Alan64

For those who wish for their maps and charts to match what they're seeing through an ocular, at night, then yes, a penta-prism seems to be the new ideal... https://www.amazon.co.uk/Orion-52055-1-25-Pentaprism-Diagonal/dp/B07C85Z8V4 I saw that one, the only one I believe on the market at present, and just the other day... https://www.youtube.com/watch?v=mJEl6Rba_VU Would that the presenter had had a wee screwdriver handy, then to take out the prism and exhibit it. It's likely made by either GSO, or Synta; the former I'd wager. The port, where an ocular would be inserted, its stop looks to be narrowed, and similar to that of this 90° GSO Amici that I have... ...with its Amici-line visible, and as the camera revealed. The line wasn't visible to the eye at the time. The clear aperture of my GSO is 20mm; that of the penta-prism: 29mm, and most generous for an erect-image diagonal. Still, the presenter didn't tilt it quite far enough to see its full aperture, there where an ocular would be inserted, and either unwittingly or intentionally as the case may have been. It may be narrower on that end. Perhaps they'll drop the price a bit in future...

Thank you. There is that, at least. Yes, the aluminum-foil tape turned out to be the ideal thickness to make the focusser tight enough to allow the battening down of the screws without it slipping out of alignment. I had tried two strips of it: far too tight; and then one of the double-sided tape with the one foil: still too tight. I had it right the first time, I found. I then ripped the last layers off; and applied a single foil, again. The decorative, scored, bronze tabs, and flat-washers, help in retaining the alignment afterwards. This was the result of my first attempt at collimating the focusser... ...much improved, but I've removed everything since, and in preparation to flock the tube. How gracious it is indeed that the current manufacturers have allowed an f/13 achromat to slip out of their factories. However would that it were an f/15 or f/18 instead. Incidentally, my brother has a C90. I've used it more than he has, at night instead, but very little at that. The Maksutov simulates this 70mm f/13 achromat; but the achromat is lighter, albeit longer, with minimal false-colour, and most importantly, unobstructed; hence my drive in the correction of this one, and with no holds barred.

I decided that what I had done to the objective-cell, I would also perform upon the focusser, and in making it collimatable as well...

The TS "Photon" is Teleskop Service's house-brand. I would venture to guess that the manufacturer of its mirrors is Guan Sheng Optical in China, aka GSO. I say this because the vendor High Point here in the U.S. carries a house-branded 150mm f/5 Newtonian, and manufactured by GSO. Mind you, I'm not stating that it is indeed, but only that it's quite probable. GSO manufactures the very popular Apertura AD8(formerly Zhumell Z8), a "Dobsonian" which is also marketed here in the U.S. The vendor Agena Astro of California sells all sizes and focal-ratios of GSO primary-mirrors and optical-flats. In addition, a U.S. manufacturer of premium "Dobsonians" sports within its base-model offering: GSO mirrors. Give TS a call and ask.

Hi Gerry, A 70mm secondary is not that bad for that sized aperture... The secondary for my 150mm f/5 is 47mm, and I don't even have a 2" focusser. The reason that one may seem too large is because it has a 2" focusser, and so to illuminate 2" oculars. The Bresser linked to previously, its secondary is 74mm in diameter. If you like the specs overall of the TS, give it a go.

For this fix, six strips of PTFE were used. Before I cut the strips to size, I treated one side of the long strip with a flame from a mini butane torch, passing the flame over it, back and forth, for a few seconds, and in the hopes of increasing the surface tension for the adhesive, in this case the double-sided tape. I tried the 0.020"-thick PTFE out first, and with scraps of that inserted loosely between the drawtube and its supports... But I could only insert those for two of them, not all three. So then I knew the PTFE would need to be thinner. In went the 0.015"-thick next. Success... The three supports on the interior required just three strips of 0.015"-thick PTFE, and the double-sided tape, as did the two of the outside supports and marked with green arrows... The outside support at the top, the oddball, required a strip of the 0.020"-thick PTFE, the double-sided tape, and two strips of the aluminum tape, stacked. It required that in order to bring its level up to the level of one of the interior strips just behind it... I placed the strip in between the molded runners, and above them in the process, thereby eliminating same. Now, the drawtube racks in and out, smoothly, straight-and-true, and with no slop whatsoever(as there was before the fix)... Afterwards, I checked the collimation; not bad, I think... But yes, it could be better, of course.

On the side, I thought that the interior of the focusser's housing was a bit too reflective, so I blackened and dulled it with a rattle-can of ultra-flat black paint, whilst carefully masking off the surfaces of the supports and the channel for the drawtube's rack. I used the blue painter's tape for that. You also want to ensure that no paint lands on the outside areas of the focusser, the supports, and in general... I also went ahead and spritzed the inside of the drawtube, as well as blackening the bevelled end of the drawtube which points towards the doublet-lens at the front of the telescope... The tip of the rack was blackened, too, there at the bottom of the image. *NOTE: In addition, you want to clean out and away all of Synta's original "glue, and what they try to pass off as lubrication, on the rack of the drawtube, between the teeth even, the gear of the pinion-shaft, and everywhere else, throughout. During this project, I replaced the "glue" with Super Lube , for example, a Teflon-based lubricant.

On the flip-side of a five-pence coin...<flip>...we have Synta's wonky, plastic focussers equipped on the refractors, too; gads. The Celestron "AstroMaster" 70 EQ, a 70mm f/13 achromat, and seen here perched upon my AT Voyager I alt-azimuth... ...and brimming full of promise and devil-may-care; more of the latter I expect. It all started when I had wanted an EQ-1 mount, and for my vintage 50mm f/12 achromat. I could have gotten the bog-standard EQ-1, in black and silver, but the mount's interfacing with a telescope is not up to current standards, but doable if one is so inclined. Standing out from that was Synta's zooted-up version, the Celestron "DeLuxe" EQ-1, which comes equipped with a Vixen-type mounting interface; and about time, too. But the deluxe version is not sold separately. If you want one, as I did apparently, you must include one of Synta's Celestron telescopes along with it. I didn't want one of Synta's Jones-Bird simulations, as I have enough work to do, so I chose said refractor instead. Much simpler, no? No, not actually... The refractor's focusser... This is not your typical plastic focusser for an imported refractor; the focusser's housing... It looks like a spaceship, and one of those 3D printings to boot. What will it take, I wonder, and for a smooth, slop-free, straight-and-true racking motion. The interior... There's another one of those pitiful, plastic, self-adhesive glides, and the only one within the entire focusser. Note the three drawtube supports. On the outside, we have these three supports, in addition... The top outside support is unique, in that it has molded runners... Next, the fix...

Said experiment resulted in no difference between using the epoxy or double-sided tape for the adhesive. Again, when the PTFE was pulled parallel to the substrate, it wouldn't budge. But when pulled straight upwards. it peeled right off. I am now looking into the possibility of increasing the surface tension of the PTFE, by passing a flame over it, and from what I had read online. In that case, scoring the surface of the PTFE might not be done, unless I scored the PTFE before the flame treatment.

I am now conducting an experiment with the PTFE and 2-part epoxy, the resin and hardener. I've found that the PTFE can be very easily scored on one side, cross-hatching it, and with an X-acto knife. I also scored a piece of plywood as the substrate. Epoxy readily grabs a hold of common plastic and wood, so I chose wood for this experiment; plastic, wood, no matter... I applied a thin layer of epoxy to both surfaces, then pressed them together. I have now set the experiment aside to cure, for at least a day. I placed a short metal rule on top of the PTFE, and a small screwdriver as the only weight to hold it down... You want to save the remainder of the epoxy, and to better discern when that between the PTFE and its substrate is cured... We shall see...

Thank you again. Yes, you always want a grease-and-oil free surface where any adhesives are concerned, paints too, and you definitely don't want to omit that in this project. For other applications, as I understand it, the surface of PTFE must be etched with a chemical compound, involving an acid I think, and then the ability to use a permanent adhesive, or a glue of sorts, presents itself. I had experimented with the PTFE and the double-sided tape a year ago or so. I could lift the PTFE straight up off the tape after applying it, with no effort, but when I pulled the PTFE parallel to the tape, it simply wouldn't budge, and I pulled with considerable force; an amazing and delightful discovery that was. For that reason, with the drawtube in place pressing tightly against the PTFE, the PTFE should never slip out, and for ever how long the tape's adhesive lasts. No matter then, just remove the old tape, clean said surfaces again, and replace the tape. Incidentally, the double-sided tape's adhesive is rather tenacious, the Scotch-brand in any event, as is that of the aluminum tape that I used. I only used the aluminum tape for its slight thickness in addition to those of the other two components. I'm thinking that there would be some cases where you would not need that extra slight thickness; this and other projects involving trial-and-error, you know.

Thank you. I do hope that this post not only helps, but also encourages others to fix theirs similarly.

I've had Synta's base-model 150mm f/5 Newtonian, an Orion-branded "StarBlast 6", since the fall of 2012. I didn't start using it much until a couple of years later. Since that time I've enjoyed it quite a bit, and eventually flocked and blackened the interior of the optical-tube. The particle-board mount that came with it had been long since abandoned, up in the attic now where it will remain until it rots, my preferring instead a tripod-type alt-azimuth for the Newtonian. There was only one thing left to do: enable the focusser's drawtube to rack in and out, smoothly, straight and true, and for an exacting collimation and the best images the parabola might produce. Until yesterday, whilst somewhat satisfactory, I did not have a focusser quite up to par. The problem all along was with these, and what I call "coffee-cake tray-liners", or for packaged cinnamon rolls, albeit of plastic instead of paper, and for the drawtube to glide against... I could actually see the wonky path the drawtube took as it was racked in and out. The rest of the telescope is somewhat first-rate, particularly the primary-mirror cell and the secondary's spider-assembly. The parabola of the primary isn't bad either, not at all, with my having witnessed snap-to focussing at high-power on at least one occasion, with slightly above-average oculars, and with a 3x barlow integrated to boot. During my initial attempts to fix the focusser, I ended up spoiling the original plastic drawtube. Then a year ago I was able to get a replacement, but only by being the original purchaser. A real stickler for that they are, Orion in California... I gave the inside of the replacement a fresh spritzing from my rattle-can of ultra-flat black, then I prepped the outside for more... ...but in satin-black. I didn't want a chromed end jutting into the light-path. That step is optional, of course, but the next is not, I daresay... PTFE, or Teflon®, sheets, and of varying thicknesses... For this step, I chose the 0.020" or 0.508mm thick sheet. The materials used: said PTFE in three 3/4" or 19.05mm wide strips, double-sided transparent tape 1/2" or 12.7mm wide, and aluminum-foil tape(perhaps 0.0025" or 0.0635mm thick, and the strips cut to the same width as the PTFE)... First, the interior of the focusser's housing was degreased with 91% rubbing-alcohol. I then applied the three strips of aluminum tape in a triad around the drawtube's cavity, then the double-sided tape, then the three strips of PTFE... Both the aluminum tape and PTFE should be degreased as well, after handling with the fingers, and before and after applying the double-sided tape, respectively. The drawtube now racks in and out smoothly, straight and true, and with no discernible slop...at long last. Incidentally, the PTFE will lift right up off the double-sided tape, easily, but pulling on it parallel to the tape exhibits the opposite effect: it will not budge in the slightest. The visual-back of my own is not 1.25", but 1.255" or so. I lined the inside with a strip of the aluminum tape, and now it's quite close to the ideal, and a snug fit for my eyepieces and other accessories... I stopped just short of extending the tape past the two holes for the locking screws, then pressed and burnished the tape down. This fix is for all imported plastic focussers of overseas manufacture, whether for a Newtonian or refractor. Would that, one day, it would not need to be so.

Yes, a 12mm Plossl is not bad, not bad at all. You may not want to go with anything shorter that a 10mm however, like an 8mm, 6mm or even a 4mm, as the eye-relief will be tighter and where you'd almost have to touch your eyeball to the field-lens of the eyepiece in order to see the full field-of-view.

That one may just screw onto the visual-back, and without having to get this, and as I had mentioned before... https://www.telescopehouse.com/accessories/meade-lx/meade-sct-thread-to-2-adapter.html You would need that adaptor, however, if you got a standard push-fit 2" diagonal. It's best to build up an eventual set of eyepieces, one or two at a time. The quality of a barlow is just as important as that of an eyepiece. Don't get the cheapest ones that you can scrounge up, but you don't have to break the Bank of England, either.

Were you able to determine that you can in fact connect a 2" diagonal to the telescope? You will need a specialised adaptor to connect one, if one is not already fitted... https://www.telescopehouse.com/accessories/meade-lx/meade-sct-thread-to-2-adapter.html The goal of upgrading to the 2" format is in realising the lowest powers with the telescope. For example, you can insert this 2" 56mm ocular for one of the lowest powers with your telescope... https://www.harrisontelescopes.co.uk/acatalog/Meade_Series_4000_56mm_Super_Plossl_Eyepiece_2_.html (36x) That's why owners of Schmidt-Cassegrains outfit them with a 2" visual-back, for the lowest powers. At the moderate-to-high powers, the 1.25" format is generally preferred. An 8mm ocular will give a power of 250x... http://www.365astronomy.com/8mm-the-planetary-uwa-eyepiece-58-degrees-1.25.html You can back off the power a bit with a 9mm... http://www.365astronomy.com/9mm-the-planetary-uwa-eyepiece-58-degrees-1.25.html (222x) ...if the atmospheric seeing will not permit 250x. Or, you can go with a 12mm... http://www.365astronomy.com/12mm-BST-Explorer-ED-Eyepiece.html (167x) The Moon and planets show considerable detail at 167x. You might wonder as to why Schmidts are not equipped with 2" visual-backs there at the factory, when they're new. The reason is simple... The hole in the center of a 200mm Schmidt's primary mirror, and through which the light from the object passes, is not 2" in diameter. It's more like 1.5", and ample for the 1.25" format. The inside of a Schmidt-Cassegrain... But given that extra 0.25" of the hole's diameter, 2" eyepieces can be used to make use of that extra bit, and for the lowest powers and the widest views that 2" oculars can provide with the design. You won't get the full view of a 2", like you would with a Newtonian or refractor, but you will get more than what a 1.25" 32mm or 40mm ocular can provide, and even lower powers in addition. It's a compromise, and simply to make a Schmidt more versatile. As a Schmidt comes from the factory, it is primarily configured for the moderate-to-high powers, and with the 1.25" format. I think that many users simply stick with the 1.25" format, aside from the more adventurous.

For the record, when observing at night, it makes no difference if the images are backward or upside-down, therefore always use a star-diagonal at night. Now, you can use an Amici at night, but the view may be narrower, in addition to seeing what is known as an "Amici line" when viewing brighter objects...

Another question? No problem at all. You've come to the right place. Your 200mm Schmidt has a focal-length of 2000mm, and is considered a "slow" telescope, at its f/10 focal-ratio. The nice thing about telescopes with slower focal-ratios is that most any inexpensive eyepiece will work very well and provide pleasing views. For the 1.25" format, a 32mm ocular would afford one of the lowest powers practical... 2000mm ÷ 32mm = a power of 63x; a 40mm: 50x, and the very lowest power available in the 1.25" format... http://www.365astronomy.com/32mm-GSO-Plossl-Eyepiece.html http://www.365astronomy.com/40mm-GSO-Plossl-Eyepiece.html Vixen makes very good Plossls... https://www.firstlightoptics.com/vixen-eyepieces/vixen-npl-eyepieces.html I have the Vixen 6mm and 30mm... The 30mm's field-lens is extraordinarily-large, and through which to look. The Antares Plossl line-up... http://www.rothervalleyoptics.co.uk/antares-plossl-eyepieces-125.html But where a Cassegrain really puts forth lies at the moderate-to-high powers. On most nights, you can use an 8mm... 2000mm ÷ 8mm = 250x, and for the Moon, the planets, and double-stars... http://www.365astronomy.com/8mm-the-planetary-uwa-eyepiece-58-degrees-1.25.html This 9mm(222x) has a somewhat wider field-of-view... http://www.365astronomy.com/TS-Ultra-Wide-Angle-Eyepiece-9mm-1.25-66o-with-Improved-Coating.html If you can wait on the boat, and do without the chromed barrel, this is the same eyepiece... http://www.ebay.co.uk/itm/1-25-31-7mm-Ultra-Wide-Angle-9mm-Eyepiece-Lens-66-Deg-for-Telescope-Best-track-/152129833857?hash=item236ba50b81:g:G8wAAOSwAuNW3lNp Incidentally, you do not have to purchase eyepieces and accessories of the same brand as the telescope. I've encountered some who think that you do, that they must match, but that is incorrect. Any brand of telescope may use any brand of eyepiece or accessory. For a relatively-moderate power, something in the 16mm+/- range would do nicely. Avoid eyepiece sets, such as these... https://www.harrisontelescopes.co.uk/acatalog/795.jpg https://www.harrisontelescopes.co.uk/acatalog/celestronepkit.jpg https://www.harrisontelescopes.co.uk/acatalog/series4000set.jpg https://images-na.ssl-images-amazon.com/images/I/51YYSxbn9IL._SY355_.jpg It's best, rather, to put together a set over time -- over the weeks, the months, and the years even -- and tailored to your observing habits. Always give careful thought to what is placed between the eye and the sky at night, and for best results.

Very good; then what you need, for use at night, is a 90° STAR diagonal. You can choose either a prism-type or a mirror-type. A quality prism-type is more costly. Synta of China equips their current line-up of Schmidt-Cassegrains with this inexpensive prism star-diagonal... http://www.rothervalleyoptics.co.uk/celestron-90-degree-star-diagonal-125.html I have one, and it's quite good, especially for the low price... I've used that diagonal with a Celestron C90 90mm Maksutov, which is similar in design to your Schmidt-Cassegrain, and I'm pleased with the views; no complaints here. Others have had less-than-stellar experiences with it, and I attribute that to the lack of quality-control at the factory there in China. Alternatively, and unfortunately, the next step up in a prism is bit more costly... http://www.rothervalleyoptics.co.uk/baader-prism-diagonal-t-2-90-degree-32mm.html That's just the prism and body, which requires an eyepiece-holder and nosepiece to complete it... http://www.rothervalleyoptics.co.uk/baader-125-helical-focusing-eyepiece-holder-t2.html http://www.rothervalleyoptics.co.uk/baader-nosepiece-125-t2.html You'd never need another, unless you get a fast refractor in future to complement the Schmidt -- for low-power, wide-field, binocular-like views -- in which case you'd want a mirror-type. In so far as the prism-types available, indeed, in so far as all things man-made, it all depends on the level of quality desired. The mirror-types are more plentiful due to the ease in their manufacture, and consequently permeate the marketplace... http://www.rothervalleyoptics.co.uk/altair-astro-125-dielectric-star-diagonal.html Now, if you'd like to use your telescope during the day, for viewing land targets, birds, or other, you would want either a 45° or 90° AMICI(erect-image) diagonal... http://www.rothervalleyoptics.co.uk/antares-45-erecting-prism-125.html http://www.rothervalleyoptics.co.uk/antares-90-erecting-prism-125.html This is what a 45° Amici looks like(left)... The 45° would be comfortable for viewing land targets close to the ground, whilst the 90° would be more comfortable for viewing objects higher up, like a mountain top or the top of a tall tree nearby. If your visual-back might accommodate, and for use at night... http://www.rothervalleyoptics.co.uk/altair-2-dielectric-diagonal-99-quartz-push-fit.html ...then to use 2" eyepieces and accessories.

Ah, a 200mm Schmidt; I thought so. That looks to be a very nice kit, indeed. You have several options for a 90° star-diagonal, and for use at night. During the day, for land targets, there are also 45° Amici-diagonals available. But we'll need to see an image of your visual-back, there at the rear of the telescope, like this... Are you able to insert a diagonal into the v-b, then tighten the screws to hold it; or do you need one that screws onto the v-b, which is common with that type of telescope? This is an example of one that screws onto the v-b... https://www.astronomics.com/images/Product/large/11608.jpg ...and in comparison to the standard type... Also, when you say "horizontal prism", are you referring to the kind that's used during the day, for corrected, upright images? If so, that's an Amici, or erect-image, diagonal.

Hello Jimmy, and welcome. Please post a nice clear pic of the kit, and to help us to help you, like this... Or, locate the specs label on the telescope itself, and list its information here. I'm thinking that it's a 150mm or 200mm Schmidt-Cassegrain. If it is, then Schmidts do require collimating, alignment of the optics inside, especially in that it's used. That may be part of the problem. The optics could be fouled as well, and that would result in less-than-stellar images. "LX90" refers to the mount, not to the telescope primarily, so we'll need some more information. Cheers.

Iain, that's a very if not extremely good afocal snap with a phone-camera. Feel free to ramp the power up to 200x and beyond when observing the Moon. I took this shot at almost 200x with my 150mm f/5... Congratulations on the new kit!

Your Newtonian is a 130mm f/7, therefore the secondary off-set is not going to be that apparent at f/7. Note the off-set here with my 150mm f/5, on the right... On the left, an f/4, and even faster, therefore the greater the off-set. Fortunately, the off-set occurs automatically during a normal collimation procedure, and does not require a separate step to perform. Once you get the collimation-cap, and a Cheshire too, hopefully... https://www.firstlightoptics.com/other-collimation-tools/premium-cheshire-collimating-eyepiece.html ...then, you can insert the collimation-cap where an eyepiece normally goes, aim the telescope at a white, blank, illuminated wall or other, place a small camera over the pinhole of the cap, zoom in if needed, snap a shot of the scene as I have many times, then post it here for us to have a look. The collimation-cap allows you see the entire optical system inside at a glance. Incidentally, a secondary off-set is to ensure that all of the light collected by the primary mirror reaches the eye. But, again, there will not be much of an off-set with your f/7 Newtonian after a proper collimation with the cap, and the Cheshire... A Cheshire is useful for for centering the secondary mirror directly under the focusser... The secondary mirror must also appear perfectly round, as a circle, or very near to it, as shown. A Cheshire also serves to ensure that the center of the eyepiece is aimed directly at the center-spot of the primary mirror... I look forward to seeing a nice snapshot of your secondary scene. Cheers,

Yes, I have the file saved, too. Cheers.

I don't know if 'twill or not. It's embedded within an Italian website(.it). I just discovered it recently, within the last month I think.