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10-19-2015, 08:37 AM   #1
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Pentax SMC 50mm on Canon 5d Mark ii Body?

I've been shooting my favorite lens, Pentax SMC 1.7 50mm, on my Rebel T3i (cropped sensor) for a couple years now. I'm just now upgrading to a Canon 5d Mark ii body, and read in some blogs that this lens interferes with the 5d mirror (because it is larger, being full frame).

Does anyone have experience with this? I am using a k-mount to EOS adapter ring. I have been using this SMC 50 on my 35mm Canon Film camera EOS 300V without any issues. I wouldn't think that a full-frame 5d's mirror is any larger than a full frame 35mm film mirror.

A lot of posts talking about mutilating the Pentax lens to fit in the body.... hopefully I won't need to do this!

10-19-2015, 09:13 AM   #2
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Welcome to the Pentax Forums!

While it is true that the aperture lever is the most common cause for interference, the rear element of some lenses may also protrude into the mirror path. The solution for that case is to grind an indent into the 5Ds mirror. If your lens clears the mirror on your EOS film camera, it may be that the aperture lever has already been snipped and that you are OK on the 5D.


Steve

Last edited by stevebrot; 10-19-2015 at 11:29 AM.
10-19-2015, 12:41 PM   #3
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It is easy to find a Takumar 55mm F1.8 or a 50 F1.4 (7 element type) to do the same job with no modifications.
Compatibility list of M42 lenses on Canon EOS 5D DSLR
10-19-2015, 04:42 PM   #4
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QuoteOriginally posted by stevebrot Quote
The solution for that case is to grind an indent into the 5Ds mirror.
You want to grind an indent into the mirror of a professional FF camera just to adapt a $30 vintage lens?

10-19-2015, 06:56 PM   #5
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The lens lever and lever guard will be hit by the mirror.

Solutions :
1. Grind the mirror
2. Remove lever guard (easy, just 3 screws); snip of lever (angers the lens gods)
3. But a cheap Tak SMC 50/1.4 (7 element ) or a very nice Tak SMC 55/1.8

Alternative to #2, buy a broken/hased/fungused/etcPenatax 50/1.7 from ebay for next to nothing.
Snip off the lever for that lens and replace the lever mechanism with this snipped off one. (not difficult to do)
10-19-2015, 09:31 PM   #6
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QuoteOriginally posted by FantasticMrFox Quote
You want to grind an indent into the mirror of a professional FF camera just to adapt a $30 vintage lens?
Its a Mk II. In the thinking of some on this site, it is passe' and therefore expendable.

NOT!!!

I actually first read of that approach on a Canon thread over on DPReview. From what I understand it is a time-honored approach dating back to the late-60s for adapted and t-mount lenses and not just with Canon. Just as with some users on this site who convert perfectly good dSLRs to IR only, using a body solely for adapted lenses is not a huge crime.


Steve
10-20-2015, 06:00 AM - 1 Like   #7
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Why not just upgrade to a K-3 or K-3 ii, buy a M42 adapter, and eliminate the need for grinding/removing anything? Problem solved!
10-21-2015, 05:57 AM   #8
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QuoteOriginally posted by cmanley3 Quote
I've been shooting my favorite lens, Pentax SMC 1.7 50mm, on my Rebel T3i (cropped sensor) for a couple years now. I'm just now upgrading to a Canon 5d Mark ii body, and read in some blogs that this lens interferes with the 5d mirror (because it is larger, being full frame).
a risk isn't worth trying ! canon has some great AF 50mm (f/1.8, f/1.4, f/1.2, f/1) for you to try and see the difference your shiny 5D m2 over your old Rebel

12-10-2015, 12:18 PM   #9
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The bayonet on the K-Mount lenses were indeed interfering with the mirror, preventing it from opening fully and creating a half-black/half exposed image. I simply took a micro screw driver, removed the metal back plate, then remove the screws fixing the black metal piece that had the protrusion (bayonet) that was blocking the mirror. If you are confused, it is the black metal piece with the bayonet that seems to shift alignment when the aperture is opened/closed. Regardless, it seems that the black metal piece serves no function purpose on a modern digital Canon SLR, other than protecting the inner elements of the lens from dust etc. This isn't an issue if you are cautious when swapping lenses in the filed. I screwed the metal mounting plate back on, and though the inner elements of the lens are now exposed when detached from the camera, I can use my favorite lens on my Mark II. I will say that the Asahi Pentax SMC 28mm does produce some vignetting on the bottom edge of the frame in certain lighting conditions, but this is easily correctable in post.
12-10-2015, 01:36 PM   #10
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Shavnig the lens or the mirror is not worth it here. I used to adapt a Leica 19 mm to EOS FF because I had to, but it was a pain. Get a different camera or get a different lens. The old Pentax will not shine on a 5D II anymore.
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