M42 Lens adapter question.

[rdnzl]

I picked up a Minolta SLR and with it came an adapter ring in the bag along with some filters. I mounted the adapter ring on the camera, and tried one of my Pentax 50mm M42 mount lenses and found that they screw into the adapter just fine.

My question is....does adding the adapter in the "chain" so to speak, increase the focal length of the lens, or cause any need to adjust settings? It adds a half inch to the mount.

I'm sure this question has been asked somewhere on here, but my search skills came up short.

Thanks

 

[compur]

An M42 adapter won't change the focal length of the lens.

But, be sure it's not a T-mount adapter. An M42 lens will screw in part way into a T-mount adapter but the result will not be good if you mounted it on a camera.

Posting a photo of it would help if you are not sure.

 

[rdnzl]

I believe it must be a T-Mount adapter. The M42 lens doesn't go flush with the face of the adapter.
What is a T-mount used for? Telescopes?

 

[rdnzl]

I also got this adapter. It fits my Pentax M42's and attaches them to my ME Super, and others. I can see where this adapter would not change the focal length as it fists flush with the camera mount.

 

[compur]

^ Yes, your photo above shows an an M42 adapter for Pentax K-Mount bodies.

T-Mount adapters are used for telescopes and also for lenses made to accommodate different T-mounts to mount them on different cameras. One lens or scope could mount on a number of different bodies using the appropriate T-Mount. They were once quite popular for lenses and are still made for telescope use.

The "T" is for Tamron who invented them and later made other types of interchangeable mount systems such as the Tamron AdaptAll mounts. The T-mount threads are similar to the M42 threads but not quite the same and they will only screw in part way into something designed for M42.

 

[dxqcanada]

Minolta also made an adapter specifically to mount M42 lenses on their MD mount cameras.
It was called the P-Adapter, and came with a special key to attach it to the mount.

 

[petrochemist]

I believe it must be a T-Mount adapter. The M42 lens doesn't go flush with the face of the adapter.
What is a T-mount used for? Telescopes?

Both T2 & M42 are metric threads with an maximum diameter of 42mm
The standard M42 mount (AKA pentax screw, M42x1, universal screw...) has a thread pitch of 1mm and a registration of 45.46mm. I've only ever met it for things designed for camera lenses (lenses, cameras, bellows, extension tubes, reversing rings, helicoids etc.)
T2 is a more universal mount (it can even be adapted to Nikon SLRs without needing an optical element) which has a thread pitch of 0.75mm and registration of 55mm. It's often used for connecting cameras to telescopes & microscopes but also to quite a number of lenses - all my old mirror lenses have been T2 mounts.

I find it very frustrating that many e-bay sellers of stepping rings etc. use M42 to describe T2 threads and don't specify the thread pitch.

T2 adapters for SLRs are usually thicker than M42 ones, most being ~a centimeter thick without optics.
M42 (x1) to SLR adapters are typically no more than a few millimeters thick, they sometimes fit within the cameras bayonet. Sometimes they will have an optical element to allow cameras with longer registration to focus to infinity.