question on flash

Bukitimah

Senior Member
Hi, recently I took a shot using external flash. I found the bottom section of the photo dark. When I reduce the shutter speed from 320 to 250 sec, the photo is OK. I don't seem to encounter such problem with my D300. Can anyone explain? For illustration, I attach the photo to show the darken effect.

flash.jpg

F8, ISO 1000, 30 mm, S 1/320 sec

Thank you for your advice
 

PapaST

Senior Member
Perhaps the shutter is too fast and not able to sync with the flash. I think the fastest sync speed for the D600 is 1/250 and that's with using high-speed sync.
 

WayneF

Senior Member
Hi, recently I took a shot using external flash. I found the bottom section of the photo dark. When I reduce the shutter speed from 320 to 250 sec, the photo is OK. I don't seem to encounter such problem with my D300. Can anyone explain? For illustration, I attach the photo to show the darken effect.

The black band is caused by exceeding the Maximum shutter sync speed with flash.

The spec on the D610 for Maximum shutter sync speed is 1/200 second. Manual (page 234 and 327) says it can work at 1/250 second.

The spec on the D300 for Maximum shutter sync sped is 1/250 second. Manual says it can work at 1/320 second.

It is just a factor of the design speed of the shutter. There is no work around, you have to stay with what works.

HSS is a very different mode (if the flash actually supports it), which is not speedlight flash at all, and you will discover that the HSS power capability is very low (about 20%).
 
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aroy

Senior Member
Hi, recently I took a shot using external flash. I found the bottom section of the photo dark. When I reduce the shutter speed from 320 to 250 sec, the photo is OK. I don't seem to encounter such problem with my D300. Can anyone explain? For illustration, I attach the photo to show the darken effect.

View attachment 202100

F8, ISO 1000, 30 mm, S 1/320 sec

Thank you for your advice
The camera flash synchronization speed is slower than your set shutter speed (the shutter requires to be fully open for electronic flash to illuminate the whole sensor area). As others have pointed out your max is /200, any thing more and you will get the band. It will keep growing in height as you increase the shutter speed. D300 has a faster synch speed.
 

Bukitimah

Senior Member
I thought my D610 says 1/250 sec? What is HSS? The camera setting allow Auto FTP or something like that which say 1/320. According to the YouTube video, it can adjust to higher speed. I have yet to try.
 

Dawg Pics

Senior Member
HSS = High Speed Sync, which is Auto FP

I think the external flash has to be compatible to use that feature, that is, if you are using an external flash.
My d300 can use the built in flash or my SB 800 with Auto FP, from what I understand.
 
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WayneF

Senior Member
I thought my D610 says 1/250 sec? What is HSS? The camera setting allow Auto FTP or something like that which say 1/320. According to the YouTube video, it can adjust to higher speed. I have yet to try.

The D300 can do 1/320 second maximum, but the D610 can only do 1/250 second maximum. That is speaking of regular speedlight flash mode.

Auto FP enables HSS (when the actual shutter speed is set faster than the Auto FP menu speed).

The camera can do HSS (via Auto FP), and perhaps your flash can too, but to see HSS, they both do have to be capable of HSS.

HSS is called High Speed Sync, but actually it has no concept of sync. Speedlights are very high speed flash, but HSS is merely High Speed Sync (just meaning any fast shutter speed works). HSS cannot stop motion at all (HSS only has the shutter speed working for it, but speedight mode is faster). HSS is radically different than flash. The HSS flash becomes a continuous light which can work at any fastest shutter speed (continuous light has no concept of sync, and is not actually flash mode), but at only about 20% power level in order to be continuous.

HSS is described at Auto FP and HSS - What is it?
 
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aroy

Senior Member
I thought my D610 says 1/250 sec? What is HSS? The camera setting allow Auto FTP or something like that which say 1/320. According to the YouTube video, it can adjust to higher speed. I have yet to try.

To answer your query, you gave to understand how a Focal Plane Shutter works

. There are two parts to the shutter - the front curtain and the rear curtain.
. When the shutter fires the front curtain starts travelling. Depending on the shutter speed the rear curtain follows after some time. So in effect the shutter exposes the sensor in a strip. The width of the strip determines the amount of light reaching the sensor - in effect the exposure time. If the exposure time selected is more than the time required for the front curtain to reach the end, then the rear curtain follows after the exposure time is reached.
. The electronic flash fires a very short burst of light, normally between 1/5,000 and 1/15,000 of a second. So the shutter has to be fully opened for the flash to illuminate the object and the sensor to register it.
. For normal flash operation the front curtain has to travel from top to bottom (or one side to the other, depending on mechanism). The rear curtain stays put. If the speed selected is lower still the rear curtain will fire after the selected time.
. There is a limit to the curtain speed, and that is the maximum shutter speed at which a flash will illuminate the whole scene. That in effect is the sync speed quoted.

HSS or High Speed Sync is a combined capability of both the camera body and the flash to send a signal to the flash and the flash to fire at regular intervals so as to illuminate the scene in strips (synchronizing with the shutter opening that is travelling). As the normal flash take some time to power up to full strength, during HSS the flash power is reduced so that it can supply uniform light for all those bursts (in effect the flash has to calculate the number of bursts that are needed for the duration of the shutter movement, then determine at what power it needs to operate to deliver uniform light across the bursts). The faster the flash can charge the more power can be delivered during HSS.

HSS also depends on the implementation in the body. D70 with CCD sensor could HSS at 1/4000 or faster.
 
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