The DOF of the shorter lens pair makes a superior result but I still
don't understand it. After looking at the amount of extension I'd have
said the effective focal ratio of the short pair was much higher than
the 50+extension but the exposure time is the same. I don't get it.
Chuck Norcutt
Piers Hemy wrote:
> I didn't make a very good job of explaining in words the result of using a
> CCTV lens stacked on a Zuiko 20/3.5, so perhaps a couple of example images
> will do a better job (even if the subject is just a ruler, marked in
> centimeters/millimeters). The files are 150-200k jpgs.
>
> www.hemy.me.uk/Miscellany/50+25tube.jpg was taken with a Zuiko 50/3.5 with
> 25mm extension tube at 1:1, lens at f/22.
>
> www.hemy.me.uk/Miscellany/Tandem20+4.jpg was taken with a Zuiko 20/3.5 with
> 150mm of bellows extension, lens at f/3.5, coupled to a 4mm CCTV lens which
> was mounted to the Zuiko using a custom engineered adaptor. OK, I fitted
> the CCTV lens into a 35mm film canister with a hole in the base to clear the
> Zuiko aperture ring, and clamped the assembly to the Zuiko body using a
> collar (the 'precision' collar was made from gummed paper wrapped around
> another 35mm film canister and left to dry).
>
> The exposure tiume for both images was 1 second, and in each case the ruler
> was placed against the front edge of the taking lens (the 50mm or the 4mm).
> Thus the perspective is slightly different, since the 50mm is much wider
> tthan the 4mm. Also, the repro ratio may be very slightly different.
>
> I suspect the result shows two things:
>
> The Zuiko 50/3.5 can produce bitingly sharp images over a limited range -
> less than 1cm
>
> The tandem arrangement cannot match the resolution of the 50/3.5, but
> produces its best result over a wider image field - perhaps 2cm, but with
> apparently much shallower fall-off.
>
> My impression is that the optically-inferior results are pictorially
> superior - any other views?
>
> --
> Piers
>
> -----Original Message-----
> From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
> Of Chuck Norcutt
> Sent: 11 September 2005 18:57
> To: olympus@xxxxxxxxxx
> Subject: [OM] Re: OM macro lenses?
>
> --snip
>
> Wanna try again :-)
>
> Chuck Norcutt
>
>
>
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