Hi there. I'm new to the forum, new to filmmaking. I have a bit of a technical question about using close-up and split-field filters.
What I'd like to know is, is there some formula to work out how close-up filters of different diopters (+1, +2, etc) affect focus?
I have a reflex Bolex 16mm. Because it's usually quite hard to focus through the viewfinder, I tend to measure the distance to the subject using a tape measure and set the focus accordingly. With a split-field filter, where one half of the lens is covered with a close-up filter (giving you two planes of focus: a near subject and a far subject) the focus ring would be set to the distance of the far away subject (in the half of the frame not covered by the filter). What distance does the near subject (seen through the filter) then have to be to the lens for both far and near subjects to be in focus?
So, for example: far subject is 20ft away, and is in the half of the frame with no filter. The near subject is in the other half of the frame, seen through a close-up/split-field filter with dioptre +1. How close should the near subject be for it to be in focus, with the focus ring set to 20ft going through a +1 dioptre close-up filter?
Phew! If any of this makes sense I'd be really grateful for any help anybody could offer. Thanks!
What I'd like to know is, is there some formula to work out how close-up filters of different diopters (+1, +2, etc) affect focus?
I have a reflex Bolex 16mm. Because it's usually quite hard to focus through the viewfinder, I tend to measure the distance to the subject using a tape measure and set the focus accordingly. With a split-field filter, where one half of the lens is covered with a close-up filter (giving you two planes of focus: a near subject and a far subject) the focus ring would be set to the distance of the far away subject (in the half of the frame not covered by the filter). What distance does the near subject (seen through the filter) then have to be to the lens for both far and near subjects to be in focus?
So, for example: far subject is 20ft away, and is in the half of the frame with no filter. The near subject is in the other half of the frame, seen through a close-up/split-field filter with dioptre +1. How close should the near subject be for it to be in focus, with the focus ring set to 20ft going through a +1 dioptre close-up filter?
Phew! If any of this makes sense I'd be really grateful for any help anybody could offer. Thanks!