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Re: [OM] Close up filters again

Subject: Re: [OM] Close up filters again
From: Wayne Shumaker <om3ti@xxxxxxxx>
Date: Fri, 07 Jan 2022 07:53:01 -0700
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 
>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. 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?

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