Captain Scarlet

A read of Harold Suiter's "Star Testing Astronomical Telescopes" gives a very good guide through all of this, in some detail but not too text-book. And much much more besides, including a great section on Newtonian Collimation.

It is! A handful of years ago I was sitting in the cafe after a rowing outing with some crew-mates. One of them, without a car, fairly urgently needed one for an upcoming trip to commentate a regatta in Europe. Another crewmate happened to want to sell his. "Just a minute I'll go to the cashpoint", and the deal was done. £400 as I recall...

It looks as though Jupiter and Venus will be 1.4 degrees apart this Sunday, I plan to try to see them during daylight and even get a shot. They'll be 11 degrees up and just East of South at 1pm, looking from SW of London. Cheers Magnus

The laser I’m using is quite heavy, the dual-size Glatter, and the Delos eyepieces I have are heavier still and taller. I’m going to play around further this weekend and try to isolate what’s moving. The vanes and spider all seem good, as the spot doesn’t shift at all when I grab the secondary and apply torque with my hand. My best bet is it’s draw-tube flex, but I need to pin it down before I go Moonlite-ing.

Roger Clark has recently added the below to his extensive site to try to help illuminate this topic, which I found interesting... https://clarkvision.com/new_articles.html

No, first thing I checked. And the spot, wherever it was, stayed stable if I rotated the laser. Laser is a Glatter, which I confirmed is itself collimated a couple of weeks ago.

... fiddling around with this again over the weekend I put the laser in the eyepiece-holder with the laser dot on the primary centre-spot. As I moved the scope around on its mount, the spot moved around On the primary too! Up to 5mm of movement at the primary, and definitely not the primary sliding around, I shimmed that in. The focuser is a newish SW dual-speed one as supplied with their Quattro series which a friend gave me. It FEELS secure enough, there’s no *feeling* of movement when I stress it manually, but the spot also moves when I apply finger pressure to the eyepiece holder. I’m not sure if it’s tube flexure or focuser flexure, ie whether it would be sorted by getting, say, a Moonlite...

Also think about what you mean by the word "spent". If you've purchased new, then sure you've "truly lost" about 25-30% of what you paid, and you won't get that back. That's what I would consider you've truly "spent". If you've purchased second hand, you'd get most of the value back if you wanted to sell, so arguably your "spend" is quite small, could even be zero or negative. It all has value, whether it's in machined glass/aluminium form, or foldable paper, or an electronic record in a server farm in Slough... Cheers, Magnus

Superb through 15x56 binocs, lots of passing gaps in clouds. Got neighbours in too including their 10-year old daughter. They were all amazed...

Terve Praseodyymi! I'm sure you’ll have no trouble working out the technicalities if you’re an aerosol physicist... M

Well I’m now ready with my home-made cloud-seeder..

Thanks. I’d be surprised if it were different from 70mm, would just be nice to have it confirmed by someone with the identical scope...

Thanks both. I’ve seen SW’s current Dob specs at 70mm, but there’s nothing “out there” that definitively states the dimensions for their solid tube any more. But the GSO also at 70mm strengthens the case...

I’ve got some baader solar film being delivered Sunday, I’ll make a makeshift pair of filters for my 15x56s and take them to work, and sneak out during the morning, weather permitting, hopefully with a colleague or two...

If anyone has one of these, the solid tube Sky-Watcher 305mm f/4.9 Newtonian as pictured below, could you perhaps kindly let me know what the size of the secondary is please? Minor axis. My 300p is in Ireland and I’m not there until Christmas so I can’t measure it myself... Thanks in advance... Magnus

It depends what gets moved to change the focus. If the objective is moved to achieve focus, then the eyepiece will remain focused on the reticule and there will be no parallax. However if you move the eyepiece to get focus on closer objects, you’ll be moving the image plane away from the reticule and you will get parallax. ... assuming all the while there is no parallax at infinity.

It was actually on your advice if you recall at a wag meet ... I’ve kept my eyes open ever since!

Courtesy of @parallaxerr my first ever filter of any description...

Glatter laser, but you have to swallow hard before paying up. I was lucky enough to find the once-in-decade 2nd hand one a few months ago... And another vote for the Concenter too

I shake my head in wonder that people can get away with selling something, often expensive, that simply doesn't do the only thing it's supposed to, and be not designed to be adjusted by the user without e.g. digging out sealant. I'm not sure who I blame more, the manufacturer or the retailer if it's a specialist retailer. With collimating lasers it seems you'd be sending back items time after time after time: perhaps those retailers themselves should ensure they're collimated before they go out. In similar vein I've had to throw away useless spirit levels that were more than a degree out... rant over M

On a couple of mornings lately when I’ve had to get up really early and it’s been clear I’ve seen Orion Taurus and the Pleiades and thought “oh there you are, haven’t seen you lot for a while!”. They’re one of the compensations for Winter...

With the Concenter concentric-circles sighting tube in my possession, I used it to judge my prior efforts at centering the secondary at the bottom of the focus tube, and then to try to correct it. It worked well, and didn't take long. 1. My last week's effort, having centered it "by eye" and viewing from the wrong place (10cm further out from the focal plane). Clearly not centred, but perhaps not too bad ... ? 2. The same view through the Concenter. Looks a lot worse when compared to some actual circles... 3. After re-centering, much better: 4. With the primary mirror exposed, and after having done the final tweak with laser and also checked with a Cheshire, all of which were consistent: ... the only thing that remains now is to actually look at some stars!

I think most apps default to an assumption that your average polar scope shows a reversed view, and the o'clock refers to the view that you actually see...

I now have one of these. As you say John, it's expensive for what it is, but so specialized that it probably couldn't be any other way. It's also well made. In addition I have a very high quality (Glatter) laser which I've verified for collimation over a 25+m distance. I'm very much looking forward to the weekend to using this tool to see how my 2nd attempt "from the focal point but eyeballing a circle" worked out, which I did this week; and of course I'll be disassembling and starting again and comparing results with the laser. I'm one of those people who enjoys the thinking, setting up and tuning as much as the using. M

Lay it on why don't you