I was told that an fx lens on a dx body was 1.5 times the focal length. So a 200mm fx lens is 300mm on a dx body. Is that correct? But what I tried today slightly disproved that. I have the sigma 70-200mm f/2.8 lens. I also have the Nikon 55-300mm f/ 4.5-5.6 lens. I took a picture of an object from the same spot with both lenses at full zoom. I found the 300mm picture to be a little closer than the 200mm one. I shot both at F/8 with the D5200 . Anyone else ever tried that? I would say that it seemed more like 1.4 crop factor. I may be wrong or missing something but just wanted to mention it. Thanks
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The 1.5 crop factor
- Thread starter bandit993
- Start date
The same lens is the same focal length, regardless of which DX or FX body it is on. There is absolutely no change to the lens.
A DX lens simply only covers a DX sensor, and will not cover the corners of a larger FX sensor. A FX lens will.
A DX 300 mm lens and a FX 300 mm lens are both 300mm.
The difference in DX and FX is called "crop factor", due to sensor size.
The DX sensor is smaller, so it crops that image smaller, for a more narrow view... which then (with Same lens, standing in same spot, focused on same spot) makes DX LOOK like a 1.5x longer lens than does a FX 1.5x wider field of view.
It is ALL about the crop (of that same lens) resulting from the sensor size.
The field of view is all that changes. And the fact that DX has to be enlarged 1.5x more than FX, to see the same size final image.
Cropping any image smaller gives it a telephoto look. Just zooming in more in your photo editor shows this. Same thing, just a crop.
A longer lens is a more narrow view.
A smaller sensor crop is a more narrow view.
The crop will have fewer pixels, but they look pretty much alike.
See Camera Sensor Crop Factor and Equivalent Lens Focal Length
The marked focal length applies to infinity focus. If focused up close, then the focal length has to change from what is marked. All lenses must do that ,but they vary a bit in what they do, esp zooms.
A DX lens simply only covers a DX sensor, and will not cover the corners of a larger FX sensor. A FX lens will.
A DX 300 mm lens and a FX 300 mm lens are both 300mm.
The difference in DX and FX is called "crop factor", due to sensor size.
The DX sensor is smaller, so it crops that image smaller, for a more narrow view... which then (with Same lens, standing in same spot, focused on same spot) makes DX LOOK like a 1.5x longer lens than does a FX 1.5x wider field of view.
It is ALL about the crop (of that same lens) resulting from the sensor size.
The field of view is all that changes. And the fact that DX has to be enlarged 1.5x more than FX, to see the same size final image.
Cropping any image smaller gives it a telephoto look. Just zooming in more in your photo editor shows this. Same thing, just a crop.
A longer lens is a more narrow view.
A smaller sensor crop is a more narrow view.
The crop will have fewer pixels, but they look pretty much alike.
See Camera Sensor Crop Factor and Equivalent Lens Focal Length
The marked focal length applies to infinity focus. If focused up close, then the focal length has to change from what is marked. All lenses must do that ,but they vary a bit in what they do, esp zooms.
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The 1.5 crop factor had me a little confused when I was first learning about FX vs DX. I'm taking a wild guess that you felt (from your reasoning of the 1.5 crop factor) that the 200mm FX lens should come out to be about the same FOV as the 300mm DX lens. Is that what you were trying to say? If so, it's a common mistake for some folks to assume the DX designation on lenses "factors" in the crop factor. But that's not true. 300mm is 300mm is 300mm etc. The DX designation more or less tells the photographer that the projected image from the lens will not cover an entire FX sensor.
Thanks for the replies. It is very confusing. PapaSt You are right I was thinking FOV. That is interesting because the 200mm is almost the same FOV as the 300mm FOV. So there seems like the 100mm difference in the two lenses is almost nothing. Would I have seen more difference had the both been fx lenses? it seem like the mm means very little. Maybe I should have stuck to my other hobby. I know the difference between 22lr and 45acp.. hahaha Does anyone else have a problem typing on this site? If I type really slow it works otherwise it misses a lot of characters?? thanks again..
No. On a dx camera, you won't see any difference between a dx and fx lens.Would I have seen more difference had the both been fx lenses?
Here's a big long thread to read though on crop factor. Check out pictures in post #1 and #26.
http://nikonites.com/education/24328-dx-fx-photo-explanation-crop-zoom.html#post335209
I believe what you experienced is what Wayne described in his last paragraph. I think it is called 'focus breathing' if you want to google for more info. As Wayne said, you need to be at infinity to get the full zoom. To say it another way, if your subject is nearby, you won't get what you expect for a 300mm zoom. Try your comparison at infinity focus and you will see more difference.