NGC 1502

Years ago I got quite interested in the Cape Newise 8”. This was at Kelling star party in north Norfolk when the vendor had them on display. From what I can recall the concept was good but the execution difficult. Apparently collimation was very challenging. Occasionally they can be found on the second hand market, if the price was very low I might possibly take a punt….. Wow, talk about “thread drift”……guilty as charged😳

Indeed I have that book along with several similar by Richard Berry, Reg Spry, Charles Frank…. Fully agreed an optical window would be an extreme solution, but it has been done! Not an option with a basic workshop like mine but one for an optical expert with a relevant optical workshop and time to spare!

For us eyepiece junkies what a fascinating thread😊 Some rambling comments for what it’s worth… I don’t need eyeglasses to observe, but I use reading glasses for everyday use. My 3-6 Nagler has 10mm ER and I find zero problems in use…but if I do use reading glasses I can see the whole 50 degree field with the rubber eyecup folded. I own all focal lengths of TV Radians except the 3mm. As long as the click stop eyeguard is properly deployed I don’t have problems with eye positioning. I do accept others have problems. The original TV Nagler 4.8mm gets lots of complaints about tight eyerelief. When I owned one I found the eyerelief adequate for me without glasses. The problem I did have was constant fogging of the eye lens in damp conditions due to the close proximity of my eye. Apart from that it was an excellent compact high power eyepiece. My 35mm Panoptic is a lovely eyepiece. But reading various threads I discovered there were 2 versions. It would seem that both versions were optically the same. The difference was that early versions had the eyelens more deeply recessed than later versions. What year the change occurred I do not know. I have a set of original Vixen LVs. I like them a lot, especially the 30mm LV (this is not the later 30mm NLVW) In use I find the 30mm LV so wonderfully easy to use, my eye goes immediately to the right position. The 60 degree apparent field looks far larger than it is, in fact I prefer it in use to my 27mm Panoptic. And the 27 Pan is wonderful in other ways… I could ramble further, maybe later….

Hi Alan. Not sure what’s best. For deep sky fuzzies I don’t think it matters. But a top quality 6” is mainly a double star or planetary scope, that’s how I use mine. I’ve never used a curved vane spider although many have. I think the choice comes down to this:- The thick single arm secondary support you have holds collimation excellently, but gives a pronounced spike on very bright objects like Mars, Jupiter or Venus. A thin 4 vane spider holds collimation adequately. On bright planets a much less pronounced cross spike. A well designed and constructed curved vane- as said I’ve never used one, but people I trust like Gary Seronic says something like- 4 vanes concentrates the diffraction, curved vanes diffuse the diffraction across the whole field of view. Whichever you choose the diffraction is there, either concentrated into lines, or diffused across the field. An expensive option with no diffraction (other than from the secondary itself) is a full aperture optical grade window that holds the secondary in place. My only experience of that is my Edmunds Astroscan, but that’s definitely not a double star or planetary scope, but a low power wide field “sweeper” or comet catcher. You almost certainly won’t be taking that route, but when contemplating it is an option. Of course an optical window produces its own issues in addition to the cost, like how optically flat is it, how good are the coatings, where to I get one…..etc😊 DIY telescope making is a hobby within a hobby. But it’s a great hobby because the weather is totally irrelevant and you can spend many happy hours in your workshop, before binning it and starting again 😁 Yep, been there, done that! Again- corrections and comments welcome😊

I have used silicone sealant intended for construction or repair of glass aquariums to secure a Newtonian secondary. It may be that regular silicone would suffice, perhaps experts in that field would know. However given how disastrous it would be for the secondary to detach and fall on the primary, I’ve been prepared to pay the extra. Richard Berry, a well known telescope guru many years ago, used silicone to secure the primary, so it would seem a good plan. Commenting on your mention of stress released pyrex:- Again I’m not an expert on that, but wouldn’t it be possible to stress the glass by improper mounting? For instance, if edge clips as found on many commercially made scopes were clamped tight, even if the glass had been annealed and stress relieved, clamping down would surely stress the glass? If silicone was used to mount a primary, I don’t think a complete ring around the edge would be necessary. 3 blobs on the back surface should suffice. Advice from years back said support at 70% of mirror diameter from the centre, with thick nails under the mirror until the silicone had dried. This prevents the silicone from squashing flat. Once dried, remove nails. Comments and corrections welcome 😊

indeed 25585 is Richard, lives in the UK. I’ve bought items from him, he’s reliable, items accurately described and posted promptly.

In 1994 I purchased a 6” f6 Hinds primary and flat, and built it into a Dob. A recent rebuild included recoated mirrors at Galvoptics Basildon. To fix the primary to cell I used double sided foam tape. Please note I did not use double sided tape, but thicker foam tape. This secures the mirror without introducing stress to the glass. To further secure the mirror I used 3 brackets around the edge made from aluminium angle, with foam tape between bracket and mirror and between bracket and cell. Two things to note. I used top quality branded foam tape intended for outdoor use. The 3 brackets do not intrude onto the optical surface of the mirror. The views are excellent. The scope splits double stars beautifully. Saturn easily shows cloud bands, Cassini division, shadow of the globe on the rings…..quite stunning in good conditions. Similarly Jupiter is a fine sight, much belt detail, GRS, shadow transits like inky black bullet holes on the cloud tops…… Recently I took this scope to Alan’s house while he was contemplating his fine AstroSystems 6”. Mr Kipling made fine cakes, Mr Hinds made fine mirrors😊 Ed.

Hi Alan, just a thought….. You wish to make the primary cell collimatable. Presumably, as the original construction excellent it would only need a very minor tweak. I recall that the cell is fixed to the tube with 3 small screws into the edge of the cell. I know those screws are near the end of the tube, but is it possible to enlarge them a tiny bit? Then the cell could be moved a bit, hopefully to tweak the collimation into precise alignment by trial and error. Any movement could not be inwards because of the lip on the cell, but the enlarged holes could allow tiny movement of the cell away from the tube. I don’t know exactly how close those 3 holes are to the end of the tube, but you only need a smidge…. The above would allow you to fix mirror to cell as originally, then the focuser could stay as it is, plus the classic look would be retained. Ed.

Interesting comparison 👍……..as you say, a rarely used focal length. I occasionally use my Vixen LV 2.5mm on tight double stars in rare stable atmosphere. I love seeing the airy disc and diffraction rings, and of course it’s a delight when you finally split that double or triple after many tries!!

Hi Alan, please see incoming email. Cheers, Ed.

In damp cold conditions your best plan is to put measures in place before dew forms on the optics, not after. You could make a dew shield from camping mat foam. Don’t make it too short, at least 2x the aperture. Secure with velcro. Perhaps a low heat dew band around the tube, level with the front corrector plate. If (or rather when) dew does form use a 12v dew gun very carefully. Check what’s available from our sponsors, First Light Optics. Don’t be tempted to wipe dew from optical surfaces, especially outside in the dark, it’s so very easy to cause scratches. Maybe do an online search, see what others have done. Good luck! Edit- click on the FLO banner at the top. Do a search “dew prevention” lots of equipment available!

Plus 1 for BST Starguiders, great value. If it were me, I’d go that route rather than a barlow.

Very sadly the first part of the above is “sometimes” true but not always. Different folk can have a different quality of service. Agreed Asian mass produced mirrors can be excellent. Premium mirrors need rare stable atmosphere to see the difference. Many take the view that an Asian mirror is as good as is needed….most of the time. Not so sure that white is the best tube colour. If there’s stray light around the area near the focuser can be distractingly bright. As always….YMMV 😊 Ed.

The reason for using the thick foam:- My local club runs 2 dark sites. At one site the final 2 hundred yards is very bumpy and uneven. The other site has a hard road for the last 3 quarters of a mile, but there’s lots of speed bumps. The foam is not because of thin aluminium tube, just a precaution to avoid messing the collimation. Agreed that OO does use thin aluminium, but in my experience it’s fully adequate for its purpose. One advantage with OO optical tubes is they are significantly lighter than the equivalent size from other makes. My club has a 12” Meade Lightbridge for loan. I’ve borrowed it….the extra light grasp is welcome but the significant weight is not! A clubmate once owned a 12” f4 from OO UK and it wasn’t much heavier than my 10”, quite manageable in fact. One way to make a very heavy Dob more user friendly- When observing from home, if the scope can be stored in a shed or conservatory close to the observing place, 3 lockable castors fitted to the base. Ed.

I do respect the views of others…..however I have to respectfully disagree with those that say the tube is too flimsy and the secondary spider inadequate to hold collimation. I own a 10” f4.8 OO UK Dob, and have owned their 8” f6. I’m not saying they don’t have issues, but holding collimation is not a problem I’ve come across. In fact the opposite has been my experience. I’m fussy with collimation, I want each observing session to deliver the best I can get. I’ve transported my OO 10” many times to both of my local clubs’s dark sites, and to public viewing sessions by car. The optical tube goes on the back seat of my car with 3” thick foam padding between tube and seat. The tube is tied to the head restraints for security. On arrival and after setting up, a collimation check has shown no issues. Of course the 3 primary mirror clips must not be clamped tight. But neither should they be too slack, that can easily cause the mirror to shift. Depending on when the scope was manufactured, it’s possible that the 3 collimation springs are inadequate. If those springs can be compressed between fingers, they are woefully too weak. They need to be very stiff indeed to do their job. The 4 secondary spider nuts that hold the vanes to the tube must not be slack, tightening those cannot clamp the the secondary mirror. Again, absolutely no disrespect intended😊 Ed.

It’s been a long time I read up about erecting prisms. But my understanding is that the idea is to use an erecting prism with an astronomical refractor. Such a refractor used without any diagonal (often called straight through viewing) gives an upside down view, so birders for instance won’t want that. They may be ok with using a regular 90 degree (prism or mirror) diagonal, this does give a “right way up” view, but left and right reversed, and this may be acceptable. If a “correct view” is required with an astronomical refractor (as seen by our eyes, binoculars, spotting scope) then an erecting diagonal is the answer. The TeleVue 60 degree diagonal or a 45 degree erecting diagonal gives a “correct view” and at the same time a more comfortable access to the eyepiece for daytime terrestrial viewing.

I tried an erecting prism once for a refractor. My idea was to get a “correct” view, same as you get with binoculars or birding scope. This gives more intuitive star hopping and navigating the moon’s features. It works as above. Decent views at low power, but at medium to high power the sharpness was compromised. Could be ok for low power terrestrial views. Possibly the TeleVue 45 degree erecting prism may be better. You could always phone them to ask, they don’t take emails. You will get an honest answer, not sales pitch. Edit for correction- just checked, the TV erecting prism is 60 degrees. Ed.

An elasticated shower cap on the back end of the tube should help to keep the critters out. If it’s for a scope larger than 8” then a regular shower cap may not be large enough. But not too hard for a DIY job to make a larger one…. Definitely agree…..best to clean it.

Late to the party…….. I’m not envious. I am VERY envious😁 Enjoy….Ed.

If you intend to travel out of the city how will you get there, by car or public transport? You only need a small area to set up in, if the field is uneven is there no part of the field you can use? Also, if traveling by car can you set up close to the car, or would you need to park and carry equipment very far? How much do you intend to spend, what’s your maximum budget? If you have a limited budget, best to do visual observing rather than imaging. Many people new to observing find equatorial mounts confusing! Perhaps continue to use what you already have for a while, a 3” reflector used with enthusiasm can show you a lot! The above information will help folks on here give advice. All the best with your decision 😊

All the best in your endeavours…..however- Perhaps your enquiry would be better in the “getting started with imaging” section😊

Good online source-google Stellafane telescope making. Lots of links to further links. Even if you’re not building a scope it’s a great read.

Kriege and Berry book- The Dobsonian Telescope. Covers everything you need for DIY large Dob build. Includes a section for an 8” solid tube Dob.

The 7t1 is a little gem, super sharp and small. I wish I’d kept mine, I now have a 7t6, a bit more eyerelief but I never had problems with the 7t1. Only Nagler I didn’t get on with was the 4.8t1. I could cope with the shorter eyerelief, but because my eye was so close to the glass, it was forever fogging up. Apart from that, it was excellent.

You could try ENS Optical at Birmingham. They have all sorts of second hand astronomy kit. You may have to buy a complete mount, or you may get lucky and get just the part you need. Their website says they’re away at the moment. Search the website, or wait until they return and phone. Steve Astbury knows his stuff, I’ve found him helpful in the past. His prices are high, but his knowledge and service is very good. If you cannot sort it, the ETX optical tube assemblies can be removed from the mount fairly easily, and fitted to something like a german equatorial mount (GEM) with drive to the RA. Google “deforking a Meade ETX”. Another possibility is “Weasners ETX site”. Don’t know if it’s still online, but if available it’s a source of everything imaginable about all models of the ETX. Keep searching, lots of links to further links. Hope you sort it. Ed.