DX - FX photo explanation of crop zoom

[Philnz]

So to sum-up for this slow old brain of mine If I fit a old 50mm Series E lens on my DX camera it would be the same as if I fitted 35DX lens.
Model NIKON D7100 Shutter Speed 1/250 s
F-Number f/8
ISO ISO 1400
Exposure Bias Value 0.00 eV
Metering Mode Spot
Flash Off, Did not fire
Focal Length 35 mm
Lens Model 0 mm f/0.0
White Balance Details Auto1
Date/Time Original 24/07/2014 07:45:36 AM
I had the above on and this is what the EXIF tells me.

 

[Moab Man]

Sorry Philnz, no smiley face on your homework.

A 50mm on a FX camera is the same (close enough) as a 35mm on a DX camera. Any lens going on a DX camera should be multiplied by 1.5 (35mm x 1.5 crop factor equals 52.5mm) to give you the effective zoom.

50mm on FX is 50mm

50mm on DX is 75mm

35mm on DX is 52.5mm

 

[Philnz]

Sorry Philnz, no smiley face on your homework.

A 50mm on a FX camera is the same (close enough) as a 35mm on a DX camera. Any lens going on a DX camera should be multiplied by 1.5 (35mm x 1.5 crop factor equals 52.5mm) to give you the effective zoom.

50mm on FX is 50mm

50mm on DX is 75mm

35mm on DX is 52.5mm

Great get it now Takes a while. it was just that the EXif on the D7100 says the focal length was 35mm when fitted with that old 50mm must be that the camera can not read the lens.

 

[§am]

Sorry Philnz, no smiley face on your homework.

A 50mm on a FX camera is the same (close enough) as a 35mm on a DX camera. Any lens going on a DX camera should be multiplied by 1.5 (35mm x 1.5 crop factor equals 52.5mm) to give you the effective zoom.

50mm on FX is 50mm

50mm on DX is 75mm

35mm on DX is 52.5mm

Are you sure that's correct?

An FX lens on a DX body would give you the zoom (1.5x) (i.e. effective length increase), but a DX lens on a DX body doesn't give any zoom (or effective increase)?

 

[PapaST]

As I understand it, the stated focal length on a DX or FX lens is the same (35mm is 35mm). So the DX on DX body would still exhibit a crop factor. The main difference is the FX lens projects a larger area of image to encompass the entire FX sensor. Whereas the DX lens projects an area that is just enough to cover a DX sensor.

 

[480sparky]

Maybe this will help clear up some of the confusion about field-of-view and "35mm equivalent" when comparing full-frame cameras and those with crop-sensors.

Regardless of the 'comparison', a 50mm lens is a 50mm lens, no matter which sensor you're using. What changes is the apparent field of view between the two. So if you were to take a full-frame and a crop-sensor camera, set them up side-by-side with, say, 50mm lenses on both, and looked through the viewfinders of them, this is what you would see:

Neither camera-lens combination 'enlarges' or 'reduces' the apparent size of the subject. The bridge and the flowers are the exact same size in both VFs. What is different is the size of the focus screens, which is in direct proportion to the size of the respective sensors. This, in turn, changes the field of view (measured in degrees).

The comparison shown is both lenses being the same focal length. They're not meant to show the differences in detail, sharpness, resolution, contrast, etc.. or the differences between the abilities of the two sensors. Besides, they're reduced so much from their original full-size dimensions you can't use them to compare those parameters anyway.

Notice the difference is the size of the images. That is because the sensors are not the same physical size. This is reflected in the size of the images. If you were to set a FF and crop sensor side-by-side the viewfinder in the FF camera will be larger.... because it must reflect the larger sensor.


Everything is the same size in both images because the sensor is smaller. The lens projects a subject the same size.... it doesn't know which sensor is sitting behind it.

To show this, here's my D600 ("Full Frame/FX") and my D7000 ("Crop Sensor/DX"), side-by-side, with both in Mirror Up for Cleaning mode.

The blue-green rectangles are the actual sensors. Notice how the FX sensor on the left is larger (Nikon specs are 24m x 35.9mm) than the DX sensor on the right (Nikon: 23.6mm x 15.6mm)

I put a 50mm FX lens on the D600, it sees this:

When I put a 50mm DX on the D600, it sees this:

This is exactly what you would see in the viewfinder as well. These images are merely reduced in scale for posting here. No other editing was done. Notice how everything in the scene is rendered the same size?


The only difference between the two is the DX lens is not designed to cover the entire FX sensor.... it only needs to cover the smaller DX sensor. That's why the DX lens shows the black areas... both in the VF and on the sensor.

If I put either the FX OR the DX lens on the D7000 (crop sensor) , or on the D600 and shoot in DX mode, they will both record this:

When I enlarge the DX image to match the same dimension of the FX image, it appears I'm using a longer lens. I'm not. They're both 50mm. What changes is the field of view caused by the 'crop factor' of the smaller sensor.


An analogy would be like putting a film negative into an enlarger and running it up to make an 11x14. Then replace the 11x14 with a sheet of 8x10...... without changing anything else. The subjects in the 8x10 will measure the same as they are in the 11x14. There would also be no more detail in one compared to the other. Or, you could take the 11x14 and cut it down with scissors to an 8x10.... there would be no more detail when you're done doing that.

 

[Moab Man]

As I understand it, the stated focal length on a DX or FX lens is the same (35mm is 35mm). So the DX on DX body would still exhibit a crop factor. The main difference is the FX lens projects a larger area of image to encompass the entire FX sensor. Whereas the DX lens projects an area that is just enough to cover a DX sensor.

Correct. The measurement of zoom is all relative to a full frame sensor.

I too always wondered why a DX specific lens wasn't made to accurately reflect the measurement of the lens relative to a DX camera sensor. Then again it's probably not financially with doing.

 

[480sparky]

Correct. The measurement of zoom is all relative to a full frame sensor.

I too always wondered why a DX specific lens wasn't made to accurately reflect the measurement of the lens relative to a DX camera sensor.

They are. The DX 18-105mm lens, for example, is labeled 18-105mm DX.

 

[Moab Man]

Now unless I have something wrong in my understanding, the DX 18-105 is actually 27-158mm because it is still relative to FX. For thrills, I have both a 14mm DX lens and a 14mm FX lens. I will shoot them both and see how they compare and update my original post with what I find/examples. It will be a couple hours for those holding your breath waiting.

 

[Horoscope Fish]

They are. The DX 18-105mm lens, for example, is labeled 18-105mm DX.

Pretty sure all lenses optimized as such have DX in their nomenclature... To build on your example, the 35mm f/1.8G is, technically, the Nikon AF-S Nikkor 35mm f/1.8G DX while the 85mm f/1.8G (an FX optimized lens) does not have that designation. I think what's missing is an FX designator.

....

 

[480sparky]

Now unless I have something wrong in my understanding, the DX 18-105 is actually 27-158mm because it is still relative to FX. For thrills, I have both a 14mm DX lens and a 14mm FX lens. I will shoot them both and see how they compare and update my original post with what I find/examples. It will be a couple hours for those holding your breath waiting.

No. 18-105 is 18-105 is 18-105. It is NOT 'relative' to FX. Manufacturers use the FX reference to better serve their old 35mm film customers. But full-frame digital/35mm is not the 'gold standard'. There's lenses for the myriad of film formats.... medium (4.5x6mm, 6x6mm, etc), large (5x7" and up).

Focal length is determined by the optics, not the imaging format. You can put an 18mm DX lens on an 8x10 view camera and it will still be 18mm (provided you can get it to focus).

As for the difference between a 14mm FX and a 14mm DX lens, no holding of breath is needed. If you're shooting with a crop sensor camera, the FOVs of the images will be identical. If you're shooting with an FX body, the subjects in the scene will be rendered the same, identical size... the difference may be vignetting caused by the DX-format lens not covering the full-frame sensor.

........ I think what's missing is an FX designator.....

If it's not marked DX, it's FX. This holds true for all lenses designed for DSLR, as well as all pre-digital era lenses.

 

[PaulPosition]

Running a Ferrari on a race track or running it in traffic, you're still running a Ferrari; it doesn't change into a Lada because it's on a slow road.

 

[Horoscope Fish]

If it's not marked DX, it's FX. This holds true for all lenses designed for DSLR, as well as all pre-digital era lenses.

Oh I know, I'm just pointing out if they're going to label one they may as well label both.

...

 

[WayneF]

Now unless I have something wrong in my understanding, the DX 18-105 is actually 27-158mm because it is still relative to FX.

No, that is wrong thinking (and a very misleading explanation). You are imagining properties that do not exist.

The 18-105 lens is actually 18-105, always, in any situation. That is simply how it is made, and marked, 18-105.

If on FX, it is 18-105. However, it is a DX lens, meaning it will not cover the full frame of FX. All the edges and corners will be dark. So on a FX camera, you would need to select the DX mode (simulating a smaller cropped sensor), which will crop away all but the inner DX area, which hides the dark edges (but you only have the limited cropped view left).

Or, you could crop it in post processing, same thing.

If on DX, it is still 18-105. Lenses cannot change its focal lengths just because you mounted it on DX. If it says 18mm, it is 18mm.

However, on a DX camera, the smaller DX sensor crops the view (that a large FX sensor would see), so the cropped VIEW that the cropped image shows you compares to 27-157mm on FX. Just the FIELD OF VIEW.

A longer 27mm lens on the larger FX sensor captures the SAME VIEW that requires a shorter 18mm lnes on the smaller DX sensor. FX sensor shows a wide view that the DX sensor crops away, so the DX camera needs a wider lens to get it back. We are talking about the Field Of View, resulting from the smaller DX sensor cropping the total FX lens view.


Again, this is the FIELD OF VIEW, simply as compared to using the longer lens on the bigger sensor. But the lens cannot change. The sensor size changed (and cropped the image field).

The telephoto effect really does not matter if you crop the image smaller on the smaller sensor, or later in the photo editor in post processing. Both simply create a smaller image. Then when you later then enlarge either one a larger amount to appear same size as an uncropped image, the cropping simulates a telephoto view ... it shows a smaller area blown up larger, which is magnification, which we compare as a telephoto lens would have done.

Cropping of course reduces the pixel count no matter where you crop it. But the smaller DX sensor is made with more pixels (more pixel density) to compensate.

 

[480sparky]

Oh I know, I'm just pointing out if they're going to label one they may as well label both.

...

So let's open that can of worms. A 70-300 FX lens should be labeled:

FX: 70-300mm
DX: 105-450mm
DX in 1.3 crop mode: 137-585mm
With adaptor and mounted on a J-series camera: 189-810mm.

 

[Horoscope Fish]

So let's open that can of worms. A 70-300 FX lens should be labeled:

FX: 70-300mm
DX: 105-450mm
DX in 1.3 crop mode: 137-585mm
With adaptor and mounted on a J-series camera: 189-810mm.

I don't know if you're deliberately reading into what I'm saying or...

My point is, simply: Nikon states in their catalog description, "optimized for DX" or "optimized for FX". DX lens barrels carry this monicker. I'm suggesting the designation should be uniform across all lens barrel, because at present, they are not. DX lenses get a "DX" monicker and so it appears logical to me the same naming convention be applied to FX lens barrels.

...

 

[WayneF]

I don't know if you're deliberately reading into what I'm saying or...

My point is, simply: Nikon states in their catalog description, "optimized for DX" or "optimized for FX". DX lens barrels carry this monicker. I'm suggesting the designation should be uniform across all lens barrel, because at present, they are not. DX lenses get a "DX" monicker and so it appears logical to me the same naming convention be applied to FX lens barrels.

...

The lens is simply marked according to what the lens actually is.
It is not marked by how it might appear on different cameras with different size cropped sensors.

It is the cameras job to tell you that.

First lines from the D3200 manual specifications:

Type Single-lens reflex digital camera
Lens mount Nikon F mount (with AF contacts)
Effective angle of view
Approx. 1.5 × lens focal length (35 mm format equivalent); Nikon DX
format


This of course does not say the lens focal length changes.
The field of view of the smaller cropped sensor is all that changes.

 

[Moab Man]

This is why I refer to it as an effective zoom. Understood, it is still 35mm whether it's DX or FX. But what you see is an "effective" zoom due to the crop factor. I will in a little bit, as I am on my phone at the moment, post the pictures. A 14mm DX lens on a DX camera still has an effective zoom of 21mm and not the 14mm labeled on the lens.

This is where this thread is digressing and going to confuse people due to arguing points that don't really matter when what you see is what matters and not the semantics of it. My point is that whatever the number is on the lens, DX or FX, when mounted on a DX camera you will see an effective zoom factor of 1.5. It doesn't matter that it's not really zooming, or that the lens is still 35mm whether its DX or FX, or the fact it's just grabbing a small slice from a larger field of view. What matters is what the end product is that the shooter receives. So no matter how we get there, and why we get there, a DX lens labelled 14mm will give you a view of what we would see on an FX camera lens combo of 21mm.

I will post the two pictures when I return home.

This is where we start to frustrate those trying to understand this concept when we argue over the details that just don't matter relative to the image the camera generates.

This is a lot to type from a phone.

 

[480sparky]

I don't know if you're deliberately reading into what I'm saying or...

My point is, simply: Nikon states in their catalog description, "optimized for DX" or "optimized for FX". DX lens barrels carry this monicker. I'm suggesting the designation should be uniform across all lens barrel, because at present, they are not. DX lenses get a "DX" monicker and so it appears logical to me the same naming convention be applied to FX lens barrels.

...

The 'naming convention' of full-frame lenses has been the same since the F-mount was invented in 1959. No designation = full-frame.

 

[WayneF]

This is why I refer to it as an effective zoom. Understood, it is still 35mm whether it's DX or FX. But what you see is an "effective" zoom due to the crop factor. I will in a little bit, as I am on my phone at the moment, post the pictures. A 14mm DX lens on a DX camera still has an effective zoom of 21mm and not the 14mm labeled on the lens.

Sorry, but it is you that does not get it yet.

A 14 mm lens has a 14mm field of view, always, no exceptions.

It is just the smaller DX sensor (cropped sensor) that cannot see it all of its wider view.
This is absolutely no fault (or property) of the lens, which is always 14mm.

The effect is simply and only due to the smaller camera sensor, cropping away some of what the lens otherwise sees. Blame the sensor, it is stupid to blame the lens.