580EX and autozoom

[clickman]

:D Hi, its nice to be here with you. This is my first post in this forum.
I have a fairly good idea as to how the autozoom works in the 580EX flash and about the sensor size detection feature which is dictating the flash to zoom accordingly.
I also know that the max zoom is 105mm.
What I don't know is whether this meant to be in relation with the actual focal length of the lenses or the effective focal length ?
If the max zoom is 105mm for a full frame sensor, then the equivelant actual focal length of a lens on an APS-C sized sensor would be about 60mm.
Am I right?

[EricKonieczny]

it is the actual focal length of lense.

I have the 20D, and use my 28-105mm for my walk around lense with the 580 all the time.

So you can zoom to 168 with the 1.6 factor

[David1943]

If the max zoom is 105mm for a full frame sensor, then the equivelant actual focal length of a lens on an APS-C sized sensor would be about 60mm.
Am I right?[/QUOTE]

No, you have it the wrong way round - 105mm x 1.6 = 168mm equilevant angle of view.

Happy snapping, David :)

[clickman]

ok, I've got that, thanks for your answers.
So if that is the case, at the wide end of the coverage, which is 24mm (14mm with wide panel), a 24mm lens on a 20D will zoom the flash to 38,4mm and a 15mm lens will not move the zoom at all (to the effective position of 24mm) since it is already on that position, the minimum of 24mm.
So effectively for every lens at the range of 15-24mm used on the 20D there is no vignetting produced by the flash because the actual flash coverage is equal or bigger of that lens effective range. Correct?

[PacAce]

ok, I've got that, thanks for your answers.
So if that is the case, at the wide end of the coverage, which is 24mm (14mm with wide panel), a 24mm lens on a 20D will zoom the flash to 38,4mm and a 15mm lens will not move the zoom at all (to the effective position of 24mm) since it is already on that position, the minimum of 24mm.
So effectively for every lens at the range of 15-24mm used on the 20D there is no vignetting produced by the flash because the actual flash coverage is equal or bigger of that lens effective range. Correct?
That is true, as long as you have the 17mm wide angle angle in use with this lens.

[EricKonieczny]

And hence the problem with the compatibility of the 10-22 on the 20D with the 580EX

I used this combination and sometimes the coverage is adequate witht he ambiant light and other times there is major vignetting.

The flash will not go wide as 16mm after the 1.6 factor applied.

[clickman]

And hence the problem with the compatibility of the 10-22 on the 20D with the 580EX

I used this combination and sometimes the coverage is adequate witht he ambiant light and other times there is major vignetting.

The flash will not go wide as 16mm after the 1.6 factor applied.

Doesn't the use of the wide panel cover that angle?
Or even if it does, the extreme wide angle weakens the light strength so much which is practically useless?
I'm thinking to buy the new Tamron 11-18 and your experience with the 10-22 is of great value.