I wanted to thank you for the retrofocus analysis on the small size of
the 40/2. I suppose I could have figured that out on my own had I
thought to connect all the dots but sometimes I see all the dots and
fail to connect them.
Chuck Norcutt
Moose wrote:
> Manuel Viet wrote:
>
>>Le lundi 06 Novembre 2006 14:02, Chuck Norcutt a écrit :
>>
>>>here's Khem when we need him? Why did Olympus decide to produce a 40mm
>>>f/2? Optimum focal length for producing a low cost moderately fast
>>>normal lens? If so, why was that Zuiko 50/1.8 the "normal" lens.
>>>
>>
>>I seem to remember reading an interview where Maitani stated that he wanted a
>>full line of lenses at f/2, and was using the 40mm himself. Ah, there it is :
>>
>>http://www.geocities.com/maitani_fan/om_interview_2.html
>
> In a broader and more technical sense, a 40/2 'pancake' lens makes
> eminent sense, and they have been made by others than Oly. The distance
> from film plane to lens mount flange for most 35 mm MF SLRs is between
> 42 and 46.5 mm, with OM at 46 mm.
>
> As lens focal length gets shorter, there comes a point where a
> conventional, semi-symmetrical lens design like that used for almost all
> 'normal' lenses in the 50 mm range, can no longer be used, as the rear
> element would get hit by the mirror. This point is at around 40 mm. So
> down to there, the shorter the focal length, the smaller the lens can
> be. (F2 @ 40 mm requires a 20 mm front element; a 50 mm lens requires 25
> mm, 85 mm=>42.5 mm.)
>
> Beyond that point, wide angles require retrofocus optical designs, which
> locate the rear node behind the actual last element. These get bigger
> and more complex, so around 40 mm is the smallest lens that can be made
> for SLRs. Interchangeable lens RF cameras don't have mirrors, so the
> lens can project back almost to the film. As a result, their lenses
> shorter than 40 mm are smaller and lighter and optically simpler than
> comparable SLR lenses.
>
> As to why f2, why not? Faster retrofocus designs are complex, large and
> expensive compared to slower ones. The original OM WAs are relatively
> slow for those reasons. Most lenses using the same basic optical formula
> used in 40/2s are actually faster than that. Take a look at the
> similarity in optical layout of the 40/2 with the 50/1.8 and 1.4. So f2
> at 40 mm isn't any big deal, nor anything like the achievement it is at
> 35 mm, let alone 21 mm.
>
> Moose
>
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