Back focus confusion

[Carl Martin]

Originally Posted by Keith Forman

Ok, Brian... You have obviously worked the higher end. Let me ask you about Back Focus adjustment tools. It seems like I saw one for a top end cam, and it was going for $800-$1000. Isn't this like a screwdriver, or is it that specialised of a tool?

Paolo- So glad you have a sense of humor. Could you loan it to my wife? She isn't finding any of this amusing, like when I talk about spending $400 for a battery, $1,000 for a capture card... If I showed her a focus card for $350, she'd be calling a lawyer or a shrink!

Hey Keith,

Try this place. They sell HD back focus charts for $97.00

http://www.testequipmentdepot.com/

I hope this helps,

Carl

[Paolo Ciccone]

Originally Posted by Keith Forman

If I showed her a focus card for $350, she'd be calling a lawyer or a shrink!

That's cool, they are both usually well off, you can sell them your video services to them ("You need a new TV commercial ...") ;)

[K. Forman]

Somehow, I think she'll be the one that would end up with all my video equipment.

[Brian Drysdale]

Originally Posted by Keith Forman

Ok, Brian... You have obviously worked the higher end. Let me ask you about Back Focus adjustment tools. It seems like I saw one for a top end cam, and it was going for $800-$1000. Isn't this like a screwdriver, or is it that specialised of a tool?

Most people use the Siemens Star on a chart, even on high end productions. I've got a chart from Panavision that, as well as the star, also has an Annular Focus Target, which uses the peaking to check the back focus. It cost £12. You can also download, print out and then laminate a star for even less.

The difference on the high end cameras is that you need to regularly check the back focus. Every time you change a lens, if the temperature changes you have to check the back focus. So, focus pullers (1st AC in USA) are checking the back focus throughout the day and setting up charts takes up time when time is an expensive. It can also be difficult in confined spaces.

It then becomes worthwhile having these more expensive optical units: it saves time, especially when using prime lenses - you don't need to measure distances. On a feature film, an extra set up at the end of the day could pay for the unit. A point to remember is that the production will often hire items like this as part of the camera kit.

[K. Forman]

Originally Posted by Paolo Ciccone

I perform an "intermidiate stop" with the chart framed fully and check the focus at that point. I use the backfocus chart in the back of the DSC card, it creates a "bowtie" effect that is easier to follow. I also use peaking in addition to FA. Crank the peaking all the way up. Use that to check the focus and, every now and then, push the FA button.

What does the peaking do, and how does it help check the focus? I'm trying, but can't seem to get the back focus adjusted right either.

[Paolo Ciccone]

Originally Posted by Keith Forman

What does the peaking do, and how does it help check the focus? I'm trying, but can't seem to get the back focus adjusted right either.

Peaking is a "edge enhancement" function, t will draw a white border around the edges when the image is in focus. Crank it all the way up, point the camera at the subject and rotate the focus (not backfocus). Yuo'll see it when the image is in focus. Once you get the hang of it use it for backfocus adjustment with a Siemens star or a DSC backfocus chart.

[Stephen L. Noe]

Here is the Panavision Chart. You can print this on 11x17" and 600dpi printer.

Click here for PDF

Have fun back focusing.

[K. Forman]

Thanks Stephen, I've been having soooo much fun as it is. It's at the point, I'm not sure if it's the cam that isn't focused, or me. It goes either way some days.

[Stephan Ahonen]

Peaking enhances the highest visual frequencies in the image, such as sharp edges, while leaving softer edges alone. So when you achieve perfect focus, the edge will appear to pop out. I've worked with camera operators who can't stand peaking for whatever reason, but it's their loss, peaking is really the best way to know exactly when you're in focus especially on a smaller viewfinder or one that is a lower resolution than the camera.

[David Tamés]

Being of the mind of "maximum performance" for "the minimal price" as long as there is "no sacrifice in quality," for years I've been using a Siemens Star chart for back focus adjustment and checking focus when setting super-accurate marks that I simply printed out myself with a high-resolution printer. Any printer 600 dpi or better will do just fine, no reason to spend money on fancy charts, put the money on the screen.

Stephen L. Noe included a link to a Panavision chart, this PDF is courtesy of the nice folks at JVC:
http://www.jvcpro.co.uk/getResource2...t1.pdf?id=6145

and it includes along with the Siemens Star Chart some instructions on how to use it along with a little history, the chart was developed in the 1930s by German industrialist Werner von Siemens in order to set up the focus on the film cameras he was manufacturing and the rest, as we know, is history.

[Scott Harper]

Correct me if I'm wrong, but do they not include this chart in the camera's manual? Also, just curious, how often should this back-focus be performed if we are not changing lenses?

[Robert Aldrich]

"It's one of the worst designed sites I can remember seeing recently. I don't think they have warm cards... but hey, with a navigation system like theirs maybe they do. ;-)"


Their cards are so expensive to make, they couldn't afford a decent web designer...