Overview

Mosaic Imager (Blanco 4-m Prime Focus)

The NOAO MOSAIC Imager II (as did the BTC before it) takes square filters 146 x 146 mm, 12 mm thick. We are slowly increasing our stock of filters in this size, so if you don't see what you need here, please contact us. What do we have, and what are the focus offsets?

SOAR and Schmidt

The SOAR Optical Imager (minimosaic of two 2Kx4K EEV CCDs) and the Schmidt use 4 inch square filters up to 10 mm thick. We have quite a selection of filters in this size, see the 3" & 4"filter list . Recent acquisitions are:

• Sloan digital Sky Survey (SDSS) set ugriz, 4 x 4 inch. cwl/fwhm are u (3513/628), g (4759/1430), r (6265/1483), i (7734/1500), z (9100/1400). These are nominal figures, note that the long wavelength cutoff for the z filter is CCD dependent.
• Calcium H&K filter, 4 x 4 inch. cwl/fwhm is 3960/100, peak transmission 50%.
• For SOAR - a dedicated Johnson-Cousins UBVRI set, an SDSS ugriz set, and a Stromgren uvby set.

Cassegrain focus imaging (1.5-m, 0.9-m)

For Cass imaging we use 3 inch square filters up to 10 mm thick. We have quite a good selection of filters in this size too. The cass filter wheel assembly has two wheels holding up to 8 3x3 filters each. We also have a single module that can hold 5 4x4 filters, so filters in this size can be used if we don't have a 3x3 equivalent.

Oh No! CTIO doesn't have the filter I need!!!

Now and then people have asked to use one or more of our 2x2 inch interference filters due to not having it in 3x3 or 4x4 inch size, being prepared to accept some vignetting. Be warned! Most of these filters are many years old, and some have seen a lot of use. If you want to use some weird filter it's better to (a) buy one yourself, or (b) convince us to buy it for you. Filters can take a long time to make (several months to over a year for the 146x146 mm narrow band filters). Prices vary with manufacturer, and the specifications you ask for, we can recommend if you like. Plan on spending $2500 - $5000 for a 146 x 146 mm filter, half that for 3x3 inch or 4x4 inch.

Alistair Walker 17 April 2000, updated 4 April 2006