How many "stops" of performance gain for FX over DX are there?

as topic, I hear people talking about getting FX for its low noise, better colour, etc... Just how much performance difference are we actually talking about? 2 stops? 3 stops? And what's the jump from FX to say a medium format or even a digital back? I know there's a diminishing return as it goes up the ladder but I am curious to know.

(Note: The D600 and D800 are about even in terms of where they are with high ISO noise, both from my experience and from what DxOMark says, so it doesn't matter which one you want to compare it to, but I've shot more low light with the D600, so I speak to it.)

Depends on what you're jumping from. I personally wouldn't measure the differences between the sensor types purely in those terms, but if you want me to limit my discussion of the differences to just ISO noise, speaking from experience my D600 at ISO 6400 is "cleaner" than my D7000 was at ISO 1600 in most situations, so we're talking 2+ stops. I'd put my D7100 at about a 1-stop disadvantage. Most of the current generation DX cameras seem to be on a par with the D7100 in terms of ISO noise, at least according to DxOMark, with the D7100 actually scoring slightly below both the D3300 and D5300. So, in general, you're talking 1 stop difference for ISO noise. Go back a generation or three and it's a whole 'nother ball of wax.

That said, there are many other factors that must be considered when comparing the sensor types and if you look hard enough around here you'll find many of us have already expounded on them to great degree - so put your physics hat on and start looking.

Thank you for that.

Pretty much just as I suspected. I guess I am just trying to justify myself to not getting FX gear for the money over the small performance gain. I know I have much to learn before I am anywhere near my D7100's limit.

SpikeyLemon said:

as topic, I hear people talking about getting FX for its low noise, better colour, etc... Just how much performance difference are we actually talking about? 2 stops? 3 stops? And what's the jump from FX to say a medium format or even a digital back? I know there's a diminishing return as it goes up the ladder but I am curious to know.

Click to expand...

Not so much a performance gain but an aesthetic one, FX offers considerably greater depth of field control.

If you use DXO for comparing D7100 and D810, then

. ISO sensitivity : same
. S/N 18% : from 5db at ISO 100 to 3db at ISO 12800 (same at ISO 300 and 800, 1000 and 3200, respectively)
. DR : 0.6EV at ISO 100
. Tonal range : 0.9bits at ISO 100
. Color Sensitivity : 3.2bits at ISO 100

So not much difference, but every bit of noise reduction helps

I would use FF more for its wide frame than lower noise, so that landscape shots are easy with older AIS wide angles.

STM said:

Not so much a performance gain but an aesthetic one, FX offers considerably greater depth of field control.

Click to expand...

If you consider 1-stop as "considerably greater depth of field" then I will agree with you, because that's all you get. I'm not sure about the "control" part, unless you mean to say "greater access to DOF", which again is true, but only 1 stop true.

To better understand this, take a look at these photos (which would have been better served with a 50mm and a 75mm lens, but who makes a 75mm lens - so the 85mm DOF will be slightly less than the 75mm would have been with the same field of view)...






In each case you can see that the FX camera will exhibit greater DOF for a particular view at the same aperture, but if you compare the FX photo from the next stop down (i.e. DX f/2.8 vs. FX f/4, DX f/4 vs. FX f/5.6) you will see that they are approximately the same (and would have been closer were they using focal length equivalent lenses from the same spot).

When you get down to fast primes that difference can be considerable, for sure, in terms of the amount of bokeh - but it's still only one stop.

BackdoorHippie said:

In each case you can see that the FX camera will exhibit greater DOF for a particular view at the same aperture, but if you compare the FX photo from the next stop down (i.e. DX f/2.8 vs. FX f/4, DX f/4 vs. FX f/5.6) you will see that they are approximately the same (and would have been closer were they using focal length equivalent lenses from the same spot).

When you get down to fast primes that difference can be considerable, for sure, in terms of the amount of bokeh - but it's still only one stop.

Click to expand...

Am I reading this wrong or don't you mean to say the DX "camera will exhibit greater DOF for a particular view at the same aperture"??

But the FX gains on the DX by using higher ISO, faster Shutter and smaller aperture to achieve a similar or slightly greater DOF.

I ask partly because I thought that was what I had already learned and partly because that is what the pictures appear to show. BUT, I may not have had enough coffee yet this fine day.

BackdoorHippie said:

If you consider 1-stop as "considerably greater depth of field" then I will agree with you, because that's all you get. I'm not sure about the "control" part, unless you mean to say "greater access to DOF", which again is true, but only 1 stop true.

To better understand this, take a look at these photos (which would have been better served with a 50mm and a 75mm lens, but who makes a 75mm lens - so the 85mm DOF will be slightly less than the 75mm would have been with the same field of view)...

In each case you can see that the FX camera will exhibit greater DOF for a particular view at the same aperture, but if you compare the FX photo from the next stop down (i.e. DX f/2.8 vs. FX f/4, DX f/4 vs. FX f/5.6) you will see that they are approximately the same (and would have been closer were they using focal length equivalent lenses from the same spot).

When you get down to fast primes that difference can be considerable, for sure, in terms of the amount of bokeh - but it's still only one stop.

Click to expand...

It boils down to focal length and maximum aperture of most of the zooms, which are generally pretty slow.

BackdoorHippie said:

If you consider 1-stop as "considerably greater depth of field" then I will agree with you, because that's all you get. I'm not sure about the "control" part, unless you mean to say "greater access to DOF", which again is true, but only 1 stop true.

To better understand this, take a look at these photos (which would have been better served with a 50mm and a 75mm lens, but who makes a 75mm lens - so the 85mm DOF will be slightly less than the 75mm would have been with the same field of view)...

In each case you can see that the FX camera will exhibit greater DOF for a particular view at the same aperture, but if you compare the FX photo from the next stop down (i.e. DX f/2.8 vs. FX f/4, DX f/4 vs. FX f/5.6) you will see that they are approximately the same (and would have been closer were they using focal length equivalent lenses from the same spot).

When you get down to fast primes that difference can be considerable, for sure, in terms of the amount of bokeh - but it's still only one stop.

Click to expand...

It boils down to equivalent focal length and maximum aperture of most of the zooms, which are generally pretty slow.

STM said:

It boils down to equivalent focal length and maximum aperture of most of the zooms, which are generally pretty slow.

Click to expand...

I see. So you're positing that FX cameras tend to have faster glass available within certain focal ranges. While I won't argue, I believe that's both changing, and more a matter of cost more than availability. The trinity lenses can be used on both, so the only place you "lose" range is at the ultra-wide end. Of course, a 36-105mm lens is less flexible a walk-around than a 24-70mm, and a 14-24mm (21-36mm) isn't exactly an ultra-wide, so I understand your point. Thankfully 3rd party makers like Sigma are starting to see the value in filling this void and are putting out great lenses like the 18-35mm f/1.8 at a price point that makes FX users drool uncontrollably. So sometimes trading up involves a bit of compromise as well.

SpikeyLemon said:

as topic, I hear people talking about getting FX for its low noise, better colour, etc... Just how much performance difference are we actually talking about? 2 stops? 3 stops? And what's the jump from FX to say a medium format or even a digital back? I know there's a diminishing return as it goes up the ladder but I am curious to know.

Click to expand...

Performance can be taken different ways relative to the objective. It boils down to what you want the camera to do. If I wasn't into landscapes and Oof elements, I would have stuck with Dx.