Dumb question

[Rider]

I used to know what these things are. One of them has a greenish piece of glass attached.

Related (I think), I also have what look like closeup filters, except that they don't appear to have threads. They say something like "Kodak Series VI Telek 2" on the rim.

Any clue what these things are?

[chassis]

Are these what you have?

http://silverbased.org/series-filters/

[Rider]

I think so.

[Doremus Scudder]

You have a slip-on adapter for filters and slip-on lens hoods.

The set-up on the left is a 11/32-inch slip on filter adapter. It looks like there is a green, probably series filter, (i.e., no threads) held in by the threaded lens hood. The filter size (26mm) is pretty small, and not standard, I believe (not sure what it was intended for, maybe a rangefinder camera).

On the right, it looks as if you have two slip-on lens shades mounted one-within-the-other. I can't see if there is a filter in this set up.

The slitted rings on the adapter/shades were meant to slip over the outside of the front of a lens. Older lenses do not have accessory threads. There were many sizes, many of them unique, that eventually were unified to some extent in the "Series" system. They were standard and very common for years. See the link above for more info.

An example of how this worked/works: I have a 100mm wide-field Ektar. It needs a special slip-on adapter that steps up from the outside lens diameter to Series 6. Then, threadless Series 6 filters and accessories can be used, held in place by a threaded retaining ring or a threaded Series 6 lens hood. To use modern filters on it, I bought a Series 6 to 52mm step-down filter so I can use my slew of 52mm filters.

Hope this helps.

Doremus

[Rider]

With respect to the Telek "closeup" filter, the above quoted website has this to say:

"Among the other Series oddities you sometimes see are Kodak’s “Telek” attachments: These were lenses with negative diopter powers... (The strongest -4 Telek can almost double the focal length). Unfortunately these are really only practical for cameras offering groundglass focusing, e.g. a Press camera."

Why do you suppose that is? I don't see why it can't be used on any camera, albeit the focussing distance will be reduced (can't focus on infinity).

[Bob Salomon]

With respect to the Telek "closeup" filter, the above quoted website has this to say:

"Among the other Series oddities you sometimes see are Kodak’s “Telek” attachments: These were lenses with negative diopter powers... (The strongest -4 Telek can almost double the focal length). Unfortunately these are really only practical for cameras offering groundglass focusing, e.g. a Press camera."

Why do you suppose that is? I don't see why it can't be used on any camera, albeit the focussing distance will be reduced (can't focus on infinity).

Because you needed the bellows to get enough extension to focus a Telex adapter. A helical focusing mount did not have enough extension to use them.

The formula to determine the required extension for negative lenses is:

new focal length = old focal length x 40/40+D where D is the dioptric power of the negative lens.

an 8" lens with a -2 negative lens would need 13.3" of extension to reach infinity but the image on the film will be almost 2x the size of the 8" lens image size.