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Re: [OM] scales in m/ft

Subject: Re: [OM] scales in m/ft
From: julian_davies@xxxxxxxxxxxxxx
Date: Thu, 3 Oct 2002 13:12:45 +0100 (BST)
The theory of the reversing ring is to exploit exactly those corrections for 
distant focusing when the relationship between object distance and flange - 
back becomes abnormal (ie the distance from the lens to the film becomes 
greater than the distance from the subject to the film. The assumption is 
flawed in that the distance from lens to film will never get into the optimum 
working range for the lens, unless the lens is already capable of high quality 
close focus, at which point you just use it non - reversed anyway etc etc. So 
for a lot of hassle, you get a minor improvement.
Extension rings are not a better answer as you just push a lens further outside 
its optimum working range.

Julian

>  from:    Thomas Bryhn <thomas.bryhn@xxxxxxxxxx>
>  date:    Thu, 03 Oct 2002 11:37:08
>  to:      olympus@xxxxxxxxxxxxxxx
>  subject: Re: [OM] scales in m/ft
> 
> At 22:11 02.10.02, derek fong wrote:
> >I read (and tried) a tip in a National Geographic article about turning a 
> >50mm lens into a macro lens.  You have to unmount it from the camera, 
> >focus it to infinity, then hold the lens reversed in front of the open 
> >body and move yourself to focus on your subject.  Not the most elegant 
> >solution but it's cool to know that it works.  =)
> 
> If you haven't already seen how a normal lens is constructed visit the eSIF 
> and look at the 50/1.8 in particular. Normal lenses are basically 
> symmetrical lenses, with small corrections made to make them perform best 
> at infinity (or at least focused at something very far away). So what 
> happens if you reverse a symmetrical lens? Nothing, except you've lost the 
> convenience of automatic iris operation, and introduced a small extension, 
> similar to an extension ring. Not worth the troubble, IMO use an extension 
> tube instead.
> You would however expect to see an increase in performance by reversing the 
> 50/1.8 at magnifications much larger than 1:1, but then we're no longer 
> talking cheap and simple setups, because it will inevitably involve rather 
> long bellows extension, *very* sturdy tripod and/or dedicated lighting 
> equipment.
> The only semi-useful thing a reversing ring can do is to reverse wide angle 
> lenses. You'll easily get high magnification with only the short extension 
> provided by the ring itself, but you'll soon find that working distance at 
> high magnifications is very short, and you'll still be left with the desire 
> for "sturdy tripod and/or dedicated lighting equipment".
> My advice and conclusion: Buy one or more extension tubes, drop the 
> reversing ring.
> 
> Regards,
> Thomas Bryhn
> 
> 
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