Melting 3D printed patch stops

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EVILsteve
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Melting 3D printed patch stops

#1 Post by EVILsteve » Wed Jan 12, 2022 5:35 pm

This is on a Nikon alphaphot with a 3d printed holder and patch stops for darkfield mounted right below the condenser diaphragm. The petg starts to melt within 3 minutes if the light intensity is much more than about 1/3 to 1/2 the full brightness or more. It does this right below the iris opening where the light is concentrated from the light source. Is this normal? It's not convection heat from the halogen as I can sit one of the patch stops on top of the light source without melting it just where it seems to focus right below the abbé condenser.

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josmann
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Re: Melting 3D printed patch stops

#2 Post by josmann » Wed Jan 12, 2022 7:30 pm

Hi Steve,

I don't know about this scope in particular, but I would be surprised if any scope was melting filters when properly aligned. I could see a little heat warping or softening but are you saying the light is being focused down to a point at the iris and you're getting melting like you'd get with a magnifying glass focusing the sun? That's definitely not what the light field should be like! It should be rather broad, evenly spread, and roughly cylindrical as it impinges anything at the iris plane.

dtsh
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Re: Melting 3D printed patch stops

#3 Post by dtsh » Wed Jan 12, 2022 8:11 pm

If I am undestanding correctly, that seems like an awful lot of IR if it isn't simply heat coming off the lamp housing, perhaps there's a missing IR filter?

EVILsteve
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Re: Melting 3D printed patch stops

#4 Post by EVILsteve » Wed Jan 12, 2022 8:42 pm

It's just like a magnifying glass and the sun. I'd held sheet of paper vertically to see the beam path and it's focused but not pinpoint like you'd try to achieve with a magnifying glass. I'd wondered about IR there is no filter that I'm aware of unless it's the clear cover over the light source lens. I ordered a blue filter thinking that would stop some red light.
It fully melts the stops though. I designed a holder with a slot they slide into and it mets them enough to droop and necessitate cutting it out. Even tried printing new stop holders and moving the stops higher and lower to get it out of the focused spot thinking I'd happened to pick a bad spot but I'm just moving a few mm either way and could achieve better results.

Makes me wonder what I've been doing to my eyes.

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josmann
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Re: Melting 3D printed patch stops

#5 Post by josmann » Wed Jan 12, 2022 9:15 pm

Hmmm, we need someone with alphaphot experience here to understand how this might happen. My best guess is that it's missing a diffuser element somewhere but I'm not sure if these had one - same re: IR filter. Halogen bulbs definitely put out enough heat and light to melt stuff if focused to a point but the illuminator system shouldn't be focusing this light so strongly. If you hold a tissue paper between the field lens and the condenser and move it up and down, it should pretty much be a circle with the diameter of the field lens all the way up and down.

EVILsteve
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Re: Melting 3D printed patch stops

#6 Post by EVILsteve » Wed Jan 12, 2022 9:37 pm

I believe I'm missing a piece I do not have the protruding section on the bottom past the mount like this one on eBay that looks like it has a diffuser attached. theres a frosted lens directly above the bulb. I will confirm this when I'm back home tonight.


https://www.ebay.com/itm/144304671443?m ... olid=10050

Holding a tissue up shows slight focusing from memory checkibg that the other day is guess it would focus at least a meter above the top of the scope.

Hobbyst46
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Re: Melting 3D printed patch stops

#7 Post by Hobbyst46 » Wed Jan 12, 2022 9:52 pm

A blue filter is not an efficient blocking filter. To block halogen radiated heat (namely, IR) you need an IR blocking filter. For example, type KG5 from Schott, Germany or equivalent.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

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josmann
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Re: Melting 3D printed patch stops

#8 Post by josmann » Wed Jan 12, 2022 9:58 pm

EVILsteve wrote:
Wed Jan 12, 2022 9:37 pm
I believe I'm missing a piece I do not have the protruding section on the bottom past the mount like this one on eBay that looks like it has a diffuser attached. theres a frosted lens directly above the bulb. I will confirm this when I'm back home tonight.
Ah, interesting, yeah that would make a lot of sense! 10 bucks is a nice price if that's all there is to it. Please take some photos if you can!

MicroBob
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Re: Melting 3D printed patch stops

#9 Post by MicroBob » Thu Jan 13, 2022 4:10 pm

Which colour does the stop have? PLA or PETG in black might become too warm just from the absorbed visible light. In this case a layer of aluminium foil would solve the problem.

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