DX Mode

Bear Dale

Senior Member
Can someone explain please what DX mode is?

Does that mean on a FF body if you put the cam into DX mode (DX are crop sensor lenses yes??) you get the extra reach like a crop sensor cam?


<Nikon Newbie Alert, sorry for all the questions>
 
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Bikerbrent

Senior Member
One key point of DX mode is that on a D750 with 24 megapixels in FX mode, in DX mode it becomes the equivalent of a 10 megapixel camera. So yes, you get the extra reach of a crop sensor but at a high price in resolution and cropping capability.
 

lokatz

Senior Member
Hi Quintrex, Guess you know the difference between full frame (FX in Nikon terms) and APS-C format (DX), with its smaller sensor size. All Nikon FX cameras have DX mode, in which they simply ignore all the pixels outside of the DX area. That makes them behave like a DX camera, with the benefit of an effective longer reach (and smaller file size) and the drawback of lower resolution.
 

nickt

Senior Member
To say things another way, the image is simply cropped in camera to dx dimensions. If you took a shot with a dx lens and put the camera in fx mode and cropped the result yourself, it would be the same. And it really doesn't matter if the lens is dx or fx, dx mode crops it down the same. A 50mm fx lens and a 50mm dx lens both cast the same size image. The dx lens was just designed with budget and weight in mind and might show vignetting or edge distortion if used on a full size sensor. Since the dx sensor is smaller and the same distance from the lens, it doesn't catch the entire image cast. Because the dx sensor doesn't catch those fringes, some corners (figuratively and literally) can be cut in the dx lens design. That is why you can use either a fx or dx lens on a dx camera without care or difference, the dx sensor is not catching the fringe areas anyway.
The dx extra 'reach' comes from enlarging that smaller sensor area to be a comparable size to an fx image.
 

480sparky

Senior Member
DX and FX are physically different sized sensors. FX sensors are larger.

DX lenses are not designed to project an image in the camera large enough to cover the larger FX sensors. As a result, there's black corners and edges when doing so. "Shooting in DX" means the camera is going to ignore the pixels on the FX sensor that are outside the image projected by the lens. Literally, the camera's firmware crops the image.
 

ISOhappy

Senior Member
In the past, DX mode was not something I'd want to use on an FX camera because the final image has a relatively low number of MP left. Like someone mentioned above, the D750 in DX mode only gives a 10MP image (as opposed to 24MP in FX mode). In this case, it's better to just use a DX camera to begin with. However, the D850 has a pixel density that nearly matches (but not quite) that of the DX cameras. It's very close to D500 in terms of pixels per unit area, but can't quite match the D7200. So, when you shoot the 850 in DX mode,you end up with a 19.4MP image. A lot better than the other FX cameras :cool: OTOH, the D500 give you a 20.9MP image and the D7200 24MP.

I'm still waiting for the tests (if anyone does them), but a DX crop from the D850 should look very similar to a full shot from the D500. I actually think the D500 will do slightly better, but we'll have to wait and see. I think if someone wants to use the D850 in DX mode occasionally, it could come in handy, but if you shoot it in DX mode the majority of the time, you might as well save a bunch of money and get a DX camera instead. Hope that helps!
 

PapaST

Senior Member
Maybe I've had this wrong the whole time, but as I understand it, if you shoot from an FX camera and switch to DX mode you're not really gaining any "reach". For instance shoot a pic with a 24.3MP FF D600 and then shoot the same pic in DX mode (effectively making it a 10.1MP DX sensor). Blow both those up to 100% and you should have the same pic essentially with the FX just having more image around the outer edges. Now if you shoot a 24.3MP FF D600 then switch to a 24.1MP D7100 and blow both of those up to 100% you should see that "reach".

I always understood DX mode in FX cameras being beneficial for performance reasons, not for gaining reach.
 

480sparky

Senior Member
Maybe I've had this wrong the whole time, but as I understand it, if you shoot from an FX camera and switch to DX mode you're not really gaining any "reach". For instance shoot a pic with a 24.3MP FF D600 and then shoot the same pic in DX mode (effectively making it a 10.1MP DX sensor). Blow both those up to 100% and you should have the same pic essentially with the FX just having more image around the outer edges. Now if you shoot a 24.3MP FF D600 then switch to a 24.1MP D7100 and blow both of those up to 100% you should see that "reach".

I always understood DX mode in FX cameras being beneficial for performance reasons, not for gaining reach.


A 500mm in a DX body will record a narrower field of view than a 500mm on an FX body simply due to the DX sensor being smaller.
 

ISOhappy

Senior Member
Maybe I've had this wrong the whole time, but as I understand it, if you shoot from an FX camera and switch to DX mode you're not really gaining any "reach". For instance shoot a pic with a 24.3MP FF D600 and then shoot the same pic in DX mode (effectively making it a 10.1MP DX sensor). Blow both those up to 100% and you should have the same pic essentially with the FX just having more image around the outer edges. Now if you shoot a 24.3MP FF D600 then switch to a 24.1MP D7100 and blow both of those up to 100% you should see that "reach".

I always understood DX mode in FX cameras being beneficial for performance reasons, not for gaining reach.

I've always found it to be a confusing topic, but my understanding is the extra "reach" comes from the higher pixel density that DX cameras usually have. When two cameras have the same MP but different size sensors, like the D750 and the D7200, the one with the higher pixel density (D7200) will allow you to crop much more and still have a detailed image. It's all about how many pixels you can put on target.

It gets a little more complicated with the D850 because it has enough px density to match the DX cameras. So in that case, it really does have the same "reach" as, say, a D500. If you crop the 850 down to DX size, it should look the same as if you took the shot on the D500. I say should, because there aren't really any tests out to show this yet. I did see one comparison, and I thought the D500 shot was ever so slightly better, but this was at ISO 25600.
 

480sparky

Senior Member
I've always found it to be a confusing topic, but my understanding is the extra "reach" comes from the higher pixel density that DX cameras usually have. When two cameras have the same MP but different size sensors, like the D750 and the D7200, the one with the higher pixel density (D7200) will allow you to crop much more and still have a detailed image. It's all about how many pixels you can put on target.

It gets a little more complicated with the D850 because it has enough px density to match the DX cameras. So in that case, it really does have the same "reach" as, say, a D500. If you crop the 850 down to DX size, it should look the same as if you took the shot on the D500. I say should, because there aren't really any tests out to show this yet. I did see one comparison, and I thought the D500 shot was ever so slightly better, but this was at ISO 25600.

It has nothing to do with the number of pixels. "Reach" means a DX sensor will record a smaller FOV than an FX sensors does simply because it's physically smaller.

Imagine taking a pair of scissors to an 8x10 print and cutting it down to 5x7.
 

lokatz

Senior Member
We may be getting into semantics here, but I don't think reach and pixel density are connected. As I understand it, 'reach' means how far away can a given subject be for me to still be able to fill the frame with it.

A longer lens automatically has more reach because you can be farther away from that same subject. A DX camera has more reach than an FX camera because you can be farther away from the subject and still fill the frame. The question that comes on top, which is the one you bring up, is how much resolution do you get in the resulting image. A D850 in DX mode has the same reach AND almost the same resolution as a D500. A D750 in DX mode, for example, still has the same reach, but much lower resolution.
 

ISOhappy

Senior Member
It has nothing to do with the number of pixels. "Reach" means a DX sensor will record a smaller FOV than an FX sensors does simply because it's physically smaller.

Imagine taking a pair of scissors to an 8x10 print and cutting it down to 5x7.

I don't think that's what most people are referring to when they say reach. If it were simply recording a smaller FOV (which you're right, it is), there would be no advantage to using a DX camera because you could simply crop the FX frame down to DX and have the same image. However, the camera with the higher px density has more "reach."

Here is an excerpt from another thread:


"Let me give an example.

If you have a 24mm X 36mm full-frame sensor with 24MP, it is 6000 pixels X 4000 pixels, meaning that each pixel is 6 microns square. Lets say we have a 300mm lens and we're photographing a 6 meter square that's 300 meters away. That's going to put a 6mm square image on the sensor. The image is then recorded on 1000X1000 pixels.
A Nikon 24MP crop sensor is 16mm X 24mm. But it's also 6000 pixels X 4000 pixels, so each pixel is 4 microns square. Put the same 300mm lens on it and photograph the same square. It will still be 6mm X 6mm on the sensor but it will be 1500 X 1500 pixels. That's the greater reach.
This is different from digital zoom in that you don't get more pixels with digital zoom since you're stuck with the same sensor.

-- hide signature --
Leonard Migliore"

https://www.dpreview.com/forums/thread/4185586#forum-post-59886918
 

480sparky

Senior Member
I don't think that's what most people are referring to when they say reach. If it were simply recording a smaller FOV (which you're right, it is), there would be no advantage to using a DX camera because you could simply crop the FX frame down to DX and have the same image. However, the camera with the higher px density has more "reach."
.....

"Reach" is about FOV, not pixel density. As in, "A 1,000mm has more 'reach' than a 500mm." You can 'reach' out further with the FOV of a 1,000mm than you can with a 500mm. Since a DX sensor is smaller than an FX, it's FOV is narrower given the same focal length. Hence, more 'reach'.

If pixel density were a factor in 'reach', then you'd have discussions about whether a D810 has more reach than a D750. Or whether a D7200 has more reach than a D7000.
 
It is just cropping in the camera. You are a lot better off shooting in FX like the camera was designed for and cropping in post production. The only real time it is beneficial is when you need to shoot a lot more frames per second and quality does not matter..
 

480sparky

Senior Member
It is just cropping in the camera. You are a lot better off shooting in FX like the camera was designed for and cropping in post production. The only real time it is beneficial is when you need to shoot a lot more frames per second and quality does not matter..


Since when did shooting in DX mode increase your FPS any? I do know it increases your buffer capacity though. But FPS?

If you're firing away and know you're going to crop a lot in post anyway, shooting in DX mode (or Crop mode on a DX body) can garner you a higher burst.
 

ISOhappy

Senior Member
"Reach" is about FOV, not pixel density. As in, "A 1,000mm has more 'reach' than a 500mm." You can 'reach' out further with the FOV of a 1,000mm than you can with a 500mm. Since a DX sensor is smaller than an FX, it's FOV is narrower given the same focal length. Hence, more 'reach'.

If pixel density were a factor in 'reach', then you'd have discussions about whether a D810 has more reach than a D750. Or whether a D7200 has more reach than a D7000.

If that's how you view it, then fine, but I personally think it's all about pixel density. Yes, a D810 does have more "reach" than a D750. If it weren't for the higher px densities you usually find on DX cameras, there'd be no point in shooting them with long lenses because you'd gain zero advantage. For me, reach = ability to crop, and the higher the px density, the more you can crop and still have a good image.

There are discussions about the extra "reach" of DX all over the internet,so I won't rehash it here. In essence, the D850 has about the same "reach" as the D500, because their pixel densities are about the same. DX mode on the 850 is simply cropping away over half the image, which can be done in post for the same end result.
 

480sparky

Senior Member
If that's how you view it, then fine, but I personally think it's all about pixel density. Yes, a D810 does have more "reach" than a D750. If it weren't for the higher px densities you usually find on DX cameras, there'd be no point in shooting them with long lenses because you'd gain zero advantage. For me, reach = ability to crop, and the higher the px density, the more you can crop and still have a good image.

There are discussions about the extra "reach" of DX all over the internet,so I won't rehash it here. In essence, the D850 has about the same "reach" as the D500, because their pixel densities are about the same. DX mode on the 850 is simply cropping away over half the image, which can be done in post for the same end result.


Believe what you will, but try googling "crop sensor reach" and you'll find thousands of results to the contrary.
 

ISOhappy

Senior Member
Believe what you will, but try googling "crop sensor reach" and you'll find thousands of results to the contrary.

I've done a lot of reading on this topic. If there is no difference in pixel density, there is no difference in "reach", period. I think we may be talking about two different things here. The crop factor is just how much the FOV changes compared to full frame. The lens is not zooming in any more, it's simply showing a crop of what you'd see on a FF camera

Reach, OTOH, is how many pixels I can put on target (bird, deer, whatever). To me, that's the real advantage of using a DX camera with high px density. It's discussed more here, but I agree with this guy's post:

"My point is that a discussion of the "reach" advantages of a format can only be effective if the participants have a common understanding of the term. The problem arises because, unlike photographic terms such as "f/stop" or "pixel count", "reach" does not have a single, universally-agreed definition.
My impression is that the most common definition of "reach" as it applies to digital image capture is that of "pixels on the duck", because that determines the maximum print or display size, but as this thread has shown, others have a different view."

https://www.dpreview.com/forums/thread/4185586?page=4#forum-post-59893935
 
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