Resource: TC’s Lens - Mamiya-Sekor SF C 145/4.0 M645 Soft Focus

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MOD Tom Caldwell Forum Pro • Posts: 36,706
Resource: TC’s Lens - Mamiya-Sekor SF C 145/4.0 M645 Soft Focus

A complex lens that really needs the manual to properly understand. Here is where a pdf can be found:

But this is not all.

Using a M645-EF adapter there is a fixed lever inside that over-rides the AF selection and sets MF mode.

This had me a bit tricked as the lens has a “handy” pull back function on its focus ring that I have taken a bit of understanding.

The general idea is for use in oem Mamiya 645 camera bodies. In AF mode the lens is always set with aperture wide open (presumably to get more light into the finder and make composition/focus easier) But wide-open can be at its softest and therefore the pull back on the focus ring reduces the aperture and helps determine exact point of focus. In AF mode releasing the pull back always returns to wide open and it was the job of the oem body to return the aperture to its set position to capture the image. Therefore Auto mode is not a lot of use when using this lens as MF on a digital camera body (not surprisingly).

However the Adapter makes sure that the lens is always in Manual mode when mounted whether or not the lens is set to “M”.

Then it gets a bit tricky. “M” mode is the preferred setting for checking the degree of softness visually (even on oem Mamiya 645 bodies). (Both the softness regulating ring and the aperture affect the amount of softness applied).

This leaves the lens working on a bit of hit or miss and inspired incantations to the fairies if pull-back in M mode is actually tried.

Mamiya recommends that in “M” mode that the lens be set to f8.0 aperture despite your desired soft setting - this will give a sharper represention and more precise focus - then reset to your desired “soft aperture” for capture. Just a minor amount of messing around and <<don’t use>> pull-back when in MF mode.

However I am confused - if in M mode pull back will in fact stop the lens down from where it is set and theoretically make focusing sharper. But it will not return to wide open if the lens is thus set (seems to stick). It will sometimes return to f5.6 and almost always return to the pre-set aperture from f8.0 and smaller. In my initial confusion I thought that the aperture was merely sticking and a lens fault. But taken off the adapter and used in A mode the pull-back works as Mamiya describes.

Mamiya says “don’t use pull-back” in M mode but if it were to work and not “stick” it might be exactly what MF lens users might need. Ie: set aperture, pull back for smaller aperture with less soft-fuzz, and use focus ring, then release pull-back and use preset aperture fo desired soft-focus image. But as the reset does stick and mostly in the widest settings it is a nuisance as the user does not easily know what aperture is actually in use for the capture.

Therefore the actual procedure is clear - in M mode don’t use the pull-back feature as recommended but set the aperture required before capture. Set it to f8.0 or smaller beforehand if more precise focus is necessary.

Note also that pull back seems to make a random new aperture from any setting and as this can stick there even if the aperture lever is reset. It seems to need a full actuation rotation to be assured that it can return to wide open.

This is a sort of nearly there phenomenon where it would be nice to be able to use the pull-back function in M mode but it seems that it is not reliable enough to be trusted.

Others who have used this lens might like to comment. If there is a way to modify the lens so that on release of pull-back in M mode the lens will always return to the pre-set aperture on release it would be brilliant.

The use of the distance scale markings on the soft focus strength settings are well described in the manual. Sufficient to say briefly here that the focal length of the lens changes depending upon the soft focus strength setting and are not one-sided dof markers. In other words the coloured marking lines on the barrel show the focal length estimation from the distance scale for each different strength. The scale is infinite between minimum (blue) and maximum (orange) and partial settings can be made.

This is a very interesting lens and I will have to work harder in order to fully master it.

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Tom Caldwell

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