[Nesster]

My daughter and I have used the AF280T on several cameras and in several situations, with excellent results - off camera or on, usually with it set in Auto mode. But we've set aperture and shutter speed manually.

So I figured I'd try it with the Program Plus - it reads ASA from camera, and feeds back the correct aperture and shutter, which the camera then sets. No TTL with the Program plus, but it works great.

Then, I wondered what would the K100D do in Program mode, with the AF280T attached? Wonder of wonders, the flash reads ASA from K100D and instructs K100D to set aperture and shutter... except the K100D also adjusts shutter between 50 and 180 depending on ambient light.

I didn't know this. The AF280T (and the AF200T) work in dedicated mode with the K100D, not TTL but well enough.

Examples (these are from my daughter's stream, though I took them):
indoors, shutter set to 1/60:



Outside, shutter set to 1/180, f/8... without flash the camera would have selected f/6.3 at 1/180.

[SOldBear]

I posted this a while back in another thread. It's about AF200T and K10D but I think it's also applied to AF280T and K100D (or K20D, K200D, K-M):

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Here's how the AF200T works on my K10D:

1. When the AF200T is ready, shutter speed on the K10D can not exceed 1/180 sec, no matter what mode the K10D is in. If the K10D mode is P, Sv, Av, the default shutter speed will be set at 1/50 sec. But you can change shutter speed (1/180 sec is always the limit).

2. The modes easiest to use are P and Tv. In these mode, the K10D automatically set the appropriate aperture based on (a) the ISO setting on the K10D, and (b) the "auto" setting on the AF200T. For example, with ISO setting of 400 on the K10D, if the switch on the AF200T is "auto green", the K10D will set aperture at f/11. If I change the switch on the AF200T to "auto red", the K10D will automatically change the aperture to f/5.6.

3. In mode P and M of the K10D, you can change the aperture. Hitting the green button will reset to shutter 1/50 sec and aperture as in (2) above.

4. In P mode, if you change the aperture, the shutter speed will change back to 1/50 sec. If you change the speed, the aperture will change back to the default value as determined in (2) above.

5. In Tv mode, the aperture is determined as (2) above. You can change the speed (still 1/180 max) but can not change the aperture.

6. Sv is kind of cool. You can not change the shutter speed, which is fixed at 1/50 sec. But you can change the aperture from the initial value (as (2) above). The K10D will appropriately change the ISO setting so you always get a perfect exposure. Note that this is different from (3) above: in P and M, the aperture change does not cause the ISO setting change.

So here what I would do:

- K10D in M mode. I will change shutter speed depending on the subject's movement and on how much I want the ambient light to contribute to the exposure. I will change the aperture as a means of exposure compensation. If needed, I hit the green button to reset the aperture and the shutter speed to the default values.

- If I want to control the DOF via aperture setting, I'll set the K10D to Sv mode. A minor inconvenience is that the shutter speed is fixed at 1/50 sec.

[Nesster]

Yes I'd seen this - the main modification to your list has to do with item 1 - the default is 1/50 in low light conditions, but outdoors what surprised me was the K100D will up the shutter speed depending on conditions, up to the 1/180 max.

[AndrewG NY]

I'm going to assume that 1/50 vs. 1/180 shutter speed selection in various modes is at least in part a function of the lens focal length and level of ambient light.

What confuses me in this explanation is the discussion about using Sv to manage aperture rather than sensitivity. I have this equipment and may try this out later but am wondering if what is actually happening here is the use of P-shift in Sv...it doesn't make much sense that ISO would be overridden in Sv.

One other thing is that is mentioned here is that you can set shutter speed while in P. In a sense this is true but when changing shutter speed in P what you're really effectively doing is temporarily switching to Tv or invoking P-shift depending on how your camera's custom settings are configured.

One other small possible variable--I would need to double-check but I suspect that the AF200T and AF-280T might have different recommended/auto aperture values for red & green modes. Or I just may be thinking of something else.

[eyou]

i was actually about to sell my 280t cause i got 2x sb-28, but then i realized that i can use these modes with the 280t and fire the flash. sb-28 only work in manual so its great off camera. on camera i will probably use my 280t

[Nesster]

I'm going to assume that 1/50 vs. 1/180 shutter speed selection in various modes is at least in part a function of the lens focal length and level of ambient light.


One other small possible variable--I would need to double-check but I suspect that the AF200T and AF-280T might have different recommended/auto aperture values for red & green modes. Or I just may be thinking of something else.

Yes, seemed to me the camera was stepping up the shutter speed - depending on lighting at least, I didn't try a different focal length - to values between 1/50 and 1/180.

It sets aperture based on ASA and what setting the flash is on.

Re. the other bits, as I only have the K100D, the various program shifts etc are beyond me. I will try the shutter speed override in Program mode sometime though.

Seems like a 'dedicated' flash brings definite benefits over a plain old auto thyristor one.

[AndrewG NY]

i was actually about to sell my 280t cause i got 2x sb-28, but then i realized that i can use these modes with the 280t and fire the flash. sb-28 only work in manual so its great off camera. on camera i will probably use my 280t

The AF-280T offering swivel in addition to bounce is also especially useful when using on-camera, both for bouncing off something other than the ceiling (like a back or side wall/curtain) and for bouncing off the ceiling when shooting in vertical/portrait orientation.

[AndrewG NY]

Yes, seemed to me the camera was stepping up the shutter speed - depending on lighting at least, I didn't try a different focal length - to values between 1/50 and 1/180.

It sets aperture based on ASA and what setting the flash is on.

I'm sort of assuming it uses the regular program/autoexposure logic for determining minimum shutter speed. I think on older film cameras, it would normally just set to sync speed...this logic made pretty good sense when the bodies were usually syncing only in a narrow 1/60-1/125 range and tended to only offer full stops for shutter speed plus maybe one in between (like 1/100) explicitly for this purpose. And until AF lenses, the camera didn't know the focal length so it wouldn't have been able to respond to that either.

Re. the other bits, as I only have the K100D, the various program shifts etc are beyond me.

Understood. Some of that was directed towards SOldBear's response.

Seems like a 'dedicated' flash brings definite benefits over a plain old auto thyristor one.

I think you're right about that. Not to mention that the Pentax flashes generally have D-SLR safe trigger voltages while the third-party flashes are all over the place. The dedicated flashes also allow the in-viewfinder flash indicator to illuminate when done charging and stuff like that too.

[code4code5]

I tried this out last night sitting in my dimly lit living room. I was suprised to find that with the 18-55 kit kens on my K20 and AF280t, at 18mm the shutter speed would be set at 1/50. As I zoomed in toward 55, the shutter speed would go down to 1/80. I'm assuming that because the flash head does not zoom, the camera and flash are compensating the the light "lost" outside the frame and taking into consideration the abundance of light in the center. The shots that I took, however, were under-exposed when bouncing.

Maybe I'll just stick with M mode, but it sure is fun playing.

[AndrewG NY]

I tried this out last night sitting in my dimly lit living room. I was suprised to find that with the 18-55 kit kens on my K20 and AF280t, at 18mm the shutter speed would be set at 1/50. As I zoomed in toward 55, the shutter speed would go down to 1/80. I'm assuming that because the flash head does not zoom, the camera and flash are compensating the the light "lost" outside the frame and taking into consideration the abundance of light in the center. The shots that I took, however, were under-exposed when bouncing.

Maybe I'll just stick with M mode, but it sure is fun playing.

I don't think the metering logic is smart enough to know anything about whether the flash head zooms or not with regards to shutter speed. Regardless, the AF280T is only rated to 28mm equiv (18mm APS-C) so I think it's fair to say its coverage at 18mm is going to be borderline at best. I think that Pentax has sold a clip-on wide angle coverage adapter that would increase coverage at 28mm and make 24mm(?) usable.

The way that auto flash varies output is by squelching flash output at time of exposure when it thinks enough light has been emitted. Sort of 'glass is full, turn off the tap'. This is using not your in-camera meter but instead a crude little center-weighted pinhole sensor on the front of the flash body. Worth noting that this sensor doesn't know anything about zoom so it may be only evaluating based on a partial view (maybe only 35mm equiv angle?).

Remember that in the scenario you're describing the factors that would contribute most to exposure would be aperture and ISO. The difference between 1/50 and 1/80 is only EV 2/3 for ambient light but this effect would be much reduced since so much of your light is actually coming from the flash which doesn't care about 1/80 vs. 1/50 since all of its light is being emitted for a duration of 1/1000 of a second or so. I find that when using the flash, I usually want to use ISO 400 or 800 as a starting point.

[Mike Cash]

I tried this out last night sitting in my dimly lit living room. I was suprised to find that with the 18-55 kit kens on my K20 and AF280t, at 18mm the shutter speed would be set at 1/50. As I zoomed in toward 55, the shutter speed would go down to 1/80. I'm assuming that because the flash head does not zoom, the camera and flash are compensating the the light "lost" outside the frame and taking into consideration the abundance of light in the center.

More likely is that the camera was just adjusting shutter speed in order to keep it over the 1/f rule of thumb. Makes sense if it is calculating in 35mm equivalents and the algorithm is left over from the pre SR film days.

[SOldBear]

The shots that I took, however, were under-exposed when bouncing.

I could be that the flash just ran out of juice. Bouncing robs a lot of light.

Please try it again at higher ISO and larger aperture. You should be able to tell whether it is the case of not enough light power.

[axl]

The dedicated flashes also allow the in-viewfinder flash indicator to illuminate when done charging and stuff like that too.

I have AF280T and AF160SA and I can't get in VF confirmation of when flash is charged.
Do I have to be in some mode on camera?

BR
Peter

[Ex Finn.]

You do get the flash symbol?, maybe it is charging up really fast and the blinking is not noticeable.
Just checked mine, only blinks twice before charging up.

Camera set to Auto pic.
Flash set to Auto Green, ASA 200, finder a check off.

Cheers Mike.

[axl]

ah, so when it stops blinking the flash is charged... got it, yup checked and it's like that...
Thanks