Thursday, February 10, 2011

A flash meter is a flash meter

This picture has nothing to do with today's post, except that it was taken with a Metz 45 CT1. I think around 1982. I used the Metz Tele Attachment 45-33 while taking the picture with the 50mm lens. That is why the flash illuminates only a part of the picture like a spotlight. The Tele Attachment illuminates an 135mm lens angle for FX format. There will be a separate blog with some experiments for the Tele Attachment. I just used this picture today, because I do not want to post a blog without at least one picture, and a series of pictures regarding today's topics would have been less entertaining.

The user poppy left a comment at the blog Batteries or Rechargeable he or she had an issue with the flash metering. In short the flash was used in full manual half and quarter, but the flash meter showed the same reading. Unfortunately poppy did not write what type of flash meter was used. The assumption from poppy was that flash meters are generally built for studio flash and that they have inconsistencies when used with on camera flashes.

Hmmmm, I thought that should be tried in practice.

I own only one external meter the Gossen Mastersix. You have seen it in the Batteries or Rechargeable blog. Today I took a number of 45ers and the Gossen to see if it meters consistently.

First I tried the 45 CT4 with M 1/2 and 1/4. The meter worked fine. For each setting I fired a number of flashes and the meter showed the same result for each. As expected it also showed f32 for full power f22 for 1/2 and f16 for 1/4. So the meter works?

Well then I used a Metz 45 CT5 with Mecamat 45-30 That allows manual settings from full power to 1/64 as described here. I got fine results up to 1/16 power. Then the Gossen showed me that It could not measure properly by displaying its error code "uuuu" instead of an aperture. I guess that the flash needs a minimum duration to be measured. 1/16 has the duration of 1/8000s that still worked. 1/32 has the duration of 1/16000s and that no longer worked.

After all Gossen is a German make, so something like that should be in the manual?
I looked it up and it amazingly says Flash duration 1/1000s to 2s.

Hmmmmm, 1/1000s is not very generous and would indeed limit flash metering to studio units. It seems to work to 1/10000. Either there in a typo in the manual or the careful German engineers did not want to commit to the full specification and left one zero off to be on the safe side.

Poppy has been on to something.

If you want to buy a new or used flash meter, you should find out how short the flash can be to be measured. I know now that 1/16 for my 45ers and 1/8 for the SB800 and SB900 is the minimum manual power I need to be able to measure it with my flash meter.

That is good to know.

Thanks Poppy.

Tuesday, February 8, 2011

The Flash "Kind of" Double Exposure

Most of the time I pre-visualise my pictures. I scout out locations at the time of day I want to shoot and make some test pictures, so I normally pretty much get what I planned. Not so in this case.

The picture was taken on the palm Island on a spot where I could have a nice silhouette of the Atlantis Hotel at sundown. The basic idea was, to shoot a model with an antique car , a Bentley S2.

The plan and most of he pics were something like this.

I wrote before that the sun moves fast fast fast near the Aequator and there is not much time between sunset and darkness. So I had to constantly dial up the time to keep the background from becoming pitch black. After a lot of shooting the Owner departed with his car and I started packing up, when the Model suggested a few more shots without the car. OK.

With the car gone there was space now an she started to pose and jump.
The flash set up was a SB900 on Camera for fill and as a master and three Metz 45er into one large shoot through umbrella. (Three 45er seem to be overkill, but we started out with a lot of ambient light and I needed the power then. Later I continued with two, just switched one off.)

The picture above was actually the last frame shot at that day.

I like it a lot becaus it looks like a wild multiple exposure. It was in fact just one shot.

What happened?

Obviously the Hotel switched on the lights.
The sky was still relatively light. (In the direction of sun down.)
The foreground was already completely dark.
The exposure time had crept up to 2 seconds and I shot hand held.
The foreground is illuminated by the umbrella cumming from left behind me.
As it's ambient light level is very dark the picture looks like a single exposure.
The jump is kind of frozen in this part of the picture.
The sky and the lights from the hotel are bright in relation to the flash exposure (f 14).
That's why it looks like a double exposure in this parts and the jump has movements.

I was totally surprised by the result, but it can be mostly explained.

But look at the "shadow". If you observe closely you will notice that it is no shadow at all. Because it is not actually on the ground where it should be.

Frankly I havn't figured out a good explanation.
There is one more picture for you below. let me know if you can explain the shadow.