I have a D200 with SB800 and I understand how High Speed Sync works. What I can't find anywhere is a chart/formula to determine max shooting distance at various shutter speed, aperture & ISO settings. Page 106 of the SB800 manual has a chart and formula that does exactly the kind of thing I want except it applies to the F5 and only at shutter speed 1/300.
I've searched the web high and low without luck. I figure with all the expertise on this forum, if I can't get the answer here I'm doomed to failure. Maybe someone is good enough with math to enhance the formula by including shutter speed? I thought maybe Nikon had updated the manual. Nope!
All flash units have a guide number (GN), which is a term to rank the power and how far a flash can shoot. The SB-600 has a guide number of 98 and the SB-800 has a guild number of 125 (more powerful than the SB-600).
The math is used to set your aperture for the GN of your flash and distance from your subject: Aperture = GN / Distance. Shutter speed is not calculated when using flash.
Example: SB-800 GN 125 divided by the distance from the subject 6 feet equals a aperture setting of F2.5. A distance of 10 feet changes the aperture setting to F12.5
I hope this helps and Im sure someone with experience will add to or correct my post.
Never argue with a fool, the people around you cannot tell the difference. Anonymous
Never argue with a fool, the people around you cannot tell the difference. Anonymous
Unfortunately, that all goes out the window in the high-speed sync (Auto FP) mode because the flash fires multiple times, at lower power levels, in other to light the scene while the shutter slit passes over the film/sensor.
As far as I know, Nikon hasn't published any GN equivalents or other detailed specifications for determining flash range in Auto FP mode. Unlike normal flash, it is dependent on the shutter speed, which throws another variable into the calculation.
Fortunately, Nikonian bclaff has performed and published some measurements of the power level in Auto FP mode. Those can be seen here. The main conclusion that I draw from his results is that Auto FP mode is of limited use. Unless the flash is very close to the subject, it probably isn't going to be up to the job.
Thanks for your responses. After seeing the analysis done by "bclafff" perhaps it is understandable why Nikon has not updated their documentation.
The reason I'm interested in high speed sync is that I recently switched from a D70(sync 1/500) to the D200(sync 1/250). I shoot high school wrestling and I'd like to be able to use that higher shutter speed with the D200. I may do a little trial and error. That is, get close, take a shot, move back take another shot. Find where it drops off. I will be shooting at f/2.8.
Below is the chart/formula from page 106 of the SB800 manual that I referenced in my original post. Unfortunately, shutter speed is not a variable in their formula, it is fixed at 1/300. It would be great if a math guru could update it, if that's even possible.
If you compare page 42 of the SB800 manual with page 45 of the SB80DX manual you would see they are the same for the most part. But in the SB80DX, it listed the GN when in fp mode so I think the SB800 would be the same.
Thanks Chan Tran. This inspired me to look in the SB28 manual and it has yet further info on the subject. Page 49-51. Interesting is that pg 51 has a chart with shutter speeds. Finally! It clearly shows that guide number does drop when HS sync is used and continues to drop as shutter speed increases. However, it doesn't appear to drop as much as I expected based on bclaff's measurements (see above post). Does the D200 behave differently than film cameras? And, why didn't Nikon provide more info in the SB800 manual? Hmmm...onward with trial and error testing.
I don't know about the SB-28 chart, but I can't see how it applies. The chart in post#3 is specifically for the F5 and is only for 1/300s (!). Assuming you use that chart as 1/320s values for the D200 then my chart helps you estimate for other shutter speeds.
It's possible I don't have a good understanding of this. I thought the SB28 chart was significant because it includes several shutter speeds and applies to several cameras (F5, F100, F90). I didn't think the chart's drop in guide number from shutter speeds (for example) 1/250 to 1/500 was quite as dramatic as your analysis. Here is the chart.
I don't have any flash unit that supports high speed sync but I think if you use a flash meter and measure a manual mode high speed sync would work. I think the exposure equal to the amount of light of 1 flash.
That won't work for most cameras due to the way shutters work. The sync speed for a mechanical shutter is the limit unless the flash does Focal Plane (FP) sync. For example, your technique will work for the D70 but not the D200.
I do mean to let the flash goes into high speed sync (rapid strobing) but with the flash meter to measure only 1 flash. I believe the exposure is equal to only 1 flash as the repeating flashes are only for when the slit moving to a diffent part the sensor.
>Sorry if I am reading you wrong as everyone seems to be >missing the obvious. > >Doesn't the screen on the back of the flash give this info >when set to go?
Hi Dave, It does indeed. However, the chart from the SB800 manual (see my 2nd post) states that for FP high speed sync, "The farthest flash shooting distance cannot be read on the SB-800's LCD panel". That said, you got me thinking so I checked it out and here is what I found:
With the D200 set at FP high speed sync. and the 18-200 lens at 200mm. The SB800 displays FP on the LCD and the distance scale reads 66ft.
Wow, sounds great! Unfortunately, this is way too good to be true and when I set the D200 to normal 250 sync it still reads 66ft.
So, the distance scale is bogus when using FP sync and actually reflects the distance when not using FP sync.
Bill! I had problem getting my point across. My original theory (which I think has flaws) is that the flash will emit several low power flashes during the exposure. Each of the flash pulse would correspond to a position of the shutter slit on the image sensor (or film). So if we can measure the power of a single pulse that would be the power of the flash. Although it emits several pulses but one pulse for each area of the film so to we only need to measure the one pulse. However, if Nikon were to do this they have to know exactly where the shutter curtain is at during the exposure and I think this is very difficult as shutter travel time can vary quite a bit from one camera to the next as the tolerance is not very tight.
No, I think perhaps I have not gotten my point across
Due to limitiations in the speed of recharge, in FP Sync you get several lower power than normal power flashes as the slit moves across the frame; so the range of the flash is greatly reduced. What we would want, but is not possible, is for several normal power flashes as the slit moves across the frame; and no reduction in range.
BTW, it's "obvious" that what matters is how much light reaches the film/sensor, not the power level of the flash per se.
Mmmmm, I don't doubt you are right and I have not checked but from memory here is what I saw. D200, 17-55 @ 55, ISO 100, A-Mode @ f5.6, SB-800 FP high speed - range 15 feet. This reading may be affected by the available light and could be complete hokkum but it was enough to convince me that FP was only useful for specific shots.
Edit:- Just checked and the 15 feet was for with the diffuser fitted. FP did not make any difference to the reading - as stated, pity.
Always look on the bright side of life de dum de dum........... :) :) :) Dave C Scottish Nikonian My Gallery
When I use 1/250 second at f/5.6 on my D200 + SB800 on Manual + umbrella on indoor shots, it looks slightly underexposed (maybe 1/3 stop or less) - than when I use 1/125 at f/5.6 (correct exposure). At speeds between 1/250 and 1/125 there are smaller differences but still visible.
Now in theory there should be NO difference, OK, up to and including the official sync speed of 1/250 second? (The ambient light is too low to add anything to the exposure, and I am allowing a LONG recycle time between shots, way longer after the red-lght comes back on).
Is this connected with your findings on SB800 output vs. shutter speed? And if so, isn't Nikon being a little naughty in quoting 1/250 as the "safe" maximum sync speed for full exposure?
Flash power for both bodies starts to drop off at about 1/160s. This is suprising given the rated maximum flash duration of 1/1050s. So it appears that the tail of the flash decay is about 5 times longer than the specified flash duration. I would expect a much shorter duration for anything other than full power due to the quenching circuit which is not used at full power. Perhaps this will be another later test and post.
The steep drop in output from 1/250 to 1/320 (D200 graph) indeed shows the high speed FP function kicking in, but what surprised me was that the output at suposedly OK 1/250 was so way down from maximum. Basically it means for me, that I cannot rely on full output flash shots at 1/250 to be identical exposure to shots at 1/125.
So it seems to me that electronic flashes have ALWAYS had the same skew distribution of output vs. time. When my old Nikon FA film camera's shutter speed was faster than the sync speed, I got a very obvious black bar across the frame. Maybe the slightly increased exposure at 1/125 second was still there but I had not noticed it, because of no black bar and the film exposure was compensated for in the printing process.
I do appreciate all your extremely meticulous tests on your website; they add a useful scientific dimension to the wonderful art of photography.