... The replacement lens for the poor one in my APM 152/1200mm ED arrived Monday December 2nd. Sorry for not posting earlier, but I've had quite a hard week at work, so I've not had much energy to post.
Would you believe it, if I told you, it was clear Monday evening, the same day the lens arrived? Well, it was. The seeing was not super good, but quite usable. Quite hazy, though, and very cold.
Interestingly, the new lens has a much lower serial number, 223 (the old one was 252).
I set it up shortly before dinner and initially, I wasn't very impressed. There didn't seem to be much of an improvement and I saw massive spherical undercorrection in the star test and ronchi test. There was, again, a halo around bright stars, although not nearly to the same degree as before. This was after almost an hour of cooldown. I was so disappointed I actually took the lens off the scope again to check if it was assembled incorrectly. This didn't appear to be the case. I put it back in and put the scope outside for an hour with the lens cap and the rear plug off.
An hour later, I tried again. Much better. The halo was *almost* completely gone and views were drastically improved. Low power views were insanely good in a 17mm ES92. Contrast was through the roof, considering the conditions. Despite somewhat hazy skies and a barely visible winter Milky Way I could see much detail in a lot of deep-sky objects, proving that the scope is a powerful deep-sky machine. Some highlights:
- M33 spiral arms and NGC 604 as a clearly visible little glow (71x)
- NGC 206 in M31. Hints of dark bands in M31 (71x)
- NGC 404 extremely obvious near Mirach (71x)
- NGC 7789 a huge cloud of pinpoint stars
- details in NGC 7662 at 600x
- details in IC 2149 at 600x
- NGC 2158 near M35 partially resolved (71x)
- hints of details in NGC 2022 (179x)
Once the scope was fully cooled to ambient, it began to deliver some impressive double-star views. Theta Aurigae was extremely easily resolved at 179x. I looked at Gamma Andromedae at 600x and the spurious disks were tight and sharp with hard outlines, albeit with maybe slightly too prominent diffraction rings. The first lens, #252, never showed views this good, no matter how long I let it cool, there was always a haze around brighter stars.
I suddenly discovered that it was well past my normal bedtime, so I mildly panicked at packed up in a hurry, so I forgot to do a ronchi test after the scope had fully cooled, which irritates me now. Ah, next time, I suppose.
I hope to soon get a clear night with the Moon high in the sky, so I can get a better assessment of the scope's capabilities as a planetary instrument. It clearly has enormous potential as a visual deep-sky instrument. A downside is that it apparently takes a very long time to cool down. I had not expected a cooldown time in excess of 1.5 hours for a doublet. Some planning ahead will obviously be needed and it's not a scope for quick views, at least in the cold season.