At 1/5/2022 10:25 PM, Moose wrote:
>On 1/5/2022 9:42 AM, Wayne Shumaker wrote:
>>I recently acquired a 500D and have been testing on the sony 100-400. One of
>>the reasons I was interested in the magnetic filter approach that now eludes
>>What I notice is that at 400mm the working distance ranges from 50cm at
>>infinity (hence 500D name)
>It's 500D because it has a focal length of 500 mm. That's also a diopter of
>That also means, as you have noticed, that the longest focal distance, from
>the front of the lens, is 500 mm. That's true of all C-U lenses. At their
>focal distance from subject, "rays" leave them parallel. And the primary lens
>at infinity focus expects parallel incoming "rays".
>But note that this is working distance from front of lens, not the traditional
>focal distance from film/sensor plane.
>> to about 28cm at lens MFD. However it does not seem like the magnification
>> changes all that much.
>Nature if the beast, true for primes, as well. Picture one of those single
>lens diagrams. At longer FDs, say 1:40, the subject side is roughly 40x the
>sensor side (lots of leverage ð??? ) long and the sensor side short, so
>relatively little movement of the lens has a big effect. Now picture it at say
>1:4. Then it takes lots more lens movement to get much focal difference.
>> Only tweaking the Zoom does the magnification really change.
>The lovely thing about using zooms for this is that flexibility.
>>It is a different way of working to a traditional macro lens where distance
>>sets the magnification.
>But only within the relatively limited rage of focus.
>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. ð??? )
>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. My 500D (77mm version)
does not seem to have much curvature on either side.
>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
>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. ð???
>See You Moose
Just curious. With CU you make effort to get a good match, yet you pursue soft
focus effects as well. Can the CU lens that has dragons possibly give you some
interesting soft focus effects?
Themed Olympus Photo Exhibition: http://www.tope.nl/