Captain Scarlet

19 minutes ago, PeterW said:

Don’t scratch your worktop! What’s the top thread that EQ6!has, I’ve wondered about a more convenient head for it!

Peter

EQ6 bolt thread is M12 I think. This head is designed to fit via the 3 horizontal bolts to an EQ5-type, or directly on to a 3/8" photo thread. I already have an EQ6-3/8 adapter, resulting in:

Stellarvue M2 heavy duty alt az mount. I knew it was going to be bigger than I expected. But it’s even bigger than bigger than I expected!

very excited to have a good alt az to top my previously redundant SW EQ6 tripod. Courtesy of @Steve Clay

Completely clouded over for the occultation, as per the pic below. But around an hour later I missed the actual re-emergence due to cloud but was unlucky, as there was more blue sky by then than cloud. It was interesting for a number of reasons:

- When using my (Baader V) RDF to try to line up on the Moon, I couldn't see it at all naked eye in a perfectly blue sky.

- When scanning the general area with 10x50 bins, I immediately found Venus, extremely prominent and a clear crescent. Even through the bins, and knowing exactly where it was, the Moon was barely evident.

- Locating Venus through the scope was a bit trickier, as my initial Solar Alignment was done approximately through cloud. So I used a trick that often works: slew away somewhat in a random direction, and re-request the hand controller to find the object. Sure enough, bright Venus shot past in the re-slew so I knew roughly where it was, and immediately found it at around 50x mag in the 6" Intes and 35 Panoptic.

- Venus was much bigger and much brighter than I was expecting. The Moon was barely visible. The two in the same FoV was magical though, as mentioned above, very "looming". I observed for a while but as the Sun stayed out, the view got worse and worse in wobbly heat haze.

Memorable.

11 hours ago, markse68 said:

I’d never think of doing this with more expensive or complicated eps but ...

Now why don't I believe this for a single moment?

Get the two of us into a room together with any sort of astro stuff and tools, and woe betide any astro stuff lying around  . Just remains for @John to send either of us his 13mm Ethos for some improvements...

Seriously though, very interesting!

M

24 minutes ago, Stu said:

I think it’s because the corrector (which is 127mm) actually diverges the light beam, meaning that you would need an oversized primary to maintain the 127mm aperture. 
 

@Captain Magenta did a fantastic post on the 180 here.

 

... one of the upshots of that was that the primary on the skymax 180 is 200mm, allowing full use of the width of the corrector. I have a skymax 150 in London for which I’ll make the same measurement when I’m back there. Alas I don’t have any more a skymax 127, it would be interesting for someone to quickly pop the back end off and have a quick measure...

Haha I also thought Inderby was a surname. I only twigged when I bought something...

I started off in astro a few years ago by getting a reasonably heavy-duty goto mount, the az-eq6, thinking go-to was obviously where it's at. I used (use) it mostly in alt-az mode. Then, after a year, a 2nd hand SkyTee2 came up, with the ADM saddles, and I thought "it'd be good to have something a little more portable and at least trying out fully-manual".

As it's turned out, I use it all the time. Far more than I expected I would. it's really good.

4 hours ago, PeterW said:

Customs payment request.... only been nearly a month since posting I’m from the west coast of US..... Getting closer.

Peter

Sounds just like the secondary mirror I ordered early November to be assured of getting it pre Christmas, and which eventually arrived in Feb!

1 hour ago, OlivierB said:

Hi Magnus,

thanks for sharing, this is the post I have been looking for since I got my own Skymax 180.

One question : did you measure the length and inner diameter of the baffle attached to the primary ? I would like to undestand the effects of primary moving on vignetting or obstructing the light cone coming from the secondary.

Cheers,

Olivier

Alas Olivier I didn't! You might be able to get a reasonable idea from the photos, but it's a simple matter to quickly take the back off and measure it up. I'll try to do that over the next day or so.

M

It also tastes not very nice. I find it tastes “grey” as it were. At our “offices” (former locations where people used to congregate during working hours) there are pure water dispensers which are marketed as supplying ultra pure water therefore ultra good for you <eye-roll>
M

I am not an Astro-photographer (yet), I’m almost exclusively visual . So I partly judge astro-photos by how well photos represent the purity and “pinpointness” of stars compared to how they look through an eyepiece. Most images, to my untutored eye, do not come close to the visual experience from the star point of view, even if the nebulous objects are well beyond visual. Your image here is an exception ... to my taste you’ve got it spot on. Really really lovely, as I think I said before.

An image I’d willingly print and display even though not mine!

M

Quite stunning.

Next out I’m going to be having a hunt around the head of Draco, where it seems there are some nice ones...

The optical "tricks" for collimating a secondary only really make sense if the eye is placed at and only at the primary's (reflected) focal point. Because only from that point do features on the outer “surface” of the cone (ie the edges of either mirror) collapse to a perfect circle.

The two main optical tricks are:

- Getting the secondary to appear perfectly circular, even though it's actually elliptical.

Only from the focal point should this ellipse appear as a perfect circle.

- Getting the primary's mirror clips symmetrical and "just in view"

Only from the focal point should you just about see the edge of the primary. Rack in closer, and obviously you'll see more of the primary. Rack out a fair distance, if you can still see all the clips it means the secondary is larger than strictly necessary (not necessarily a bad thing, but you're trading off CO for illuminated field).

What this means is that one shouldn't really rack in or rack out to get better views of mirror edges, everything should be done with the eye at the focal point.

M

22 minutes ago, Trikeflyer said:

I’ve always fancied one of these. Never used one but if I was looking for a first one, I’d definitely have one of these

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5506_TS-Concenter-2--colimation-eyepiece-for-Newtonian-Telescopes.html

Steve

+1 for that, I have one, have lent it a couple of times and the borrowers have been amazed at how much more accurately and quickly they've been able to place the secondary than with anything else

Seriously though, my understanding is that any straight edge will produce a diffraction spike perpendicular to that edge: in fact one perpendicular spike for each "side" of the straight line within the aperture. So a straight spider vane, having 2 "sides" inside the aperture, will produce two spikes, one for each side of the vane. But a straight edge to the aperture itself will produce just one spike, as it has only one "side". Thus a circular aperture can be considered as an infinite number of small straight edges, each producing its own small perpendicular spike, thus manifesting as a ring: a diffraction ring.

Another example is the single straight edge that often appears on skywatcher (and others?) newtonian secondary mirrors, from where it's been held for silvering, which usually produces an annoying single spike slightly offset from one of the main spider-vane spikes.

... but 3 diffraction spikes do produce 3 corrections

8 minutes ago, Barry-W-Fenner said:

I really like the look of this scope.  The 3 piece spider vane is a good idea. I assume this reduces the number of diffraction spikes produced ....

I think it will produce 6 diffraction spikes...

edit: should've refreshed view first to avoid repeating the point

One of my first used and upgrade purchases getting into this pastime (don't like the word hobby) was an ADM saddle for my AZ EQ6. When it arrived I couldn't understand why my hex keys wouldn't properly fit. Then I thought "surely not Imperial in this day and age..." and of course so it was.

It’s been a cloudy week since I walked into the glass doora dn the Full Moon has come up, but last night although forecast cloudy again was totally clear all the way until around 1am.

Lack of astro darkness, big Moon rising, and a school night notwithstanding, I decided to have a session. Partly to collect useful twilight data using my SQM-L, partly just to quell the “longing to observe” urge to play with my toys that starts after a few days not doing so, and partly to get more experience using my Nexus-DSC controlling my AZ-EQ6 (a bit glitchy in Nexus/SynScan/PC-Direct mode as the supplied cable wouldn’t communicate with the mount).

Given it was likely to remain quite bright, I eschewed my 12” and instead opted for my Mak180 and restricted myself to a small number of doubles. The darkness-level started off at 13.75 around quarter to 11 with the Sun about 6.5 degrees below the horizon, climbed up to 20.25 around half past midnight before brightening again as the Moon rose.

I used the bright times to do the alignment, a learning process using the NexusDSC which I managed to utterly confuse a couple of times and start from scratch. Very few and mundane targets but I just wanted to get something in and some practise with the Nexus.

First proper target was Izar, fairly close to my 2^nd alignment star (Arcturus), and it showed lovely and crisp at 148x using my 19.2 DeLite.

Next I went for zeta Herculis, which using the same scope a week earlier I had completely failed to separate or even see a hint (just after walking into glass door). This time, with seeing not bad at all, at 450x (6mm Delos) there was very clearly a sharp spot exactly on the diffraction ring around 5 o’clock as I was viewing it, where it should’ve been apparently with a vertical diagonal. Quite pleased at that.

I moved on to the Double Double, and still at 450x was treated to the widest clearest separation I’ve had on that system that I can remember. Two pairs of diffraction rings with seemingly oceans of black in between each pair, the whole system spread all across the eyepiece view. The Mak is clearly a good performer. 450x on this and previously on zeta Herculis provided surprisingly satisfying prolonged viewing.

I finished off with Mizar, Alcor and Ludwig’s star (and plenty of dimmer ones in and around) with the whole ensemble filling the view at 148x

Very happy with the way the Mak 180 performed; a little more experience with the NexusDSC in what I would call “compromised mode” as the supplied USD-RJ45 doesn’t communicate with the mount thus having to be used in Synscan PC-Direct mode; and I managed to avoid breaking my nose again!

Cheers, Magnus

51 minutes ago, CentaurZ said:

You beat me to it by hours, Captain; nevertheless I'll post what I had already written....

Ah my apologies! I hadn't realized it was such a significant event, else I wouldn't have trespassed on what is most definitely your turf!

Magnus

Not sure if it's already been signposted, but around 0900 BST on 19th June it looks as though a 4% Moon will be occulting an 8% Venus. Not sure if it'll be visible at that small phase with each around 23 degrees away from the Sun...

M

Really beautiful. There appears to be no streaking: were you using a tracker? I identify with your philosophy: 99% visual, but I occasionally get tempted to stick a wide angle lens onto my astrotrac.

M

24 minutes ago, ymb said:

Hello Captain !

Your post is a pleasure to follow, I like each steps of your investigations with clear explanations and comments, even sketch and graphics.

As I understood the retaining ring of primary mirror is even larger than the secondary baffle so how do you expect to decrease obstruction by removing the baffle ?

Again really thank you for sharing such well built article...

 

 

Thanks.

I had 2 purposes removing the baffle, initially it was indeed to reduce the CO but I did quickly realize the ring around the primary was as you point out much bigger, 63mm in fact, and I did understand then that there was no point from a CO point of view.

Aside from that, the baffle was not attached to the secondary concentrically, so the exercise became instead to reattach it properly positioned.

Cheers, Magnus

On 07/05/2020 at 21:25, Louis D said:

Since the 250PX has a 25% central obstruction by diameter .... However, the 180PRO has a 23% obstruction, and so should be slightly better than the 250PX.  ....

Actually that's not quite true for the Mak 180. While the secondary mirror spot itself is indeed 23% of the aperture, the retaining ring around the middle of the primary mirror is 63mm across, meaning the "working CO" of this scope is actually 35% unfortunately.

Cheers, Magnus