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Forum: Pentax K-30 & K-50 12-03-2013, 09:57 PM  
Flash Photography with K-50 & SMC-M 50mm Lens
Posted By elliott
Replies: 7
Views: 1,970
Your shutter speed depends on what you want to do with the ambient light. Slower shutter speeds will give you more ambient light in your photos, but will not affect the flash exposure at all. The fastest you can have is 1/180s.

Sticking to the numbers earlier, if your subject is at 3m and your ISO is 400, then your aperture will be f8. Now if there is a large room behind your subject that is lit at about 10EV and will not be lit by the flash, then you could set a shutter speed of 1/60s and the room would appear to be normally lit and your subject will be properly lit by the flash. Faster shutter speed would make that room appear to be darker. So you can just green button meter to get an appropriate ambient exposure or underexpose the ambient if you want to.

Using the pop up flash without P-TTL is no different from using a manual hotshoe flash, the concepts are all the same, you just can't change the output of the pop up flash unless you have a K-3.
Forum: Pentax K-30 & K-50 12-02-2013, 06:10 PM  
Flash Photography with K-50 & SMC-M 50mm Lens
Posted By elliott
Replies: 7
Views: 1,970
There are ways to do it.

Pre-focus the lens at a reasonable distance, I think 3m would get you a decent framing on something the size of a cat at 50mm. Then setup your exposure to match this distance, you'll want a small aperture so go for 400 ISO and f8 if you are focused at 3m. When they are in focus (or close enough, f8 gives you plenty of DOF) just hit the shutter.


Hotshoe flashes with auto mode simplify this a lot. Just match the aperture and ISO on the camera to the aperture and ISO the flash is expecting and you don't have to worry about distance at all, just shoot.
Forum: Pentax K-30 & K-50 12-02-2013, 04:55 PM  
Flash Photography with K-50 & SMC-M 50mm Lens
Posted By elliott
Replies: 7
Views: 1,970
That is normal, the P-TTL flash system won't work without a lens that has A contacts for exposure. It will just fire full power every time. You can get around this by stopping down, the GN of the onboard flash is 12 meters at 100 ISO. The formula to calculate the aperture you need is f = GN/distance. So at 1.5m away you'd want the aperture to be f8 (12/1.5), with the subject 3m away you'd be at f4 (12/3) and so on. If you're using 200 ISO just double the GN, ISO 400 double it again and so on. If you are more comfortable with feet instead just use 40 for the GN and estimate distance in feet.

The K-3 introduced manual control for the onboard flash to help with this. That way you can turn down the flash power for closer subject you might want to shoot at a wider aperture.

Your best option is to get a hotshoe flash, especially one with the auto mode that has its own light sensor.
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