Nikon 70 - 300 DX versus 70 - 300FX

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ManVan

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If I've read it right Tony Northrupp (on you tube) seems to say that DX lens are preferable to FX lens on a crop body. I use a 70-300 FX lens on my D7200 and wonder if I should consider swapping for the new DX version.

The weight saving would be an advantage but am starting to wonder if there may be IQ benefits as well.

The FX is f4.5 - f5.6 but the equivalent on a crop body would be f6.5 - f8.4 whereas the DX lens would be exactly what it says on the tin f4.5 -f6.7 therefore faster.

Have I got this a wrong?
 
Yes, you have it wrong. A f4.5-f5.6 on a FX is still the same on a DX camera. The DX camera just uses a smaller portion of the image circle.
 
JackBell said:
Yes, you have it wrong. A f4.5-f5.6 on a FX is still the same on a DX camera. The DX camera just uses a smaller portion of the image circle.
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This - the numbers mean exactly the same on your camera irrespective of whether it's a DX or FX lens.

If you didn't have either then the DX one might be worth getting but as you already have the FX version I don't se much point in changing.
 
JackBell said:
Yes, you have it wrong. A f4.5-f5.6 on a FX is still the same on a DX camera. The DX camera just uses a smaller portion of the image circle.
Click to expand...


Nawty said:
This - the numbers mean exactly the same on your camera irrespective of whether it's a DX or FX lens
.
Click to expand...

Thanks for your replies guys. I've always thought the same as you but it seems current thinking is that crop factor should be applied to fstops as well as focal length.

Off to do some more research.
 
ManVan said:
Thanks for your replies guys. I've always thought the same as you but it seems current thinking is that crop factor should be applied to fstops as well as focal length.

Off to do some more research.
Click to expand...


Only in terms of depth of field but not in terms of exposure, which is what really counts.
 
Nawty said:
Only in terms of depth of field but not in terms of exposure, which is what really counts.
Click to expand...

Indeed. And the same 'correction' would apply to both lenses anyway whether they're dx or fx. Unless you need to save some weight I cannot see any real benefit in swapping.
 
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