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Re: [OM] Manual Oly SLR with shutter above 1/2000 sec??

Subject: Re: [OM] Manual Oly SLR with shutter above 1/2000 sec??
From: Christopher Biggs <chris@xxxxxxxxxxxxxx>
Date: 27 Oct 1998 07:52:47 +1000
Sean Chan <sean@xxxxxxxxxx> moved upon the face of the 'Net and spake thusly:

> Yes I'm aware the 3 and 4 do 1/2000...I was looking for above that
> (1/4000+).
> Reason for my question was a few weeks ago I had an ISO 100 film put in my
> OM-4Ti with a 50mm F1.4 (which happened to be set at the largest aperture).
> Perth had a beautiful sunny cloudless day and I was keen to take some
> pictures
> of my mum's roses.

Sean, assuming the 50/1.4 has the same close-focus limit as my 50/1.8
(i.e. 450mm), and set at f/1.4, you have a depth of field (with circle
of confusion limit 33 micron) of only 7.6mm.  (three tenths of an inch
for you Merkkans).

Your "blur factor" (my name for the ratio of circle-of-confusion-limit
to image-circle-size-of-point-at-infinity) is a wonderful 236 times.

BTW, at 450mm your object-space covers about 160x100mm (i.e about 4x6
inch) which will do one bloom full-frame.   Backing off will give you
more DoF.

If you stop down to f/4 you get a depth of 21.6 mm, which is getting
close to just enough to keep a small rose in focus.  At f/8 you get
double that (43.3mm) which will hold focus across a medium-sized
bloom.

Even down to f/16 you only get 87mm depth of field, which still won't
give sharp detail across a "fully open" bloom.  (BTW even at f/16 your
blur-factor is 21x, which is quite good).

Flower photography is a frustrating business.  Tripod is essential
(notwithstanding the ninnies with canon EOS, macro lens,
on-camera-flash and no-tripod at the last Queensland Rose Society show
a few weeks back).

Given the above results, you can see why nobody complains about their
macro lens being "slow" at f/2.8 or f/3.5. :-)

One other thing, "sunny cloudless day" is perhaps not the best time to
do flower photography.  Shadows can be very hard to manage in these
conditions.  A makeshift "soft-box" made from some plastic shopping
bags can help to soften the sunlight and give perfect shadowless
lighting (and the lessened intensity may just solve your shutter
problems).

HTH,
        Chris.

p.s. Does anyone want the software I wrote to do interactive 
        calculations like the above?  It's written in Forth, 
        which will be familiar to anyone who's used one of 
        HPs Reverse-Polish calculators.  

--
------------------------------------------------------------------------
--- Christopher Biggs - Stallion Technologies - chris@xxxxxxxxxxxxxx ---
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