>>> Does this make sense? > >No, it does not. Not according to the physics as I understand >it. > >A sensor's noise is best considered in terms of the amount of >noise per square millimeter of sensor. No matter how you >slice up each millimeter, the noise is essentially the same. >In other words, doubling or halving the number of pixels per >millimeter will not change the noise in each millimeter of >sensor.
If this is true, then pixel density on the chip is a non factor. Correct?
>Regardless if you use the TC or not, you end up with the same >noise, especially in a very high ISO situation like you have >here.
I agree. What you DO end up with is less light.
>When you take off the TC, you get to increase exposure by one >stop, and that is the obvious benefit to doing so.
>What is somewhat hidden under the covers is that by shrinking >the image by 1 stop of focal length, you are increasing the >noise when you have to stretch those square millimeters of >pixels more in the final output.
I am confused by this statement. Could you explain what you mean by "shrinking the images by one stop"? I am assuming you mean that as we decrease the focal length (in my presented case from ~420-300mm, we must then increase the final image by the same amount thus exacerbating the noise problem. If this is what you mean, then yes I agree.
>You have a D800. If you shoot a properly exposed ISO 6400 >image and then display or print it at some reasonable output >size I suspect it probably looks pretty good. Even if it has >some challenging tones in it, like those OOF blurs that can >look so ugly in a lesser (older) camera.
This is correct. As we are starting with a LOT more information, as we shrink the image, the noise shrinks proportionately. If viewing at 100% this advantage is lost.
>Now if you look at that image at 100% pixels I suspect it >looks pretty ugly. At least that is the comment I have heard >a number of times from "pixel peepers" who do the >same.
>You are doing the same thing when you drop the TC and go with >DX. The image size on each sensor, with the same lens and >focal length, is the same size and it contains the exact same >amount of noise.
Disagree. I get less noise because I've gained a stop of exposure.
>When you drop the TC and go with higher >density DX, you get the same pixels across your cropped final >output
Also disagree. This ONLY holds if the sensors are the same pixel density. This would be true if we were talking about a D3s vs A D300. But in the case of a D400, D7000, etc., this would NOT be true.
>The result is a net push, or it should be. If it is not, then >all the physics behind sensors, and the basic theory of >"unpredictable photons" (shot noise) needs to be >rethought.
I don't think it's an issue of physics so much as you are considering certain things as constants that are NOT constants. They are variables.
>Here is another way to look at it. Your 300/2.8 has a front >element of 107mm diameter. If you calculate the area of that >element that is called the "light gathering power" >of the lens.
>No matter what you do with that lens, no matter how you >stretch the effective image across the sensor with TC's, and >no matter how many pixels you pack into that sensor, the same >number of photons hit the sensor across your final cropped >subject frame.
>The theory of imaging noise says that while a certain number >of photons *should* hit each sensor well (pixel), the actual >number will vary, and that is shot noise. It is a statistical >game where the more photons you drop onto that pixel, the more >consistent the actual measured result (less noise).
>The key here is that the same is true if you look at the >amount of light that hits the sensor per square millimeter, or >any unit of measure you prefer.
I also agree with this.
>In the final analysis, if all else is equal between the DX and >FX sensor
And this is where the wheels fall off the wagon. All else is NOT equal. I am not dealing in theory here. I am dealing in real world cameras that I have in my possession.
>(they have the same noise per square millimeter and >they will if they were designed around the same time)
Correct, but nothing in our scenario holds to this constant. The only way I cam get the real world equivalent of this is if I consider a D3 and a D300. The D7000 is a generation newer, and the D400 may be another generation beyond that.
>there is >one and only one way to reduce noise in the case where you >have a fixed size subject and a fixed working distance: make >the front element of the lens bigger.
Disagree here as well. The performance of the lens could also be increased. That would not show as large a gain as making the front element larger.
The other issue here, and I touched on it earlier, is that what you are saying is that pixel density does not have a bearing on sensor performance for any given generation of sensor technology. And I believe that to be untrue. Sadly, there is not an easy, empirical way to test this as manufacturers tend not to produce the same sized sensor with varying densities in the same generation of technology. I may be wrong about this, but if you have strong evidence to the contrary, I'd love to see it.
>And it doesn't matter what focal length lens you start with, >or end with after adding or subtracting TC's. The amount of >light across your intended final crop that hits that sensor is >the only thing that matters, and that is controlled purely by >the size of the front element.
Again, assuming everything else in the system is constant. And it is not.
>When it comes to noise, there is simply no free lunch. Lenses >more or less cost so much per square inch of front element, >and they weigh so much per square inch of front element. And >those square inches of front element control the noise level.
>All the above is why I previously said that I am "old >school" and that I do not believe you can scale up >sensors indefinitely and transparently trade focal length for >pixel density. And why I have trouble with your idea that the >Pros are all going to small lenses and DX cameras.
The pros aren't all going to small lenses and DX cameras. The pros were forced AWAY from big lenses and DX cameras. To compensate, they went to even bigger lenses or took a hit in aperture and put on TCs. The first two professional generations of Nikon's cameras were DX. It wasn't until the D3 that this changed, and pros were left with the choice of going with the D3 and losing effective focal length or moving to the D300 and keeping what they were used to. Of course, at the expense of ISO performance compared to the larger sensor. Now that pros have the choice of DX, with the sensor performance of the former D700/D3 or very nearly so, there is a lot less pressure to stay full frame. On the other side of the aisle, the Canon folks are just beginning to go through this. As their pro cameras have been a 1.3 crop and with the 1Dx are finally going full frame. And the forums are full of people talking about how to cope with that much as we saw with the change from the D2x to the D3.
>You have, in different replies here, suggested FX does and >doesn't have excess high ISO performance, depending on the >context and shooting situation, which makes it hard for me to >keep up with a moving target . But once you show me a 3 >stop underexposed image as your best way to cope with a real >world situation, I gotcha!
My D3s has the best ISO performance of any camera I own. The D800 has the same sized sensor, and uses exactly the same glass. It has a sensor that is at least 1, if not two generations further along. Yet it's ISO performance is not as good. I am left to conclude that the pixel density plays a significant role.
>You can certainly change the FOV via high density DX to >deceive yourself into thinking you have a "longer focal >length" and if your long lens technique is beyond >reproach you can (in theory, avoiding diffraction issues as >you generally can when shooting wide open) transparently trade >pixel density for focal length and get equivalent resolution.
And this is the game I am playing. Not only this game, but the game of increased aperture because I get to shoot at F2.8 instead of F4.
>There is sort of a free lunch here, but only in regard to >resolution in terms of pixels across the subject.
And that... is enough.
>But there is no free lunch when it comes to noise. Noise is >solely a function of your front element size, and nothing else > .
Ok, if you insist.
>The above assumes all else equal, that the sensors are >identical in terms of performance per square millimeter.
Which we know they are not in the examples under discussion.
>But consider that in a reply elsewhere here today you >suggested that FX is near ideal but DX still has some room to >improve. If that is the case, then you are also suggesting >that the DX/FX trade is even worse than the push I suggest >above because the DX sensor inherently does not perform as >well as FX on a per square millimeter basis - which is how the >"ideal performance" is computed.
True. And there is a balance point between the advantage of FOV across a more dense sensor (16MP/24MP DX) versus the less ideal performance of that chip. I know from my own use, that even as outputs are equalized, the D3s outperforms my D7000 in ISO performance. What is not yet know, is if the D400 improves upon the performance of the D7000, equals it, or performs less well. If it performs equally, then the increased pixel density should give an advantage if we are still doing significant reductions for final delivery. Much the same as my D800 vs my D3s. If the performance of the D400 is worse than the D7000, then we will have to see how much worse, and if the resolution increase can balance the performance loss to some degree.