# 42mm screw mount question



## xiangji (Aug 16, 2009)

I've seen a Sirius lens with a 42mm screw mount which is for a Praktica cameras. 

It is a manual lens for 35mm cameras, I was wondering if i used it with a canon - screw mount adapter would it work on my 40D?

Not with AF obviously... but as a manual lens.

cheers


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## Overread (Aug 16, 2009)

With a screw mount adaptor yes it would work on your camera, though of course with no AF and no aperture control through the camera (though those nice old lenses have a manual aperture ring for that).
The only part I am not sure of is if the camera would be able to stopdown the lens when taking the shot. I know that the (few) M42 lenses I have do have a manual switch to close the aperture blades on the lens, whilst not ideal it does mean you can close then should the camera not be able to.


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## xiangji (Aug 16, 2009)

I'm looking for a cheap macro lens to play with so was looking at getting an older manual lens. I use a zenitar 16mm fisheye which is fully manual, it doesnt bother me not havign the AF to be honest.

Any good sources for finding older lenses?


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## Overread (Aug 16, 2009)

This forum was sent my way a while ago - its dedicated to older Manual focus lenses and stuff
Manual Focus Lenses :: Index

(forgot I had this in my links list)


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## xiangji (Aug 16, 2009)

cheers ill take a look


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## Dwig (Aug 16, 2009)

Overread said:


> ...
> The only part I am not sure of is if the camera would be able to stopdown the lens when taking the shot...



It won't. You have to close the lens down manually just before taking the shot and then reopen it afterwards.

Not all M42 lenses have their own stop down ring (sometimes labeled and "O-C" ring for Open and Close) or switch. If the lens does, as to almost all Takumars from Pentax, then this manual stop down is reasonably easy. When a lens lacks the switch/ring you have to turn the f/stop ring itself, which is somewhat more difficult as you have to look at the ring or count clicks to get to the desired shooting f/stop.


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