2 replies to this topic

[rmorein]

See

 

Six-in-One Adjustable 58mm Infrared IR Pass X-Ray Lens Filter 530nm to 750nm Screw-in Filter for Canon Nikon Sony Panasonic Fuji Kodak DSLR Camera

 

I have several 55mm and 58mm lenses to which 2" filters can be adapted, but with light loss. That  is one motivation. The other is the possible utility of a variable passband.

 

Aside from general quality issues, and high unwanted transmission out-of-passband, this filter appears to incorporate a polarizer. Does this automatically imply a 1-stop minimum loss, even in passband?

 

Opinions?

Edited by rmorein, 08 November 2024 - 12:24 AM.

[PEterW]

Hmmmm, here is an industrial version with clear data on the bandwidth performance, but it costs a bit more.
https://www.thorlabs.com/newgrouppage9
The picture explaining how this cheap one works makes no sense, it could just be a red filter with a set of polarisers(???), so may not tune with wavelength. If someone has a spectrometer that goes out into the near IR it would be very interesting to measure the actual bandpass and how it varies with the tuning, then we could understand exactly what we’ve got. With NV filtration the strength of the blocking out of the pass band is as important as the band that is passed, as this affects the contrast in the image.
You could do a quick test with a few known wavelength long pass filters (eg 685, 780, 850, 930nm) and an NV unit. Tune this filter to visible red and then pop on the NV with a known long pass as well, then tune the variable filter to longer wavelengths. If it works as advertised then you should begin to see an image as the filter bandpass moves into the long pass filter pass and. Repeating with a different cutoff long pass filter should show that the tune angle needed to reach the known long wavelengths changes.

Peter

[rmorein]

A  crude test, pointed at a CCFL lamp. At the 750nm mark, complete extinction toi my eye. At 530 nm, a saturated red. As one moves away from complete extinction at 750 nm, yellow is immediately, clearly evident. Moving towards 530nm, there is no evidence of yellow increasing relative to red.There is no evidence of a sliding corner frequency.

 

The cell is nicely made.

Edited by rmorein, 09 November 2024 - 08:12 PM.