Broke my diffusion filter - need help figuring out what to do

[macnmotion]

I have a Nikon inverted diaphot, circa 1985. It came with a round filter that seems to diffuse the light from the halogen bulb before it reaches the condensor. It just got knocked off of the microscope and shattered. I assume that I need this diffusion to properly operate the scope? It's a phase contrast setup.

The problem (one of them) is that I live in Thailand. There will be no replacement here. I either have to order something from outside the country or figure out what I can do to replace it myself with some material I can find here. Can anyone help? In the user manual it's called "the diffuser."

The filter in question is the first one on the left in this photo:

filters.jpg (180.17 KiB) Viewed 2771 times

[blekenbleu]

I replaced a missing Optiphot illumination diffuser with a very generic glass round of matching diameter:
https://www.amazon.com/dp/B0041V9IX4

Note that it is described as "frosted", rather than "ground glass" or "diffuser", offering more search options.
IMO, illumination diffusion is a relatively uncritical; if heat is not a concern,
even a round of clear plastic rubbed against fine sandpaper for awhile might work.

[macnmotion]

I replaced a missing Optiphot illumination diffuser with a very generic glass round of matching diameter:
https://www.amazon.com/dp/B0041V9IX4

Note that it is described as "frosted", rather than "ground glass" or "diffuser", offering more search options.
IMO, illumination diffusion is a relatively uncritical; if heat is not a concern,
even a round of clear plastic rubbed against fine sandpaper for awhile might work.

Thanks so much. I'm not sure if plastic would be safe being so close to the lamp, but I can try. Finding something frosted is a good idea. I have a friend who would be able to cut the correct size if I can find some frosted glass. Tomorrow I'll try viewing without the filter to see what the difference is.

[apochronaut]

If the filter is close to the halogen lamp, it may be heat proof glass. I don't know your microscope but in some systems that diffuser is a heat shield, keeping the heat away from the collimating lens, a much more costly item to replace if broken.
if it is not a heat proof disc, I have a lot of them in several diameters and about 1mm thick. I can send you one packed securely in an envelope for the cost of the postage. I'm sure it would be less than 5.00.
I have sent some embedded in a piece of corrugated cardboard. They have all arrived safely.
If interested, send me the diameter. I'll see if I have a match.

[macnmotion]

If the filter is close to the halogen lamp, it may be heat proof glass. I don't know your microscope but in some systems that diffuser is a heat shield, keeping the heat away from the collimating lens, a much more costly item to replace if broken.
if it is not a heat proof disc, I have a lot of them in several diameters and about 1mm thick. I can send you one packed securely in an envelope for the cost of the postage. I'm sure it would be less than 5.00.
I have sent some embedded in a piece of corrugated cardboard. They have all arrived safely.
If interested, send me the diameter. I'll see if I have a match.

That's really nice of you to offer. How can I know if it's heat proof glass?

[macnmotion]

I believe the diffuser is not heat resistant based on this page of the user manual. It first lists the diffuser in step 11, and then discusses adding an optional heat absorption filter. Note that the filter holder on my scope is a different version than in this manual but the location is the same.

I'm wondering if I should eventually add a heat resistant filter. Actually I wonder if there is one already in there -- the scope was given to me without much instruction, I never thought to look. I can look (per Fig. 17). Also attached is a chart at the end of the manual, which again infers that the diffuser is not heat resistant. I'm trying to find the diameter.

Screen Shot 2023-02-10 at 22.57.15 copy.jpg (127.47 KiB) Viewed 2720 times

Screen Shot 2023-02-10 at 23.10.54.png (99.12 KiB) Viewed 2720 times

[Hobbyst46]

One type of heat absorption filter is Schott KG3 or KG5. They come in various sizes and thicknesses.

As a quick temporary test of the efficiency of diffuser, even a piece of baking paper can be used. It is (relatively!) heat resistant.

The problem with most makeshift diffusers however is that much of the brightness is lost to scattering. So a dedicated microscope diffuser would be best.

[BramHuntingNematodes]

Wet scrubbing clear glass with a high grit (800+) sandpaper can produce adequate diffusion. Do it by hand and do it outside!

[macnmotion]

If the filter is close to the halogen lamp, it may be heat proof glass. I don't know your microscope but in some systems that diffuser is a heat shield, keeping the heat away from the collimating lens, a much more costly item to replace if broken.
if it is not a heat proof disc, I have a lot of them in several diameters and about 1mm thick. I can send you one packed securely in an envelope for the cost of the postage. I'm sure it would be less than 5.00.
I have sent some embedded in a piece of corrugated cardboard. They have all arrived safely.
If interested, send me the diameter. I'll see if I have a match.

Here are the final details. The filter is not heat proof it's just a diffuser filter. It's 45mm in diameter. If you have anything that would work, I'd be more than happy to pay you for both the filter and shipping. Let me know via DM so we can share details. Again, I greatly appreciate it.

This morning I took a look without the diffuser and the resulting image is much harsher. Not sure if that's my own bias but I don't think so.

[apochronaut]

If the filter is close to the halogen lamp, it may be heat proof glass. I don't know your microscope but in some systems that diffuser is a heat shield, keeping the heat away from the collimating lens, a much more costly item to replace if broken.
if it is not a heat proof disc, I have a lot of them in several diameters and about 1mm thick. I can send you one packed securely in an envelope for the cost of the postage. I'm sure it would be less than 5.00.
I have sent some embedded in a piece of corrugated cardboard. They have all arrived safely.
If interested, send me the diameter. I'll see if I have a match.

Here are the final details. The filter is not heat proof it's just a diffuser filter. It's 45mm in diameter. If you have anything that would work, I'd be more than happy to pay you for both the filter and shipping. Let me know via DM so we can share details. Again, I greatly appreciate it.

This morning I took a look without the diffuser and the resulting image is much harsher. Not sure if that's my own bias but I don't think so.

I will check. Not sure if I have anything 45mm. give me a couple of days.

[macnmotion]

Some super glue has at last rendered the filter usable for now. It's not a long term solution, and I have no idea what heat will do to the glue, but I'll give it a try for now.

Here is a photo of the repair, followed by comparison images without (top) and with (bottom) the repaired filter (all settings identical). You can see that without the diffusion filter the contrast is very harsh, certainly not pleasing to my eyes. Photos taken with 40x oil immersion objective, and phase turret rotated about 70% toward the Ph1 annulus to give some oblique contrast (my current preferred imaging setting).

super glued diffusion filter.jpg (246.17 KiB) Viewed 2620 times

compare with and without diffusion filter.jpg (148.2 KiB) Viewed 2620 times

[apochronaut]

That one doesn't look to have that much diffusion to it.
The closest I have found so far are some light blue 37.5mm ground glass. If you are filtering a bit to the blue end anyway, those kill two birds with one stone as long as it can cover the beam enough.
I will keep looking. I have a box of filters specific to the AO 20 filter carousels but I know I put some other odd sizes in there too.

[dtsh]

Your typical superglue will be good to around 80C, but will break down beyond much more; there are formulations which are more resistant if you can't find any other solution.
I occasionally use it for holding small/thin parts for machining and hit it with a torch for a moment to break the glue.

[macnmotion]

Your typical superglue will be good to around 80C, but will break down beyond much more; there are formulations which are more resistant if you can't find any other solution.
I occasionally use it for holding small/thin parts for machining and hit it with a torch for a moment to break the glue.

Thanks. If what I used degrades I'll see if I can order something more heat resistant. I'm hoping it's only a temporary need, I'm trying to come up with a longer-term solution.

[apochronaut]

I gather you need the full 40mm and a neutral filter? I can keep looking.

[macnmotion]

I gather you need the full 40mm and a neutral filter? I can keep looking.

It's listed at 45mm. I should have the watch glass I ordered in the next 2 weeks, I can try to sand that down. I also wondered about diffusion film used with studio lights, not sure if that can withstand the heat. And a friend here has some thin acrylic. He can cut me a disk and I can try sanding that, but again I don't know about the heat from the halogen lamp. Something will work. I guess I should also see of I can find an official Nikon replacement somewhere online. I could have it sent to relatives in the USA who could send to me.

[apochronaut]

I don't have one that big, only rectangular and thick. A couple of thoughts. Heatproof plastic kitchenware is most likely Nylon, which has a melting temperature above that of boiling water, probably 230 F. or thereabouts. Some frosted item's bottom, coffee cup or measuring cup that you can verify as heat proof might be a donor. I would measure the temperature at the actual location after 15 min. at full power.
Or a frosted glass utensil , if you know someone who can cut it for you.
Another possibility is something from silicone rubber, a large spatula blade or bottom of a measuring cup for instance. I have seen transluscent ones. Cut thin to the right thickness. The melting temperature is very high, over 1000°. I would always verify the material and gest proof nature.
https://www.ebay.com/itm/185289206721?h ... R-7j9oLMYQ

[macnmotion]

I don't have one that big, only rectangular and thick. A couple of thoughts. Heatproof plastic kitchenware is most likely Nylon, which has a melting temperature above that of boiling water, probably 230 F. or thereabouts. Some frosted item's bottom, coffee cup or measuring cup that you can verify as heat proof might be a donor. I would measure the temperature at the actual location after 15 min. at full power.
Or a frosted glass utensil , if you know someone who can cut it for you.
Another possibility is something from silicone rubber, a large spatula blade or bottom of a measuring cup for instance. I have seen transluscent ones. Cut thin to the right thickness. The melting temperature is very high, over 1000°. I would always verify the material and gest proof nature.
https://www.ebay.com/itm/185289206721?h ... R-7j9oLMYQ

All good ideas, thanks a lot for them all. That's a smart idea to measure the temperature at the location, I hadn't done that. I'll do it on my next session which will certainly go longer than 15 minutes. I appreciate your having checked your supply, thanks again.

[blekenbleu]

45mm Diameter Microscope Optical Diffuser Frosted Glass
https://www.ebay.com/itm/275090743723

[Alan Smith]

You can frost most types of glass (borosilicate/Pyrex/ common soda glass) using sodium hydroxide solution. Cold and weak it takes a while, but at 0.2M solution strength (look it up) and a temperature of 20-30 C overnight is usually enough. The interesting thing about this method is that the surface is chemically etched evenly all over - no scratches etc.

The principal requirement for doing this well is to ensure the exposed surface is clean- no greasy marks etc. To frost one side only cover the other with PVC insulation tape and use it to hang your glass in the middle of the solution. I am obliged to point out that lye is extremely caustic and you should wear eye protection and gloves when messing with it. Also when you add the pellets of lye to the water (NEVER the other way around) some heat is evolved- add it too fast and the solution may boil - so do it bit by bit. Leave to cool before using it for frosting.

If you wish to check progress haul your glass out of the pot rinse it under the tap and blot dry- the frost effect is invisible until you do this. If it's too slightly frosted out it back and be patient.