FX vs DX in mirrorless

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The differences can be complicated and controversial. For example I can tell that m4/3 has a shallower DOF than FX and I would be correct. Put a 50mm lens on an FX body and a 50mm on an m4/3 body and m4/3 will give you shallower DOF. The problem is when you add field or angle of view (FOV) into the mix. FX 50mm = m4/3 25mm FOV, the 2x crop. 25mm being a wider lens will give you greater DOF.

So the difference comes down to what you're looking to do and why. These are tools, different tools serve purposes. Define what job you want to do and then look for the best tool for that job.
 
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I am just trying to understand in my mind what the difference is between DX and FX
If I can be frank, I've gotten the impression instead that you're far more intent on telling everyone what the difference is. If you truly want to gain an understanding, I recommend that asking questions rather than making statements will be far more productive. I can't begin to tell you how much I've learned here, and that happens almost entirely by asking questions and seeking critique.
 
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I believe David is correct in his statement. He is not matching the angle of view. The cameras are at the same distance and same f/stop, and as such will not show identical content. In this case, the FF has more DOF. You can run the numbers on a DOF calculator. For a 50mm lens at 10 feet at f/2.8, the DOF calculations I see are 2.06 for FF and 1.02 for m4/3rd's.

--Ken
 
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I also think David is correct -
If you use the same 50mm, the image on the film surface is identical, including bokeh. The only difference is the film size. That is, how much you are cropping. The smaller film area requires more "enlarging" to make the same, say, 8x10 print. Therefore, the same small point in the picture gets larger in the smaller format film. So it appears less focused. If you use the same DOF definition, m4/3 gets shallower DOF.
 
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Assuming the focus is at the same point in both situations, it would actually be exactly the opposite.
Sorry I should have included maintaining the same distance from subject. It won't be the same shot, but it would give you a shallower DOF.

Now to get the same shot you need to use the 25mm instead of the 50mm or increase the distance between you and the subject. Either will result in greater DOF which is why people think of m4/3, or any smaller sensor, has a greater DOV than FX.

A couple of boarding videos if you're interested:
One of them (if I remember correctly) also gets into pixel density and image sharpness, I think it's the first one but I can't remember.
 
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I don't know what the reasons :) , but I'm a fan of FX sensors, big sensors but not big as medium format... I always had two parallel mirrorless systems in the past until last year: Fuji APS-C and Full frame (Sony A7 series and now Nikon Z6). I did notice the difference between FX and DX. If not because of convenient JPEG image quality (colors of Fuji) and small size of the WHOLE combo body and lens of DX, I would never owned a APS-C system. Yes, I know wild-life photographers do need APSC for extra reach.
The reasons probably are DR like Pa said, also ISO performance (not much as in the past), and more important to me, better FX lens collection. FX lens optical quality is usually better than DX lenses. And if I use DX bodies with FX lenses, that's not wide enough. I usually need wide end more than tele end.
Once time when I had Sony A7R3 42Mp, I often used a button on Sony GM lenses to convert the FX 42Mp to DX mode 18PM to get 1.5x reach when needed. I were happy with results. Too bad Nikon doesn't make that button in their S primes. Many people have both systems.

In my limited knowledge about photography, I think DX bodies are advanced for extra reach, saving cost, size and weight. But I don't dare to say FX give better IQ than DX cameras do...even IF it's true :).
People when compare (and defense) APS-C system vs FX system, they usually forget to take optical and build qualities of FX lenses into account, IMHO.
 
In the past, I had the two-camera setup, too, with a APS-C camera body and a FF camera body, and it really was convenient, especially for having the APS-C camera mounted on the tripod with a long lens and then the other camera available for other types of shooting. For macro shooting I prefer FF, as I think it picks up more detail in the subjects. Probably that is related to the fact that FF lenses are usually higher quality (and more expensive) than APS-C ones.

On my Sony A7R IV, the ability to switch from FF to APS-C is a function within the camera body, not on the lenses. I have not actually tried that out yet, since I don't have any APS-C lenses anyway. One can program one of the custom buttons on the camera body to make that process go quickly rather than fumbling in the menu. There is also a convenient "hold focus" button on most of Sony's lenses, which is great when I'm shooting something and need to readjust the composition a bit; I hit the joystick, focus where I need to, use the "hold" button, then shift to the position I want for composition and take the shot. I believe that this button can be reprogrammed to a different function if the user chooses to do that, though.
 
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For macro shooting I prefer FF, as I think it picks up more detail in the subjects. Probably that is related to the fact that FF lenses are usually higher quality (and more expensive) than APS-C ones...On my Sony A7R IV, the ability to switch from FF to APS-C is a function within the camera body, not on the lenses. I have not actually tried that out yet, since I don't have any APS-C lenses anyway.
You can use a full-frame lens on an APS-C camera and you can use a full-frame lens on a full-frame camera set to a crop mode. My point is that you can get the best of both worlds when you believe for whatever reason that the APS-C format is the way to go.
 
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You can use a full-frame lens on an APS-C camera and you can use a full-frame lens on a full-frame camera set to a crop mode. My point is that you can get the best of both worlds when you believe for whatever reason that the APS-C format is the way to go.
You can also shoot a DX (APS-C) lens on a FF (FX) body. Trenchmonkey does so, setting the camera at a 1.2 crop (rather than a 1.5 DX crop). At focal lengths over 75mm there is no discernible vignetting (he was using a Sigma 50-150, f/2.8 lens). I shot with that lens on my D850 for a while and liked the lens but it wasn't a great match for my style and subjects.
 
Actually, nht800 first mentioned the thought about optical quality in FF lenses in his post above mine..... Having used both types of lenses and bodies through the years, I tend to agree that the FF lenses are of higher optical quality, but certainly these days all lenses are of excellent quality that exceeds many of the lenses from the past. In my Nikon days most of my lenses were FX lenses but I had a few DX lenses as well, as in some cases they did what I needed and wanted. I was not "arguing" anything, I was simply commenting, but yes, of course if one goes to all the trouble and expense of buying a FF camera one is likely to need and want FF lenses on it anyway. Since I am starting fresh with a new system, obviously I am going to put my money into the lenses which will meet my needs. I want to take full advantage of that 61 MP! With the Sony A7R IV, though, Sony has designed the camera so that if I chose, I could buy a APS-C lens and stick it on the camera and go into the menu and change to APS-C mode and shoot, coming out with still pretty decent resolution (26 MP). Kind of like having two cameras in one!
 
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Gotta chime in on the sharpness thing....

The Z6 has an AA filter while the Z50 does not.

so the Z50 is sharper.... (ish)

The z6 has larger pixels so has less quantum noise.

The D500 and D850 both don't have AA filters and the pixel pitch is almost identical so both are very sharp...

Cheers,
alexis and Georgie Beagle

" use the same lens and only the pixel peepers will notice..... In regard to the D500 vs D850 mom clips wings with the D500" - Georgie Beagle
I just want to chime in on the sharpness. I compared the D750, Z6 and A7III and I felt the D750 had sharper raws than the Z6, while the A7III has the sharpest SOOC raws between the 3 cameras. Others online have also noticed the same comparing the D750 and Z6. The difference isn't really a big deal unless you're pixel peeping! ;)
 
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It appears people are saying that there is not much difference (or not at all) on sharpness between FX and DX (like D500). I think it is because the test is "weak". Given the same MP, there is a difference. But with today's 20-24 MP, you have to do a more critical test to see the difference. If you compare 8x10 prints, there would be no difference, so make it bigger and bigger.... My point is that today's 20MP is far greater than we (or even pros) need in a normal shoot, so the resolution difference between DX and FX is a moot point. If so, the lighter DX is a better choice. Unfortunately, there aren't many DX lenses on the longer side, or there aren't many good (fast) DX lenses - period. The DX is treated as a second-class citizen. For instance, F 70-200mm f/2.8 or F 500mm f/5.6: There are no DX versions. True, you can use these on your DX body, and you get an extra 1.5x telephoto factor free on the long side. But that's a default benefit you get automatically. But if there were a DX version of the same spec, the lens would be smaller/lighter due to smaller image circle requirement, and the DX system will truly benefit from being DX. Alas, Nikon would be very hesitant to produce DX 500mm f/5.6 or DX 70-200mm f/2.8 just for you. And would you buy two 70-200mm f/2.8 lenses, one for DX and one for FX - so that one weekend you can carry a lighter DX 70-200mm with your Z50? Probably not, so don't blame Nikon. They are in the business of making money. On the other hand, if you are a truly DX-only photographer, you are out of luck. Nikon would not support you fully. You are always in the shadow of the big FX brother. Well, in life, one has to be practical and pragmatic. I would be content with one FX 70-200 f/2,8 for my Z7 and Z50 - only if I could afford one.
 
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It appears people are saying that there is not much difference (or not at all) on sharpness between FX and DX (like D500). I think it is because the test is "weak". Given the same MP, there is a difference. But with today's 20-24 MP, you have to do a more critical test to see the difference. If you compare 8x10 prints, there would be no difference, so make it bigger and bigger.... My point is that today's 20MP is far greater than we (or even pros) need in a normal shoot, so the resolution difference between DX and FX is a moot point. If so, the lighter DX is a better choice. Unfortunately, there aren't many DX lenses on the longer side, or there aren't many good (fast) DX lenses - period. The DX is treated as a second citizen. For instance, F 70-200mm f/2.8, or F 500mm f/5.6: There are no DX versions. True, you can use these on you DX body, and you get an extra 1.5 telephoto factor free on the long side. But that's a default benefit you get automatically. But if there were a DX version of the same spec, the lens would be smaller/lighter due to smaller image circle requirement, and the DX system will truly benefit from being DX. Alas, Nikon would be very hesitant to produce DX 500mm f/5.6 or DX 70-200mm f/2.8 just for you. And would you buy two 70-200mm f/2.8 lenses, one for DX and one for FX? so that one weekend you can carry a lighter DX 70-200mm with your D50. Well, in life, one has to be practical and pragmatic.
Fuji and the m4/3 group are the only ones that have really put much effort into make "right sized" lenses.
 
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In the early days of digital there was a distinct and virtually universal belief that cropped-sensor cameras were just a temporary phase, waiting simply for technology to return us to the full-framed world that existed in films days. The 35 mm format ruled, and there was a definite stigma associated with small sensors.

Anyway, I see point in belaboring the point. As someone smarter than I said many years ago, worry less, shoot more.
 

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