Yes, that starts to make a kind of sense. I'm not so sure about the
macro-focussing range as an explanation as I once had a Micro-Nikkor
(55mm/3.5? - it's been so long!) and, from memory, the actual elements
were very small although in a standard Nikkor barrel size.
However, I suspect that creating a very large image circle may be a cheap
way of reducing image distortions and vignetting - the centre may be more
rectilinear and evenly lit - as many older, cheaper off-brand lenses seem
substantially bigger than their Zuiko eqivalents (i.e. I have an old
Vivitar/Panagor 28/2.5 which is three times the size of a Zuiko 28/2 - 62mm
filter ring!)
Andrew
>At 11:38 10/7/00 , Andrew Fidles wrote:
>>
>>Hmmmm. How then do you explain the size of the 80/2.8 Planar on a
>>Rolleiflex? A lot of quite fast lenses on folders were TINY compared to
>>35mm lenses of equivalent speed. Surely the lack of focussing movements
>>can't explain it all, especially given the built in leaf shutter.
>>Andrew
>
>Yes, and a couple of other very small lenses are the Rollei 35S f/2.8
>Sonnar, as is the original 50/1.5 Sonnar for the ZI Contax (focus helical
>on body, not lens).
>
>There are other design considerations (or goals) which muddy up the waters
>on lens objective diameter versus its speed. One of them is minimum focus
>distance. Another is how much bigger the image circle diameter is than the
>film gate diagonal.
>
>Minimum focus for both of the above Sonnar lenses is 3 feet. The minimum
>on the Sekkor I mentioned is about 2 feet, and going from 3 to 2 feet
>extends the lens considerably further. Minimum focus distance is a very
>real problem in making a fast macro lens that focus to infinity also.
>Classical close focusing by continuing to move the lens farther away from
>the film plane does reduce the light. The image circle grows considerably
>at very close distances, as is the extension required. It's the reason an
>extension tube reduces effective aperture. I haven't seen many older
>(vintage) cameras that get below 3 feet with a "standard" lens.
>
>Cos^4 falloff is another issue, especially for shorter focal length lenses.
> One of the standard methods for reducing it is designing a larger image
>circle to put the falloff outside the corners of the film gate. I don't
>think the older cameras (i.e. the folders) did this as much and you see
>more falloff in their lens formulations. Many, but not all, older
>(vintage) camera lenses do exhibit more falloff leading me to believe at
>least a sizeable portion of it is due to an image circle diameter closer to
>the film gate diagonal.
>
>I don't know what the minimum focus distance is on the Rolleiflex and its
>f/2.8 Planar, but it must be somewhere between 3-4 feet? Most older
>cameras do not focus "standard" lenses below that.
>
>-- John
>
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