Polarization analyzer being used without polarization on the condenser, what would happen?

[Topcode]

I am thinking about DIYing a polarization setup for my swift M10T microscope, because well, it doesn't really have any built in support for such a thing. This isn't really too big a deal, there are a pretty large number of examples of people using polarizing film/filters on scopes that don't have built in support. The issue is, I really don't want to get dust on my camera, because dust on a camera means you need to take flats, and flats are really hard/impossible to take with microscopes (at least, with my SMZ-U they were impossible for a few reasons, I assume similar reasons apply to compound microscopes). So this means, I would probably leave the analyzer in, just 24/7, because otherwise I would risk dust.

So, when using dark field, bright field, rheinberg, oblique, etc, what impacts would leaving an analyzer in, but not polarizing the light from the condenser, cause? Besides the general dimming from the transmission that is. Would it be fairly noticeable?

[PeteM]

A good quality polarizer (becoming an analyzer, where you're leaving it) should be OK. It will lose a few percent of light and provide two more surfaces to degrade contrast. Best if they are coated.

If you have a trinocular head, there's probably a way to get an image to your sensor in a way that is sealed from dust.

[Topcode]

A good quality polarizer (becoming an analyzer, where you're leaving it) should be OK. It will lose a few percent of light and provide two more surfaces to degrade contrast. Best if they are coated.

Only a few percent? wouldn't it block over a stop of light, since the light would be unpolarized coming into it?

If you have a trinocular head, there's probably a way to get an image to your sensor in a way that is sealed from dust.

Well it will be sealed on the trinocular, until I would take it off, and remove/add the polarizer, then it becomes vulnerable to dust for a period of time. Which yeah, would probably be only be maybe less than a min at a time, but thats more than enough time for dust to get on it. On my SMZ-U microscope, the camera has left its position on the trinocular maybe twice in its lifespan, for less than 30 seconds before being covered up with a cap, and is as a result, completely dust free. And on my telescope, where I regularly swap filters, dust builds up quite fast on the camera sensor, and has to be blown off or cleaned fairly often, or corrected with flat frames, which due to having multiple objectives, different illumination, and condenser iris positions, is more or less impossible to do on a microscope.

[Tom Jones]

I used to work in a clinical lab where the urinalysis microscope, a Nikon Labophot 2, had an analyzer mounted at the base of the binocular head. That meant that all we had to do to check crystals for birefringence was to put the polarizer over the light output port. It worked pretty well and was barely noticeable. A couple of the techs didn't even realize what had happened when all they needed was the analyzer for a quick pol exam. Our service guy had put it there to make life a bit easier.

No that I think about it, I was given that microscope a couple years ago when they upgraded to an Olympus. I haven't checked to see if the analyzer is still there. It's on my to-be-overhauled shelf.

Give it a try. It can't hurt anything and it will be easy to remove if you don't like it. If you're in a decent environment dust won't be an issue during the swap.

[Topcode]

I used to work in a clinical lab where the urinalysis microscope, a Nikon Labophot 2, had an analyzer mounted at the base of the binocular head. That meant that all we had to do to check crystals for birefringence was to put the polarizer over the light output port. It worked pretty well and was barely noticeable. A couple of the techs didn't even realize what had happened when all they needed was the analyzer for a quick pol exam. Our service guy had put it there to make life a bit easier.

Do you remember if there were any specific artifacts that made it more noticeable compared to observing without it?
Either way, that is definitely reassuring to hear! Thanks!

[Scarodactyl]

It might cause issues in some heads if they have e.g. prisms that interact with polarized light. In that case you might want to use a circular polarizer with the wave plate side oriented up.

[PeteM]

Our eyes' response to light (as with sound) is a log function, so while a single uncrossed polarizer may lose a stop of light it isn't particularly noticeable. For some microscopes we outfit for kids, a polarizer is kept semi-permanently between the head and stand. If it's of decent quality, it's not noticed.

There can be cases (such as heads with non-strain-free glass that Stephen noted) where it's a problem or when you need every last bit of light for something like high magnification DIC. In those cases, you can replace the polarizer/analyzer with something like a clear UV filter.

[Topcode]

That's a good point about strain/other interaction with polarization, that could cause issues. Hopefully the optics in my scope are relatively free of that stuff, but I guess I wont know until I try it.

Yeah, the human eye is pretty good at its job of seeing (well, most peoples are, mine are a bit subpar in terms of being functional) but modern cameras have often around 6-8 stops lower dynamic range than the typical human eye, so they are a lot less flexible, though I can probably just increase the lighting and be fine. I prob wont even use the eyepieces more or less at all, I tend to use live view from the camera on my other microscope, its just easier to me.

[Alexander]

An average pol filter cuts about 75 % of light out, but as others have mentioned, this is barely noted by the human eye. A camera needs two stops more to expose pictures properly.

There will be no problems leaving the analyzer in all the time.