John

Talrads and the Rigel Quikfinder are calibrated for use in darkness, unlike other red dot finders, which are usually too bright at night even on the minimum setting. So it is very hard to see the Telrad / Rigel reticules in daylight even at full brightness but at night they are just right.

To be honest I was rather skeptical when I heard that the primary mirror size had been increased on these. This would require a primary cell re-design and a number of other manufacturing changes. Normally, when a manufacturer makes these sorts of changes they release the revised scope as the Mk II or SE or something similar with a fanfare of publicity. I can't recall anything like that happening with the mak-cass 180, apart from the switch to the "black diamond" colour scheme I wonder if something else was causing the apparent reduction in effective aperture that Neil English reported ?

The Baader zoom very nearly gets there. If you add the instantly changeable focal length, that is enough to swing it for many. There are a couple of high end zooms that are as good as the very best fixed focal length eyepieces, the Leica ASPH zoom being one. The price attached is, as you might expect, rather high though.

I think it is also the term used for glass which incorporates lanthanum oxide during the melt stage ?

I've tended to take the view that if a company uses FPL-53, they have selected a very expensive glass type so are likely: a) to select a suitable and equal quality mating element. b) to take some care over the figure, polish and coatings of the lenses. I've owned 9 ED doublets over the years from a range of manufacturers and still own 3 of them. I can't say that I've come across one that has been less than a very good performer. Remember that Lanthanum is a group of glasses, not just one glass type. The figure and polish of the lenses is also a key part of the performance potential.

Very interesting Gaz. So the diameter of the primary has not changed between your scope and the one that is the subject of this thread: The "stopped down aperture" issue was reported on by Neil English when he owned one for a while. Could any other factor cause this that has subsequently changed or is the whole thing a myth perhaps ?

Nice report Stu, and spiky friend I didn't observe last night but I did see quite a few Plato craterlets the night before last. I think I counted 8 with the 12 inch dob. Illumination when they show as pits with tiny ramparts is the most helpful. It's harder to spot more than "the big four" under more direct illumination, when they appear as bright spots on the dark floor of Plato.

My scopes are stored indoors. I used to share diagonals between them so I did take them off the scope at the end of a session then. Now they all have their own diagonals. As you say, no wrong answer. When I put a scope out to cool though I do tend to point it downwards and remove the diagonal to allow warm air inside the tube to escape a little easier. Don't know if this really makes much difference though

I have the Pentax XW's in the 10, 7, 5 and 3.5 focal lengths. I went for the Delos in 14 and 17.3mm because of the field curvature that Louis mentioned with the XW 14 and 20m although I've alse read that many folks don't have a problem with those. I find that I use the 5mm and 7mm XW's the most, the 3.5mm occasionally and the 10mm rarely but they are all very good performers.

I leave the diagonals in my refractors when they are not in use. I'm sure that it's OK with other designs as well.

Vixen NPL plossls are good quality and quite reasonably priced. The GSO plossls are also good quality for their cost - often branded Revelation in the UK. I've owned other brands plossls that have been OK but the above seemed a bit better than OK for their cost. Worth bearing in mind that with the plossl design, the eye relief is around 75%-80% of the focal length so below around 8mm the eye relief can get a bit tight for some. The ones to avoid would be the really low cost ones - there are some listed on e.bay (new) at less than £20 per eyepiece.

I know the problem. That's one of the reasons that I use 100 degree eyepieces with my 12 inch dob.

Yes, I saw those in the Hyginus Rille last night as well. Similar looking feature but with a quite different formation cause. The moon is a fascinating place

Great observing Mike. I need a 12 inch aperture to see that feature and only then when the seeing is very good and then 250x - 300x magification. You must have superbly acute vision

The Baader Q-Turret 2.25x barlow gives 1.3x if the lens element section is screwed directly into the bottom of the 1.25" eyepiece barrel on their Classic series eyepieces. The actual amplification given with other eyepieces depends on the distance between the last element in the eyepiece and the barlow lens element - the greater the distance, the more the amplification factor is. As you can see, the barlow elements need some room up inside the 1.25" eyepiece barrel so designs which use a lower lens set within the barrel are unlikely to ba able to accommodate it.

Ah, yes I understand now. On a dobsonian mount the 12 inch F/5's are very good for visual observing. Not for imaging though !

That is a good re-design taking on the shape that Tele Vue have used on the 31mm Nagler. The Nirvana 28, when I tested it, was a very good eyepiece but the eye cup (face cup !) did take some getting used to !

Last night I observed the crater chain near the crater Davy known as the Catena Davy. What a fascinating feature - there are 4 larger craters in a line and lots of much smaller ones joining those together in a line right across a plain and up and over a rampart as well. Resolving the smaller craters in the chain was challenging and needed high powers and steady moments. The formation of this feature is thought to have involved a multiple simultaneous impact strike by a fragmented body. It must have been an amazing event as it happened ! What other similar crater chain features are there to explore on the Moon ? This is Catena Davy as the observer sees it (good conditions, high magnification) and also, below, an amazing oblique image from NASA's Lunar Mapping and Modeling Programme:

A good 8 inch SCT can be very satisfying. Slightly surprised that your 12 inch newtonian was not also delivering excellent views though but the SCT format is much more compact of course.

The only filter of this type that I have used was a William Optics VR-1 minus violet filter which I tried with a Skywatcher 150mm F/8 achromat. The filter did reduce the violet halo surrounding the lunar limb by about 50% I reckon. The price for that was a pale lemon / yellow tint to the whole image. In the end I decided to try other means of correcting the CA in these scopes.

So do I

Very, very nice Steve.

Lunar illumination does need to be "right" to get the most out of them. Last night was pretty good with the craterlets appearing as tiny pits with ramparts. Under more direct illumination they appear as bright spots which I think makes spotting the smaller ones much harder.

Orion Optics by any chance ? I had a 10 inch F/4.8 Orion Optics for a while. I didn't feel the need to use a Coma Corrector with that even with Ethos eyepieces. I suspect that I'm less bothered by coma than I am astigmatism.

Baader 24mm - 8mm zoom plus a 30mm Vixen NPL ? That would cover pretty much all the observing bases. You don't really need a barlow for visual with a 2000mm focal length scope.