Photometers for Vision Science

Compiled by L. Ziegler, Montreal, Quebec 13 Oct 1995
Edited by Andrew B. Watson, 12/6/95

Updated 9/22/00

From the advice I received, when looking to purchase a lightmeter or
photometer for psychophysics, you might want to know if it

is a photometer, that is, compensates for the human spectral sensitivity function. If not, is a photometric head (a lens assembly) available and what is the additional cost?
measures video monitor screen luminance correctly? (temporal integration, aliasing can cause problems with video )
saturates at high screen luminances without you realizing it (to test, use neutral density filter; see if #1 really reduces your reading 90%).
reads directly in cd/m^2.

Someone mentioned current advertisements for photometers can be found in
a magazine published by the Society for Information Display.

DISCLAIMER: This information is provided as a guide. It is compiled from network contributions and it is not definitive or exhaustive. The compiler and contributors cannot guarantee its accuracy.

North American Suppliers

Minolta: Minolta Instruments Division; 101 Williams Dr. Ramsey, NJ 07446; 1-800-724-4075 or FAX (201) 825-4374.; Contact: Andrea Hunt (201) 818-3517, or main (201) 825-4000; In CANADA:; Minolta Canada Inc. / Instrument Systems Division; 369 Britannia Road East / Mississauga, Ont. L4Z 2H5; (905) 890-6600 FAX: (905) 890-7199 / Contact: Neil Trotter.; T-1 illuminance meter (app. $1000 US); LS-100 luminance meter (app. $2500 ); Chroma Meter CS-100 (app. $5600) gives CIE coordinates for color; LS-100 (app. $ 7k US); LS-110 (app. $3k) highly recommended. Reads directly in cd/sq.m and; employs a reasonably small field; serial port for PC interface.
Graseby Electronics (or Graseby Optronics ): 12151 Research Parkway; Orlando Fl. 32826-3207 USA; Engineer: Jim Ritzel (407)282-1408 / Fax (407) 273-9046.; - market what was UDT (United Detector Technology); Everything from hand-held model GO352 at $475 to a multi- (8) channel; IEEE-488 compatible "power/energy" meter (model S390) for $8200+head etc.; New hand held colorimeter with lots of bells and whistles.
Tektronix, Inc.: P. O. Box 500; Beaverton, OR 97077; (503) 627-7111; J-16 Need integrating head to prevent aliasing if measuring video displays; J-17 photometer + J-1803 measuring head (app. $1800 US)
Photo Research Inc. (the Pritchard series ): 9330 DeSoto Avenue; Chatsworth CA 91311; Tel: 818 341 5151 FAX: 818 341 7070; In Canada:; Optikon Corp; 1099 Guelph Street; Kitchener, Ontario; N2B 2E4 Canada; Tel: 519 745 4115 FAX: 519 745 6922 "; Outside North America:; Micron Techniques Ltd.(Supply Photo Research Kit); 22 Ashley Walk; Mill Hill, London NW71DU; Tel: 81 343 4834 FAX: 81 343 4286 "; 3000 N. Holywood Way; Extensive line of devices from scanning to hand held spot photometers
International Light: 17 Graf Road; Newburyport, MA 01950-4092; (508) 465-5923
Optronic Laboratories: 800-899-3171 or (407) 422-3171
EG&G Gamma Scientific: (619) 279-8034
Edmund Scientific: 101 East Gloucester Pike; Barrington, NJ 08007-1380; Orders: (609) 573-6250 FAX: (609) 573-6295, Tech Support (609) 573-6879; Email: TechSup@edsci.com; $90 upwards.
Oriel, Inc.: Stamford, Conn
(Goldilux - reads in lux and footcandles)

Suppliers Outside North America

Cambridge Research Systems LTD: OptiCAL, CRT Gammma Correction System (w/serial port interface); (1250/2125 pounds).; Information at: http://www.demon.co.uk/crsltd/
Micron: supply Photo Research Kit
Macam (Scotland)

REPLIES TO NETWORK REQUEST, AUGUST 1995

On the subject of light meters, you may want to check out the
line of photometers from Photo Research (the Pritchard series).
If you don't need to measure too many things in the mesopic level
or lower, check out the Minolta CS-100. It does color too.

Hoover Chan - For CVNet: cvnet@skivs.ski.org
Smith-Kettlewell Eye Research Institute

These companies sell photometers, light meters, etc.

photo research: 818-341-5151
optronic laboratories: 800-899-3171 or 407-422-3171
eg&g gamma scientific 619-279-8034

Jack Beusmans, PhD
Nissan Cambridge Basic Research; 4 Cambridge Center; Cambridge, MA 02142.
Email: beusmans@pathfinder.cbr.com
WWW: http://pathfinder.cbr.com/
Tel: (617) 374-9670 Fax: (617) 374-9697

In general I find that the use of a photodyne system which measures watts or
a licor meter which measures quanta are the best. I do not work on humans so
the terms of lux etc... are meaningless so a photometer which is based on
the human spectral sensitivity function is not very useful.

Victor Rush
Department of Biological Sciences
University of Victoria
PO 1700
Victoria BC Canada V8W 2Y2
ph 604-721-7145 fax 604-721-7120
vrush@sol.uvic.ca

We are into colour measurement more than light measurement, but most
companies handle both. We currently use a hand held colorimeter from
Minolta for our routine laboratory work. They come in various forms. The
one we have cost about 5K, but I have used a smaller less expensive one. A lot
depends on whether you want the capability for hooking up to a computer.
For information contact: Minolta Instruments Division, 101 Williams Dr.,
Ramsey, NJ 07446; 1-800-724-4075 or fax (201) 825-4374.

Graseby Electronics produces a wide range of light meters ranging in price
from about $500 US to $5000. Their latest product is a hand held colorimeter
with lots of bells and whistles. For product information contact Graseby
Electronics 12151 Research Parkway, Orlando Fl. 32826-3207 USA (407)282-1408
or Fax (407) 273-9046.

I dont have addresses for Canadian distributors. In Canada, Optikon sells
light meters. They distribute Prichard photometers which can be expensive.
I am not sure what sort of product range they offer. They can be reached at
Optikon Corp. Ltd, 410 Conestogo Rd. Waterloo Ont. N2L 4E2. The most
recent number I have for them is (519) 885-2551 or Fax (519) 885-4712.

Most major companies selling light meters advertise in Information Display
the monthly publication of the Society for Information Display. There
is usually a reader service card that you can send in to them to get
product information from any of their advertisers. They also have a new
product section which reviews new display related products such as light meters.

I hope this information is of some help.

Sharon McFadden
Human Engineering Sector
D.C.I.E.M.
P.O. Box 2000
North York, Ont. M3M 3B9

I have one suggestion for a light meter-Oriel inc in Stamford, Conn. has
Goldilux meters that read in lux and footcandles. I would also like to request
that if you receive any other suggestions, could you forward them to me as well?
I am beginning a psychophysics experiment myself (with non-humans) and I am
looking for a radiance/irradiance meter or a very sensitive luminance meter.
Thank you in advance.
Dave Levenson
University of California at Santa Cruz
Long Marine Laboratory
Santa Cruz, CA 95060
USA
(408)459-3345
davemabi@cats.ucsc.edu

I use the SPECTRA PRITCHARD photometer which I purchased from
PHOTORESEARCH in California. Canadian distributor is Optikon in Montreal
and/or Kitchener in Ontario. The photometer is expensive but well worth the
cost. Good luck. H. Mikaelian.

H. H. (Mike) Mikaelian
Department of Psychology
University of New Brunswick
Fredericton, New Brunswick Canada
E3B 5A3
martini@unb.ca Voice: (506)-453-4707 FAX: (506)-453-4505

Do you need lumens, color temperature, radiant spectra, or what?

If you can give me a paragraph on the field, and
how it affects color choice or judgement of color
matches, or texts that would be of interest to
color technologists, I'd like to post the info on my
COLORING Pages at http://www.infi.net/~color/.
One place we always need help from the pyscho field
is in putting words on the visual judgements of
goodness of matches: 1) excellent 2)good 3)barely
accepatable 4)marginally unacceptable, and 5)unacceptable.
We then check these human judgements against numerical
values derived from various color difference equations,
to rate McAdam vs CIELab vs CMC, etc.

While you're visiting, you might want to look at
the little ColorTron, a US$1,200 Mac color sensor that
could be of some value in your work; our COLORING
list members discuss it at
http://www.infi.net/~color/tools/colortrn.html.
The company that makes this might have other tools that
could work for you, if the ColorTron doesn't. And the
prices are certainly right -- 'till now, I haven't seen
spectro's that cost less than maybe 10K$. You'll find
the maker's e-mail, fax, and phone numbers at the link.

Hope this is of some value to you.

Bill
--
Bill Dawes wmdawes@infi.net Color Technology and the Internet
804 748-8639 Fax: 804 768-8170
13020 Birchleaf Chester, VA 23831-4614 USA
http://www.infi.net/~wmdawes COLORING at http://www.infi.net/~color/

Any good photography store will have stable, inexpensive spot & incident
light meters. Get one or more, benchmark them against a trusted meter, and
they will provide a resonable calibration. (very stable, easily within 0.1
log units over long time periods)

Check any buyers guide for the more "scientific, expen$ive" units.

http://ucaussie.berkeley.edu/kh/ken.html

I have been using the Minolta LS-110 for a couple of years and find it
satisfactory. It reads directly in cd/sq.m and employs a reasonably small
field. There are problems in measuring lines and points, but they can be
overcome (see e.g. my paper in Vision Research in 1985).

Gerald Westheimer
gwest@violet.berkeley.edu
["The oscilloscopic view: Retinal illuminance and contrast of point and line
targets". Vision Research. Vol 25(8) 1097-1103, 1985 (Ed.)]

We have good experience with the Minolta LS-110. It's easy to use, and best of
all, you can read itout from a computer. Unfortunately, this is not something
supported by Minolta, so you will have to adapt one of their cables and do a
little programming. Source code for doing this is available for mac and pc
(contact me for this). Reading is via serial port.

Frans W. Cornelissen
Laboratory for Experimental Ophthalmology (LEO)
University of Groningen
P.O. Box 30.001, 9700 RB Groningen, The Netherlands
Tel: + 31 50 614173 (work)
Fax: + 31 50 696743 (work)
E-mail: f.w.cornelissen@med.rug.nl

/* Mac version by Frans W. Cornelissen, with suggestions from Eli Brenner.
PC version by Erik van Wijk, Fysiology I, Erasmus University Rotterdam,
The Netherlands. Contact him at wijk@fys1.fgg.eur.nl.

Minolta.c

C-routines that can be used to read out the Minolta LS-110/LS-100 */

I'm sure you'll get more comprehensive responses from some CVNetters who do
more photometry than I do, but I've had reasonable success dealing with:

International Light
17 Graf Road
Newburyport, MA 01950-4092

(508) 465-5923

Their catalog and perhaps a phone consultation should get you what you
need.

By the way, I would be interested in finding out what you come up with in
the way of advice about photometry. There may be suppliers especially
attuned to psychophysics or merely cheaper than those I know about, so
please drop me a note about anything interesting.

Philip J. Kellman
Professor of Psychology
Co-Director, Cognitive Science Research Program

University of California, Los Angeles
405 Hilgard Avenue
Los Angeles, CA 90024-1563
(310) 825-4159
Kellman@cognet.ucla.edu

Here is the address and phone number for Minolta Canada in Toronto:

Minolta Canada Inc.
Instrument Systems Division
369 Britannia Road East
Mississauga, Ont. L4Z 2H5
Voice: (905) 890-6600
FAX: (905) 890-7199

The person I was dealing with there was Neil Trotter. I ended up getting a
Minolta Chroma Meter CS-100 which cost the university $7500 (ouch). This
meter gives CIE coordinates for colour as well as cd/m2 measures and can
be hooked up to a computer, so this may be more than you are looking for.
I know that they have other, less expensive, scientific light meters,
though.

Larry Symons
Department of Psychology Phone: (613)545-2881 (office)
Queen's University (613)545-2476 (lab)
Kingston, ON (613)545-2499 (FAX)
Canada K7L 3N6 e-mail: SYMONSL@PAVLOV.PSYC.QUEENSU.CA
SYMONSL@QUCDN.QUEENSU.CA
Web Homepage: http://pavlov.psyc.queensu.ca/other/symons/symons.html

We have two Minolta meters that we have found to have
a good combination of price and performance. Both are
versatile, small, light, operated on standard 9V batteries,
etc. We have a T-1 illuminance meter (about $1000 US I think)
and a LS-100 luminance meter (about $2500 US). We looked around
a bit before getting these, and I think they are good choices
for general use. For more specialized things (color, scotopic
values, etc.) some other choices would be better. Minolta makes
a few other instruments that might be of interest too, and my
impression is that they are all pretty good values. One contact
I have for them is Andrea Hunt (in New Jersey, 201-818-3517), and
a general number is 201-825-4000. I think either number would work
for getting them to send you some literature on their instruments.

Mike Flannagan
The University of Michigan
Transportation Research Institute
2901 Baxter Road
Ann Arbor, Michigan 48109-2150
mjf@umich.edu

Minolta makes a nice set of photometers/colorimeters, that
are relatively inexpensive.

Lew Stelmach, Ph.D. | Communications Research Centre
(613) 998 2005 voice | 3701 Carling Ave.
(613) 990 6488 fax | Ottawa, Ontario,
Email: lew@dgbt.doc.ca | K2H 8S2 Canada

Tektronix has a variety of photometers that are ideal for
psychphysics. About $4k all told. I have one I am happy with. Contact
Tektronix and if you are having problems figuring it out, contact me,

Ralph Siegel, Ph.D.
Assistant Professor
axon@cortex.rutgers.edu
phone: 201-648-1080 x3261
fax: 201-648-1272

Center for Molecular and Behavioral Neuroscience
Rutgers, The State University
197 University Avenue
Newark, NJ 07102
Graduate program information: http://www.bns.rutgers.edu/

For additional information and reprints use Mosaic:
http://www.cmbn.rutgers.edu/cmbn/faculty/rsiegel.html

Please echo your "harvest" to the CVNet list.
It is a problem of general interest.
4 issues most of us will want to know at a minimum are:
1. Is the sensitivity great enough to handle computer monitors,
?
2. What units is the reading presented in? A shutter speed and
f/stop is no good.
3. Is there a correction filter to make the meter's sensitivity
approximate the photopic sensitivity of the "Standard Observer"?
4. Besides total luminance, is there an output of the CIE
color coordinates?

Nothing's simple, but at least the complexity we all have to
live with is getting cheaper to master.
--jerry

Jerry Nelson, Ph.D.
Lab Neuropsychology
NIMH / NIH Bldg 49 1B80
49 Convent Drive MSC 4415
Bethesda, MD 20892

jnelson@ln.nimh.nih.gov
tel 301/496-5625
FAX 301/402-0046
tel+FAX home: 703/448-4543

The Tektronix J-16 unit comes with radiometric, illumination and focussable,
aimable luminance probes. Good for all applications except video. Beware of
video, 'cause aliasing of sampling frequency with frame/line rate gives
spurious results. You need an integrating unit for video I think. But for
ordinary optical path measures, we have found the Tektronix unit invaluable.
Note error = +/- 16%.

You might get better information from our colour and photmetry guru here
(Prof. Stephen Dain) to whom I have copied this message.

Phil Anderton p.anderton@unsw.edu.au

I used to use a Macam Light meter made in scotlan for routine photometry and
radiometry but was unimpressed by their quality. I got a scratched detector
in the original model, sent it back for replacement, recalibration, and got the
same detector and calibration back. I couldn't refuse to pay because the stupid
agent had factored out the import cost and the original supplier had already
been paid and di not care. It worked fine but was a bog standard meter for
steady extended sources.
When I go some real money I bought an International Light IL1700, which I
then thought was the bees knees. It covers about 20 log units, measures
flashes as easily as steady lights, and can convert any units.
It is grat for measuring things like brief flashes which other meters cant do.
I have recently learned it too has a limit - The new ISCEV standard for
calibrating VDUs requires you to use a spot meter so you can look through
at a fixed point, see the whole of the area you are measuring and include
the ambient light falling on the spot, along with the emitted light.
Despite repeated queries International Ligfht have not yet come up with
a spot meter. It is such a simple thing that most ordinary photographic
light meters have them! Im still waiting to see if they can offer a third party
or add on solution.
Thus, it all depends on what sort of lights you want to measure & the optics
involved. Apart from the spot problem, the IL1700 is expensive ($A7,000) but
the best I have seen yet.

+-------------------------------+
| Vaegan | Work Phone : +61 2 231-1833
| Manager Visiontest Australia | Work FAX: +61 2 232-3086
| Unit 5, 5th Floor, | Email : vaegan@unsw.edu.au
| 187 Macquarie St, | ^^
| Sydney, NSW, 2000 | 00
| AUSTRALIA. | ...... \__/ .... bye!
+-------------------------------+ NIL ILLEGITIMUS CARBORUNDUM

Cambridge Research Systems produce OptiCAL, a light meter designed for use
with CRTs. OptiCAL is generally supplied with a CIE matched photopic
response sensor, or alternative sensors can be supplied, for example for
small spot measurements.

As well as being a photometer and contrast meter, OptiCAL is often used in
conjunction with the VSG2/3 visual stimulus generator, a sophisticated
framestore for creating visual stimuli for psychophysical experiments.

If you would like to receive more details please let me know, and I will
mail a brochure to you - or you can take a look at our web page at the URL
given below.

We're very happy for you to distribute details of our photometer. Please
check the price - it is 1250 british pounds or about 2125 US dollars.

Carol Luscombe
Cambridge Research Systems Ltd
http://www.demon.co.uk/crsltd/

My name is Rob van der Willigen; currently I work for Hermann Wagner as a
graduate biology student on behavioral correlates of depth vision in Barn
owls. Before this I worked in Nijmegen (KUN, holland) in a biophysical lab on
sensor-fusion. There I did (audio-visual) psychophysical experiments
on humans and other primates. At the moment I am building my experimental
set-up and programming visual stimuli on a SGI-INDY STATION using
OPEN-GL.

I came across your question:
What is a good light meter for routine lab use ?

Well, there are several options, but I narrowed it down to
two choices, these are:

(1) Minolta Luminance-Meter LS-100 (app. $ 7000,-)

or the LS-110 (depends on how small the measured surface has to be)

(2) Tektronix J17 photometer + J1803 measuring head (app. $ 5000,-)

The following things you have to consider:

* Most important is the measuring distance and the size of the
surface that has to be measured.

DEVICE Measuring DISTANCE SIZE MEASURED SURFACE
LS100 1014 mm 14.4 mm diameter
(this can be enhanced by a filter up to 1.3 mm in diameter with
a measuring distance of 205 mm )
LS110 1014 mm 4.8 mm diameter
(this can be enhanced by a filter up to 0.4 mm in diameter with
a measuring distance of 203 mm )

J17/J1803 304.8 mm 43.18 mm
(with this device it is also posiible to measure directly on
the surface of a screen or other light emitting device
when measuring distance 0 mm the measured surface becomes 12.7 mm)

* What has to be measured color / radiance / LED Luminance / illuminance
Luminance etc. ?

The J17 Tektronix device provides a wide range of special
heads the J1803 head for example is a Luminance measuring head
which can be used for Displays, televions and medical use. But there
are a least 8 other heads available, depending on the application
one can use them with the J17.

I chose the Minolta LS100, because I am only interested in
measuring Luminance. But there is another advantage. With LS100
one can directly see what is measured. It functions like a camera.
Disadvantage is that there is a limited measuring distance of 1014 mm
when no filter is used, that can be problematic. It is not possible to directly
measure the luminance on the surface of the stimulus. Moreover
I have some experience using the LS100,
and it is verey easy to calibrate and to handle.

The J17 has the advantage that one can measure on the surface of the stimulus.
(and when used in combination with J1803 it is cheaper).
And in addition it is not restricted to soly measuring Luminance, one can buy
just another type of head that suits the specific needs.
However one can not use it as a camera. This makes it difficult to
determine what is measured when the measuring distance is more than
severel centimeter from the source.

If you have more questions, or you didn't understand what the above
given information feel free to send me e-mail.
--
Rob van der Willigen | Institut fur Zoologie TUM
Phone: +49 89 3209 3750 | Lichtenbergstrasse 4
Fax: +49 89 3209 3674 | D-85747 Muenchen
Email: willigen@tyto2.zoo.chemie.tu-muenchen.de | Germany

In the UK, I've found the most useful people to be Micron, who
supply Photo Research Kit (which I would highly recommend). If you
need to know more, let me know and I'll try to dig out their
details.

NEIL PARRY
Clinical Vision Scientist,
MANCHESTER ROYAL EYE HOSPITAL
email: nparry@fs1.mci.man.ac.uk
phone: +44 161 276 5571
fax: +44 161 273 2028
smail: Vision Science Centre
Manchester Royal Eye Hospital
Oxford Road
Manchester M13 8WH
UK

There are smaller, less expensive spotmeters around but if this is going
to be your only or even primary photometer and you haven't $40,000+ to
spend on a Pritchard system, you might want to call Graseby Optronics in
Orlando, FL and ask for their catalog and price list. They market what
used to be UDT (United Detector Technology) line of radiometer /
photometer hardware. You can put together a reasonably good, fully
calibrated system to measure just about any kind of light you might have
bouncing around your lab. Photometers range from a hand-held optometer
(model GO352) at $475 to a multi- (8) channel IEEE-488 compatible
"poeer/energy" meter (model S390) for $8200+ (but in this case the "+"
means plus all the attachments NECESSARY to measure anything; e.g. the
detector head. At Wills Eye Hosp., I put together a system based on the
2-channel S380 meter and here I recently bought a system based upon the
less expensive single channel S370 meter. Overall cost depends upon the
exact configuration of your system and the number and kind of
calibrations you order.

Configuring a system with all the options and pricing flexibility they
have can be somewhat confusing, but the information sent with their
catalogue will help a lot and wo will their engineers if you get stuck
and call them.

The phone number that I have for Graseby is (407) 282-1408. The engineer
I talked with a couple of years ago when I configured my last system was
Jim Ritzel (at the same number). Perhaps they have a Canadian
distributor that would be more convenient for you but I don't see any
listed as I leaf through my old catalog.

Mike Fendick, O.D., Ph.D. Nova Southeastern University
fendick@alpha.acast.nova.edu College of Optometry
1750 N.E. 167th Street
(305) 949-4000 ext. 1408 North Miami Beach, FL 33162

We've had good success with measuring luminance and chomiticity coordinates with
the Minolta Cs 100 line of hand held photometers and chromimeters. Also Photo
Research puts out an extensive line of devices from scanning photometers to hand
held spot photometers. Their address is
Photo Research
3000 N. Holywood Way
Burbank, CA

Keep in mind that if it is called a photometer then it is by definition
already corrected for the human spectral sensitivity response, i.e. it reads
in cd/m^2 or footLamberts or milliLamberts or some other luminosity unit.

Bill Kosnik
TASC, Inc.
210-536-4798
william.kosnik@platinum.brooks.af.mil

I use the Minolta type, myself and I am glad to see that it is rated as
one of the favorite choices.

Regards,
Lucia M. Vaina

I checked the price for their luxmeter: 375US$ with NIST calibration
certificate. A good deal to me. [Refers to Optikon, Waterloo, Ontario]

Chengwu
chengwu@sciborg.uwaterloo.ca

These are some quick notes on some lab photometers. Use them as you see fit.
-Beau

Minolta CS-100

This is a simple hand-held colorimter which gives readings in xyY. The
measurement area is a disk of several degrees diameter, viewed from a distance
of severeal meters. It works fine. It also has a non-standard serial interface
which may be read with considerable difficulty by a parallel port and home-made
software on a lab computer. Contact Jeff Mulligan jbm@vision.arc.nasa.gov for
details.

Tektronix J17

We recently acquired a Tektronix J17 LumaColor Photometer with J1803 Luminance
Sensor head. This is a small, hand-held photometer with a separate suction cup
sensor suitable for luminance measurements on a video monitor. The package cost
about $1805. This device has moderate accuracy of about 5% +- 2 counts, and
has limited sensitivity at the low end. While measurements can be read directly
from a nice backlit LCD display, we bought it primarily because it incorporates
a serial interface (RS-232D) through which it may be connected to a computer
for automated calibration measurements. We have written a small piece of
software to read measurements from the photometer into a Macintosh via the
serial interface. It seems to work.

The J17 is designed to serve as a combined photometer/radiometer/colorimeter,
with the addition of appropriate sensor heads. We have only tried the
luminance head.

PS Don't forget to order the AC Adapter (we did).

Pritchard PR-880

If you have money to burn, demanding requirements, or have a
need to impress, you get the PR 880 for about $18,995. This device makes
photometric, radiometric, and colorimetric measurements with high
accuracy and sensitivity. Measurements can be read from the LCD
display, or via a serial interface/command language.
It has five standard apertures (0.125, .25, 5, 1, & 3 degrees). With
the standard MS-55 lens and a 3 degree aperture, minimum sensitivity is
3x10^-5 cd/m^2.

Andrew B. Watson
MS 262-2 NASA Ames Research Center
Moffett Field CA 94035-1000
(415) 604-5419 -3323 fax
beau@vision.arc.nasa.gov
http://vision.arc.nasa.gov/