Best method for setting back focus?

Finnegan

Finnegan

Well-known member
I'm sure this thread exists elsewhere here, but the search feature seems to be broken at the moment as the site is being revamped. What's the best way to set backfocus? I recently purchased a SGBlade 35mm adapter and have been setting backfocus by alternating between the camera's focus and the lens focus until I can achieve the sharpest possible image - this is the method suggested by the manual.

Other people have suggested that I turn the adapter off, leave the cam's iris wide open and focus on the grain in the achromat without a lens mounted, set that as the focus point, then put on a lens and manipulate focus from there.
 
Finnegan said:
Other people have suggested that I turn the adapter off, leave the cam's iris wide open and focus on the grain in the achromat without a lens mounted, set that as the focus point, then put on a lens and manipulate focus from there.
Click to expand...

That's the correct way to do it. It eliminates all but one variable (that of the GG focus).
 
the way I do it.
put your lens on,
open iris on both,
point the camera to a well lit white board, (fill the whole screen)
get the best focus on the grain, (adapter off)
done!
 
I'd suggest checking it as the manual suggests and doing it often, particularly if the camera is heating up or cooling down. With the adapter running, frame up a high detail object (peaking on), set best focus on the 35mm lens, then again set best focus on your video camera. As the camera heats/cools you'll find that slight backfocus errors will occur correlating with expansion/contraction. With camera's like the EX1 the focus field has some depth we definitely find it easier to set with the adapter running. It doesn't matter if you're not using the Brevis MP.2 .... the same rules apply to all adapters. This habitual backfocus checking will also ensure that an accidental "adjustment" at some point does not ruin a series of shots.

Cheers,
Dennis.
 
Dennis Wood said:
I'd suggest checking it as the manual suggests and doing it often, particularly if the camera is heating up or cooling down. With the adapter running, frame up a high detail object (peaking on), set best focus on the 35mm lens, then again set best focus on your video camera. As the camera heats/cools you'll find that slight backfocus errors will occur correlating with expansion/contraction. With camera's like the EX1 the focus field has some depth we definitely find it easier to set with the adapter running. It doesn't matter if you're not using the Brevis MP.2 .... the same rules apply to all adapters. This habitual backfocus checking will also ensure that an accidental "adjustment" at some point does not ruin a series of shots.

Cheers,
Dennis.
Click to expand...

Dennis,

I wonder why there's such a difference between what the manufacturers suggest (setting it with the adapter running) vs what users actually do (adapter off)?

Is it that much more complicated to set with the unit running and, as such, doing it with it off is perceived as a time saver?

FWIW, the SG Blade manual says to set it with the ground glass spinning. They say it's more accurate than doing it by the method mentioned in the previous responses.

Bob
 
Bobonli said:
FWIW, the SG Blade manual says to set it with the ground glass spinning. They say it's more accurate than doing it by the method mentioned in the previous responses.

Bob
Click to expand...

See, this is what I don't understand because you're actively dealing with more variables which increases the chances you're going to miss your mark and end up with soft focus in some shots. Intuitively, the method where you set the backfocus first by focusing on the grain in the disc seems to be right. But then again, I'd be a fool not to trust the people who designed the machine.
 
Think about it guys - are you photographing the grain on a static piece of glass?

- No you're photographing an image that's a result of the focus from both your 35mm and your video camera. If you focus on the image itself you are much safer.

Dennis is correct though i suggest carrying a resolution chart on a piece of foam core. Also be careful - some adapters don't have good corner to center focus and your best overall focus could be just past the best center focus.

Lenny Levy
 
When I was a focus puller and the pro35 had just come out, we were taught to focus on the non-vibrating(switched off) ground glass against a bright back ground or into a bounced light board. That way giving optimum clarity on the GG to sharpen up on. This was via P&S technik themselves. If you attempt to back focus with the a lens and image, your just putting more variables into the equation.
Plus, the image ends at the ground glass. If thats sharp and your focused correctly on your lens, then you should have no issue.

Glad I don't FP anymore....leave that to another sucker...

Best

J
 
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