15mm Altair ULTRAFLAT

[Nightspore]

I originally acquired the 15mm Altair ULTRAFLAT in April 2019 for my 80ED DS Pro Evostar. It was a month later that I managed to get first light with the 15mm Altair EP. Fast forward a couple of years and it really hasn’t been used since then. There are various reasons for this situation. I initially bought the ULTRAFLAT eyepiece to solve a weight problem. Not my weight obviously as I’m a bit skinny. A 15mm focal length EP gives a 2mm exit pupil for 40x on the 80ED, which is a great mid-range magnification for the scope, particularly for many open clusters.

 

 

At the time I carried the 80ED out in its supplied ‘Jason Statham’ hard case instead of a soft (and therefore lighter) bag. The case had provision for accessories, including eyepieces. Progressively over time the case seemed to get unnaturally heavy. I was taking a 15mm Celestron Luminos out in the case among other eyepieces and assorted accessories. I’m one of the few people who actually like the Luminos range. The eye relief and eye placement suit me and the overall ergonomics are very good. The 82° FOV and large field stop are outright luxurious. I even like the twist-up eyeguard and excessively shiny housings (well sort of).

 

 

I can live with some of its peccadilloes like the slight edge of field brightening and occasional glaring. However, I just can’t live with its weight. The Luminos is 140g heavier than the 15mm Altair which is just over 200g. I have a much smaller 15mm GSO SuperView, and although I like it a lot, it just wasn’t the same. I even have a 16mm T5 Nagler which is very lightweight and the dreaded ‘ring of fire’ wouldn’t be a problem for rich field. I’m not a fan of long eye relief and can tolerate quite short lengths for lunar and planetary viewing. I’ve always considered the T5’s 10mm relief was ample for concentrating on high magnification targets but I wasn’t keen on it for low power sweeping. The Luminos was also unwieldy in the 80ED’s stock focuser which doesn’t rotate.

 

 

The ULTRAFLAT series were apparently designed in the US by Mark Ackermann and are actually manufactured by Kunming United Optics. APM owned the exclusive rights for two years. They are now sold under a variety of brand names and housing liveries. Although the range has ‘only’ a 65° AFOV they were reputed to have a very flat, sharp field.

 

 

It’s very similar in size and weight to a 19mm Tele Vue Panoptic and even resembles it in many respects. It had 5° of field over my 15mm TS Optics Planetary EP and was smaller and more compact. The barrel had no undercut but was equipped with Baader-style safety kerfs. Which is almost as good as a smooth barrel.

 

 

I was quite impressed with the Altair when I first used it with the 80ED. It was easily rotated in the diagonal. The field was incredibly flat with a dark background and the colour separation and acuity were superb. As far as I could tell it was like this right up to the field stop with no discernible chromatic or spherical aberrations. I could detect no eye placement issues and the purported 16mm eye relief felt comfortable for rich field sweeping.

 

 

However, the rubber eyeguard seriously started to bug me. There’s nothing actually wrong with it and it can be rolled down out of the way. For most people it wouldn’t really be a problem. I’m partially paralysed in my right hand and arm. So fiddling about with stubborn rubber eyecups can regularly involve getting greasy fingerprints on the eye lens.

 

 

Recently I’ve discovered that I have a spare Baader lens cap that fits the eyepiece with the guard rolled down. This does change things a bit and I plan to use this lightweight eyepiece with small aperture grab and go refractors more often.

 

 

I ended up with a 15mm TV DeLite for the 80ED. I replaced the stock focuser on the Evostar with a MoonLite rotating crayford.

 

 

Then finally with a Sky-Watcher (Long Perng) rotating Crayford.

 

 

Due to its light weight I intend getting the ULTRAFLAT out with smaller refractors, particularly my 60 EDF.