AC130: Who is using the AREA IRIS Function??

C

ChrisHarding

Well-known member
Hi Guys

I was just wondering who has some tech advice on the 130/160 area function??? If I set the function to either iris or focus/iris I would have expected that the camera would expose just for the target area??? If you push the function joystick, the target turns yellow and placed exactly on a subject's body with very strong backlighting behind them..the iris change is really very minor and it certainly doesn't expose for the target area at all...it sorta tries to adjust and you get a few extra zebras on the background but it's nothing like the exposure should be....I still need to adjust the iris!!! Any bright ideas what I'm doing wrong????

Also, while we are on the exposure subject..if you are in autoiris and the exposure isn't to your satisfaction, you CAN use the iris ring (still in auto) to do a bit of adjustment either more open or more closed..the manual doesn't mention this at all BUT it seems to work and stays at your tweaked setting (I'm not sure when the autoiris takes over again??? maybe when the subject matter changes????) Is this just a freak setting or is it designed to be able to be tweaked ??? You can also do the same with focus, even if focus is in auto!!! What I would like to know is when the tweaked setting is "removed" by the auto function ...or is it still applied if the camera position/subject changes?????

The manual is very vague!!!!! Would Barry's book cover this topic at all..I'd hate to order it from the USA (and pay half as much again for postage) to find out it's not covered????

Thanks for any help

Chris
 
The area iris function lets you set a specific section of the screen that the camera uses to evaluate the exposure. It works like you think it should. I don't know what your exact situation looked like, but it's possible the backlight was still overpowering the exposure? Try just experimenting with it to learn how it works. Point the camera at, say, a shot that has a window in the left side, and a darker interior bookcase on the right, and then use the area iris feature and you'll see that it really does make a huge difference.

As for the iris ring in auto -- yes I cover that in the book. When you use the iris ring in auto, you're establishing a preferred level of overexposure or underexposure. Autoexposure is still working, you haven't overtaken it, you're instead telling it "whatever the exposure you think should be, I'm advising you that I want it to be a half-stop over" (or whatever level you've set). Turn on the iris meter in the lower right corner of the screen, and look for the green dot. As you change the iris ring, you'll see the green dot moves, that green dot is showing you the level of over- or under-exposure you're asking the system to apply.

Moving the iris ring (when in auto-iris mode) is basically the same functionality as changing the A.Iris level scene file setting.

As for ordering the book and paying half-as-much again for postage, I don't know where would cost that much to ship? If you're in Europe you can order from amazon.co.uk and pay low local shipping rates, or walk into one of any of hundreds of dealers and get it over-the-counter. In other countries, you should only be paying whatever Amazon.com charges for shipping, which shouldn't be all that much; priority mail flat-rate should only be about $15 or so.
 
Thanks a million Barry

Yep I found a supplier in the UK and their postage rates seem a lot better than USA to Australia!! You definately should get a national bookstore or camera supplier to stock what must be the 'bible' for users!!! locally for us.The 160 is pretty popular here!!!

Chris
 
A neat idea of course (especially for me!!) but sadly I'm not really geared to supply others successfully...I feel it would be better for the 130/160 community as a whole if the book was available from camera suppliers..A lot of us buy from Global Media Pro so that would be a neat arrangement. Otherwise those that really want it can just grit their teeth and pay the mailing costs and sit and fret until the book arrives...Actually I have a buddy in Wisconsin so I'll probably end up asking him to grab me a copy within the USA and then on-ship it to me !!

Chris
 
well become a distributor for him. sell to the retailers.:smile: including the one you mentioned.
 
It was just easier to order from Amazon!!!

Now, more importantly, for those who have toyed with the area function I MAY be wrong but after testing I have come to the conclusion that the Area target does NOT expose the overall camera iris JUST for the target area but it seems to measure the exposure both in the whole screen (and then store that reading) and then measure the exposure just inside the target area (and also stores that reading) Based on rough estimates it appears that the logic then measures the difference between the two readings and then applies either the difference or a percentage of the difference to the iris. Now, If you take a scene with a slightly brighter background and sit someone in front of it, with the target off, the subject isn't really in shadow or backlit but there face is a little bit darker as the cam has exposed for the whole scene...enable the target (with it over the persons face) and voila, the background over-exposes a bit and the face lightens up!!! Exactly as one would expect..!!!

Now take a more severe case wher someone is standing on the edge of a body of water with bright light reflecting off it. With area function disabled their face is severely in shadow, almost featureless in fact!!! Put the target over their face and enable the fuction and you will NOT be happy...exposure doesn't change very much and the face is still very featureless and very badly under-exposed. Now I think that because the overall scene is so bright and the target area is so dark, the difference calculated by the camera is just not enough to retain some background definition AND expose the face correctly!!! In this case using Area function seems to be a waste of time as the exposure difference is just too great for the camera to correct and a manual iris correction is needed (or push the backlight button if you are lazy!!)

Dunno if any others have tested the area function in this way but it seems to me that it's brilliant when you have a small difference between background and subject...it seems to work really well there!!!

Anyone have any different theories????

Chris
 
Unless it's called a "spot meter", that's exactly how I would expect it to work. Most metering systems bias towards the center, but measure the whole frame. At least with these cameras you can just grab the iris ring and compensate when necessary in auto iris mode.
 
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