On 1/7/2022 6:53 AM, Wayne Shumaker wrote:
...
On 1/5/2022 2:32 PM, Mike Gordon via olympus wrote:
A 2 Diopter CU lens is a bit strong for optimum IQ on that long of a tele. I
think Moose compared to a Nik 5T and found that one a bit better on the lens
her tested it on---?PL 12-60 IIRC.
It is very idiosyncratic how achromatic CU diopters perform on various lenses.
There may be many ways to obtain the same mag using focusing distance and FL
combo's and some yield better results than others.
Indeed, here there be dragons. How does the specific lens react with the
specific C-U lens? I carefully tested my PL 100-400 @ 400mm with both a Canon
500D and a 5T, everything else identical. Although the stronger diopter of the
Canon produced a larger image, it was distinctly inferior in resolution whether
the 5T was upsized or the Canon downsampled, to match magnifications.
You might think all achromatic diopter lenses are created equal. But it's not true. Single element ones
and older achromats seem to use bigger curves. I didn't check the Canon 500D before returning it. The
power is the combination of the curvatures of front element front and the rear of the rear element. +4
and - 3 = 1 diopter. But so does +2 and -1. The Nikons use weaker curves than, for example, the old
Minolta series. This appears to affect how well a C-U lens and a particular primary lens get along.
With very complex lens designs, perhaps even primes with many elements, I think it's impossible to say
how any particular combo will perform without trying it. (As good an excuse as any for owning 15
different ones. 😉 )
I mostly use the rare, 1.5 diopter Pentax T132 for the PL 100-400 lens; lower
mag, but much better working distance, and a nice optical match for the lens.
Seems you are the repository for things that once were.
Some old stuff is crap, some is gold. One hopes to have the smarts to tell the difference. In the particular cases at
hand, that's not simple.
I made an effort to find various achromatic C-U lenses in order to find the combos that worked for me. That's worked
out well. I've kept the old crap for a couple of reasons. One is that I'm not interested in selling on the 'Bay. The
other is that crap can turn to gold with a different primary lens.
I have the old Minolta 55 mm set, labeled No.1, 2 and 3 (0.9, 2.0 & 3.8 diopter). the first time I tried one of them, it
was bad. Different C-U lens, different primary lens, worked great.
I am persistent, and sometimes resourceful. The weakness of the Panny ZS200 compact is close focus at longer FLs. With
stick on LensMate filter adapter, I used the Minolta N0. 0 C-U with great success.
My 500D (77mm version) does not seem to have much curvature on either side.
Oddly enough, I have a diopter curvature measuring device, gifted by someone
doing a clear-out.
My speculation about a relationship between curvature and performance is just that. As MikeG has said, "The plural of
anecdote is not necessarily data."
My return of the 500D was based on careful, empirical testing, on a particular lens. Yours, on a different lens, may be
good. I used a flat target, tripod, etc., and had another lens to test it against.
Having tried the Sigma 1.7 diopter AML 72-01 in the field, I found the range
of focus too short for my taste. Didn't really surprise me, as the 1.5 diopter
5T is already too strong for my use on 100-400. I'm sure the stronger 500D
would not please me, optical performance aside. The 5T works well on PL 12-60
though.
Happily, my fav C-Us for my most used zooms happen to be the correct filter thread size for each, no
adapters. A little bonus from the universe. 😉
See You Moose
Just curious. With CU you make effort to get a good match, yet you pursue soft
focus effects as well.
Apples and cucumbers. One overall goal, to make images that please me, two different
approaches, and types of images. 😁
Can the CU lens that has dragons possibly give you some interesting soft focus
effects?
I suspect not, with achromats. The differences are a lack of great sharpness, not real softness. Single element -
lenses, possibly. I tried a B&W 67E NL 0,5, single element, 0.5 diopter on the PL 100-400. Schott glass or not, it
wasn't good.
Single element, low diopter lenses may be a useful soft focus tool. LensBaby started out with lots of variations on
50mm. Since then they have gone wider, but only slightly longer, @ 80-85 mm. I'm hatching a plan to mount single element
C-U lenses alone as medium to long soft focus lenses.
The SIMA single element Soft Focus 100/2 (again ancient) works well. I'd like
something longer.
Alternate Perspectives Moose
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What if the Hokey Pokey *IS* what it's all about?
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