[MossyRocks]

I want to take that out for an astro spin just because. I'm not expecting greatness but one never knows with older lenses. Some are surprisingly great.

[interested_observer]

Just some pure speculation on my part. The line of Zeiss/Contax C/Y lenses was announced back in 1975. This is the same time frame where Zeiss and Pentax were cooperating together with the various lenses like the SMC Pentax 15mm F3.5, etc. Then, in 2013, the grandson of Dr. Erhard Glatzel (Zeiss' chief lens designer) made some posts on Reddit looking for some information on some Zeiss lenses he inherited from his grandfather that no one ever heard of - or had some vague rumors about some prototypes may have existed (two lenses in question are the Distagon 25mm f/1.4 and Distagon 18mm f/2.8).

I can see that during this timeframe Pentax may have participated in the development of prototypes - it seems that the range of 18mm to 25mm focal lengths, with fast apertures was an area of interest of Dr. Glatzel. This Pentax 20/f1.4 fits right into this wide and fast area. I've also read in a couple of places that Pentax's SMC coating was the item that Zeiss had an interest in and that their first version of their T* coating was a relabeled SMC.

• My grandfather was a well known optical designer for Carl Zeiss. : photography
• Grandson of Famed Zeiss Designer Owns 'Holy Grail' Collection of Glass | PetaPixel
• http://forum.mflenses.com/distagon-25-1-4-and-a-distagon-18-2-8-t56101.html
• Zeiss Prototype lenses reappear - FM Forums
• Remember the person who was the grandson to the famous Zeiss lens designer? He posted some more information about his lenses on mflenses.com and it turns out two of the lenses are the only ones known to exist. The Distagon 25mm 1.4 and 18mm 2.8. : ph

Just trying to put 2 and 2 together, to come up with 5.5..... (fuzzy math).

[c.a.m]

Just trying to put 2 and 2 together, to come up with 5.5..... (fuzzy math).

Very interesting thoughts.

May I add my findings from an online search? (Not sure whether this info has been posted before.)

The lens was introduced at Photokina 1976. I haven't been able to determine how many samples were displayed there, nor have I uncovered any pictures of the lens on display.

December 1976 issue of Camera 35 magazine. Their Photokina report mentioned the introduction of the Pentax ME and MX and also mentioned several lenses: "Pentax has a wide angle Zoom, 28mm f/3.5 to 45mm f/4.5. They have a 200mm f/2.5 telephoto lens. Then there's the unbelievable 20mm f/1.4, not to mention the 28mm f/3.5 shift lens."

Dec. 1976, Camera 35 magazine: Ultra-Compact Pentax ME and? | Flickr

Photo Technique magazine, December 1976: Photokina report on new lenses. "SMC Pentax 20mm f/1.4 -- the fastest 20mm lens made (as far as we know)."
as seen in this thread: https://www.pentaxuser.com/forum/topic/pentax-advertising---the-1970s-55566#comm578988

Then, there's this interesting account of the lens from Marco Covina: LOÂ* SMCÂ* PENTAX

English translation: LOÂ* SMCÂ* PENTAX

"... after meticulous cross-research, which lasted for a long time, I finally got my hand on the original project of this monster, signed by Dr. Takahiro Sugiyama, the "20mm specialist" of the Asahi house, father among other things of the famous and appreciated SMC Pentax- M 20mm f / 4..."

Refers to the lens as "SMC Pentax-M 20mm f/1.4." Mentions seven design options, each with a slightly different optical design.

Mentions Zeiss/Erhard Glatzel: "It has always been rumored of the adoption of an aspherical surface but I have to deny the inferences: the Pentax-M 20mm f / 1.4 is based only on spherical elements, a detail in fact curious, since [Asahi] had just tried its hand in the transformation in aspheric of the Zeiss-Takumar Distagon 15mm f / 3.5, an attempt rejected even by Zeiss itself, which after having designed both options (by the hand of Erhard Glatzel) decided to produce the simpler spherical version with its own brand."

Patent: https://www.freepatentsonline.com/4095873.pdf


Hope this adds to the knowledge base of this intriguing lens.

- Craig

[gofour3]

May I add my findings from an online search? (Not sure whether this info has been posted before.)

Good stuff and adds to the mystery of this lens. It does sound like a few 20/1.4's were manufactured and intended for sale, as they had serial numbers. Sounds like it was pulled from production due to the high cost and not up to Pentax's high optical standard at the time.

Phil.

[zbrueningsen]

I seriously love all of this:
History, mystery, and a lot of intrigue!

[Digitalis]

I want to take that out for an astro spin just because. I'm not expecting greatness but one never knows with older lenses. Some are surprisingly great.

The lack of an asphperical element in the 20mm f/1.4 is going to put it at a distinct disadvantage compared to the DFA21 when it comes to astrophotography.

[Joetitch]

As a serious aside what would be the advantages of a 1.4 on 20mm?
Great for bragging rights but in application?

[MarkJerling]

So here is what I've learned about the lens and some pictures.

For the Lens database:
Regular K-mount with the newer M-style font and lens speed format. Since it doesn't say "Pentax-M", I would list it as a K-mount prime.
Weight is 465 grams
Diaphragm is 8 blades
Front lens cap is a 77mm, same as the k-mount 300mm and 400mm lenses.
Minimum focus is .8 ft / .25m

Compared to the brand new 21mm Limited lens, the 20mm is a little shorter but is also lacking the 21mm's built in lens hood.

As you can see in the pictures the speed of the lens comes from one oversized front element, the rest of the lens is a normal size. Also you can see that unlike most of the old wide angle lenses Pentax made from this time period, the 20mm lens has a full size rear element.

I will post some image tests in another post.

Wow! Thanks for sharing. And congrats on your buy. That must be one of the rarest of rare Pentax lenses ever.

[interested_observer]

As a serious aside what would be the advantages of a 1.4 on 20mm?
Great for bragging rights but in application?

Astrolandscape - it's pretty dark out at midnight, no moon and 100 miles to the nearest large city with a light pollution dome. Plus, there is precious little light from the stars that actually gets to us mortals here on spaceship earth.

[ZombieArmy]

As a serious aside what would be the advantages of a 1.4 on 20mm?
Great for bragging rights but in application?

Focusing at night duh.

[Joetitch]

Astrolandscape - it's pretty dark out at midnight, no moon and 100 miles to the nearest large city with a light pollution dome. Plus, there is precious little light from the stars that actually gets to us mortals here on spaceship earth.

As what I DON'T know about photography would fill a set of encyclopaedia, how does this work in relation to DOF?

[Adam]

My understanding is that something like seven prototypes were made, and that's it.
The K 20/1.4 never made it to sale. Of course

Crazy! @dkpentax do you mind if we add some of your pics to the database?

[pschlute]

As what I DON'T know about photography would fill a set of encyclopaedia, how does this work in relation to DOF?

With a 20mm lens focussed at infinity, even f1.4 gives you a DOF that extends from about 30 feet in front of you. For the celestial bodies themselves, they are all at infinity, so DOF does not impact them. What will be of more concern is the resolving ability (sharpness) of the lens at f1.4 (centre and edge), and whether the trade off between light gathering ability and sharpness is a good one.

I think most serious astrophotographers use stacking anyway so any foreground elements in the picture can be exposed and focussed separately from the sky. The picture does not have to be taken in one go.

[Joetitch]

With a 20mm lens focussed at infinity, even f1.4 gives you a DOF that extends from about 30 feet in front of you. For the celestial bodies themselves, they are all at infinity, so DOF does not impact them. What will be of more concern is the resolving ability (sharpness) of the lens at f1.4 (centre and edge), and whether the trade off between light gathering ability and sharpness is a good one.

I think most serious astrophotographers use stacking anyway so any foreground elements in the picture can be exposed and focussed separately from the sky. The picture does not have to be taken in one go.

Thanks now I want one (maybe)😁

[MossyRocks]

The lack of an asphperical element in the 20mm f/1.4 is going to put it at a distinct disadvantage compared to the DFA21 when it comes to astrophotography.

That doesn't mean I don't want to try it for astro. It might get good after a stop or 2 or it might be a stinker as legacy glass is kind of a crap shoot with some lenses being surprisingly good. I am always curious how a lens performs for astro and a D FA21 is something that I want as I really could use something good between 12mm and 28mm.