Lunar Observing Report February 12th 2011- Lichfield - 66% Waxing Gibbous It was with some trepidation that I ventured out on Saturday after my last experience with the new Televue 3.7mm Ethos. Would I suffer the same problems of kidney beaning blackouts and that horrid yellow/red ‘flaming halo’....? I’d had some thought provoking responses from far more 1 experienced observers to my query on the American forum; ‘Cloudy Nights’. Suggestions ranged from making sure the eyepiece was seated correctly in the diagonal, atmospheric distorsions, faulty eyepiece etc, yet the most common theme appeared to be the link between my scopes f/ratio (greater than f7), a small (less than) 0.5mm exit pupil, ultra wide (110-FOV) with a large eye lens - as well as trying to view a bright full moon too! As one commentator stated, ”the brightness of the full moon causes your eye's pupil to constrict, which makes it all too easy to sample only a portion of the (already small), exit pupil with your eye pupil (and interfering with eye placement), especially when you're looking 55 degrees off axis! Before trying to look around, I'd suggest trying to look on axis and letting your peripheral vision soak in the 110 degree field.” Also, “diameter of exit pupil figures are mostly consigned into side-to-side tolerance for eye positioning, and typically the manifestation is not so much blackouts but dimming of the view as one clips part of the light for any given point by letting the eye wander too much to one side or the other. Once the exit pupil gets this small, however, the difference in size is not very significant to eye positioning. What's more significant is 110 degrees versus 100 degrees, since the larger the apparent field the tighter the tolerance for the distance your eye must be kept from the eye lens. That's where the blackouts come from typically, i.e. getting too close to the lens, since this exacerbates the effect the slightest side-to-side positioning error, some of which is probably inevitable. .... Lastly, “as the exit pupil grows smaller, the width of the light-cone within which the image properly converges decreases, even though a relatively slower (say f/8 vs f/6) scope will have a longer vertical (i.e. on-axis) zone within which the image appears to come into satisfactory focus; even so, the width of that zone narrows as you move axially in either direction from the point of ideal focus. So, even modest mis-alignments of your eye and the exit pupil can induce seeming eyepiece misbehaviors such as blackout zones and flares around the edge. An ultra-wide AFOV eyepiece with a big eyelens such as the 3.7E doubtless requires quite a bit more critical internal bending of light through much wider lenses than a significantly narrower AFOV eyepiece with a much smaller eyelens. One of the most impressive things about TeleVue's eyepiece design quality is how generous, relative to exit pupil and eyelens Eratosthenes size, the forgiving zone of aberration-free view is, but there comes a point for every person's eyes where the small exit pupil size simply falls too far below a critical size”. 1 So, with all this taken on board, I decided to set up early evening whilst the sky was still blue - apart from being something of a novelty to look at the moon against a blue (rather than black background), it would give the scope and eyepiece plenty of time to cool, I‘d be able to see what I was doing (for a change), there would be less contrast and glare (so hopefully less eye problems) and I thought I may have a go at doing some quick sketches this time... Andy had kindly brought me a year’s subscription to the BBC’s Sky at Night Magazine for Christmas, and the January edition had a feature on Apollo 14, so after my recent success at identifiying the Apollo 15 landing site, I set myself the goal of finding NASA’s preceeding Apollo exploits... This time I made sure that the 2” barrel extension was seated properly within the 2” Televue Everbright diagonal. From the outset the experience was far more enjoyable - less bright (so I was not squinting through the eyepiece). I focused in on the terminator around the large crater formation Eratosthenes. Unlike last time (full moon), there was a healthy dose of contrast - rich blacks and ultra sharp whites (I can only compare the whites to being cooler than the 31mm Nagler’s noted warmer whites and my Takahashi 5 and 7.5mm LE eyepieces which also display a warmer tone). I swapped between the Taks and Ethos and could not see any loss 1 of light from the extra glass within the Ethos. In fact, sharpness and contrast appeared slightly higher in the Ethos, but that was probably down to the additional magnification and cooler tone.What cannot be dismissed though is absolutely huge field of view compared to the five element Erfle design of the Takahashi eyepieces that only offer a 52º apparent field of view. This definitely does allow far more time to concentrate on your target (well to allow the vibrations to settle and find that critical eye placement!) I could only see a small amount of the ‘flaming yellow/orange’ halo out at the extreme edge, say between 20 past the hour to a quarter to.... It would virtually disappear as I made a concerted effort to re-centre my eye and ‘force’ it open... The halo was no where near as off putting as before - and I would not want to put anyone off the purchase of such an eyepiece now (it’s not going back to Telescope House or being put N Eratosthenes up on ‘UK Astro Buy and Sell’ anyway!) As I moved around the lunar surface I did not note any flaring, yet I still experienced a small amount of kidney beaning.... as I spent more time observing I was able to get this under control E W by ‘fixing’ my eye placement. It was slightly more problematic later when I tried my hand at some quick sketching - as I looked to and fro between S eyepiece and sketchpad I had to re-find that critical zone where the 1 blackouts would disappear.... perhaps for that need, ‘Uncle Al’ at Televue will have to produce a 4.something - 5mm Ethos! Over time I tried to relax and allow my eye to find a comfortable, centralised position without trying to take in the whole field. Once ‘centred’ I took my time to move my eye in and out of the rubber cup and find that proported 15mm of eye relief - to be found somewhere between the large concave eye lens and the (non- 2 adjustable) outer regions of the rubber eyeguard. It was only then that I rotated my eye around to take in the field. I could manage a small amount of ‘head’ movement, but, too much and the halo would start to re-appear and 3 the blackouts would start to re-form. I think I am at the extreme envelope of magnification and FOV with this eyepiece/f8 focal ratio as the American * guys had mentioned. Certainly on those few exceptional nights we enjoy in 4 the UK, I have been able to use my 2.8mm, 3.6mm Takahashi eyepieces with some success as well as ‘Powermate’ the 6mm Ethos (a rather heavy and 5 cumbersome combination for my liking), so I am leaning towards the extra Mare FOV being the problem rather than magnification and exit pupil. 6 Nubium 7 So, onto the observing report for the evening! The area to be observed happened to be not far from the previous observing session. Using the 60 mile wide crater Copernicus (1) as a reference point I headed down to a half way point ( approximately 18° West 6° South) between the distinctive set of craters;* Herschel (2), ‘trio craters’ Ptolemaeus (3), Alphonsus (4), Arzachel (6) and Alpetragius (5). Herschel is at the head of this multiple crater formation situated on the northern slope of Ptolemaeus - about 25 miles in diameter with high terraced walls (about 11,400 deep), so has a good amount of shadowing within it. Its floor dominated by a central mountain that glints in the sunlight. If you study this feature closely you can see the 8 mile crater Herschel G that just takes the slightest of nicks out of its larger cousin’s bottom! Much larger (yet looking far shallower and therefore lighter), is Ptolemaeus. Stretching over 93 miles and estimated to be somewhere in the region of 3.92-4.55 billion years old.... Its flat looking floor does give up a series of ghost craters and small craterlets to the determined/patient observer (just visible is craterlet Ammonius - 5 miles diameter at the 10 o’clock position - at the top left of the red number 3). Further south is the far more interesting crater Alphonsus (4). Alphonsus is estimated to be in the region of N 3.9 billion years old and shares a good section of its northern walls with Ptolemaeus. Smaller at 71 miles wide, it has high terraced walls with a deeply ridged protusion that extends into the higher crater on the eastern (left side). E W There is scarring at the bottom area where there appears to be a crater hole punched out of the south wall (6 o’clock position).