If you still think the measured light output is lower than specs is due to degradation over time, dirty, etc.. then you should try to measure brand new units. All of them measured under I would say.
I can imagine that the measured underexposing is due to dirt on the fixed diffuser of the flas head - dust and dirt on this diffuser gets heated by the infrared light of the flash and burns the acrylic diffuser surface to black.
Yes, I thought about something like that. Or maybe a slightly dislodged fiber optic at the flash head end. However, I'm not really sure if/how that would explain the erratic readings that apparently plague OP. It would be nice to see an actual table of measured flash readings just like @Chan Tran posted to see if there's a pattern to the deviations between the expected and realized flash output.
Another thing I wondered is whether there might be a calibration issue. We've established that the manual flash output relies on an optical measurement/integration of measured light at the head itself. This implies that the fractional output will have to be computed on the basis of a calibration value of the full output of the flash - after all, only if you know how much 100% is, you can cut off at 50%, 25% etc. I imagine this is part of the service settings that can be done with Nikon's configuration tools. IDK if it's possible to DIY this somehow.
You're missing the point, Chan. I fully agree that the manufacturers claimed output is overstated. That's what I said in my original post.
The bottom line is that it doesn't really matter for practical purposes.
There are really only three ways to determine exposure:
1) A handheld flash meter (like the Sekonic)
2) A flash metering system in the camera and/or flash
3) A manual calculation based on actual flash output.
Knowing the actual flash output is only useful in method 3, where you need to do a manual calculation to determine exposure, based on camera to subject distance. In your example with a ceiling bounce, you could use method 1 with a handheld flash meter at the subject to determine exposure. You could also rely on the reflected light measurement from the camera/flash system, as in method 2. Both methods 1 and 2 should indicate underexposure if there's not enough light. Method 2 would be fast and easy, while method 1 could be somewhat inconvenient, depending on the situation.
That leaves method 3. You could take your known flash output, and then measure the distance from the flash to the ceiling. With that you'd have to estimate the reflectance value of the ceiling and determine how much light loss is at the ceiling. After that you'd have to measure the distance from the ceiling to the subject, and then calculate the amount of light hitting the subject, in order to determine the exposure. ..... several hours later you'd be ready to take a picture.
The bottom line is that for practical purposes, you either have to rely on the handheld meter or an in camera/flash metering system to determine exposure. Knowing the perfect guide number isn't going to help in any useful way, other than to tell you your range is limited with any flash.
forget manual calculations. What you need is a good flash meter, such as a Gossen LunaStarF2 or something similar.
I do not think age has to do with flash unit having less power than specs. My Nikon SB-900 is the newest and it measured worst. The SB-800 that measured higher is the older unit.
AFAIK that is to be expected, as the SB 900 has officially a lower guide number than the SB-800.
I remember when the SB-900 was introduced, and in a Nikon forum the users complained about that fact.
The SB-800 has a guide number of (official value) of 42 at ISO 100 and 50mm reflector position.
And the official value of the SB-900 is either 36 or 38, if I remember right.
Official values of the SB-900 is less but the measured value is close to 1 stop lower.
If the SB-900 has a GN of 36 (see above), and the SB-800 GN 42, that is almost one stop difference (if the SB-800 would have GN 44 it would be exactly one stop).
But my SB-900 delivers 1 stop less light than specs. My SB-800 delivers 2/3 stops less light. So my SB-800 delivers 1 1/3 stop more light than the SB-900.
I measured both flashes at 35mm zoom (instead of 50mm) and the SB-900 the specs is 34 and measured. 24 so it's 0.94 stop less.
The SB-800 specs is 38 and measured at 30 which is 0.7 stop less than specs.
What I said is that the SB-900 which is newer and less likely to wear out has greater variance from specs.
The sensor you're talking about in the flash head is probably used for error checking.
It's pretty clear on what the A mode is doing.
That's not what follows from Nikon's service manual; it's pretty clear in several places that the internal sensor is used for actual exposure control, specifically in M mode.
Also, electrically speaking, it doesn't make sense to check whether the flash fired with an optical sensor. It's easier (=cheaper) to check it by verifying the flash cap discharges. Since it can only discharge rapidly through the bulb, you can work out based on a simple voltage measurement whether the flash actually fired. Truth is, Nikon did the sensible thing and used an optical sensor to actually control flash output, also in manual mode. As @forest bagger explained, and as explained in the service manual. You got it wrong; no biggie, I had to look into it as well. No harm in admitting it, is there?
Not on how exposure is controlled, though. It likely uses the same internal light sensor in conjunction with aperture information issued by the camera body.
There is only one M mode. You can change the power ratio in this mode. There is a built in graph on the display to calculate the distance, zoom, and aperture but the flash power doesn't change unless you change the power ratio.Doesn't the SB-800 have 2 different M modes; is it possible that they work differently or do you think that mode difference just affects the calculations displayed on the LCD?
they can't use the same sensor for A mode
I understand that the OP did this. For example he set the flash on manual, flash head straight forward, 1/2 power, at 11ft. The aperture should be f/8. He would then put the flash at 11ft from his Sekonic meter and made the meausrement. He found the meter said something less than f/8.View attachment 375814
The full power GN in feet is 125. At 1/2 it's 88. GN88 at 11ft is f8. 88/11=8. It would indicate f/12.5 only if the power is set at full power.Using the data provided in the spec sheet and GN table in page 42 of the manual, shouldn't the LCD display indicate f/11 or more (rounded from the calculated f/12.5) rather than f/8?
GN for 100 ASA at M1/2 for 35mm zoom = 88 (ft)
The full power GN in feet is 125. At 1/2 it's 88. GN88 at 11ft is f8. 88/11=8. It would indicate f/12.5 only if the power is set at full power.
Uuugh... you are correct.... my dyslexia strikes again... sorry. No wonder I generally do flash Ralph's way, with a flashmeter, or A-mode.
I do use the A mode or use a flash meter. When I don't have the flash meter I guess instead of making a calculation. The calculation only works for straight on flash which I rarely use flash that way except for fill flash.
That's very true. Guessing takes experience...
It's distressing that both the GN table and the flash's calculator is wrong. At least they seem to agree.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?