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. 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) and the same for a 60mm
lens on 4/3 shooting at 1:2 (half size).
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. The 1:1 case for any lens is easy
since object and image distances are always equal to each other at twice
the focal length. Here the working distance is 240mm minus the distance
from optical center to the end of the lens.
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.
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... but is not without
its own set of problems.
Chuck Norcutt
On 9/15/2013 6:54 PM, Moose wrote:
> On 9/15/2013 5:46 AM, Chuck Norcutt wrote:
>> Although it seems I'm the only one who took notice it was only because
>> the result was really good. I personally have no interest in the lens
>> no matter how good it is primarily since I do very little macro and
>> can't justify the money for it when I have workable alternatives... the
>> OMZ 50/3.5 and the Vivitar Series 1 90/2.5 with 1:1 converter. Just to
>> show how little macro I do I haven't even tried to fit one of these to
>> my E-M5 yet let alone use them.
>
> It's just not the same. It wasn't even the same with the 5D, where the lenses
> weren't monsters compared to the camera. I
> have both those lenses and have used them extensively on a copy stand for
> flat copy work. Both are excellent.
>
> But for work away from the 'lab', the lack of AF is a negative. Hand held,
> it's really problematic. Even with a tripod,
> I suspect most folks here would have trouble nailing focus without magnified
> live view. So fine if one has few subjects
> and lots of time. Not for me.
>
> I have used the Tamron 90/2.8 AF, 1:1 Macro lens, extensively at times, less
> often at others, although I always carried
> it in the field. I think the good close focus at the long end of the 28-300
> on the smaller sensor of the 60D made it
> necessary for fewer subjects, especially those hard to get close to.
>
>> Neither have I tried to use my auto extension tubes. But I'll get there
>> eventually.
>
> They are cool, so small and light, and bring closer focus in seconds.
>
>> My future lens
>> purchases will likely be the 75-300 next and maybe some day the 9-18.
>
> That's the way I'd go. I do end up using the Panny 20/1.7 occasionally for
> the speed at night and in dark places.
>
>> Even if I could easily afford the 60/2.8 I think I'd hesitate based on
>> short working distance of the short focal length.
>
> As I posted before, the working distance is pretty good for the high
> magnification. In practice, I suppose the ability
> to go closer than my other lenses seamlessly, without extreme magnification,
> will be of more use than 1:1.
>
> It'll be interesting to see how much I use it. I've always liked macro
> lenses, starting with my dad's 55 mm
> Micro-Nikkor, all those decades ago (which I now have). long zooms that get
> close at the long end have lessened the
> need, but I think not eliminated it.
>
> With decent technique in taking and in post, the zooms deliver pretty good
> detail, but not nearly up to the 60/2.8.
>
>> I also hesitate over the 9-18 since the the 24mm equivalent of the 12-50
>> seems to cover most
>> of what I need and panos usually cover any wider needs.
>
> The place the 9-18 delivers, although I've used it for landscapes, is in
> closer quarters. When in close(ish), panos
> don't work. The depth of subjects like this cause havoc with a pano approach.
> <http://galleries.moosemystic.net/MorroBay/ElfinForest/slides/_MG_1155ptl.html>
>
> These, too, are impossible without a single, SWA shot.
> <http://galleries.moosemystic.net/MorroBay/HearstCastle/Main/slides/_MG_1273.html>
> And.
> <http://galleries.moosemystic.net/MorroBay/HearstCastle/delMonte/slides/_MG_1244.html>
>
> Well, perhaps not with full pano gear that carefully rotates around the front
> lens node? But I'm not going to carry that
> stuff around out in the woods, even if it does work. In Hearst Castle, I was
> always being rushed to get a single shot
> off after everyone else stepped out and before the guide got on my case.
>
> I'd have the Panny 7-14, if it weren't twice as big and heavy as the 9-18.
>
> Lensatic Moose
>
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