I am getting ready to convert to digital instead of film. As I figure out the changes that will go with it, some I can solve, others require help. This is one of them.

The digital camera has a focal length multiplier factor of 1.6. This means that the lenses are 1.6 times longer than on a film-based 35mm system. Ok, except for wanting really wide angle, this is fine (Imagine, a 300 2.8 turns into a 480 2.8!).

Now the questions. Does the FLASH know about this change? If I have a 28mm lens on the camera, will the flash know to set the head for a 45mm lens (think this setting is at 35mm)? Does the camera "tell" the flash the correct "length" or is it something that I have to set manually? BTW, my primary lenses are 28-70 and 70-200.

flash extenders. Lastly, as my favorite lens is 70-200 for most of my sports, and the high need to use flash for a lot of shooting, are there extenders available for flashes (I use a 540EZ) that can help it narrow the light some? The 540 only goes to a 105, but with the digital, and the 70-200, this just is not going to work well. Any suggestions (besides strobing everything -- not logistically feasable) would be greatly appreciated.

Thanks

-- David Primm (dprimm@isunet.net), July 11, 1999

Answers

David, I do not know the answer to your main question. I just want to make a side comment related to your statement of a 300 2.8 turning into 480 2.8. I would think the f-number would also increase by the same factor of 1.6, because the lens diameter remains the same while the effective focal length increases by a factor of 1.6. That will turn the 300 2.8 into a 480 4.5 (still not too bad!).

-- Subhasis Laha (slaha@lucent.com), July 12, 1999.

The flash doesn't need to be told anything. The lens still sees the same scene, but the digital sensor uses a smaller section of the image. Although you could narrow the flash slightly if you need more output, it's hardly worth the effort.

-- Danny Weber (danny_weber@compuserve.com), July 12, 1999.

Where can I get hold of these magic lenses that change their focal lengths and maximum apertures? Of couse, they do no such thing. As Danny points out, the 'film' is smaller than 24x36mm, so the angle 'seen' by the camera is smaller. (You can achieve the same effect using conventional film by just taking a pair of scissors to the film.) If the factor is 1.6, then the light-sensitive area would be 15x22mm.

An intelligent camera will 'tell' the flash unit what angle to cover. I don't know whether David's equipment will do this.

-- Alan Gibson (Alan.Gibson@technologist.com), July 12, 1999.