Compatibility List of Some Pentax Full Frame Lenses on Canon 5D Body

As I promised last time, below are the full details:-

(Do read my last article for the technical bases if you're going to try any "surgery" on your lens(es)! And, do it at your own risk!!)

Lens Model	Compatible?	Reason of Incompatibility (If Not Compatible)	Technical Remarks	Comments about the Image Quality on 5D
F 17-28/3.5-4.5 Fisheye	Yes	-	Mechanically it is compatible but the built-in lens hood would cause vignetting near 17mm as the K-to-EOS adaptor makes the lens rotated when installed.	Excellent and Perfect, as it used to be on my film Pentax SLRs!
FAJ 18-35/4-5.6 AL	No but Still Yes	No aperture ring!	Maybe I shall still try to modify it just as an always wide opened ultra wide lens. It maybe possible to fix the aperture at wide opened position (or any aperture position) just with a screw, just like I did with my DA 18-55 and tested it before. Edit 4-19: Succeeded! See Full Story Here.	Good to Very Nice. Samples Here.
FA 24-90/3.5-4.5 AL	Yes	-	Original pedal-type lens hood will cause vignetting at the wide side, owing to the rotated lens when mounted.	So far my experiences with this lens on 5D is quite good, accurate colours, somehow nice bokeh and if stopped down a bit, resolution is good from corner to corner and vignetting will become less obvious. It is interesting to note that this lens performs much better on the 5D than on any of my APS-C cropped Pentax DSLRs - even the bokeh is different and the bokeh on 5D is nicer, real surprise! Might do a head-to-head comparison later on to see how this compact Pentax 24mm standard zoom could compare against my much more expensive Canon EF 24-105L which was almost 3 times for the prices I paid.
FA 28/2.8 AL	No	The rear lens element is protruding out too much and has conflict with 5D's large mirror when it moves. (I found it out simply by attaching a piece of Kodak lens cleaning paper (in two folds) and fixed it close to the glass as possible, so as to protect the rear glass surface before I pressed the shutter release button to try)	-	-
F 35-70/3.5-4.5	No	1. The little barrel for the rear glass element protruding out too much; 2. The protection ring with plastic protruding protector for the aperture coupler is linked to the aperture control mechanism and is in one piece => Destructive modification is required, even if not because of the first reason.	I am really sorry about the failure as the Pentax F 35-70 is the best very first standard kit zoom ever made on Earth! And actually I have already removed the protruding part of the plastic protector to try - the position is just so critical so that I was not sure if it could work if not tried - not possible just by observation :-(
FA* 43/1.9 Limited	Yes	-	-	Perfect!
F 80-200/4.7-5.6	Yes	-	-	Very good for a super lightweight Tele-zoom of this spec. Stopping down to f/8 will yield very sharp images.
FA* 85/1.4	Yes	-	1. Requires dissembling of mount and proper techniques and great care are required! (My Hints: Work under bright illumination, put on the workbench a large piece of white paper, put it flat as the workspace, and get proper screw drivers and forceps. More importantly, always face the lens with mount-side upwards during the surgery!) 2. Screws for mount and aperture coupler are thread-locked with special glue. Much force is required to get the screw unfixed (and with great care at the same time so as to not damage the screws and any slippage of the screw driver which might even scratch the glass!).	Perfect, as long as the focus is correct! (mostly correct with the focus indication by 5D) This lens is just Wonderful on the 5D! Excellent lens will always be excellent!
DFA 100/2.8 Macro	Yes	-	1. Requires dissembling of mount; 2. The aperture controlling/coupling mechanism would get off its position after the mount is removed. It's needed to be put back into proper position before resemble back the mount.	1. This lens' colour rendition on 5D is far better, accurate and consistent than on my *ist DS and K100D. I just wonder if this is related to the more intelligent and more accurate Auto White Balance of the 5D than those Pentax DSLRs. Anyway, a big surprise and a real bonus to me. 2. The resolution is very high at the centre but even at f/8, very extreme corners are having some kinds of blur when shooting infinity objects. My FA*85 just blows it away just at f/4, with corner to corner sharpness with very high resolution. New Samples Here! (Macros)
F* 300/4.5	Probably, but have not yet succeeded	This luxury top-of-the-line 80s Pentax AF lens is so sturdy to dissemble! I could not even turn any of the screws which fix the mount! I suspect these are thread locked by special type of strong thermal glue. As I do not have a heater screw driver with (precise) temperature control at my home, I gave up! If I had one, I would try starting from the lowest temperature first :-( )	The mount is needed to be dissembled first. I guess if I could remove the mount, this lens should be compatible! :-(
Tamron 1.4 MC4 Teleconvertor	Yes	-	Dissembling of rear mount is required.	Acceptable performance, degrade the F*300/4.5 image quality somehow but still an usable combo.
Sigma 28/2.8 KPR	No but I still can use it, see the right!	This cheaply designed lens actually cannot be dissembled and removed by parts for the aperture coupler without destroying it - very maintenance unfriendly! So, I just do it by blending it fully downwards to avoid any conflict. At least, I still did not cut it!	-	Acceptable colours, high resolution at the centre but at (not even very extreme) corners the 5D outclasses this Sigma prime, stopping down way down to f/11 only shows little improvement, and at near wide opened, the blurs are just so obvious.

During the course of dismantling the aperture coupler, I found that there is a trick to adjust the exposure tendency of all those Pentax lenses by fine tuning the aperture coupler' exact position, in a precise way. This is valid from any F to the latest DFA lenses. For example, my FA 28/2.8 AL did tend to overexpose by about 1/3 EV on my K camera and now it exposes just as accurate as my FA Limited or the FA*! So, that aperture coupler can be the evil which just introduces more exposure errors, as long as exposure accuracy (which is of prime importance indeed) is concerned.

I am now being very happy for using my good to excellent Pentax lenses on my 5D as each of which is of some kind of unique characters and quality. Of course, I am still hoping that there will be a Pentax Full Frame DSLR body to come, although it is not likely in the foreseeable (near?) future :-(( If the day really comes, all my those somehow modern (but yet all discontinued, including my FA 43 which is of the better old version) Pentax AF lenses, will have their full automatic functions re-activated again, instead of now they are just "manual" lenses on my 5D! :-( And, to some: don't tell me to put my those excellent Pentax Full Frame lenses on any of the current Pentax DSLR bodies, the produced results and image quality is no way as good, or just not even come close! Believe it or not!

Read Also:- K-Mount Metering and Exposure Bases - A Technical Brief