That proved my point that flash manufacturers intentionally claimed high output for their flashes than actual. If it's the manufacturing variation then you would find some units deliver more power than specs. So far I have never found one that has actual GN higher than specs,
Yes it does, whether intentional or not. But I don't think there are many who ever doubted that fact.
Of the few I've measured, the closest I've found was an elderly pair of Vivitar 285's. I consider them outlayers.
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.
Chan,The display and your measurement for the SB-800 matches exactly
I attached the display for 1/1, 1/2 and 1/4
View attachment 376091View attachment 376092View attachment 376093
Chan,
The uncanny consistency of our read outs gives me the distinct sense that I mislead everyone on how to read my test results. I think I mis-remembered my entries for the SB800. The first figure (which matches your read-out) is in fact my SB 800 read-out, and the value in brackets is the shortfall from that value at the Sekonic meter! So under-exposure, albeit generally not bad.
I found another flash gun in a box - a Nikon SB-20 flea market special. I tested it the same way, and updated my results here. It's pretty good for a flash from the late 80's. But it doesn't come near its stated GN number.
Thanks to all for the collective perspective. Interesting to hear confirmation that the actual output of these units diminishes over time.
I've tested lots of flashes with a Minolta Auto Flash and flat diffuser at 10 feet. I've never found a flash (new or old) that produces exactly the power that is listed in the user manual. Some are a little more powerful -- like the Vivitar 283 -- and some a little less. Add this factoid to the "soup", but as said, if you are using the camera in TTL flash mode with appropriate camera-controlled flash unit(s). it won't make a difference.
Thanks both for re-kindling this discussion.
Over the past few months I've used the SB800 extensively with a Dslr for three shoots on-location, used in an 'off camera" mobile studio set-up alongside a Godox unit I own. Over about 1200 exposures it did really well, so I think the unit is solid. I'm sure it's fine in TTL mode - negs certainly seemed fine with a few shots processed from my N80. So practically speaking, the unit works fine.
But that Manual exposure rear display - the one based on an 'ideal' GN output scenario, is downright misleading. In my initial post I had been testing the unit in Manual mode - which of course is rarely used in practice these days. So quibbling about overly optimistic LCD displays may have sounded like hair splitting in that particular instance. But my intended primary use for the unit has always been to use it in "Auto" mode with a Mamiya 7, or a few other non-Nikon cameras I have. Looking again at the LCD display right now- in 'Auto" mode it gives me a an exposure range (distance) at a given ISO / aperture / focal length. This is information I will definitely rely on when using it with my Mamiya 7 to set aperture on the camera and / stay in exposure range for a given aperture. I hope the display is more reliable in Auto mode than in manual mode!
I just got the Mamiya back from servicing etc, so I haven't had a chance to run a test with the flash & camera combined.
Flashes came with two types of Guide Numbers.
The most common type - far more common for amateur users - was a Guide Number that assumed some scene characteristics that incorporated reflectance from nearby surfaces such as floors and ceilings - the sort of characteristics that would be encountered with most normal, everyday photography by the majority of users.
As a result, for most users in common situations, the Guide Number gave good results rather than over-exposed results.
In other, more commercial or professionally marketed flashes, the Guide Number was more a measure of the light output itself. It was up to the user to incorporate their experience with modifiers and reflective scene characteristics when determining exposure.
In some cases the supporting information for the first type of flash included the information about the assumptions about scene reflectance used in the calculation of the Guide Number.
Watt-second rating is not the same as Guide Number. Both have definitions and they are different. Equating them is unnecessary confusion.
Uhm! Nobody was talking about Watt.Second.
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