I think you should consider upgrading your flash system because I don't
think the T20 sitting in the hot shoe on top of the OM-1 is really versatile
enough for Macro Flash photography :-0
A better setup IMHO would be the T32, the Wide Adapter/ND Filter Set T32 and
either the Power Bounce Grip or a generic flash bracket with TTL Auto Cord T
and TTL Auto Connector Type 4. This last setup assumes that the camera you
have is an OM-1n since the connector can't be used with OM-1. A cheap
alternative for the Cord and Connector is a standard PC flash cord and a
generic hot shoe with a PC connector; this can also be used with the OM-1.
The advantages of this setup are (1) that you're much more versatile in
controlling the Guide Number (GN) - the flash has two manual settings (GN32
and GN16), and the Wide and ND flash filters can be used to reduce the GN
further; (2) it is much easier to aim the flash at the subject.
An alternative would be one of the T28 Macro Flashes, the T Power Control
and the Wide Adapter/ND Filter Set T32. This is more expensive and harder to
find but basically gives the same advantages, and adds the modelling lights.
Another suggestion is a third party flash that gives much control of the GN,
like the good old hammer flash Metz 45 CT-1 combined with the Metz Mecamat
45-43, or a modern flash like the Metz 40 MZ-2 or 40 MZ-3. The 45 CT-1 can
be found everywhere and doesn't cost too much; the Mecamat is more difficult
to find but is essential because it adds manual GN control and 11 selectable
Auto apertures and spot metering. The 40 MZ-2 has 12 Auto apertures.
The option to change the GN is so important because its about the only thing
left to influence:
- TTL flash is not available with the OM-1(n)
- Normal Auto Mode (computer flash) is only an option when there are are
many Auto apertures to select from; the pathetic two or three Auto apertures
of the T20 and T32 just aren't enough. With the Metz flashes mentioned above
hower Auto flash becomes feasible.
- Sticking to GN based manual flash, you can't change the shooting distance
because it is fixed by the desired magnification, and you don't want to be a
slave of the one and only GN and adapt the aperture to it, because you want
to use the aperture where the macro lens performs best (ususally F8) or the
one that gives you the desired DOF. Of course changing the flash distance by
putting it on a tripod is also possible, but not really an option with macro
photography.
When you start bracketing using the GN there are a couple of issues to think
of:
- the given GN for any flash is based on average reflections and is reduced
when there are no reflections or increased when there are more than average
reflections (you can use this when you build a macro light tent)
- the given GN also assumes normal shooting distances; with short distances
the GN is reduced by 1 or 2 stops
- finally of course there's the light reduction when you use extension
units:
magnification - light reduction in F-stops
1:5 - 1.2
1:2 - 1.5
1:1 - 2
2:1 - 3
3:1 - 4
4:1 - 5
5:1 - 6
So at 1:1 a setting of F8 on the lens effectively is F16. Lets's assume you
use the 80mm Macro lens. The extension is about 11cm, the distance from the
lens to the subject is about the same, so the distance from the flash to the
subject would be about 25cm when it is mounted on a bracket or Power Bounce
Grip. So the GN you want to achieve at that can be used as to guide to start
GN-based bracketing is GN=F*d=16*0.25=4 (meters, 100 ASA ;-). With the T32
this would be achieved by setting it to Manual GN16 and using the ND8
filter:
The T32 manual GN's are for normal photography (and between brackets for
macro photography, using 1 stop reduction because of distance):
GN32-setting GN16-setting
No filter 32(22) 16(11)
wide filter 22(16) 11(8)
ND4 filter 16(11) 8(5.6)
ND8 filter 11(5.6) 5.6(4)
Coarse bracketing is done by changing the GN by using different filters,
fine bracketing can be done by changing the aperture. Using the ND8 filter,
shooting at F5.6, F8, F11 and intermediate settings on slide film would be
the proper setting for 1:1, F8.
When you have one of those Metz flashes you can try -with the lens at F8-
using the Auto apertures F11, F16 and F22 (you must use the effective
aperture) for coarse bracketing. Note that these Auto apertures don't exist
on the T flashes :-(
I think this little example prooves the merits of TTL OTF flash for macro
flash photography. These calculations just drive you nuts, and you have to
do them all over again for every extension and every aperture. With TTL all
you have to do is turn the exposure compensation dial to bracket. So how
about a nice cool OM-3Ti? ;-)
Hnz
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