Ricochet

I don't think it is you. I think that if you've got a 21E (which is a logical choice to achieve maximum FoV), 17mm is just too close. Maybe the idea with the Ethos focal length options is that you can choose either 21/13 or 17/10.

Does your Cheshire have crosshairs at the bottom? If it does, do those crosshairs line up with the doughnut on the primary however you rotate the Cheshire?

If it was my decision I would start with the 12.5mm. Start with/spend the most on an eyepiece that will give an exit pupil in the 2-2.5mm range and then work from there.

I don't think there is any need for a ~12mm if you've already got a 14mm. The two focal lengths are too similar to significantly change the views, unless you are hitting atmospheric limits, which I doubt with the telescope in question. For DSOs I subscribe to the theory that focal length steps of root 2 are as close as you should have, which corresponds to a doubling or halving of brightness for extended objects, and is what your eye sees as one "step" in brightness. I have 10 and 14mm XWs and have never needed anything else between the two (or anything between the similar 5-7-10-14 steps).

A 10" Dobsonian is a large, heavy scope that will require carrying in two parts. It also sits quite low to the ground so you need good sight lines from your observing location to see low objects. So long as you can easily and safely transport it from the storage location to the observing location then it is an excellent choice of telescope, and will show nebulae well under dark skies, and be able to show star clusters well even under light polluted skies.

Look between south and south-east sometime after 23:00. Jupiter will be the brightest thing in the sky, but quite low down so you may have to move around a bit to find a good sight line. Once you have found Jupiter, you can find Saturn by looking to the left of Jupiter, perhaps slightly down too as the planets travel in an arc. Saturn will also be visible with the naked eye, and will look like quite a bright star. Provided that you can see low down enough, both of these objects should be very easy to find. If you have not already done so, I would recommend getting a planetarium app for your phone/tablet so that you can compare what you see in the sky to what you should be seeing. My recommendation for this is Sky Safari.

The binoviewers have a light path that is approximately 110mm long, so to get them to focus with no barlow or corrector you would need to wind the focuser inwards by 110mm. With a Newtonian this is not possible, and so you have to add a barlow or corrector to the nose piece which reduces the amount of in focus required. A 1.5x corrector is not much of a change, so it is unlikely to reduce the required in focus enough for it to be within the limited focus travel typically found on a Newtonian focuser. If you were to attach the nose piece from a 2x barlow to the front of the binoviewer, you would likely find that it acts like a 3x barlow, and might allow you to focus the binoviewers in the Newtonian (might!). The C9.25 is a completely different telescope. Unlike your Newtonian, it focuses by moving the primary mirror itself. This means it has a large range of focus travel, enough that you should be able to focus the binoviewers with no barlow/corrextor attached. However, moving the mirror so much will introduce aberations, and the narrower the light cone, the better the binoviewer will perform, so you will get a better image by using some sort of corrector, even in the new scope.

When you are looking for anything, it is best to start with your lowest power (highest focal length) eyepiece and no barlow. Once you have found the object you can increase the power. I assume that it is M31 you are looking for rather than M32. They are right next to each other but it is easier to see M31. From a dark site M31 will be really large, but from a suburban location you will only be able to see the core, which is much smaller.

Yes, you should avoid touching the optics. Let them dry naturally, don't wipe them. Mirrors have the most fragile coatings, eyepieces the hardest (on the exterior lens faces at least). Unless you get some sort of organic matter on the objective it is usually best to leave it. If you ask most experienced astronomers when they last cleaned their telescope(s) the answer will usually be in years.

Great news. It's always better when something is user error than when there is a fault with the telescope.

6" Rich field frac with a white tube Heavy though, if the listed weight is correct.

I think it looks great. I'd be happy to have that set up stood in my garden for everyone to see. You've done really well to have created that from the parts you were (mis)sold.

If you've got a garden and you don't have to carry the scope far, get an 8" dob, perhaps a 10" if you're happy carrying it in two trips. If you don't have a garden and need something relatively easy to transport, try a 127 Mak, the AZGti mount looks like a nice option to me. If it has to be a refractor then get a 100 or 120mm ED doublet. Assuming you want the telescope for visual observation that is.

Mono for DSOs, bino for lunar and planets. I don't need to wear glasses with either, but if I did I don't think it would change my preferences.

You are correct, the magnification given by a 5mm eyepiece and a 10mm eyepiece with a 2X barlow will be roughly the same. Technically, there may be a slight difference because your eyepiece focal lengths wont be exactly 5 and 10mm, and your barlow is unlikely to be exactly 2X, but the numbers are close enough that you probably won't notice the difference through the eyepiece. What will make a difference is the quality of your 5mm, 10mm and barlow. If you have a poor 10mm or barlow, then the combination will also be poor and worse than a decent 5mm eyepiece. However, if you have a poor 5mm eyepiece then the image will be worse than the combination of a good 10mm and 2X barlow. A top quality barlow will be unnoticable in the optical chain and looking through a barlowed 10mm will be just like looking through the 5mm from the same series. In fact this is exactly what I do for my high power DSO eyepieces. I have 10 and 14mm eyepieces, which then become 5 and 7mm eyepieces when combined with my 2X TeleXtender. Generally: If the eyepiece type has an eye relief that scales with focal length, using a barlow allows you to use an eyepiece with a longer, more comfortable eye relief. The eye relief of a specific eyepiece is actually slightly extended when used with a barlow. If the field stop of the eyepiece is close to the diameter of the barrel, the barlow may cause slight vignetting. The magnification factor of a barlow depends on the distance between the barlow lenses and the eyepiece lenses. If the eyepiece is poorly corrected at fast focal ratios, the barlow decrease the beam angle, simulating a slower focal ratio telescope, and the eyepiece may perform better than it does without the barlow in the optical chain. 2, 3, and 4 apply only to barlows, not to telextenders/powermates. As an aside, eyepiece designs that are not scaled tend to have a barlow type lens set built into the nose of the eyepiece. The Starguider series under discussion here are an example of such eyepieces. They have a common set of four lenses at the top of the eyepiece, and the different focal lengths are produced by varying the strength and distance of the "barlow" housed in the nose. For instance if you look at the 8, 5 and 3.2mm variants then the 8mm is very short, the 5mm is a bit taller and the 3.2mm taller again. All the designers have really done here is taken advantage of point 3 above to create three different focal lengths. The 18, 15 and 12mm show a similar progression, but presumably with a lower power "barlow" in the nose. Point 5 shows why the shorter Starguiders tend to be the better ones. If you specifically want a comparison between the 5mm Starguider and barlowing the 10mm MA that came with the scope, then my vote would be for the Starguider, which really is a very nice eyepiece for £50, whilst the 10mm MA is reportedly quite poor. The Starguider will have better eye relief, a wider apparent field of view (60° vs 50°), be sharper in the middle and be better corrected at the edge.

The view being reversed does not matter for astronomical targets. If you are noticing this because you are trying to use the telescope for terrestrial observations then it would explain your focusing issues. Terrestrial targets will require the eyepiece to be further out than the focuser is designed for. If this is the case then try the telescope on astronomical targets and see if the problem with focusing persists.

Thanks, Louis. The camera aperture being analogous to a very small pupil explains it well. I can't visualise why the Mak is modifying the exit pupil of the eyepiece though.

Indeed, and it is that performance at fast ratios that you are paying for with TV eyepieces, as well as the often forgotten quality of coatings, which I imagine perform better across all focal ratios, even as the difference in correction decreases. Yes, I find myself referring to it surprisingly often. I believe that is the general consensus. I've got a 28mm Nirvana, and it is a very good eyepiece, but I do see issues as I look to the edge that tie in quite well with the assessment given, albeit without any measurements on my part. Astigmatism, I agree with, CA, I can't say I recall, but then I'm only using it in a Newtonian so there is no additional CA from the scope, and also I think a bit of FC. However, this is really being quite picky and it is only through time and practice that my eyes and brain have become "sharper" and I have become able to judge, or even notice such details. If noticing such details becomes too distracting then things can get expensive quite quickly. Sometimes it is better to think back to earlier times when such things were not noticed and remember to just enjoy the views.

A thread I think well worth reading is http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483 which attempts to give measurements for the aberration size for quite a large selection of eyepieces. The 16mm Nirvana is listed under United Optics UWA(N) and the author agrees with you, the 16mm is poorly corrected. According to the above website the Luminos is a touch better at f4 but about even at f10.

Some of those are quite extreme. Is some of the problem made worse by having the wrong spacing between the eyepiece and camera? If you were to see that visually many of those eyepieces would be completely unusable.

Nice, thanks for sharing. You should definitely mask the edge of your primary to tighten up the stars. The bright star just right of centre in the last photo shows it best, there are three gaps in the diffraction spikes all around the star, where the mirror clips are blocking the bad mirror edge. If you mask the rest of the edge you will cut out all of the other spikes, except the four caused by the secondary spider.

What if you turn the brightness down on the laser? Does the reflection ever drop to a level where you can see the reflected beam instead? If that doesn't help then another barlow is probably the way to go. The barlow you've got looks like the one sold by FLO under their Astro essentials brand. I've got one of that type and I don't recall it having that issue when I tried it.

What a finder!

I got mine off eBay. None there now though, possibly as supplies have dried up during the lock down.

Good news if it was just the collimation that was the problem. Lasers are notorious for producing incorrect collimation. Any error in setting the secondary produces double the error in the primary collimation. Unless you have a Howie Glatter laser (maybe!) I think it is best to only use a laser for primary collimation using the barlowed laser technique.