Projection Lenses Questions and Answers with formulae
Source: Navitar Presentation Products
Frequently Asked Questions
Q. How do I calculate what size lens I require?
If you need to calculate the correct lens size you require, please use
the following formula for a very close approximation. If you have any questions,
please call and speak to one of our engineers.
Lens Focal Length = Projection Distance x LCD Panel Size
(diag. or width)
Screen Size (diagonal or width)
First, you must know the following information:
1. Screen size in inches (diagonal or width).
2. Projector LCD panel size in inches (diagonal or width).
3. Projection distance in inches (measured from the front of the video projector
housing to the screen).
It is very important that you be consistent. If you use the
diagonal screen size measurement, then you must also use the diagonal measurement
for the projector LCD panel size. If using screen width, then use the LCD
panel size width. If you are working in inches, then you need to do all of
your calculations in inches. You can convert the lens size to millimeters
at the end. Please note the following information:
Screen Diagonal x 0.8 = Screen Width
LCD Diagonal x 0.8 = LCD Width
1 Foot = 12 Inches
1 Inch = 25.4 Millimeters
Example: You have an 80’ projection distance from the screen
to the front of the LCD projector housing. The screen is 10’ wide & the
LCD has a 1.3" diagonal.
Lens Focal Length = Projection Distance x LCD Size (diagonal
Screen Size (diagonal or width)
Lens Focal Length (Calculated in Inches)
= (80’ x 12") x (1.3" x 0.8) = 960" x 1.04"
10’ x 12"
Lens Focal Length (Calculated in Millimeters)
= (80’ x 12" x 25.4) x (1.3" x 0.8 x 25.4mm)
(10’ x 12" x 25.4mm)
= 24,384mm x 26.416mm = 644,127.74mm = 211mm
For this application, we recommend the 6-9" zoom lens,
Q. If my image is 10 feet wide, how high will it be?
An easy way to determine image height is to take the image width and divide
it by its aspect ratio. The aspect ratio for standard video is 1.33:1.
Image Height = Image Width = 10’ = 7.5’ (7’6"
Aspect Ratio 1.33
The aspect ratio for HDTV and most "letterbox" formats is 1.77:1,
therefore a 10 foot wide HDTV image will be 5’8" high.
Q. How do I convert a diagonal measurement into width?
Just as most TV sizes are given in diagonals, the same is true of LCD panel
sizes. This is why we multiply the LCD panel size (a diagonal measurement)
by 0.8 (4x3 standard format) or 0.87 (16x9 wide screen format) to determine
the "Aperture," which is the "Width" measurement.
Standard Format (4x3 : 1)
Width (or Aperture) = Diagonal Measurement x 0.8
Wide Screen Format (16x9 : 1)
Width (or Aperture) = Diagonal Measurement x 0.87
Q. Why do some lenses only work on certain projectors?
The most common reason for this is due to the physical internal and external
designs of the projector itself. For example, the position of the LCD panel
or electronic components inside the machine are simply not compatible with
all lenses. The design of the outside projector cover can also determine whether
or not some larger lenses can be used with that particular projector model.
Q. Is it difficult to install a new LCD lens in a projector?
Installing a new lens is relatively simple. There is no disassembling involved
and no heavy electronics to take apart. In fact, many projector manufacturers
are now designing their projectors to make it easier to remove the prime lens.
Installation instructions are included with each NuView lens sent
out. You can also find a complete set of instructions on our website (click
here for online installation instructions). If you have any doubts,
contact your dealer for the name of an authorized service center or trained
professional in your area, or you can contact the Navitar directly.
Q. Will I lose all of my remote control features?
All NuView lenses are manual lenses, that is, you must focus or
zoom the lens by hand (your power zoom and power focus functions will be disabled).
If your projector has a lens shift function, you will retain this feature.
For fixed installations, the picture size and focus need to be set only once
and readjustment is not necessary. Set it and forget it!
Q. At what distance will my lens focus?
Most NuView lenses will focus as close as 3 to 4 feet
in front of the projector and all lenses are set to focus to infinity, therefore
focusing at long distances will not be a problem.
Q. What do these terms mean?
Zero Offset Most LCD projectors have a built-in angle
of projection, usually upwards a few degrees. A "zero offset" or
"on axis" lens projects straight out in front, so it is necessary
to place the projector in a position that is perpendicular to the center of
your screen. This is typically the case when using wide-angle and fixed lenses.
MCZ (in the catalog #) Literally, it stands for Multi-Coated
Zoom (MCL is for Multi-Coated Lens). This is a new manufacturing process
developed by Navitar, in conjunction with our sister company, Navitar Coating
Labs, Inc. The process increases the brightness, contrast ratio and color
saturation of our "Xtra Bright" lenses.
Prime Lens The "prime lens" is the factory
installed, manufacturer’s lens that comes with your projector.