Why Zeiss exposes 1 stop brighter than Nikkor

I suspect many folks have an enormous amount of time available thanks to the pandemic. Also, could be result of searches while not realizing they are reading a ten year old post. Who knows, and what's the harm?

The thread may be old, but the topic is current.

What is it with answering on 10 year old posts lately?

I feel younger already. :)

The OP was last seen on this forum in January 2011!

I always hate threads that just come to a stop, with a 'Where's the OP gone after all these suggestions?'

 

We want to know what the resolution was!

 

If you search for the subject online it will turn up a potentially very useful thread that has just snapped with no conclusion.

 

....but by being found and opened it will climb it's way up the rankings and thus appear higher up in the results table, so the next searcher finds it too.... and..and..and.....:(

Well . . . Since, as noted, someone may find this thread on a search, I'll throw out another possible answer:

 

The OP was shooting in Nikon's Matrix metering mode with a, then, current Nikkor lens and a, then, new Zeiss. Nikon doesn't publish the CPU specs for their lenses so the third party suppliers need to reverse engineer the specs in order to produce CPUs for their lenses. It may be that Zeiss didn't have that engineering quite worked out.

 

Or course, it would have been nice of the OP had told us which of the images was better exposed.

T versus f/ stops accounting for one whole stop exposure difference? I don't think so. Not with any multi-coated lens.

 

More likely to be vignetting upsetting the matrix metering, or maybe a misaligned AI tab on one of the lenses.

 

We may never know..... and really, after 10 years why should we care?

Metering is done with the aperture wide open. Nikon uses a rather delicate mechanical coupling to set the final f/stop and relies on free movement of the diaphragm. If the lens is not fully open at the start, or doesn't close far enough for taking, the exposure will be greater than calculated. A quick check would be to test the lenses on a different camera. Any stickiness in the diaphragm, for example by oil contamination, would tend to cause over exposure.

<p>A zoom lens has more elements and will transmit less light than a prime lens. This is normal.</p>

 

The problem with your explanation is that the metering occurs after light has passed through the lens.

Well, if we're going to continue to beat this ancient thread to death, let's re-examine the 'evidence'.

 

1. Sticky aperture or bent actuator: The OP's first examples were with both lenses set wide open. The OP also reports that the image brightness difference was constant across a range of apertures. This pretty much eliminates a faulty aperture actuator or oily aperture blades as the culprit.

 

2. The T-stop versus F-stop thing: Pretty much a red herring IMO. The TTL metering would/should have taken the transmission of the lenses into account. So even if a different shutter speed was set by the camera, this shouldn't have resulted in an image brightness or drastic histogram difference.

 

However, the OP should have set both the shutter speed and aperture manually in order to check if there was a difference in transmission between the two lenses. This doesn't appear to have been done.

 

3. Vignetting: My experience is that the degree of vignetting certainly affects matrix metering. Or CW metering for that matter.

 

Also, if the OP was judging from JPEGs, then the Nikkor lens may have had automatic vignetting correction applied, while the Zeiss lens remained uncorrected.

 

Therefore vignetting remains a possible cause in my book.

 

4. Lens faults: Another possibility. A misplaced AI tab perhaps? Or a poorly programmed CPU? But the latter would surely show up as incorrect EXIF data.... or maybe not.

 

My conclusion is that options 3 or 4 are the most likely explanation(s), but I may well have overlooked something.

 

And is this the face of anyone that cares?:)

Edited July 15, 2020 by rodeo_joe|1