What is camera back focus
What does back focusing mean?
Back Focus, or back-focus, is the error of having a subject be accidentally out of focus, and sharp focus instead falling behind or past the subject.
How important is back focus?
Back focus directly impacts your ability to use accessories with your telescope. With limited back focus, you may not be able to use Barlows, focal reducers, binoviewers, SLRs, and 2 in eyepieces.
How do you get back focus?
To calculate the backfocus of your setup, add up the backfocus of all the separate components. For example, if we take an Atik 460EX camera, this has a backfocus of 13mm. If we then add in an EFW2 filter wheel, this has a backfocus of 22mm.
How do you know your back is focused?
The Simple Way to Check Backfocus
- Place a Siemen’s Star Chart on a Wall. …
- Position the camera at level height about 10 feet away. …
- Mount a zoom lens or mid-range prime lens. …
- Open up the iris of the lens all the way. …
- Focus by eye using a viewfinder or monitor. …
- Check to see if your eye focus matches the lens marking.
Do filters affect back focus?
The main thing to remember is simple: when you insert a filter it will push the focus farther away – and you need to add to the adapter length as a result.