this lens club back in 2011 defined a " pancake lens " for its purposes:
Originally posted by Douglas_of_Sweden 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
Pancake lens club - Page 13 - PentaxForums.com
looks like some of the posters did used a " full frame " sensor camera body