Should I buy a microscope with infinity corrected optics?

If you want to buy a new device from one from the “big four” microscope manufacturers (Olympus, Nikon, Leica, Zeiss), then you probably have not much choice anyway. Originally, infinity optics were reserved for high end research microscopes, but in the last years the companies started to change their complete line of microscopes and are now increasingly offering infinity optics also for routine and laboratory microscopes.

The advantage of infinity corrected optics is not so much image quality, but rather the flexibility of being able to add filters into the light beam without changing the focus of the microscope. The microscopes can therefore be modified in a more flexible manner.

If you go for infinity optics, then you are bound to a particular manufacturer. Infinity optics are not interchangeable between manufacturers, because there is no uniform standard. If you buy an infinity microscope from a smaller company, then be aware that they might not have a large of a selection of parts. I have heard of cases when people were in need of a particular infinity objective for their microscope, but had problems finding one, because the company was too small and only manufactured a small number of these particular objectives. Consequently, the available parts were quite expensive.

Most low cost educational and routine microscopes do not use infinity corrected objectives, because the manufacturers are too small to justify the establishment of their own infinity standard. There is still a large market for the older DIN 160mm standard and there are plenty of them on ebay. If cost is an issue, then you most likely will not go for infinity microscopes. If you are interested in DIC microscopy, then most likely you will need to go with this standard.