Since I made the decision in January 2015 to sell my Celestron C8, I have made several changes to other parts of my setup which have again made an 8″ Catadioptric Scope a realistic prospect on my mobile setup. At Kelling Heath Star Party in 2015, I bought an iOptron Minitower II Alt-Az mount, mainly as a smaller alternative to the HEQ5 for visual and Electronically-Assisted Astronomy. That, combined a Starlight Xpress Lodestar has meant that I was ready to go back to trying an SCT or similar scope again, it was just a matter of waiting for a good used one to come along, as they tend to be quite pricey on the used market.
However, finally, I had the chance at an 8″ Meade LX90 ACF OTA (Optical Tube Assembly). This was originally a fork-mounted tube that has been ‘de-forked’, and I got it for a very good price at an Astronomy event, as it had no mounting hardware to speak of, and was cosmetically not perfect due to having a few dents taken out of it after a tumble. It was being sold by a very reputable dealer, who had refurbished it himself, and I had no qualms about trusting his record on these sorts of things (quite rightly it seems after testing…). A friend who has the skills and tools was good enough to knock up some very sturdy radius blocks to attach it to from 30×30 aluminium bar.
It comes with UHC (Ultra-High-Contrast) coatings, and Meade’s ACF optical system, which uses a parabolic secondary mirror along with a modified corrector plate to provide a very flat field right to the edge of the field of view. Although it looks similar to one, it’s optical system is different enough that it isn’t regarded as an SCT. Although having a very flat field to begin with, it has the slight disadvantage that it isn’t 100% compatible with the normal f/6.3 reducer/flatteners used on standard f/10 SCTs, as the ‘flattening’ function of these isn’t required, so they end up over-correcting the edges of the field. Therefore, I’m still on the hunt for a suitable reducer that doesn’t also have a flattening function.
This OTA sits beautifully on the iOptron Minitower II for visual and also Electronically Assisted Astronomy with the Lodestar. The total weight of the tube, finder, diagonal and target EP is about 8Kg, which is just over half of the payload of the diminutive Minitower. So far, the results for visual have been great. I’m yet to test it with the lodestar, but I’m hoping it’ll be good for smaller objects such as galaxies and planetary nebulae.
Visually, I’ve had some marvellous views thorough it. The field is very flat, even across the whole field of my 28mm 68 degree Maxvision eyepiece. Its light enough to grab-and-go in the car with the iOptron MiniTower II and my eyepiece cases for a session at my Society’s out-of-town dark site. The Minitower II itself is a dream to quickly set up and get going, and the GoTos with it are very accurate even after a single star alignment.
All-in-all, a great investment that has already had plenty of use visually, and will be getting tested for imaging and Lodestar Live usage in the near future. Watch this space!