Ricochet

Ah, sorry I thought you were talking about the one supposed with new astromasters (that I forgot to insert an image for). If you've got the old style then anything else is probably better, but for day time use a red dot may not always be bright enough.

If anything the closer to the main tube the finder is, the more accurate it will be on terrestrial targets, as the parallax between the scope and finder will be reduced. On my spotting scope "sight" I have two markers. One is for infinity and one is for close range, with the target somewhere between the two depending on distance. As with my previous answer, I doubt you will see any improvement by changing the RDF.

Does the photo below show the telescope and red dot finder you have (but perhaps on a different mount)? If so I don't think there is any difference in stability between the two finders. The star pointer is just a slightly jazzed up version of the standard one. It will, perhaps be slightly easier to use as it projects circles instead of the standard red dot.

Yeah, that's the barlow I was talking about. Optically it is good. The only real downside of it is that it only has a simple screw to hold the eyepiece in place.

Yes, the TeleXtender does the same job as a regular barlow. If the cheap barlow is the same as the one FLO sells under their astro essentials brand then it is actually pretty good optically. Orthos are good choices with a binoviewer.

There is no reason not to clean a modern eyepiece as far as I am aware. The coatings will be fine if cleaned properly. The only thing to watch out for is that cleaning fluid should be sprayed onto the cleaning cloth, not the lens. If you spray it onto the lens it can travel down the edges of the lens and dissolve the blackening on the lens edges and/or leave marks on the internal lens surfaces. Generally the method is Blow loose particles off with a rocket/bulb blower Brush off any slightly more stubborn particles with a soft lens brush Use the rocket blower again Clean oils off the lens with either a lens pen or cleaning fluid and cloth

28mm Nirvana, 14mm and 10mm XWs and a 2x TeleXtender for DSOs. For Lunar/Planetary binoviewers are the way to go and simpler, smaller eyepieces are easier to use.

I think a few turns on all of them would be a good idea. In my mind at least, compressing the spring should make not harder for the bolt to turn. Also, if they are screwed in further, there is less chance of one coming out again when you collimate in future.

Cheers John, I meant BCO, I even thought that's what I'd typed.

The primary collimation knobs will pass through springs. Make sure that the screw that came out still has its spring, because if it falls out at some point in the future, you'll have a hard time finding it again.

I assume you mean contact lenses. If you are using glasses instead of contact lenses then the need to wear them while observing depends on the amount of astigmatism in your observing eye. See the following chart: Astigmatism is given on your glasses/contact lens prescription as the cylinder/CYL value. Exit pupil is eyepiece focal length / telescope focal ratio. In this case, the BCOs are the way to go.

The problem with the 6mm Ortho is that it only has 5mm eye relief (the distance between the lens and your eye). The 10mm Ortho, plus a 2x barlow will be much more comfortable to use. If you buy a good barlow the effect on the views is negligible. I do realise this requires buying two things instead of one and exceeds your budget. Alternatively, if you prefer comfort over the high quality views of the BCO line, you could buy a BST Starguider (5/8/12mm). These are not quite as good optically, but are great all round eyepieces, with a 60° field and 16mm eye relief across the range.

I've got Baader Clicklocks on my dob (2" and 1.25") and they are excellent. Every scope should have them.

The radius of curvature for a Newtonian is equal to its focal length. The radius of curvature for a doublet refractor is 1/3 of its focal length. The higher the radius of curvature, the flatter the image. You will see it most obviously with stars. Focus the centre of the FoV exactly and then look at the stars at the edge. Refocus to see the difference. I can see it in my 14mm and 8" f6 (fl 1218mm), but it isn't really an issue. Focusing slightly off centre keeps everything quite tidy across the field for my eyes. If your scope has an even longer focal length than mine then you will see even less of this effect. In fact, if you look for it, you might notice that the predominant issue is actually astigmatism at the edge. This is also shown in the diagram below, where the amount that the two lines pull away from the centre is field curvature, and the difference between the two lines is astigmatism. I can see why you would have had trouble with FC while using that scope.

Try Sky Safari. I think the lowest version of that is free now. If not look for Celestron Sky Portal, which is a Celestron branded version of Sky Safari. It expects you to be connecting a Celestron telescope, but you can ignore that and use it as normal.

Unfortunately, the National Geographic branded scopes are at a price point where barlows and eyepieces that produce unusable magnifications just so they can write that magnification in the box. The 8mm by itself will probably be the point at which the most detail is in the image, but at only 87x magnification the image will probably be too small. Adding the 3x barlow will be too much, adding a 2x barlow (to effectively make a 4mm eyepiece) will probably be too much as well, so really you need something between the two. If you bought a 2x barlow with a nosepiece that unscrews, then you can screw that directly to the 8mm where it will effectively be a 1.5x barlow, and you could compare the views with each combination to find the optimum. The downside is that all the planets will still be very small. On a PC you can download Stellarium for free. If you want an app for your phone I would suggest Sky Safari, although Stellarium Mobile is also an option.

You will need to screw the nose piece from a barlow to the front of the binoviewers. With no barlow the binoviewers have an optical path length of about 110mm. This means that you would need to wind the focuser in 100mm from the point at which you normally focus to use them this way. Different barlows will change the amount of in focus required by different amounts, so you will have to experiment with the barlows you have to see if any of them produce useful results.

If you do end up buying Starguiders instead of/as well as the Nirvanas, the 5, 8 and 12mm are the ones you should consider. The longer ones will not be well corrected in an f5 scope.

It sounds like you had one of the longer focal lengths, the 25mm by any chance? The 5, 8 and 12mm work well with an 8" Dob, although the eye relief is the same. The X-Cel LX's are pretty similar, but with a touch more eye relief, maybe a touch better in terms of correction for a couple of the options (7, 9mm?). Did you have eyepieces other than the 18 and 24mm ES82°s? With my 8" Dob I use 5/7/10/14/28, which is a pretty good coverage for DSOs.

Typical. I bought it last week. 😂

What was the problem with the BSTs? If we know the problem we can try to avoid it with any suggestions, although the BSTs are probably the best all rounders at the £50 price point. Also, when you say you had 2" ES eyepieces, were those 100° eyepieces or are we only talking long focal lengths in the series with narrower fields of view so only low magnification observing?

I think I might have seen it. Mag 2.5 sounds about right for the object I saw, which was a satellite like object, following the same path as the ISS, which didn't match up to anything on Orbittrack. The problem (aside from the relative faintness) was that it was something like 12 or 13 minutes behind the ISS. I was expecting it to be a bit closer and was just about to head back inside when I noticed it moving across the sky.

Just the final step of collimating the primary? Assuming that you're using a tool where you have to look through the focuser to see the result, then you can always get a second person to slowly turn one of the knobs while you look though it. If you don't have anyone to help then try to identify which direction a particular knob moves the doughnut and then just concentrate on adjusting in that one direction. to get it roughly right. When that axis is roughly right, test a second knob. In theory you should be able to collimate without needing to move the third knob, but a small tweak on it at the end might be easier.

Going from 76mm to 130mm should show quite an improvement. Quantitatively, you're looking at almost double the resolution and being able to see stars almost two magnitudes dimmer. Where was the light? Pointing down the tube and illuminating the front of the mirror, or behind the mirror shining through it? Did you get any photos of the problem that we can see? How far in from the edge of the mirror was this coating degradation? A mirror coating will degrade over time and it is likely to start from the edge. If the issue is only a few mm into the mirror, then what you could do is to make a black card ring that can sit either on the mirror itself, or on top of the mirror clips, and mask the damaged area.

Nice. I look forward on your report on which 80mm scope is the one to buy.