[cyberjunkie]

After reading a few positive reviews on the Internet, i found a Vivitar 2x teleconverter, with electric contacts, and marked P/K-A R-P/K.
As the name suggests, it HAS the Ricoh pin (which is not a problem, as it won't get stuck on AF Pentax cameras), and SIX electric contacts.
Mine has the back flange (camera side) colored in black, so the black enamel should be scratched a little, just where the seventh electric contact of a modern Pentax camera comes in contact with the flange. Other way the diaphragm values can't be read in the viewfinder (or on the top LCD). The converter should work well without that small modification (and the EXIF should include diaphragm values), but IMHO it would be a pain where the sun doesn't shine

That's what i learned with my Internet searches.
I saw it fit to assemble all the infos i got for the convenience of future user searches.

Now it's the turn of my own question:
do you know anything about the optical layout of this converter?
The very positive reviews i found made me think that's a seven elements construction, but the pictures i've seen show that it is too short to be a 7E.
If nobody has any reliable information about the optical layout, i'm asking the owner of this converter to "read" the reflections.
With modern coatings is not that simple, especially glass-to-glass reflections can be barely visible. It's better to do it in a room with a single lamp, and orientate the lens until the reflections of the lamp separate one from the other. Some will be small, other big. The colors will be different, that would help a lot, but some reflections would almost overlap, so a little care is needed.
Faint reflections come from a glass-to-glass surface (glued elements). Glass-to-air reflections are stronger.
Once you learn how to do that, it isn't that complicate.
This is a trick that is known by all collectors of old objectives, but in the digital age got almost forgotten. Though it could be invaluable, if you need to identify the optical layout of an unknown lens.
With modern zooms it's almost useless, too many elements!

A side note:
there are almost no informations about the "optical recipe" of teleconverters. That's weird, cause the number of elements/groups of nearly every lens is known....

cheers

P

[marcusBMG]

I had one of these, echo your technical comments re contacts etc. I didn't think much of it, most noticeable characteristic was a yellow colour cast. My assumption was that it was a 4 element design. My review is under soligor PKA/KR in the tc's list.

I have a related question I see many tc's, various brands, designated "MC7". Is this an indication that they are all an optically similar/same standard design then?

[cyberjunkie]

MC7 stand for multicoated, seven elements.
What i know for sure is that many similar teleconverters, sold with different names, were actually produced by Kenko (which, AFAIK, is/was a brand name owned by Hoya, a japanese optical glass manufacturer and the previous owner of Pentax).

cheers

P

[dms]

My understanding is it is 4 element, and the macro version is 7 element.

---------- Post added 05-28-14 at 10:33 AM ----------

Also, as I recall the 7 (or 5, etc) designation in the model number refers to the mount type (Nikon, PK, etc.). But I also remember the model number was of a form 7-#, 5-#, etc. but my memory may be faulty/this goes back decade(s).

[cyberjunkie]

From what i remember, it's the "22" in Vivitar 2x 2-22 that indicates the Pentax K mount.
MC4 and MC7 should indicate that the teleconveter is multi-coated and that it has either 4 or 7 elements.
Of course that doesn't apply to Vivitar branded TC's, which don't have MC4 or MC7 in their names.
It is/was the Kenko ones.
Btw, some Vivitar and Kenko converters look exactly the same...

cheers

P