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Hello Edrun,
The problem stems from the fact that you have much lower photon flux at
the focus with the 10x objective because of the lower numerical
aperture.  One thing you can try is to use a lower beam expander with
the 10x if you have any control over this with the Zeiss interface.
Another option is to zoom in to the region of interest as close as you
can.  This works because when you zoom, you put the same number of scan
raster lines on a smaller area.  The result is that there is more laser
energy per unit area over the course of a scan period.  Also, try to
slow down the scan so the laser spends more time in each spot,  and
increase the resolution of the scan as much as possible to concentrate
laser energy/unit area.
-Karl

Edrun Andrea Schnell wrote:

>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Hi everyone!
>
>We have a Zeiss LSM510 confocal microscope with a Coherent two-photon
>laser. We have done successful frap-experiments with the C-Apochromat
>40x/1.20W objective earlier, but now we have to change to the C-Apochromat
>10x/0.45W because of the experimental set-up. This has lead to problems
>with bleaching the samples, we're not able to bleach the ROI's
>sufficiently. We have a high effect out of the two-photon laser (~920 mW
>right after the cavity/~100mW after the objective for 780 nm). One thing
>that works from time to time is to crop the images before chosing an ROI.
>Have any of you had similar problems? Do you have any tips as to what to
>do about this problem?
>
>Thank you!
>
>Edrun Andrea Schnell,
>Dept. of Physics,
>Norwegian University of Science and Technology
>
>