Request for comments

[rjlittlefield]

(I see this posting has created a second page. Be sure to see response about 'undo' at bottom of previous page.)

Now, let's talk some more about the optics...

With the 105 set on f/5.6, you're using an aperture that is too wide. This hurts you for two reasons. First is that it allows lens aberrations to soften the image. Second is that it reduces DOF per frame, forcing you to shoot a deeper stack with smaller steps. You will get better results with less work by stopping down to something around effective f/16.

I am puzzled by this comment:

cannot set the 105 on infinity as it will not focus, it has to be set at min.focus

Imagine for a moment mounting the Minolta 50 mm on a film camera in the usual way, focused at infinity. Take note how far away from the lens the film would sit. Now imagine that without changing the lens focus setting, you remove the Minolta lens from its imaginary camera and reverse it in front of your 105. In this configuration, when a subject is positioned exactly as far from the Minolta lens as the film was, then the Minolta lens will "push" that subject backward so that the 105 will see it as being at infinity.

This is the relationship for which the Minolta 50 mm was designed, and where it will be sharpest.

When you set the 105 mm to its minimum focus, you are forcing the reversed 50 mm to work in a focus relationship that is different from what it was designed to do. This introduces aberrations that further soften the image. The fact that your combo is so soft could well be due to the added aberrations combined with the wide aperture.

Can you describe in more detail what you mean by "cannot set the 105 on infinity as it will not focus, it has to be set at min.focus"?

With the 105 set on infinity focus, the subject should be in focus when it is positioned as described above, the same distance that film would be from the Minolta at its own infinity focus.

What happens that is different from that?

--Rik

[gypsey]

I carried out a series of tests with the 105 at apertures ranging from 4.8 to 9 using three different apertures on the reversed 50mm
1.7/2.3 est./9.5 est.
The results were very enlightening. There were significant differences.
With the wider apertures of the 50mm 1.7/2.3 the best results were with the 105 at f9
With the smallest aperture on the 50mm est. f/9.5 the best result was with the 105 wide open at f/4.8

The moral of the story seems to be that when using a new lens or combination, one has to experiment to find the best settings. I have seen the reference to the 'sweet spot', but had not realised how sour the other settings can be.

Thanks for your suggestions
gypsey