Removal of aperture control lever and the guard

alegznn · 12-29-2014, 12:45 PM

I have a question for K-mount experts. I own a manual Pentax lens (50 mm f2), which I would like to adapt for use with Canon EF mount. To do this I will have to remove the aperture control lever and the guard that protects it. I still have a Pentax DSLR, which is now used by my daughter, so I would like to retain the possibility to use this lens also on Pentax cameras. Will it work on Pentax cameras with the aperture control lever and the guard removed? I know that the aperture control lever can be removed and then installed back when needed so, can I find somewhere instructions for removing the lever so that it could be reinstalled later? I found instructions for converting K-mount lenses for Canon, but according to them it is necessary to cut the protruding part of the lever with clippers and I would like to avoid that. However the guard will definitely have to go as it will interfere with the mirror in my Canon.

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Adam · 12-29-2014, 12:54 PM

It will still work on Pentax DSLRs, but the diaphragm will be fully manual so the viewfinder will get darker as you stop down.

Not a Number · 12-29-2014, 08:09 PM

Why not pick up a screw mount lens and adapters for the Pentax and Canon. You can leave the f/2 for your daughter the use and you both can use the screw mount lens. All without modification.

aleonx3 · 12-29-2014, 08:32 PM

Some k-mount lenses, you can remove the aperture control lever from the lens (this process is reversible), so it behaves more-or-less like m42 lens (yet with k-mount) and use Av mode instead. Of course, then you will use stop-down metering, and not worrying about hitting the 'green' button, and it also supports exposure compensation. However, if you plan to use the lens to stop-down to f8 or more, then you will have a hard time getting the focus as it will be too dark looking through the viewfinder.

**jbondo** · 12-29-2014, 10:31 PM

Originally posted by alegznn

which I would like to adapt for use with Canon EF mount

alegznn, I use numerous Pentax K lenses on multiple Canon and Pentax bodies, and I often carry both brand bodies and interchange the Pentax lenses between the systems. Before you even think about modifying the lens, please first confirm the model Canon you want to use this with. Most of the APS-C Canon bodies do not require any lens modification. The mirror is smaller on the these, and it clears the lever. If you want to use it on a Full-Frame sensor body (6D, 5D, 1D...) you only need to modify the lens if you want to use the optical view finder. You can even use an unmodified Pentax lens on the Canon Full-frame body if you activate live-view mode before attaching the lens, and then detach the lens before deactivating live view. If you are shooting on an older Canon film body, you must modify the lens.

alegznn · 12-29-2014, 11:40 PM

jbondo, I own a full-frame Canon 6D. I was surprised to learn that I could use the lens without modification in live view mode, thank you for the information. Still, I think I better perform this modification just to be on the safe side.

---------- Post added 12-30-14 at 10:45 AM ----------

Originally posted by Not a Number

Why not pick up a screw mount lens and adapters for the Pentax and Canon.

Not a Number, I haven't been able to accumulate a collection of old Pentax lenses yet. I really like the photos I was able to shoot with that 50 mm lens on my Pentax that's why I would like to try it on Canon.

Not a Number · 12-30-2014, 12:44 AM

Originally posted by alegznn

I really like the photos I was able to shoot with that 50 mm lens on my Pentax that's why I would like to try it on Canon.

Well the black part with the shield is held in place by 3 or 4 screws on barrel of the bayonet. You can remove it and probably leave it off but you might get some light reflecting around inside. The lever is sometimes held on to a ring with a couple of screws. It might be spot welded on budget lenses.

Here are some disassembly instructions for the M 50mm f/2.0
Pentax 50mm repair 1

An exploded parts diagram for the SMC Pentax-A 50mm f/1.7 can be found here (Password: Pentax)
http://www.pentax-manuals.com/manuals/service/smca5017.pdf
The screws that hold the shield part are labeled T-CSS in the diagram. Though different lenses there should be some similarities.

Get yourself some JIS drivers and maybe a lens spanner and have a go at it. Heed the warning about the little ball bearing.

pinholecam · 12-30-2014, 01:23 AM

The guard is just 3 screws.
That's pretty obvious.

The lever though is attached my some sort of weld or riveting.
So you got to snip it off 8f you want to user it on the 6D

Not a Number · 12-30-2014, 01:33 AM

I think you can leave the whole ring and lever assembly (O-X76 on the A f/1.7 diagram) out. I didn't drip down my f/1.7 down that far to see.

alegznn · 12-30-2014, 06:28 AM

Many thanks to everybody for the advice and info!

**jbondo** · 12-30-2014, 07:07 AM

Originally posted by alegznn

modification just to be on the safe side.

Good plan. The 6d takes longer to cycle after stopping a burst (or single for that matter) in live view, so you get faster shooting rates if you do the lens mod. Also If you are using a chipped adapter, the focus confirmation only works when using the optical viewfinder.

12-29-2014, 12:54 PM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	It will still work on Pentax DSLRs, but the diaphragm will be fully manual so the viewfinder will get darker as you stop down. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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12-29-2014, 08:09 PM	#3
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Why not pick up a screw mount lens and adapters for the Pentax and Canon. You can leave the f/2 for your daughter the use and you both can use the screw mount lens. All without modification.

12-29-2014, 08:32 PM	#4
aleonx3 Veteran Member Join Date: Jul 2007 Location: Brampton, Ontario Photos: Gallery \| Albums Posts: 3,996	Some k-mount lenses, you can remove the aperture control lever from the lens (this process is reversible), so it behaves more-or-less like m42 lens (yet with k-mount) and use Av mode instead. Of course, then you will use stop-down metering, and not worrying about hitting the 'green' button, and it also supports exposure compensation. However, if you plan to use the lens to stop-down to f8 or more, then you will have a hard time getting the focus as it will be too dark looking through the viewfinder.

12-29-2014, 10:31 PM	#5
jbondo Loyal Site Supportaxian Join Date: Sep 2013 Location: Texas Photos: Albums Posts: 503	Originally posted by alegznn which I would like to adapt for use with Canon EF mount alegznn, I use numerous Pentax K lenses on multiple Canon and Pentax bodies, and I often carry both brand bodies and interchange the Pentax lenses between the systems. Before you even think about modifying the lens, please first confirm the model Canon you want to use this with. Most of the APS-C Canon bodies do not require any lens modification. The mirror is smaller on the these, and it clears the lever. If you want to use it on a Full-Frame sensor body (6D, 5D, 1D...) you only need to modify the lens if you want to use the optical view finder. You can even use an unmodified Pentax lens on the Canon Full-frame body if you activate live-view mode before attaching the lens, and then detach the lens before deactivating live view. If you are shooting on an older Canon film body, you must modify the lens.

12-29-2014, 11:40 PM	#6
alegznn New Member Join Date: Dec 2014 Posts: 3 Original Poster	jbondo, I own a full-frame Canon 6D. I was surprised to learn that I could use the lens without modification in live view mode, thank you for the information. Still, I think I better perform this modification just to be on the safe side. ---------- Post added 12-30-14 at 10:45 AM ---------- Originally posted by Not a Number Why not pick up a screw mount lens and adapters for the Pentax and Canon. Not a Number, I haven't been able to accumulate a collection of old Pentax lenses yet. I really like the photos I was able to shoot with that 50 mm lens on my Pentax that's why I would like to try it on Canon.

12-30-2014, 12:44 AM	#7
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Originally posted by alegznn I really like the photos I was able to shoot with that 50 mm lens on my Pentax that's why I would like to try it on Canon. Well the black part with the shield is held in place by 3 or 4 screws on barrel of the bayonet. You can remove it and probably leave it off but you might get some light reflecting around inside. The lever is sometimes held on to a ring with a couple of screws. It might be spot welded on budget lenses. Here are some disassembly instructions for the M 50mm f/2.0 Pentax 50mm repair 1 An exploded parts diagram for the SMC Pentax-A 50mm f/1.7 can be found here (Password: Pentax) http://www.pentax-manuals.com/manuals/service/smca5017.pdf The screws that hold the shield part are labeled T-CSS in the diagram. Though different lenses there should be some similarities. Get yourself some JIS drivers and maybe a lens spanner and have a go at it. Heed the warning about the little ball bearing.

12-30-2014, 01:23 AM	#8
pinholecam Pentaxian Join Date: Oct 2009 Location: North Photos: Gallery Posts: 4,706	The guard is just 3 screws. That's pretty obvious. The lever though is attached my some sort of weld or riveting. So you got to snip it off 8f you want to user it on the 6D

12-30-2014, 01:33 AM	#9
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	I think you can leave the whole ring and lever assembly (O-X76 on the A f/1.7 diagram) out. I didn't drip down my f/1.7 down that far to see.

12-30-2014, 06:28 AM	#10
alegznn New Member Join Date: Dec 2014 Posts: 3 Original Poster	Many thanks to everybody for the advice and info!

12-30-2014, 07:07 AM	#11
jbondo Loyal Site Supportaxian Join Date: Sep 2013 Location: Texas Photos: Albums Posts: 503	Originally posted by alegznn modification just to be on the safe side. Good plan. The 6d takes longer to cycle after stopping a burst (or single for that matter) in live view, so you get faster shooting rates if you do the lens mod. Also If you are using a chipped adapter, the focus confirmation only works when using the optical viewfinder.