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Re: [OM] Can't believe this happened! Hope it didn't happen to you

Subject: Re: [OM] Can't believe this happened! Hope it didn't happen to you
From: Moose <olymoose@xxxxxxxxx>
Date: Mon, 02 Nov 2009 02:14:58 -0800
Carlos J. Santisteban wrote:
> Hi Moose, Ken, Joel and all,
>
> From: Moose <olymoose@xxxxxxxxx>
>   
>> I'm still mystified by the allure of the 50/1.2.*  It's only 1/3 stop
>> faster than f1.4.
>>     
>
> Well, it's closer to be half a stop faster ;-)
>
> At such small f-numbers there's a lot of rounding in action, but half-stop 
> faster than F1.4 (or f/1.4142135..., the square root of two) should be near 
> f/1.19 -- f/1.2 seems accurate enough to me. OTOH, a third of a stop faster 
> than 1.4 is more like f/1.26.
>   

 From a strictly mathematical standpoint, I slightly disagree.

f1.4 + 1/4 stop = 1.26
f1.4 + 1/3 stop = 1.22
f1.4 + 1/2 stop = 1.15

So, f1.20 would be very slightly less than 1/3 stop faster than f1.41. 
Because I wasn't sure how to do partial stops using direct math, my long 
ago created spreadsheet calculates the reduction of lens area, then from 
that the diameter and from that the focal ratio, working down from f1.0 
to f64 in 1/2, 1/3 and 1/4 stop increments.

None of this precision matters, considering normal sample variations in 
real lenses. For example, Modern Magazine tests showed:

50/1.2 measured f-stop = 1.26 measured focal length = 52.48
50/1.4 measured f-stop = 1.44 measured focal length = 50.94
50/1.8 measured f-stop = 1.86 measured focal length = 51.87

In the case of these particular samples, the f1.2 was barely within 
their standard of ± 5% and was only 1/4 stop faster than the tested f1.4.

> ...
>> The difference in optical performance vs. the >1,078,000 50/1.4 in
>> Gary's tests is pretty minor - except wide open.
>>     
>
> Despite being the best version of 50/1.4 Zuikos, it's far to be class-leader 
> in any way, at least at the widest apertures :-(
>   

I'm not sure what this might mean in context. I was only talking about 
the Zuiko 50/1.2 vs. 50/1.4.

>   
> ... Precisely. According to my astro-tests, this is the worst of its class... 
> but in real-life, terrestrial pictures it shows a certain look, very 
> difficult to describe but surprisingly nice to the eyes. I believe Ángel
> Lobo agrees with me about this ;^)
>   

I am not convinced that what's best for astro is best for terrestrial. 
Based on Gary's 1:40 tests of an extended subject, none of the other 
brand 50 mm lenses were noticeably better than the comparable Zuikos in 
resolution.

> Moose wrote:
>   
>> Yeah, I'm assuming that those characteristics would be much the same for
>> those two lenses. Both come from the later stages of OM lens
>> development, use the almost identical double-gauss design
>>     
>
> 'Almost' is the key here. There are no evident differences on the optical 
> design of the several 50/1.4 Zuikos, neither between the 55/1.2 and 50/1.2, 
> but there are notable performance _and_ character differences.
>   

Yes, I understand that. What I was saying is that the latest 50/1.4 
design and the 50/1.2 design were made at about the same time, with the 
same glasses and coatings available, and probably by the same designers. 
So one would expect them to be more like each other than like the much 
earlier 55/1.2 and single and early multi coated 50/1.4s.

Moose
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