They say no good plan ever survives contact with the enemy, or classroom, or market, etc. First I had to find a 140mm objective with a 5.3 focal ratio. The sellers of objectives are not exactly thick on the ground. However, I got lucky in the form of Ales Krivanek at iStar Optical. Ales was just introducing a new 140 mm (5.52”) F/6.5 Apochromatic (APO) Fluorite Triplet. Combined with a 0.75x reducer/flattener I would get a focal ratio of 4.9. Slightly undersampled on a good night, but but I would rather be a bit under than over anyway.
So I took a gamble on the new design and placed an order. It wasn’t really much of a gamble as iStar has a good reputation around the web. I started on the optical tube assembly (OTA) design while I waited for the lens. It turned out I was going to have plenty of time to design. The COVID-19 pandemic hit and Japanese glass making ground to a halt.
Realty check indeed……
It was many months before Ales was able to fulfill the order, no fault of his. It was a time for all of us to be patient. While I was waiting, Starizona came out with a new 0.65x reducer/flattener called the Apex ED. And what was even more interesting was they had tweaked their design to work well with the new 140mm APO. Ales decided to offer the combination on his website and alerted me to the Apex’s availability. So I added it to my order.
Now I had a very interesting combination which yielded the following specifications:
Wow! The sampling is pretty much bang on for my average seeing. Perhaps a little undersampled under good skies but I don’t mind that. The focal ratio means it’s very fast compared to the old SCT. And because the field of view is so much wider I get the equivalent of a 12 part mosaic with the SCT in one exposure!
I can’t wait!