Hi,
On the subject of extension tubes and the 50/3.5 macro. I notice that the
only specs in eSif, or anywhere else I've seen, are for the 25mm tube to
reach 1:1. What I've been wondering is, can you go beyond that; ie, adding
another 25mm to get even greater enlargemant? And if so, how would one
figure out what the ratio would be with a given amount of extension?
Thanks,
Darin.
----- Original Message -----
From: "Moose" <olymoose@xxxxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxx>
Sent: Saturday, July 16, 2005 7:12 PM
Subject: [OM] Re: adding to macro
> Wayne Culberson wrote:
>
>>I think a 25mm extension tube will take the 50/3.5 to 1:1. I'm not sure
>>how
>>much extension is needed for the 90/2, but I would guess about 50mm of
>>extension.
>>
> The optical rule is that extention to the focal length is requires for
> 1:1 and to 1/2 the fl for 1:2, so the 50/3.5 requires 25mm and the 90/2
> requires 45mm.
>
>>A 25mm extension tube can be made from a basic 2x converter by
>>removing the glass. They are practically free.
>>
> The very common and cheap used Vivitar 2x-21 telexender can be very
> easily converted into a 26mm auto tube. Just remove the 3 screws on the
> back and carefully work the rear assembly off. Unscrew the rings and
> such holding the lens elements, remove the elements, remount the rear
> assembly, and you are done. Two of theses stacked would work for the
> 90/2, although you should check the auto diaphram action to make sure it
> works correctly through two relays.
>
>>Extension tubes produce light loss only.
>>
>>
> True, but no more than if the focusing helicoid extended to 1:1 by
> itself. No matter how the lens is moved farther from the film plane for
> close focus, there is light loss requiring increased exposure. Before
> TTL auto exposure, tables of extention factors were required.
>
>>......Also, the vivitar 2x macro takes the normal 50/1.8 to 1:1.
>>
>>
> Actually, any 2x telextender will convert a macro lens that focuses to
> 1:2 to one of twice the focal length, two stops slower and focusing
> directly to 1:1. The Tamron SP 90/2.5 macro lenses specifically
> recommend doing this with their matching 2x converter. They become 180/5
> with the converter and focus directly from infinity to 1:1. And it works
> very well <http://www.moosemystic.net/Gallery/Tam902.5/>. However, the
> Oly 2xA does not physically fit the 90/2.
>
> The Vivitar and Panagor macro teleconverters do the same thing for 50mm
> normal lenses. They take a lens like the Zuiko 50/1.8/1.4, etc. that
> normally only focus down to 1:7 and convert them into 100 mm lenses that
> focus to 1:1. They would still be a fine choice for extending the close
> focus of a macro lens, and would actually go closer than 1:1, with their
> added extention.
>
> Moose
>
>
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