If you are not blessed with having extremely deep pockets and rather want a more budget-friendly solution that operates at the sweet spot of price and quality, higher magnification comes with the tradeoff of having lower focus depth. This means for smaller droplets getting everything into focus becomes a more elaborate task than you might wish. Also, drops that are shooting at an angle will start blurring faster. In traditional image processing, this leads to lower accuracy for detected edges and the detected object size can vary significantly.

On the bright side, there are ways to correct this. On the darker side, they start to get into Bessel-Functions and more complex mathematical modelling really fast (for those interested, I can highly recommend the PSF-Generator as an online tool). To simplify the process for users and still get the benefit of blur-resistant image processing, we have modelled the defocus blur and included it into our new software for the UltiStrobe and NanoStrobeX.

But what does that mean? It does not mean that focusing will be irrelevant in the future, but it means that even blurry drops can be calculated with high accuracy (left image - upper right number in white indicating the blur index). And yes, I did a bit of cherry picking here by selecting two great images. But it is backed by the statistics (right image) showing that the relative volume deviation fluctuates below 2% with a CV/RSD of less than 1% across the whole measurement range. Considering the high blur, these are great results for the non-linear effects of real world optics.

Note: The tests were conducted with a 150 µm diameter (nominal value) circular object etched into an optical glass. The off-focus distance was measured with a 10 µm accuracy. For the calculation of the mean and standard deviation 1000 images were taken at each position. An UltiStrobe Demo Stand with a magnification 2X lens was used for image acquisition.