Could someone with a D200 and SB-800 try something

Nikon AF Nikkor 50mm f/1.8D

03/15/2007 02:03:15 AM · #1

Could someone with a D200 and SB-800 please try something?

Iâ��m puzzling over strange TTL flash results and would be grateful is someone could try this test.

Working indoors with low ambient lighting and manual exposure such that with no flash the image is rendered black or almost so (I used ISO100, 1/100sec, f8). Take a picture of something â��normalâ�� with each of the following settings using matrix metering and without any exposure or flash compensation:

1. Using the built-in speedlight set to TTL.

2. Set the built-in speedlight to commander mode and use:
Built-in set to TTL / 0 comp
Groups A and B both set to -- (ie. off).

3. Using the built-in speedlight set to commander mode:
Set built-in and group B to -- (ie. off)
Group A to TTL / 0 comp.
Hold the SB-800 close to the built-in flash and set to Remote Group A so it fires instead of the built in speedlight.

To my mind all these settings should amount to the same exposure, or very nearly so. The first one is simple, itâ��s just TTL flash using the built in speedlight. The second one is the same, it just happens that the built in speedlight is also acting as a commander and because the other CLS groups are turned off they should not enter into the exposure calculation. And the last one is just substituting one TTL flash for another. The fact it is a different flash should make little difference to the exposure as the camera controls the exposure not the flash. Needless to say, this is not what I am seeing and I donâ��t know why. I figure it is just my understanding of the system, but Iâ��d like to know if others can duplicate my results. Maybe my D200 needs calibrating, I just donâ��t know.

Anyone got any ideas?

If you give this a try, let me know how you get on, I would be most grateful.

Mike

deapee

Kodak V803

03/15/2007 02:40:04 AM · #2

Originally posted by zardoz:

Needless to say, this is not what I am seeing and I donâ��t know why. I figure it is just my understanding of the system, but Iâ��d like to know if others can duplicate my results.

uhm...what results are you getting?

Nikon AF Nikkor 50mm f/1.8D

03/15/2007 02:59:10 AM · #3

Originally posted by deapee:

Originally posted by zardoz:
Needless to say, this is not what I am seeing and I donâ��t know why. I figure it is just my understanding of the system, but Iâ��d like to know if others can duplicate my results.

uhm...what results are you getting?

Compared to test 1, that is the simple built in TTL, I'm seeing about 2/3 to 1 stop down for test 2 and about 1.5 to 2 stops down for test 3. Way bigger differences than I would expect. The effect diminishes but never quite goes away as the ambient light comes up and the flash becomes a fill rather than the main source.

I first noticed because I am constantly using a lot of + flash compensation with remote flash. I then started doing tests and found this strange result.

deapee

Kodak V803

03/15/2007 03:23:56 AM · #4

How far away is the object/objects that you're taking a picture of? Are you using full metering, partial, or spot? I mean in all honesty, it would help a lot if you post up some unedited, resized-only photos labeled 1, 2, and 3 respectively.

To be honest though, you do have to fiddle a lot with exposure when you're in low light...TTL might be TTL, but nothing's that simple, really. Not to mention the fact that the metering system has problems with metering flashes when you're working with certain objects with certain reflective properties at certain distances, especially in low and tricky lighting situations to begin with and normally at apertures less than f/16 anyway.

In either event, like I said, some unedited resized pics would be nice.

03/15/2007 04:19:13 AM · #5

Thanks for your help deapee

I get the same result with matrix, center and spot metering, any ISO any EV within reason. As I said in the last post the effect does diminish as the ambient light comes up, but it is always there. The same result at any distance within the flashes capability (for the example tests I gave the distance was about 3M). The subjects I used for testing varied considerably (For the test example I gave it was a pile a washing), I even went into a room with no mirrors or TV or anything else reflective as I thought that might have been affecting things.
I appreciate that TTL isnâ��t all-capable but the consistent underexposure with commander mode seems odd. What is strangest of all is test 2. I donâ��t understand why TTL mode with the built-in speedlight should give consistently 1 stop less exposure when commander mode is turned on but all the groups off, apart from the built-in master, compared to TTL with commander mode turned off. I dumped all the test pics I did so Iâ��ll have to do them again and post them so you can see.

Message edited by author 2007-03-15 04:24:13.