View Finders Confusing Views

Dear Charlie,

I attended your show for Panasonic in Atlanta and have recently purchased a Computar viewfinder as you suggested. I have already started to use it, but am having some trouble understanding how to use it and Computar does not seem to be much help. I have a job where I will use Panasonic 1/3" color cameras. I have ordered 1/3" lenses for many of these cameras but can not find the size I need in 1/3" format for some locations. I know I can use 1/2 format but how do you calculate the lens size that will give me the same view as a 1/3" lens. My viewfinder says 32mm at the «" position and is blank at the 1/3" position. Can you suggest any literature to help me understand my new tool better?

Sign me Lens-less Darrell in Tennessee

Dear Lens-less Darrell,

The fastest response would be to remember that everything is mathematical when it comes to lenses. That is you can go up or down to get the results necessary. According to your view finder, you need a 32mm at 1/2.... To calculate to a 1/3" lens, the fastest method would be to first calculate for a 1" format and then back down to a 1/3" format. First you would take 32 X 2 = 64mm to formulate your 1" format need.... Then you can then take 64 / 3 = 21.333 which would be your 1/3" format need.

Finding a 21.33 mm lens however is like pulling teeth from an elephant at a dead run. You need to move your camera closer or farther away to get the scene (field of view) that you need or you need to compromise on the size image or field of view that you have designed. Remember also that a 21mm lens is a 21mm lens no mater what format size it might be. That is, you may be able to find a 21mm (or close) lens in a 1/2 or 2/3" or 1" format. These will work on your 1'3" camera as well as if they were 1/3" format. Remember that your lens must be a format size equal to or greater than the format size of the camera to work properly. The focal length (21mm in this case) is what determines the final scene size of your image.

One thing that will prove to be a valuable asset to you would be to look at the Veri-focal lens. This is a specially designed manual zoom lens that is low cost and will give you the ability to obtain a 21.33mm position. A Veri-focal lens would have a limited range of manually adjustable focal length. In your case, you would look at a lens in the 12.5mm to 25mm range. Then it would be a simple mater of setting up your image with a monitor in the field. Most of your major lens manufacturers will have a supply of Veri-focal lenses that fit into various formats and ranges. You can look to Computar, Fujinon, Rainbow, and Tamron for such lenses.

I sincerely, hope that this will help you with your current problem... Let me know. If there is anything else that I might be able to help you with...please feel free to call, email, fax, or whatever. I am in your service.

Charlie Pierce