Mystery Lens Filter. ID help!

I recently acquired a lot of lenses and filters from ebay. Most of the filters were clearly marked and in great shape. I have one mystery, however. This filter has only a number "2" inscribed on the side, nothing more. Not even the filter diameter (49mm). It is clearly some type of multi-focal filter, but it is very unusual. It is very heavy, probably weighs at least 4 or 5 times as much as a 49mm multi-coated Hoya UV filter. It even weighs more than the giant multi-vision filter I'll post in the reply to this thread! It rotates, and is threaded to accept a filter on top of it. Has anyone seen anything like this?





Here are a few sample images. Clearly, it blurs/magnifies a portion of the image.







Does anyone know what this is, who made it, or where it might have come from? How much it might have cost? Does it allow me to glimpse into the spirit realm? I can throw together some better images, if that will help anyone.

This filter is just plain fun. An added bonus is that it auto-focuses just fine, as the area in the center of the lens is without distortion. The effects are obviously different at different distances from the subject, but still always quite fun. It rotates, but the diagonals seem to be the most interesting.





Some quick samples:

It's most likely a diopter. Diopters are a cheap option for near macro photography, allowing closer focus and magnification but degrading image quality. They are usually labelled with the strength of the magnification from 1-10 with bigger numbers denoting greater magnification.

Your own photo is in line with this guess in that it magnifies a portion of the image. The reason that it looks to blur part of the image is that at close focus you have limited depth of field. The closer you get to the subject the more pronounced this effect will be.

I just took a few images that would support that analysis. My card reader seems to have gone missing at the moment, I'll post them when I get a chance. Odd that it only magnifies a portion of the image, it makes focusing on the magnified part quite difficult. Is the partial magnification lead supposed to lead to a different effect altogether?

Yes, it's a 2 Dioptre close-up lens (not a filter at all), very usful for macros etc. They often come in sets, i.e 1, 2 and 4 Dioptre, which can be used in conjunction if you want to get really close. Not as handy as a macro-zoom lens, but useful to have and keep in your gadget bag ;-)
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Tony-H

Sorry, dumb of me ... clearly on a closer look your supplementary lens is not just a close-up lens, but is more like a bi-focal lens. I've never come across anything like that before ... very odd !

EagerBeaver said:

Yes, it's a 2 Dioptre close-up lens (not a filter at all), very usful for macros etc. They often come in sets, i.e 1, 2 and 4 Dioptre, which can be used in conjunction if you want to get really close. Not as handy as a macro-zoom lens, but useful to have and keep in your gadget bag ;-)
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Tony-H

Click to expand...

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Tony-H

EagerBeaver said:

Sorry, dumb of me ... clearly on a closer look your supplementary lens is not just a close-up lens, but is more like a bi-focal lens. I've never come across anything like that before ... very odd !

EagerBeaver said:

Yes, it's a 2 Dioptre close-up lens (not a filter at all), very usful for macros etc. They often come in sets, i.e 1, 2 and 4 Dioptre, which can be used in conjunction if you want to get really close. Not as handy as a macro-zoom lens, but useful to have and keep in your gadget bag ;-)
--
Tony-H

Click to expand...

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Tony-H

Click to expand...

Maybe it's some obscure specific application but can't for the life of me work out what. Something medical or for archiving (magnifying something at the bottom of the image)?

Alternatively, are you supposed to use it to focus on something close as well as something far away (i.e. the little crescent focuses on a foreground element and the rest keeps the background in focus)? Would seem pretty specific though and I can't imagine it working well for that application.

The filter is probably a "split diopter." This type of diopter is used to get two parts of a scene (one distant, the other close) in focus at the same time. Typically one half of the diopter is used to achieve focus on some very near object in the foreground, while the other half is focused on a distant subject in the background.