71FL Astrographs

Since the dedicated tube is not ready yet, I try to use 7025 and a special tube which was machined before. Total tube length is 110mm.  Fortunately, by chance, this length looks quite right.  It has been focused around one third of focuser at the infinity.  Also as expected, focusing point is close each other between 7866 and 7704 super reducer.  This setup allows to focus from the infinity to 7-8m distance object. So,  at this moment, 110mm looks right length both for 7866 and 7704. See initial setup,

71FL + 7704 (260mm F3.6)

71FL + 7866 (260mm F3.6)

Now 7866 can be used with Series 80 scopes. Feather Touch focuser may be simply replaced with helical focusers. One issue is the weight balance. As you can see, it’s way back heavy, especially with 7866. I guess Takahashi’s FS-60C tube holder should be good one since it is designed to offset the unbalanced OTA. I will double check  by such a holder I own.  I will make star test in these setup over the weekend. Once I look at the image thru camera viewfinder, wow I was asking, did I see such a bright and clean viewfinder image before? It’s quite bright optics.

~ by tedishikawa on July 28, 2010.