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[OM] Re: OM macro lenses?

Subject: [OM] Re: OM macro lenses?
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Thu, 22 Sep 2005 18:26:31 -0400
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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