58mm Square Filters For The IFW-3"
The new 58mm square filter standard from Optec offers a clear diagonal measure of 79mm or 3.1 inches. This size makes full use of the aperture available with the 3-inch line of Optec instruments. The large 35-37 mm square CCDs are covered without vignetting with these filters.
These filters have the same quality and transmission specifications as our popular 50mm round LRGB H-alpha and OIII filters. Scratch and dig is held to 60-40, wavefront distortion to less than 1/4 wave, and peak transmissions greater than 90% in the pass band. Filter thickness is 2mm.
Finally, the price of the Optec 58mm square filters is less then the premium 50mm square filters available from others. A complete set of LRGB and H-alpha filters to fill one of the 58mm square 5-position filter wheels for the IFW 3" cost only $1590.00. This set includes The LRGB set #17274 and the H-alpha filter #17275.
Shown above is a diagram based on the new PlaneWave CDK 12.5 inch telescope which has a f/8 cone and a wide well corrected field. Cameras with the KAF-09000 CCD have a diagonal image area that is 52mm accross. A 50mm square filter would have to be mounted within 5.4 inches of the CCD to avoid vignetting the corners. This would not allow the use of TCF-S3 to be used between the filter wheel and the camera since its back-focus distance alone is 5.5 inches to the mid point of travel. The use of 58mm square filters provide about 9.5 inches between the filter and CCD which allows the TCF-S 3-inch to be used. Having the filter far from the CCD avoids shadows from dust spots or filter defects from effecting the image. In addition, the ghost images and halos from multiple reflections between the filter and the CCD surface are also reduced.
Additional Tabs and Spacer Kits
If you are in need of additional tabs. spacers, or screws for your IFW/IFW-3 filter wheel, call or email Optec to purchase one of the following kits:
- #17580: Tab and Spacer Kit for Eight 25.4mm Round Filters
- #17581: Tab and Spacer Kit for Five 50mm Round Filters
- #17582: Tab and Spacer Kit for Five 2-inch Round Filters
- #17585: Tab and Spacer Kit for Six 50mm Square Filters
- #17585: Tab and Spacer Kit for Five 58mm Square Filters
- #17587: Tab and Spacer Kit for Nine 50mm Round Filters