So, I just can't stop.
I snagged an Istar 8" F9 achromat objective about a month ago. I did a previous lite weight OTA wrapped around a similar, no-name lens that was of "OK" optical quality, even when stopped down to 6.5". The OTA build came out good but I parted that scope out due to the under-performing objective.
But I've always wanted to take another shot at one if I ever came across an Istar 8" F9 objective so when one showed up here and on Amart, the owner and I came to agreement on price and I took delivery of the lens.
Here is a very preliminay DPAC in "green" of the objective. Just hover the cursor over the pictures to read the titles. I'll post others in other colors once I have it in an OTA.
Overall, it is a decent lens with maybe 1/5 to 1/6 wave of over-correction in green and a little bit of a regional turned edge (which completely gone at 7.5" aperture). At focus, not shown, the lens is fairly smooth but shows a broad, shallow bowl/hill over its surface which I suspect accounts for the over-correction.
And speaking of the over-correction, This is the second fast achromat in a row that has shown over-correction in green. The other, a 6" F6.5, is documented in this OTA build thread:
All of my previous achromats were neutral in green or slightly under-corrected.
Other than the narrow turned edge and ratty green light used for the 8" (a green LED party bulb, which is a normal LED bulb with a plastic green cover, hence the yellow and blue fringing), the 6" and 8" are really very similar to each other in overall correction. Maybe both are sourced from the same vendor in China. Not shown was a quick look at the 8" with a 7" aperture mask, which did indeed clean up the edge as well as reduce the over-correction somewhat. I may have finally found a use for my Chromacor U2.
I will update as the build progresses.