[UncleVanya]

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)

Correctly stated above by enoeske. The flash power will let you reach more distant subjects but will optimize similarly for the same subjects. So a portrait shot in the same lighting indoors on the same camera will likely look about the same if you leave the decisions to the camera. You can override the camera and make different decisions. One way to do this is to switch to Manual.

[flipster]

Seriously, it was just a snapshot in a room, like thousands more I've taken in my lifetime. So I wasn't trying to just light him (I'm not that advanced at this point, anyway, though I get the concepts).

I of course assumed in auto mode it would have an algorithm more like, say, *I* would use ;-) (because I know best, of course!) to maximize photo quality. If I have it in auto mode, I'm assuming I'm not shooting a moving object, at least not a very fast moving object, and I would also assume that I wasn't too concerned with getting a a ton of field depth, and I would also try to go with the lowest ISO that would allow for, say, a shutter speed no slower than 1/60, certainly no slower than 1/30. In that situation, I personally would like to stay at 800 ISO or less. F4-ish should be fine. I just expected it to think more like me and assumed that since it didn't, it couldn't because the flash isn't powerful enough.

I need to play some more.

[UncleVanya]

Seriously, it was just a snapshot in a room, like thousands more I've taken in my lifetime. So I wasn't trying to just light him (I'm not that advanced at this point, anyway, though I get the concepts).

I of course assumed in auto mode it would have an algorithm more like, say, *I* would use ;-) (because I know best, of course!) to maximize photo quality. If I have it in auto mode, I'm assuming I'm not shooting a moving object, at least not a very fast moving object, and I would also assume that I wasn't too concerned with getting a a ton of field depth, and I would also try to go with the lowest ISO that would allow for, say, a shutter speed no slower than 1/60, certainly no slower than 1/30. In that situation, I personally would like to stay at 800 ISO or less. F4-ish should be fine. I just expected it to think more like me and assumed that since it didn't, it couldn't because the flash isn't powerful enough.

I need to play some more.

Using the K50 if you have it you would select a different SCN mode for forcing the flash to work the way you want. i can't recall but I think it's night portrait maybe? There are other ways to game the system as well. The default thinking from Pentax on this makes no sense to me but that's the way it is setup.

[BrianR]

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.

That's 9 times the power output (inverse square law).

[/COLOR]Woah. PENTAX AF360FGZ AF .... GN 119. Pretty sexy for $150.[COLOR="Silver"]

It has similar power to the Metz, this is 119ft @ iso100, the other units were in meters. The AF360FGZ has a guide number of 36m@iso100 (when zoomed to 58mm), the AFG540FGZ has a guide number of 54m@iso100 (when zoomed to 58mm).


Such a long shutter sounds like it was trying to balance the flash with the ambient in some way. Different "Auto" modes might prioritize differently.

[jatrax]

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.

Actually it is correct. Auto Thyristor flashes do not communicate with the camera. They certainly work, I love my SB-26. But the OP specifically asked about the exposure feedback system used by the onboard flash which an auto thyristor would not be capable of using.

[UncleVanya]

Actually it is correct. Auto Thyristor flashes do not communicate with the camera. They certainly work, I love my SB-26. But the OP specifically asked about the exposure feedback system used by the onboard flash which an auto thyristor would not be capable of using.

OK my turn... neither correct nor incorrect; it was a tangential answer. The original statement was that the camera couldn't control it and that you would have to control it at the flash. But this implied that the flash would be manually set (perhaps not intentionally). The point of an Auto-mode flash is that you can set an f/stop and be reasonably assured of getting good flash exposures without communication between the camera and the flash or the lens and the flash. In practice it isn't as automated (you can't change f/stops on the fly and expect the flash to understand and compensate) but it is sufficiently automated to make it much simpler than shooting with manual flash power (albeit less predictable in some scenarios).

[flipster]

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)

So basically you're saying my problem probably has more to do with the Auto-algorithm than the flash itself.

[enoeske]

So basically you're saying my problem probably has more to do with the Auto-algorithm than the flash itself.

Yes. It sounds that way.

[UncleVanya]

Have you read this? https://www.pentaxforums.com/forums/125-flashes-lighting-studio/300073-compre...ht=flash+guide

[C_Jones]

I have three AF360FGZ units. I use them on and off my camera for lighting. The ability of them to communicate wirelessly without any other accessories is nice, and the unit type performs very well with my Pentax cameras (K-5IIS and K-3II). Note the K-3II comes without a flash (pop-up) so a flash head is required for it to perform wirelessly with other external off camera flash units.

The K-50 has wireless capability.

The pricing on Amazon for the AF360FGZ is quite reasonable presently.

[MPrince]

Actually it is correct. Auto Thyristor flashes do not communicate with the camera. They certainly work, I love my SB-26. But the OP specifically asked about the exposure feedback system used by the onboard flash which an auto thyristor would not be capable of using.

But that's not what you said. You said "manual flashes such as Nikon" and implied they only work in manual mode. Auto thyristor flashes do not need to communicate with the camera and do not need to be controlled manually in order to provide a properly exposed image.

[Lowell Goudge]

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.

This is 100% correct and the fault of the user (sorry flips ter) but letting the camera make all your choices for you is a conscious decision, and therefore user error.

The Pentax exposure algorithm , as enoeske correctly stated will follow trying to match the program curve for shutter speed first, then opening aperture and then suutter speed down to hand hold limit, and then add flash for fill.

Too many things to let the camera control without you taking charge.

What I do is turn auto ISO off when using flash. Then,mi set shutter and aperture to under expose the scene by between 1/2 and 2 stops, depending on how much illumination separation I want between subject and background.

Then, using spot metering, (P-TTL uses the regular camera metering) I expose for the subject. Camera almost always gets the exposure spot on.

[clackers]

So basically you're saying my problem probably has more to do with the Auto-algorithm than the flash itself.

Flipster, unless you're looking to Elevate Your Photography, don't worry about buying another flash.

It's a DSLR, you've paid for one so that you have control over the settings.

For a snapshot, put it into Av mode, dialing in Exposure Compensation as required. For a better pic, choose Manual and expose for the background minus one, minus two stops, whatever you like. A sunset you want to keep will be different from an ugly cluttered wall you want to hide.

Put the flash up and take the pic. That's it.

P-TTL can be adjusted a couple of steps down by rotating the dial if you want it to be more subtle.

The default Auto setting you've experienced is an attempt to get both subject and background lit, but only you know whether you want that or not.

[Moropo]

I had a similar question a year ago.

Please look at this thread:

https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/283237-w...-up-flash.html

[mcgregni]

Its difficult to know the exact figurings of the various algorithms programmed into the cameras for automatic flash with automatic exposure modes (P, Av, Tv etc), as there's nothing published from Pentax about it AFAIK .....

But, the general principle (like with Nikon and Canon as well), is that if the ambient (natural / background) light is sufficient for a successful exposure, allowing for hand holding at the focal length detected, then the flash will automatically act as a 'fill-in' exposure. This will be automatically reduced by around 0.7 - 2.0 stops from what would be required for a 'full' flash exposure on the subject. This all depends on the background light levels, if there's a lot of backlight etc ... but the principle is that the camera tries to balance the foreground subject with the background light but with a more subtle flash effect.

Otherwise, if the ambient lighting is not sufficient for successful hand-holding, then the camera will simply apply a 'full' flash exposure to try and correctly and fully illuminate the subject .... this is based on the nearest and largest object which returns reflective light back to the camera.

Bear in mind that these automatic calculations are limited by the maximum aperture available from the lens, the auto-ISO limits pre-set, and the focal length (which determines the longest exposure time that the camera will choose). You can remove the exposure time limit by switching the Camera Flash Mode from 'Auto' to 'Slow-Speed-Sync' ..... this is intended for use at night or low-light scenes, sunsets, city-scapes etc, when you want a long exposure time for the background plus a flash exposure for a subject near the camera.

However, whilst there are always good situations and times for using automatic modes with flash, in general the best control over things is through Manual camera mode, and definitely I think that ISO should be fixed for flash work. That way you can hold control over the ambient light (or remove it altogether) and then rely on the P-TTL auto exposure with Flash Compensation adjustments to fine tune the flash effect.

Regarding guide number and flash power, TBH for direct front-on flash use then the GN of pop-ups is plenty .... in fact its more likely to be too high and cause overexposure at wide apertures / high ISOs etc because the distance is too close. You need the extra power from a full-featured flashgun because it can swivel and tilt and allow bounce flash, and this is the way to get nice, soft and directional light, and make on-camera flash look like off-camera flash! But some bounce surfaces like walls can be quite dull, and so you need power ...