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Re: [OM] Close up filters again

Subject: Re: [OM] Close up filters again
From: Moose <olymoose@xxxxxxxxx>
Date: Wed, 5 Jan 2022 21:25:12 -0800
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 me.

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 2.0.

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 😁 ) 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.

But this also implies more working distance and less critical to getting exact 
distance to subject as magnification can be adjusted with zoom.

(from wikipedia the magnification would go from 0.8 to 1.05 with this lens at 
400mm. The lens focal length probably changes at MFD though as ~28cm was what I 
measured vs 33cm calculated)


My first OK photo with the 500D CU at 400mm/F9 hand held.


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.

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

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