Focomats, Focotars, and extension tubes

[Graybeard]

Hello All-

I have a couple of Leitz Focomat Ic's (and a box of parts from a DOA third enlarger).

One of these came fitted with a 1952 vintage Focomat (Leitz P/N DOOCQ) with a firmly attached (via a setscrew) DOORX extension tube. The lens board on which this Focotar mounts has a substantial recess from the front edge of the helicoid tube.

The second Focomat Ic came fitted with only a 1957 vintage DOOCQ Focomat (no extension tube). The focus cylinder in which the lens mounts has a smaller recess from the front edge of the tube. Clearly, Leitz seems to have eliminated the need for the DOORX extension tube by moving the lens mount further from the tube. This Focotar has an asterisk at the end of its serial number. I calibrated and used this Focomat for years with no problems.

I just fitted an El-Nikkor 50mm/2.8 to the second Focomat (the one with the shallow recess) and, after a modest bit of time setting the thing up properly, now works properly with the Focomat autofocus at f2.8.

The scrapped Focomat the provided my parts collection has the more deeply recessed lens board. It came fitted with a camera taking (collapsible) Elmar 50mm/3.5 lens, fitted with the extension f-stop ring.

I ask the forum why Leitz used the extension tube in the first place - is anyone familiar with this? I invite comments on this bit of Leitz arcana.

 

[M.Hilo]

[FONT=&quot]Good question !

I am not sure, but think it has to do with more than one parameter:

1) the automatic focus,

2) the better position of the lens (lower) while working in the normal autofocus reach.

3) the possibility to remove the tube when bringing the enlarger up the column for large prints. I print a lot of 50X60cm (20X24) and need to bring the enlarger up the column quite a bit. [FONT=&quot]Sometimes I have problems because I can't [FONT=&quot]get the neg in focus. I [FONT=&quot]always solve that somehow, generally by lowering, or raising the enlarger along the column. Your question makes me realise I should try to take out the tube next time I enlarge outside t[FONT=&quot]he automatic focus reach[/FONT], it will probably make things easier . . .[/FONT][/FONT][/FONT]

What may speak against this is that the non automatic Valoy II also came with these tubes.[/FONT]

[FONT=&quot]These tubes were also coded 17675. Leitz provided a wrench with the Focomats which makes it possible to loosen the bolts of the column. Not many people know this wrench can also be used to loosen the 17675 tubes. These have slots inside the diameter which take one side of the wrench. Then you’ve got something to turn the tube with . . .[/FONT]

I am having all kinds of problems with posting this answer, it is the last time I try. I think things are wrong with this site . . . . no, sorry it works now, even if quite slow . . .