Ricochet

The first thing I thought when I saw the M42 thread was that I could screw a clicklock to it.

Yes. The magnification given by any particular combination of eyepiece and telescope can be found by magnification = focal length (telescope) / focal length (eyepiece) so the shorter the eyepiece the higher the magnification. If the apparent field of view (AFoV) of each eyepiece is the same then the true field of view (TFoV) will be larger in the eyepiece with the longer focal length. If the apparent fields of view are different then it may not be true. You can approximate the true field of view using TFoV = AFoV / magnification or substituting in the previous equation TFoV = AFoV * FL(eyepiece) / FL(telescope) Sharp detail is a lot more complicated as it is limited at low power by aberrations in your eye and diffraction at high power so you can’t say either high or low power is sharper. As for eyepiece suggestions I would suggest getting a DSO eyepiece that will give an exit pupil in the 2-3mm range which in your telescope means an eyepiece with a focal length in the 10-15mm range. For planetary a 1mm exit pupil is a good starting point, so a 5mm eyepiece, but this will give you 240x which may be above atmospheric limits some of the time so I would suggest a 7mm in addition to this. The 5/8/12mm BST Starguiders will work well in your scope and I believe the OVL Nirvanas excluding the 16mm will also work well in your scope so you could get the 5mm Starguider and the 7 and 13mm Nirvanas. Alternatively, the 3-8mm SvBony Zoom has been getting some good reviews recently, especially in the 5-8mm part of the range, so would work well for your planetary eyepiece and you could get this instead of the 5 and 7mm individual eyepieces.

I think a maksutov will be better than an achromat for planetary but have a narrower maximum field of view for wide star fields. The 127 mak would perform better than the 102 and seems to be the Goldilocks size for the mak design. The skywatcher AzGti mounts are controlled from your phone or tablet but have dual encoders so you can move the scope manually without losing alignment. However, I’ve not used one to know how well they work in manual mode. Both the 102 and 127 Maks are available on this mount. Note that some of this range are AzGte rather than AzGti, which means that they don’t have the dual encoders. I think you will need to go outside for the phone to pick up gps in order to use the goto system and aside from the window glass degrading the view, the chances of a planet being in the right place to view from inside through a window is very small. Using a goto system with children is often recommended as it means you can move quickly from one target to the next without the children getting bored waiting for you to find it. If you don’t want a full goto system then the Celestron Starsense Explorer is a manual system that you can attach your phone to to aid with finding objects. However, the mounts are not so well regarded and there are no maks in the range.

This is going to be your main problem given your location in London. Your pupil size won't be the limiting factor, rather how (un)acceptable you find the greyness of the sky at any given exit pupil. You will have to try to judge how your 30mm performs in this regard to decide whether it is worth trying a longer focal length with a lighter background sky. The one downside of the 30mm UFF is that it "only" has a 70° field. If we use the approximation of TFOV = AFOV * FLeyepiece / FLtelescope then the 30mm UFF should have about the same TFOV as my 21E, approximately 1.75°, although I would say the 21E just fits the Pleiades so perhaps that is a sign of the differing distortions in the two eyepieces. Switching to my 28mm Nirvana increases the field to ~1.9° and frames the cluster that little bit more nicely and so for this size of object provides a worthwhile alternative, but as @John says, the shorter focal length eyepiece tends to provide the better view when you don't need the extra field of view. If you do go for a longer eyepiece then check that the AFOV is wide enough that the TFOV does increase over your 30mm and look for reviews that discuss the edge performance as you don't want to be buying an eyepiece where the extra field isn't actually usable, which is quite likely with cheaper eyepieces.

Astro baby is wrong. Cheshire for all secondary steps, collimation cap for the primary. Use the edge of the Cheshire to get the secondary circular and concentric under the focuser. Insert the Cheshire the appropriate amount so that the circular edge and your secondary appear to be the same size to make this step easier. Use the Cheshire crosshairs to adjust the secondary to align with the primary doughnut Use a collimation cap to adjust the primary so that the peep hole is centred in the primary doughnut. You can still use the Cheshire here but the crosshairs obscure the dot and doughnut.

Look at this Celestron red dot finder scope: https://www.firstlightoptics.com/finders/celestron-starpointer-red-dot-finderscope.html See how the rdf has two screws at the bottom that adjust the clamp to grip to the rail on your telescope. Now look at this Skywatcher rdf: http://skywatcher.com/product/red-dot-finder-slide-in/ It has a different foot but look at only the top section. You can see the exact same two screws as on the Celestron finder. The bottom stalk is removable and just an additional part that you do not need for your telescope. This is the same for all Synta finders that you are probably seeing on Amazon, they all fit your scope, you just have to remove the additional lower part. The only thing that you need to watch out for is that you don’t buy a JOC (Bresser/Explore Scientific) rdf as their rail/clamp is a slightly different size.

Given this, which other telescopes do they also stock and have you compared the prices to online retailers? If there is a suitable smartphone going spare (or your grandson has one) that can be used for the app then the Starsense Explorers are decent choices, aside from the 127 you have seen and the tripod mounted 114.

I suspect this 4" rule comes from the same basis as the idea that for DSO observing you only need to make eyepiece steps that at least double or halve the brightness of the image, which is done by choosing root 2 (1.41) or larger jumps in eyepiece focal length. To double the brightness of an image with mirror size changes we need to double the area of the mirror, which again means we should be considering at least a root 2 change in aperture. For a 6" scope this would require at least an 8.5" scope, so we have to skip the 8" and choose the 10", for an 8" scope we need 11.3" so we have to choose the 12", and for a 10" we have a borderline situation where the maths says we need 14.1" but it is probably close enough that it still works in the real world. If we go smaller than this then it suggests there is a suitably large gap between a 5" and an 8", which is smaller than our 4" rule, and I think we see enough people with both an 8" dob and Hertitage 130p to say that this probably still holds. What I need the dob mob to weigh in on is how this holds up for the really large apertures. If you've got a 14" is a 20" a suitably large step up or is 18" large enough? Is the next worthwhile step from a 20" an 28"? When it comes to refractors then I suspect that if you are using it for DSOs then the same rule will apply, so it probably isn't worth buying a 120ST if you already own a 102ST, but a 150ST would give a different enough view to be worthwhile. Of course the 120ST is still an improvement that you could buy it and not keep the 102ST (and the same applies to the Newt/Dob examples above). However, frac usage isn't so heavily biased towards DSO observing and we see a lot of people using them primarily for double star and planetary observations. In this case it isn't the light gathering capability that matters but the resolution of the telescope, which is proportional to the aperture. The ideal increment is probably not the doubling/halving that we assume with DSOs else the next step up for someone who owns a 4" frac would be an 8" frac. I think @Nik271's suggestion of a 20% increase in aperture sounds reasonable, but that is bad news for the financial controllers of everyone who owns a 4" frac as that would mean that having a 5" frac in addition to the 4" is a worthwhile propsect. Focal length is not an important characteristic for visual planetary, unless in terms of focal ratio of telescopes of the same type. I would suggest that you should really be considering aperture (good) and central obstruction (bad), and that your experience with the 70ED vs C5 is largely a result of the large central obstruction of the C5. Actually, I think it will make a big difference for some types of objects, but you need to consider which objects you are observing. When observing DSOs we have two sorts of objects: extended objects and point sources. For extended objects the brightness of an object is a function of exit pupil whereas with point sources the brightness is more a function of aperture. The background sky is a type of extended object so if you try to observe an extended object like M31 the ratio of object and sky brightness will remain the same so there is only a marginal improvement from in increase in magnification (at the same exit pupil) when moving to a larger scope. However, if you wish to observe open star clusters then you are observing a group of point sources. In this case a larger scope will make them brighter and by decreasing the exit pupil you can make the background sky darken more quickly than the stars and so they become more visible. In the case of globular clusters like M13 then you have an interesting case that at small apertures they appear as extended objects but once you step up to a medium and large scopes they start to be resolved as point sources and then you can see more with larger scopes (minimum of 8", 10" or 12" will open up more "smaller" globulars).

I dont think anyone makes kits to convert dobs to full goto. If you bought a large enough goto mount you could mount the OTA on that. Your best bet is probably to buy the cheapest Celestron Starsense Explorer and fit the phone bracket from that onto your dob which will give you push-to for finding objects, which is what I assume you want the goto for.

No, you will need a monopod. The smaller field of view means that in addition to needing some support you could also do with a red dot finder. It will be easier to switch from one view to the other with a tripod rather than a monopod. It might still be possible with a monopod. At the cheaper end the general advice is to stick with porros. Once you pay enough you can get good roofs but I don't know where the cross over is. 10x50 binoculars can be hand held and so are much easier to pack in a bag. I guess the question really is how much space do you have in the bag?

That's a great find, about half the price of the versions stocked in the UK.

The reports on the tech are good enough that I have considered buying a cheap Starsense Explorer and modifying the cradle to fit my dob. The cheapest frac is currently £169 and the difference between the two dob lines is about £200 so I guess it's in the right ballpark for the cost of the tech, and it is only the tech your are paying extra for as these are essentially the same scopes built in the same factory on the same production line. I'm not sure there can be any real height difference between the two either so I would put any listed size differences down to being measured by different people on different days with different tape measures. If you prefer to pay extra for mechanical quality then I think the Bresser is probably the best, then the Stellalyra and then the Celestron/Skywatcher. Height wise they are going to be very similar if not identical. The real difference is the weight. I'm often glad that I didn't go bigger than my 8" when I have to pick it up at the end of the session and so I would lean towards the 8" for your daughter. I use 7/10/14mm XWs with my 8" so your Delos eyepieces can definitely be used there. At longer focal lengths I've got a 21E and 28mm Nirvana. Cheaper options would be the 20mm APM XWA (or clones of) and the 30mm UFF. The real field of view provided by those two is going to be pretty similar so based on the resultant exit pupils maybe go with the 30mm UFF with the 8" and the 20mm APM if you choose the 10".

I think that both supplied eyepieces will have eye relief that is too short to use with glasses and so you will have to take your glasses off to view through the telescope. When you are focusing remember that it is a focuser and not a magnifier and that you should turn the focuser to make stars into the smallest points of light you can. The advice to set up during the day usually applies to roughly aligning the finderscope with the main telescope. Terrestrial views are closer than the "infinite distance" astronomical objects are at, and so anything you focus on during the day will require the focuser to be more extended. The only way focusing during the day will help is that when you focus at night you know you will have to wind the focuser in a bit. My advice would be to try using your telescope at night without your glasses and see how you get on. If your astigmatism is mild it might not make that much difference. I wear glasses but currently do all my observing without glasses. If your astigmatism proves to be interfering with your views through the telescope then you will need to purchase some eyepieces with long eye relief that allow you to use them with glasses, for which we will need to know your budget.

As per my advice in your previous thread your best bet for planetary views is to buy a 2x barlow like this Astro Essentials one. You can save money buy buying this exact same barlow with any other brand name, or the Celestron Omni, direct from China on eBay. With your telescope you ideally want a 4 or 5mm eyepiece for viewing the planets but Plossl eyepieces this short have even smaller eye relief which is not comfortable so you can use a barlow with a longer focal length eyepiece to get the same magnification in a more comfortable manner. You already have a 10mm so with a 2X barlow this is the same as a 5mm eyepiece. When funds allow you could also upgrade to a slightly better 10mm or buy another eyepiece. For nebulae and other DSOs longer focal lengths (lower magnifications) are needed and in terms of pure focal lengths the supplied eyepieces are ok, but I would advise widening your maximum field of view with a 32mm Plossl or 23mm SvBony Aspheric. A 12.5mm Plossl might be a slightly better all round focal length than the 10mm for this which with a 3X barlow instead of the previously suggested 2X would emulate a 4mm eyepiece for the Planets.

Unfortunately, the Astromaster Newtonians come with those erecting 20mm eyepieces that only have about 40° fields. I would suggest that it would be very useful to get something with a wider field of view to help with finding objects. A 30/32mm Plossl will give the widest possible FoV but perhaps with a background that is a bit grey in light polluted skies. Another option would be a 23mm SvBony Aspheric which is very cheap due to the plastic construction and lenses but optically quite a nice eyepiece. They are available on Amazon/eBay but currently Aliexpress has what looks like a good deal. I think the 10mm is also a good performer, but the 4mm is not so good. In terms of barlows a 2X barlow would give a larger (hopefully better) view of the planets with either the stock 10mm or the Aspheric. The Astro Essentials barlow is another item that is optically very good. It is available under a variety of different brandings, most cheaply directly from China through eBay or Aliexpress. If it looks the same as the Astro Essentials one, it is the same barlow. In an ideal world I think the 2x barlow, 5/8/12mm BST Starguiders and the 23mm Aspheric would make a good set, but new Starguiders are over budget and would have to be sourced as and when they turn up on the second hand market.

I think an 8" dob is a great scope. Reading through the "background" the 8" Celestron Starsense immediately comes to mind but having read further this size of scope may not be the best for your circumstances. A full size 6/8/10" Dob is best stored assembled on the base, pointing upwards. The circular base board is the widest part and is a bit under 2ft in diameter. You need about an inch clearance between the mirror and inside wall of the OTA so whichever size mirror you go for the OTA will be about 2" wider. The OTA is about 4ft long so adding in the base height and clearance you are going to need a storage space 2ft square and 4.5ft high in your flat. In the car I always found that the OTA would fit across all three back seats and would be almost touching the doors either side and so the base went in the boot. This limits you to only being able to drive with yourself and one passenger unless you have enough space to be able to put one or two seats down and have the OTA pointing forwards from the boot into the rear seat space. It is definitely not a scope that will fit in the car for the holidays unless all your other luggage fits in a roof box. With regards to moving it to your observing locations, as you live in a ground floor flat and don't have to carry it down stairs, it will be suitable to be used from your communal garden. However, how much surrounding buildings obstruct the skies may dictate whether this is a suitable observing location. If your block of flats is a two storey house-height building surrounded by other house-height buildings then it is probably fine, but if these are high rise flats surrounded by other similar buildings then you are probably better off planning to transport your chosen scope elsewhere when possible. An 8" dob is not a scope that I would suggest you can carry down to the local park or take on public transport. You can carry it a short distance from your flat to the car, drive to a location, and then carry it a short distance from the car to the set up spot. In addition to the scope itself you will require a height adjustable chair and probably end up with a case full of eyepieces so taking it to and from the car is at least a two trip process if you're on your own, unless you can devise a way to take it in one trip using a trolley or carrying some items on your back. You would lose the benefit of the stability, but not the cheapness of the mount. I suspect you would be looking at a way of converting the mount to sit on top of a tripod, or buying a whole new mount, after a few sessions. Personally, I would say anything from 150X up is a good ballpark figure to aim for. Two important criteria for planetary performance are aperture (bigger is better) and % secondary obstruction size (smaller is better). The 8" is f6 whilst the 6" is f5 so it is likely that the 8" is better on planets due to both aperture and secondary obstruction. The slightly longer focal ratio also means that the coma free (sharpest) area in the centre of the view is also bigger. When it comes to the eyepieces the f5 scope will be slightly harder for the eyepieces to correct so the image will be slightly worse as you move from the centre to the edge of the field of view. In terms of 3mm vs 5mm eyepiece if you go for a simple design like a Plossl or Ortho then eye relief is a function of eyepiece focal length and so shorter eyepieces are more difficult to use (so barlowing a longer focal length is more comfortable). If you go for something more complex like the BST Starguider then it's picking up the knowledge that in that particular line the 3.2mm isn't as good an eyepiece as the 5/8/12mm so again barlowing a longer focal length is preferable, but at the top end there is no difference in performance as far as I am aware between the 3 and 5mm Delites. The 200X limit is again a ballpark and highly dependant on atmospheric conditions on the night. This very much includes the atmosphere inside the telescope and so ensuring any telescope is sufficiently cooled before high power use. Bigger scopes take longer to reach equilibrium and so this could also be a consideration where you're having to take any scope out from your warm flat into the cold night. About a minute edge to edge of the field of view. You will probably want to keep it a bit more centred so on an unpowered scope you might want to move it every 30s or so. With a bit of practice and possibly fettling the mount this isn't an issue. I don't even think about it with my 8". Some (tripod based) mounts have slow motion cables which makes tracking easy, and the long flexible cables are good for preventing vibrations being transmitted to the scope (this isn't an issue with dob mounts). It isn't the screw mechanism per se. There are some high quality micro focusers that work in a similar way. The issues arise from it being made from plastic and having some play in the threads. PTFE tape is usually used to tighten up the slack and it will be happier with lightweight eyepieces. You could do, but depending on conditions it might be too much. 5/6/7/8 might all be useful, but if there is only the budget for one I'd probably go for a 7mm. Proper winter clothing. It is so much colder at night so you need more substantial clothing than if you go out during the day. There are two similar sounding degrees, Physics with Astronomy and Physics with Astrophysics. Astronomy is more what we observe and why whilst Astrophysics is the complex mathematical equations that govern how things work. If choosing the latter being really on top of her game in terms of A level maths and, if possible, Further Maths is going to being to be a massive advantage throughout the whole degree.

Ursa Major 6” f8 Dob if you can stretch your budget a bit. Unfortunately, £250 doesn’t go very far so the only thing in budget that potentially could go on your mount is a Skywatcher 102mm Mak. The 127 would be better but is over budget. The 72ED is also a better planetary scope than the Skyhawk but again over budget. The dob will be better than all of these. In fact if you want something better than the dob above for anything “near” your budget you’re probably going to have to look at a bigger dob.

This is true, but the mini-dobs are so low to the ground that you need to find some way to raise them up and I think that very quickly you will be looking for some way to adapt them to sitting on a tripod. In this size of Newtonian I quite like the look of the Bresser Nano 114 because it comes on an Alt-Az tripod rather than an EQ mount or mini-dob base. Whether or not this is anywhere near the level of portability you want is another question. Ideally you want a carbon fibre photographic tripod that is lightweight and folds down to a small length and the Bresser has a Stainless Steel tripod with only two sections per leg. The Skywatcher Heritage 100p, which is the Skywatcher branded version of the Orion Skyscanner, comes with a 3/8" thread on the bottom of the base so you can mount it on top of a photographic tripod. Additionally, the heritage 100p/Skyscanner come with a proper Vixen dovetail. which will make fitting them to a different mount in the future much easier. The Starblast looks to have a tube cradle fixed directly to the mount which is not so easy to switch over (the cradle may be able to removed and screwed to a dovetail). They can easily removed from the base, but the mini-dob bases aren't really designed to be taken apart so you have this big lump of a base that won't fit in a backpack. While the 100/114mm dobs are relatively short scopes, they are quite chunky so if you do get one in a backpack I don't think there will be much more room for anything else. The Newtonian design requires space between the mirror and inside wall of the OTA so they are wider than their aperture. For the 114mm scopes you are probably looking at a tube width of 140mm, while with the refractors you were looking at earlier only the dewshield has to be wider than the aperture, the OTA can in fact narrow to be smaller than the aperture (I don't know the spec for the ST80, it could be 80mm until the focuser) Binoculars are definitely the easiest thing for you to carry but the downsides are that they only have a fixed magnification and if you observe whilst standing, looking at anything over say 45° is uncomfortable. If you're camping you may have something you can put on the ground to lie on to alleviate this problem. Personally, I think binoculars are fine if you're only observing for five minutes, but anything over this and I'd much rather have either an ST80 or small Newt like the ones you've been looking at.

No mention of budget but I would be looking for something like: Mount: Skywatcher AZ4 or AZ5 Finder: A 8/9x50 RACI would be nice given the narrow FoV of the telescope but this will require some sort of red dot in addition. The Rigel would be a good choice given that it is relatively small and has a self adhesive mount you can simply stick to the OTA. Diagonal: whichever mirror or prism star diagonal fits your budget. Eyepieces: A 32mm Plossl as a finder/low power and then some shorter options. 12/18/25mm Starguiders would work well.

Assuming that you have enough in your budget to buy some eyepieces, the 200p dobsonian. It is not a close call at all between the two lines of scopes. The eq mounts bundled with the astomasters mean that despite being smaller they aren’t really any less bulky. Optically, the 200p wins on both aperture and the quality of the mirror(s). To get started you will need to buy a selection of eyepieces because you can’t use a telescope without an eyepiece. The 200p comes with two focuser extension tubes, one for 1.25” eyepieces and one for 2” eyepieces, so make sure that both are included with the scope that you buy. The finder scope is also a requirement to be able to find anything so check that is included. With regards to the condition of the scope have a look at the condition of the mirrors. Check that they aren’t smashed or scratched and that the reflective coating appears to be in good condition. Check that the focuser moves in and out smoothly over its whole range. The base units are made from chipboard like flat pack furniture so check for any obvious damage and that the movement is smooth in both axes. Additionally, the standard 6/8/10” dobs are too low to observe whilst standing so you will have to also budget for some sort of height adjustable chair. The size of these scopes does mean that they are not suitable for carrying up and down stairs, over long distances or on public transport.

You can remove the rubber top to gain maybe a couple of mm, but the eye lens retaining ring is slightly recessed so there is a proud lip around the top of the eyepiece which could potentially scratch the glasses.

Given this, which eyepieces do you currently own? In my opinion zoom eyepieces work best when you need that fine granularity for high power observing, but are not so useful at low and mid powers where you don't need anything closer than root 2 changes in focal length. My (f6) grab and go setup has only three eyepieces; a 3-6mm zoom, a 13mm and a 24mm (approx 2X steps for mid/low powers). If you already have something to cover the mid power then the 3-8mm zoom most people are suggesting might still be the best option so long as your astigmatism is mild enough to get away with not using glasses at the resulting exit pupils. Assuming your scopes are the f5 versions then the 3-8mm zoom will result in exit pupils between 0.6 and 1.6mm. Reading from the Televue graph below if you have less than 1.5 dioptres of astigmatism you should be OK to use the full range of the 3-8mm zoom without needing your glasses. Televue: Determining When To Use Eyeglasses Televue: DIOPTRX

I agree. Decent glass is the difference between trying to identify a bird based on shape or feather patterns. I've no idea about purple people though. Sadly, this is way out of the stated budget, especially if we start looking at spotting scopes.

Your requirement for glasses friendly eye relief and budget make this a very difficult choice. The previously mentioned 12mm BST Starguider will work well in your F5 scope. has a 60° field and comes in under budget at £55, but you might find that the effective eye relief pushes your glasses into your face and makes observing uncomfortable. I did when I tried glasses with the 25mm (having already sold my 12mm by the time I started wearing glasses). An alternative at £59 is the 12.5mm Stellalyra LER which has a slightly smaller 55° field and a longer eye relief (as long as the lens isn't recessed). When it comes to a 25mm I think it becomes impossible to find a suitable eyepiece within your budget. Most of the cheaper "modern" designs use varying strengths of negative lenses below a common upper set of lenses to create the varying focal lengths. The longer the focal length the lower the power of the negative lens and the higher the telescope focal ratio needs to be for the eyepiece to give a good image. In the case of the 25mm BST Starguider there is no negative lens group at all which means that it's great at F12 but awful at F5. Given this common problem my advice would be to completely blow your budget and buy the 24mm Stellalyra UFF as your lowest power eyepiece. These are the same as the old goldlines, of which the 15mm is the worst eyepiece I've ever used. Only the central 20° or so was usable at F6. The shorter focal lengths may (should?) perform better because, as with the Starguiders, they use negative lenses in the nose to create the shorter focal lengths.

I think the general consensus is that while they are very dark face on they tend to be more reflective at shallower angles and so breaking up a flat surface by giving it a texture will give the best result. There is a thread in the diy section about mixing sand or sawdust into the paint to achieve this. I used Musou black and flocking on my 72ED in three ways; flocking inside the dewshield, flocking that was then painted inside the OTA, and paint straight onto the inside of the drawtube. The painted flocking gave the best result and the straight paint the worst. The finish when painting it onto a larger smooth surface wasn’t very good either, but on small areas it worked fine. I can still see reflections from very bright objects from areas coated only in the paint, although I think it is still better than the factory paint.