Bob Dolph Answers Questions on FOV Angles, Tangled Cable Pull Boxes
Q: Enjoyed your article (Tech Talk, June 2004). For a 1/3” format, what are the FOV angles for a 20, 30, 45 and 60mm lens?
Fred Rydberg, Waite Park, Minn.
A: Glad you liked the article. I can think of two sources that will help you get the FOV angles. Try the below Web site at:
http://www.sweeting.org/mark/lenses/#calc
Select CCTV lenses and don’t forget that you will typically be interested in the horizontal FOV angle, but you can also find the vertical FOV angle. Watch for that in your selection when using the calculators.
You might want to contact Rainbow CCTV and get a pocket calculator wheel that will come in handy in the field for estimating. The FOV view angles are listed on the wheels. You can call them at (800) 654-5367 or E-mail them at [email protected]. Someone in sales should be able to get you a complimentary calculator wheel.
Transfer the angles to only your overly sheet as illustrated in the article (see June 2004 print edition of SSI). Please note that angle measurements will vary slightly from manufacturer to manufacturer, but the technique I showed in the magazine article will give you some good estimates for selecting lenses.
Q: I get very frustrated with cable boxes that always get knots and kinks in them when I am pulling wire out of the boxes. Any suggestions for smoother pulling?
A: One of the biggest culprits that cause cable pull boxes to get tangled is banging them around in your truck and from job site to job site. Try to use boxes for only small jobs and use just enough for a single job. If you take cable boxes from job-to-job have a dedicated area in your truck were you can secure the boxes and keep them from getting banged around. Keep boxes dry as well.
On big jobs, I would suggest a cable rack and using spools rather than boxes. You may also want to look at some of the new cable that is spooled in tight forming plastic bags rather than boxes. Several techs have indicated few snags with these and they take up less space. Hope this helps.
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