Hi all,
I noticed a very interesting phenomenon today whilst playing with the 100
f/2.8 and auto telescoping 65-116 tube:
I cranked the lens all the way out and extended the tube all the way out,
then moved the tripod until this combination was focused. Then, I collapsed
the tube all the way in, and it was still focused, at the new magnification!
Looking through the viewfinder as I did this, the image lost focus gradually
until quite fuzzy at half way through the travel and then regained the focus
as I continued to the fully collapsed position and new magnification .
Hmmmm. Very interesting. And practical as well--a two position macro of
sorts.
Out of curiosity, I cranked the lens all the way in to infinity with tube
fully extended, and moved the tripod until this combination was focused.
Now, as I started to collapse the tube, it went out of focus and then quickly
regained focus at half travel. As I continued to full collapse, it went out
of focus and that was it.
I tried this with a 200 f/5 and 50 f/1.8, but they never came back into focus
at any point in the travel.
What is happening here?
-Tim Clark
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