Captain Scarlet

16 minutes ago, markse68 said:

oh- that doesn’t look like it’ll hold very steady like that Magnus- I guess if you have enough tension it should though? Where did you order the carbon tube?

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.

7 minutes ago, JamesF said:

There's (what I assume to be) another shot at the top of this page:

https://www.bbc.co.uk/news/science-environment-55160768

I have to admit that I'd not realised the Moon was quite so small.

James

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

3 hours ago, billhinge said:

Lol, seems funny seeing other cats around my old tripod and box, my second hand Scottish Fold has a thing about boxes

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.

5 hours ago, John said:

The overall weight is about the same. I just wanted to use the Uni 28 with the T-Rex Mount

At some point I will compare the EQ6 steel tripod + pillar extension with the Uni 28 and see how they compare in terms of performance and convenience with this mount.

I suspect there will not be much in it but I do like wooden tripods

 

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:

8 hours ago, PeterW said:

What is the R^2 of your regression? Interesting stuff. I’ve seen notes about the variation due to different effects like the milkyway. Be interesting to see your time series data.

Peter

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

1 hour ago, markse68 said:

Fascinating stuff Magnus! I’ve been thinking of building a diy SQ meter and if i do i’d really like to try out your equation to see if it predicts my readings. One question though, what about transparency? Doesn’t moisture/dust in the air greatly affect SQ by bouncing back local light pollution?

Mark

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.

9 hours ago, faulksy said:

why didnt you just extend the tube at the bottom by say 100mm then mount your primary further down ?

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]
 

On 12/08/2020 at 21:16, Tom Rielly said:

Here is my MK66 from Bill Burnett (ITE) which I bought from him in 2001. Love this scope!

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

12 hours ago, scarp15 said:

Very fine mirror upgrades and interesting modification to accommodate this. What will you use to fill in the original focuser hole and all of the small holes?

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

A couple of years ago, 2018, I bought a blue-tube 12” Skywatcher 300p Newtonian from @neil phillips, to use at my dark location (21.8) in SW Ireland. It has ridden my AZ-EQ6 atop a Berlebach Planet. I have thoroughly enjoyed using it and it has given me wonderful views. Weighing in at over 26kg including rings, eyepieces finders etc,the mount, in visual-only Alt-Az mode, has had no problems handling it.

I am a serial upgrader, so the first modification I made was treating it to a Lacerta dual-speed upgrade kit, which was very good but only a little later I further upgraded to a Baader Diamond Steeltrack, which really is a luxury. In November last year I ordered a Hubble Optics 1/10 wave secondary mirror, which finally was delivered in January, and in March I fitted it. It was a direct replacement for the OEM Skywatcher 70mm secondary, so no design mods were needed.
In May 2020 I really treated myself to a 1/10 wave Orion Optics 300mm mirror, and that arrived in early November. My first intention was to simply replace the existing SW mirror with the OO one. But it was not that easy. The SW mirror is 305mm as opposed to the Orion’s 300mm,but that  the difference was easily accommodated by the SW mirror cell. The bigger problem was the focal length.

The SW mirror had a focal length of 1500mm, and of course the positions of the focuser and the spider/secondary were in just the right place for that. The Orion mirror has a focal length of 1590mm, 90mm longer, and a little geometry and some scale drawings showed that simply plonking the new mirror in and leaving everything else unchanged was not going to cut it. Doing that would place the secondary too close to the primary to be able to collect-and-bounce the whole (longer) converging light-cone, losing the outer part of the cone and effectively turning my scope into a 10.5”.

Given the extent of tube I had available, I was going to have to move spider/secondary and focuser at least 70mm further up the tube to use the full aperture. Very luckily, I had exactly and only 70mm available. Phew!

Of course, I couldn’t resist nonetheless giving the mirror its First Light in a “simply plonked-in state” as a de facto 10.5”. Waiting weeks to get all that work done would be too trying for my patience. And besides, Mars wasn’t going to wait for me! I quickly collimated the new arrangement, was rewarded with a lucky clear night, and got an absolutely astounding view of Mars: from time to time as the seeing briefly settled, I felt I was looking at a picture-atlas of the planet’s features. Whether it was the seeing that night or the new mirror, who knows.
Anyway, First Light out of the way, major tube surgery beckoned. This is where it gets a bit more detailed. I needed to drill lots of new holes.

I was going to have to move the secondary’s spider-holes 7cm further up the tube, and similarly the main focuser-holes. Drilling small (up to say 5mm) holes accurately into a thin (0.9mm) steel plate is not difficult, given a set of sharp drill-bits and starting small, moving up the sizes. But drilling an 80mm hole into a thin, CURVED piece of plate was a totally different kettle of poissons. Flat plate would’ve been easy using a hole-bit and arbor, just secure the plate down on to a flat, say, wooden surface, and allow the rim-bit to wear its way through the steel. But the curve of the plate meant that as soon as the edge-bit made the first full penetration, the next tooth of the bit would just catch and everything would stop.

I thought of using a jig-saw, but trying to get that to make a circular hole in a thin plate seemed daunting. I don’t have a bench or a drill-press, or a machine-shop.

In the end I opted for the hole-bit and arbor, and angled the fast-rotating circular bit about, to gradually eat through the different parts of the circle as evenly as I could. It did catch-and-jam a few times, but I got there. However, once the inner disc finally detached, it did so at speed and across the room, bouncing off two walls before coming to rest. It was very sharp-edged. If it had hit me, there would have been bleeding! Lesson learned luckily without injury.

Some filing away of thin sharp metal edges and other de-burring, and cardboard-black painting any newly exposed shiny steel, and the focuser was re-attached, plus finder-bracket.
Next installment should show me having re-attached the spider and secondary assembly, having put the tube back onto the primary cell, having e-collimated and ready for true First Light!

Cheers, Magnus

I had calendar-bookmarked this morning for this, but drilling rain the last 2 days put paid! Lovely pictures above though go some way to softening the disappointment.

M

32 minutes ago, John said:

...  I'm just a "sky tourist" really ...

haha what a masterpiece of modest understatement!

So yes then. Flats would be the thing. I’ll take some shots and post up, and have a go at doing the calcs myself as well.

Btw out of curiosity ... do you not sleep? 😉

M