IMO that's not true. They need to be compared by each person in the way they intend to use them.
From what I've read the autofocus of the D5 and D500 has advanced significantly as well.
I find comparison of the DX against the FX in DX Crop Mode is helpful:
I'm having a little difficulty making sense of your sentence. First, we're talking about shot noise, which is not caused by the sensor. It's caused by the random nature of photons, and the SSNR (Signal to Shot Noise Ratio) is proportional to the square root of the number of photons you collect. The number of photons you collect is determined by the size of the lens objective; it doesn't matter whether the lens sends those photons to a DX sensor or an FX sensor or an M 4/3 sensor or a 1/3" video sensor.
I certainly wouldn't go as far as saying "almost all cases." It's very common in the sports and wildlife photography disciplines: DX + 135 f/2 = FX + 200 f/2.8, DX + 200 f/2 = FX + 300 f/2.8, DX + 400 f/2.8 = FX + 600 f/4, DX + 600 f/4 = FX + 800 f/5.6, etc. That's not even considering TC's.
This generally occurs with shorter lenses. For example, there's no DX setup equivalent to an FX camera with an f/1.4 lens unless you could find a focal-reducer for the DX camera. And there are not many f/2 zooms yet (I'm sure Sigma will continue addressing that).
Now this one really doesn't make sense. I could save thousands of dollars if the D500 could substitute for the D5, taking the same photos. For my purposes, the main reason it doesn't, is the lower mechanical durability of the D500; the lack of an equivalent to the 80-400/5.6 for DX is also a drawback, but it could do well with just the 70-200/2.8. There's a good chance I'll add a D500 as a backup.
For many of us, those two comparisons are actually the same.
Hmm. If I am taking a picture of a rock in a field, and I change from FX to DX crop, the rock changes size? No, you didn't mean that. Perhaps you are using "subject" in some technically correct form with which I am unfamiliar. Given the widespread misuse of "exposure" I have to allow for such cases, I am well aware that your technical knowledge is way ahead of mine. But I am not arguing facts (I think we agree on them), here, but rather, frames of reference.
No, the lens receives photons from the same size radiator, and casts the same size image circle. The sensor receives the same number of photons. But it throws away 5/9 of them because its effective area has been reduced. What changed (on the input side - obviously the image changed)? The active sensor area, that's all. So it is the sensor area which affected the noise.
That's right. When you take the same photo you get the same shot noise. And to take the very same photo on a smaller sensor, you need to use a longer focal length, a different ISO, a smaller f-number (but the same aperture diameter), a different sensel pitch (but the same pixel count) and a different lens sharpness (to deal with the different sensel pitch). That seems like a lot of bother, and not something that can commonly be done. What is commonly done is using the same FX lens on both FX and DX bodies,. Another thing that is not uncommon is cropping.
Why? Do most FX users take only the same photos as DX users? Perhaps at long focal lengths. But not in the focal ranges most commonly used. There is a shortage of equivalent DX lenses for common FX lenses. And being constrained WRT both DoF and shutter speed is the exception, not the rule, IME.
... or identical ISO. it is not a lie. It is a viewpoint that comes from a world where from 200mm on down, there isn't an equivalent lens for DX that can make the same photo as common FX lenses. FX lenses are used on both FX and DX bodies. And on the DX body that FX lens is making a noisier picture at the same focal length and aperture number. When the only equipment change is the senor's size, it is quite reasonable to say that it is the senor size that is behind the difference in noise.
Larger lens + same sensor gives you an advantage, but not the same photo. Larger sensor + same lens give you an advantage, but not the same photo, IDK why you want to exclude the one case but not the other.
Well, if you've been at the long end of the focal range, it's easy to see why you have your viewpoint.
The Lord gives out a constant amount of wisdom, but people differ in wisdom receptor size.
In my statement above, "subject" includes everything that appears in the image, whether it's of artistic interest or not. You were saying that the SSNR for the entire image would decrease when simply changing from FX to DX crop; I was only pointing out that the change to SSNR can be equivalently viewed as caused by decreasing the area of everything in object space which contributes to the image.
shorter focal length
same entrance pupil (or lens objective) diameter
I would say it is common. Sports and wildlife photography isn't "uncommon" and in the focal length range under 200mm, new DX lens models are appearing such as the Sigma 18-35 f/1.8 and 50-100 f/1.8 which will make it even more common.
Doesn't work for me, and I wouldn't even want to count the number of threads I've seen from users changing up from DX to FX, who want advice on what new lenses to buy.
Because it was a primary constraint from my leading post.
It can be the same photo: 70-200 f/2.8 at 200mm, vs. 200 f/2.
Hence my next sentence, which you decided not to include in the quote.
The input change is the change in sensor area. This other equivalent view is a change in output.
Yup.
Doh!
Now you are being picky (but correct). If you want to explain the importance of the distinction to practical photographic decisions, I'm all ears.
We appear to have different ideas of what constitutes "common". I'm going by unit sales of lens (including in kits) where uncommon means < 10%.
Hence your outlook. But many people who use dSLRs do this.
Sure. Because they only have DX lenses, and want to use all of the FX sensor.
Which was a reply to my post, which imposed no such constraint.
? When it is the same photo there is no advantage.
That's great.
One should normally be shooting at base ISO, and I am unaware of DX cameras with lower base ISO than FX. Now when the greatest exposure you are willing to get, given constraints from max aperture and motion blur, gives less than desired brightness at base ISO then one can consider differing ISO on different sensor sizes. Of course, when DoF and shutter are both constrained then you get the same image, and the larger sensor has no advantage.
I think of object space as the input and image space as the output, but it's not strictly necessary as rays follow the same paths in either direction.
Sometimes, yes - but not always.
Correct. Your post specified no constraints - and that is precisely the problem. Without them, your statement that the D500 will have more shot noise than the D700 due to its smaller sensor is not consistently true.
You cannot be serious! It would mean having a true ISO-less camera (there are few) and adjusting every underexposed image in post.
So we agree.
See how much effort could have been spared if your first post had included constraints?
I am not sure about that. If that's the case, D810's picture with higher mega-pixel downsized to the same size of D610 lower mega-pixel level, the noise should be less instead of more right?
Correct.
As I said earlier, a different conceptual framework.
OK
OK, however, your first posts proposed constraints that are only applicable to a minority of shooting situations: same photo. When one restricts the larger sensor to the shooting envelope of the smaller sensor, then it will have no shot noise advantage. But some people buy larger sensor cameras to take advantage of their larger shooting envelope.
OK, I'll buy that. Once it becomes clear that one is having a discussion about equivalence, one should specify constraints. What I am less convinced of is that one needs to specify these constraints in a discussion that has not yet turned too technical.
WIth a non-ISO-less camera, under what conditions would you prefer to shoot at 1/500, f/4, ISO 400, rather than 1/125, f/4, ISO 100? (Assume motion blur is not a consideration, but DoF is.)
I seem to remember saying we agreed on the facts a couple of post ago.
Or how much we could have saved if your first posts had discussed situations under which sensor size does and does not make a difference, rather than unilaterally imposing one set of constraints which require a change of equipment in addition to the sensor?
You wrote, "Since the D500 has a smaller sensor than the D700, it will have more shot noise."
Those assumptions are almost never relevant to my photography, so I have no comment. I can't recall the last time I used ISO 100, or even ISO 200, for anything other than sensor testing.
Since my constraints were stated, it should be trivial for the reader to deduce whether or not the information I offered is germane to their photography. When constraints are not stated, it is somewhat less trivial.
Yes.
Your thinking is correct.
