I've recently had some issues with lens adapters where the mount between the adapter and the lens is quite loose because the bayonet tabs do not have proper spring loading. This has been quite annoying as the torque required to turn the focus ring is enough to move the lens within the mount which makes fine focus adjustments a pain. Using a "precision engineering solution" I managed to (temporarily at least) fix the problem on my m4/3-to-EF and EF-OM adapters.

As shown in the photo below the bayonet tabs are scored to create a rudimentary spring effect.



If you get a small flathead watchmakers screwdriver you can insert it into the gap and open it up just a tiny bit. This is enough to get it to hold the lens in place without any free play. The metal used in the cheap adapters is not great quality and is quite soft and I suspect it will return to it's former state before too long and need to be opened up again. The soft metal also means if you are a bit rough with the screwdriver you may end up with some tiny metal shavings that will float around inside the adapter and may get inside your camera body or lens. I've noticed that even when you get a brand new adapter you need to check that it has been deburred correctly and there are no fine filaments of metal left that may come off.

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Nic
E-M5, GH1
Flickr Photostream
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I did this with a loose OM-4/3 adapter a couple of years ago and have been hanging heavy lenses off it since - it remains tight and I'd recommend this technique if you have a loose mount adapter.

I had the opposite problem with a Sony Alpha adapter that was too tight, so I had to kind of crimp that part with some pliers. I also had to tighten the screws on the lens mount side, because they had worked themselves loose somehow. I guess that's the quality you get for $20.

The screws on my m4/3 to EF adapter weren't particularly tight either.

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Nic
E-M5, GH1
Flickr Photostream
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Had different problem with my M-mount adapter. Seems like the lens doesn't attach tightly and the locking spring then pushed the lens slightly outward. Only a little, but enough to ruin infinity focus.
Suddenly worse adapter that goes past infinity doesn't look so bad.

Applying force with fingers when using seems to help, but that's just brute and adds up to the hand shake.

Well, probably a price for cheaper adapter.

I got a $30 adapter on ebay. The bayonet connection between the camera (EPL-1) and adapter is fine and snug, but it had a loose fit to the lenses on all but one of my Rokkor lenses. I just stuck some packing tape on the surface of the mating flange at the adapter/lens interface . Everything is good now.

As a test I initially tried using tape on the adapter flange but it will quickly start to peel and it forces the lens to sit fractionally further away from sensor. Most adapters cause lenses to focus beyond infinity so this probably isn't an issue but is something to be aware of.

By opening up the gap in the bayonet tabs as described in my initial post the lens is pulled tighter against the adapter flange.

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Nic
E-M5, GH1
Flickr Photostream
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I too bought auction adapter, and while "ok" for casual use, I ended up spending the obscene amount of money the novoflex (Canon FD) and voightlander (Nikkor F) adapters cost.

While I won't stop griping about the price for a chunk of machined metal, I have to say they are far better than the auction knockoffs. I get infinity (canon FD knockoff went past infinity), and secure fit without light leakage. Both are easier to mount quickly compared to the knockoffs.

I'll probably end up at the point where I go to Novoflex. I figured the ebay cheap-o would at least let me try the old lenses again.

Thanks for the tip. I first tried the RainbowImaging N/F -> m4/3 adapter and that had a light leak. So I had to settle for a Voigtlander and no problems since.

Then I tried a RainbowImaging C/FD -> m4/3 adapter and it had a slight play on the m4/3 end which caused display to black out at the wrong end of the turn. So I had to settle for a Novoflex and no problems since.

Then I tried a Fotodiox P/K -> m4/3 adapter and it has the precise problem described here. Curiously, the mounting feels very tight (in a rough way) but when mounted it has some play. I'll try the remedy described here but looks like I will have to eventually splurge for a Voigtlander P/K -> m4/3 adapter.

Chinese adapters lack consistency in terms of quality. I know there are perfectly good copies (of the same model) out there too, just that my bad luck seems much more consistent that I never got a good copy.