Hi Guys

I went totally manual this season and had a couple of issues especially with my Sigma F1.8 lens and depth of field so I'm passing on my stuff ups so you don't make the same mistakes!!

Getting enough DOF at wedding guest table interviews, I have always tended to get in nice and close at 18mm on my stock lens to film guests giving comments at weddings and while the auto focus was slow, the DOF was always OK. The idea was, if I'm close I get better audio over and above the room noise. With my fast Sigma lens I did a bunch of interviews and to my horror found that when two people are in the frame, even at 18mm, one can be out of focus. The DOF at 18mm F1.8 and only 3' away from your subject is a scary 0.54' (yep 6") so of course you cannot frame 2 or 3 people so I make the habit now of shooting from what I estimate as "3 paces" away from the subjects which is around 9' to 10' and of course your DOF expands nicely to nearly 6' which is plenty to keep even a group of 3 people huddled together all in focus. With the zoom locked at full wide and at F1.8 the DOF goes from at crazy 6" at 3' to a very comfortable 10' if you are 12' away ... basic hint is don't get in too close.

If you are used to the stock lens wide open at F3.5 shooting from 6' away is quite practical even if the AF is a little off as the DOF is still 5' but with an F1.8 lens you only have a little more than 24" which isn't enough to keep a couple both sharp.

Chris

I think for anyone using fast primes wide open it won't come as a surprise that the dof can be very narrow and becomes even worse the larger the sensor gets. That's why I like shooting with m4/3 camera's, I often get the question why my 12mm at f2.0 has such a large dof during the first dance and that's because I increase my distance to the subject so the dof becomes wider, if I would be using a 24mm at f2.0 on a full frame camera I would struggle to maintain my focus under exactly the same circumstance.

The only option would be to close the iris down but that is only a workable option if you have a camera like the sony a7s where you can compensate using very high iso's, shooting at f3.5 with any other camera to have a deeper dof would not be possible as f3.5 won't allow you to shoot in darker venues. F2.8 is the absolute minimum, with my m4/3 camera's I shoot at f1.8 and f2.0 all of the time without much issue, only at longer telephoto lengths, like my 75mm, focus does become an issue but never on my 12mm, unless I shoot something from a close distance.