PTTL Question

**eccs19** · 06-23-2012, 06:04 AM

So I was out playing in an arena the other day. (Roller Derby) I was out on the floor with the derby girls, but seems my flash didn't work the way I was expecting it to. Admittedly flash isn't even close to a strong point for me. I was shooting in full manual mode on my K5 (Metz 50 flash unit). I had no problem getting the flash to fire, but it didn't seem to make much of a difference unless I was close to being metered to ambient light. I thought that if I set my camera to a particular exposure, the flash would give me the light I need for a correct exposure. Does this only work if I'm shooting in a auto mode, (AV) or is PTTL more meant for filling in the ambient light? In my case should I have been using the flash in manual mode at a power level that work for what I was shooting? I was hoping that PTTL would work so that I wouldn't have to adjust my settings if my subject was closer or further away. Any idea what (if anything) I was doing wrong?

Thanks in advance.

Ole · 06-23-2012, 07:21 AM

The aperture you used could have been too small for the flash light to have any effect at the distance you were shooting at.

P-TTL should otherwise work as you expected but the aperture needs to be opened sufficiently up.

Anvh · 06-23-2012, 07:32 AM

There is a limit to the amount of flash light off course.

**eccs19** · 06-23-2012, 08:11 AM

Just to confirm, when using the flash, I was shooting at ISO 1600, F3.5 and max shutter sync speed. shooting anywhere from 70-200mm at a distance ranging from 15 feet to 40 feet. If I had thought about it, I would have put the flash into manual mode just to see how much I would have got at full power, but I'm just surprised I wasn't getting much better than ambient light. I had better luck freezing the action by just bumping the ISO and shutter speed, just ended up with more noise.

aleonx3 · 06-23-2012, 08:41 AM

Your camera meters off the ambient light whereas your flash follows the inverse square law which falls off very quickly when the subject is further away. You can use wireless flash trigger and move the flash closer to the subject to achieve better result.

sterretje · 06-29-2012, 11:37 AM

With those settings you should have had plenty power. The guide number would have been 200 meters (50 x 4) at 105mm zoom setting of the flash; divide by 3.5 and you have more than 50 meters reach (more than 3x the distance that you mention). I assume that you did not bounce against a 10 meter high ceiling or so. Did you use a diffuser or bounce card? That might have reduced the reach significantly. Another thing might be reflections of the flash light on a reflective surface which can cause underexposure in pTTL (and automatic flash mode).

Maybe a sample shot will help somebody to analyze what went wrong.

**eccs19** · 06-29-2012, 12:34 PM

Originally posted by sterretje

With those settings you should have had plenty power. The guide number would have been 200 meters (50 x 4) at 105mm zoom setting of the flash; divide by 3.5 and you have more than 50 meters reach (more than 3x the distance that you mention). I assume that you did not bounce against a 10 meter high ceiling or so. Did you use a diffuser or bounce card? That might have reduced the reach significantly. Another thing might be reflections of the flash light on a reflective surface which can cause underexposure in pTTL (and automatic flash mode).

Maybe a sample shot will help somebody to analyze what went wrong.

That was my thinking. I thought that I should have had lots of power, but it didn't seem to work that way. Lighting was straight on, no bouncing, no modifier at all. I was doing it with wireless PTTL, but I wouldn't think that should have made a difference. I'm at work, so I don't have a sample I can post, but I'll try to remember to post something when I get home.

**Lowell Goudge** · 07-12-2012, 01:14 PM

show us some photos, but I suspect the issue is that the ambient light dominated to the point where the flash did nothing.

When I shoot flash, for things like this, I deliberately set the ambient light exposure to about -2 stops, and use either spot or center weighted metering. The reason is that with P-TTL and matrix metering it may be trying to get the whole scene to meter correctly, and if you know the scene is about -2 stops, then the background will get exposed with the flash and you will burn out the subjects that are closer.

I am suprised, by the way that no one took exception to flash at a sporting event. normally it is not allowed.

amoringello · 07-12-2012, 04:28 PM

I have to agree, at those settings the flash would have been VERY noticeable.
But the K5 tries very hard to balance the flash, at least it really seems to to do much more then the earlier body versions. I have had it kick the flash up a notch because it was firing at a much lower power than I would have liked. PTTL is very finicky and you sometimes just have to play with up'ing the power on the flash. Of course, many times I've had to kick it down a stop or more. Ya just never really know until you get out there and use it in that particular environment. (I hate PTTL more than anything and will not use it if I can help it)

But, from your description, that doesn't sound like the problem either.
I agree also with suggestions to show some photos and maybe it will help someone here figure out what is going on.

**eccs19** · 07-12-2012, 04:40 PM

Here are some samples. EXIF should be in the images. The first one was shot at ISO 560 and I had to bring the exposure back in post by a good 2 stops to get it to the level you see here. The others were what I finally shot at. ISO 1600, and even then I had to bump the exposure in post by about a half stop. Again all shot in P-TTL mode.

As for Lowell's comment about using flash during the event. Apparently it's very common for them to allow flash, but given the ISO peformance of the K-5, I think I'll probably not use it. These shots were just during their practice while learning how things work, and what technique I want to use. My first real go at shooting Roller Derby, so all practice is good. If I was smart, I would have shot a few shots in manual at 1:1 just to see how it worked, but I was hoping to use P-TTL just because then I wouldn't have to adjust my settings depending on how close to the camera they were.

**Lowell Goudge** · 07-12-2012, 06:07 PM

one thing I see that might be giving trouble is reflections off the glass. Look at the last photo. This is an interesting point, you have a high percentage of the frame that is white, that can skew the metering.

Again in the last photo, yes the flash did work you can see the skin tones darken on the girls legs as they get further away. (inverse square law at work) but the lighting is pretty well balanced without flash based on background)

amoringello · 07-12-2012, 06:56 PM

Well, you can certainly see reflection of the flash. If it was merely from the specular highlight problem with PTTL, the image would be significantly under-exposed... so you're on the good side of PTTL at the moment.

PTTL is probably kicking the power down on the flash because it isn't needed much. Bring down the ISO and you might see more effect, assuming the flash is not firing at full power. Again, the flash should be powerful enough to light well beyond 15-30 feet.

Alternatively, set the flash in manual and to full power. If only for one shot, and you should see quite a difference.
If you cannot see the flash at full power on manual, then the ambient is just too powerful and the drop-off of the flash cannot overpower it at the distances you're shooting.
At that point, get closer or get a more powerful flash.

**eccs19** · 07-13-2012, 07:13 AM

Originally posted by amoringello

Bring down the ISO and you might see more effect, assuming the flash is not firing at full power. Again, the flash should be powerful enough to light well beyond 15-30 feet.

The first image was actually at a lower ISO, and I had to bump the exposure in post by over 2 stops, that was the ISO I was hoping I could use, but it just didn't seem to balance out till I got to 1600. I can't believe that I needed to be at 1600 for the flash to have enough power. I will definately have to try manual next time just to see. This will tell me right away if the flash has enough power.

**Lowell Goudge** · 07-14-2012, 04:33 AM

Originally posted by eccs19

The first image was actually at a lower ISO, and I had to bump the exposure in post by over 2 stops, that was the ISO I was hoping I could use, but it just didn't seem to balance out till I got to 1600. I can't believe that I needed to be at 1600 for the flash to have enough power. I will definately have to try manual next time just to see. This will tell me right away if the flash has enough power.

Just remember.

Distance = (ISO/100)^.5 x GN / Fnumber

Because GN is based upon 100 ISO at F1.0

If I take the numbers you posted and convert them, you were shooting from 5-15 meters, at F3.5 and ISO1600

A ISO 1600 the GN is 200 assuming the 50 in the flash model stands for the GN (4xthe published number) shooting at F3.5 largely negates that so your maximum working distance would be 50 meters. You should be OK. Even at that aperture and ISO800 you should be within your distance estimate, but note, distance can be tricky to guess

**eccs19** · 07-14-2012, 05:11 PM

Just want to thank everyone for their input and suggestions. I'm obviously going to have to play with P-TTL a bit more just to see how it works in different conditions. I still think I'll do the derby with natural light, but I still need to figure out lighting for when I do need it.

06-23-2012, 06:04 AM	#1
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510	PTTL Question So I was out playing in an arena the other day. (Roller Derby) I was out on the floor with the derby girls, but seems my flash didn't work the way I was expecting it to. Admittedly flash isn't even close to a strong point for me. I was shooting in full manual mode on my K5 (Metz 50 flash unit). I had no problem getting the flash to fire, but it didn't seem to make much of a difference unless I was close to being metered to ambient light. I thought that if I set my camera to a particular exposure, the flash would give me the light I need for a correct exposure. Does this only work if I'm shooting in a auto mode, (AV) or is PTTL more meant for filling in the ambient light? In my case should I have been using the flash in manual mode at a power level that work for what I was shooting? I was hoping that PTTL would work so that I wouldn't have to adjust my settings if my subject was closer or further away. Any idea what (if anything) I was doing wrong? Thanks in advance.

07-12-2012, 04:40 PM	#10
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510 Original Poster	Here are some samples. EXIF should be in the images. The first one was shot at ISO 560 and I had to bring the exposure back in post by a good 2 stops to get it to the level you see here. The others were what I finally shot at. ISO 1600, and even then I had to bump the exposure in post by about a half stop. Again all shot in P-TTL mode. As for Lowell's comment about using flash during the event. Apparently it's very common for them to allow flash, but given the ISO peformance of the K-5, I think I'll probably not use it. These shots were just during their practice while learning how things work, and what technique I want to use. My first real go at shooting Roller Derby, so all practice is good. If I was smart, I would have shot a few shots in manual at 1:1 just to see how it worked, but I was hoping to use P-TTL just because then I wouldn't have to adjust my settings depending on how close to the camera they were. Last edited by eccs19; 07-25-2016 at 05:56 PM.

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06-23-2012, 07:21 AM	#2
Ole Administrator Join Date: Sep 2006 Location: Copenhagen, Denmark Photos: Gallery \| Albums Posts: 4,408	The aperture you used could have been too small for the flash light to have any effect at the distance you were shooting at. P-TTL should otherwise work as you expected but the aperture needs to be opened sufficiently up.

06-23-2012, 07:32 AM	#3
Anvh Veteran Member Join Date: Sep 2011 Posts: 4,616	There is a limit to the amount of flash light off course.

06-23-2012, 08:11 AM	#4
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510 Original Poster	Just to confirm, when using the flash, I was shooting at ISO 1600, F3.5 and max shutter sync speed. shooting anywhere from 70-200mm at a distance ranging from 15 feet to 40 feet. If I had thought about it, I would have put the flash into manual mode just to see how much I would have got at full power, but I'm just surprised I wasn't getting much better than ambient light. I had better luck freezing the action by just bumping the ISO and shutter speed, just ended up with more noise.

06-23-2012, 08:41 AM	#5
aleonx3 Veteran Member Join Date: Jul 2007 Location: Brampton, Ontario Photos: Gallery \| Albums Posts: 3,996	Your camera meters off the ambient light whereas your flash follows the inverse square law which falls off very quickly when the subject is further away. You can use wireless flash trigger and move the flash closer to the subject to achieve better result.

06-29-2012, 11:37 AM	#6
sterretje Veteran Member Join Date: Dec 2008 Location: Roodepoort, South Africa Photos: Gallery \| Albums Posts: 3,561	With those settings you should have had plenty power. The guide number would have been 200 meters (50 x 4) at 105mm zoom setting of the flash; divide by 3.5 and you have more than 50 meters reach (more than 3x the distance that you mention). I assume that you did not bounce against a 10 meter high ceiling or so. Did you use a diffuser or bounce card? That might have reduced the reach significantly. Another thing might be reflections of the flash light on a reflective surface which can cause underexposure in pTTL (and automatic flash mode). Maybe a sample shot will help somebody to analyze what went wrong.

06-29-2012, 12:34 PM	#7
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510 Original Poster	Originally posted by sterretje With those settings you should have had plenty power. The guide number would have been 200 meters (50 x 4) at 105mm zoom setting of the flash; divide by 3.5 and you have more than 50 meters reach (more than 3x the distance that you mention). I assume that you did not bounce against a 10 meter high ceiling or so. Did you use a diffuser or bounce card? That might have reduced the reach significantly. Another thing might be reflections of the flash light on a reflective surface which can cause underexposure in pTTL (and automatic flash mode). Maybe a sample shot will help somebody to analyze what went wrong. That was my thinking. I thought that I should have had lots of power, but it didn't seem to work that way. Lighting was straight on, no bouncing, no modifier at all. I was doing it with wireless PTTL, but I wouldn't think that should have made a difference. I'm at work, so I don't have a sample I can post, but I'll try to remember to post something when I get home.

07-12-2012, 01:14 PM	#8
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,890	show us some photos, but I suspect the issue is that the ambient light dominated to the point where the flash did nothing. When I shoot flash, for things like this, I deliberately set the ambient light exposure to about -2 stops, and use either spot or center weighted metering. The reason is that with P-TTL and matrix metering it may be trying to get the whole scene to meter correctly, and if you know the scene is about -2 stops, then the background will get exposed with the flash and you will burn out the subjects that are closer. I am suprised, by the way that no one took exception to flash at a sporting event. normally it is not allowed.

07-12-2012, 04:28 PM	#9
amoringello Veteran Member Join Date: May 2008 Location: Virginia, USA Photos: Gallery Posts: 1,562	I have to agree, at those settings the flash would have been VERY noticeable. But the K5 tries very hard to balance the flash, at least it really seems to to do much more then the earlier body versions. I have had it kick the flash up a notch because it was firing at a much lower power than I would have liked. PTTL is very finicky and you sometimes just have to play with up'ing the power on the flash. Of course, many times I've had to kick it down a stop or more. Ya just never really know until you get out there and use it in that particular environment. (I hate PTTL more than anything and will not use it if I can help it) But, from your description, that doesn't sound like the problem either. I agree also with suggestions to show some photos and maybe it will help someone here figure out what is going on.

07-12-2012, 06:07 PM	#11
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,890	one thing I see that might be giving trouble is reflections off the glass. Look at the last photo. This is an interesting point, you have a high percentage of the frame that is white, that can skew the metering. Again in the last photo, yes the flash did work you can see the skin tones darken on the girls legs as they get further away. (inverse square law at work) but the lighting is pretty well balanced without flash based on background)

07-12-2012, 06:56 PM	#12
amoringello Veteran Member Join Date: May 2008 Location: Virginia, USA Photos: Gallery Posts: 1,562	Well, you can certainly see reflection of the flash. If it was merely from the specular highlight problem with PTTL, the image would be significantly under-exposed... so you're on the good side of PTTL at the moment. PTTL is probably kicking the power down on the flash because it isn't needed much. Bring down the ISO and you might see more effect, assuming the flash is not firing at full power. Again, the flash should be powerful enough to light well beyond 15-30 feet. Alternatively, set the flash in manual and to full power. If only for one shot, and you should see quite a difference. If you cannot see the flash at full power on manual, then the ambient is just too powerful and the drop-off of the flash cannot overpower it at the distances you're shooting. At that point, get closer or get a more powerful flash.

07-13-2012, 07:13 AM	#13
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510 Original Poster	Originally posted by amoringello Bring down the ISO and you might see more effect, assuming the flash is not firing at full power. Again, the flash should be powerful enough to light well beyond 15-30 feet. The first image was actually at a lower ISO, and I had to bump the exposure in post by over 2 stops, that was the ISO I was hoping I could use, but it just didn't seem to balance out till I got to 1600. I can't believe that I needed to be at 1600 for the flash to have enough power. I will definately have to try manual next time just to see. This will tell me right away if the flash has enough power.

07-14-2012, 04:33 AM	#14
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,890	Originally posted by eccs19 The first image was actually at a lower ISO, and I had to bump the exposure in post by over 2 stops, that was the ISO I was hoping I could use, but it just didn't seem to balance out till I got to 1600. I can't believe that I needed to be at 1600 for the flash to have enough power. I will definately have to try manual next time just to see. This will tell me right away if the flash has enough power. Just remember. Distance = (ISO/100)^.5 x GN / Fnumber Because GN is based upon 100 ISO at F1.0 If I take the numbers you posted and convert them, you were shooting from 5-15 meters, at F3.5 and ISO1600 A ISO 1600 the GN is 200 assuming the 50 in the flash model stands for the GN (4xthe published number) shooting at F3.5 largely negates that so your maximum working distance would be 50 meters. You should be OK. Even at that aperture and ISO800 you should be within your distance estimate, but note, distance can be tricky to guess

07-14-2012, 05:11 PM	#15
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510 Original Poster	Just want to thank everyone for their input and suggestions. I'm obviously going to have to play with P-TTL a bit more just to see how it works in different conditions. I still think I'll do the derby with natural light, but I still need to figure out lighting for when I do need it.