NGC 1502

The observatory column is usually concreted deep into a large volume of concrete. If you did that with a tripod you’d have either 3 large concrete blocks or one enormous block. Tripod legs tend to get in the way, a column much less so, also depending on how long the optical tube is, at some positions the lower end of the tube contacts the legs necessitating the “meridian flip” that interrupts imaging or visual. As already mentioned, the column can be inexpensively done. The column is a tried and tested solution. Ed.

Hi Steve. My B400 scopeside filter shows white with LED. S/N 2010 212. HTH, Ed.

Hi again Paul. You sound a bit downhearted, but your ED 120 will give lovely pinpoint stars compared with most reflecting telescopes. Although more aperture gives greater resolution in theory, I love how much smaller refractors show double and multiple stars and open clusters. Most reflectors show blobby stars in comparison, unless it’s a specialised long focal ratio / tiny central obstruction instrument like a 6” F12 or an off axis Herschillian with no secondary mirror. These long scopes are a pain to adequately mount of course. Ed.

Globular clusters respond well to aperture and magnification. Your ED 120 will give lovely pinpoint stars, but something like an 8/10/12” reflector will go deeper and show a blizzard of stars, not just a fuzzball. I’m not a fan of high magnification for the sake of it, but globulars often can look spectacular at 200x and above, especially with a larger scope and with good conditions, transparent sky and the object at as high an elevation as possible. HTH, Ed.

Hello Rob. A 6” reflector should very easily split the double-double into its 4 components at 125x or higher. It sounds like you’ve been into astronomy for a long time having owned the 8” OO and also know how to collimate. But how high an elevation was Lyra when you viewed it ? In May it’s rising in the NE as it gets dark. Poor seeing will be worse if your target is not high up. Some will say a 6” doesn’t need much cooldown, but if it’s just come from a warm house it will take while for that to happen. If it were me, I’d recheck collimation, make sure the scope is fully cooled then try again when Lyra is higher. If that doesn’t work, a consolation prize is the “double-double’s double”, Struve 2474, also in Lyra, easily split into 4 components at much lower magnification. Good luck with your 6” scope, very capable and low hassle. Ed.

Hi and welcome ? Please don’t follow my mistake - My first eyepieces were very basic 0.96” fitting. Upgraded to basic 1.25” fitting. Upgraded to long eye relief. Joined my local astronomy club in 2002, members had wide field eyepieces, I upgraded to cheap widefield, ok ish, but fuzzy away from centre field. Upgraded to more expensive widefield......... Each upgrade involved cash of course. It would have been far cheaper in the long run to bite the bullet and get top eyepieces much earlier, and had the benefits years ago. Not saying you must get TeleVue, less expensive stuff that’s very good is available. And you can be satisfied with a few top eyepieces.......I have too many but I’m not alone in that.....? Ed.

Hello to a member in NZ ? If it were me, I’d try adding substitute weights ( food tins, bags of sugar ) and see if it affected the azimuth movement. If the movement was good, I’d be ok with adding a battery of similar weight. You may find that adding significant weight unevenly on one side only may not be ok, but the same weight distributed evenly is better. Not an exact science of course. As to lubricating the bearings, with regular Teflon pads there are differing opinions on that. Some use car polish on the mating surface. Grease is a bad idea, as it collects dust and grit quickly. But some Dobs like yours have a ‘lazy Susan’ roller bearing, don’t know what’s best with those, although grease is also probably a bad idea. Ed.

So did I. I’ve heard a rumour that digital photography may be coming. But there’s no way that will be successful.......? My non-metered Asahi Pentax and Weston lightmeter are going strong........? Ed.

I like this idea, gentle air flow through the tube assembly can prevent dew formation on the optical surfaces or at least slow it down. It’s a solution I’ve adopted for my own scopes. Ed.

No worries about the tardiness of your reply, most of us DIY types are aware of how long jobs take, plus life in general is full of other things to occupy our days..... BTW, Alan and myself are members of the same club. Regarding the distance from the focuser to the front end of the tube. One consideration is that it’s best if stray light cannot reach the inner end of the focuser. A greater distance from the focuser to the end of the tube can fix that, but at the expense of a longer tube that may be harder to transport - my scope tubes are often transported across the back seat of my car. But it’s simple to make a slip on extension to the tube, this need not be structurally strong, just rigid enough to keep its shape. Commonly available camping mat foam is good. I’ll check back now and again to follow your progress with interest. Cheers, Ed.

This modification would not be difficult with basic DIY skills and a visit to a sheet metal supplier for a strip of aluminium the same thickness as the tube. The aluminium could be cut by hand with tinsnips, but a far neater job would be to ask for it to be cut on a guillotine at the suppliers. Sheet aluminium is easily bent by hand and bolted to the tube. With care a strong and neat job could be done. The way that OO Newtonians are now made means that an extension tube on the focuser is needed for visual use, or removed to add a camera etc for imaging. But for purely visual use a focuser extension tube looks a bit ungainly especially with a large eyepiece. With the primary mirror further from the secondary that’s sorted, and also the optical edges of the secondary are not used. It’s at the edges of the secondary where sometimes it’s less than optically flat, especially at the ends furthest and nearest to the primary. A simple optical diagram will reveal all this. Ed.

That’s great Alan. I think that Dobs in general are good in so many ways, simple in concept, low hassle to set up or pack up, largest aperture per £ spent, most issues are a DIY fix. Not knocking technology but one of our fellow members at our recent observing session gave up in frustration with his go-to. Technology is great when it works ( like now as I type this ) but when it doesn’t play ball...........? Ed.

Yes, I agree about that. I’ve done DIY modified spring loaded versions that make secondary alignment so easy. Also the way the secondary is untidily siliconed to the holder may work, but looks crude. There are better ways to mount the secondary with it being held in a shell, without distorting it of course. Looks nicer and more professional, and allays fears that some have about the secondary coming unstuck and dropping onto the primary. None of this would be hard to do during production. Ed.

Stu, looking at that thread the ventilation looks excellently done, especially compared to how those older and much more basic OO cells were done with hardly any ventilation. I’m not knocking OO, but I also recall the Europa models had a 6mm thick bar across the full diameter to support the secondary. The current OO Newtonian primary cells are beautifully done, excellent ventilation, built in fan, 9 point mirror support even with the smaller sizes. Those thick secondary supports are long gone, replaced with a proper 4 thin vanes. Ed.

Alan & myself are members of our local club and we both have similar OO 10” Dobs. The pic of the OO cell in the first post that has multiple holes is my own. I think that Alan’s choice of 3 larger holes looks better. I’ve had the 10” for about 8 years, at times there was a definite cooldown issue when there was just the single small vent hole, so the extra holes were added to help. I’ve recently added a fan. This was added to increase the airflow around the primary to reduce dewing of the primary. Last October Alan & myself were at our club’s dark site and both us us suffered dewed primaries. I’ve read posts that claims that solid tube primaries don’t dew up........our experience says otherwise, it was however a very damp night. Of course Newtonian secondaries are much more prone to dewing, but at least a 12v dew gun can be pointed down the focuser. Primary dewing is much more of a problem, I’m hoping that a fan will promote air flow and reduce dewing on those extra damp nights, as well as a quicker cooldown. Ed.

All good ideas above. One thing that could be tried is to file the ends of the 3 collimation screws into a more rounded profile. That means that the ends of 3 the screws that contact the secondary holder or washer have less area in contact. With a larger contact area there’s more rotational effect on the secondary holder when a screw is turned than when the end profile is smaller. I share the frustration that these issues can cause. It’s a matter of trial & error to find what works, or doesn’t of course. Hope you sort it. Ed.

Many thanks for that.........?..........happy to hear from anyone else. Ed.

Hi everyone. TeleVue makes two 1.25” fitting Barlows, a 2x and a 3x. They are very different in physical length, the 3x being much longer. Does anyone know if they are optically the same, and if an extension tube were added to the shorter 2x version, the effect would be the same as using the 3x ? I know that actual magnification can vary according to the eyepiece to Barlow lens distance, or if when using a Barlow with a refractor the magnification changes if it’s used before or after the diagonal. But does anyone know the answer to my specific question above ? I know I could phone TV and get an honest answer, but just wondering if anyone on here knows - optically the same, just a different length ? Thanks in advance, Ed.

When I got my S&T pocket sky atlas, I completely took it to bits, laminated all the pages and rebound in a plastic folder. Probably too late if you have a tatty one, but perhaps an option for some. Well done for having a tatty atlas, much better than a pristine one that’s not seen a lot of use...... Ed.

This could be a useless comment because I’m not at all familiar with what you’re constructing. But instead of gluing, could you use removable screws instead, enabling easy dismantling for modifications ? Or is there some reason that you must use glue ? 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.

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.