globular

The range without the 14mm does indeed look like the usual 2x steps in fov area... i.e. root(2) = 1.4 steps in fl. When the range first came out, however, they couldn't get the 17.5 quite right.... so brought out a 14mm instead.... as that was the longest fl they could get right. When they finally cracked the 17.5 they brought that out too... but (rightly) didn't withdraw the 14mm.

Short answer: My tip is to close your observing eye when it's not at the eyepiece. And use your other eye for everything else under a dim light of whatever colour you find works best. Long answer: I've read all sort of stuff about what colour light is best. I concluded that I needed to try them all for myself. So I tried lots of different things... different colours at different intensities... and concluded that I preferred red.... but the best thing was to observe with my right eye at the eyepiece... and use my left eye (with the right closed) for sketching / changing EPs / etc under a dim red light. It took some getting used to but I find even very dim light (of any colour) spoils dark adaption. Some of my colour 'research'... * the aim is to use a light that can seen by our cones, because these are the only receptors with enough resolution, but at the same time preserve and avoid bleaching out the more sensitive rods. Red light is the best wavelength for this. * red / orange lighting need to be brighter to be useful than white or green light. Lower lumens is more important than the colour. * most light sources are not monochromatic - except red which are typically 630 or 660 nm. A red light is therefore more likely to reduces the sensitivity in only the red cones, leaving the blue and green dark adapted. Other colours, unless very carefully filtered, will impact all cones. * a low level blue-green light in the 520 nm range, which is the area of the maximum sensitivity of the eye, will allow 'good' vision at very lower levels which will not decreasing the sensitivity of the eye too much

Skysafari has LDN and none are in the right place. I got skysafari to highlight all entries in it's library (EVERYTHING not just LDN or dark nebulae) for that region; and got this: And zooming into the target areas gives this: You can see Gerry's two dark areas (yellow).... but there are no catalogued items in SkySafari in them (other than the odd star and a bit of overlap with NGC 6996 and NGC 6997). <shrug>

Call them GDC1 and GDC2 - Gerry's Dark Conundrum 1 & 2.

If you scale, rotate and superimpose the two images (lining up the key stars) then you get this: Which, to my eyes, suggests that Gerry's target is not B353 nor the Birds Nest. It's around there somewhere though.

Looks like their centres are about: 20h55m37s +45°02' and 20h55m09s +44°50' Endless cloud here, but I'll try as soon as I can.

Can you have some ready for my foggy month John?

They did set the end time to be prime time evening on a bank holiday monday... so maybe they had an idea? (But I know nothing about ebay really)

11 will get the rainy months.... 1 the foggy one.

Anyone want to club together for a 'time share' ownership? 12 of us at £200 each (ish)... and you get 1 month a year to enjoy them. Maybe I should have thought of this more than 3 1/2 hours before the auction ends?

You may have spotted from some of my posts that I like to think things through and do the maths. It doesn't stop me just trying anyway though - nothing better than giving things a go for myself. And I agree, magnitude calcs are only ever approximate and vary wildly by conditions and person to person. I have been to 21.5 in the Shropshire Hills and 21.6 on North Yorkshire Moors.... but only with my eyes and binoculars, not with my telescope. I'm not sure I want to take my scope anywhere darker as I fear it might spoil my enjoyment in my back garden - I still get lot of wows here and don't want to risk spoiling that... yet anyway.

I love the big on/off knob. Did I say that out loud?

How would you go about moving the EP off axis while the telescope/lens stays on axis to measure edge aberrations? This is really needed to stop telescope off axis aberrations being captured. (Which is much harder to minimise with careful telescope selection than is the case on axis.) I wonder how Ernest did it? I think we need a 3D printer to ..... are we drifting off topic??? 🤔

No, @vlaiv I don't know. Hopefully Don will be back with an answer. I would hope, however, that they were done on the eyepiece alone. As soon as you do something like your idea then you are measuring both the EP and the lens (and the camera). But with only the EP changing between each tests it would give a nice relative performance. (And wouldn't be far off absolute performance I'm sure). I like your idea though... you should do it. Just need someone with a huge EP collection to collaborate with 😉

I agree with you @vlaiv: I was just pointing out the notes he made to accompany the table in case you hadn't seen them.

I think his arc minutes are relative the the eyepiece AFOV, not the TFOV you'd get when used in a telescope. So to convert to the language you are using you have to divide his figures by the magnification you'd get by putting the EP in your telescope. Or as he puts it: "Note : I hope it's clear that in order to determine how these aberration spots will affect the resolution of the telescope, you need to multiply the spot size by 60 (converted to arc seconds) and divided by the magnification given by the eyepiece in the telescope. For example, an aberration spot with a diameter of 20 ang. minutes when transferred to objects of observation in a telescope with a magnification of 100x will smear stars up to a diameter of 20 * 60/100 = 12 arc. seconds" These numbers still seem quite large. I think he tries to address this in a further note: "Note that the real resolution of the eyepieces can be noticeably better than these numbers, since the resolution is influenced not so much by the total size of the aberration spot, how much energy distribution is in it. If there is a sharp peak in brightness in the aberration spot (this is especially typical for spherical aberration and coma), and the aberration halo is dim, then the resolution can be three to four times better than the full spot size." When I first saw this table a year or so ago I didn't really take the numbers on face value.... but figured someone measuring using the same technique across different EPs should result in a useful guide to the relative quality of the different EPs.

I can do M101... I meant the individual NGC you highlighted.... e.g. NGC 5449 is mag 14.0. 8" limiting mag is 14. Bit off because of central obstruction.... maybe 13.9. My skies are 20.4.... a bit unlikely to get it. Fun trying.... but I doubt I'll get 'em.

Most of these are at or beyond the limiting magnitude of my scope. I can't always play with the big boys. 🙃

I was a bit surprized at how all the dark nebulae are in and around the milky way. Here is a plot of the LDN: But then I thought about it some more and realised there is dark nebulae all round... but it's only the milky way ones that are "set off" enough to pick out. May be????

Hi Mark, yeah it makes sense... and I've checked the simulation and it has a leading shadow before opposition and a trailing one now. Not sure why you can't see it. I can't because of cloud

Skysafari's simulation does show a shadow..... following the transit not leading it. Not sure how accurate it's meant to be. I looked over the past few transits and they all have a training shadow. When did you observe a leading one and I'll check then too.

May be then @Don Pensack your previous closing remark should have been: "I feel like Job. My life has been filled with wars, economic chaos, a pandemic, cancers, and injury. I just want to live out the few years I have left without the plague of Paracorr eyepiece holders.😆"

I feel your frustration @Don Pensack. I'm not making light of the very real issues you and others face. It sounds like the design of the Paracorr holder has a) thumbscrews that compress a compression ring when tightened and b) relies on the springiness of the compression ring to retract itself back into the housing as the thumb screws are loosened. Is that right? If so, from your description above, it sounds like the compression ring in your Paracorr has lost some of it's spring and is not retracting itself fully when the thumb screws are loosened. This only partially retracted ring does not snag on straight barrels because there is nothing to snag on. But an undercut barrel needs the ring to retract at least as far as the extra diameter of the barrel verses the undercut or it might snag. The latest tapered undercuts may snag less, as they help to retract the ring as the EP is removed, although I suspect they will have issues to from time to time too with faulty rings. I can see how you would blame the undercuts for this... as it only happens on barrels with undercuts... but the real problem lies with the holder. i.e. straight barrels do not highlight the fault in your holder, but undercut ones do. I suspect a nice new springy compression ring will fix the problem.

I feel left out. I have EPs with undercuts and I've never had a problem. What am I doing wrong?

I'm going to use that one with my doctor. When he next says "you could do with losing some weight" I'll say "my heft is a sign of quality".