FF vs. APS-C - Aperature Behaviour

[HDNitehawk]

I was recently in a forum and a member there mentioned that an aperature of a given lens behaves differently on different sensor sizes.


His example was based on the 85L f/1.4. The moment you putthis lenson an APS-C body the lens behaves like a 136mm f/2 lens. Is this correct (I understand the difference between FF and APS-C, it's the f/xx value that's got me wondering between the two)?


So confused!

It seems every time crop factor comes it gets more confusing by the time you get to the end of the thread than at the start.


But.....Check this out for yourself.


Go to the DOF calculator. Enter 100mm at F1.0 for both camera at 10 feet.


Note the DOF of both lenses. Then if change the F of the 7D to F1.6. At that point the DOF of both lenses at the same distance will be identical.


I think this was what that individual was referring to.


In that respect they will carry the same identical 1.6 to 1 ratio.


If you try and prove that ratio in other ways, like comparing a 160mm on a full frame to a 100mm on the crop, the DOF ratio is not there. Nor if you try 100' compared to 160', the results will not hold the ratio.


So the crop ratio is only true to the F stop and the field of view. Other factors will come in to play in the other situations and I would think those would be the dynamics of how the lens passes the light and the width of viewable light on the sensor.


Now if you put a 100mm lens that is a F1.0 lens (if there were such an animal) on your crop camera, it does not change the fact that it is a F1.0 lens.

[HDNitehawk]

[View:http://www.robgalbraith.com/public_files/Canon_Full-Frame_CMOS_White_Paper.pdf]











"With all these benefits, it’s only natural to wonder why all DSLR cameras aren’t full-frame. Ultimately, the issue is money. Research, development, manufacturing and distribution costs are all independent of camera size, so a smaller camera will not cost appreciably less than a larger one for any of these reasons. The end cost difference between small mirrors, mirror boxes, chassis and so forth, and larger ones is not that great. The difference is the sensor."


Interesting this is Canon's thinking. If it weren't for the cost difference all cameras might be full frame.


And I think this paper addresses the "Noise" argument as well.

[clemmb]

The per pixel noise is identical with identical pixel sizes, but as you have more pixels, the effect of the noise is lessened.
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Agree. I was not understanding your first post on this. We are in agreement.


Mark

[Kamelot]

I'll argue that we're both right about noise, because I think we were looking at it in different ways.


Both cameras have the same pixel size and bits per pixels, so the buckets aren't 5 and 10 litres, they're both the same. I wasn't arguing about the total light captured, but the total captured per mm, or per bucket. The same amount of water will be captured in the center buckets in each case, as they're the same size and depth. That's what makes me right.


Due the the extra buckets, you can downsample, and get the effect of less noise (Daniel had a whole big thread all about it), but at the original capture size, the noise is identical at the pixel level. Or due to the extra resolution, when printed, any noise will be rendered smaller, and thus less visible. That makes you (and DxO) right.

Yeah, maybe i wasn't reading your post carefuly. Maybe you were saying some truth []


I know that Daniel's thread about all pixel size and dependency of that. In previous post forgot to mention the key think. I already edited it.


And in my opinion, the pixel size doesn't matter if the overal pixel surface is larger.


It does'nt matter if you have 1,6 square metre and you will split it to the 10 smaller squares or to the 20 squares . It still will be the same 1,6 square metre surface. And if you will compare it to the only 1 square metre surface, does not matter, how large the squares on that 1 square metter will be. The overal surface capacity will be smaller. Bigger surface can collect more light, and the noise is smaller. That's what i wanted to express []

It all depends on how you're measuring the noise. The per pixel noise
is identical with identical pixel sizes, but as you have more pixels,
the effect of the noise is lessened.

Yes, i agree. And want to add.. like were said in that big thread, that you can not compare pixels one by one (if this
is larger - good, smaller - worse). One pixel does not do the job. The
picture comes from collection of pixels.

[DavidEccleston]

Yes, I muddied things up by bringing up pixel level arguments without saying why. By showing the noise is equal at the pixel level, I show that the noise advantage of FF is due to pixel size and/or the bonus pixels at the edge. Is has nothing to due with effective apertures, which was the whole point of my original post. The noise advantage is a separate argument. The effective aperture argument is all about DOF changes. Jon pointed out a nice benefit of FF, which had nothing to do with the original question, and I just wanted to point that out (and then defend my argument when everyone said I was wrong ).

[conropl]

It does'nt matter if you have 1,6 square metre and you will split it to the 10 smaller squares or to the 20 squares . It still will be the same 1,6 square metre surface. And if you will compare it to the only 1 square metre surface, does not matter, how large the squares on that 1 square metter will be. The overal surface capacity will be smaller. Bigger surface can collect more light, and the noise is smaller.
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I am not sure that is correct. Sorry, I may be getting a little off topic here, but there has been a lot of bucket analogies going on where just the surface area is considered. However, (keeping the analogy going) there are losses that happen when you start breaking up the information into successively smaller buckets. Lets assume your buckets are square and fit together tightly into a rectangular array... you still have all the added edges that exist and that goes up as you go from 10 buckets to 20 buckets in the same area. There are losses at the edges. So unless you improve the technology to reduce the losses around the edges, then the "noise" is going to go up.


Probably more important is the losses you get when converting light energy to electrical energy at the photo site. I do not claim an relevant expertise here, but it would seem reasonable to expect that as you reduce the size of the pixel, you also reduce the the light gathered at that pixel, and therefore reduce the electrical signal that you are trying to produce to transfer that information. I guess my point is, as you reduce the pixel size (and increase the number of pixels for the same area) you are reducing the electrical signal at each pixel- require more amplification and processing, and you would have more efficiency losses... so unless you have an increase in technology (pixel, electrically, and processing), then you will get more noise and losses.


So, to give you a little different perspective on the analogy: Let's say you have two bucket arrays, one with 10 buckets and one with 20 smaller buckets covering the same area. Now put a whole in the bottom of each, and add a tube to take that water to a point that will monitor the the water that drains from each bucket. Now the set of 10 buckets has less connections, less tubing, less losses due to leaks at the connections, and less friction losses in the tubing.Also, because the 20 bucket set has less water to look at, your monitoring equipment needs to get better to be able to measure the differences and account for the added losses.


There are many reasons for more pixels (e.g., cropping), butmore may not always be a good thing unless there is an upgrade in the technology thatis used to handle the detrimental effects.


Sorry this got a lot longer than I expected.


Pat

[Kamelot]

I see and of course understand your point conropl. And you are correct. But if we have 1 biger pixel and 4 smaller pixel, you can not say, that this one bigger will produce stronger signal with less noise. Because maybe that 4 smaller pixels together would produce 2 time stronger signal comparing with that 1 bigger pixel (if the smaller pixel number would be enough bigger).


The main misunderstanding comes from that we are trying to meausre noise level, but do not compare things equaly.


Because there is 3 varying things:

1. pixel size
2. sensor size
3. technology

If we would compare only one thing, leaving two others as constant, there will be less misunderstanding []

[HDNitehawk]

Because there is 3 varying things:

1. pixel size
2. sensor size
3. technology

When the Canon White Paper was written, the 1Ds II was canon's flagship with 16.7 megapixels. Now we have the 5D II at 21 megapixel meaning smaller denser pixels.


#3 matters more than 1 and 2. We know that 5D II will handle noise better.


#1 and #2 are only valid arguments if, you are applying the same technology to both.

[conropl]

But if we have 1 biger pixel and 4 smaller pixel, you can not say, that this one bigger will produce stronger signal with less noise. Because maybe that 4 smaller pixels together would produce 2 time stronger signal comparing with that 1 bigger pixel (if the smaller pixel number would be enough bigger).
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Given the same technology, each area is receiving the same light. So four pixels would have more edges which do not gather light the same, and there has to be some finite space between pixels that do not gather information. This all causes the need to make processing assumptions about what is happening at the edges. Therefore, given the same light energy, the larger pixel gathers more information with less processor interpolation required. And I also contend that when youconvert light energy into some signal, there are losses every time you have to do that. With 4 pixels compared one large one, it would seem you have four times the likelihood of having conversion and processing errors/losses.


I agree with HDNitehawk... technology change is the big equalizer. Comparing the 5DII and the 7D. The pixel density on the 5DII is less than the 7D. The 5DII may have more pixels, but they are spread out over an area 1.6 times bigger. So if you cut down the 5DII sensor to the same size as the 7D, you would only have 13.1 mega pixels compared to the 7D's 18 mega pixels. The 5DII has bigger pixels but less of them over the same area. The end result is a sensor that handles noise better IMO.

[conropl]

[View:http://www.robgalbraith.com/public_files/Canon_Full-Frame_CMOS_White_Paper.pdf]











"With all these benefits, it&rsquo;s only natural to wonder why all DSLR cameras aren&rsquo;t full-frame. Ultimately, the issue is money. Research, development, manufacturing and distribution costs are all independent of camera size, so a smaller camera will not cost appreciably less than a larger one for any of these reasons. The end cost difference between small mirrors, mirror boxes, chassis and so forth, and larger ones is not that great. The difference is the sensor."


Interesting this is Canon's thinking. If it weren't for the cost difference all cameras might be full frame.


And I think this paper addresses the "Noise" argument as well.






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HDNitehawk:


Nice paper... it explains a lot. Thank's for sharing.