50mm APO-Summicron - reported aperture smaller than 50mm Summilux-ASPH?

[IkarusJohn]

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19 hours ago, jaapv said:

That assumption is incorrect. It only denotes that the mathematical relation between the aperture and focal length is the same. It does not  tell us anything about the amount of light passing through the lens other than a more or less accurate derivative. 

So, when used on a manual film camera, Leica’s lenses at the same f/stop will provide different illumination? What you suggest is that an external light meter will not provide accurate readings for different lenses? That would seem a novel suggestion.  

[jaapv]

Well, not THAT novel. This has been known since lenses are used.  Anyway, half a stop on film?  Are you going to see that or even measure it  outside an optical laboratory? It is well within the sensitivity variability of film. (One of the reasons why cine film is bought in one batch for an entire film)

It has only become visible since we have EXIF. Say, twenty years. And as general knowledge maybe since DXO started publishing the tables.

[IkarusJohn]

34 minutes ago, jaapv said:

Well, not THAT novel. This has been known since lenses are used.  Anyway, half a stop on film?  Are you going to see that or even measure it  outside an optical laboratory? It is well within the sensitivity variability of film. (One of the reasons why cine film is bought in one batch for an entire film)

It has only become visible since we have EXIF. Say, twenty years. And as general knowledge maybe since DXO started publishing the tables.

But not significant. Looks like another Rabbit hole Jaap.

Having taken the time to test the theory, no issue for me.  Not sure I trust DXO enough to bother reading it.  Perhaps a reflection of my sloppy metering.

[Jeff S]

Back in my film days, I was aware that in order to conduct precise film speed and development time tests, one should standardize both camera and lens (and meter). But I usually ignored the lens requirement, given typically broad latitudes.

Jeff

[jaapv]

Fully agree. In real life half an EV value is neither here nor there. On digital even less so. 

However, the thread was not about any pictorial results, it was about the theoretical background of the fact that f2.0 is not always f2.0.

[wizard]

vor 11 Stunden schrieb jaapv:

Anyway, half a stop on film?  Are you going to see that or even measure it  outside an optical laboratory?

True, no issue at all on negative film. But on slide film, half a stop is clearly visible. I have used color slide film extensively from 1973 onwards, so do know how that sort of film reacts to over- and underexposure. Essentially, with color slide film, there is almost no exposure latidtude.

[jaapv]

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The is true again With important shots I used to exposure bracket. In general I preferred a slight underexposure

[farnz]

4 hours ago, jaapv said:

The is true again With important shots I used to exposure bracket. In general I preferred a slight underexposure

I used exclusively (the original) ISO 50 Fuji Velvia 120 for 15 years for landscape work and I shot it at ISO 40 to slightly overexpose compared with box speed.  I found that dark shadows were just a killer with Velvia.

Pete.

[jaapv]

Not much experience with Velva. I always found that Kodachrome had pleasing intense colour with slight underexposure

[IkarusJohn]

7 hours ago, farnz said:

I used exclusively (the original) ISO 50 Fuji Velvia 120 for 15 years for landscape work and I shot it at ISO 40 to slightly overexpose compared with box speed.  I found that dark shadows were just a killer with Velvia.

Pete.

I’m still using Velvia 50 in my SWC. 

[mediumformula]

 

In Post #117 in the following thread, a member tested the 8 element 35 Cron with the v4 'KOB' and showed that the 8 element was about a half stop slower.