NGC 1502

If it were me, I’d email Lunt and ask their advice on etalon cleaning. A best guess is that it takes a surprising amount of dust etc to make a noticeable difference, at least that’s what myself and many others have found with conventional optical components. Ed.

A simple way to decide is this ( assuming the scope is fully assembled ) :- Rack the focuser out to where it normally is to achieve focus on a distant object. Put your eye close to the focuser without an eyepiece in position. You will see the primary mirror’s reflection in the secondary. Ideally the edge of the primary reflection should be fully within the secondary reflection with a bit of space all around. If that’s what you see then the current secondary is about the correct size. A replacement secondary a bit larger ( within reason ) won’t cause a problem in practice, even if theory suggests otherwise. If the secondary is not large enough then not all the primary mirror’s light is being intercepted so reducing the scope’s effective aperture. Hoping that helps, Ed.

What johninderby said ..................👍

I’ve reserved 2 for binoviewing 😁

Good morning all 😀 Castle Point Astronomy Club has a new website - www.cpastro.club Lots going on at this southeast Essex club, everyone welcome - usually tea coffee & biscuits available 👍 Ed.

Indeed - for visual observing polar alignment can be “near enough is good enough”. For astrophotography you need to be much more accurate with polar alignment. Ed.

Lots going on here. I’d just like to comment on one thing that’s been mentioned...... Having a slightly oversized secondary mirror is a good idea. It does give more latitude to get collimation sorted. Also it’s often said that secondary mirrors can have issues at the edges of the reflective surface, so an oversized secondary avoids using those outer edges. Also a slower focal ratio makes things less critical. That’s why I prefer my 8” f6 Dob to my 10” f4.8, easier to collimate and with good eyepieces coma is a non issue for me. I’m often at my club’s dark site, I take my 10” for the extra light grasp, but at home my 8” gets used........I could borrow a larger club scope, but the instant set up of a solid tube is just so convenient 👍 Of course as always.....your mileage may vary.......🙂 Ed.

+1 to previous comments..........👍

Hi Dave. I’ve read your post with interest because last year at a bring & buy sale at my local club I bought a pair of the Tento 7x50s from a clubmate at a bargain low price 👍. They are in top condition, with no faults apart from a tiny bit of slack in the central focusing, this could be fixable as a DIY job but I’m reluctant to meddle as the bins work so well. I’ve compared them several times with my Jenoptem 10x50s. The Jenoptems give a more contrasty view, perhaps because of the 5mm exit pupil compared with the Tento’s 7mm. The Jenoptems are super sharp in the central 60-70% but outside of that get mushy, perhaps the design was pushed too wide ? But now in my 70s I’m finding that I can hand hold 7x a lot steadier than 10x. The Tento’s hold sharpness better towards the edge of field and this plus the noticeably steadier view means I use them more. Of course many would say that for older users a 7mm exit pupil may be wasted, I do understand that, but I like the view so that’s what counts. And thanks for reading my post, I’m looking forward to reading your findings when you can...... I always hesitate to use “pair” when talking about a “bi” nocular but “pair” is so widely used I usually comply 😀 Cheers from Ed.

Yep, low tech / science, fabulous combination 👍 Cheers, Ed.

A simpler fix is to use regular electrician’s black tape, experiment to find out how many layers to fill the gap between finder and its mount. Any basic DIY shop will have suitable tape. Or sellotape would work too..... Ed.

Indeed, SGL is probably the top UK based astronomy forum, and it’s free 👍 this is a great resource and ideal for those who would otherwise find being a member of a local club difficult. In my area there’s quite a few who cannot get along to my club, by the time they are home from work, eaten etc they quite simply do not have the time to come. Shift work and family commitments are common. I used to belong to the Society for Popular Astronomy. Although they cater for beginners some of their members do advanced stuff so it’s a great organisation, always friendly and welcoming. But the forum is underused as mentioned. Cloudy Nights is great, but occasionally some of the posts can at times get very argumentative indeed 😳 Ed.

Thanks for the reminder - a whole hour of astronomy 👍 Ed.

Hi Tim. If it were myself I’d just do the best I could with securing the secondary as close as you can to the central position, then carefully star collimating at 150-200x with the star central in field of view. As the SCT primary is factory set this makes collimation simpler for users. One thing not mentioned so far is cooldown, you may already be aware but worth a mention. Ed.

Hi Tim, welcome to SGL 👍 If it were me I’d measure carefully from the edge of the secondary holder to the edge of the corrector plate on opposing sides. If the measurements are close I’d be happy with that. A rigid rule would be better than a flexible tape measure. Take care not to contact the optical surface of the corrector plate. Have you noticed any issues that lead you to suspect a problem with secondary position ? Ed.

+1 for the previously mentioned Binocular Sky monthly newsletter. Take a look in the Observing Section - binoculars. Welcome to SGL 👍 Ed.

Yes, I’ve noted a Radian problem in daytime too, but they were designed for nighttime astronomy where I don’t have any issues. I think that in daytime when the eye’s pupil is tiny, it can lead to blackouts. Fully agreed the Pentax XLs and later XWs were / are great eyepieces. As always, different folk can quite genuinely find what suits them doesn’t work for someone else. It’s been a long journey for me to finally arrive at an eyepiece set I’m happy with - Panoptic 27mm, Radians 14/8/5mm. Ed.

Indeed, the Radian colour cast issue is something I could never detect myself. The other issue often raised with Radians was blackouts. But all the long eye relief eyepieces I’ve ever tried could be made to blackout if my eye was too close to the eyelens. If the Radian eyeguard is correctly deployed, zero problem, just a sharp comfortable view...... Ed.

Ok, but no problem around here ( Essex ) and ordinary steel screws will be ok, or try a boat supplier for stainless. Cheers, Ed.

An alternative to ebay is your local DIY store, I know you’ve tried that but almost all such shops should have something suitable. Try B&Q or Wilco. If the length of the screw is too long, easy to shorten it with a vice + hacksaw and a file to clean up the cut end so the thread will still accept a nut 👍 Ed.

Hi Alan, emailed you with a possible solution....... Ed.

Good stuff Brian 👍 As you are on Canvey Island you would be more than welcome at your local club - Castle Point Astronomy Club - most Wednesdays at 8.00pm. Free tea / coffee, and if you’re quick, biscuits too 😁 Your first meeting is free and If you join, we have two members only dark sites...... Ed.

Difficult to say, so many variables :- sky transparancy, level of light pollution, is the moon up, scope cooling and collimation plus optical quality, waiting for culmination of Neptune, experience of observer. I’ve not observed Triton myself with my 10” Dob. There’s all sorts of formulas to try to give a theoretical answer, but it’s a best guess opinion..... Ed.

Hi and welcome to SGL, lots of folk here happy to help. I’ve not watched the video. However, the scope needs to be balanced in both directions. As you know, the tube assembly can be slid within the tube rings to balance it In declination. And in right ascension you can balance it by sliding the counterweights on the shaft. Balancing is achieved with the lock screws on each axis released. The balance doesn’t have to be absolutely precise, just get it as close as you can. Balance each axis separately. For polar alignment, many tutorials show how to achieve that to a precision necessary for astrophotography. That precision is not required for basic observations. Just point the polar axis north as best you can and you will be ok. One thing to mention is the red dot finder on your scope. At my local club over the last few years two different visitors have brought along the same scope you have for advice, struggling to use the finder. So did we when trying to help. I’m sorry to say this, but that finder is not fit for purpose, whoever designed it didn’t understand what’s needed. I can see that finder in your second photo. I do realise you probably don’t want more expense, but if you want to use your scope with the least frustration, then a regular design red dot finder, available from companies like our sponsors First Light Optics, would be very well worth getting. Hoping that helps, Ed.

If you already have a TV Everbrite diagonal you have one of the finest diagonals possible. Just make sure that when the eyepiece is inserted into the diagonal the nosepiece does not contact the mirror, especially if you add the Baader barlow lens. TV eyepieces would not contact the mirror, all TV products are manufactured to avoid problems when used together, but TV could not be expected to take account of another manufacturers product specifications. Ed.