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DX verses FX

LenShepherd 10 3.6k United Kingdom
19 Oct 2011 10:28PM

Quote:Len, I fitted the 105 VR Micro to a body, set the aperture wide open to f2.8 and then manually focused closer. At half life-size, the aperture display said f3.5 and at 1:1, it was f4.8.

The Nikon macro lens aperture "trap" Smile
The aperture displayed is not the one used for exposure!
To check this out set the aperture to f4, focus at infinity, press depth of field preview and observe the aperture blades stop down.
Now repeat at 1:1 focus - and observe the aperture blades stay open.
Now set the lens to infinity focus minimum aperture f32 - that is what you get in the readout. Change focus to 1:1 and you can get f51.
Getting technical a symmetrical 105mm f2.8 macro lens (if one exists) at 1:1 transmits f5.6 light due to lens extension.
The lens would also double it's physical length to 210 mm. This looses 2 stops dof. The aperture stays the same size becoming effective f5.6 gaining 2 stops dof to cancel out the loss due to extension - so nothing to worry about - with a symmetrical lens.
AF macros are not symmetrical and achieve 1:1 mainly by changing the angle of view and not physical length. This change in angle of view changes the effective focal length and effective aperture compared to infinity as you focus closer.
For reasons Nikon do not explain, possibly to do with metering, the display aperture and taking aperture are different on the 60, 105 and 200 AF macros.

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miked70 9 225 3 South Africa
20 Oct 2011 7:10AM
Nikon 35mm f1.8 (DX lens)
Nikon 50mm f1.8 (DX lens) (the new lens)
Nikon 70-200mm f.2.8 VR2 (FX lens, I thought) New

all of these are what i call FX/DX lens means they will work perfectly on either format
the others will be crop on FX body so by buying this type of lens you do not need to replace them if you go to FF body for full benefit
peterjones Plus
16 4.7k 1 United Kingdom
20 Oct 2011 11:02AM
I guess that DX v FX may be a favourite debating point.

I own both systems using my FX system for weddings and other pro jobs; to walk around taking pictures for myself or/and for stock I prefer the lightweight DX system.

I know that a DX sensor will crop my image but have no effect on the actual focal length of my lens; a DX sensor everything else being equal will increase my DOF slightly; a DX lens will have no effect on perspective, the only effect on the latter is my choice of distance to the subject and the distance of the subject to the background.

Many lenses do change their focal length slightly as you focus; the importance of the characteristic is up to the individual; I know it therefore I can forget it.

I prefer FX for weddings for it's greater dynamic range and ability to cope with a very high ISO; for example I have achieved very acceptable images at 9000 ISO with my D3S in very dark churches.

Horses for courses and each to their own; if I wasn't a pro photographer I would probably just own the DX system.
LenShepherd 10 3.6k United Kingdom
21 Oct 2011 9:46AM

Quote:Nikon 35mm f1.8 (DX lens)
Nikon 50mm f1.8 (DX lens) (the new lens)
all of these are what i call FX/DX lens means they will work perfectly on either format

The 50mm f1.8 D and G lenses are FX - maybe you mean the recent 40mm DX macro.
Whilst the 35mm f1.8 DX has a wide image circl, corner quality on FX is quite low - which is probably why Nikon designate it a DX lens,

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