Captain Scarlet

2 hours ago, BS269 said:

I do really like the idea of having a very high powered one. On a clear night I’m always drawn to the moon and planets. Would you say it’s got a large enough aperture for good detail on them? I’m really stuck between the between the Newtonian or the mak. Newtonian is larger but I don’t have the experience to know how much difference the extra 1” (or 3”) will make. They’re also a lot cheaper so I could buy more gear to compliment planetary viewing with it. But the mak just sounds far more appealing to me. Would you say there’s a notable difference in viewing quality between a 180 mak or an 8” newt?

7-8" is certainly enough for very good views of Moon and Planets. The two scopes each have similar aperture, and are both "centrally obstructed". The mak slightly loses out on both counts to the newt, likely not at all noticeable to the eye though, but maybe wins out in collimation quality. The mak should not need recollimating from its factory settings, whereas you will have to do the newt yourself, and regularly for the primary. If you're happy collimating a newt, then that's not a problem.

The newt is far more versatile at 1000mm, you can go very wide-field if you want: for example a 35mm eyepiece gives you 29x magnification. But the newt will be a bit more unwieldy. As to how the views might differ, the aperture etc being similar suggests the views mag for mag should be similar. I haven't done a side by side comparison of my two, they live in different places, but I might bring them together soon and compare them.

It sounds to me though that in your heart of hearts you really want the mak...

M

I can't speak for the C9.25, but I do have an 8" and a 12" SW Newtonian, and currently 3 maks including the mak 180. To answer your question, yes I can definitely recommend the 180 mak, I really really like it, it performs well to my taste. Even after having completely reduced it to its component parts and reassembled and re-collimated it. See here.

One big difference between the 180 mak and, say, an 8" newt is the focal length. My SW 8" f/5 newt is focal length 1000mm, whereas the 180 mak is nominally 2700mm, and with an external R&P focuser more like 3000mm. In other words it's designed for very high magnification, and in that respect some would call it quite specialized, for planets and double stars. I've happily regularly used it on the Moon with a 6mm eyepiece, giving close to 500x magification. But I've also quite happily used it with my 35mm Panoptic eyepiece at only 77x magnification.

They only rarely seem to come up for sale used, which says something!

M

I can’t help feeling that somehow my image here image doesn’t quite fit the bill, something’s wrong ...

Aha!! Fixed it  :

Exquisite.

M

Very nice Dom, not sure how I missed this! I have a Samyang 14/2.8, but not actually used it yet! You've inspired me to get it out again. Lovely image.

M

I spend an amount of time in two different places, one rather light polluted and one most definitely not (though usually quite cloud-polluted  ).

The telescope I preferentially reach for in each place is completely different. In the Bortle 6-7 place, I instinctively reach for my high-quality 105mm refractor, for exactly the reasons @Stu mentioned.

In my dark place, I first go for my 12” newt, for the fact I can see spiral detail in M51, cloud lanes in M31 and so much depth in M13. I’d go for bigger if I had it...

Horses for courses.

M

If you look on lightpollutionmap.info, select atlas 2015 and click on your location, you’ll get a very good indication of the best sqm value you should expect at zenith. I have collected lots of actual sqm-l data from two very different locations and that website is spot on for both of them.

1 hour ago, John said:

Tele Vue stickers are useful for covering up marks

 

 

Trouble is, Televue stickers are very expensive. The free eyepieces that come with them aren't complete rubbish though.

3 hours ago, CentaurZ said:

On December 21 the two will appear to have an angular separation of only 6.1 arcminutes, the narrowest ... until 2080. However, those separations are not small enough for Jupiter to occult Saturn. ... the next ... will occur during 7541. ...

In the diary. Now, where's my elixir?

Could it be just that the clutches are too tight, so when you loosen them off to move they are still binding? IE the clutch torque "offset"? I have a SkyTee2 so am following with interest...

4 hours ago, alex_stars said:

... With respect to f2 I plan to infer that one day by imaging a planet at a given BF and then back-calculate f2. Basically confirming the assumption of Magnus that EFL = 2700.0 mm when the supplied VD and 2" diagonal is used.

Enjoy and hope that is useful to others.

Cheers,

Alex

Skymax180_equations.pdf 308.95 kB · 1 download

Very interesting, and thanks, to add to the sum of knowledge.

I too plan something similar re establishing f2, I’ll photograph a pair of stars of known separation and infer system EFL from that. Clear nights have been in frustratingly short supply lately though!

M

I have a bagful of Delos’ and I have to say up front I’m KEEPING them 😉. They work really well for me. The reason I’m posting is to suggest you might also consider TV DeLites, I also have a couple of those, see my sig, and I think the DeLite 18.2 is my favourite eyepiece in my whole collection. Certainly when tested against the Delos 17.3 they always end up level. Both ranges have 20mm eye relief.

Can I also ask, where are you based? How are your skies?
 

Cheers, Magnus

10 minutes ago, DaveS said:

I have a supposedly SQI of 21.66, and the last clear nights when I was out the sun was at about -14 deg and the sky was still noticeably lighter than under full Astro Dark at -18 deg.

Yes I think that's consistent with this data: it shows that you should expect at least a full magnitude brighter than your full darkness at that sun altitude and with your rather low level of light pollution...

Nice read.
My next two eyepieces, filling in perfect 1.4x gaps in my collection, are going to be 24mm and 13mm. The 24mm is definitely going to be the panoptic. The 13mm I want I’m not sure I’ll be able to afford for a while though.

I've been in SW Ireland since March, and my neighbour has been looking after where I live SW of London. As a gesture of thanks for his efforts, a couple of weeks ago I sent him unannounced a Heritage 150p, as he has expressed an interest in my astro shenanigans in the past.

Last Monday I had to go back to London for a week or so after an unexpected terribly sad family event. But I did get to have a strange night's observing, followed by an afternoon.

Wednesday I think I was out on my patio near midnight with my LZOS 105mm refractor on Skytee2, cruising through Ursa Major as I recall, and I could hear he was using his scope the other side of the 8 foot brick wall between our patios. then I heard him whisper-shout a faint "Magnus?". What ensued was me guiding him around the sky, shouting as quietly as we could over the wall.

I think I started him out on too difficult a very first ever target, Epsilon Lyrae. His 12-year-old daughter (it was really her present) was operating the iphone and instructing him as to what he should be seeing. They hadn't been able to line up their RDF properly, so their navigation was a little difficult. But they eventually did find the Double-Double, but couldn't quite split the pairs. They were just aware that one of the doubles was not a point. To be fair, even with my 4" using similar maginfication I couldn't quite split one of them either.

I then directed them to Mizar/Alcor. They were using a SW LET 25mm eyepiece (30x) and again trying to find it without a finder or RDF. Nonetheless they found it quite quickly, and I found it so gratifying when I heard over the wall "Ah, found it. Oh. Oh. Oh my goodness, Oh God that's lovely! Sophia [his 12-year-old], come and look at this!".

I arranged for the next afternoon to go round and see how well it was collimated "out of the box" (not very well, as it turned out), and to see if we could find "daytime Venus". Around 1pm, I went round, collimated it, it was quite a bit out, and hunted around for Venus, 29 degrees or so away from the Sun. Having resaerached where it should be using the app "Sky Guide" (which I really like) he found Venus quite quickly through 10x50 bins, and eventually I found it in the scope. He was amazed a planet was so visible when you found it yet so not-noticeable, in total broad full-sunshine (30 degrees C !!!!!). I swapped in my DeLite 18.2 instead of his SW 25mm LET, and there really wasn't that much difference! I'd given him also my 9mm  and 25mmm LETs that came new with my mak180. Those LETs are a very good improvement over the regular OEM SW eyepieces.

So, all in all, I recruited one, very likely two, to this game of ours, and had a very memorable evening and afternoon. To offset the otherwise sad reason for my week's return to London.

M

The Skywatcher 25mm LET eyepiece is a very similar focal length to your 28, but is a 1.25" ... I would exchange it for that if you want as close to like-for-like. I very recently bought as a gift to my neighbour a SW Heritage 150p scope, and I gave him my 25mm LET which I had lying around. I had an observing session with him last night and I was very impressed with it. Much, much better than the stock one that came witht he scope. We compared it to my DeLite 18.2mm which I brought with me, a MUCH more expensive eyepiece, and the comparison was very good!

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p9041_Skywatcher-LET-25-mm-eyepiece-with-50--apparent-field-of-view--1-25--barrel-size.html

Cheers, magnus

I have several astro-related things with bubble levels on them. Even on expensive stuff, such as the EQ6 head on my Berlebach Planet tripod, and on all the others, the bubble level isn't even remotely accurate. I always use a premium straight level in both horizontal axes  if I want to get things level. Putting a dot where true level is on your bubble levels is also a good idea. - I hadn't thought of that.

M

I took an SQM-L darkness reading last night, at 51.4 degrees North, of 19.01 at around 1245, very close to mid-summer. That is basically as dark as it ever gets here (near London,UK) even in deepest winter. I’ve just posted elsewhere in this section my data and reasoning why, but basically in areas of moderate-high light pollution, loss of Astro darkness is “not a thing”.

M

4 hours ago, JamesF said:

Very interesting post, Magnus.  I similarly took my (blue) 127 Mak apart quite some years back, partly to clean it.  Sadly I didn't measure everything as you have done.  I have a vague recollection however that the focus rod receiving plate was not bonded to the mirror cell, just threaded on, and therefore could work loose over time.  I'll have to see if I can find the photos to check.

James

I'd be very interested to see those pics. It will be interesting too to see if one can tell whether the primary mirror is oversized or not from them. I traded my 127 for a 150 last year and similarly didn't have a look inside.

M

Some interesting inferences about Astro Darkness:

- As the Sun sets, the "darkness level" is the same at all places regardless of your local level of light pollution, until you reach your local "darkest level". In other words, with the Sun at 6 degrees below, the darkness level is the same in Bortle 6/7 as it is in Bortle 3/4. But as soon as the darkest level is reached, the continued setting of the Sun has no further effect.

- This means than Sunbury here, Bortle 6/7, reaches its darkest level when the Sun is a bit more than 12 degrees below, only just out of Nautical Twilight. In other words, Sunbury-on-Thames never ever gets better than Nautical Twilight, which is reached with the Sun at 12 degress below the horizon.

- This further means that the concept of "losing Astro Darkness" isn't really meaningful in light-polluted places. Astro darkness is never achieved anyway at any time of year.

- It also means that, in Bortle 6/7, there is always some time, even at midsummer, when the sky can be as dark as it can ever get any time of year, which in Sunbury happens at 12 degrees of Sundown, whereas the very highest "low point" of the Sun is 16 degrees at midsummer.

- Another interesting feature is the "dip" in darkness level for the few degrees after "most dark" has been reached, and the "undip" a bit further on: people putting lights on, I guess, and gradually turning them off later on.

Cheers, M

On 22/06/2020 at 11:06, alex_stars said:

Regarding the collimation, as I understand you, you only use the larger hex collimation screws, never the smaller sunk-in “locking screws”, right? Are the locking screws more or less to define the initial mirror position and then work from there with the collimation screws? Just wondering as I always was looking for a collimation instruction for the Skymax.

The collimation screws are a fairly common arrangement, what some people call "push-pull" and others call "set-lock". Both descriptions more or less describe what's going on, but neither describes it very well. I'm going to add my own not-very-good description of what's going on:

For each pair of screws, both are necessary to fix the position of that corner of the "locking triangle" inside. The larger screw threads into the plate on the other side, effectively fixing a distance between the plate and the head of the bolt. Without the smaller grub screws (which simply push onto the plate), there is nothing to stop the larger screw-head moving away from flush to the outside of the OTA. To change the collimation at one corner, both screws need to be changed to accomodate a new spacing.

Cheers, M

I have a Unihedron SQM-L sky quality meter, and since I got it a couple of years ago I've collected quite a bit of data from two sites I'm regularly at. One is near Baltimore in SW Ireland, which lightpollutionmap.info reckons is 21.85. And the other is in Sunbury-on-Thames West of London in the UK, which the same site says is 19.05. Based on my data, it seems that both are reasonable estimates of what their skies can achieve under the best conditions.

I've collected a lot more data since my post about this a year ago, particularly for periods of twilight, and I've changed my regression model to account for the sun's position below the horizon.

A chart of measured values (and my estimator model residuals) are shown below.

For those that are interested, my estimator-equations for the two locations are:

SQ_sunbury = 18.897 + 0.2992 x sunalt - 0.0609 x sunalt^2 - 0.2496 x moonphase - 0.0186 x moonalt

and

SQ_baltimore = 21.661 + 0.1020 x sunalt - 0.0656 x sunalt^2 - 0.7319 x moonphase - 0.0160 x moonalt

(in each case moonalt and phase are set to zero for moon below 10 degrees below, and sunalt is actually its altitude above -18 degrees elevaltion, and zero if below that elevation)

These expressions, for the data I've collected so far, each give a square-root-of-sum-of-squares value for "actual minus model" of around 0.3 magnitudes.

Cheers, Magnus

I’ve just bought one of these as a present for a neighbour who’s done me some huge favours lately. I’m looking forward to looking through it...

19 minutes ago, PeterW said:

Details of the EQ6-3/8 adapter please.. then I could use “any old” camera tripod head.

thabks

peter

https://www.berlebach.de/?bereich=details&id=123&sprache=english ... and specify the 3/8" and eq6-ness to the right

23 hours ago, PeterW said:

After Turtle mail from the US (posted 20may), it has arrived. Initial impressions good, rubber winged eyecups added, waiting for stars to appear.

 

Peter

What spec are they? can't quite see. 4x34? Will be very interested to have a look through in due course