>At  9:32 AM 2/8/96 +0100, Ciro Di Ciro wrote:
>>For example, I know that it's better use a XY step smaller than the beam
>>diameter of the laser.
>>Now, I know that the spot diameter of my 60X is 0.21 mm and the spot
>>diameter of the 100X is 0.23  mm.
>>My question is: do I have a better resolution with 60X instead of 100X ?
>>It is the opposite of that my logic suggest...have some confused ideas about
>>this problem.
>
and Shingo Kashima wrote:
>
>I cannot believe the spot diameter is so big such as 0.21mm. I am afraid
>you wrote mm instead of um(^_^;). The theoretical spot diameter is
>calculated with the following expression:
>
>  theoretical spot diameter = (2*wavelength)/(Pi*NA)
>
>If you are using Ar laser(WL=488nm) and objectives with NA1.4, the
>theoretical spot diameter is (2*0.488)/(Pi*1.4) = 0.22um.
>The expression above is under assumption that the Gaussian beam diameter is
>equal to the pupil diameter of the objective, and if the Gaussian beam
>diameter is bigger than that of the objective, the spot size becomes
>smaller. The pupil diameter of 100x objective is smaller than that of 60x
>objective if both NAs are equal, and the Gaussian beam diameter from the
>laser is generally constant, therefore theoretical spot diameter of 100x
>objective is smaller than that of 60x. So I suppose these differences are
>caused by an error in measurement or the aberration of objectives.
>
 
My guess is that the 100x objective is NA 1.3 and the 60x is NA 1.4 -
that's certainly the case with ours.  This would explain the difference
and yes, you would (and do) get better resolution with the x60.
Our Zeiss x63 NA 1.4 gives a significantly better FWHM on 100nm
fluorescent beads than the 100x NA 1.3, though this may be in part because
the x63 is a plan-apo.
 
                                Guy Cox