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Re: [OM] Extension ring for 1:1?

Subject: Re: [OM] Extension ring for 1:1?
From: "Paul Farrar" <farrar@xxxxxxxxxxxx>
Date: Thu, 17 Sep 1998 13:20:20 -0500 (CDT)
> Thanks all for the extension ring info. So, I think that means I need a
> 25mm for my 50/1.8? Do they make 12 or 13s so you can get 1:2, or put
> the together to get 1:1? Thanks, John.
> 

No. Not for that lens. That lens has 7mm of focus travel built in, so
you need the full set of 7, 14, and 25mm.

50/1.8  by itself   0-7mm extension  0 - 0.14X
50/1.8+7mm          7-14mm   "       0.14 - 0.28X
50/1.8+14mm        14-21mm   "       0.28 - 0.42X
50/1.8+14mm+7mm    21-28mm   "       0.42 - 0.56X
50/1.8+25mm        25-32mm   "       0.50 - 0.64X
50/1.8+25mm+7mm    32-39mm   "       0.64 - 0.78X
50/1.8+25mm+14mm   39-46mm   "       0.78 - 0.92X
50/1.8+25mm+14mm+7 46-53mm   "       0.92 - 1.06X

The 50/3.5 macro has 25mm of travel built in, but you still need all
the tubes for best quality because it has a close-focus correction
mechanism that is activated by the degree of focus extension, meaning
you should always use the shortest tubes possible. This lens costs
about the same as the set of tubes, so if you are only interested in
0 - 0.5X, it might be a better buy.

The extension tubes are also very handy for the telephotos because 
most have rather distant close-focus limits.

Paul

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