Pixies

It's appearing in my back garden a little earlier now and much higher. Definitely fainter than last night, and only visible in bins from Edinburgh.  

First night out at a pub since lockdown ended! My friend was interested in seeing the comet later, so I went out down to the beach, at midnight as the cloud cleared to try and find it.

Unlike 6 days ago, it was not easy to see with the naked eye, and in 10x50 bins was much less defined than before. The seeing wasn't great, with some high hazy cloud. The comet was positioned nicely, closer to Talitha than Talitha Australis, within the triangle bound with those 2 and another bright star nearby. By then my friend's enthusiasm had waned and he wasn't coming out again.

Anyway, back home and pottering about (and on here). At 01:30 I decided to go back out into the garden to have a quick pan with the bins before bed. Nice and clear straight up, with the summer triangle bright. M13 was visible, as was M31 but that hazy cloud was still around. I found Neowise again. It had obviously moved since I saw it 1:30 hours before. It was now placed directly between all 3 stars making up the triangle.

The ISS was passing overhead when I came back in.

The plus version is great for the observing list feature alone.

I also like how you can add the FOV circles for your scope/EP combinations, Telrad circles, etc.

6 hours ago, furkin said:

Which are the good suppliers here in the UK ?

First Light Optics are the site sponsor and are very well regarded. There are plenty of others - have a look in here:

https://stargazerslounge.com/forum/90-supplier-reviews/

6 hours ago, furkin said:

I'm still not getting the notifications to my PC.  I've turned On & Off the notify switch - to Noah Vale !

Click on 'Follow' at the top right of the page.

10 minutes ago, John said:

The Astromaster 130 uses a parabolic primary mirror. F/5 is too fast for a spherical mirror to produce acceptable results.

For a spherical mirror to produce decent images it has to be F/7 - F8. The Skywatcher Explorer 130 I believe does use a spherical mirror but that is F/6.92. I think the Astromaster uses the same mirror set that is use in scopes such as the Heritage 130 and the Skywatcher Explorer 130P.

I've observed with a couple of Astromaster 130's and they can produce very good views. The finder scope was the weakest link with the scope.

I hope you are happy with your new scope though.

 

I'd seen some reports about this. But then there's this:

https://www.celestron.com/blogs/knowledgebase/does-my-astromaster-130-have-a-spherical-or-parabolic-mirror-what-is-the-difference

I know that's from 2011 - but if Celestron are saying that it had a spherical mirror back then, perhaps there are still some out there with them? 

Hi,

There are reports that the later Astromaster 130eq scopes have a spherical primary mirror, rather than a parabolic one. Could it be spherical aberration that is causing these poor images?

"Turn left at Orion"

There, I got in before anyone else did!

Also, you can use "Mire de Collimation" to check for concentricity of the elements in you image: 

You only see the offset when you observe the shadow of the secondary in the primary.

When you are looking at the reflection of the primary in the secondary (via the cheshire/collimation cap) you won't notice the offset.

For all intents and purposes - ignore the offset. You only need to worry about it if you were installing the secondary mirror onto the holder.

The 45 degree angle faces towards the light, so that it's illuminated when you look down it and the dot and cross hairs are easier to see.

35 minutes ago, Pixies said:

yep - that's not far off.

Secondary looks good. You just need to adjust the primary so that the dot is centered in the doughnut.

Sorry - I mis-read the original post. I was only looking at the first picture (I blame the phone browser). Please ignore

yep - that's not far off.

Secondary looks good. You just need to adjust the primary so that the dot is centered in the doughnut.

You can print off the scale here:

https://www.blocklayer.com/protractor-print.aspx

On 30/06/2020 at 19:52, Dippy said:

Thank you! I am going to try this one out.

I found that they started to slip when the pads became smoother with use. I've added a couple of strips of draft excluder and that's fixed it.

All this exit pupil chat reminded me that the family, including myself, need an eye test. So I called up my opticians to see what the arrangements are. Currently in Scotland, opticians are still only doing emergency work.

But I asked about getting my maximum dark pupil dilation measured when things were back to normal. She was very interested and said they will have a go - but would have to use a dim red light. Apparently there is equipment that can do it without using visible light, but not on the NHS!

One interesting thing she mentioned is that when you are trying to measure it yourself, if you eye is trying to focus on something close, like a mirror, this will cause your pupils to contract. Worth bearing in mind, depending on how you are doing it.

OK - here are some pics. Sorry for preaching to those who obviously understand this, but this is more for confirming I've got this right.

This is my 203 Bresser Dob (fl=1213mm). I don't have a wide-field eyepiece yet, so the 25mm plossl that came with it will have to do.

mag = 1213/25 = x 48.52,   exit pupil = 203/48.52 = 4.18mm

You can see this in the first pic. It's obviously bright (daylight) so you can see internal reflections, etc. and you don't get that 'hovering over the glass' appearance of the exit pupil. The secondary mirror is 60mm diameter - the 'shadow' of this will appear as (60/48.52) = 1.24mm

Now if I splashed out on a 41mm TV Panoptic eyepiece, I would get a 203/(1213/41)= 6.9mm exit pupil and a 60/(1213/41) = 2mm diameter secondary shadow. If my eyes were young that'd be fine, but my (young) middle-aged eyes are probably nearer a 5mm max pupil size, so that 2mm diameter obstruction would be significant.

So that's my excuse for not getting a 41mm Panoptic.

29 minutes ago, tony210 said:

Hi - interesting topic - over 50 your looking at less than 5mm in most cases- so in my case although I always wanted 7x50 binoculars - 10x50 or8x42 will best fit my pupils now- such is life....

Yep- but binoculars again don't have the secondary obstruction. So my understanding is that the larger exit pupil is wasting light - but won't actually make the viewing worse. Whereas with a reflector, as the exit pupil gets larger than the actual pupil, the shadow of the secondary gets large enough to cause the view to dim.

When you look at the exit pupil hovering above the EP lens for a bright view, this makes sense. You can imagine placing your eye over it and just getting the secondary mirror shadow, rather than the light around it. I'll see if I can find a good pic

8 hours ago, POANDY said:

When I saw the moons, I thought it was a distortion in the image!!

That's exactly what happened to me when I first view Jupiter through binoculars. I thought they were some kind of internal reflections.

And got it!

I was about to go out when I realised that I could see it from the back garden! However, some telephone lines intersected the tail, so not very suitable. My son came out and as I tried to point out the location so that he could try the binoculars, he said "I can see it"! So his eyes were a lot better than mine!

Then I went back down to the beach with the camera and tripod to take some pics. I got a few that I was happy with and by the time I had finished (12:30 am) I could easily see it with the naked eye. So I thought I'd try using my 10x60 RACI finderscope on a tripod. I went back out and it looked great in the finder - but I just couldn't get a phone camera snap, so just enjoyed the view. Before I went back in I could see Cassiopeia, so I pointed the scope in the usual place and found M31 immediately. I was surprised as the sky was so light, perhaps the viewing tonight is particularly good.

So back home and out to the garden where the 8" Bresser doc was cooling. Not many clear nights recently, so I wasn't going to miss any chance.  Aligned and tested the new Telrad on my normal starting point - M57. Got there immediately and surprised just how clear everything was. It's only just got back to Nautical darkness here - another 2 weeks or so before proper astronomical darkness, so it really did look like it was good viewing tonight. I used the bins to check M13 and wow - it was really clear! I swung the scope to it and what a sight! I'm sure I could see the 'propeller'! In an 8" dob in July in Edinburgh?

i thought this was going to be the night of all nights, but when I looked up i noticed that Arcturus had vanished. The clouds rolled in at 01:30. 😢

Anyway, here's my best pic of Neowise (mucked about in UFRaw):

Lovely clear night in Edinburgh and I can see it in bins, but not quite naked eye.

About to head out with the camera

There are a few 10" Besser Dob owners on here - worth considering, although they are a little pricier that the 10" Skyliner, they're the same as the flextube.

I got an 8" Bresser, when I was originally looking for the 8" Skyliner. I haven't regretted it. 

All have long waiting times now, though.

36 minutes ago, johninderby said:

Strictly an amateur but enjoy making things. 🙂

Having recently finished renovating the house I bought a few years ago I now have loads of tools. All sorts of power tools so no problem knocking up a dob base. 😁

Looks fab! How did you cut the curves for the Alt bearings?

You'll need a bottle opener too!

I'm more of a lambic man, myself.

The clouds cleared briefly enough for me to find it. Visible to the naked eye, but hardly obvious with local light pollution. Looks great in 10x50 bins, though.

Couldn't make out any structure to the tail but the nucleus is bright and distinct - more so than on Tuesday morning, but that was a bit later and nearer to dawn.

I was going to get a camera/tripod and take it down to the beach, but the clouds don't look promising, and I've had a few beers by now, so time for bed. Still nowhere near as bright as Hale-Bopp, but great to see another with the naked eye.