Dear Tamara Buijs,

Can you rise the equipment with dry nitrogen? This is the usual way to prevent condensation even for very low temperatures.

Regrads Michael

I have some dry nitrogen that I use for the low-vibration airtable. You mean just blow that onto the bottom of the coverslip? 

That will help.

I will give it a go, thanks!

Whenever something like this happens it is due to a temperature differential, where moisture will form on the colder surface (think of a glass of ice water in a 24C room).  We have had this issue often in environmental chambers that heat from below and get condensation on the top of a culture dish.We solve this by heating above the dish to equal the temperature. Air flow should help but you may need to cool the entire area below the coverslip (I'm assuming your using a cooling stage that uses conduction).

Hi Andrew,

Thank you for your answer.

I actually cool the cells on the coverslips by perfusing cold solution over it.

The temperature of the cells can be changed really fast this way, but I don't have any way of controlling the temperature of the stage unfortunately.

Update!

I have solved this problem by using an immersion objective.