Captain Scarlet

The unit of measurement is magnitudes per square arc-second. In other words, a reading of 20 will be equivalent to the brightness of  a single mag-20 star occupying every square arc-second of sky...

8 minutes ago, bomberbaz said:

Cheers Robin. If one came along at the right price I would be very tempted. I am very good at talking myself into buying eyepieces. 

I'll have to be quick on the buzzer then. I too am in the market for one

M

Yes in fact it's your fault

Your comment on your "what a night" report caused me to go back to Suiter's book and re-read the turned edge section. My mirror and view seems to tick all the boxes: markedly different in- and out-focus diffraction rings; tight diffuse glow around bright objects, especially noticeable at high magnification; and (I think I recall this, though I need to re-test it) residual softness still detectable a long way defocused one side vs the other. I'll start off by simply putting the mask over the top of the spider so I can place it, remove it repeat while always looking through the eyepiece.

Turned edge on the primary? I'm currently trying to deal with a suspected case on my 300p. Easy to test, just make a cardboard edge-mask and see if that makes a difference.

23 minutes ago, DaveL59 said:

the cat seems pretty amused by your efforts  

Yes the three of them pretty much dictate the rhythm round here!

... to try to mitigate or test for Turned Edge on my newt...

I recognize that adapter!

That lens will mean f/4 I think. To avoid increasing exposure time, which at 30s will cause stars already to be becoming streaks and the MW slightly smeared, you’ll need to increase ISO to adjust for the reduced exposure. From f/1.4 to f/4 is 3 stops, so ISO will need to be 12,800 on that basis. It’ll be very grainy though.

Try that and perhaps 6400, or reduce exposure time to 15-20s and compare the results.

I have a 6D and ISO 1600 with f/1.4 (I think) gave me a reasonable  result at 24mm FL. I used that for 45 seconds but not too much difference from 30 if shooting raw.

i documented my efforts in that exact direction here, but beware it’s a bit long and rambling!! http://www.slidingseat.net/stars/stars.html#startingout

I am currently at a lovely dark bortle 3 site, 21.8 on a decent night, but mainly live SW of London Where it’s bortle 7 19.1 not far from @Stu. Naked eye, I find exactly the same ease/difficulty to discern Alcor at both places! I think what makes it more difficult naked eye is its proximity to much brighter Mizar.

i should add, I can make out Alcor from both places...

Thanks for the heads up. Just tried, but a stubborn band of low cloud just where it should be...

I've just found the program Aberrator, so rather than try to combine and compare with separated images from Suiter's book, I can now make my own composites. Potential for me to waste a huuuuge amount of time!

yes mine too on good nights are symmetrical either side...

Yes not sure whether my problem was tube currents or atmosphere or local seeing. Temp was steadily dropping from 12 degrees to 5-6 over 2.5 hours and it is a 12". In-focus diff rings were reasonably sharp, out-focus were spiky and wobbling around. I must consult my Suiter to see...

I tried very, very hard on Zeta Herculis last night with my 12", mostly at 250x but did try 429x. Seeing wasn't good, though transparency was amazing. There was, maybe 30-40% of the time, a hint of something bluish in the right place but never any sort of separation, just a shifting splodge, no hint of any rings at best focus for that or any other star. Iota Cass was a nice triple though, though the brightest component again was somewhat blurry (are there more than 3 in iota Cass?). Pi Aquilae was behind a set of branches. Izar was reasonably decent though...

I'm just planning my night's viewing using my spreadsheet, and to start off I'll be shamelessly plagiarizing the difficult doubles you chose @markse68. When I looked for the details of zeta Herculis in my databse, I found that in my "comments" column I've annotated it "Stu's Nemesis" !

12 minutes ago, Stu said:

Wow, lucky you John. Basically invisible in any scope here 😞. Will try it tonight to see if things have improved with the transparency lately.

I've generally been able to get M51 in Sunbury quite readily through my scopes? Or is it transparency just lately?

Well I’ve had a rush of blood and ordered a Nexus ii, based on this mention and having read the post mainly between @Ships and Stars and @jetstream about the same. If it fails to give me satisfaction at least I know where @Stu lives  .

Also, only for the time being, failed to order the Sky & Telescope Pocket Sky Atlas, but only because my amazon account is UK and I’m in Ireland...

7 hours ago, John said:

The Sky & Telescope Pocket Sky Atlas has a special chart dedicated to the Virgo / Coma galaxy cluster. It's quite good for navigating from galaxy to galaxy I find. Still possible to get a bit lost in there though !

Thanks John, I might get a copy...

The chart I used, the Tirion one, seems quite large-scale (or is it small-scale) for what I was trying to do. Elsewhere in the sky it might have been fine, and I still want to get used to the "paper method", but this area is so crowded I may need to investigate something like the SkySafari route or have something automatic but less clunky than the hand controller. I do have SkySafari Pro on my phone ... what are the alternatives? Nexus you mention, is that the Nexus DSC that I quickly found on a search?

Last night, Monday, after a UK bank holiday weekend, the forecast was for a clear night and although a full-ish Moon, she wasn’t set to rise until after 2am. It had been very windy during the day but as the evening went on it died down completely.

The night turned into probably my most memorable so far. My 12” newt on the AZ-EQ6 worked perfectly, goto was more or less spot on (I aligned with a cross-hair eyepiece), I used a chart for the first time ever, the night was beautifully clear and still. It was twilight when I started at 11pm, the North-Western horizon still clearly bluish, the meter showing 20.3 at zenith. By the time I finished, just after 1am, it was 21.8, M13 was naked eye and the Milky Way through Cygnus and Cassiopeia was stark even though only 20-30 degrees up and on my “bright horizon”, looking towards Cork, Clonakilty and other South coast towns.

I started off - naturally - with Venus, now only 15%. A lovely sight, just a fingernail, but at only 10 degrees up it was showing CA and wobbling in the atmosphere.

Next stop was Izar which was quite clearly two differently-coloured stars, and the “distinct-ness” showed that the scope was performing well, and that I was going to have a good night. To affirm I also went to Epsilon Lyrae, the double-double which showed the same clarity. Excellent.

Whilst in Lyra, I had a quick look at the Ring Nebula, M57. As usual, a lovely bright Polo.

Now I moved to what I’d been anticipating, having previously photographed a fragment of a chart, Tirion’s Deep Sky Atlas, for viewing on my phone: The crowd of galaxies in and around M84 and M86. Rather than just dabbing the buttons, looking and moving on, I tried to match each one to what my chart was showing. Quite tricky with one axis reflected, but I did sort of manage it. Much more rewarding: I got M84 and M86 obviously, also NGC 4388 making a triangle of the three; and moved on from there, seeing two other close pairs of brightish: NGCs 4413 and 4425; and 4438 and 4435. And then further along 4461 and 4458, 4473 and 4477. Which, on looking up elsewhere and at photos, reasonably well seems to describe Markarian’s Chain! There were clearly other smudges around too not marked on my “chart”.

Two or three nights previously, with FullMoonlight interfering, but not high enough early enough to actually view, I’d been out to finish collimating my Skymax180 after complete disassembly (about which huge post very nearly ready…), and finished off with a view of M13. In that 7” scope, in this very dark location, M13 is predictably impressive. So with that image fresh in my mind I turned my 12” last night towards it. The contrast was suitably arresting. Sooo beautiful and deep and well-resolved. And I can never observe M13 without seeing if I can find its little companion, NGC 6207, which was a nice core and surrounding smudge.

I finished off with Polaris and its extremely blue companion before packing up just after 1am.

No fireworks but a lovely lovely clear night, not bad seeing by what I could, er, see, and the clearest MW this Spring. I’ll have to drag myself out of bed one of these early mornings and get Saturn and Jupiter…

Cheers, Magnus

9 hours ago, DaveL59 said:

or even a dab or nail varnish on the end - far better than superglue which might make it real hard to remove when you really want to.

I recently re-glued a secondary baffle to the inside of a skymax corrector plate using a couple of dabs of superglue (I knew what I was doing). I wasn’t satisfied though, and pulled the baffle off again leaving bits of baffle and superglue remaining. A little acetone-work completely restored the area to pristine condition. Acetone completely dissolves superglue.

I suspect that the “convergence” phenomenon is something you can acquire once you’re very experienced, a “professional skill” if you like. I might give it a go now that I have a small amount of experience under my belt.

I do observe though that RACI finders are the single item in the “for sale” section that never last more than a few minutes!

Goodness yes the evening of 24th May if clear should present a fantastic photo opportunity: 5% Moon, 4% Venus and 60-odd% Mercury all within 10 degrees of each other! Relative brightnesses should be quite forgiving.

It's in my diary.

Thanks, Magnus

3 hours ago, lnlarxg said:

a transformative collimation tool

yes that about describes it!