heat filters?

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nanometer
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heat filters?

Post by nanometer »

I would like to get a heat filter for my microscope. I did a search here but couldn't really find a direct answer (maybe my search terms were not correct).

I see two different types: an absorbing filter and a dichroic-type heat reflection filter.

I guess my preference would be for a 0-deg reflection filter as something like the FM01 (thor labs) has higher transmission efficiency on the short side. My biggest preference would be for a 45-deg reflection filter and semi-transparent, because I already use a 45-deg plate-type beamsplitter in my Diavert to feed a flash beam.

What do you all use, and where do you get them? (on ebay, I found lots of absorbing filters but no dichroic type). Otherwise Thor or Edmunds would seem to work.

Thanks

Steve

Pau
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Post by Pau »

For non angled use this is likely what you want:

https://www.ebay.com/itm/Optical-Filter ... 0005.m1851

It also protects you from UV if you use a halogen lamp driven at high power

Also available in smaller sizes, although the Thorlabs price is pretty similar
The flash tube really doesn't need it and I would not want to direct the reflected IR to it
Pau

enricosavazzi
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Post by enricosavazzi »

Pau wrote:For non angled use this is likely what you want:

https://www.ebay.com/itm/Optical-Filter ... 0005.m1851

It also protects you from UV if you use a halogen lamp driven at high power

Also available in smaller sizes, although the Thorlabs price is pretty similar
The flash tube really doesn't need it and I would not want to direct the reflected IR to it
I am not so sure this NIR-rejection filter qualifies as a heat filter. Strictly speaking, to get rid of radiated heat you must reflect/absorb significantly higher wavelengths (2,000 nm and higher), while this filter has significant transmission already from 1,200 nm.

This filter certainly removes NIR, which is a big part of the direct emission of a halogen bulb (although not as much as an incandescent bulb). Heat indirectly generated within the illuminator housing may however pass through this filter.

The "old-fashioned" heat absorption filters are only partly successful, since they heat up quickly by absorbing NIR and then start emitting long-wave IR themselves. In the past, for heat-sensitive subjects like living organisms, I have seen relatively large water-filled laboratory flasks (1 liter or so) used as heat filters.

One would probably be better off by using a power LED to emit VIS, since they emit almost no NIR and never heat up enough to emit large amounts of thermal IR.
--ES

nanometer
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Post by nanometer »

Thanks Pau. I grabbed one, and I didn't see it on ebay as I didn't use search terms that would have showed it.

To be clear, I wasn't worried about the flash beam heat, but since I already have a flat beamsplitter in the system so I can use both the lamphouse and the flash, I thought it would be nice to combine both purposes together.

I would like to reduce my cooking of the protozoa to extend my look time into a sample.

Steve

Pau
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Post by Pau »

Enrico, you're probably right about long IR transmission. I have no info about the importance of it and at what extent it could arrive to the sample as the optical glass present in the illumination train and condenser has only partial transmission at that wavelengths
Likely combining it with a heat absorption one will solve it.

Steve, did you grab the Omega I linked?.
Pau

nanometer
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Post by nanometer »

Yes, I got the Omega. I have to agree though that heat is generally at much longer wavelengths than the NIR. I'll see if I notice a difference with this filter.

edit: I picked up a KG3 heat absorption filter too. Can never have too many filters :)

WalterD
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Post by WalterD »

Hi nanometer,

I was also searching for a heat (absorbing) filter and discovered one in my Orthoplan kit, Leitz sparepart no. 514 027.

Best regards,

WalterImage

Pau
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Post by Pau »

I have the very same KG 1 and BG 38 filters that came mounted together in a filter cassette from a HBO equipped Zeiss Universal microscope. They are absorption filters from Schott.
You can see their spectra at the Schott site https://www.pgo-online.com/intl/schott- ... lator.html

I don't use them because now I only use LEDs both for white illumination and fluorescence
Pau

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