>>The beauty of this set up is that it is cheap and also you can use the
>>prime lens to control DOF, exposure etc. Just leave the reversed lens
>>wide open.
>Now that is what I would have done. But this lab guy stopped his
>reversed 1.2 down! Why?
I've done a bit of lens reversal macro work with my 50/1.4 and 100/2.8
taped together. I typically only use this though when I need LOTS of
light. Extension robs light and if you are doing wildflower work can make
your day pretty unproductive. The main disadvantage that I've run into is
the lack of sharpness around the edges (ie. the focus point changes as you
move to the edge of the picture. For flower work this is a moot point, but
critical studio work may not be flat fielded enough.
Why would a person stop the reversed lens down? You wouldn't want to. The
reversed lens is acting as a magnifier only! It is not focusing the image,
only enlarging it. Very similar to a pair of glasses for far-sighted
people. Glasses don't flip the image over. They are only changing the
focus and image size.
Stopping down a reversed lens (used as a supplimental lens) will not affect
sharpness of the image in any way. In fact, as far as exposure is
concerned, it will only vignet the photo, but leave the middle of the image
the same.
The only reason I can think of as to why this guy stopped down the 50/1.2
lens is to reduce stray light coming in from the side of the picture.
Essentially he would vignet the stray light out, but leave the main image
alone. A 50/1.2 lens has a lot of room to play with on the edges. He
could stop down to around F2 before any vigneting becomes apparent.
Ken Norton
Quincy (micro-not macro) Illinois.
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