Captain Scarlet

I think thicker vanes won't affect the diffraction spikes, the spikes are all about the total length of edges in the light-path (including the edge of the aperture). Thicker vanes will just result in a little more total obstruction. But shiny surfaces parallel to the light-path, especially those actually inside the llght-path, my instinct tells me will result in disproportionate glare around bright objects. A reflective inside of the tube itself will also be glare-inducing-contrast-reducing, but because it's outside the main light-tube-cone its effect should be reduced. But then again the sheer area of the inside of the OTA will offset that (i.e. make it worse). I plan to test the vane-reflectivity effect by introducing a long wide shiny blade into the light-path when next observing. Actually flocking the vanes may be the next step. Such fascinating fun, these thoughts fill my mind when going to bed and send me to sleep!

... on reflection, pun intended, I decided to reorientate the side-support grubs in the mirror cell so there is no chance of the mirror getting “jammed” between two nylon tips at the bottom. Rather have it resting not-quite vertically on a single one. that involved rotating the whole tube in its cell by 60 degrees. while I was at it, and this is the reflection part, I removed the spider again and the secondary to paint the spider-vanes cardboard black. They were actually very reflective, and the last thing one wants is a parallel reflective surface in the light-path. Before and after pics...

Ive always plumped for Araldite, I’ll get some JB weld on your recommendation, thanks

Lightpollutionmap.info is a very good resource (how I hate that word apols). The way to use it is to set the overlay to Atlas 2015. It’s a simulation of how the darkness will appear at zenith at best to an observer on the ground. I’ve calibrated it to two very different places, one 19.0 and one 21.8, and they’re both spot on with that overlay. The other overlays are views of how bright it looks from the satellite, a different thing. Cheers Magnus

I too had reservations about how stable it would be, but after collimating it and trying to move it around in situ with laser etc still in the focuser I wasn’t shifting the spot even with a reasonable amount of “wrist-torque”. I was surprised. The carbon tube I ordered directly from klaushelmi.de, I think he supplies astroshop.de with their pre-specified carbon tube upgrades. Going direct to him makes a decent saving. On my 300p I’ve worked out it’ll save me 4-5 kg as well as making it very much stiffer. Magnus

Latest ... I made the mistake of drilling the central hole for the focuser first, then realizing that I had to sacrifice a bit of the calculated distance to the spider holes because of the presence of the inner flange of the end-ring of the tube. I thought there would be plenty enough leeway in the secondary holder to accommodate the shorter separation. There wasn’t. As the picture shows to the eagle-eyed, I’ve had to back the secondary-holder by one screw on the spider-vanes to give me an extra 10mm, allowing the secondary to catch the whole light-cone. New longer carbon tube now ordered so hopefully won’t have to live with this bodge for too long.

It's not. It's just a very big spacecraft.

The most important thing when using a laser for collimation is that the laser itself is collimated. With a glatter you can be sure that it is. With that settled, as you say, you can collimate the secondary by “hitting the centre of the primary”. you can then still use the same setup to collimate the primary by observing where the reflected laser-spot return hits the face of the laser, and adjusting the primary until that return dot is on top of the laser hole. But that only really gets you roughly there. a much better way, after doing the secondary, is to put a Barlow in front of the laser, observing where the SHADOW of the primary’s donut returns to the laser-face, and centring that. You may need to use a piece of paper to see where that shadow falls in front of the focuser tube, that’s what I use. so you can do it all with just the laser, reasonably accurately, and with a Barlow extremely accurately. the tublug basically combines the whole thing into one unit. cheers, Magnus

I had to look that breed up. Very nice!

Never saw those cats before, they just emerged from the box, I assumed @billhinge didn’t want them 😉😺

Courtesy of @billhinge, a berlebach Uni to replace a steel SW. Herewith pre- and post-assembly and placed in front of my Planet, even with the distance-perspective it’s still dwarfed by the Planet: Cheers, Magnus

Just had a quick thought to check and find out Uranus is only around 4 degrees from the Moon at the moment (28-Nov nearly midnight). So went outside with my Nikon 12x50s and found it immediately! Very chuffed, a first for me, a Gas Giant through bins. I intended to put this in the "who's playing tonight" thread, but it seems to have disappeared. Cheers, Magnus.

I’ll be interested to hear your result John. My own part in this same transaction is that I symmetrically bought the wooden Uni tripod from @billhinge of which John’s EQ6 head was a spare, to directly replace my SW steel tripod. So I too will do a like-for-like comparison. Personally, I think the steel tripods are quite springy, but we’ll see...

Was out on a walk to catch the lovely flat yellow light of a clear winter’s late afternoon. Only a long lens seems to match how the brain processes a low-down Moon:

R^2 is around 98%, and the sqrt(sum-of-squares) of the residuals-from-modelled, the quasi std-dev, is 0.34 mags for this model. (This model is for "Moon Up" data. I run a different model for "Moon Down" excluding the moon's properties of course, which gives a quasi-SD of 0.12 mags. And another for "All together" which gives 0.41. All 3 R^2 are 98-99%). I'll compile my data and send it to anyone who's interested. I also have a similar series for my London location, a 19.05 site, so opposite ends of the LP spectrum so to speak. Apologies to @Ships and Stars , sorry I don't mean to hijack your superb account and thread. M

I can calculate the variables in the equation, sun alt, moon alt, moon phase, proximity to MW etc, but things like transparency airglow and light cloud veil are difficult to estimateor see, so they will contribute to the final errors in the regression.

I did consider that but I didn't as easily have the means to achieve it. I was also concerned about losing rigidity: having some flexure in an extra segment that far down might mean the whole thing became uncollimatable. Whereas I could start drilling holes straight away. BTW I have read your own "dob-build" account: very inspiring! I plan to go "big dob" myself at some stage I hope in the not-too-distant future.

“I've been getting readings much lower with the SQM than the LP map suggests. I know conditions change and readings go up and down, but the readings seem a lot brighter than I was expecting.” I have several hundred readings now from two sites with my sqm-l, and the best readings from each match quite closely to the lightpollutionmap.info modeled values. I have regressed a model from each site and find that sun altitude above -18 degs below, same sun alt squared, moon alt, moon phase, are all significant factors in estimating darkness to expect. But I like you have been disappointedly flummoxed that lately my readings have been rather brighter than expectedgtomy dark site, 21.8. On a hunch I added “angular proximity to MW” as a factor to my model, and the variation was explained! Essentially in the summer months you’re pointing the meter at zenith to the MW and it makes a big difference! My best formula for my 21.8 location based on data so far is SQ = 21.949 + 0.2436 x sunalt - 0.0697 x sunalt^2 - 1.9336 x moonphase - 0.0330 x moonalt + 0.005657 x MW_prox_to_zenith [alts and MW prox in degrees and phase in space 0-1.000. And where sunalt is no. degs above -18 and zero below, similarly moonalt is actual moonalt but zero below -10 degs]

Nice mount! I too generally mount my Intes 603 on my Stellarvue M2! So lovely when finely balanced. Magnus

Honestly I was incredibly stupid. It flew off the bit with great energy and would’ve taken my ear off if unlucky!

A couple of books, courtesy of @Second Time Around, as soon as I received them I lost 20 minutes of my life getting absorbed in the surprisingly fascinating theory behind optimizing mirror supports to allow various “sags” to cancel each other out!

... simply unscrews, as multipl-y suggested above. Mine was barely torqued up, loose in its thread in fact. M

I have just such a (SW OEM) finder-scope which is surplus to my needs. I’ll give it a go and see how easily and how (and if...) the rear plate comes off...

There’s so much more than just star testing in the book, it’s a compelling read for me. Also the pleasure of this whole hobby for me is much more than simply the observing, the instruments and the physics are all in there. Sure ones needs experience to interpret star tests, but experience needs to be accumulated and one necessarily has to start as a beginner. cheers, Magnus

I have a huge roll of acetate sheet, so I plan to simply cover the larger holes with pieces of that, painted blackboard-black. The smaller holes I may just cover with tape. In due course I'll be replacing the steel tube with a carbon one made to measure (saving at least 5kg) so this is an interim stage. By then there'll be only the primary cell left. M