DX or not DX..that is the question

W

weardalered

Suspended / Banned
Messages
121
Name
Clive
Edit My Images
No
I am refering to a DX lens of course.

My question is this. If I purchase a FX lens and use it on a DX camera where the main picture area of interest would be a small area in the centre of the lens, would I obtain a sharper picture than if I use a DX lens of the same focal length?

Would the crop factor be the same?

TIA
 
Crop factor is the same so a 50mm DX lens will give the same image as a 50mm fx lens if you use them on the same body.

The other question is a bit harder to answer. Potentially the the FX lens could be sharper as many lenses are softer in the corners than the centre. Because DX chops the outer edges off (or more accurately doesn't see them) then you may benefit. It might also vignette less. However all of this very much depends on the two lenses you're comparing.
 
As I see it, the only difference, as mentioned above, is that a DX lens is made specifically for DX crop sensors. This means that the image circle produced is smaller, as it only needs to cover the smaller sensor. The main benefit to this is physical size and weight of the lens, as it uses smaller elements.
As already said, the focal length is the focal length, the difference is the field of view.
Of course the other factor to consider is whether in the future you intend to go to full frame, as the DX lenses would not be Fully usable on the FX camera.
 
GHP said:
As I see it, the only difference, as mentioned above, is that a DX lens is made specifically for DX crop sensors. This means that the image circle produced is smaller, as it only needs to cover the smaller sensor. The main benefit to this is physical size and weight of the lens, as it uses smaller elements.
As already said, the focal length is the focal length, the difference is the field of view.
Of course the other factor to consider is whether in the future you intend to go to full frame, as the DX lenses would not be Fully usable on the FX camera.
Click to expand...

Generally speaking, all other things being equal and all that, an fx lens should be better. The fx lens gives a larger image circle, and the centre of the lens is generally the best optical quality, so just using the centre should be better.


Having said that i've owned both nikon 35mm primes , the f2 fx and f1.8 dx. the dx is the better lens, .....
 
probably a silly question, but if you use an FX on a DX body, isn't there a chance of the larger light field causing problems inside the light box ? ie secondary reflections off the sides - probably a daft question:cuckoo:
 
not a silly question!! i've never heard of any such problems discussed, even among the more 'anal' technical forums!
 
vizzair said:
probably a silly question, but if you use an FX on a DX body, isn't there a chance of the larger light field causing problems inside the light box ? ie secondary reflections off the sides - probably a daft question:cuckoo:
Click to expand...

The light box is matt black to absorb any surplus light. The lens forms a circular image, both DX and FX, so there is always a need to absorb the light not going to the sensor / film
 
OK, so that's confirmed my initial thoughts, thanks for the replies.

What I was coming round to was that I have en eye for the newer 18-200 DX lens, but thought if there was going to be a huge difference then I would look at an equivalentish FX lens.

I also need to sell my Sigma Bigma.
 
weardalered said:
I have en eye for the newer 18-200 DX lens, but thought if there was going to be a huge difference then I would look at an equivalentish FX lens.
Click to expand...
There isn't really an equivalentish FX lens. The FX "equivalent" is the 28-300, but it's only equivalent in the sense that 28-300 on FX gives you a similar range of compositions as 18-200 on DX. Most people would probably say that 28mm isn't wide enough for a walkaround lens on DX.
 
I've heard it said that a few FX toggers are a little annoyed that their 24-70 f2.8 performs better on a DX body than it does on a FX one. I can certainly vouch for the quality of a 24-70 on a D7000 as thats what I mainly use now. I have no problems of reflecting light around the lightbox either.
 
It depends IMO.

Put a 17-55mm (DX) against something like a 24-85mm (35mm/FX) and the DX lens will probably be the sharper, even though they have similar uses (albeit the latter having a variable aperture).

You have to compare apples-with-apples in every case I feel and not just looking at it as a FX vs DX comparison....
 
You must log in or register to reply here.
Back
Top