OT: Focus Charts

p@mast3rs wrote on 12/19/2005, 4:14 PM

How are they used? How does one read them? Also, where can one puchase them or can you download one and print it out and use that? I keep seeing focus charts and have never used them ever. Hopefulyl someone can help.

Comments

Serena wrote on 12/19/2005, 4:34 PM

Have a read of http://medfmt.8k.com/mf/resolution.html
also see
http://www.graphics.cornell.edu/~westin/misc/res-chart.html

In the latter look beneath the blank rectangle (picture doesn't open) for the pdf version.

Coursedesign wrote on 12/19/2005, 7:50 PM

Are you talking about the trumpets commonly used for checking back focus?

p@mast3rs wrote on 12/19/2005, 7:53 PM

Yeah. Like the ones that DVRack provides for its customers.

http://www.dvrack.com/

I believe they call them calibration charts.

Serena wrote on 12/19/2005, 8:16 PM

OK, check the 2nd reference in my response.

Serena

p@mast3rs wrote on 12/19/2005, 8:18 PM

much appreciated. :)

p@mast3rs wrote on 12/19/2005, 8:19 PM

doh, file not found Serena.

p@mast3rs wrote on 12/19/2005, 8:24 PM

woohoo, got it. Much much thanks.

farss wrote on 12/19/2005, 8:53 PM

You do need to know how to use and more importantly read them. There's been some very silly claims made over the years by those who didn't know how to read them.
Probably someone will find a link or offer a better explaination than this but in brief the trap is assuming that because you can still see lines they're being resolved. That's incorrect, aliasing will make lines appear well beyond the resolution limits of a system. The real limit is when the lines FIRST appear to merge.
Bob.

Serena wrote on 12/19/2005, 9:04 PM

Good point Bob. The references I mentioned provide several links to other documents detailing the use and analysis of charts. Follow those through and you should avoid misinterpretations.