[Fkid]

Hello,



I've recently purchased a D800 and a 50 1.4 G.



Doing tests of the same scene through all the aperture values (ex: 1/250 f1.4, 1/125 f2.0, 1/60 f2.8 etc..), I noticed some changes in luminosity (apart from 1.4 and 2.0 due to vignetting).

I supposed it should be a small problem with that copy of the lens, so I returned it to the shop and get another one.

And the new one has exactly the same behaviour. This is:



f4 - f5.6 - f8 all perfectly equal. I choose them as the point of reference.

f2.8 a bit lighter than the reference.

f1.4-f2.0 a lot darker, due to vignetting so I accepted it as normal.

f11-f16 exactly equal between them, but both a bit darker than reference. (1/6 of a stop).



So if the same behaviour repeated in two different copies I guess it should be a design thing.



I've discarded any issue with the shutter speeds, d-lighting is off, etc.



Ok, the changes in luminosity are small, but I've never seen something like this. Since digital I've always shot canon, mainly with L glass, but I think, except wide open, all lenses I've shot keep the luminosity without changes along all aperture range.



So: is that normal with the 50 1.4 G?



Thanks

[popo]

I'm not sure where to find it again, but camera manufacturers were found to be boosting the exposure slightly at wide apertures. It was a small but detectable effect. I know Canon were doing this, but can't remember specifically if Nikon were too. There was a simple test, which was to twist the lens slightly so that it no longer coupled electronically to the body, and repeat the same exposure settings. You can then examine the RAWs to see if the resulting exposure really was the same. Of course care should be taken to remove other variables, such as flickering lights in the test area.

[Fkid]

That was a nice idea to test, but as a G model doesn't have an aperture ring. I have just checked, and when I start to twist the lens, the diaphragm just starts to close.



I have tested it under different sources of light, and shutter speeds, so I would discard these variables.



And with that same particular behaviour in 2 different copies, I think it has to be a design issue.



Is not a major problem, if you know it and expect it. It's just strange.



As I said before, I haven't shot with too many different lenses in digital, so I couldn't say if this happens in more lenses. It's just the first time I see it.



I also have to note that, apart from this, I find the lens quite nice.

[Brightcolours]

Cameras of all brands capture less light with big apertures, some light gets lost due to the nature of how the light hits the microlenses. All manufacturers amplify the signal to hide this effect.



Canon regulates the aperture totally electronic, and is in general a bit more precise with it than Nikon. I think it is not too unusual what you are seeing with your 50mm f1.4, the differences are small as you state.

[mst]

Yep, that's normal. The aperture is controlled mechanically instead of electronically (except on the PC-E lenses), so unlike to what you're used to from Canon with their electronically controlled apertures, there is some variation in the movement of the aperture blades between two shots because of the mechanical link. You can actually move the aperture lever manually when the lens is not mounted, it's a pin at the rear end of the lens.



If you do series of multiple exposures with the same aperture setting, you'll most likely notice a slight variation of exposure betwen the shots. The smaller the aperture, the more a slight variation in blade movement becomes noticeable. Up to 1/3 of a stop is pretty normal and not something I would worry about.



-- Markus

[netrex]

So, it's "better" to do f/1.4 in complete manual mode then (manual lens) so the camera doesn't know it's f/1.4 and won't boost the exposure? I'll have to test this with my f/1.4 lenses in with the aperture ring both at A and on complete manual.

[Brightcolours]

[quote name='Alexander ' timestamp='1343814637' post='19660']

So, it's "better" to do f/1.4 in complete manual mode then (manual lens) so the camera doesn't know it's f/1.4 and won't boost the exposure? I'll have to test this with my f/1.4 lenses in with the aperture ring both at A and on complete manual.

[/quote]

If you are not using the bigger aperture to capture more light to keep the exposure time short, I guess you can think of it as "better".

[Fkid]

Thank you all!



Just to be sure I get it right (this is my first nikon ever): so, the amount of aperture in a G lens is defined by the amount of movement the camera gives to the rear pin?



Is not like a mechanical camera where the rear pin always go to the end and the blades just get stopped mechanically at the correct point by the position of the aperture ring, right?



Then, is possible that my camera just moves the 2d stop (don't count wide open) too little, the 3,4 and 5 perfect, and the 6 and 7 a little too much? and I will see this in every G lens?



I only have this lens by now, so I can't check it.