Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

If you are interested in the transmission characterisitics of the 
material of the objective, the NA should not be a big 
issue. You can put an iris in the 
beam and make it thin before entering the objective. Do take the iris 
transmission as the baseline (this of course will tell you nothing about 
the transmission of the peripheral, high angle rays)..

With an iris and with no integrating sphere available, you should still be able 
to get a reasonable estimate of the wavelength dependent transmission 
from a simple spectrophotometer.

Sudipta

On 
Mon, 3 Sep 2007, Mark Cannell wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Hi Andrew
>
> While I can see that method would work for lenses designed to work in air, 
> wouldn't total internal reflection be a problem for lenses with an NA over 
> 1.0? The only way I can think of doing it is to use two objectives of the 
> same type looking at each other at a common focal point with the right 
> immersion medium between them. Then the overall transmission would be half 
> that of a single lens...
>
> Cheers Mark
>
> Andrew Resnick wrote:
>>  Search the CONFOCAL archive at
>>  http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>>
>>  We've done similar measurements, it's not too difficult.
>>
>>  The main trick is handling the large NA lenses.  Our setup was light
>>  source -> objective -> integrating sphere -> spectrometer.  After
>>  normalizing to the source, we obtained really good data.  It's pretty
>>  easy, actually.
>>
>>  Andy
>> 
>>
>>  At 08:45 AM 8/31/2007, you wrote:
>> >  Search the CONFOCAL archive at
>> >  http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>> > 
>> >  Dear all,
>> > 
>> >  one of the main differences of objectives is their transmission 
>> >  efficiency at certain wavelengths. One way to compare this is the 
>> >  trial-and-error method, however, this is not straight forward.
>> > 
>> >  My idea is to use a combination of spectrophotometer and a lamp with a 
>> >  more or less even spectra (i.e. Xenon) on some kind of optical bench. 
>> >  This would make the setup independent from the manufacturer. Beside the 
>> >  distance between the light source and the detector, there are obviously 
>> >  more things to consider: different diameter of the back focal plane, 
>> >  different focal lenghts...
>> > 
>> >  I would like to hear about your opinion about how to measure objective 
>> >  transmission. Have you ever done this in your lab? Did you find a setup 
>> >  that worked for you?
>> > 
>> >  cheers,
>> >  Michael
>>
>>  Andrew Resnick, Ph. D.
>>  Instructor
>>  Department of Physiology and Biophysics
>>  Case Western Reserve University
>>  216-368-6899 (V)
>>  216-368-4223 (F) 
>
>

-- 
Sudipta Maiti
Dept. of Chemical Sciences
Tata Institute of Fundamental Research
Homi Bhabha Road, Colaba, Mumbai 400005, India
91-22-2278-2716
www.tifr.res.in/~biophotonics