Explore Scientific 6.7mm

[Nightspore]

I’d been contemplating a wide angle 7mm eyepiece for my Sky-Watcher Evostar 72ED DS Pro for some time. In February (due to unexpected and unseasonal extremely clement weather) I had a couple of sessions using the 72ED in conjunction with a 7mm TS Optics HR ‘Planetary’ eyepiece. I was impressed with viewing the Orion Nebula and various open clusters including the Little Beehive at 60x, a magnification which seems to suit the Evostar for some reason. I tend to use the little 72mm Evostar either for high powered (around 120x ~ 168x) lunar/planetary viewing or low powered (around 12x ~ 30x) rich field observing. Deep sky observing at around a 1mm exit pupil with a small and relatively fast refractor was a decidedly new and interesting experience.

 

 

I considered a few alternatives including a 7mm Tele Vue Nagler, a 7mm Celestron Luminos, threading a Barlow element onto my 10mm Luminos, or a 6.7mm Explore scientific. After several seconds of contemplation the 6.7mm ES won. The Explore Scientific 6.7mm, 82° eyepiece is 90mm in length, 43mm wide, weighs 228g, has a 9.5mm field stop and an alleged eye relief of 15.7mm. It is also argon purged and waterproof. In the ED72 it gives a 62.6x magnification for 1°, 18’ and 32” of TFOV with an exit pupil of 1.1mm.

 

 

First light was with a rising Saturn. This was a relatively easy target to achieve focus with. I didn’t expect much at about 63x but despite transparency issues the well contrasted image was sharply defined. Having around one and a third arc degrees of field as Saturn tracked past was a bit of a luxury. The colours appeared slightly ‘cool’ as with other ES eyepieces I have but were very effectively and pleasantly separated in my opinion. I could see Titan and even some surface detail on Saturn itself. The Cassini Division was visible in the rings which also appeared bright and delightfully contrasted. The eye relief is probably close to what Explore Scientific claim although I couldn’t resist pushing my eye right up to the lens to get a sense of the whole 82º.

 

 

As there was a fair bit of low cloud, and I wasn’t exactly spoiled for choice, I decided to have a butcher's at some of the brighter stars. Arcturus looked good and was a rich orange-red colour (to my eyes). The binary Cor Caroli split into its constituents nicely revealing the colours of both stars. Due to the transparency it took me longer than I expected to locate M3 with an 82º EP. Its faint fuzzy white core was satisfyingly impressive at this magnification. Albireo in Cygnus was another obvious choice. The rich star fields of the Summer Triangle are best observed at lower magnifications but it was fun sweeping around them. The 6.7mm is well corrected almost to the edge of field. Brocchi's Cluster aka ‘The Coat hanger’ was a bit close-up at 62.6x. M27 could also be glimpsed. Mu Cephei aka Herschel’s Garnet Star was very nice and I started to sweep Cassiopeia and Perseus. The Owl Cluster was large and beautifully framed in the field of view even if the ‘owl’ was technically upside down. The show stopper was the Perseus Double Cluster. I could get both clusters comfortably in the field of view. I was so impressed with the view that I rotated the diagonal so I could sit comfortably to observe for an extended period. I later changed to much longer focal length 2” eyepieces but I thoroughly enjoyed using the 6.7mm ES and the ED72. I shall look forward to viewing the Orion Nebula with it later in the year.