Thomas Bantel wrote:
>
> Vesa Perala wrote:
> >
> > Sorry, I checked 100-400@100mm (f4.5) only when EOS-3 was set for
> > half-stop scale (it was around 2 a.m. anyway when I made the tests).
> > I may do (just for "theoretical interest") it once more with
> > 1/3-scale selected and see how the jumps are between 5.6 - 5 - 4.5.
> >
> > IF f3.5 is f4 + half-stop it is also interesting to see if f3.5
> > at 1/2 and 1/3-scales is equal or not.
> >
>
> I think you already did a plenty good job, but yes, this would be
> particularly interesting.
Hehe, maybe it's just me, but sometimes I'm really interested in
stuff like that, although it's practically irrelevant IMHO.
Well, sometimes I just desperately want to KNOW exactly how it
works ;-) Probably some tech reps at Canon have a good laugh
about my wild guesses. So, to add to their amusement, I just had
to do some experiments yesterday night, which - so I hoped -
might give me some answers.
First, I needed an f/4.5 lens. So I dug out my good old
100-300 f/4.5-5.6 USM lens - which is rarely used by me nowadays.
My first, simple experiment was, to switch the camera in AV mode
set to f/4.5, once in 1/3 scale mode, once in 1/2 scale mode. Then,
while looking closely at the aperture blades from the front, I
pressed the DOF preview button in order to see if the aperture
would close down a little. Well, it didn't. Absolutely nothing.
So my conclusion was, f/4.5 is wide open with this lens, no matter
which scale I use.
My next thought was to find out about faster lenses. I used my
35 f/2 lens for this. Will f/4.5 be the same with 1/2 and 1/3
scale? Hmm, but how to test it?
My first idea was to switch the aperture from f/4.5 with 1/3 scale to
f/4.5 with 1/2 scale and look at the blades to see if they would
move. Oh well, I found out pretty fast that you cannot change
CF settings while pressing the DOF preview button on an 1N :-(
My second idea was to remove the lens while still pressing the
DOF preview button. This way, I at least managed to keep the
lens stopped down at f/4.5 (1/2 scale) Then I switched to 1/3 scale
mode and still f/4.5. Proud to have tricked my equipment, I
remounted the lens (with DOF preview button pressed) and watched
closely if the blades would move... Arghh! They DID move. Yes,
they first opened up to wide open and afterwards stopped down
again :-( No way to see a possible difference of 1/8 stop.
And, what was at least interesting again: The f/stop was altered in
this process! After remounting the lens, it was set to f/4, even
though my last setting had been f/4.5. Well, at least another
additional mystery to investigate after the total disaster with
the 1/2 and 1/3 stop issue. ;-)
Thomas Bantel
*
****
*******
***********************************************************
* For list instructions, including unsubscribe, see:
* http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************
