FX vs DX Image Quality Comparison (yes.. this again) Your Thoughts?

spraynpray

From the press release:
"This is also the first Nikon DX lens to feature an electromagnetic diaphragm; this innovation electronically adjusts the aperture within the lens, resulting in consistent exposure during high speed shooting. "
I wonder which high speed DX camera will require an electronic aperture :-??

Canon have had an electro-magnetic aperture since forever and they aren't all hi fps bodies. Do you think the mechanical aperture is really the limitation to achieving higher fps?

JonMcGuffin

Wow, this has managed to get so off topic; I'm surprised.

Nobody has done the "test" but I think it's pretty fair to say that strictly looking at the IQ quality of the sensor in terms of it's ability to produce a sharp image and assuming there is no need to get beyond ISO 800 or so, DX and FX are virtually identical yes?

In other words, FX sensor alone doesn't just automatically give you "better" pictures. We've discussed here that Dynamic Range of D7200 is virtually on par with D750 when we're in the ISO 100-800 range. Lenses have a greater impact on optical integrity than the sensor itself. Larger sensors do have some definite benefits, and also some aspects that are unique but they aren't necessarily producing better images for the sake of the size of the sensor.

donaldejose

Jon: I think that is correct and you should also throw in a qualifier about the size of the print. We like to compare DX with FX at 100% but we don't really print at 100% most of the time. In a way print size is like ISO; DX and FX are about equal at the lower numbers and FX shows it superiority at the higher numbers.

WestEndFoto

Wow, this has managed to get so off topic; I'm surprised.

Nobody has done the "test" but I think it's pretty fair to say that strictly looking at the IQ quality of the sensor in terms of it's ability to produce a sharp image and assuming there is no need to get beyond ISO 800 or so, DX and FX are virtually identical yes?

In other words, FX sensor alone doesn't just automatically give you "better" pictures. We've discussed here that Dynamic Range of D7200 is virtually on par with D750 when we're in the ISO 100-800 range. Lenses have a greater impact on optical integrity than the sensor itself. Larger sensors do have some definite benefits, and also some aspects that are unique but they aren't necessarily producing better images for the sake of the size of the sensor.

A lens produces an image circle. Most of the time you will want to use most (the FX frame) of the image circle. Occasionally, you may only want to use a certain portion of it (eg. PC lenses). For the occasional application (eg. BIF) where you have an incredibly sharp lens (eg. A Nikon supertele) that can take advantage of a higher pixel density than the D800 offers, you may want to use a DX sensor as the DX sensor has a higher pixel density.

This particular advantage is not an advantage of DX, but a result of Nikon's marketing department choosing to have a higher pixel density on a particular DX sensor than the current lineup of FX sensors.

spraynpray

Wow, this has managed to get so off topic; I'm surprised.

Nobody has done the "test" but I think it's pretty fair to say that strictly looking at the IQ quality of the sensor in terms of it's ability to produce a sharp image and assuming there is no need to get beyond ISO 800 or so, DX and FX are virtually identical yes?

In other words, FX sensor alone doesn't just automatically give you "better" pictures. We've discussed here that Dynamic Range of D7200 is virtually on par with D750 when we're in the ISO 100-800 range. Lenses have a greater impact on optical integrity than the sensor itself. Larger sensors do have some definite benefits, and also some aspects that are unique but they aren't necessarily producing better images for the sake of the size of the sensor.

A lens produces an image circle. Most of the time you will want to use most (the FX frame) of the image circle. Occasionally, you may only want to use a certain portion of it (eg. PC lenses). For the occasional application (eg. BIF) where you have an incredibly sharp lens (eg. A Nikon supertele) that can take advantage of a higher pixel density than the D800 offers, you may want to use a DX sensor as the DX sensor has a higher pixel density.

This particular advantage is not an advantage of DX, but a result of Nikon's marketing department choosing to have a higher pixel density on a particular DX sensor than the current lineup of FX sensors.

It has always been thus though.

WestEndFoto

I am really just trying to drive home the point that lenses come first and then you pick a suitable camera for the lens.

PB_PM

Bingo. IMO one of the primary reasons to go FX is for the lenses, the sensor size is almost secondary. Yeah, that's a very weak almost.

WestEndFoto

Yearh, if I had less money, I would downgrade to a D5500 before I would compromise on lenses.

spraynpray

OK Guys, since nobody else has done it, I have just take a few snaps with my D7100 and D750. Please don't ask me to shoot something else or with different setting - ain't going to happen.

The three shots are of a corner of my garden, straight out of camera. Settings are the same but I shot two with the D7100, one at the same aperture and one a stop faster to offset the DoF difference between DX and FX. There is NO pp apart from the sun dodging in and out (I had to compensate 1/3rd stop to get more similar exposure), no sharpening for screen on export. The shots are full size on Flickr if you want to peep or play. They aren't fine art and there is a slight difference in framing due to camera positioning in tripod and possible slight difference in corrected focal length. The lens is my 24-120 on both bodies. It was very gusty. Enjoy, and do tell me what you see:

WestEndFoto

The D750 has more recovery in the shadows, but that is the only obvious difference.

You have certainly demonstrated that at web resolutions, there is not much difference with this lens.

If I was able to see the images at the highest resolution, I suspect that I might like the DX better, as the soft corners of this lens will not be visible (if this is an issue with this lens stopped down). It would also be interesting to shoot this lens at F8 on the D750 and F/5.6 on the D7100. I wonder if diffraction at F11 will overpower any differences between the cameras.

I suspect that the real limiting factor here is the lens in which case mush will pretty much look the same no matter what camera you use when you look closely enough. It would be interesting to see the comparison on a super sharp prime that was sharp across the frame. Say the 85 1.4G shot at f/8 where it is sharpest in the corners. Even my D800 is the limiting factor in this scenario so I doubt that the higher pixel density of the D7200 will be relevant. I wish I had a D7100/7200, then I would do that test.

JonMcGuffin

@spraynpray - Thank you so much for doing that!

spraynpray

@WestEndFoto: They are full res on Flickr.

@JonMcGuffin: You're welcome.

heartyfisher

due to my net access problems can you please put links so that I can get to them without going through the proxy :-(

WestEndFoto

@WestEndFoto: They are full res on Flickr.

@JonMcGuffin: You're welcome.

I tried to download the originals but could not.

spraynpray

Argh - Flickr! I've changed the copyright to public domain @WestEndFoto - does that do it for you?

spraynpray

@heartyfisher:

https://www.flickr.com/photos/spraynpray/19632377045/in/dateposted-public/

https://www.flickr.com/photos/spraynpray/19011429013/in/dateposted-public/

https://www.flickr.com/photos/spraynpray/19011433603/in/dateposted-public/

Photobug

@spraynpray - Thank you so much for taking the time to run the test.
Both are excellent cameras.
The key here is viewing on the web the delta is so small.
Thank you.

WestEndFoto

Argh - Flickr! I've changed the copyright to public domain @WestEndFoto - does that do it for you?

That works. I have been meaning to create a new Flickr site to use to contribute to Nikon Rumours, as sometimes I would like to post an image that I don't really want to put on my regular Flickr sites. I will do that and set up Lightroom to upload to it. I will then take a close look at the images.

WestEndFoto

OK, here is a first comparison between the three images. I have cropped the dark area to the left.

First:
D750 at f/11


Second:
D7100 at f/11


Third:
D7100 at f/8


I am paying close attention to the shadows. It is interesting that on Lightroom I can see more detail in the shadows than on Flickr. However, there is no difference between the two cameras on either setting that I would not attribute to variation in the testing environment. The D7100 comes ahead by a smidgen, but that could just be a variations in the natural light.

More comparisons are to come.

WestEndFoto

Now for all three, I have moved the Lightroom Shadow Slider to +100 to examine what kind of detail is in the shadows:

First:D750 at f/11


Second:D7100 at f/11


Third:D7100 at f/8


Again, there is really no difference. There is a difference in sharpness, but I will comment on that later.

There is at first glance more detail in the D7100, but if you look at the leaves that are lit, they seem to be a little more exposed. The effect is very subtle and frankly, I am surprised that Spraynpray was able to get this close on his exposure. Good job.

This result does not surprise me, as the two sensors have very similar dynamic range. This attribute is not a function of DX or FX, but of the sensor technology that Nikon is using. By sensor technology, I mean the hardware produced by Sony and software produced by Nikon.

This is the area where Nikon is far ahead of Canon.

Note that this is not a high ISO test, but merely a test to bring detail out of the shadows.

WestEndFoto

Now back to the centre.

First:
D750 at f/11


Second:D7100 at f/11


Third:D7100 at f/8


If you look at the small green branches to the slightly lower right just to the right of the bamboo, you will see that the D750 comes out a bit sharper.

I would not attribute this result to the superiority of the D750 however. Note that the D750 is shot at 52mm and the D7100 is shot at 35mm. It may very well be that the lens is simply sharper at 52mm. This seems more likely to me than the D750 sensor being sharper than the D7100 sensor, even though the D750 sensor is a generation ahead. Both are 24 megapixel sensors.

This is my educated guess though. I could be wrong. Maybe the D750 sensor is that much more sharper.

That said, I don't see this evidence of FX's superior IQ. I attribute it to most likely the lens' selected focal length, second most like the generational gap between the sensors and third more likely as some sort of FX advantage.

WestEndFoto

Now down to the corner.

First:D750 at f/11


Second:D7100 at f/11


Third:D7100 at f/8


Notice how soft the D750 is. However, this is a lens issue, not an issue relating to the D750 or FX.

FX is using the soft corners of the lens, while DX is only utilizing the sharper centre.

If you look at Nikon's MTF chart for this lens (see link below), you will see that it is quite soft in the corners. Now you have to take it with a grain of salt, as the MTF chart is measured at f/4.0. It will not be as soft at f/8 or f/11. However, typically lens are softer in the corners regardless of which f-stop you are shooting at, so this result does not surprise me.

http://www.nikonusa.com/en/Nikon-Products/Product/Camera-Lenses/AF-S-NIKKOR-24-120mm-f%2F4G-ED-VR.html#!

WestEndFoto

The verdict, which is my opinion based on what I have seen.

There is no difference between FX and DX with this particular lens, except that DX will produce better across the frame sharpness as it is only using the centre of the lens.

There is some evidence that FX is producing better centre sharpness, however, this may be a result of lens sharpness performance differences at different focal lengths.

spraynpray

Thanks for taking the time to look at them @WestEndFoto.

What do you think of the sharpness of that 24-120? I think it is pretty unspectacular.

WestEndFoto

And now further thoughts (opinions).

I believe that it would have been a better test if rather than changing the focal length on the lens to achieve equivalent framing, it would have been better to zoom with the feet. Also, the lens performs better at the tele end according to Nikon's MTF charts (see S30 and M30, as that is a sharper measurement than S10 and M10) so I might have shot at 120mm.

My suspicion is that had this been done, the only substantive result would be that the sharpness advantage in the centre of the D750 would disappear while the other results would have been similar.

Why?

Because I believe that at f/8, this lens outperforms both sensors for resolution in the centre. They will therefore be equivalent and DX will have an advantage as it only uses a sharp centre. However, one will have to be mindful of the crop factor and evaluate their focal length needs accordingly.

Now what happens if sensor performance starts to exceed lens performance. This can happen in two ways:

1.
Megapixels goes up.

2.
The lens is opened up and gets softer.

Now there are no sensors for FX currently in production where an increase in megapixels will be a factor. The 36 megapixel D810 sensor will have a roughly equivalent pixel density as the D750.

However, the lens can be opened up. I see this effect on my 85mm 1.4G. Above about f/4.0, my D800's 36 megapixel sensor is the bottleneck. Below about f/4.0 and very obviously wide open at f/1.4, it is the lens.

Now lenses have resolutions just like sensors. The resolution is different depending on the f-stop, usually going up as you open it up but starting to go down as it becomes diffraction limited.

If you want to maximize the resolution that you get out of a lens and you have a sensor that can take advantage of it (because it is a high resolution lens that has not been made yet - say 100 megapixels or because the lens is wide open and therefore soft), then you need to use more of the lens and in this regard, FX is better than DX. Given the same pixel density to start, when the pixel density increases, the point at which there is no additional benefit with a certain lens, you will achieve a higher resolution image from the FX sensor simply because it is using more of the lens.

A similar argument can be made for light gathering power. With a DX lens, light will fall onto the area outside of DX coverage that an FX sensor would utilize. This disadvantage of a DX sensor could be resolved by focussing the image on the DX sensor area by redesigning the lens, but FX lenses are not designed this way - they are designed to focus on an FX sensor. Note that this is not an ISO argument as ISO measures how much light falls on an area measured in a standard way, where I am talking about how big the area is.

This is why I have invested in FX. I buy FX lenses because they are better than the DX lenses on offer and the FX sensors utilize all of the lens, not only half.