Issue with XF 100 (iris value display on lcd)

[Fabrice Hoss]

Hello,
I am still in love with my XF 100 but I noticed a change during my last shooting in Florida (I am a video reporter). Although my set up was manual (focus, shutter, iris), the iris value on my lcd (following letter f) was changing when I was zooming... Nothing changed on the picture (neither darker or brighter) but still : 1.8, 2.0, 2.2, 2.4 the numbers were changing when I was zooming in or out! Never happened before... And I can't find a good explanation... That's why I decided to post this topic today... If anyone experienced the same problem... Please share! Thanks to all,
Fabrice

[Chris Hurd]

Hi Fabrice,

If you take a look at the front of the camera, on the lens itself, it says f1.8-2.8

These numbers indicate that the lens is *not* a constant aperture, but is instead a variable aperture lens. Those numbers tell you that the lens has a maximum aperture of f/1.8 at full wide, and a maximum aperture f/2.8 at full telephoto. Therefore when changing focal length from full wide to full telephoto, the iris will indeed ramp down from f/1.8 to f/2.8 and it is made to operate that way. In other words, the maximum aperture at full tele cannot go any larger than f/2.8 and for what it's worth, just about every camcorder in this class operates the same way.

For future reference, if there are two max. aperture values printed on the lens, such as f1.8-2.8, that's how you know that it is not a constant-aperture zoom. To prevent the iris from ramping during a zoom, you will have to set the max. aperture manually to the value of the telephoto end of the lens. In your case this would be f/2.8. Hope this helps,