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FX ON DX
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Jan 28, 2020 18:00:54   #
kfoo Loc: Arkansas
 
What are the disadvantages or advantages of using an FX lens on a DX body? Thanks in advance.

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Jan 28, 2020 18:19:03   #
Rongnongno Loc: FL
 
Advantages = long answers that will not help you.
Differences:
- Wide angles will not work as expected due to the multiplying factor (MF).
- The camera sensor will use the center of the lens so sharper and objects appear closer due to the MF. Side effect, less distortion and less diffraction.

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Jan 28, 2020 18:19:05   #
rmalarz Loc: Tempe, Arizona
 
It should work just fine. It just provides a larger image circle than needed. That could theoretically cause some unwanted internal reflections, etc. However, the chance of that is very slim.
--Bob
kfoo wrote:
What are the disadvantages or advantages of using an FX lens on a DX body? Thanks in advance.

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Jan 28, 2020 18:19:19   #
Bill_de Loc: US
 
Possible disadvantage is added weight compared to a similar DX

---

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Jan 28, 2020 19:03:44   #
Hamltnblue Loc: Springfield PA
 
Advantage is that you would have an FX lens if you ever decided to move to full frame.

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Jan 28, 2020 19:17:22   #
flyboy61 Loc: The Great American Desert
 
Rongnongno wrote:
Advantages = long answers that will not help you.
Differences:
- The camera sensor will use the center of the lens so sharper and objects appear closer due to the MF. Side effect, less distortion and less diffraction.



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Jan 28, 2020 19:36:29   #
IDguy Loc: Idaho
 
Disadvantages: Cost and weight.

Some claim DX designed lenses give better image quality on DX cameras.

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Jan 28, 2020 20:34:04   #
TriX Loc: Raleigh, NC
 
Disadvantages:
1) higher cost
2) higher weight

Advantages:
1) a company’s best lenses are typically FF (FX)
2) you are using the center of the lens which is the best quality
3) if you move to FF later, no need to change lenses

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Jan 28, 2020 21:15:46   #
richandtd Loc: Virginia
 
When I had a Nikon D70 I bought FX lenses so when I could effort a FX format I’d be ready and my D810 was happy I chose that path.

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Jan 28, 2020 21:36:44   #
rehess Loc: South Bend, Indiana, USA
 
Rongnongno wrote:
- Wide angles will not work as expected due to the multiplying factor (MF).
I am not certain what you expect of a wide angle lens; a 18mm FX lens works exactly the same on a "APS-C" camera as a 18mm DX lens does.

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Jan 29, 2020 01:39:06   #
SteveR Loc: Michigan
 
I prefer fx lenses on dx bodies. You get the center part of the lens and avoid distortion from the edge of the lens.

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Jan 29, 2020 05:21:09   #
jlg1000 Loc: Uruguay / South America
 
Another disadvantage is that FX lenses are designed for a resolution of 24mpx over a FF sensor, so their angular resolution tends to be smaller than a DX lens.

Therefore the percieved megapixels of a 24 mpx DX sensor, get reduced to 13 - 15 if used with a FX lens.

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Jan 29, 2020 05:35:47   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
kfoo wrote:
What are the disadvantages or advantages of using an FX lens on a DX body? Thanks in advance.


Cost, bulk and weight are the negatives. Usually image quality is better because you are using the center third of the lens where there are fewer aberrations and distortion. You also have more options - consumer grade zooms and pro lenses, the latter offering considerably better build quality, moisture/dust sealing, etc etc etc.

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Jan 29, 2020 06:42:04   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
jlg1000 wrote:
Another disadvantage is that FX lenses are designed for a resolution of 24mpx over a FF sensor, so their angular resolution tends to be smaller than a DX lens.

Therefore the percieved megapixels of a 24 mpx DX sensor, get reduced to 13 - 15 if used with a FX lens.


I debunked that myth from Tony Northrup years ago.

What the P-MP score means is that on any given camera a score that equals the actual pixel count is a theoretically "perfect" lens. When any lens is put on a camera, there will a perceptual "loss" of resolution, or more accurately, it will not allow the camera to display as sharp an image as the "perfect" lens.

For example - the excellent full frame Sigma Art 85mm F1.4 scores as follows:

D810 (36.3mp sensor FX) = 36 P-Mp
D300S (12.3mp DX) = 11 P-Mp
D500 (20.9 mp DX)) = 19 P-Mp

This lens works well with high mp and low mp cameras, regardless of sensor size.

A lens that is less "sharp" like a full frame Sigma 150-500 tests as follows:

D700 (12.3mp FX) = 7 P-Mp
D300S (12.3mp DX) = 5 P-Mp
D500 (20.9 mp DX) = 6 P-Mp

And last but not least - a DX lens like a Sigma 18-200 shows the following:

D300S (12.3mp DX) = 5 P-Mp
D500 (20.9 mp DX) = 6 P-Mp
D5600 (24.2mp DX) = 6 P-Mp

So that lens does not really perform well on high MP sensors - higher resolution sensors are not going to produce perceptually sharper images the lens is clearly the limiting factor.

The inference here is that if you have a 150-500 it will perform best on a D700, returning a P-Mp score of 7 against a possible 12.3 mp or 57% of the sharpness of a perfect lens. The worst case would be a DX camera with a dense sensor, the D500 at 20.9 mp, only shows a P-Mp of 6 against a possible 20.9mp, or 29% of a perfect lens.

The minor differences you are seeing between formats have to do with the print magnification factor. Smaller sensors have to be magnified (enlarged) more so images will appear less sharp.

The correct way to use this P-Mp score is to see which lenses will provide the most resolution on a given body, comparing the P-Mp to the actual Mp.

Your assumption that somehow an FX lens that shows a lower P-Mp score on a DX body isn't taking into account pixel density, and is ignoring the magnification factor.

FWIW, there is no lens that tests at 24 P-Mp on a DX body - the closest is the Sigma Art 85, which shows 20 P-mp on a D5600 or 83% of it's resolution. The same lens on a D810 (with a slightly lower pixel density) is 36 P-Mp - or 99% of it's resolution. You are not likely to see any lens surpass the performance of this lens on any body, and on a 12.3mp DX camera a score of 11 P-Mp or 89% is outstanding, as is the 83% on the D5600.

This is not an easy metric to wrap your head around - I had several lengthy email exchanges with the techs at DXO Mark and this represents how best to make sense of it all.

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Jan 29, 2020 06:44:13   #
david vt Loc: Vermont
 
TriX wrote:
Disadvantages:
1) higher cost
2) higher weight

Advantages:
1) a company’s best lenses are typically FF (FX)
2) you are using the center of the lens which is the best quality
3) if you move to FF later, no need to change lenses


Nailed them!

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