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Re: [OM] T32 for Macro--question

Subject: Re: [OM] T32 for Macro--question
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Fri, 11 Jul 2014 16:53:38 -0400
Here's the true skinny on the T32 for macro question. This is based on pure observation and real data. No speculation or computer models involved. Dr. Mike had asked the question... how close can you get to the subject with a T32 wearing an ND3 filter in auto mode before the T32 goes bonkers and screws up the exposure.

I first double checked the spec of the T32 in auto mode. If you are working with ISO 100 the three auto mode settings on the T32 relate to apertures f/4, f/5.6 and f/8. At f/4 the distance range is given as 1-8 meters. At f/5.6 it's 0.7-5.6 meters and at f/8 it's 0.5-4 meters.

Since I was working with my E-M5 I had a lower limit of 200 ISO which moves the three auto ranges up to f/5.6, f8 and f/11. My test platform was my Bogen tripod with head and camera tilted down toward the floor. The target was a color advertising flyer surrounded by my large medium gray white balance target. The head was wearing a macro slider to help vary the distance. I was shooting in subdued daylight in my house with the the lens set at f/5.6 and shutter speed 1/60 sec. According to the camera that was 3 stops down from the ambient light. In other words the flash was going to have to provide most of the light.

My first test was to try and validate the T32's specs without using a filter. My test setup was going to make it difficult to shoot from as far as 1 meter so I decided I'd start with 1/2 meter at ISO 200, f/5.6 and see if it worked. By the specs that should be pushing it a bit. And it turned out it was but not by much. The resulting exposure was a bit bright but certainly not enough to blow the highlights. I also tried the exposure with my Sekonic L-358 flash meter which reported that the proper exposure should have been 1/60 at f/6.3. Since I had the camera set at 1/50 and f/5.6 the meter was telling me the flash unit was 1/3 stop too bright. My eyes would agree with that. Close enough.

Next up, change nothing except add an ND3 filter to the flash head. My first thought was that the flash ought to keep huffing and puffing through the filter to get the exposure correct. But no way did it do that. What I got was an exposure that was about 2-3 stops down. Don't ask me why it doesn't try to push through the filter. My first thought was maybe it tries to but doesn't have enough power to do it. But I don't think that's the case. Just remember the data point even if, like me, you can't make sense of it.

So, the flash doesn't push out any more light just because you've hidden the flash head behind a filter. So let's try and lie to the flash using the ISO slide. I put an ND3 filter on so I'll tell the flash that the camera is using a ISO 25... three stops slower than ISO 200 to compensate for the filter. When you do this the aperture indicator on the flash also moves down by 3 stops to f/2. Ignore it. Leave the camera at f/5.6 as it was. Take the shot. Whoopee. This is a better exposure than the first one which was a bit bright (probably from being too close to the target at 1/2 meter). But this one's at 1/2 meter too and the exposure looks dead on. Strangely the Sekonic says the correct exposure is 1/60 at f/3.2 when we just took it at f/5.6 So much for the Sekonic. I have no idea why it says 3.2. That means it believes there was 1-2/3 stops less light than was actually there.

OK, can we get closer with this same setup. Yes. I moved the flash head down to 1/4 meter from 1/2 meter. Same thing. A very good exposure, no blown highlights. I didn't try the Sekonic.

Then I moved the flash head down to 0.16 meters. I couldn't go any closer than this without some major adjustments to my setup. I also decided it was unwise to go closer than this since I had had to tip the T-32's flash head in to try and keep the target illuminated. I also had to change the m.Zuiko 12-50 to macro mode to get it to focus. But once again I got a very good exposure. I tried the Sekonic again which said the correct exposure was 1/60 at f/6.3. and this time only 1/3 stop away from the actual.

Anyhow, the bottom line is the T32 with ND3 will deliver proper exposures to as close as you can get and still keep light on the target. To get the correct exposure slide the ISO dial to a 3 stop lower ISO but keep the same aperture.

Chuck Norcutt








On 7/10/2014 6:09 PM, Chuck Norcutt wrote:
I haven't found it yet but I now know there is an ND3 filter somewhere
in the house.  I'm still thinking about how to do this... I think it's a
non-trivial task.

Chuck Norcutt


On 7/9/2014 8:16 PM, Mike Gordon via olympus wrote:
Dr. Manual Flash writes:
Eventually, it went about a stop beyond the recommended aperture which
I attribute to a relatively high ambient light level and/or maybe too
close to quench.


I'm going to have to rethink my fill flash completely. I may have to
go
back to fully manual. :-)

As long as Dr. Flash has his meter out I wonder if he can put the 3 stop
ND filter on the T32 and see how close  one can get before it starts to
overexpose  in auto mode compared to baseline .

I wish the ISO setting on the T32 would really change the flash output.

Student of Dr. Flash, Mike





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