NGC 1502

Hi everyone. Advanced notice of an event jointly organised by the British Astronomical Association and Castle Point Astronomy Club on Saturday 27th April 2019 at Rayleigh in Essex. The theme of the event is “galaxies” and various talks will take place. CPAC are celebrating their 50th anniversary and will be having a display of the club’s work. A few trade stands will be present. There’s on site parking and nearby is Rayleigh station on the Liverpool Street to Southend on Sea line. Booking has now opened, full details are here www.britastro.org/rayleigh2019 Sould be a great day out ? so maybe see you there, Ed.

The basic collimation check for binoculars is to view a sharp edged straight line at a distance. A roof line works well. Focus as best you can with your eyes close to the eyepieces. Relax your eyes as you slowly move them away from your face. Bad collimation will show if the two sides of the roof line don’t line up. You could try several times, allowing your eyes a while to relax. The right hand diopter adjustment could simply be stuck, or possibly at one end of its travel ? Unless the bins are top notch models, professional servicing will cost far more than the value of the binos. Russian bins were regarded as being excellent value. I have the Russian 8x30s for birding, 7x50s for astronomy, both as pictured above. I also have Zeiss Jenoptem 10x50s that give a “better” view in some respects, but I get a noticeably steadier view with the 7x50s. Ed.

Sounds like a good plan, but make sure you are focusing on a distant object before fixing the primary cell. I’m not an imager, but I think you’ll find that to reach focus for that, the focal plane needs to be further away from the tube than for an eyepiece. Yes, the focal plane of the primary must coincide with the focal plane of the eyepiece to achieve focus. With simpler eyepieces you can often see where the focal plane is if you look into the chrome barrel. The field stop is normally at the focal plane. With more complex eyepieces it often happens that the focal plane is between the lens elements. TeleVue eyepiece specifications tell you where that is in relation to the top of the chrome barrel. There’s all sorts of ways to correct mistakes, as already mentioned you can reposition the primary, pinch a bit by more fully tightening or slackening the collimation adjustments, add spacers between focuser and tube....etc. That’s one of the great things about Newtonians, a tinkerers’ delight ? Ed.

Although I’ve constructed several Newtonians from parts, I’ve never made the tube, I’ve used plastic tubing from builder’s merchants etc. Nor have I ever ground and parabolised a mirror. ( I realise you’re also using a ready made mirror ). But of course there’s lots more that needs sorting out, including the mount. A great source of relevant information can be found at- stellafane.org After having acquired or made the tube, the next thing is to sort out the primary cell, secondary vanes and focuser positions so that the telescope comes to focus. A good idea is to get the focus position at mid focuser travel. As most focusers have generous travel, this gives a fair margin of error if your calculations are not spot on. The focal length of the primary mirror equals the distance from its aluminised surface to the middle of the secondary then out through the focuser hole to the focal plane of the eyepiece. Sounds a bit daunting at first, especially working with mirrors that have easily damaged optical surfaces. But go steadily and carefully, you’ll get there. You can give yourself a bit more wriggle room by having elongated holes to fix the primary cell. This means you can shift the cell towards or away from the secondary a bit. It’s a lot easier shifting the primary than moving the secondary, because you’d also have to move the focuser. Have a good look at Stellafane, Cloudy Nights DIY section, or of course not forgetting folks on SGL ? Enjoy the build and please let us know how it goes, good luck, Ed. Edit - it’s a good idea to make a full sized drawing. The back of a roll of wallpaper is ideal for that. A drawing helps to sort out the primary, secondary mount and vanes, and also focuser positions already mentioned.

Whatever theory may suggest, 300x is still very high with almost any telescope. With my 10” Dob, I’d only go that high on the rarest of occasions. I do use 200x often, but mostly 44x, 86x & 150x. Smaller and sharper beats larger but fuzzier. But as always, there’s varying opinions out there. Optical surfaces can look quite iffy but still deliver great views. Just carefully clean without obsessing over every smudge. Collimation is far and away more important. Ed.

Looks like a worthwhile project, have a look here - www.cave-astrola.com Ed.

Indeed, some cheaper RDFs don’t go dim enough. Probably the ideal solution is an electronic one. However I’ve had good results from painting red nail varnish on the light source. Allow each coat to dry before adding more. If you’re of male gender, you risk a sideways glance in the shop if you buy nail varnish.....? I’ve also tried placing transparent red sweet wrapper in front of the light source, but that’s no good, just gives a huge blurry blob. Better is transparent red sheet. More money, but Telrads, Rigel Quickfinder and those better quality metal RDFs do go dim enough. HTH Ed.

Agreed Nigel, the felt option is not one I personally would use, the lack of air flow around the back of the mirror would make cooldown longer, and you’re right, when I wanted to remove my Astro-systems mirror for a recoat, it took me ages. The silicon I’ve successfully used is one specifically labled for building aquariums. That may have been an expensive option, but I’d sooner spend a bit more and get it right. And I was daft enough to sell that wonderful Astro-systems 8.5” F5 scope, complete with a fabulously engineered alt-az mount....... Ed.

The 3mm ( at least ) thickness for the silicon is important to allow the probable difference in expansion and contraction for the glass and cell. If you get it wrong, then the mirror can be stressed, easy to see with a triangular shape to a defocused star. The “triangle” can be quite subtle and easily not noticeable...... And yet, back a few decades Astro-systems of Luton glued the mirror to the aluminium using a circular piece of what looked like green snooker table cloth, to make a “sandwich” of mirror/glue/cloth/glue/aluminium - this was over the whole of the back surface of the mirror, it worked very well indeed. That’s probably because the glue didn’t penetrate the thick cloth and so allowed the glass and aluminium to expand and contract independently. At least that’s how I understand it. Peter Drew on here could comment I’m sure, because he was one of the top people at Astro-systems. Apologies if my understanding is off the mark...... And Neil, if I were you, I wouldn’t fix your mirror to the ceiling ? Ed.

I’d probably feel a bit naffed off myself if a freshly coated mirror didn’t look perfect. But your earlier post mentioned that you got good views from the mirror before the recoat, so I think the coaters would be right in saying the less than perfect coating will be ok. Hope you feel a lot better when you get first light from the refurbished mirror. Have a look at some of the more famous objects to cheer yourself up ? HTH, Ed.

No problem Louis, as I mentioned, others may find differently to myself. I think eyepiece choice is a personal one, what suits one person may not suit another. I do find however that eyepiece usage is quite different by day than at night. During the day, with a dilated pupil, I find my short eye relief eyepieces very uncomfortable to use, but at night they are fine. I have a type 1 Nagler 4.8mm, with a listed 7mm eye relief. By day I find it almost unusable, but at night it’s ok. Longer ER would be better of course. However, with my eye so close to the glass it mists up more easily. No doubt the Pentax XL range were excellent and highly regarded. I used to have just one, the 10.5mm and I found the 65 degree field noticeably better than the 60 degree Radians. If they had been easily available when I bought the Radians I may have built up a set. Ed.

I would agree. On Cloudy Nights I saw lots of posts about the “coffee tone” colour ( sorry color ? ) they were supposed to have, but comparing with other makes I could never detect that. Poor old “uncle Al” great guy who’s products sometimes come in for unwarranted criticism. Ed.

Just a comment on the Radians, and very definitely not to argue, just for balance for anyone considering used Radians. I’m a Radian fan. If the eyecup is set too low, that means your eye is inside the 20mm eye relief, and kidney beaning is certain, same as any other long eye relief eyepieces. So setting the adjustable eye guard to suit you is crucial. Get that right and I find they are excellent. Others may possibly find different. And if you find the eye guard action too slack or too tight, it’s a DIY fix. Ed.

That’s my thoughts too. With my 10” Dob, 150 -200x are good, but only if the seeing is steady enough. I keep a 9mm Ortho handy for 133x and find that better at times. A smaller and sharper view beats larger but fuzzier, good planetary views are much more dependent on steady seeing than eyepiece choice. +1 for Orthos. I find the eye relief ok down to a 6mm, although I don’t wear glasses. Ed.

My local branch of Snappy Snaps ( Southend on Sea ) recently gave me a free bag of 35mm film containers. As they process film and sell it too, they accumulate empty containers and just put them out to recycle. Ed.

It’s possible to aluminise, but you probably know the kit is very expensive, and specialised. An astronomy venue I used to visit ( Fieldview astronomy B&B ) had the kit, but they had issues with uneven coatings, and the pump took hours to produce the required vacuum in the coating chamber. Not sure, but I think they gave up on the idea. They also changed the business to cater for the birding community when the starcamp moved from Thetford to Kelling Heath and greatly reduced the numbers of astronomy visitors. Ed.

Hi Niel, one of the great things about basic Dobs is the way simple DIY fixes work so well. About the only thing we can’t do is re-aluminise the mirrors. I’m really fortunate to have Galvoptics just 10 miles away, a family firm I’ve used several times with no problems. You could use furniture sliders as a temporary substitute for Teflon, would get you up and running. Yet another simple low tech fix........? Ed.

Great scopes from a sadly different era, although many of us prize kit like that ? Indeed the mirror needs a recoat, but you may be surprised at how well it would work as it is. Best wishes with your “new” scope, Ed.

Most built in dew shields are too short, but can easily be made longer using above methods. If that’s not adequate, and it probably won’t be on chilly nights, there’s heating bands that gently keep the objective just a fraction above ambient, or a 12v hairdryer from a battery pack. Ed.

I’ve made several dew shields for small telescopes from regular camping mat foam. It’s widely available from ‘outdoor’ type shops, is lightweight, doesn’t absorb moisture ( just gets wet ) and is easy to cut. No reason why it won’t be fine for binoculars. I once found the foam in black which is ideal, but any dark colour would be ok. HTH Ed.

Lots of good advice already given. I’d like to add : Best not to check mirrors by shining a light down the tube at night, most look horrid like that. Check in normal daylight. If you decide to clean, leave it for a few days, then think - is this really necessary? If you go ahead, get everything you need ready, choose a time when you won’t be disturbed, don’t rush, don’t fuss over every tiny spot or streak. Don’t start late in the afternoon when it looks like it’s going to be clear........ HTH, Ed.

Well Dave, shame your in Dorset, but at least we can chat on here, with no petrol costs ? Noticed in your signature you have some circle T Orthos, I have some of them too. Looks like we’ve both got it bad ? I’ll check back tomorrow, Ed.

Hi Dave. What made me ask the question of a collimatable cell, is because the pic in your first post showed a black objective cell that’s flared out to larger than the tube, same as mine, to accommodate the 3 pairs of screws. I’m no Vixen expert, but I’ve noticed that later versions had a slimmer cell that was not collimatable. I’m guessing that Vixen decided that as their build quality was very good, and slow focal ratios are not at all critical for collimation, non-collimatable cells were fine. I’m fond of classic stuff, my elderly Claud Butler bicycle, early Asahi Pentax cameras and Takumar lenses, a collection of Weston exposure meters, just ooze nostalgia for me. Cheers from Ed.

Hi Dave1, that’s a very nice scope, great for planets and double stars. The correction will be excellent. Pics below of my shorter F11.4 version. As you can see, mine has the original focuser, and a collimatable cell. Agree that yours will be an 80s scope. Looking at your lens cell, is it collimatable ? Of course, at F15 it will be very tolerant indeed of any slight deviation from spot on. Later versions of mine came with a non-collimatable cell, probably because Vixen decided that would be fine. Thanks for sharing a lovely classic, Ed.

Just had excellent service from ENS. Item sent promptly, great condition as described. Not the cheapest, but if it’s a reliable source that accurately describes what is for sale, that in itself is worth a bit extra money. And of courage you can phone first to ask questions about an item, which is what I did, and got friendly helpful advice, with no hard sell. Would buy from them again. Ed.