TAKO. INTERNET SEIT 1996.
Olympus-OM

Re: [OM] Zooms at Dawn - the 50mm shootout - Teaser

Subject: Re: [OM] Zooms at Dawn - the 50mm shootout - Teaser
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 20 Apr 2010 11:15:31 -0400
I have a Vivitar 2X macro converter that I've never used.  I discovered 
it on the bay about a year or two ago quite by accident and it was going 
for a low price.  I guess I should give it a try... if I can focus it.

Chuck Norcutt


Ken Norton wrote:
> Moose thus grunted:
> 
>> Undoubtedly someone has gone to the trouble of designing an internal
>> focusing prime with close to constant effective focal length, but it's
>> got to be tricky and expensive to do. OK, maybe nobody has built one;  I
>> just want to cover my bases.
>>
> 
> 
> Please, somebody, tell me who makes that lens!  I'll get one today!  (well,
> maybe not today, but you get the point).
> 
> 
> 
> In any case, most of them do change focal length as focused closer. That
>> was one factor in my choice of the Tamron 90/2.8 macro, which uses a
>> conventional long helix to focus. The Canon 100/2.8 macro is IF. So as
>> one focuses closer, the working distance gets even shorter than would be
>> expected with conventional design.
>>
> 
> 
> Exactly. This is one of those reasons why I've been such a fan of my lowly
> 100/2.8 with extension tubes. I get fantastic macro quality as well as
> serious working distance. Extending the 300/4.5 gives me stupidly long
> working distances.
> 
> 
> 
>> With any lens at 1:1, the the focal plane to subject distance is 4x the
>> focal length. The Canon 100 mm, instead of 400 mm, has a close focus of
>> 1:1 @ 310mm, for an effective FL of 77 mm.
>>
> 
> 
> Moose, I agree with your calculations. However, I am remembering something
> that might alter that equation. I hope that somebody on this list has one to
> confirm or deny my allegation.
> 
> Vivitar made a 2X Macro/Teleconverter. This was a brilliant piece of
> engineering that included an extending section of the tube which moved the
> lens farther away from the film-plane which yielded close focusing and then
> the 2X optics further magnified the image. If you placed a 50mm lens on the
> Vivitar, you could achieve an effective coverage of a 100mm lens, but the
> working distance remained about that of a 50mm lens. Also, the bokeh
> characterists remained that of a 50mm lens--just blown up bigger.
> 
> It all had to do with the position of the 2X optics themselves. If you
> placed a normal 2X teleconverter on the back of a 50mm lens and then
> extended the pair from the film plane, it acts like a 100mm lens in working
> distances, etc., but when you extend the 50mm lens first and then multiply,
> it acts pretty much like a 50mm lens. Anybody with a 2X and some extension
> tubes can easily experiment with this and see for themselves.
> 
> The reason why I mention all this is because certain modern
> lenses--especially the 14-54 and 12-60 act like shorter lenses with
> teleconverters built in. The working distance of the 14-54 in macro is
> stunningly close.  Like REALLY close. As in even at the 54mm setting the
> lens hood is shading the subject. The 14-54 really does, to MY eye, look
> like it is being internally extended (focused closer) giving a bit of
> shorter focal length to begin with, and then multiplied by the second lens
> group at the back of the lens.
> 
> AG (it's all smoke and mirrors) Schnozz
-- 
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/

<Prev in Thread] Current Thread [Next in Thread>