John

The pupil guides that Tele Vue supply with some of their eyepieces do mask quite an area around the edge of the eye lens but you can still see the full field and, from what I recall, with no vignetting

The truss design has advantages with cooling. In the winter months warm currents of air from the body can get into the light path though. I found that a light shroud helped with that and keeping stray light out of course. Also for keeping debris off the primary mirror. I'm just not sure that, in the apertures that we amateurs generally use, that the cooling of the optics themselves, in terms of the optical figure, makes a lot of difference Keeping the light path clear of air currents certainly does make a lot of difference though.

Yes, that's what I thought

Interesting experiment. The ultimate low scatter, high transmission eyepiece is reputed to be the "ball" eyepieces comprising a single spherical element. Miniscule AFoV and eye relief though. Siebert produced a commercial version, the Planesphere series: https://www.siebertoptics.com/Planesphere.html

Makes sense to me Kev I don't find that I need to use the fan on the primary cell of my 12 inch dob. The tube seems to cool quite effectively in 30 minutes with the top cap off.

Perhaps the label should state "Do not consume this telescope eyepiece or attempt to use it as a drinking vessel" to be sure. Sort of thing that made "Wonko the Sane" the person he was. Funnily enough, he lived in California Douglas Adams was ahead of his time ........

Do you have a 2" diagonal ? The 2 inch fitting gives you the wider field of view so is good for low to medium power viewing but for higher powers there is no advantage to the larger fitting.

I've used my Lunt 1.25" Herschel Wedge quite often with my ED120mm refractor and the combination works well and safely.

The scope is a 130mm F/9.2 triplet so about the same size as the 127L. Perhaps a touch heavier at 9.5kg.

Is the cooling about removing warmer air from within the tube and, if possible, disrupting the boundary layer or is it about actually cooling the glass temperature ? I've always considered the former to be the key thing rather than the latter ?

The washing line might have been enough. Veiwing a star when it is near a hard edge such as a roof roof ridge can do the same.

I use the ADM clamps but there are alternatives as @johninderby shows above. Another issue to consider is the overall height of the mount. The 127L is a long scope. If you observe when seated then the stock tubular steel tripod option for the Skytee II might be OK. If you prefer to stand then you will need something taller. Mounting a large aperture, long refractor, effectively, throws up some interesting challenges !

You already have a BST Starguider 8mm which is one of the best of that range and the zoom. I think the 16mm Nirvana would bring something new - it's field of view will be much wider than the zoom.

I'm trying to think of an example of an eyepiece / scope combination where the exit pupil might exceed the diameter of the eye lens

I would go for the Aero ED 30mm over the Panaview 26mm. The 26mm is not the best in the Panaview range, the 32mm is better but the Aero ED 30 is better again. Also a 26mm 2 inch 68 degree eyepiece does not show much more sky than your 32mm plossl does. Given your other eyepieces are already quite good, I would hold on for the Nirvana's to become available otherwise you might not get any improvement in performance without spending substantially more.

I don't think the AZ5 would cope with a 127L. The Skytee II would but do upgrade the dovetail clamp before putting the scope on the mount. The stock clamps are very poor quality. An alternative would be a Giro Ercole if you can find one. I've put some quite heavy scopes on my Giro Ercole and Skytee II mounts:

The Nirvana is a much better eyepiece in an F/4.7 scope than a Hyperion.

Having longer eye relief is a popular feature these days and that sometimes requires the use of large lenses. Not all the wides and ultra wides have massive lenses though. The Panoptic 24mm and Nagler 31mm have more modest eye lenses. The Explore Scientific 17mm 92 is the largest of the ones that I own:

Orion Optics offer a dobsonian mount option for their newtonians. You can pick the specification from their options or, if you are really patient, they will make something to your precise specifications: https://www.orionoptics.co.uk/home.html I think the answer to some of your questions is that the market is relatively small overall. Two or three decades ago there were more companies in the UK making dobsonians and telescopes generally but back then the chinese made instruments hit the market which had a big impact. In europe there are some other choices: https://www.teleskop-express.de/shop/product_info.php/info/p5999_TS-Optics-12--f-5-truss-type-Dobsonian-telescope---made-in-Germany.html https://www.teleskop-express.de/shop/product_info.php/info/p2236_Geoptik-Nadirus-12-Truss-Dobsonian-Telescope---12-inch-Aperture-f-5.html https://www.sumerianoptics.com/products

Interesting thread this, as the owner for the past 6 years or so of an Orion Optics SPX 12 F/5.3 which I use as a dobsonian for visual use. The optical tube was originally purchased for imaging (not by me) and I've seen photos of it on a huge observatory based equatorial mounting. Tube flex has not been an issue for my visual use of the scope but I can see that it might affect an imager with a heavy rig hanging out the side of the scope. The original owner of my scope who did image successfully with it (deep sky and planetary) used a number of additional tube rings along the tube presumably to increase rigidity. As a visual scope on a dobsonian mount, it has been superb I have to say

Great image from @davhei - thanks for sharing your view of the event Thick clouds and persistent rain here so nothing worth getting out of bed for

Thats fine. So the range of movement of the finder just isn't enough by the sound of it. On a different scope the next step would be to adjust the position of the finder bracket on the scope but it does not look like that is possible with the design used on the Heritage 150 - it's a simple rail that the finder clamps onto by the look of it ?

How far away was your target ?

Looks like the finder is skewed as far as it will go in the azimuth axis. Is it jammed there ?

I've heard that these stickers are required by the state of California specifically. https://www.p65warnings.ca.gov/