--- [EMAIL PROTECTED] wrote:
> On Fri, 2 Feb 2001, Bob Meyer wrote:
> > Anyone who's old enough to remember manual focus
> > SLRs with a split-image "rangefinder" in the
> > viewfinder is
> > probably familiar with what happens when you mount
> > slow lenses on the camers (or view with the lens
> > stopped down). For those without that experience,
> > I'll tell you: one half of the split-image blacks
> > out. ...
>
> Hi Bob,
>
> I also used to think the split-image blackout was
> due to the lens aperture limit.
>
> Then I put a split image focussing screen in my EOS
> 1000FN and discovered that blackout is entirely due
> to positioning of the eye relative to the centre of
> the split prism!
>
> If one side blacks out (even at f/1.8), I just move
> my eye relative to the viewfinder until both halves
> of split images become visible again. The effect is
> still there, but less subtle when using the
> triangular "microprism" collar.
>
> The split images are still visible even if I mount a
> lens with effective aperture f/11 (f/5.6 + 2x TC).
> It *is* harder to focus, no because of "blackout",
> but because the two split images have a greater DOF.
>
> The situation is similar to using FTM during DOF
> preview.
Hi Julian and Bob,
I have to agree partly with you both (which of course
means I partly disagree :-)
Having owned a range of split image MF cameras I know
that some of them "black out" at a given aperture and
no matter how much you move your eye relative to the
split you simply *cannot" get both halves clear (or
even partly clear) at the same time.
I used to own a Chinon SLR which I occasionally used a
500 f8 lens with. No matter how I tried one half
always stayed black. It was accepted fact at the time
that this was due to the difference of the angle
between the two halves: the greater the angle the
earlier it blacked out. I seem to recall that my Canon
A1 was *slightly* better in this regard.
Yesterday I put a split image focusing screen into my
RT. Two statements: 1. Great. 2. Don't know why they
didn't come that way standard!. (The first of those
two statements may be redundant!). Anyway, I checked
this with a 5.6 lens yesterday and I could see both
halves quite clearly even in quite dim light. Being
used to the concept of having to shift my eye in
relation to the split at that aperture I was surprised
that very little blackout occurred even at low light
levels. From this I presume that the angle of the two
halves is slightly shallower than I was used to with
MF cameras (which may make sense in an AF camera).
And remember that the viewfinder on an RT doesn't get
as much light going to it as say a 630, due to the
pellicle mirror.
This morning I tried Julians suggestion of stopping
down the lens to f11, and sure enough, by judicious
eye placement both halves were clear. Now this is
something that I'm definitely not used to. Well
*wasn't* is probably the correct term.
Interestingly though I found that the RT doesn't AF
while DOF preview is being used even at apertures
wider than f5.6.
BTW Julian, what camera model did the focusing screen
come from that you put in your 1000FN. I've read on
the list that Canon actually list part numbers for
different screens for the EOS 50/Elan II even though
they're not advertised as having interchangeable
screens (as of course is also the case with the
1000FN). I wonder whether the same is true of the EOS
30/ELAN 7 series? Mind you, I think I'd prefer the
standard 3 and 7 point AF screens in them than a split
image one anyway.
Regards
Gary
__________________________________________________
Get personalized email addresses from Yahoo! Mail - only $35
a year! http://personal.mail.yahoo.com/
*
****
*******
***********************************************************
* For list instructions, including unsubscribe, see:
* http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************
