Where to place filters in light path?

[gslab]

My Reichert Microstar IV has some broken light filter components. The blue filter has been removed (It's very common for them to break) and the Neutral Density filer has some "pitting". As a work around can I put new filters (maybe for photography) anywhere within the light path between the bulb and the condenser aperture? Has anyone made their own filters with glass paint/stain or gels?

[DrPhoxinus]

I have a 410 and the filters are a known problem.

I have successfully used filters right over the bottom lens.
One favorite of mine is a blue filter that screws on a telescope eyepiece

Gerard

[BramHuntingNematodes]

I think ND filters and blue filters can be put anywhere. I am not sure about diffuser best practice as my homemade scratched glass leaves artifacts when placed after the collector lens. It may be the scratch pattern is too coarse.

The neighborhood camera and film developing store was a staple in suburban America for decades and has by now all but vanished. Their outdated surplus stock is still being liquidated, and you can pick up lots of photographic filters, especially if you are not particular about the size, by the dozens cheaply. I bought a lot of 60 or so various quality glass filters, most in their original packaging, off of the 'bay for $25 recently(not at auction, but the listed price)-- it doesn't make sense to make them at this point.

[mrsonchus]

I think the theoretical-at-least best position is away from any of the image congugate planes, where any texture, pits scratches etc would be close to focus when the specimen is in focus - so keep them away from the sepecimen, the field-iris (who's edges are focused for Kohler) etc. Closer to the condenser's iris would be better I think, where it will not be focused with the image.
A really useful item is the linear rotatable variable ND filter as screwed onto camera lenses. I've used one and compared images whith those using 'fixed value' ND filters and found no difference at all. Blue filters are useful to counteract the red/yellow of filament lamps, including Halogen, which become more-so as they are turned down from their design maximum brightness. Here's a link to the type of variable ND that I have used in the past....

In my BX50 I have a blue filter for colour-correction and various fixed-value ND filters. If you're looking for a genuine Olympus blue (daylight-correction) filter I have a couple spare, with the Olympus boxes, that I could sell-on for a reasonable price.

[BramHuntingNematodes]

The fixed ND filters can be useful if your imaging depends on any manipulation of polarized light, as I think the variable ND filters work by cross polarization. I guess alternatively you could either introduce a depolarization mechanism into the train or utilize the polarization left over from the variable ND filter.

[gslab]

Thanks for the replies.
mrsonchus, can you define "image congugate planes" . That is definitely sounds like something that I should understand. And for the blue filter, is that a filter specifically for your BX50? what size is it, and would I put that over "light Port" like with the camera filters, or try to fit it into the space vacated by my missing filter?

BHN (love that moniker by the way) are all ND filters polarizing filters, or just the variable ones? can you make your own variable ND filter by putting two polarizing filters together?

[BramHuntingNematodes]

Thanks for the replies.


BHN (love that moniker by the way) are all ND filters polarizing filters, or just the variable ones? can you make your own variable ND filter by putting two polarizing filters together?

Just the variable ones as far as I know, however polarizing filters are quite common and also will dim the light. You can definitely make a variable filter with two polarizers, and photographic polarizers have rotation built into them already. Just screw two of the same size together and twist!

Deep blue filters, by limiting the refracted light to high frequency may enhance resolution, particularly when the light source emits a lot of red light like a tungsten filament. I admit the effect is very subtle when already using a low red filter on a camera lens and 5000k LED bulb, but there are likely other bottlenecks in my resolution keeping me. From the full benefits. You can fit it over your light source. It doesn't matter much where it is if it's clean.

[Charles]

Polarizers can be used as Neutral Density filters but Neutral Density filters are not polarizers.

[Hobbyst46]

Deep blue filters...You can fit it over your light source. It doesn't matter much where it is if it's clean.

If I place a glass filter directly on the glass cover of the field aperture (the beam port in the base of the microscope), for example, and even if it is not scrupulousely clean, it remains transparent and does not interfere with the image. However, if the filter is placed 5-10mm or so above the same glass cover, then every small dust speck on the filter is visible in the image.

[MichaelG.]

If I place a glass filter directly on the glass cover of the field aperture (the beam port in the base of the microscope), for example, and even if it is not scrupulousely clean, it remains transparent and does not interfere with the image.

... and Koehler wins again !!

MichaelG.