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Mixed bag with an achromat


Zermelo
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Last night was my first proper chance to try out my second-hand Bresser AR102S. Clear skies were forecast by CO until 04:00, or 21:00 (Meteoblue), or 22:00 (Metcheck).  In the end, the cloud came in at around midnight. In fact, it turned out to be an excellent night in terms of both transparency (7 stars in the little dipper) and seeing (it settled down to about Pickering 8/9 overhead).

This is the first fast refractor I've used, so I was interested to try it on a range of targets.  The 102s is a straightforward F/6 doublet (no Petzval), so the received wisdom was that its real chance to shine was on larger DSOs and starfields at low to medium powers, and to expect some CA on brighter objects, especially at higher magnification. I replaced the stock diagonal with a Tak prism, which I was initially unsure about as prisms are sometimes thought to give some CA themselves on fast scopes. I had also replaced the stock finder with a 9x50 RACI.

I managed the following:

Open clusters: M103, NGC457, M45, M39, Perseus double cluster

Globulars: M56, M92

Galaxies: M33

Planetaries: NGC7027, NGC6752

Doubles: Ras Algethi, HD 170375, gamma Arietis, epsilon Arietis, iota Cassiopeiae, Double-double

Planets: Jupiter, Saturn, Uranus

 

My other scopes are a 150mm Newtonian and a 127mm Mak, and for most of the list above I had previous observations from them to compare with.

The open clusters were very pleasing. Stars were very sharp, and at medium powers there was a nice contrast against the background. Some of the clusters showed a good variety of colours, and seemed (compared with the other scopes, though I may have imagined this) to show a more obvious diversity in magnitudes, like a sound recording with a greater dynamic range. The view of the Pleiades was particularly easy on the eye (in spite of it showing up my own astigmatism on the lower powers). There was a blue haze around some of the main stars, which I initially wrote off as colour fringing. But on more careful inspection I noticed that the haze effect wasn't quite uniform around each star - there was a little wispish irregularity. Also, the colour was definitely a deep blue rather than a violet, and I'd already seen the "purple haze" around a bright star while I was aligning - a different colour. So I wonder if I was seeing nebulosity rather than an aberration? I thought I'd read that M45 only showed that with instruments larger than my 102mm.

The two globulars were good, possibly a little less bright than in the 150mm, but not significantly so. The resolution of individual stars seemed as good as it had been in either of the other scopes.

I had seen M33 a couple of times before in the Newt, but only as an amorphous patch with just a hint of irregularity. This time there were still no spiral arms, but I was pleasantly surprised to see very obvious darker and lighter patches, and a clear nuclear area.

The planetaries were both smaller ones, obviously non-stellar in the eyepiece, but showing no real shape or structure. One of them hinted at a bit of blue-green colour.

I had included some doubles in the list to explore both the colour fidelity and resolution of the Bresser. I knew that my other two scopes ought to be superior double hunters, but I was again pleasantly surprised by the 'frac. On iota Cas I split the A/B/C components neatly at 180x (AB sep is 3"). The Lyra double double was split at 120x, both pairs crisp and rock solid (2.4" and 2.3"). Most impressively, epsilon Arietis at 180x showed two, almost equal white stars with their Airy discs just barely touching - that's apparently 1.3" (the seeing was very good by now). Ras Algethi, while an easier split, showed an impressive orange colour for the primary that I'd previously seen only as a more dullish red.

Finally, the planets. I'd managed just a few seconds of Saturn on a previous cloudy night and had been impressed. This time I had several minutes as it crept between houses. At 120x it certainly wasn't large, but I could clearly see the planet's shadow on the rings, and definite hints of atmospheric banding. The Cassini division was just about visible at the extreme ends of the rings, one of those you-wouldn't-see-it-if-you-didn't-know-it-was-there sights. There was little light scatter around the disc, and no false colour that I could see.  Jupiter, though, did certainly show some violet fringing (though in its current position it had been showing a little atmospheric dispersion CA in any case with the other scopes). Apart from that, it was probably as good as I'd previously seen it - four bands were clearly visible. The moons were, if anything, better than before, being sharper (that also helps with the focusing). The addition of a yellow filter removed the fringe, but didn't improve the detail.

So overall I was very happy with the 102's performance. The purple fringing was less prevalent than I'd expected, and it seems to be more generally useful than I had supposed. Colour rendition is good and the resolution better than I'd hoped. I think I'll stick with the prism diagonal as I didn't notice any adverse effects. I'd expected my next purchase to be a fringe killer filter, but now I'm not so sure.

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That's a good catch of objects and a nice report. The nebulosity enmeshing the Pleiades is certainly visible in your 102mm refractor, and can be seen in smaller instruments too. I believe its visibility is an indication of transparency and so if you're seeing nebulosity you have a reasonably good sky. Below is a sketch I made of the Pleiades a few years ago, using a 100mm refractor. 

IMG_20160205_175527.JPG.8141fecf4ac4948e3e44ea9d7fe36d7a.thumb.JPG.0ac38d48f80207608bbe55310228dfba.JPG

 

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1 hour ago, mikeDnight said:

That's a good catch of objects and a nice report. The nebulosity enmeshing the Pleiades is certainly visible in your 102mm refractor, and can be seen in smaller instruments too. I believe its visibility is an indication of transparency and so if you're seeing nebulosity you have a reasonably good sky. Below is a sketch I made of the Pleiades a few years ago, using a 100mm refractor. 

IMG_20160205_175527.JPG.8141fecf4ac4948e3e44ea9d7fe36d7a.thumb.JPG.0ac38d48f80207608bbe55310228dfba.JPG

 

Hi Mike, that's a fabulous sketch.

I have never seen any nebulosity with my 4" refractor, though I am in suburban skies (Bortle 5 I think). Can you remember how dark the skies were when you made the sketch? I would love to glimpse the nebulosity visually; I did manage to photograph it recently which I was very chuffed at!

Thanks,

Malcolm

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Nice report @Zermelo. I’ve read some not very good things about the AR102S scopes, but it seems you either got a good one, or the reports are a bit harsh.

I had a very quick look at M45 through the 130mm last night and was surprised to see so many halos around the major stars. I put it down to fogging up of the eyepiece but wasn’t convinced either way. I need to give it another go when it is better placed (it was just in a small gap between a tree and rooftop last night), would be great to get the nebulosity from home.

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4 minutes ago, Stu said:

I’ve read some not very good things about the AR102S scopes, but it seems you either got a good one, or the reports are a bit harsh.

... or perhaps I've not observed through anything better to compare it with 🤔

I tried to find reviews, but turned up very little. There are more of the 127S, but that has a different design.

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1 minute ago, Zermelo said:

... or perhaps I've not observed through anything better to compare it with 🤔

I tried to find reviews, but turned up very little. There are more of the 127S, but that has a different design.

Ah, based on a quick Google search I think I was thinking of the XS which is f4.5, not the S which should be better at f5.9.

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I find the AR102S (f/5.9) a very convenient and easy 'scope to use - a great widefield grab 'n' go.  You can get 3 or 4deg of field at 4 or 5mm of exit pupil, and mag can reach about x240.  The hex focuser is good and smooth.  CA only happens around the edge of bright objects - it has never bothered me.  I replaced the finderscope with a Baader Skysurfer - perfectly adequate with such a wide field.

I'm sure it will continue to give you much satisfaction.

Doug.

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I've had my 102s for a few months now, and the only refractor I have to compare it with is an ST80, so I'm far from knowledgeable, but I do find the 102s very nice for wide field, and the star colours and contrasty views are lovely .  With the negligible cool down , easy portability and overall convenience of the thing I have it set up ready to go outside at a moment's  notice when there's a gap in the clouds.

I don't make a lot of effort to plan for its use, it just lets me take advantage of those brief opportunities that present themselves, so I just enjoy scanning around , sometimes completely at random , viewing familiar favourites and accidentally coming across interesting things (and finding out what they were afterwards when the clouds send me indoors !) I was impressed to find it managed a decent view of the Ring Nebula , something I'd not expected it to do as well as it did : not as good as the 150 heritage (as you'd expect) but still a nice distinct little 'smoke ring'.

I've a basic RDF on mine,  which I swap for a solar finder for daytime use, and a £10 Chinese diagonal from Amazon (allegedly dielectric, but who knows) Along with a small altaz head and photo tripod it makes for a very simple , cost effective package.

Heather

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1 minute ago, cloudsweeper said:

I find the AR102S (f/5.9) a very convenient and easy 'scope to use - a great widefield grab 'n' go.  You can get 3 or 4deg of field at 4 or 5mm of exit pupil, and mag can reach about x240.  The hex focuser is good and smooth.  CA only happens around the edge of bright objects - it has never bothered me.  I replaced the finderscope with a Baader Skysurfer - perfectly adequate with such a wide field.

I'm sure it will continue to give you much satisfaction.

Doug.

Coincidence ! The Baader skysurfer is the RDF I have on mine too ... only because one came up at a good price second hand on here 🙂  It's far nicer than the spare stock skywatcher RDF I had on it before (which has been put on permanent ST80 duties now) . I rather liked keeping the 'scope (sort of) German too !

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Thank you for the really nice report @Zermelo. I am in the market for a small frac (again) and reading your excellent nights work has enthused me even more . I really like Bresser scopes , i have in the past owned a 102/460 and used a 127L , which incidently gave me my best view of the inner planets . 

 

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3 hours ago, MalcolmM said:

Hi Mike, that's a fabulous sketch.

I have never seen any nebulosity with my 4" refractor, though I am in suburban skies (Bortle 5 I think). Can you remember how dark the skies were when you made the sketch? I would love to glimpse the nebulosity visually; I did manage to photograph it recently which I was very chuffed at!

Thanks,

Malcolm

Hi Malcom,

 I'm not sure about the Bortle rating of my sky. I did try to find out a few years ago, but I don't think its accurate as I've seen things beyond what I imagine I should. I think it was similar to yours. The nebulosity around some of the Pleiades is something I see regularly and without much effort. At first it looks like a light mist around the brighter stars and you might first think youre looking through a slightly misty sky, but looking at other stars of similar magnitude there's no haze visible. The longer you look, especially if you shield yourself from surrounding light, the more extensive the nebulosity becomes. The Pleiades is now with us again so you'll have plenty of opportunity to bag the nebulosity visually. It may help if you use an eyepiece in the 20 to 10mm range in your 4", as this should give you a dark enough sky background to help the nebulosity stand out. Longer focal length eyepieces may show a lighter sky background and so wash out the subtle nebula.

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4 hours ago, Tiny Clanger said:

Coincidence ! The Baader skysurfer is the RDF I have on mine too ... only because one came up at a good price second hand on here 🙂  It's far nicer than the spare stock skywatcher RDF I had on it before (which has been put on permanent ST80 duties now) . I rather liked keeping the 'scope (sort of) German too !

Heather - all my 'scopes have Skysurfers, they are fine RDFs, better than stock/cheapo ones.  (Almost all - the Dob has a Rigel and a RACI.)

One further point about the AR102S.  I have an 8SE (SCT) GoTo, and the 102 goes on its mount, as long as you stay lower than about 60deg.  Having GoTo (to an extent) with the 'scope makes it even more desirable!

Doug.

Edited by cloudsweeper
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1 hour ago, mikeDnight said:

Hi Malcom,

 I'm not sure about the Bortle rating of my sky. I did try to find out a few years ago, but I don't think its accurate as I've seen things beyond what I imagine I should. I think it was similar to yours. The nebulosity around some of the Pleiades is something I see regularly and without much effort. At first it looks like a light mist around the brighter stars and you might first think youre looking through a slightly misty sky, but looking at other stars of similar magnitude there's no haze visible. The longer you look, especially if you shield yourself from surrounding light, the more extensive the nebulosity becomes. The Pleiades is now with us again so you'll have plenty of opportunity to bag the nebulosity visually. It may help if you use an eyepiece in the 20 to 10mm range in your 4", as this should give you a dark enough sky background to help the nebulosity stand out. Longer focal length eyepieces may show a lighter sky background and so wash out the subtle nebula.

Thanks for the tips Mike. That's one of my goals now this winter; to look for the nebulosity!

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I’ve often wondered how the AR102 performs for the money. Am thinking I should hold out till I have a bit more to spend though but certainly sounds like it should do a fair job. 

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