Had a weird experience last week. While shooting an interview overlooking a bright city background with the FX9 in Autofocus with the Sigma 50mm E mount lens in AF, I noticed the entire image pulsing in and out as if it was searching for the proper focus . Presumably the image size was pumping due to focus hunting , but throughout the square remained over the subjects eye . The f stop was very high f13 or so. I turned off AF and it was fine. What the heck????
sigma 50 af pumping on fx9
- Thread starter LennyLevy
- Start date
Yeah the AF on the Sonys are great , but the big Achilles heel is a bright background , the only time Ive had trouble with the fx9 AF , ( I have the Sigma 50 and always use it for interviews its AF work fine with Sony cameras ) .. bright backgrounds is really not your friend , at least for interviews you never want that anyway. Also set both speed and sensitively to 1.. best setting for interviews . Did you have face only set too, very important for interviews .. I would have gone down to way more open Iris ,by using the VND too .. at f13 you don't need AF anyway 
you could set it and go to sleep , less the BG is in focus less chance the AF wants to go there ..
you could set it and go to sleep , less the BG is in focus less chance the AF wants to go there ..I needed F13 because I wanted the city background for content reasons and it It looked great . Wasn't overexposed, but I got what i could with the instruments available. Is the bright background an issue for the AF ? Why? T hat's what surprised me. My speed and sensitivity was higher probably 3 or 4 - I'll check. Someone else told me that was the problem.
Hi ..I don't know the techie side , but yeah bright / or BG with bright lights affects the AF .. Contrast and Phase detection .. strong backlight just seems to throw it off , you can see it in P. Blooms video about AF .. his model is walking with a car head light behind here , each time the AF fails , when the car is not there ie no harsh back light , it works perfectly .. I have the Sigma 50 mm f1.4 and with the fx9 , I would definitely use the VND before I got anywhere near f13 on an interview .. 2.8 you can still still see its a city night , I mean where you lighting the subject with a very powerful light ? .. interviews , face only , 1 and 1 is the way to go .. the last thing you want is the focus to go anywhere but the face , so sensitivity 1 ( locked on ) is a no brainer .. and speed 1 so your not getting any quick shifts .. pulsing , people move forward or backward but will end up back in the same place .. face only in theory anyway , if there is no face the AF actually stops working .. but yeah the only time I had trouble with AF , with the fx9, was the sun coming out and hitting a window in the BG of an interview , and suddenly it wouldn't work , had to go to manual .. thats how it is so far , but generally speaking you want the BG darker than the subject anyway so its rarely a problem for interviews .. it doesn't work so well on dark skin either , and supposedly slog less , as less contrast , but I havnt had trouble in slog compared to 709..
Doug Jensen
Carbonite Member
VND = electronic Variable Neutral Density filter
The irony of this statement is that the Sony AF is by far the best out there at the moment
.. but its not just switch it on and lean back with a donut , there is a learning curve , Philip Bloom recently put out a two part video on the Sony site thats good, it took him a while to work things out too and admits he was wrong on earlier video,s .. for set up interviews if you know the set up its pretty much 99,9% solid these days , Fx9 now has the same touch focus as the A7 / fx3 .. but often of course its easier just to do manual focus ..Sorry wasn't meaning to come off like that , just that the deeper DoF ,AFAIK will also make the AF prone to hunt ,as that BG is now in focus and the AF can see the contrast , especially if its sun lit hard lines on straight building edges., But face only , 1 & 1 will definitely help with interviews .. you could also put your Zone Area over the subjects face too .. and avoid really burnt out windows right behind people. Its amazing how much you see people post about problems with,AF and image /edge artifacts ,when they have set up an interview with a massive 8 stops over window 4 feet directly behind their interview subject !
Liam Hall
Veteran
The irony of this statement is that the Sony AF is by far the best out there at the moment
Actually it was a point of fact; it was the only time I have had cause to use the FX9 as we needed to match an earlier shoot. The real irony is I nearly bought one when it came out but was worried about the compatibility with my lenses. The FX9 is a great camera, I'm not disputing that, but my day with the FX9 proved my decision was correct and also reinforced what you say about not relying on AF. I do love AF though!!
Yeah I use AF on every interview now ( well except when the sun comes out on the greyest day in the history of mankind
and hits the BG window.. and specific walk and talk or car /person coming directly at me , but most general B roll its actually easier to do it manually , than go through the motions of setting the best AF settings , which you could do but it tales 10 times longer than just turning a bit of metal ..