Mamiya C330 55mm lens focussing behaviour, strange or not?

[Jonny TLR]

Hi folks,
I’ve just purchased a Mamiya c330 55mm 4.5 TLR lens and I just wanted to clarify if the way it’s focussing is as it should be. With the bellows fully in, it’s very out of focus, I would have expected that to be infinity focussed. With the bellows out about 7mm it looks sharp at infinity. Otherwise it seems to focus on everything distant and close fine as far as I can see. Is this behaving as it should or is there some kind of back focus issue going on?

Many thanks for any responses.

 

[miha]

Perfectly normal. The bellows have to accommodate various focal lengths.

 

[Neil Grant]

it's normal behaviour for this lens and others in the range. Focusing beyond infinity too.

 

[Jonny TLR]

That's very reassuring, thanks for the quick response!

 

[grahamp]

Solid mount cameras have to have optics designed for a common film distance from the mount, which places a constraint on the optical design. By using a bellows, Mamiya got some flexibility in how they designed the lenses, but at the expense of a common infinity focus point. You should be collapsing the bellows all the way in order to change lenses, so it becomes second nature to rack back out to around the right infinity distance (visually, by scale, or just experience).

 

[Neil Grant]

.. the C 330 camera has a focus distance indicator on the LHS from behind. It's in the form of a hexagonal rod, rotatable to match the lens in use. It's possible to read off the focus ranges for the various lenses and where the infinity point would be. The bellows needs to be substantially extended for many of the lenses and this does have an impact on handling. The 55mm lens is easily provoked into flare - scattering the image with pentagonal shaped light patches. Best not to poke it into the light.

 

[flavio81]

Hi folks,
I’ve just purchased a Mamiya c330 55mm 4.5 TLR lens and I just wanted to clarify if the way it’s focussing is as it should be. With the bellows fully in, it’s very out of focus, I would have expected that to be infinity focussed. With the bellows out about 7mm it looks sharp at infinity. Otherwise it seems to focus on everything distant and close fine as far as I can see. Is this behaving as it should or is there some kind of back focus issue going on?

Many thanks for any responses.

What about the focus scale on the body? Your lens should be sharp at infinity when the focus scale is exactly at infinity.

 

[MattKing]

The focusing scale on the bodies of C330s is, at best, aspirational!
Particularly with the wider lenses.
It isn't that it is wrong. Its just that it isn't really capable of high precision.