on 11/12/2005 09:39, Chuck Norcutt at chucknorcutt@xxxxxxxxxxx, wrote:
> BTW, where is John? I don't recall seeing any posts
> from him for quite awhile.
Chuck,
This is the last JLind email I flagged, on which BTW he disusses with Moose
one of the questions I had thought to pose him after his research at Puerto
Vallarta.
Fernando.
=========================
on 7/06/2005 23:17, John A. Lind at jalind@xxxxxxxxxxxxx, wrote:
> At 03:50 PM 6/7/2005, Moose wrote:
>
>> The 50/3.5 has its best performance at f8-11 and declines below that. F22
>> is available, but shouldn't be used for critical work. If you look at all
>> the 50mm tests, you will notice a distinct tendency for f16 ratings to be
>> lower than wider apertures. The 135/4.5 macro offers apertures down to
>> f45, but the performance slide starts at f22 and by f45 is really iffy,
>> worse than the 50/3.5 at f22.
>
> Both those lenses stop down that far because they're macro's. I have just
> done a series of them pushing to 1:1 which is life-size on film and more
> magnification than I had used in the past. Depth of field can be extremely
> shallow when simply making a "close-up" between 1:8 and 1:4
> magnification. Crank it up to 1:1 magnification and it's extremely shallow
> making the photography of anything but a relatively flat, and keeping the
> desired subject material within the depth of field nearly impossible.
>
> The recent photograph of the dwarf Iris took several hours to
> accomplish. About 2 hours was spent getting lighting direction and its
> quality of diffusion on the Iris how I wanted them. About an hour was
> spent making various photographs, where critical focus was placed on it,
> and making minor tweaks with the axis of lens related to the axis of the
> Iris blossom so that areas of it were almost exactly the same distance from
> the film plane . . . and that was stopped down to f/11. I could have
> gotten to f/16 if I'd had sufficient light power . . . but at 1:1 using
> lens extensions, there's also a 2-stop light loss and could only get to
> f/22 with the flash meter at full power with the light as close to it as I
> could without causing a number of other problems. The depth of field in
> the Iris photograph appears to be about 1/8th inch or less (for about an
> 11x14 print). How I would have loved to stop down to f/16 (max for the
> 85/2) but couldn't.
>
> The 50/3.5 stops down to f/22 and the 135/4.5 stops down to f/45 to allow
> the greater depth of field when it's desired at high magnification . . .
> the trade-off being some softening from aperture diffraction to gain
> additional depth of field. With high magnification macros, something is
> either in or out of the depth of field; there's nearly zero "boundary" zone
> before it's unmistakably out of focus.
>
> -- John Lind
>
>
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