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Re: [OM] Speaking of lenses [was Speaking of sharpness ... ]

Subject: Re: [OM] Speaking of lenses [was Speaking of sharpness ... ]
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Wed, 02 Oct 2013 20:25:54 -0400
Yes, I know there is no 120mm full-frame macro lens.  I only used 120mm 
so one could directly compare the advantages of the 60mm on 4/3 to a 
hypothetical full-frame equivalent.  4/3 and 1/2 lifesize is a big win 
for much less lens extension compared to a full-frame 1:1 solution.

Chuck Norcutt


On 9/16/2013 1:05 AM, Moose wrote:
> On 9/15/2013 8:21 PM, Chuck Norcutt wrote:
>> Basically what Moose said.  But I didn't answer this question quickly
>> because I wasn't sure exactly how it would work out.  Now I've had a
>> chance to do some calculations and can quantify it a bit.  I say "a bit"
>> because the only calculations I can do is from the optical center of the
>> lens.
>
> More likely, two nodes, one as seen from the subject end, and another seen 
> from the camera end. The front one is used
> for panoramas.
>
> I think the space between them adds length to the simple lens calculation, 
> which makes simple calculation from image
> plane impossible. If the front node location and focal length at the repro 
> ratio were known, working distance could
> easily be calculated.
>
>> As Moose points out some lenses move their elements
>> independently, some change focal length and none of them may have the
>> optical center of the lens at the physical center.  Then, even if you
>> know where the optical center is located the working distance is
>> measured from the end of the lens, not the optical center.  So take what
>> you're about to read as an approximation which will be somewhat
>> different from lens to lens.
>>
>> First, let me accept that for a 1:1 output from a 4/3 sensor we really
>> only need to make the image 1/2 life size on the sensor.  There are
>> probably some valid quibbles about doing this but if we reject it we
>> really can't talk about equivalent focal lengths for even non-macro use.
>>
>> So, what I've done is calculate the object/image distances for a 120mm
>> lens on full frame shooting at 1:1 (life size)
>
> This is completely impractical, as there aren't any such lenses for 35 mm FF. 
> The flagship FF macros from C&N are
> 60/2.8s. I believe I've read that the Canon is actually about 40 mm @ 1:1.
>
> Tamron makes a 90/2.8 and I believe the Pentax is the Tamron rebranded. All 
> the contemporary 120 mm macros lenses are
> for MF or LF. I have the Tamron, and it's as good or better in the macro 
> range than OM 50/3.5, Tamron MF 90/2.5 and
> Kiron MF 105/2.8. I tested them all side by side.
>
>> and the same for a 60mm lens on 4/3 shooting at 1:2 (half size).
>
> This is OK, as there are at least three macro lenses for 4/3 format in that 
> general range, PanLeica 45/2.8, ZD 50/2 and
> M.Z 60/2.8
>
>> For the full frame 120mm case at 1:1 the object distance (center of lens
>> to object being photographed) and the image distance (center of lens to
>> the film/sensor) are both 240mm.
>
> But total distance from image plane to subject may be greater, if front and 
> rear nodes aren't the same. A clearer
> example of widely differing nodes may be telephotos, where the front node is 
> in front of the front element, and the
> reverse for SLR lenses wider than about 38 mm.
>
>> ...
>>
>> For the 4/3 60mm lens at 1:2 the object distance is 180mm and the image
>> distance is 90mm.  Note that the image distance is only 1/2 of the
>> object distance.  While the 120mm lens does have a working distance
>> advantage over the 60mm lens the difference is not double.  That's
>> because we allowed the 60mm lens to get away with a 1/2 life size image.
>>     Note that the object distance of 180mm is 3 times the focal length
>> when set for 1/2 life size instead of only twice the focal length as
>> required for life size.
>>
>> One advantage for the shorter lens that I hadn't thought of at first
>> (but which clearly falls out of the calculations) is that, although the
>> full frame 120mm lens has a working distance advantage the extension
>> required for the 60mm lens is only 90mm from optical center instead of
>> 240mm for the full frame lens.  That's a lot of extension which brings
>> its own problems beyond working distance.
>
> But there is no such lens for this format. The Zuiko 135/4.5 is unique, as 
> far as I know, and it only goes to 1:2 with
> the 65-116 Auto Tube.
>
>> Finally, while doing this little exercise I referenced John Shaw's book
>> "Closeups in Nature" wherein he speaks of the "fear circle"*.  When
>> you're outside the radius of the fear circle little critters ignore you.
>>     When you get inside the fear circle they tend to get out of your way
>> quickly.  Long focal length is still the answer...
>
> Which is why so many of my small critter shots are taken with a tele at 300 
> mm (which is probably less at closest
> focus.)
> <http://galleries.moosemystic.net/MooseFoto/index.php?gallery=California/Sugarloaf_Ridge_SP&image=_MG_2819cria80.jpg>
>
> Today's spider shot was right on the edge of that circle. After two 
> successful shots at about 1:2, I tried moving in
> closer, and it felt compelled to move away.
>
> Bottom line; I think the M.Z 60/2.8 has as much or more working distance as 
> its actual competitors. It also has a far
> more practical hood design for close work than the others.
>
>> but is not without its own set of problems.
>
> YeahBut - What's the alternative?
>
> The Short and Long of Moose
>
> * Related, no doubt, to the dreaded Circle of Confusion. :-)
>
-- 
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