FX1 iris controls... not a happy customer
 

Hi,

I have recently bought an FX1 and I'm not sure if I'm doing something wrong or if the iris controls are just not as good as what I'm used to.

I previously used a panasonic DVX100, a much older camera but the iris could be fully opened whether zoomed in or not. As i often film people standing in front of windows I found this invaluable.. however ont he FX1 it is my understanding that the iris can only beopened to 1.6 when zoomed out, reducing to something like 2.4 when zoomed in... I know it has the backlight feature which is handy but I am really not happy with these controls. Does anyone have any advice on how to film backlit subjects?

If i cant solve this problem I may well have an FX1 for sale.... :(

David, just about all prosumer cameras with built-in lenses exhibit the same behavior. I haven't used a DVX myself, but I'd be surprised if it wasn't the same. Here are a few old threads on the topic:

http://www.dvinfo.net/conf/showthread.php?t=37475
http://www.dvinfo.net/conf/showthread.php?t=46081
http://www.dvinfo.net/conf/showthread.php?t=68551
http://www.dvinfo.net/conf/showthread.php?t=71695
http://www.dvinfo.net/conf/showthread.php?t=76033

The FX1 f-stop rating is 1.6 to 2.8 from wide to fully zoomed in. Most zoom lenses (video and photo) exhibit this behavior.

You might need to gain up by 9+db, which represents about 1 1/2 stops.

yeah I gained up to 9 and even 15 in some situations but it just wasnt enough..

I am certain that the DVX enabled you to set the iris to "OPEN" and I never had any problems with faces infront of windows appearing in sillouette.

Thanks for the links to other threads, i'll look through them now.

The f "number" is actually a mathematical representation of iris diameter to focal length. So in other words, f2.8 when zoomed in IS "wide open." it's the same diameter as the 1.6 when the lens is wide; it hasn't closed any.

All zoom lenses work this way. That's why when you buy a lens at a camera store it'll say something like "f2.8-5.6" depending upon the zoom.

Some zoom lenses have a constant aperture (usually f2.8 like the Nikon 80-200mm AF-D), but they tend to be more expensive to produce.



This is actually incorrect information. F-stop is a ratio. For instance, an f-stop of say 2.0 lets in the same amount of light whether the zoom is at 50mm or at 300mm (in 35mm equivalent). But then again, "wide open" is a misleading term when referring to zoom lenses.

You also have to put shutter, and gain in manual to control the Iris, otherwise it will not work. The reason you think that it is not enough is because you are shooting into the window, the camera is still in shutter priority mode and it goes up automaticly when it sees that much light from the window, so be sure to put everything in manual, gain, shutter, iris.

That's a good point, Khoi. Sony's implementation of auto/manual controls can be confusing to someone coming over from the DVX100.

Conversely, if you are a manual shooter, you must put two of the exposure controls in auto mode (preferably gain and iris for low light, iris and shutter for daytime) in order to the use the backlight and spotlight functions.

regarding the last 2 posts..

admittedly its my fault as I didnt practise too much with the camera, but did read the manual before this weekends shoot.. i found trying to get some sort of manual control quickly and simply very very difficult..

It sounds like it might be the shutter that is automatically adjusting. it seems a lot of the time there is no on screen suggestion that shutter/gain is in manual or auto mode...

Am i right in saying if i push either the iris, gain or shutter button i get the numerical value on the screen and this therefore means manual mode is activated..

in which case, is it possible to activate manual control on all of gain shutter and iris simultaneously?

If you don't see any settings on screen then it is auto, so in order to be in full manual, you need to see gain, shutter, iris, if one of those is not on screen then you are in that mode is still in auto.
I haven't use FX1 in over a year but if you put everything in manual and then if you need to go auto there are switches on the left side near the back that says something like auto lock.., you can switch back and forth on that swich and instanly be in full manual.

That's what I said ;). It's not a physical size.

Just to be quite clear on this, the DVX100 (all its variants) have a ramping max aperture of f/1.6 to f/2.8. These are theoretical of course, design, production and build tolerances will vary these figures, and T stops (actual transmission figures) generally are quite a lot different again.

tom.

Thanks for clarifying that Tom. I think Panasonic is a little confusing on their website since they claim the lens is f1.6 whereas Sony and Canon (as well as Nikon and other SLR makers) list the range of f-stops on their zoom lenses.

Yes, I too have noticed that Boyd. It's a form of 'limited info' as if Panasonic feel too much will swamp our little minds. The fancy DVX100A and DVC30 brochures I have don't mention this loss of a stop and a half as you zoom anywhere in them, not even in the specifications. This is a camera and you're not told of this??

My though is that the main competitor of the day was the PD170 - in fact Panasonoic show a silhouette of the 170 to show how much better 'balanced' their DVX is. Trouble is they were always having to hide the fact that it only had a 10x zoom that was half a stop slower than Sony's 12x.

tom.

Of course, as you all know well, the reason cheaper zooms are slower at longer focal lengths is that the glass isn't big enough. To get f/1.6 instead of the current f/2.8 (at max focal length) the front element would be something like 88mm diameter (instead of 50), with proportionally greater weight and a several multiples of the cost. The cost of a prosumer camera body would become trivial in comparison. Check out the cost of Zeiss and Arri constant aperture zoom lenses to get some idea of how much your chosen trade-off is saving you.

Very true Serena, but back in the 70s Super-8 camera manufacturers such as Canon and Nikon were making 10x zooms with an f/1.4 maximum aperture that held throughout the zoom range. That's half a stop wider than the popular f/1.6 of today.

And all this while feeding a 'chip' (the Super-8 frame) that was almost exactly the same size as a current 1"/2.7 chip - just a tiny fraction smaller than a 1"/2 chip. Lots of us look on the half inch chip as a biggie.

tom.

Tom, I don't recall 10x f/1.4 zooms on S8, and would have thought that max apertures were more like f/2.0 and f/2.8. However I don't have any of the old literature to check! I remember being surprised to find that zooms for still cameras couldn't hold max aperture during the zoom, and somewhat disappointed when moving to video that the same thing was present there. http://www.visualproducts.com/store0...&Cat=8&Cat2=20

My 1974 Canon 1014E had a 10x f/1,4 zoom (see? It's in the name) as did the Nikon R10. The sound on film 1014XL-S had the same. They're shown here:

http://super8guy.com/

tom.

Ah, well. Yet another reason to keep using film!

Not exactly: it only means you've manually locked the setting for whichever button you pushed. If you want a full manual exposure on an FX1 you have to push all three buttons for iris, shutter *and* gain, then set each of those to the values you want as indicated on the LCD or viewfinder. Otherwise the items you haven't locked will continue to auto-adjust, resulting in an incorrect exposure for strongly backlit subjects.

If you want to be able to quickly switch back and forth from auto to manual exposure on the FX1, lock any two of the three exposure items and switch the third on and off auto as needed. For example, lock the gain and shutter but leave the iris on auto until you need a manual exposure, then lock the iris and set it as needed. There is no single exposure-lock button on the FX1 like there is on some other video cameras (e.g. Canon GL1/GL2, Sony A1U, etc.).

hmm thanks all for your advice..

i had another chance to play around with the camera this weekend. I found that occasionally when shooting in manual mode in a dark environment i can set manual iris to as open as possible, set shutter to 50 and leave gain how it is as i am put off by the picture noise i have gotten in the past by using gain on different cameras. Anyway, in this manual mode as far as I know the camera is set up to let as much light in as possible but occasionally when i flick back to auto lock, it gets brighter. How can this be? Is it something to do with the picture profile setting as I havent really ever bothered changing these.. I have always left it on PP3...

You sure you've got that right - you flick back to auto lock and the recorded image gets brighter? I simply cannot see how this would happen, as in auto it will bump to max gain (+18dB) and widest aperture for the focal length in use. You're still on the default shutter speed, right?

tom.

You've answered your own question. Picture profiles *usually* are set up to affect gamma, color. Clearly, your PP3 is reducing available light. Turn it off.

When you switch back to auto mode that allows the gain to go back to maximum, which will make your picture brighter unless you had gain at the full +18db in manual mode. And as DSE said, make sure your camera settings aren't limiting the maximum gain amount - there's a setting which does exactly that for those who want auto-exposure with gain limited to some specific value.

thanks again guys.. i should have worked out that the gain was boosting up in manual mode. Seems silly that it would do this outside in very very bright light tho? Do you know what I turn off in the specific picture profile to stop it limiting available light? I didnt know you could turn the PP off totally.. i thought you had to have one selected..

All things considered, I have just purchased a 2nd FX1 so once I work out how to use the light settings effectively I'm sure i'll be very happy.

You certainly don't have to have any PP selected. They all move the image away from the default setting, which you may find perfectly acceptable.

great.. so in theory with PP off, shutter set to 50 or 60, gain to +18 and iris as low as possible I should get the image as light as possible, is that correct? I will have another play around tonight but I think this issue should be solved now. Thanks a lot.

That's sort of correct. Of course you can slow the shutter speed as well to get greater exposure of the chips, but you'll get subject and camera movement recorded as a blur. For static shots of a building at night, say, I often use 1/3 sec and f/5.6, and have the gain at zero.

tom.

Creating a picture profile with everything at the default EXCEPT turning on black stretch will help a little in dark places. But be sure you haven't selected either of the cinematone settings, you will lose as much as a full stop from them.

How can your shutter speed be slower than your frame rate?

Frames get duplicated.

Tom's right. But since it's an interlaced camera you also take a resolution hit. If the shutter is open for 1/30th sec then the same data is written to each 60i field and you lose 50% of your resolution. If you're shooting standard definition or downconverting and capturing as regular DV this shouldn't be much of a problem however. There are 1080 lines to start with, so chopping that down to 540 still gives you plenty for a 480 line DV image.

Interesting. I was thinking of it like film through the gate which would limit the density possible from exposure. I'll have to play around with that a bit.

I'm sorry - that should have been attributed to Ian!

Easy. Select shutter speed and turn the dial to give you the speed you'd like. From 1/3rd sec to 1/10,000th sec, the choice is yours.

It's interesting that in Avid, if I step through footage I shot at 1/30 field by field, I do indeed see that the same data is written to each field, but I can also see the entire field move up and down a scan line when I toggle back and forth. I would think this gives a one scan line vertical blur.

Or am I just off my rocker?