[Leica] RD-1 users: Light loss with fast lenses?

[pklein at 2alpha.net (Peter Klein)]

Thanks, Henning and B.D.  I find it interesting that the fastest lenses 
specifically designed for DSLRs so far have been f/2, and most are 
slower.  Why?  Is it just marketing--they guys with spreadsheets have 
decided that "the public" wants mostly slow zooms, plus or two f/2 or 2.8 
macros? Or are there some genuine technical reasons why lenses faster than 
f/2 are a problem for digital as things stand now?

There is a Sigma 30/1.4 announced, which should be available for C and N 
first, and for the E-system after that. I will be very interested in how 
this lens performs.  I am also very interested why a third-party lens maker 
is coming out with a superspeed "normal" digital lens before  the major 
manufacturers came out with their own.

There actually is relevance to Leica in all this.  I always keep coming 
back to available light.  So I want to use fast lenses.  Eventually I want 
a digital RF, though the R-D1 wasn't that camera for me.  I wonder whether 
my Leica and V/C f/1.4  and f/1.5 lenses are going to give me the same 
speed on digital as on film.  It was quite disconcerting to discover, on 
the E-1, that when I opened my 50/1.4 from f/2 to f/1.4, I only got a third 
of a stop more light.  I honestly think it's more than just a t-stop vs. 
f-stop issue.  I think sensor issues such as Henning mentions are partially 
responsible.

That's the reason for my question about the full speed of fast lenses on 
the R-D1.

Add to the mix the fact that film lenses at both full and minimum aperture 
meter in odd ways on DSLRs. The same Olympus 50/1.4 lens mis-meters in 
opposite directions on different DSLRS--underexposing wide-open on an E-1, 
overexposing on a Canon 300D and the Olympus E-300.  My old Vivitar 70-150 
zoom meters the same shutter speed at f/11 and f/16, giving a one-stop 
underexposure at f/16.

None of this prevents using fast film lenses, but you have to do some tests 
to know how your own equipment works.  Squirrely stuff happens at the 
extreme ends of that aperture dial.  My 50/1.4 OM lens takes great pictures 
at f/2, but there's not so much point in opening it to f/1.4 as there would 
be with film.  I hope a Summilux won't suffer the same fate on a digital RF.

--Peter

At 10:54 AM 3/11/05 -0800, Henning Wulff wrote:
[explanation of T-stops deleted for space]

>  should add that older lenses especially, and then rangefinder
>lenses on the R-D1 in particular, will have more fall off at the
>corners as discussed here and at various other places, _and_ will
>also have somewhat lower exposure levels at the center with fast
>lenses due to the edge rays necessarily striking the center more
>obliquely when the lens is used wide open, and thus exhibit some of
>the same 'vignetting' at the center due to non-perpendicular rays.
>
>It might be that the E-1 is more sensitive to this as it was designed
>with 'digitally optimized' lenses in mind, and less compromised for
>the sake of older lenses which did not have their ray bundles as
>perpendicular to the sensor array as the E-1's own lenses.
>
>This isn't very noticeable on my 20D and might not be that noticeable
>on the R-D1 as the latter is definitely intended for 'non-optimized'
>lenses

B.D. wrote:
Keep in mind that Olympus long resisted the use of the old Zuiko lenses
on the E-1, and when they finally gave out an OM to E-1 adapter, they
listed the aperture range at which the lenses should be used - and not a
single lens was recommended for use at anywhere near the maximum F stop.
So it's hardly surprising that you're finding what you're finding.

That said, I've used the 50 1.2 on my E-1 - at 1.2 (why else would I use
it?) - turning it into a 100 f 1.2, and have gotten some surprisingly
good results. I also used the 21 f2.