Slave flash with DSLR

It's been a long time since posting, so this may be goofed up. But
I've owned a Pentax K10D DSLR for about 1 year, and am still finding
things about it that confuse me.

Recently I wanted to take some flash shots with a new Sigma 180mm
Macro lens, and also found some could use a supplemental flash for
better fill lighting. I dug out an old (30+ year old) slave flash,
with its light sensor trigger, and set up to shoot. Much to my
amazement and disappointment, every shot with the slave flash
triggered by the on camera flash was terrible. Most were just
"black", neither flash registered on the image. I was incredulous,
what happened?

OK, so I ran a few followup tests - like shooting in Bulb mode, with
the on camera flash OFF, and triggering the slave flash with a manual
cable switch, WHILE the shutter was open. These also were almost
black, in fact they were darker than those taken with the ambient
light alone.

Clearly there is something about this DSLR that is far different than
the previous P & S cameras (CoolPix 950 and CoolPix 995) that I've
done this sort of Slave flash with the light sensor trigger. This
procedure worked flawlessly with those cameras, so what is different
with this Pentax DSLR?

Am I missing something obvious? Thanks for knowledgeable
responses.

Olin McDaniel
To reply by email, please remove "abcd" from Return address
-----------------------------------------------------
"Ignorance is treatable, Stupidity is incurable. Sometimes
the difference is hardly distinguishable, however."

On 2008-07-29, Olin K. McDaniel wrote:

Recently I wanted to take some flash shots with a new Sigma 180mm
Macro lens, and also found some could use a supplemental flash for
better fill lighting. I dug out an old (30+ year old) slave flash,
with its light sensor trigger, and set up to shoot. Much to my
amazement and disappointment, every shot with the slave flash
triggered by the on camera flash was terrible. Most were just
"black", neither flash registered on the image. I was incredulous,
what happened?


Your camera flashes twice -- a preflash to meter the scene and decide
how much to fire as its main flash.

This preflash fires your slave light, which has two effects.

1. The slave cannot recycle fast enough to be triggered by the main
flash.
2. The slave flash convinces the camera that it's really quite bright
out there and it only fires a low-power main burst.

So you end up with underexposed shots.

You need a newer slave that understands and ignores preflashes.

Putting most cameras into manual-flash will remove the preflash, IIRC
this is not true for Pentax. But I can be wrong, try it.

--
savvo orig. invib. man

On Tue, 29 Jul 2008 12:31:15 GMT, Olin K. McDaniel wrote:

Clearly there is something about this DSLR that is far different than
the previous P & S cameras (CoolPix 950 and CoolPix 995) that I've
done this sort of Slave flash with the light sensor trigger. This
procedure worked flawlessly with those cameras, so what is different
with this Pentax DSLR?

Am I missing something obvious? Thanks for knowledgeable
responses.

I don't understand why the pictures came out almost black when
using Bulb mode, but there are two reasons that often trip up other
photographers. First, DSLRs have a maximum flash/shutter synch
speed, usually 1/250 sec or less. Make sure that you're not using a
very fast shutter speed or the best you can hope to get is properly
exposed sliver, with most of the frame black. The other reason
(when not using Bulb) is that a "dumb" slave will trigger at the
first flash from the camera's built-in flash. Unfortunately, this
normally happens before the camera opens its shutter, due to the
camera firing "pre-flashes". These are used for purposes such as
determining the proper exposure,

On Tue, 29 Jul 2008 12:31:15 GMT, Olin K. McDaniel wrote:

. . . oops - accidentally hit the laptop's mouse button while
typing, which prematurely sent the reply . . .

Clearly there is something about this DSLR that is far different than
the previous P & S cameras (CoolPix 950 and CoolPix 995) that I've
done this sort of Slave flash with the light sensor trigger. This
procedure worked flawlessly with those cameras, so what is different
with this Pentax DSLR?

Am I missing something obvious? Thanks for knowledgeable
responses.

I don't understand why the pictures came out almost black when
using Bulb mode, but there are two reasons that often trip up other
photographers. First, DSLRs have a maximum flash/shutter synch
speed, usually 1/250 sec or less. Make sure that you're not using a
very fast shutter speed or the best you can hope to get is properly
exposed sliver, with most of the frame black. The other reason
(when not using Bulb) is that a "dumb" slave will trigger at the
first flash from the camera's built-in flash. Unfortunately, this
normally happens before the camera opens its shutter, due to the
camera firing "pre-flashes". These are used for purposes such as
determining the proper exposure, eliminating red-eye, and for use as
an autofocus aid (some cameras use a dedicated bulb or LED, others
use the built-in flash). Also, make sure that the flash is
operating at full power, and not at 1/32 or 1/64, if it has that
capability.

On Tue, 29 Jul 2008 11:54:11 -0400, ASAAR wrote:

On Tue, 29 Jul 2008 12:31:15 GMT, Olin K. McDaniel wrote:

. . . oops - accidentally hit the laptop's mouse button while
typing, which prematurely sent the reply . . .

Clearly there is something about this DSLR that is far different than
the previous P & S cameras (CoolPix 950 and CoolPix 995) that I've
done this sort of Slave flash with the light sensor trigger. This
procedure worked flawlessly with those cameras, so what is different
with this Pentax DSLR?

Am I missing something obvious? Thanks for knowledgeable
responses.

I don't understand why the pictures came out almost black when
using Bulb mode, but there are two reasons that often trip up other
photographers. First, DSLRs have a maximum flash/shutter synch
speed, usually 1/250 sec or less. Make sure that you're not using a
very fast shutter speed or the best you can hope to get is properly
exposed sliver, with most of the frame black. The other reason
(when not using Bulb) is that a "dumb" slave will trigger at the
first flash from the camera's built-in flash. Unfortunately, this
normally happens before the camera opens its shutter, due to the
camera firing "pre-flashes". These are used for purposes such as
determining the proper exposure, eliminating red-eye, and for use as
an autofocus aid (some cameras use a dedicated bulb or LED, others
use the built-in flash). Also, make sure that the flash is
operating at full power, and not at 1/32 or 1/64, if it has that
capability.


Thanks to both you and Saavo, maybe you hit half of the problem
correctly. I didn't realize this Pentax DSLR gave the preflash,
UNLESS it was programmed to do so, for redeye reduction. I'll study
the book in more detail to get a possible answer to this. The event
of a "preflash" would clearly explain the first set of tests. And all
these were shot with the On-camera Flash popped up, which itself
limits the shutter speed to 1/180 or less if so chosen.

But that's why I chose to run the additional series of tests, in Bulb
mode. I set the slave flash at about 1/3 closer to the subject than
the camera which I had mounted on a tripod, and had a push button
switch wired from me to the flash. I pressed the shutter button, and
when I heard it open, I fired the flash. I did this at several
f-stops, some of which SHOULD have been totally washed out. All I
got was the 0.6 second exposure with the indoor ceiling light, and
that was clearly dark and yellowish - no flash effect at all! And I
did this several times, knowing the flash fired while the shutter was
open. Or else I'm losing my mind, could this be, you reckon?

Olin

To reply by email, please remove "abcd" from Return address
-----------------------------------------------------
"Ignorance is treatable, Stupidity is incurable. Sometimes
the difference is hardly distinguishable, however."

On Tue, 29 Jul 2008 16:49:55 GMT, Olin K. McDaniel wrote:

But that's why I chose to run the additional series of tests, in Bulb
mode. I set the slave flash at about 1/3 closer to the subject than
the camera which I had mounted on a tripod, and had a push button
switch wired from me to the flash. I pressed the shutter button, and
when I heard it open, I fired the flash. I did this at several
f-stops, some of which SHOULD have been totally washed out. All I
got was the 0.6 second exposure with the indoor ceiling light, and
that was clearly dark and yellowish - no flash effect at all! And I
did this several times, knowing the flash fired while the shutter was
open. Or else I'm losing my mind, could this be, you reckon?

Try some simpler tests. Change the aperture and shutter speed and
take several pictures with the shutter open longer, for 4, 2, 1, and
1/2 sec., popping the flash at the midpoint that the shutter is
open. If the flash isn't noticed in any of these, then that
suggests that the flash's output might be *much* smaller than what
its rating suggests. Is the flash set at full power? Is it set to
manual or some type of auto mode? In auto mode, the flash might
need to be set to the aperture and ISO that the camera is using. If
it's a "smart" flash that's trying to provide the right exposure,
based on the amount of light that reflects back from the subject,
setting it to a wider aperture and higher ISO than the camera is
using might cause it to put out far less light than is needed.

Try also to position the flash so that part of the flash head is
in the frame with the subject. If it's producing far too little
light to illuminate the subject, the flash head/tube should still be
bright enough to be clearly seen in the resulting picture. The
results you get will determine the next steps to take in the
troubleshooting process.

On Tue, 29 Jul 2008 18:16:04 -0400, ASAAR wrote:

On Tue, 29 Jul 2008 16:49:55 GMT, Olin K. McDaniel wrote:

But that's why I chose to run the additional series of tests, in Bulb
mode. I set the slave flash at about 1/3 closer to the subject than
the camera which I had mounted on a tripod, and had a push button
switch wired from me to the flash. I pressed the shutter button, and
when I heard it open, I fired the flash. I did this at several
f-stops, some of which SHOULD have been totally washed out. All I
got was the 0.6 second exposure with the indoor ceiling light, and
that was clearly dark and yellowish - no flash effect at all! And I
did this several times, knowing the flash fired while the shutter was
open. Or else I'm losing my mind, could this be, you reckon?

Try some simpler tests. Change the aperture and shutter speed and
take several pictures with the shutter open longer, for 4, 2, 1, and
1/2 sec., popping the flash at the midpoint that the shutter is
open. If the flash isn't noticed in any of these, then that
suggests that the flash's output might be *much* smaller than what
its rating suggests. Is the flash set at full power? Is it set to
manual or some type of auto mode? In auto mode, the flash might
need to be set to the aperture and ISO that the camera is using. If
it's a "smart" flash that's trying to provide the right exposure,
based on the amount of light that reflects back from the subject,
setting it to a wider aperture and higher ISO than the camera is
using might cause it to put out far less light than is needed.

First of all, I don't believe it fits your term of "smart flash", I
think it has a fixed output, that may be changed manually as described
below.

Perhaps I should have said this initially, but this flash unit is one
I bought 30+ years ago, and it was without its case. I mounted it in
a small plastic case myself, and found the schematic for the sensor to
fire it as a slave, and built up that circuit myself. My poor memory
fails me, but I "believe" the flash was a Vivitar brand, but not sure
and clearly have no idea of the model number. The only clues about it
a
1- It has a knob below the actual flash, that can rotate between
settings of L, N, and D - showing through an opening in the knob.
2- All my paperwork that came with it is long gone, but there are a
few notes that I taped to the case that give a table of Guide Nos.,
like for film of ASA 100 the Guide No. is 96, and for ASA 160 its
Guide No. is 120. In addition I put a statement "For Non-Auto in L
and ASA of 400, use Guide No. of 190" on the case. I no longer have
any idea what this meant. But all the recent testing I've left it set
in the L position, not knowing if there is a better one for slave
usage or not.

Remember I acquired this thing many years ago and used it heavily with
my film cameras, and it was triggered by the camera's shutter
contacts. I have no idea what voltage is applied to those contacts,
but my film cameras could accommodate it.

Then some years later I built up the sensor detector to fire it when a
camera's onboard flash fired. That worked well for many years, both
with film and early digital cameras. As stated initially, it worked
well with the most recent Nikon CoolPixes that I own, and still does.
The first time I've run into this trouble is with this Pentax K10D.
When using it with the CoolPix cameras, I experimentally got the
settings for them, by shooting a series of shots with it as a slave.

There is one other thing I discovered today, that may or may not be
pertinent. All of my failed efforts to use this flash were with this
brand new Sigma 180mm Macro lens. And all the tests with it on the
camera with the flash raised up, the camera automatically (in Av mode)
selects 1/180 sec. for most aperture settings. Yet today, I replaced
it with my 40mm Pentax lens, and under the same conditions it selects
1/60 sec. for similar aperture settings. And to my amazement, if I
fire this flash manually with the camera in Bulb mode, the flash DOES
now have a significant effect. Different than with the new Sigma
180mm Macro lens in Bulb mode. I'm frankly baffled to discover that
finding also.

Try also to position the flash so that part of the flash head is
in the frame with the subject. If it's producing far too little
light to illuminate the subject, the flash head/tube should still be
bright enough to be clearly seen in the resulting picture. The
results you get will determine the next steps to take in the
troubleshooting process.

After the findings with the shorter lens, is this really going to head
us down a useful path? Please don't take offense, I don't follow the
thoughts here.

Olin

To reply by email, please remove "abcd" from Return address
-----------------------------------------------------
"Ignorance is treatable, Stupidity is incurable. Sometimes
the difference is hardly distinguishable, however."

On Wed, 30 Jul 2008 01:57:10 GMT, Olin K. McDaniel wrote:

After the findings with the shorter lens, is this really going to head
us down a useful path? Please don't take offense, I don't follow the
thoughts here.

Of course not. You discovered that it's not a camera or flash
issue, but that one particular lens seems to be the cause of the
problem. It's also not very easy following your thoughts, since
you indicated that the shutter speed used was 0.6 seconds, yet you
now indicate that you discovered that the Sigma lens in Av mode
switches the shutter speed to 1/180th sec. When the flash didn't
work (with 0.6 sec shutter speed), your camera was operating in
Bulb, not Av mode, right?

If the Sigma lens isn't newer than your camera, you might want to
contact Sigma, as I've read quite a number of accounts of their
lenses having to be sent back to have their firmware updated to work
properly with newer DSLR bodies. I don't recall any of these
messages being about incompatibility problems with newer Pentax
bodies, but I suppose it would be worth checking.

On Tue, 29 Jul 2008 22:57:25 -0400, ASAAR wrote:

On Wed, 30 Jul 2008 01:57:10 GMT, Olin K. McDaniel wrote:

After the findings with the shorter lens, is this really going to head
us down a useful path? Please don't take offense, I don't follow the
thoughts here.

Of course not. You discovered that it's not a camera or flash
issue, but that one particular lens seems to be the cause of the
problem. It's also not very easy following your thoughts, since
you indicated that the shutter speed used was 0.6 seconds, yet you
now indicate that you discovered that the Sigma lens in Av mode
switches the shutter speed to 1/180th sec. When the flash didn't
work (with 0.6 sec shutter speed), your camera was operating in
Bulb, not Av mode, right?

Sorry if I confused you. The answer is "some of each", when I shot in
Av mode, the camera set the shutter at 1/180th sec. Then later, as
part of my diagnostic tests, I went to Bulb mode and after tripping
the shutter manually, I then fired the flash manually, and then
released the shutter button. The 0.6 sec. was about the fastest I
could do this, and that was what several shots in this Bulb mode
showed.

If the Sigma lens isn't newer than your camera, you might want to
contact Sigma, as I've read quite a number of accounts of their
lenses having to be sent back to have their firmware updated to work
properly with newer DSLR bodies. I don't recall any of these
messages being about incompatibility problems with newer Pentax
bodies, but I suppose it would be worth checking.

This is a brand new lens, at least for the Pentax brand. They have
offered this lens for the Nikon and Canon, plus of course Sigma,
cameras for a couple of years now. But even my latest B & H catalog
fails to show they carry it for the Pentax. It was from their web
site that I found it was now available. Unfortunately, the reasons
for which I do not know, this model does not use the HSM focusing
motor that the other models use. Perhaps, it's because Pentax has
Shake Reduction built into the camera body and not the lens like most
of the modern ones for Nikon and Canon have. But this may be wrong
also, since I don't recall if these models have that in the lens
either. Anyway, this is a very newly offered product, and does differ
from those more largely sold versions.

Thanks for your interest in helping me. I'll try to make contact with
Sigma to see if they can help here, as you suggest.

Olin


To reply by email, please remove "abcd" from Return address
-----------------------------------------------------
"Ignorance is treatable, Stupidity is incurable. Sometimes
the difference is hardly distinguishable, however."

"Olin K. McDaniel" wrote in message
...
It's been a long time since posting, so this may be goofed up. But
I've owned a Pentax K10D DSLR for about 1 year, and am still finding
things about it that confuse me.

Recently I wanted to take some flash shots with a new Sigma 180mm
Macro lens, and also found some could use a supplemental flash for
better fill lighting. I dug out an old (30+ year old) slave flash,
with its light sensor trigger, and set up to shoot. Much to my
amazement and disappointment, every shot with the slave flash
triggered by the on camera flash was terrible. Most were just
"black", neither flash registered on the image. I was incredulous,
what happened?

OK, so I ran a few followup tests - like shooting in Bulb mode, with
the on camera flash OFF, and triggering the slave flash with a manual
cable switch, WHILE the shutter was open. These also were almost
black, in fact they were darker than those taken with the ambient
light alone.

Clearly there is something about this DSLR that is far different than
the previous P & S cameras (CoolPix 950 and CoolPix 995) that I've
done this sort of Slave flash with the light sensor trigger. This
procedure worked flawlessly with those cameras, so what is different
with this Pentax DSLR?

Am I missing something obvious? Thanks for knowledgeable
responses.

Olin McDaniel
To reply by email, please remove "abcd" from Return address
-----------------------------------------------------
"Ignorance is treatable, Stupidity is incurable. Sometimes
the difference is hardly distinguishable, however."

I have played around at length with old flashes, the popup flash and a new
Sigma P-TTL flash on a K100D, not the same camera but it may have the same
problems as the K10D, dunno. Anyway, the big problem is that the popup
flash ALWAYS has a pre-flash, no matter what mode the camera is in. This is
the invisible to the eye pre-flash, nothing to do with red eye reduction.
So, basically, to fire an old simple flash with an optical trigger (£7 on
ebay, why make them?) you have to use a manual flash on the hot shoe to
trigger any other flashes. This flash on the camera can be an old one with
no P-TTL, e.g an auto thyristor one in manual mode (or auto if it helps) or
a more modern one like my Sigma EF-500 DG Super but with it switched to
manual.

I use my Sigma in M mode in bounce mode at low power (1/64) on the K100D in
M mode, with 2 old flashes with optical triggers firing into the sides of a
light tent. Works great.