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Re: [OM] Reasonable price for a Vers. 2 Bellows?

Subject: Re: [OM] Reasonable price for a Vers. 2 Bellows?
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 23 Apr 2013 20:59:10 -0400
A closeup lens changes the effective focal length of the main lens but 
not the extension required... ergo no light loss at all.  Advantageous 
if you have a good quality achromatic closeup lens.

Chuck Norcutt


On 4/22/2013 7:20 PM, usher99@xxxxxxx wrote:
>>> I think you'll find that the exposure compensation required will be
> the same
>>> for the same magnification regardless of the means to achieve it.
>
> ...Wayne
>
> Perhaps you are referring to the known relationship for extension :
> Effective F-Stop = F-Stop x (1 + Magnification / Pupil Magnification)
> Minimal effective light lost with the CU diopter lens, but if one
> wishes the same DOF, must stop down to the same effective aperture used
> for the same mag when using extension--then I fully agree. So the VF is
> indeed brighter if using a CU lens compared to extension. Big Foot for
> example does some odd internal machinations with floating elements that
> result in 1/2 stop less loss of light than it should at 1:1. John Shaw
> said some lenses do this, but I wasn't sure it could really be true but
> is seems to be so--perhaps it is mostly FL shortening? as the working
> distance at 1:1 with Big Foot is less than it should be for 125mm. The
> 80mm macro is symmetric with PMF of 1, so that makes it easy. The PMF
> even if known gives me headache to think about as it also changes with
> focusing distance. Nykon cams will often give the true effective
> aperture in the VF with macro lenses--cooool.
>
> Let's save the full DOF thread for quiet winter days, Mike
>
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-- 
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