Cheap and interesting filters in Edmund Optics shop

Edmund Optics has a huge sale for narrowband (bandpass) filters from uv, visible and infrared range. Those filters are priced much lower than average bandpass filters of such capabilities, but still they don't offer very high transmission.

What can be done with those filters? Experiments. You can match filter to helium or neutral oxygen bands. You can also try comet imaging with narrowband filters catching C2 emission at 514/511 nm or CN at 388 nm. Gas planets have a methane absorption band at 889 nm. Venus shows some cloud structure at 418 or 986 nm and in UV 350-370 nm. At 1010 nm you can try catching night side heat glow...

For astrophotography the 24,15 mm dia filters will be best. They need a 1,25" filter cell. For thin (max ~5 mm) filters plastic SkyWatcher Moon filter cells can be used. For those and thicker ones custom cells can also be used. Gerd Neumann can mount them in single or double Astronomik filter cells. If it's double cell then it won't fit in (nearly?) any wheel so you probably will also need customized Gerd filter drawer. There is also T2 holder for thin and thick filter.

Filters of 24,15 mm diameter will work with up to semi-sized sensors like 2/3" ICX285 in Atik 314L+ and alike. Bigger sensors like KAI-4022 in Atik 4000 with a 23 mm diagonal will have some vignetting.

But there is more... A filters that glow! Lumilass filters absorb UV radiation and glow in red, green or blue band - it's fluorescence glass. Green Lumilass has such spectral performance:

Green Lumilass

There are no astronomical case studies for such filters, but for CCD cameras QE is very low in ultraviolet (unless you have a UV specific camera). So it could allow much better UV performance for average cameras with scopes that don't absorb UV.

For managing IR lasers there are also phosphor coatings (phosphor coated CCDs or glass "filters") that convert for example 1550 nm to IR wavelengths that are within CCD/CMOS range). That doesn't seems to be cheap (1-3K EUR), but still much cheaper than an InGaAs SWIR camera. Phosphor converters (available in EO) are also astro-untested.


Astronomy and Astrophotography, 27 December 2011, Piotr MaliƄski

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