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.
Nikon SB 800 vs Sekonic L558
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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.
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.
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.
I read the service manual and they didn't say what's the measurement should be. I think the procedure is in the software that they use. I test 1 of my SB-800 and although the full power is lower than what I think it should be the ratio is quite good.
At 10ft and full power ISO100 on the meter the meter should read f11 and 3/10 but it only read f/8 and 6/10 about 2/3 stop under.
now at 1/2 power it reads f/5.6 and 3/10 which is slightly less than 1/2 of the full power. At 1/4 power it read f/4 and 1/10 again slightly less than half of 1/2. At 1/8 power it reads f/2.8 and 1/10 which is half of the 1/4 power.
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forget manual calculations. What you need is a good flash meter, such as a Gossen LunaStarF2 or something similar.
I never do manual calculation because when it works it only works for direct flash and not bounce. Even when I use a flash on manual and without flash meter I just guess the settings. When you are in a place that you take pictures lots of time you know what setting would work.
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.
O.k., I understand your problem.
The sensor you're talking about in the flash head is probably used for error checking. In other words, it just checks if the flash actually fired. If it didn't, you'll get a flash error message. I don't know if this is true or not, but that would explain why they have one in the pop-up flashes built into the camera.
Instead of arguing over what may or may not be happening, here's a link to the NIkon user manual for the SB-800. It's pretty clear on what the A mode is doing.
https://cdn-10.nikon-cdn.com/pdf/manuals/Speedlights/SB-800.pdf
Instead of arguing over what may or may not be happening, here's a link to the NIkon user manual for the SB-800. It's pretty clear on what the A mode is doing.
https://cdn-10.nikon-cdn.com/pdf/manuals/Speedlights/SB-800.pdf
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- koraks
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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.
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I don't know how they control the power in manual mode but they can't use the same sensor for A mode. The A mode sensor measures light reflected back from the subject. If they use a sensor for manual power then it has to measure the light from the tube directly without andy influence from the subject.
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?
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.
There is another mode which is called the GN mode. This mode you tell the flash which distance you want to shoot at and the flash will read the zoom and aperture used then set the power level to give correct exposure without measuring the light. (this also work with non compatible camera if you set the zoom and aperture on the flash manually.
The service manual shows a second photodiode. I don't know where it's physically located on the unit; on the front side of course - should be easy enough to locate .
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 in your example?
GN for 100 ASA at M1/2 for 35mm zoom = 88 (ft)
Could the software that calculates the LCD recommended manual aperture be wonky? Perhaps the EEPROM has a bad value stuck in it's craw.
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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.
This image shows when the power was set at full. 10ft at f/13 (the GN is 125 so the f stop should be 12.5 but rounded off to 13.
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Uuugh... you are correct.... my dyslexia strikes again... sorry. No wonder I generally do flash Ralph's way, with a flashmeter, or A-mode.
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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.
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.
The flash calculator is based on the published GN purely. But it does give reasonably OK expsosure though. May be they rate the GN based on a group of viewers. Take a group of people and show them a bunch of pictures at various level of exposure and ask them which is acceptable with the least exposure. (not the on that is best)
Finally I did a test of the output of my SB 800 in manual mode again - inspired by Chan. I also tested a few other flash guns I have to hand, including a Miranda which is the first piece of photo equipment I ever bought and still going strong, in 1987 (Oh if only I'd stopped there!).
Test was done in my regular living room, at 6 metres. I can do it again in feet if easier, and can do it at 10/11 feet as Chan did. This was just spatially convenient.
I did everything at 35mm @ iso 100 - the Vivitar 2800 doesn't have a zoom adjustment but probably covers 35mm. Despite a lot of searching I could not find a manufacturers specified GN number for the Godox at 35mm, although I did find a comment on dPreview extrapolating that it is likely 35 at 35mm. The published spec is 60 at 200mm, at iso 100.
First observation - the SB800 is pretty close to the LCD spec throughout the power settings (always under-exposed according to the Sekonic but not by much). Actual measured output is listed and in brackets the degree of under-exposure compared to the LCD specification.
Second observation - I didn't expect the SB800 to be more powerful than the Godox, a lightly used unit that is about 15 years its junior. The Godox is also physically bigger.
Third observation - The Godox entries only list the output read-out as measured by the light meter. It was late at that point - not sure if I forgot to write in the Godox LCD proposed f-stop, of it doesn't actually list one on the display. I'll clarify later.
The Vivitar and the Miranda only have full output in manual mode. The Miranda has a clunky manual zoom head (the front fresnel can be slid forward) - but the stated GN at the 35mm position is 25.
I will test the SB 800 in auto mode later with a Fuji x100 Mark 1 that I have. Voltage-wise I think it's safe (?). I can use a remote trigger maybe.
Test was done in my regular living room, at 6 metres. I can do it again in feet if easier, and can do it at 10/11 feet as Chan did. This was just spatially convenient.
I did everything at 35mm @ iso 100 - the Vivitar 2800 doesn't have a zoom adjustment but probably covers 35mm. Despite a lot of searching I could not find a manufacturers specified GN number for the Godox at 35mm, although I did find a comment on dPreview extrapolating that it is likely 35 at 35mm. The published spec is 60 at 200mm, at iso 100.
First observation - the SB800 is pretty close to the LCD spec throughout the power settings (always under-exposed according to the Sekonic but not by much). Actual measured output is listed and in brackets the degree of under-exposure compared to the LCD specification.
Second observation - I didn't expect the SB800 to be more powerful than the Godox, a lightly used unit that is about 15 years its junior. The Godox is also physically bigger.
Third observation - The Godox entries only list the output read-out as measured by the light meter. It was late at that point - not sure if I forgot to write in the Godox LCD proposed f-stop, of it doesn't actually list one on the display. I'll clarify later.
The Vivitar and the Miranda only have full output in manual mode. The Miranda has a clunky manual zoom head (the front fresnel can be slid forward) - but the stated GN at the 35mm position is 25.
I will test the SB 800 in auto mode later with a Fuji x100 Mark 1 that I have. Voltage-wise I think it's safe (?). I can use a remote trigger maybe.
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Interesting. That should give you some confidence in the SB-800. Yet it still begs the question of why you saw bigger differences from the Sekonic initially. Both are professional equipment and should be reliable and accurate.
The 2800 is a bit surprising. I have one but rarely use it because it is flimsy and limited capability. But a stop lower makes me wonder... was the wide-angle panel in place? Regarding angle of coverage, you probably make a good assumption on it being roughly equivelent. The manual says
The 2800 is a bit surprising. I have one but rarely use it because it is flimsy and limited capability. But a stop lower makes me wonder... was the wide-angle panel in place? Regarding angle of coverage, you probably make a good assumption on it being roughly equivelent. The manual says
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