the same from the lens no matter what size film you have in there. It records the portion that covers it. Well the 'pixels' that cover the sensor record the light & their size does matter with reference to the strength of the signal. Bigger pixel pitch = cleaner images, given that the rest of the process chain is the same that is. But that has nothing to do with how big or small a sensor is.

There is no maths or equivalent needed with light transmission of a lens once correctly mounted. F/2.8 is always F/2.8 as it's the physical ratio, T/2.8 is also always T/2.8 as it the measured transmission through the lens. It's not that hard a concept but there is so much incorrect information on the net about it I can see why it get to be complicated.


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Apr 21, 2019 07:36 as a reply to  @ Two Hot Shoes's post |  #84

Actually, there is math involved. You are ignoring something:

"Sensor size: as mentioned above the amount of light is constant from any given lens"

This is correct, the problem is how much you "catch". The exposure at a fixed area (let's say the center) is the same. The amount of photons recorded via the sensor is vastly different on a larger sensor. A FF sized sensor has an area of 864 square millimeter, an APS-C (1.5x) sensor has an area of 370 square millimeter. Given that each square millimeter is getting the same illumination intensity when using the same settings, the larger sensor collects 864 / 370 = 2.34 times the amount of light. That's why larger sensors deliver a "cleaner" image with less noise.

So, again it does not only matter how much light is passing through a lens, it also matters how much of it you (can) collect.




  
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cug
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Apr 21, 2019 07:43 |  #85

EverydayGetaway wrote in post #18848965 (external link)
An f2 lens on a 135mm sensor will expose exactly the same as an f2 lens on an APS-C sensor... so why even fret about it? I get that technically there is more light going through an FF lens to cover that larger image circle, but if that light is straight up not needed for the APS-C sensor, isn't it a pointless consideration?

It isn't because the light collected directly correlates to the signal to noise ratio. That's the reason, why larger sensors have a cleaner image at the same exposure settings (until read out noise kicks in). See my post above.

So, if you can ignore the slightly higher noise in the end result, and most of us can nowadays, you can deem this a pointless comparison. Unless, of course, you also want/need the other effects of a larger sensor: the difference in "circle of confusion" aka the difference in depth of field the different relations produce.

Therefore, while in practicality often not or only minimally relevant, different sensor sizes and the resulting effects on the image exist and should be understood before considered pointless.

Again, if you compare, please compare ALL aspects of the system, not isolated pieces – because the arguments made are for or against said systems. Not the isolated piece of values set on a camera. The resulting recording also counts.




  
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Apr 21, 2019 09:30 |  #86

I think this breaks it down pretty thoroughly...
https://www.cambridgei​ncolour.com …al-camera-sensor-size.htm (external link)

The advantages of the APSC sensor in size and weight trump (sorry) any advantages of the FF sensor.
I personally see no reason to ever go back to that large collection of heavy gear I used to lug around.

If I wanted the best, and the shot NEEDED the best, I'd go rent something larger.
And for ME '...I never need more than two people in the car'. YMMV


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Post edited 6 months ago by Two Hot Shoes. (4 edits in all)
     
Apr 21, 2019 10:48 |  #87

cug wrote in post #18849094 (external link)
Actually, there is math involved. You are ignoring something:

"Sensor size: as mentioned above the amount of light is constant from any given lens"

This is correct, the problem is how much you "catch". The exposure at a fixed area (let's say the center) is the same. The amount of photons recorded via the sensor is vastly different on a larger sensor. A FF sized sensor has an area of 864 square millimeter, an APS-C (1.5x) sensor has an area of 370 square millimeter. Given that each square millimeter is getting the same illumination intensity when using the same settings, the larger sensor collects 864 / 370 = 2.34 times the amount of light. That's why larger sensors deliver a "cleaner" image with less noise.

So, again it does not only matter how much light is passing through a lens, it also matters how much of it you (can) collect.

Yes and no, but I do see why a lot of people think that.

And that's not why a larger sensor delivers a cleaner image, it has little to do with how much area a sensor has and so much more to do with how much area each of the photo sites have. Go cover part of your sensor [reducing the available area to the light] and see if you suddenly have an under exposed image, I'm guessing you already know the answer to that but perhaps it's needed to be seen first hand. Like I said earlier I can see why so many people have a problem with this although it is a very basic idea.

Think about the Sony 12mp A7s and the 42mp A7r and how those are at producing high ISO images. Same size sensor but different sized photo sites, 8.40 & 4.8 microns respectively. If you think of the sensor as being a box containing lots of little light gathering disks or squares, a box measuring 24mm X 36mm. It's not the quantity of the disks in the box that matters [for cleaner images] it's the individual size of those disks. So yes and no on the size difference as you state above.


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Apr 21, 2019 12:25 |  #88

Two Hot Shoes wrote in post #18849152 (external link)
And that's not why a larger sensor delivers a cleaner image, it has little to do with how much area a sensor has and so much more to do with how much area each of the photo sites have.

Did you actually read my post? It doesn't look like it. I explicitly pointed out two cameras with same sensor pixel counts and different sensor sites. That's the easiest to understand.

Two Hot Shoes wrote in post #18849152 (external link)
Go cover part of your sensor [reducing the available area to the light] and see if you suddenly have an under exposed image,

That makes no sense even with your own argument. The parts that are uncovered get exactly the same light as before. You basically just crop.




  
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Apr 21, 2019 12:28 |  #89

EverydayGetaway wrote in post #18848965 (external link)
I guess I'm having trouble understanding your point. Hopefully I'm still worthy of a response and you don't just view me as a "moron", I'm genuinely curious :lol:

I can certainly understand/appreciate the argument in terms of how the crop factor effects DOF and FOV, but the argument about light transmission doesn't really seem to matter in any practical sense unless I'm missing something.

Same here. FF has bigger sensor, that's why you need bigger lens as you need to have bigger diameter for same aperture. Light per unit area is same, that's why same aperture.


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Apr 21, 2019 12:33 |  #90

cug wrote in post #18849094 (external link)
This is correct, the problem is how much you "catch". The exposure at a fixed area (let's say the center) is the same. The amount of photons recorded via the sensor is vastly different on a larger sensor. A FF sized sensor has an area of 864 square millimeter, an APS-C (1.5x) sensor has an area of 370 square millimeter. Given that each square millimeter is getting the same illumination intensity when using the same settings, the larger sensor collects 864 / 370 = 2.34 times the amount of light.

Same light is passing through because both FF and APS-C lenses have same aperture. FF needs bigger lens for same aperture to cover bigger area of sensor.

That's why larger sensors deliver a "cleaner" image with less noise.

At pixel level for same technology in APS-C, FF or even MF, no pixel level have same noise, no cleaner imager. Wait when GFX100 MP comes out. It is same sensor at XT-3, basically 4 of XT-3 sensor stitched together.

So, again it does not only matter how much light is passing through a lens, it also matters how much of it you (can) collect.

You collect same light per unit area, pixels whatever. It is for bigger sensor you need to collect light for more area, so for that you need bigger lens. Simple. No math needed.:)


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I just switched to Fuji
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