I was asked a question about the Open Iris FA (Focus Assist) the other day so I thought I'd just put down my explanation here in case any one else had come across it and wasn't sure or hasn't explored it as yet.
The open iris FA is quite a useful tool and as far as I know, the Varicam LT is the only camera that actually has it. It's important to note that this is really designed to work with Canon EF lenses, however there is still some benefit with PL glass as well.
Here's where it's useful. There are times when your focal point in a shot may be too bright or dark to distinguish clearly making focus difficult. Open Iris FA is designed to temporarily normalise these shots so the focal point is easier to see.
Here's some common examples and what Open Iris FA will do when applied.
Scenario 1: Dark contrasty Scene. Subjects face is in the shadows. Lens set to F5.6.
In this case Open Iris FA, when applied will open the lens up. If needed it will go to the fastest stop. If that's still not bright enough to "normalise" the shot, it will add around a stop max. of gain. You then set focus. Press Open Iris FA again to turn off and it will then remove the gain and automatically return to the stop you originally set. In this case F5.6.
Scenario 2: Dark Contrasty Scene. Subjects face is in the shadows. Lens Wide Open.
In this case your iris is already open so by turning it on the camera will gain up by around a stop. Not much, but could be a big help.
Scenario 3: Very Bright Scene. Subject is brightly lit. Lens set to F5.6.
In this case Open Iris FA will again open the lens up to Wide Open. This may seem counter intuitive as the scene will then be even brighter, however it then gains down the required amount to normalise the shot. You set focus. Turn it off and again any gain adjustment is removed and F stop is returned to the original setting.
Scenario 3: Very Bright Scene. Subject is brightly lit. Lens Wide Open.
In this case, again you're already wide open so the camera will just gain down to normalise the shot. You set focus. Turn it off and gain is removed.
Note: If you ever use the Open Iris FA and forget to turn it off hitting the record button will automatically do it for you before the recording starts so there's no chance you can record at the incorrect exposure. The process takes about 500ms.
Using Open IRIS FA with PL Glass only requires one extra step to achieve the same result and that is that you will manually need to open the iris yourself and then return it to the previous setting once complete. This scares me a little as there's always a chance someone could forget to reset Iris before recording.
Anyway, that's Open Iris FA. Hope this actually helps someone.
The open iris FA is quite a useful tool and as far as I know, the Varicam LT is the only camera that actually has it. It's important to note that this is really designed to work with Canon EF lenses, however there is still some benefit with PL glass as well.
Here's where it's useful. There are times when your focal point in a shot may be too bright or dark to distinguish clearly making focus difficult. Open Iris FA is designed to temporarily normalise these shots so the focal point is easier to see.
Here's some common examples and what Open Iris FA will do when applied.
Scenario 1: Dark contrasty Scene. Subjects face is in the shadows. Lens set to F5.6.
In this case Open Iris FA, when applied will open the lens up. If needed it will go to the fastest stop. If that's still not bright enough to "normalise" the shot, it will add around a stop max. of gain. You then set focus. Press Open Iris FA again to turn off and it will then remove the gain and automatically return to the stop you originally set. In this case F5.6.
Scenario 2: Dark Contrasty Scene. Subjects face is in the shadows. Lens Wide Open.
In this case your iris is already open so by turning it on the camera will gain up by around a stop. Not much, but could be a big help.
Scenario 3: Very Bright Scene. Subject is brightly lit. Lens set to F5.6.
In this case Open Iris FA will again open the lens up to Wide Open. This may seem counter intuitive as the scene will then be even brighter, however it then gains down the required amount to normalise the shot. You set focus. Turn it off and again any gain adjustment is removed and F stop is returned to the original setting.
Scenario 3: Very Bright Scene. Subject is brightly lit. Lens Wide Open.
In this case, again you're already wide open so the camera will just gain down to normalise the shot. You set focus. Turn it off and gain is removed.
Note: If you ever use the Open Iris FA and forget to turn it off hitting the record button will automatically do it for you before the recording starts so there's no chance you can record at the incorrect exposure. The process takes about 500ms.
Using Open IRIS FA with PL Glass only requires one extra step to achieve the same result and that is that you will manually need to open the iris yourself and then return it to the previous setting once complete. This scares me a little as there's always a chance someone could forget to reset Iris before recording.
Anyway, that's Open Iris FA. Hope this actually helps someone.
