We don't have a pancake lens club! What a disgrace! A camera forum of the most pancaking lens maker of all, and we have no pancake club.
Better amend this mistake asap. Hereby I institute the Pentax Forums Pancake lens club!
Next step: Define what is a pancake lens. It is supposed to be thin. But compared to what?
Pentax have four lenses that has been outright marketed as pancake lenses:
The SMC Pentax-DA 21/3.2 ltd, 63mm wide x 25mm deep
The grandpa: SMC Pentax-M 40/2.8, 63mm wide x 18mm deep
The SMC Pentax-DA 40/2.8 ltd, 63mm wide x 15mm deep
The SMC Pentax-DA 70/2.4, 63mm wide x 26mm deep
One factor in common is that they all have a physical depth less than half of their diameter. That sounds like a plausible first order rule for what a pancake lens is.
But that also declares a couple of other Pentax lenses as pancakes: M20/4, M28/2.8, M/A/F/FA50/1.7 and M/A50/2. Is that OK?
Are any of the Takumar lenses pancakes by this definition? That extremely flat fish-eye must be considered a pancake.
In K mount I know there were pancake lenses from Chinon, Ricoh (28mm and 40mm), Cosina, and more recently the Voigtlander Ultron 40/2.
There were at least one Nikon pancake lens, and several Zuiko Olympus pancakes for the OM system, as well as a Minolta 45mm pancake.
I have a Russian pancake, the 50mm industar, but there were at least also a 28mm pancake, maybe more.
And one of my favorites is the Konica Hexanon 40/1.8.
And for sure there must be lenses I don't come to think of right now.
With the arrival of the mirrorless digital cameras, a new generation of pancake lenses has been born.
So please, post your photos with pancake lenses, and of pancake lenses, mounted on Pentax cameras, or any other camera.