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Steve Spencer wrote:
Ok, so we can all agree this is an f/2 lens, or at least I hope we can all agree. I think we can all agree that the lens has strong vignetting when it is not corrected. My lens performs just like the lens that Bastian reviewed. Here is a link to his picture depicting the vignetting:
https://phillipreeve.net/blog/wp-content/uploads/2022/04/vignetting_Voigtlander_VM_28mm_2.0.jpg
As you will see there the corners are definitely darkened at f/2 and there is even some darkening on the long edges (but very little to no darkening on the short edges). This tells us there is a circle with a 24mm diameter in the center that does not have significant reduction in illumination. I don't think it is accurate to call that a small section in the center, but call it whatever you want we can describe the actual measurement of the bright area in the center.
Further given this, IMO, rather larger 24mm circle with little to no effect of vignetting I can't see how changing the aperture on your lens from f/2 to f/2.4 doesn't change the shutter speed. If I were you I would investigate both your camera and lens to see if they are functioning properly. Opening up the lens to f/2 from f/2.4 should get you about a 50% increase in shutter speed and that is what I see with my camera (M10) and my copy of the lens. Now I do always use center weighted metering and perhaps you will have better luck if you switch to center weighted metering if you are using something else. Of course one of the advantages of center weighted metering is that it isn't affected very much at all by vignetting when exposure on the outer part of the frame is not much of a concern.
Finally, it should be noted that either six-bit coding this lens or selecting in Lightroom corrections for the Leica 28 summicron, nicely cleans up the vignetting. The majority of my shots using a rangefinder I crop to 4 X 5 aspect ratio, so I don't bother with vignetting correction for most of my shots, but when I need it with this lens it does work quite well with all the usual caveats about increasing noise in the corners.
So, this is a f/2 lens with a lot vignetting. Each individual user will have to decide how much the vignetting bothers them and even whether it is a deal breaker for the lens and if it is not how they want to handle it. Personally, I find it a mild annoyance but not really that big of a deal....Show more →
Both my lenses and camera are functioning fine. A difference in exposure is absolutely noticable from f/2 to f/2.8. From f/2 to that half step position, which I refer to as f/2.4, the difference is so small that keeping the shutter speed the same results in two images that look identical with exception of little brighter small central area. The 28mm Elmarit that I had, my Color Skopar 35mm, and Summicron 50mm all show a much wider spread affect of exposure with the first half step.
In terms of my attempts at matching brightness at the centre, the difference between f/2 and the half step to f/2.4 on the Ultron 28mm is around 0.25 stop.
I get it, its an f/2 lens because (unverified) the aperture measurement is theoretically wide enough to claim the nominal value. It may or may not be a rounded value too. Who knows. But as much as aperture should be aperture value, so should focal length be focal length. But then we have situations like the Leica Q with its 28mm lens.
Anyways. I suppose I was more questioning the point at which one should accept a claim of a lens being f/2. Suppose the next lens that comes along and claims its f/2, but with a transmission change across an even smaller portion at the dead centre. Still acceptable?
Here are two images shot with the Ultron 28mm. Both have the same shutter speed and ISO value. Aperture was the only thing changed from f/2 to the next half step f/2.4. It would seem this is perfectly acceptable for most. I find it disappointing and pointless that the lens has an f/2 aperture that may technically classify as f/2 but functionally falls short. Again, the difference in brightness in Lightroom is around 0.25 stop to match brightness. Lets even round that up to 0.3. Still a fair bit away from the supposed 0.5 stops at dead centre!
(The lens is in camera coded to the Summicron 28mm ASPH)
1/45sec, f/2
1/45sec, f/2.4
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