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01-12-2016, 10:25 AM   #1
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Popup Flash Strength and Hotfoot Flashes

This came up recently ... I'm on my 3rd pentax DSLR. They've been great, especially outdoors - and since most of my low-light indoor pictures are snapshots that don't really need to have super crisp cleanliness, so a little noise wasn't an issue. So I've never really put much thought into this.

I just got a K-50. My brother asked me last weekend at a family gathering how powerful the flash was. I kind of shrugged. Good enough, I suppose.

Then I took a shot of my newest little cousin from about 4 or 5 feet away, with the flash. Looked good enough. But ... it chose 3200 ISO. With a flash. Indoors. Really?

Back in the film days, I routinely used 400 speed film with a flash with great results. So I looked and made sure I had the ISO set to Auto 100-512000. Yup.

So I limited it to 100-400. Not surprisingly it chose 400. Surprisingly, it chose a 1/8" shutter speed (at F4.5) . It is the Tamron 28-300 at about 135mm, and again the camera said it chose F4.5. You'd think that'd be plenty of light at that distance for a faster shutter speed.

Which leads me to believe the answer to my brother's question is "not very".

My two questions are ... what are your thoughts on this, and 2) is there a flash setting that will essentially allow you to substitute a hotfoot flash for the popup that would use the same exposure feedback system the popup presumably uses? Or do you HAVE to go to manual exposure settings once you put a hotfoot flash on there?

01-12-2016, 10:42 AM   #2
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QuoteOriginally posted by flipster Quote
Or do you HAVE to go to manual exposure settings once you put a hotfoot flash on there?
No. But you do need a Pentax flash or another brand that understands P-TTL protocol. A manual flash like Yongnuo or Cactus or even a Nikon or Canon will fire, but you have to control the flash strength on the flash the camera cannot do that.

QuoteOriginally posted by flipster Quote
how powerful the flash was
Flash strength is rated by something called the flash guide number: https://en.wikipedia.org/wiki/Guide_number The camera manual or online review will always give you the guide number for a flash so you can compare strength.

---------- Post added 01-12-16 at 09:44 AM ----------

Not sure why the camera is selecting those settings. Maybe someone else with more knowledge of the on board flash can help you with that.
01-12-2016, 10:44 AM   #3
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QuoteOriginally posted by flipster Quote
This came up recently ... I'm on my 3rd pentax DSLR. They've been great, especially outdoors - and since most of my low-light indoor pictures are snapshots that don't really need to have super crisp cleanliness, so a little noise wasn't an issue. So I've never really put much thought into this.

I just got a K-50. My brother asked me last weekend at a family gathering how powerful the flash was. I kind of shrugged. Good enough, I suppose.

Then I took a shot of my newest little cousin from about 4 or 5 feet away, with the flash. Looked good enough. But ... it chose 3200 ISO. With a flash. Indoors. Really?

Back in the film days, I routinely used 400 speed film with a flash with great results. So I looked and made sure I had the ISO set to Auto 100-512000. Yup.

So I limited it to 100-400. Not surprisingly it chose 400. Surprisingly, it chose a 1/8" shutter speed (at F4.5) . It is the Tamron 28-300 at about 135mm, and again the camera said it chose F4.5. You'd think that'd be plenty of light at that distance for a faster shutter speed.

Which leads me to believe the answer to my brother's question is "not very".

My two questions are ... what are your thoughts on this, and 2) is there a flash setting that will essentially allow you to substitute a hotfoot flash for the popup that would use the same exposure feedback system the popup presumably uses? Or do you HAVE to go to manual exposure settings once you put a hotfoot flash on there?
1.) The flash tries to balance the ambient exposure with the flash acting as fill light. So, ISO 3200 in indoor low light isn't that far fetched for an ambient exposure. The flash can then use less power and acts as fill. If you want your subject to be the only thing lit in a dark vacuum, then you'll have to set the camera up to do that. Its can't read your mind.

2.) Most external flashes made for a pentax camera include P-TTL, the same exposure algorithm that the pop-up flash uses. Its utilizes the same ideas; pre-flash for metering and then calculated flash for exposure. Its just more powerful, gives you more options (like front/rear curtain), sometimes lets you shoot with wireless off camera flash, and allows you to set it to manual if you desire.
01-12-2016, 10:47 AM   #4
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Using a flash on your camera other than the pop-up will give you far more versatility and strength to work with. The AF360FGZ/AF540FGZ models or the later versions of those lines (II) will work in different modes along with Manual mode. Manual mode is valuable when using those flashes due to giving you the choice of settings to control your image outcome. If you used something like TAV mode, which I use almost all of the time for other than flash use, the ISO may end up being more than you want and cause noise in the image. But if I use Manual mode, I can use a setting like 200 ISO, F10, and shutter speed of 250 to catch some possible movement of a subject, and get reasonable results without having excessive noise and having reasonable depth. The flash itself will measure how much light is needed and discharge that amount when activated when within a reasonable distance of your subject.


Last edited by C_Jones; 01-12-2016 at 11:10 AM.
01-12-2016, 10:57 AM   #5
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I think a shutter speed of 250 is beyond the max sync speed of the camera, which I thought was 1/180. Anyway, not sure why you are going to f10 in this case. Wouldn't f5.6 up to maybe f8 be the range we should be talking about?


BTW - I think pretty much all brands will chose a high ISO when auto-ISO is on and it is dark enough for a flash. My Nikon does this too.


QuoteOriginally posted by C_Jones Quote
Using a flash on your camera other than the pop-up will give you far more versatility and strength to work with. The AF360FGZ/AF540FGZ models or the later versions of those lines (II) will work in different modes along with Manual mode. Manual mode is valuable when using those flashes due to giving you the choice of settings to control your image outcome. If you used something like TAV mode, which I use almost all of the time for other than flash use, the ISO may end up being more than you want and cause noise in the image. But if I use Manual mode, I can use a setting like 200 ISO, F10, and shutter speed of 250 to catch some possible movement of a subject, and get reasonable results without having excessive noise and having reasonable depth. The flash itself will measure how much light is needed and discharge that amount when activated when within a reasonable distance of your subject.
01-12-2016, 10:58 AM   #6
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Thanks, this is exactly the kind of feedback I needed.
01-12-2016, 11:21 AM   #7
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AF360FGZ and AF540FGZ and their (II) model versions have HSS (high speed synch) .

F10 is a depth choice. Other F stop settings are not ruled out, depending on preference/need.

Last edited by C_Jones; 01-12-2016 at 03:30 PM.
01-12-2016, 12:29 PM   #8
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Shoot in a mode that isn't GREEN or Av (M perhaps) and you can force the flash to put out more power. As indicated the default is to fill with flash not to use flash as primary illumination. And 1/180th is the highest sync speed you can use without using the High Speed Sync (HSS) feature of a flash. This is a major power drain and doesn't put out much light by comparison.

01-12-2016, 12:30 PM   #9
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The camera's algorithm for flash is really conservative for shutter speed. For example, I'll use my Pentax-F 28mm f2.8 with the onboard flash a lot. The camera likes to choose 1/60 sec. for a shutter speed. Your cousin shot was probably at the max for flash, 1/180, because you shot at 135mm. Because the lens was a superzoom, the reported focal length is not the real focal length unless it's at infinity focus. So you might have been able to switch to M mode to choose a slower shutter speed. As long as your subject isn't moving too fast and you are really steady, you might get away with 1/30. Then you could have gotten away with less flash power or lower ISO.

I like to use M mode and the camera's meter to see how hard the flash has to work in a certain setting. Say I'm at a family gathering like you were, with the DA 18-55. I can set the camera to f5.6, 1/30 and ISO 1600, just a guess that those will work OK. Then pop up the flash and activate the meter. It will show underexposure in stops. That is how much the flash will try to add to the shot. I can adjust my guess settings to influence the flash contribution. I like this method better than other modes with flash.
01-12-2016, 12:35 PM   #10
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Weird. I'm looking at guide number now ... and the guide number for the K50, according to this article is 12.

Although why, then, have to use such a slow shutter speed at maybe 2 meters at ISO 400?

Basically, what I'm thinking is I need to find a significantly more powerful P-TTL flash than the built-in. I look at the relatively inexpensive Pentax AF-200FG ... it says it has a guide number of 20 at ISO 100/m. So 1.67 times more powerful.... wondering if that will be enough the way I shoot.

The Metz mecablitz 36 AF-5 says it has a GN of 36 and has a rotating head, which means I could use it with the lightsphere. Hmmmm.... that's 3 times the power of the builtin.

Guess I need to play around more and do a bit more research, but I'm probably in the market for one of these now.

Oh, look! More replies to go read. Thanks, everyone!

---------- Post added 01-12-2016 at 01:37 PM ----------

Woah. PENTAX AF360FGZ AF .... GN 119. Pretty sexy for $150.

---------- Post added 01-12-2016 at 01:41 PM ----------

Would plain TTL work as well? The difference, I understand, is TTL doesn't need to pre-flash ... but will the camera support that would be the question. Would they work together better with P-TTL. Or maybe it wouldn't work at all with just TTL, no clue.
01-12-2016, 12:49 PM   #11
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QuoteOriginally posted by flipster Quote
Weird. I'm looking at guide number now ... and the guide number for the K50, according to this article is 12.

Although why, then, have to use such a slow shutter speed at maybe 2 meters at ISO 400?.
The guide number of a flash has nothing to do with what you set your shutter speed to.

QuoteOriginally posted by flipster Quote
Basically, what I'm thinking is I need to find a significantly more powerful P-TTL flash than the built-in.
[/COLOR]Would plain TTL work as well? The difference, I understand, is TTL doesn't need to pre-flash ... but will the camera support that would be the question. Would they work together better with P-TTL. Or maybe it wouldn't work at all with just TTL, no clue.
Newer bodies do not support TTL, only P-TTL. You can get a flash with an Auto setting like the older AF540 or some 3rd party flashes that don't rely on "through the lens" tech. They have their own built in sensor.
01-12-2016, 12:54 PM   #12
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Using my AF540FGZ I see the same problems - it's not the flash power - it is the way Pentax tries to use flash.
You have to force it to work the way you want.
01-12-2016, 01:01 PM   #13
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QuoteOriginally posted by jatrax Quote
No. But you do need a Pentax flash or another brand that understands P-TTL protocol. A manual flash like Yongnuo or Cactus or even a Nikon or Canon will fire, but you have to control the flash strength on the flash the camera cannot do that.
This is not correct. Auto thyristor flashguns will work just fine. I use Nikon flashes (SB-25, SB-26, and SB-30) on camera in auto mode with great results.
01-12-2016, 01:22 PM   #14
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QuoteOriginally posted by UncleVanya Quote
Using my AF540FGZ I see the same problems - it's not the flash power - it is the way Pentax tries to use flash.
You have to force it to work the way you want.
QuoteOriginally posted by enoeske Quote
xposure. The flash can then use less power and acts as fill. If you want your subject to be the only thing lit in a dark vacuum, then you'll have to set
QuoteOriginally posted by C_Jones Quote
flash on your camera other than the pop-up will give you far more versatility and strength to work with. The AF360FGZ/AF540FGZ models or the later versions of those lines (II) will work in different modes along with Manual mode. Manual mode is valuable when using those flashes due to giving you the choice of settings to control your image outcome. If you used something like TAV mode, which I use almost all of the time for other than flash use, the ISO may end up being more than you want and cause noise in the image. But if I us
QuoteOriginally posted by MPrince Quote
t
But as long as you can set the flash unit to P-TTL mode and it's compatible with the camera it should work like the on-board flash, just with more light, no?
01-12-2016, 01:25 PM   #15
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QuoteOriginally posted by flipster Quote
But as long as you can set the flash unit to P-TTL mode and it's compatible with the camera it should work like the on-board flash, just with more light, no?
It will act like the pop-up flash, with the capability of more light. If you leave everything on auto, it won't be very different than the exposure you get with the pop-up flash (i.e., still ISO 3200 and such)
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