OPTEC APUS 2.5X SCT WEBCAM TELE-EXTENDER FOR SCT 17374
Item No. 782-23170
Manuf. No. Optec 17374
For planetary imaging with a webcam, the Optec APUS SCT 2.50X (f/25 with a f/10 SCT!) gives the optimal focal ratio for capturing all the detail. The design of the APUS SCT 2.5X Extender compensates for some SCT aberrations. Broadband multi-layer coatings are optimized for 450 - 650nm passband & reduce reflections to less than 1% per surface.
In the last few years, an interesting and exciting development has occured in astro-imaging. The use of inexpensive webcams are now capable of capturing impressive views of planets and deep sky objects. A camera costing less than $200 plus software has allowed these cameras to compete with CCD cameras costing 10 times as much. However, the very small size of the imaging chip makes it impossible to adequately capture extended nebulae objects with the most common telescopes. In addition, the advantages these chips have in capturing planetary detail is limited because the pixels are not small enough. To solve these problems, Optec has developed the APUS SCT set of WebCam Adapters, the APUS SCT 2.50X Tele Extender and the Optec APUS .36X Reducer (sold separately).
Optec APUS 2.50X Webcam Tele Extender for SCT
An extender optical adapter presents some additional challenges to the design process. In addition to a well corrected optical system that compensates for some of the SCT aberrations, the Optec Apus 2.5X Tele Extender is also manufactured with a reticule quality surface polish of 20-10 (scratch-dig). This feature reduces the amount of scattered light, which will result in an increase of contrast for subtle planetary surface features.
With an SCT of f/10 focal ratio, the Apus 2.5X will extend the f-number to f/25. Additional increase in the magnification will not result in an increase in resolution. At f/25 and considering a perfect optical system, Airyııs disk at 550 nm is already over 30 microns in diameter and would be sufficiently over sampled by the CCD array (7 micron pixels) to give the maximum resolution.
As can be seen from the APUS SCT 2.5X performance diagram, the MTF curve of the Apus 2.5X is very close to the diffraction limit and further correction really would not result in greater resolution. As mentioned before, the high degree of surface polish to increase contrast is the main advantage of this optic. In addition, all surfaces are given a muti-layer broadband coating that reduces the average reflection to less than 1% per surface from 450 to 650 nm.