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10-28-2012, 07:51 PM   #1
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how to control ambient vs flash light?

One very basic question...maybe has been answered in other thread, but I can't seem to find an exact answer, so here it goes.

Typically, on Canon/Nikon DSLR and flashes, one can control ambient exposure using the usual manual mode and flash compensation numbers (Canon might be a tad easier). I have a K-5 and AF360, my purpose is to take outdoor portraits and use the AF360 as a fill with a flash cord, I'm running on:

1) HSS on the AF360: to get more adjustment lattitude on the exposure of ambient light.
2) Manual on the K-5: I use the green button technique for reference and then adjust up and down from there, to get desired ambient exposure.
3) P-TTL: the positions and distances are not very consistent, and I'm not talented enough to use manual flash.

Now, this works well in regards to controlling the exposure of ambient light...but how do I adjust the fill (AF360)?

I've tried using the K-5's flash exposure compensation and the AF360's -3 to +1 compensation, but the amount of fill remains constant! How can I adjust the fill's power?

(On a separate occasion, I've used Av mode and the AF360's -3 to +1 compensation does work to control fill, but then I cannot use HSS. Also, the power of the flash exposure appears to be inconsistent, I don't think there's a flash exposure lock in the K-5.)

10-28-2012, 11:53 PM   #2
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I'm going to take a guess at what's going on. The AF360 is a middle-of-the-road flash in terms of power, but when you cross over into HSS territory on any Pentax flash, the max output drops by at least two stops (this is at speeds around 1/250th, it gets worse at higher speeds). Without knowing, I'm going to guess that you're too far from your subjects for HSS to be effective. So dialing in +1 Flash EV may not be having any effect because the flash is already at max output. If possible, try getting closer to your subjects and see if that helps. You might also find it helpful to shoot later in the day when the sun isn't quite so bright, and use a wider aperture lens. Unfortunately I think the best solution may be to get a stronger flashgun.
10-28-2012, 11:53 PM   #3
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It sounds like you are doing everything right. Camera in M-mode and you can use P-TTL with FEC (I'd use manual flash personally and just guess the starting point).

Since you say it seems to work on normal shutter speeds then that also suggests that it is working.

Using HSS really drops the flash output power an incredible amount. (have a look at the table page 81? of the AF360 manual) and see how its affected.
I dont know your distance to subject but maybe the light fall off when using HSS is giving the same (i guess underexposed) result whether you've dialled in -3 or +1.

ie you set the "target" at -3 from of the correct exposure and the flash fires at the full available power it can muster to try and get up to -3 and it still underexposes.
Now if you set the FEC to +1 "target" from the correct exposure and the flash still fires at the full power giving the same underexposed result as before.

Sorry i dont think I explained the last bit that well.
Putting it a different way , the -3 EV or the +1 EV is the target that you wish to have, but even when the flash fires at full power with the HSS working you can't get enough light to reach either of those targets then they will look the same.

Have you tried the alternative using ND filters to cut the ambient light more and allow you to use the flash below HSS speeds.
This allows you to use the wireless, if it will work ok in the sunlight.
10-29-2012, 12:01 AM   #4
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At least with the AF540 flash only the on-flash adjustment is really effective. Sadly enough there really isn't any way of guaranteeing that you get it quickly right every time with PTT-L. It will for example not use nearly all it's power when doing bounce flash in a large room.

10-29-2012, 05:47 PM   #5
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Thanks for your input!

When I did the tests I was indoors, so it makes a lot of sense that the AF360 was already dumping maximum output on -3. That would also explain why the -3 to +1 adjustment did work when using Av. Because of the much slower shutter speed, the flash would not be dumping max power even at +1.

I'll run a few more tests with a better light. I'll do them tomorrow in a shaded outdoor area (which is the scenario in which I plan to use this setup).



On a different topic, I've just looked at the manual (I never read it before, that shows how inexperienced I am with this flash). My unit is made in Japan (says Asahi Pentax) in 2001, and the manuals describes how to use wireless P-TTL on the MZ-S. The procedure is quite complicated, needs to slide in and out of the hot shoe to set channels and things like that. Steve1307 states that the HSS table is listed in page 81...but mine only has 61 pages!

In this case, is my AF360 compatible with the K-5? Is my AF360 a different version than the presently produced ones?

If it is the same thing as the one made now, then how can I get a newer manual?

Maybe I can get the wireless to work with my K-5, that would give me more freedom to set the AF360 closer to the subject and save some power.

Thanks in advance.
10-29-2012, 08:11 PM   #6
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I was looking at the pdf copy of the manuals which you can download here:
http://c758710.r10.cf2.rackcdn.com/files/support/manual/109_1314744916-1606409352_manual.pdf
or of that direct link doesnt work its from this page.
Downloads & Literature - PENTAX Imaging USA
This copy of the manual only "goes up to" the K20D but the AF360 is supposed to be compatible with all later bodies too.
10-29-2012, 08:22 PM   #7
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The MZ-S can do a trick that no other Pentax camera can do (someone correct me if I'm missing one), it can operate in HSS mode via the pop-up flash. All other Pentax cameras, if they can do HSS at all, require the presence of an external HSS flash on the hotshoe, and then if you want to go wireless you'll need a second HSS flash off camera.

"Why?", you might say, "that's stupid!" I wish there were a good answer, but there's not. That's just the way it is. It would be very easy for them to fix, simply delete one or two lines in the firmware, but until they do you need TWO HSS flashes to go wireless.

The Pentax flash system needs a lot of work, much more so than the AF system, and that's saying something.
10-29-2012, 09:30 PM   #8
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QuoteOriginally posted by maxfield_photo Quote
The MZ-S can do a trick that no other Pentax camera can do (someone correct me if I'm missing one), it can operate in HSS mode via the pop-up flash. All other Pentax cameras, if they can do HSS at all, require the presence of an external HSS flash on the hotshoe, and then if you want to go wireless you'll need a second HSS flash off camera. .
It think the *ist or at least one of the *ists could do it.

I can confirm that the whole 2-flash HSS wireless thing does work with AF540 (or AF360) mounted and another HSS compatible flash as the slave.


QuoteOriginally posted by maxfield_photo Quote
"Why?", you might say, "that's stupid!" I wish there were a good answer, but there's not. That's just the way it is. It would be very easy for them to fix, simply delete one or two lines in the firmware, but until they do you need TWO HSS flashes to go wireless.

The Pentax flash system needs a lot of work, much more so than the AF system, and that's saying something.
I thought it was the built in flash cannot do the triggering, ie its a hardware issue not a software/firmware issue

10-30-2012, 11:43 AM   #9
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QuoteOriginally posted by steve1307 Quote
I thought it was the built in flash cannot do the triggering, ie its a hardware issue not a software/firmware issue
I can't think of any reason why it couldn't. Just in case anyone reading is not fully aware of how sync speed works, the max sync speed is the fastest shutter speed at which the shutter is fully open at any one point in time. If the camera would allow you to shoot faster than the sync speed with a conventional single burst flash, you would get a black bar across the top or bottom of the photo depending on which way the shutter curtains run. I've done this before with my old KX. But flashes, even the pop-up flash, are perfectly capable of firing when they are told to do so, and the burst is usually very short (depends on the power), much faster than 1/180th normally.

It is my belief that the only reason that the pop-up flash can't/won't fire above 1/180th is that Pentax wants to protect us from those nasty black bars. Gee, thanks Mom. But this also means that without a HSS flash on the hotshoe to reassure the camera that, 'yes, it's ok to go above max sync' it's impossible to trigger an off camera flash wirelessly.

Somewhere in the firmware there has to be a line of code that looks something like this for when the pop-flash is engaged, or a TTL flash is detected on the hotshoe:

IF (flash_active) = true
THEN (check_for_HSS)
ELSE (Set_shutter_speed) 1/180th

Then there is another line for when the camera can't detect a TTL flash and the pop-up is down that says:

DO (disable_sync_commands)
WHILE (shutter_speed) > 1/180th

This turns off the hotshoe and the PC socket at speeds above the max sync. They really wanted to protect us from those black bars.
10-30-2012, 06:00 PM   #10
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Thanks again for the input, and the manual.

Ran the tests again...this time outdoors, with the FA50 1.4 wide open, at 1 and 2 meter from a grey wall, shutter speed at 200, and a variety of ISO, just to make sure that it was far away from dumping max power and to easily gauge exposure levels. Focus was manual...tried with in focus or completely out of focus, just to account for TTL metering differences (I always use spot).

The results were disappointing with the HSS...and even in Av mode with normal sync, the flash exposures were very inconsistent.

I'm sort of frustrated with the p-TTL system, I'm just going to go manual on the AF360 and practice until I get the hang of it. The trickier thing would to find a setup where I can use a relatively large aperture with normal sync speed. As steve1307 has pointed out, I'll get a few ND filters just for those situations that I can't use the normal sync speed. For fine tuning of the ambient light, I guess I can change the ISO by small increments. I think this way would be the only way to get more consistent and predictable exposures.

Honestly, the output of the pop up flash seems to be a lot easier to control consistently (in p-TTL) than the AF360. Seems to be that the AF360 is metering by itself in some weird way.
11-01-2012, 02:20 PM   #11
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hss is nearly useless for most intents and purposes, and it certainly is useless for what seems to be your purpose. i think what you really want is this:

ambient light means continuous light, flash (strobe) means short burst of light. the way you control the ratio between the two, even while keeping the power of the flash unchanged, is through shutter speed: as long as you're bellow the flash sync speed, you will not affect the exposure of your flash by changing shutter speed (because the flash burst is much faster than your sync speed, so opening the shutter for longer will only let in more "ambient" (continuous) light, but the same, entire amount the flash provided); now what you do in practice, to make use of this, is chose a flash power which gives you a decent aperture + iso for which the ambient light is still "significant" (you measure ambient light with your light meter first, to find out what that wanted combination is, aiming for a decent shutter speed, probably something like 1/60 on a pentax which syncs up to 1/180, so you can adjust either way to adjust the ratio, later). aperture and iso will affect exposure of both sources of light, to the same extent (for obvious reasons)

edit: here's one of my attempts (not so great, but illustrates the point); the background here is something i really don't want in the picture, the only way to get rid of it is by using the falloff from the flash (illumination decrease through distance, direct with square of distance in fact), and the shutter speed to kill the ambient light. exif is included; (note how i was too lazy to go to the flash and bump it's power up a notch, so i just bumped the iso to 125, which also increased the ambient exposure, but it was already so much underexposed it didn't bother me)



sounds more complicated than it is, just give it a try: measure your exposure for the ambient light (m mode, green button), try to find a combination which gives you a shutter of about 1/60, adjust flash power (manual) to something "reasonable" (a result you can accept as exposed okay), and play with the shutter speed without changing anything else. enjoy

Last edited by nanok; 11-01-2012 at 02:27 PM. Reason: example
11-03-2012, 06:40 PM   #12
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Nanok, thanks for your explanation!

In principle, I'm doing the same as you have stated (use the camera's exposure for ambient light, while using the flash exposure for the subject). My concern is the case when the ambient exposure calls for a speed higher than 180 at ISO 80 (like it will happen outdoors on a bright day). In theory, if one doesn't want to stop down the aperture further, the solution is to use HSS.

In my test, the HSS actually works, but I cannot get control over the flash power. In some cases, I cannot even get a constant exposure on a determine setting (at -1, for example). The flash compensation on the K-5 pop up works perfectly...so probably I'm running on the limits of the AF360's power (like other members have posted), or the AF360 is metering something else.

I know that the AF360's compensation is working fine because I'm getting flash power adjustability in Av mode (although it's not as consistent it should). The general consensus is that the Pentax flash system is sort of flaky, I guess my case is one of those problems (either that, or I'm working the AF360 incorrectly or at it's limits).
11-03-2012, 08:01 PM   #13
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One other thing you could try is adding a one or two stop ND filter if you didn't want to stop down any further. Of course it's still going to rob you of flash power, but you may find that it's easier to control than HSS. Anything more than two stops and I'm going to guess that HSS will be more efficient.
11-03-2012, 09:26 PM   #14
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Thanks maxfield...I had just purchased a ND3 a few hours ago. I'm going to start with a 49mm, which happens to be the diameter of the LTD's and FA50.
11-04-2012, 08:38 AM   #15
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QuoteOriginally posted by HSV Quote
Nanok, thanks for your explanation!

In principle, I'm doing the same as you have stated (use the camera's exposure for ambient light, while using the flash exposure for the subject). My concern is the case when the ambient exposure calls for a speed higher than 180 at ISO 80 (like it will happen outdoors on a bright day). In theory, if one doesn't want to stop down the aperture further, the solution is to use HSS.
edit: note, be careful, i did not say to use camera exposure for ambient light and flash exposure for subject, what i said is different, and it explains how things actually work. i know it's not trivial, and hard to explain with words only, but take a minute and try to understand, the outcome will be that you will no longer have to guess and wonder, once it makes sense, you're done being surprised . if you don't understand how a focal plane shutter works, and why/what flash sync speed is, try to look that up first, it will make things easier, ahem, sorry, it will make it possible to understand

mhh, maybe i wasn't clear enough. no, hss is not the solution, you simply need more flash power, or higher shutter speed sync, no other way. hss is only useful if you want to just use some fill and have very fast action going on (so you're not planning to overpower ambient light, you're using it, and you happen to need fast shutter for other reasons), and even in that case i'd argue it doesn't really work (because of oddities of the focal plane shutters with high speed action, but that's a different topic). hss basically means the flash will go of several times, so as to expose the entire frame, as the slit of the focal plane shutter travels across the sensor (if i'm mistaken please somebody correct me), so the best you will get, assuming an "ideal, never been built" flash, will be the fraction of full power of the flash which is the fraction of the sync speed you're shooting at (so if you're shooting at 1/380, that's half 1/180, you won't get more than half your flash power), of course that's oversimplified: flash doesn't discharge instantaneously (depends on flash how long it takes, i think on average some 1/5000 or so?), and flash cannot discharge consecutively at half power without delay, i think, so all things considered, you might get slightly more, but you most likely will get considerably less

QuoteQuote:
In my test, the HSS actually works, but I cannot get control over the flash power. In some cases, I cannot even get a constant exposure on a determine setting (at -1, for example). The flash compensation on the K-5 pop up works perfectly...so probably I'm running on the limits of the AF360's power (like other members have posted), or the AF360 is metering something else.

I know that the AF360's compensation is working fine because I'm getting flash power adjustability in Av mode (although it's not as consistent it should). The general consensus is that the Pentax flash system is sort of flaky, I guess my case is one of those problems (either that, or I'm working the AF360 incorrectly or at it's limits).

hss will reduce the effective power you can actually use by a lot, more as you go to higher shutter speeds. there's no point using hss if your goal is to adjust ratio between ambient and flash exposure, the only things you can do for that are adjusting: flash output (for flash exposure), shutter speed (for ambient exposure), and iso/aperture for adjusting both at the same time, in the same direction, by the same amount (so ratio doesn't change); hss only makes your life more complicated, for no reason. in fact, i expect using hss will in fact reduce the ratio in favor of ambient light (because hss is inefficient, and you will get less light from the flash at 1/360 than half what you would get at 1/180, while you will get exactly half in the case of ambient light -- i can't be sure of this until i test, but honestly i can't be bothered, i have yet somebody point out to me a useful scenario for hss, i consider it a marketing gimmick).

forget hss, if your ambient light is too strong at 1/180 for the flash to do the job you want at full power, you need more power (or a canon powershot with electronic shutter, open source firmware, and sync speed up to umpteenth of a second, check out CHDK Wiki ). there's simply no other way, because of the annoying laws of physics. and no, sync speed of 1/200 or 1/250 will not make a noticeable difference, it will just slightly move the problem away, but not enough to be noticeable, or make it nothing to worry about.

nd filter will not change the ratio, only the overall exposure (and if your problem is the flash doesn't have enough power, they won't help. they might help when flash has plenty of power to do the job, but you just happen to want a wider aperture to work with, but that's their only use in such scenario)

pttl-type systems are inconsistent by design, imho; the only way to get consistent exposure with flash is manual control, if you're in a hurry and need automatic, just do the best you can, and pray that the exposure latitude will help enough to make the inconsistencies correctable. i know other flash systems are slightly better, but if you want consistency/full control, well, you need to take control

hope this helps some.

Last edited by nanok; 11-04-2012 at 08:45 AM.
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