Lenses focal length

[Frank Fremerey]

The D600 counts 3 times as many photons per picture than the D3 in the same situation.

She has twice as many pixels on the same area too.

The "pixel budget" a value introduced by AndyE many years ago leads to finer tonality and/or finer spatial
resolution. The electronics converting photon counts to colored pixels has better input measurements to
start with. Each photosite is a measuring instrument whose results are inevitably poisson distributed meaning
the uncertainty of the result .. margin of error .. goes with roughly the square root of the measured result.

The bigger the absolute photon count of a photosite the smaller the uncertainty.

Now the designer of the recording chip can decide to either have a finer tonality like in the D750 or at the same
pixel budget a finer spatial resolution like in the D810.

That is where pixel buget ... better statistics ... finer tonality ... OR ... finer spatial resolution ... touches resolution.

In other words. If the instrument can distinguish 1 Million shades of red or only 50.000 .... OR ... if the instrument can in
stead make even the finest of hairs countable.

[Bjørn Rørslett]

Well, what you now describe has absolutely nothing to do with the starting point of this thread.

Sensor quality has nothing to do with focal length. And focal length on its own does not depend on format.

The circle of confusion is now well and truly completed.

[David H. Hartman]

The importance of a larger format gathering more total light is signal to noise ratio.

More damned lies...

D810 FX v. D810 DX vD810A FX

And again...

D5 FX v. D5 DX v. D500

More signal: more dynamic range, more image resolution, more image acutance.

More noise: less dynamic range, less image resolution, less image acutance.

If you want DX to equal FX in dynamic range you're going to need a bigger boat your going to need a faster lens.

Dave

[BW]

Sensor quality has nothing to do with focal length. And focal length on its own does not depend on format.

The circle of confusion is now well and truly completed.

Finally, at least something got completed in this thread

[David H. Hartman]

Why must a photographer use a shorter lens - is it mandatory for a DX camera?

If I want the same subject framing and the same perspective then I'll use a 70mm lens on DX and a 105mm lens on FX and I'll lose background blurring on DX as my fastest 70mm lens is an f/2.8 and my fastest 105mm lens is an f/2.5. If I'm willing to have flatter perspective then I can use an 85/2.0 lens from a greater distance to gain the same subject framing and I'll gain background blurring but I'll have flatter perspective which I won't want if the subject is a person. I've loved the 105mm focal length since the day I tried a 105/2.5 Nikkor-P in the mid '70s.

Twice I started a Nikon system with a 55/3.5 Micro followed by a 105/2.5 and then a 24/2.8. I bailed out of my first Nikon system just before Nikon started advertising multi-coated lenses.

Although I knew what to expect I was still disappointed with 70/2.8 on DX in term of background blurring as compared to a 105/2.5 or 105/2.8 lens on 35mm.

My 2 cents on why use shorter lenses on DX.

Dave

I wish the "crop factor" thing would go way but I don't think it will.

[Ilkka Nissilä]

The D600 counts 3 times as many photons per picture than the D3 in the same situation.

But to take advantage of that you need to use a longer exposure. The base ISO of the D610 is 100 and the base ISO of the D3 is 200. If you use the same exposure and ISO  then the difference is smaller.

[longzoom]

Exceptions for DX are the new Sigma Art zooms (18-35/1.8 and 50-100/1,8) that perform as well wide open at f/1.8 as their FX counterparts at f/2.8 (if only there were no focus issues with these Sigma's).

.  I respectfully disagree.  While I do not know 18-35 lens, I do know 50-100 one very well. Wide open, especially to shorter distances,  it can't create sharp image, above the central ring, to extreme corners, due to huge field curvature and associated geometrical distortions. It is unavoidable for such bright zoom. I am not able to say it is bad. For some applications, portraiture, for exmp., it is more than acceptable. Even closing down can't significantly improve that situation, you need to focusing further. 50-150 new Sigma is way better(different?) on this respect, as well as every good  70-200/2.8 lens for FF field.  LZ

[ArendV]

@ longzoom, actually I only have practical experience with the 18-35 and not the 50-100.

With the 18-35 I was actually very happy with its close-up performance wide open, also in the corners. And it may have had some field curvature but for the way I used it only needing part of my subject in focus I was very happy with its sharpness and rendering. And it was actually slightly better wide open than the Nikkor 20/1.8G that I now use, but not having reliable autofocus in the corners was not acceptable for me.

[MFloyd]

I think I will stop reading this topic, because the more I read, the more confused it becomes in my mind 😜

[Bjørn Rørslett]

It's all about circles of confusion anyway ....

Will more photons improve these circles ??

[tommiejeep]

I think I will stop reading this topic, because the more I read, the more confused it becomes in my mind 😜

MF,   this is such an emotive issue on almost all Sites. I often shoot both formats in tandem.  When I view the images they can go either way as to which turn out better (lots of contributing factors but most often the difference is me and how I'm feeling/shooting ).

I just do not normally even open the threads. The title of this one caught me out.   Logic, science be damned ... lol

[simsurace]

When one discusses this topic, it should be clear what the goal is. Otherwise we will run in circles.

If the goal is to reproduce the same photograph (same perspective, same field of view, same DOF, same motion blur (implies same shutter speed) with two formats (using the full frame without cropping) and display them both at the same size, then the exposures must be different for the two formats. The photographs will have the same brightness and noise level if the ISO is chosen appropriately for each format (different ISO for different formats).*

- What does it imply for the importance we should place on exposure in this context?
- Does anyone disagree that the two photographs look the same under any circumstance or with any viewing device?

Does anyone disagree that we can deduce from the above that if the exposures are the same for the two formats, we either get
- different DOF or
- different motion blur,
but we definitely get
- different noise levels,
- the same perspective.
(it is assumed that ISO is the same here such that image brightness is the same).

The noise amplitude is lower for the bigger format and the information theoretic reason for that is that more photons were collected by the bigger sensor if both sensors were exposed the same (same energy per unit area).

* All these considerations are made under the simplifying assumption that sensor technology is similarly mature for both sensors and that things like the exact architecture or number of the photosites are similar enough to be neglected. We also assume that we can find lenses for each format that project geometrically similar images and are diffraction-limited. All statements are approximate to the extent that these assumptions are violated, but they shouldn't usually be violated by orders of magnitude.

[charlie]

Back when I didn't know the role different sized sensors played in making photographs I saw a diagram similar to the amazing diagram below which I've (re)created just for this very discussion.
This sums it up good enough for me and I can't imagine how any more knowledge on the subject would improve my photography in real world shooting.
If you're trying to write a text book that's one thing, but if you're just making photographs it's really not that complicated. Pick up any camera, point it at something interesting.

[Bjørn Rørslett]

The sheer insistence on "the same" is about as useful and productive as demanding every photographer being at a given location should return with the exact same photograph.

Isn't time to do something useful now?

[simsurace]

As far as I can see, this topic is not about photography specifically. It is about optics and digital sensors. Photography just so happens to make use of these tools to communicate a message. There are great artists who do everything intuitively and don't care about the science behind it. But that's beside the point.
There is no artistic aspect to this topic as far as I can see. It is purely technical/scientific.
It is only because I see that we are lacking a consensus on the technical matters that I am bothering to write anything at all.
If what I write is not helpful or does not stimulate any thoughts/discussions, it is quite easy for me to quit doing it. As you suggest, I have plenty of other useful stuff to do with my time.