[basikal_kusayang]

Hi,i have this flash and i've been using it for about a year and i have a question to ask. I use this flash with my K20D.I always use aperture mode when using this flash.The problem is that the photos taken using this flash is underexposed (its dark,it seems like the flash is not powerful enough), even if i increase the exposure to +1.0.btw,the flash is in TTL mode. can i use aperture mode and use Manual mode for the flash?because when i change it to Manual mode (even sometimes it is quite difficult to press the button to change it to manual mode), it will go back to TTL when i half press the shutter. Is that normal or not?

Im a bit new to this flash technique,so please help me. Thanks a lot people

[sterretje]

Please post a sample with exif intact. Specifically interested in aperture and ISO.

You know the basics of flash (just asking, no offense intended)? The distance that you can flash is determined by guide number and aperture; see your flash manual or camera manual. Your flash has an (inflated) guide number (GN) of 53 (at max zoom) at ISO 100. If you use an aperture of f/16, the reach is 53/16 is about 3.5 meters. If your subject is further away, it will be underexposed. At wide angle, the GN will be lower (28 at widest zoom position) and therefor the reach will be even less (about 1.5 meters).

Adding 1Ev will not help if the flash is already using full power (it can't produce more than full power). Increasing the ISO will help; for each step in ISO, you can multiply the GN by 1.4; so iso100 -> 400 will result in a GN of 106.

[jatrax]

for each step in ISO, you can multiply the GN by 1.4;

Sterretje. What is the logic for using 1.4x when raising ISO? Is that the ratio between f stops?

[sterretje]

Yes, it's simply one stop. And for apertures that translates to 1.4 (square root of 2 to be exact) between stops.

[basikal_kusayang]

Please post a sample with exif intact. Specifically interested in aperture and ISO.

You know the basics of flash (just asking, no offense intended)? The distance that you can flash is determined by guide number and aperture; see your flash manual or camera manual. Your flash has an (inflated) guide number (GN) of 53 (at max zoom) at ISO 100. If you use an aperture of f/16, the reach is 53/16 is about 3.5 meters. If your subject is further away, it will be underexposed. At wide angle, the GN will be lower (28 at widest zoom position) and therefor the reach will be even less (about 1.5 meters).

Adding 1Ev will not help if the flash is already using full power (it can't produce more than full power). Increasing the ISO will help; for each step in ISO, you can multiply the GN by 1.4; so iso100 -> 400 will result in a GN of 106.

Thanks for the reply. To be honest, i dont really know in details about flash technique. I don't use the flash directly. I often use it as a bounce flash (im sorry,forgot to tell you). And I often use my sigma 10-20mm at 10mm,f4, with the flash. It is still underexpose. Even in a small room, it is not bright at all. I try not to use manual setting as it will take time and Im afraid i dont get the correct exposure. Any idea?

Thanks

[hoanpham]

You need to tell which mode in your camera, which mode in your flash.
Don't forget that you have EV adjustment in
- your camera
- your flash output in your camera (flash menu), and
- override EV in your flash, either in +/- range or as power rate (Select button).

Zero all out, and use only one setting at a time.

I use flashes manually. Try to switch the flash to manual to by pass the p-ttl to see. Manual is the only consistent.

[sterretje]

Just the ideas why you can get underexposure.

Bouncing has two disadvantages when it comes to the intensity of the light; firstly the surface that you bounce against absorbs light and it diffuses light and secondly as the distance to the subject increases it will be more spread (so less intense). Count on 2 stops loss to start off with; it might be a bit less, it might be more. Having a dark ceiling will also not help.

The widest setting for your flash is 24mm. Do you use the built-in wide panel when using the UWA zoom at 10mm? GN at 24mm is 28 (ISO100), with the wide panel you will probably loose a stop, so GN 'down to' 20. Bouncing will probably costs you 2 stops, so GN 'down to' 10. And next divide by the f-stop of 4 and the reach will be a maximum of 2.5 meters. A subject within that reach should be properly exposed if you have a white ceiling.

Direct (no bounce) flash will increase that reach to 5 meters;

I would start with some practicing / testing using a 'normal' lens (e.g. kit lens) and see how it works / if you can get it right. Do this somewhere in your own time; not when you have to get the shot during a family event etc.

Step 1
No bounce, no diffusers. Kit lens at 50mm, ISO100, aperture f/8 and a subject between 50cm and 5 meters from the camera should be properly exposed (GN is 40 according to Sigma Imaging (UK) Ltd ).
Step 2
Same setup with bounce; increase ISO if necessarily.

Next repeat the steps with the UWA.

With direct flash at 10mm, you might see some vignetting as the flash beam (using the wide panel) is just not quite wide enough to cover the field of view of the lens. Without the wide panel, you should see some severe vignetting (bright in the center, darker around it).

Im afraid i dont get the correct exposure

As you don't get correct results currently, there is nothing against manual flash. Just practice it. Once you're familiar with your flash, you will also be less worried about the time it takes to set it up.

[sterretje]

You need to tell which mode in your camera, which mode in your flash.

See first post ?

[hoanpham]

See first post ?

yes, I did. but still I forgot to reset EV some time. but it wont take long for me to discover

[Cinders]

I'm also having trouble using this flash. I like aperture priority, but the same thing happens to me, where I can't use manual settings on the flash, while in Av, because half pressing the shutter changes the flash back to ttl.

[bdery]

What is the logic for using 1.4x when raising ISO? Is that the ratio between f stops?

Doubling the speed, doubling the ISO, or switching by one stop will double the amount of light that reaches your sensor. The 1,4 factor is because for f-stops you double the area of the opening, but because area is pi*radius^2, the radius increases by 1,4 to double the area (that's the short version).

[sterretje]

I'm also having trouble using this flash. I like aperture priority, but the same thing happens to me, where I can't use manual settings on the flash, while in Av, because half pressing the shutter changes the flash back to ttl.

Did a quick check on a K100D with DA55-300 and AF540 and I can't even select manual mode on the flash while Av on the camera. So I think that it's normal.

And the solution is M mode on the camera; there is no actual difference between M and Av as you can still control the aperture of the lens.

[Cinders]

Hmm interesting.....

Anyways, I ran into another problem last night while I was testing it. I had the flash on regular p-ttl on the hotshoe, nothing special going on. I put the camera in every perceivable mode, but no matter what I did, and how I changed the ISO, aperture, etc. The shutter speed would not change from 1/30, even when I was moving the camera around to different lighting situations. The only way I was able to change the shutter speed was to go to Tv, or Manual. Shouldn't the camera realize there is a flash on it, and change the shutter speed to something faster? :\

[sterretje]

No, the camera does not do that. I did post my experience in another thread

In Av mode, the camera sets a shutter speed (in my experience) for flash that is partially based on the focal length used. In a dark scene, the K100D in combination with DA55-300 uses roughly 1/FL (1/60 @55mm, 1/125 @ 100mm, 1/180s @ 150mm). In a brighter scene the same combo uses 1/180s regardless of focal length, possibly attempting 'fill-in flash'.

K5 with FA31Ltd or DFA100WR is more conservative and uses 1 / (2 * FL) in a dark scene; not tested in a bright scene.