300mm f5.6 TeleCongo Lens ... Which doesn't exist?

I bought a 300mm f5.6 TeleCongo Lens which has not arrived yet.
The price was good, and I have read good things about the Congo lenses by Yamasaki.
I like fast lenses and f5.6 sounds really fast for 300mm.
So I went to find the manual for it. There are wayback machine archives of the Congo site.
But every reference to the 300mm TeleCongo lens that I found says it is f8, not f5.6.

So what does this mean? Is the lens some experimental thing or a one-off build?
Or maybe it is an older lens because the Wayback's oldest capture is 2004.
On the other hand all the other references I found said that the 300mm TeleCongo is an f8 lens.
Attachment 207796Attachment 207797

I found some similar lenses on a Japanese Yahoo bidding site. If I understood the site correctly, then I probably paid about double the value.
But if I like the lense it won't bother me a bit, since it was not that much to begin with.
I really wish I could find some documents for it. It does come with the box, so maybe there will be a document in the box.

I have a F8 version with a newer COPAL 0 shutter. There is no serial number. It is a very good lens.

Dan, I couldn’t find a catalogue on the net about your lens, but f5.6 version seems to be the older version of f8 version.
The ended auction link below shows the same model as yours but in copal 1 silver rim shutter which means the older than the black rim f8 version in copal 0.

https://page.auctions.yahoo.co.jp/jp/auction/p792157434

Yamasaki Optics probably changed the lens design to make the lens lighter for field work at some point.

Quote:

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Originally Posted by mhayashi

Dan, I couldn’t find a catalogue on the net about your lens, but f5.6 version seems to the older version of f8 version.
The ended auction link below shows the same model as yours but in copal 1 silver rim shutter which means the older than the black rim f8 version in copal 0.

https://page.auctions.yahoo.co.jp/jp/auction/p792157434

Yamasaki Optics probably changed the lens design to make the lens lighter for field work at some point.

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Yes, thank you for looking into this for me.

I used to sell Yamasaki-Congo lenses and when I look at the catalog from 1991 I see:

Tele-Congo Lens 300mm f5.6 for 4"x5" format
Smallest stop f64
Angle of View 30 degrees
Image Circle @f16 is 160mm diameter
Front Diameter 75mm
Rear Diameter 57mm
Overall Length 118.5mm
Distance from Shutter to Rear of Lens 35mm
Distance from Lens Seat to Film Plane 159.4mm
Filter Size 72mm
Weight 580g

There were three versions
#163 with a copal 1 shutter
#1163 with a Press 1 shutter
#2163 with an Electric 1 shutter

With all the taxes and mark-ups the #163 lens was priced at AUD$ 1190.70

Quote:

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Originally Posted by Maris Rusis

I used to sell Yamasaki-Congo lenses and when I look at the catalog from 1991 I see:

Tele-Congo Lens 300mm f5.6 for 4"x5" format

There were three versions
#163 with a copal 1 shutter
#1163 with a Press 1 shutter
#2163 with an Electric 1 shutter

With all the taxes and mark-ups the #163 lens was priced at AUD$ 1190.70

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Wonderful, in that case I think I got a bargain. I paid 250, with tax 275. So time has saved me money.
Can you tell from the image I posted which shutter I have? I guess is it the Press 1, but hope it's not the electric one, because my 4x5 has no batteries (obviously)

It looks like a Prontor Press shutter, but of an older vintage than I would expect for the lens. Anyway, it's a mechanical shutter, not electric.

Quote:

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Originally Posted by mdarnton

It looks like a Prontor Press shutter, but of an older vintage than I would expect for the lens. Anyway, it's a mechanical shutter, not electric.

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Yes, old Prontor Press or Japanese copy of one. Yamasaki was very efficient in making good economically priced lenses but they were always hostage to what the shutter makers could supply on the day. For example I've seen several Congo lenses specified with Copal 3 shutters but actually delivered in Copal 3S shutters just to get them out of the factory door.

Maris, it seems you have a lot of info on these lenses that isn't available anywhere else. Is there any chance you can scan it all and somehow make it available for posterity?