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12-22-2011, 09:41 PM   #1
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Desperate: K-Mount 50mm to Canon Adapter loose.

I recently purchased this lens adapter to mount a vintage Pentax 50 to my old Rebel XT to use this upcoming weekend for some Christmas fun.

http://www.amazon.com/Confirm-Pentax-Canon-Mount-Adapter/dp/B006LB8P6I

Upon arrival, it technically fit both the lens and my Rebel, but it wobbles just a bit when adjusting the focus ring, and I believe as a result, getting pictures in focus is hit or miss, despite the fact that they look in-focus in the viewfinder while I’m shooting. For example, all 4 of the following shots looked crisp to my eyes, but after import, it’s pretty much a 50/50 chance (no matter the fstop).

Photo Album - Imgur

Is this being caused by the not-quite-tight-enough fit of the lens adapter? The spring appears to be just a little to short to hold it in place tightly. Or, is this a common occurrence with adapting SLR lenses? Is it all my fault, perhaps?

12-23-2011, 01:44 AM   #2
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So, this is why Pentax lenses getting so scarce! This is the first time I've seen such an adapter, does it give you infinity focus with the Pentax lenses? Perhaps getting an old Canon 5D and using PK mount lenses isn't such a bad idea after all. Sorry, not much help for your question - you might have better luck asking in a Canon Eos forum - I have more questions than answers. Welcome to the Pentax Forums.
12-23-2011, 03:51 AM   #3
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I have a similar adapter and it fits pretty tight to the lens, but my focus is a little loose because I have had the lens over 25 years. Does the whole lens fit loose? Maybe try another adapter? I am going to get a couple more adapters for a couple more lenses I have so I am interested in getting one that is a good fit. I will say it is very hard to MF with most DSLR's with the stock focus screen as it is optimised for brightness and won't be very precise. I got an ec-b for my 1dsii and it really works great, but I don't know if the rebels have replacements like that.
12-23-2011, 05:08 AM   #4
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QuoteOriginally posted by excanonfd Quote
So, this is why Pentax lenses getting so scarce! This is the first time I've seen such an adapter, does it give you infinity focus with the Pentax lenses? Perhaps getting an old Canon 5D and using PK mount lenses isn't such a bad idea after all.
K-mount lenses will not work with the 5D unless you modify either the camera or the lens. The camera modification involves shaving down the mirror. The lens modification involves cutting or removing the aperture lever. I have always suggested that anyone who does this to a K-mount lens should have one of their own appendages removed.

12-23-2011, 05:37 AM   #5
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this is of interest to me , noit because i have a canon, but because this is my fall back position if pentax ever stopped making cameras.

THere are some incorrect statemements in previous posts.

First of all, there is no need to necessairly shave off the back of lenses, when using an adaptor because the adaptor spaces the lens out to the correct regestry distance.

this answers another question, about infinity focus the canon camera has the largest lesn throat as well as the shortest regestry distance making mechanical adaptors that retain infinity focus a reality for all but the old canon breach mount. Owners of those lenses are completely abandoned.

now for the issue at hand. the "looseness" described, is this rotational around the axis of the lens, if yes it does not impact focus.

If it is lens to adaptor, there is no impact at all, if it is adaptor to body, and assuming the adaptor is "chipped" to give focus indication it might cause loss of indication, but not focus shift.

if the lens can move in and out, "wobble uop and down, then focus accuracy could be lost especially on close focus, where every mm counts.

away from close focus you would not notice.

any chance on shots showing where it is Loose?
12-23-2011, 05:50 AM   #6
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QuoteOriginally posted by Lowell Goudge Quote
THere are some incorrect statemements in previous posts.

First of all, there is no need to necessairly shave off the back of lenses, when using an adaptor because the adaptor spaces the lens out to the correct regestry distance.
On an APS-C camera that is true. On a Full Frame camera like the 5D the aperture lever will hit the mirror. There is even a thread here where someone showed off their modified 5D. There are also threads about K-mount lenses purchased on eBay without aperture levers.
12-23-2011, 08:30 AM   #7
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QuoteOriginally posted by boriscleto Quote
On an APS-C camera that is true. On a Full Frame camera like the 5D the aperture lever will hit the mirror. There is even a thread here where someone showed off their modified 5D. There are also threads about K-mount lenses purchased on eBay without aperture levers.
I am suprised at this, but any way, there is another reason K mounts are missing aperture levers, and this is to fit them on Sigma cameras.

there is also a thread about this.
12-23-2011, 08:48 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote
I am suprised at this, but any way, there is another reason K mounts are missing aperture levers, and this is to fit them on Sigma cameras.

there is also a thread about this.
But there are a lot more Canon FF cameras than there are Sigmas

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