AlexK

Just got two RDF pointers from Amazon. That gunsight I'm recommending ($20) and the Svbony ($15). With the eye as close to the mirror as possible: "Gunsight" is totally adequate. Practically no parallax in the horizontal direction. Small parallax in the vertical direction far above the center, increasing to approx 20 arcmin at the very top of the window. Svbony is horrid. Bad parallax in all directions except at the very center, which is hard to catch. Is that really a concave mirror or not focused at all? Some dimming is visible in both. Svbony looks a bit dimmer, but nothing really drastic in either. Compared with my ~20 y/o cheap gunsight (very much like the new one, just without Green color, and less one reticle), its parallax is within 5 arcmin in all directions (i.e. almost unnoticeable). So either it was better made back then, or it depends on particular specimen. So the winner is: https://www.amazon.com/gp/product/B01BF5LYGW/ It comes with 5 coin batteries, allen wrenches, nice case, microfiber cloth, and overly very well made for the field (ab)use. The only good thing about Svbony is that it's all plastic, so noticeably lighter than the "Gunsight". If I would be desperate I'd try to focus its mirror (removing it from its ring and gluing it back at a better distance). But it's also made like a DIY toy (large, ugly, protruding components, lousy parts), so it goes back 100%. Oh. And Svbony has no brightness adjustments while the "Gunsight" has 5 levels. However that's not a crucial difference, as anyway both are too bright for the night use so must be modified (my method is a piece of dense red film in front of the LED and that Gunsight has a nice deep well there which will hold that piece just on friction so it will be possible to remove if necessary).

Oh, I guess for your automated observatory?

Umm... But why you want that additional shiny boxy box having the iOS app available for that already?

In my experienced opinion (I'm in the hobby from 8 years old age, also with the help of my father, all the way to professional astronomy and then back to advanced amateur, and I still remember everything 40+ years later), the GoTo is a waste of money for you, and the interest killer for your son, as it seems he is very young or otherwise not prepared for the deep technicalities a GoTo mount impose on the unprepared owner. Especialy having you mentioned he is obsessed with the telescope even when cloudy. I would highly recommend postponing the new telescope purchase and instead would strongly recommend to get him a decent Android smartphone or an Android tablet (avoid Apple products as they are dumb) along with some nice Planetarium astronomy software on it and some popular astronomy books in the digital format. That would do him MUCH more good than any GoTo gizmo. By the way, a very similar 76x700 reflector (Russian TAL "Alcor") was my third telescope upgrade in 1983 which I bought on the first ever money I earned myself gardening for neighbors all summer

If you are talking about standard multi-point cells - don't re-glue it. Replace glue-points with 3M HD Velcro dots! They are great at unloading the weight, hold the collimation very well, but easy to disconnect one by one with a pry plank (I'm using a wood ruler) when needed. To BrendanC: I'm +1 AGAINST washing in the cell. It's much dirtier than the mirror. The risk of some abrasive flake or greasy goo getting lose and ending up on the surface is like quad-fold... Don't be shy, perhaps, you will know your telescope better after the procedure. Mark and image marked everything and you will be fine. You can post your images and step by step concerns right here. We will be with you all the time! And that might became a great work-log to share with other amateurs hesitating to step into the ATM aspect of this hobby a bit Finally, learn about proper storage. My z12 have to be stored vertically but I have it stored upside down with two Mylar bags tight on each end. The primary stays perfectly clean but I'm kinda sacrificing the secondary, however so far having no issues with it either (~11 years), just gently blowing it with air sometimes (cheap photo-camera hand blower).

I've been using a car powered (12VDC) folding hair drier to fix that for some years. Then switched to the 5V powerbank and had a resistor heating the Telrad's glass and lens installed. But lately simply wiping any dew/fogging off Telrad, QuInsight, and that gunsight RDF. All of them have a large, easy to reach glass window. A piece of microfiber cloth (often accompanying cheap China reading glasses you buy online) is ideal. Try imagining that with the $400 TV one The primary culprit is your breath though. With some practice totally avoidable. The real dewing is happening due to the slow observing pace. When the device (RDF or EP) cools down too much without the radiant heat of your hands and face. But to amend that to a good extent there is no actual dew shield required just a tight fit cover (QuInsight is leveraging that method providing a trivial flip off cover for its glass on the outside (see my image of it earlier in the thread). Just flip it back when done with pointing. I'm also leveraging my warm blooded skin feature and always remember heating my working EP by wrapping it with my free hand periodically, as well as having the rest of them on my chest in the fishing vest pockets (I'm wearing microfleece under the vest which is breathable and some heat escapes to warm up EPs in the thin vest). And finally, I know the sacred Siberian "defrosting" method (don't tell anyone, it's a tribal secret!): if the EP glass got fogged/frosted at last by an accident immediately wrap it loosely with your bare hands so 4 fingers are on its body (pinkies and rings) and the rest are above the lens forming a dome; hold it for several sec with your fingers tight; then loosen and open fingers above the glass a bit and form a funnel with narrow slits between fingers and larger opening between thumbs; now exhale away from the telescope and bring your mouth to the opening between thumbs; slowly inhale the air through the funnel, so it goes through openings between your fingers; exhale away from the telescope; repeat form # 4 ~3-5 times watching for the frost/fogging gone. That "CPR" confirmed working all the way to -30C (surely if your own nose is not frosted yet, and the EP is just frosted, or started fogging in front of you, not like after several minutes).

Gotcha. The yellowish coating in the front is actually the anti-reflection film. Which purpose is exactly to reduce the light losses. But I think having the new RDF on the way you are all set. Just skip the OEG method with it, with one eye you don't have to "face" Zenith, e.g. you can look up from the corner of the eye. If the light pollution is that severe I would use Rigel close to the eye as an eyepiece, wrapping as much view as possible. Maybe even rigging an eyeguard around it. That way, even though the mirror will still reflect some starlight your eye will stay more dark adapted as well while pointing. The parallax of RIgel is significantly less than in most RDFs so keeping the eye in the same position at its back guard (which is easier touching it) would help reducing it to a non-issue. On a side note, with a small(ish) refractor, which is essentially a straight-through device when used without diagonals, you actually have the bonus: (Tadaa!) the possibility to observe laying down on your back. A common practice with binoculars is to utilize some adjustable recliner chair. You can do the same with your refractor as soon as figure the setup providing that possibility. E.g. I saw folks using their GEMs in the Alt/Az mode which helps to offset the EP position near Zenith enough to have the recliner head pillow between tripod legs.

Darkened??? Are you sure it's not a defect? Dirt/dust/grease/protective film? The bright dot is no good either, but that's rather easy to fix. Perhaps, you've got a really bad RDF (just looked through the thread and can't see you showing it or stating the model). As even on cheap airsoft gun RDFs the window is transparent enough for 3-4m stars. I had a chance to use a handful of various RDF's in the past and even though some were really flimsy, the window transparency was never an issue to even consider the OEG method. Now I see why it was hard for you. Two eyes into Zenith with one hunting for the red dot IS a torture! Hmm. Just in case. Are you aware of general basic eyes darkness adaptation measures mandatory for observing from light polluted location? Like turning off lights in your house behind you? Avoiding looking into bright light with your observing eye (e.g. a computer screen)? Wearing the eyepatch on the observing eye? And definitely begin with reducing the dot's brightness to the barely visible (I don't believe your new optical finder would be sufficient for pointing, as it's still just a keyhole in the sky, but I see the Rigel is on the way, it should fix that). Besides, how two eyes could fix the parallax existing for one eye already? If it's there it is there, move your head and the dot will shift over the sky one eye or two doesn't matter at all.

You are talking about the OEG ("occluded eye gunsight") requiring both eyes open (some sighting tools also using it, like survey compasses). But collimating sights we are discussing here are all a different thing utilizing a light beam splitter. The second eye is not needed AT ALL with all of the above discussed RDFs, folks. In fact, it's even counterproductive with these as sometimes the required "mental gymnastics" may play tricks on ya Especially if pointing over a Dob's OTA. You can quit torturing yourself already!

Sorry, but that's a common misconception. RDF, Rigel, Telrad, QuInsight are leveraging the collimation of light principle to place their reticle image at infinity, so the parallax supposed to be completely eliminated (that's the whole idea of this sighting device type) and the dot, or rings, or other reticle should appear fixed to the sky. No second eye required at all. I'm using my Telrad single-eyed exclusively and enjoying the several arcminutes accuracy of pointing every time. However, the user's eyesight and the optics used to create the collimator device is limited by its price. Thus the parallax can be easily detected in $50 RDFs due to the short focal range and severe spherical aberration of their air-blown spherical mirrors. It's much less prominent in Telrad due to the much longer focal range of the used collimator (that's why Telrad is so long) and especially good in the QuInsight due to the more expensive two-part wide field lens collimator. In military grade, 10x more expensive collimator, which I have displayed for fun above, they are also using a holographic reticle, which is compensating the collimator lens or mirror surface figure by providing a 3-dimentional reflective shape in the focal plane resulting in the much more flat collimated wavefront. They are still having some parallax, but it's already not affecting the performance and practically invisible (by the way, there are simple RDFs exhibiting a hand polished aspherical sapphire in the front, those are nearing the $1K price tag just for the starter. I believe the "two eyes" technique came from the grim times when some reputable telescope maker rolled out a beginner telescope with the "innovative" RDF sight without any "curved optics" inside I can't find any polite curse to describe that abomination, nor google for it's name and image... In practice, to reduce the parallax of small RDF's (the venerable Rigel included) the "correct posture" would be to stay behind it as far as you practically can. That way the concave mirror will have a smallish AFOV so when you finally catch the red dot/reticle in it it will be reflecting from the certain point of it. After you have it aligned with the scope it will stay there every time and show no parallax anymore, just because if you move your head to the side you will simply lose the dot Telrad would benefit from that trick as well, however its longer focal is les prone to the spherical aberration. That's why it is safe to sight from close proximity (I've been placing my nose side against the top edge of the mirror, as my Telrad was installed on the side of the OTA, QuInsight works by touching the edge with the eyebrow) and avoid the red dot hunting chore above completely. However, there are three factors making its parallax worse: the user eyesight (with any bad eyes asking for prescription optics to see stars as dots the collimation wouldn't work without glasses, you can refocus the reticle to your eyes but that's exactly what's causing the parallax, so you should focus in glasses too), the cyclic collimation pattern (collimator gets out of focus a bit due to the internal mirror gradually walking it out of perfect focal point as you change the length of the light path while aligning the reticle with the scope, using collimation screws in the same order each time, QuInsight doesn't have that issue by the way), and the ill installation angle (when the axis of the scope is at a significant angle from the optical axis of the Telrad's lens you have to align it a bit off center which is increasing aberrations).

Yeah, American skeet and trap-ers kinda laughed at me on the range too once with their rustic polished nearly with diamonds-incrustated receivers over-unders. But when I shoot 20/20 skeet 3 times in a row, and they've realized that was my first try with that modded Saiga-12 every single one came to check that wonder including from the club's booth. Surely I was banned with it ever after from any even informal competition Back to the subject: Telrad is indeed a very dated design. However its price is still too good for its functionality. The only modern rival to it is the QuInsight with its updated collimator optics. But it's nearly twice as expensive even though nearly 90% 3D printed.

Sure thing, go ahead. That's just cheap me. Though you can trust me on one thing: it's no different (and actually worse due to its miniscule aperture, impossible to reach for wiping) than my 20 years old $5 shipped off eBay from China RDF which is still kicking even on my 12ga shotgun (these are sold for ~$35 nowadays): Seriously. Just make sure you can return that nonsense. For $400 you can get an amazing Nitrogen filled true-zero-parallax internally alignable holographic gunsight: But I'd rather get another 100 deg EP for that money.

$400 for an RDF? LOL! C'mon! Even though I'm making more than that a day, I'd rather live pointing by sighting along the OTA all my life than feed this scam scheme. Telrad is a most solid choice, and definitely has many more useful properties than any RDF.

The easiest trick is to discharge the battery a bit with a higher current load. The second easiest is to cover the LED window with some nail polish (along the way it is possible to improve its aperture as well (like cover the window heavily, then scrap a tiny hole).

Congrats. I have eventually removed my optical finder and using the Orion 7220 in ACI (not RACI, as the angle is not straight ) mode in the finder shoe. Not for finding objects but simply for binoculars-like views (surely I can point with it too just replacing the wide EP with the reticle equipped one or simply centering a bright target). That ACI is great for standalone viewing too:

That's true. The darkening is indeed a noticeable factor, that's why I'm suggesting to reduce the exit pupil against the widest viable size but only a little bit which means more magnification. Though 15-16mm corresponds to a ~3mm exit pupil, which is for me kinda too much a sacrifice already for the fast 1:5 scope. My z12 is also 1:5, and I indeed love my 17mm most, but rather for its 100 deg AFOV, as best bright galaxies views I had with it were with the stock 26mm EP so far after a meticulous darkness adaptation (in the city only for a couple of seconds at a time). Then, as you have mentioned the desire to go with NB filters soon, I would ditch the zoom factor dimming, as filters are darkening the sky glow overwhelmingly better than that (however limiting you to hot gas DSO's). Filter views would rather benefit form the darkness adaptation skills and the exit pupil size than from a powerful eyepiece. In addition, with the higher zoom, you will have your targets "smeared" wider too (together with the sky glow) i.o.w. get "darkened" as well, thus that zoom darkening is truly beneficial only for faint stars and very compact DSO observing (e.g. PN). A wide field EP is not needed for these. But still, I would recommend wider AFOV EPs as they have other benefits, e.g. for pointing (star hopping, ID) and tracking (observing in the field transit), and simply giving a more pleasant impression from views. Would like to play with the darkening? Your EPs line is already quite good for that, so perhaps, get a 30mm (almost the top end of your usable range) and a 2x Barlow for more "steps" in between.

Welcome to the forum, John! Kudos to your z130 decision. It is a truly solid choice! Pun intended as the Solid OTA is the way to go in any size until you can't lift it. The best DSO EP for it given your age and light pollution would be a 25mm focal range one. Because 130mm / 5mm (average dark adapted pupil size in elderly ) = 26x, 650mm/26x = 25mm (or even simpler, as it's 1:5 mirror you can do 5mm(pupil) * 5 (aperture) = 25mm) Just look for the widest AFOV you could afford, which is not large for a 1.25" barrel, thus should not be uber-expensive at 25mm. THough the key for DSO observing in the light polluted location is actually not expensive eyepieces and not even any "magic" filters, but your skill of eyes darkness adaptation and its maintenance. I would rather dig into that direction first, as the collection you have is quite adequate already (I doubt you can get to a 5mm pupil size yet, at 4mm your 20mm plossl will work ideally). On a side note to figure your actual pupil size do the following: get a ruler (preferably with millimeters) and a camera with a flash (smartphone is OK and even better as it has the voice shutter release) to your telescope. Make sure the "Red eyes" feature of the camera is off, setup it on a tripod if you fancy. When done observing (or after at least 20 minutes of observing) something uninterrupted at night, your eyes will be dark adapted as much as they can in the given realistic environment so pupils will be widened to the max (or you can just sit outside for 20 minutes, just don't look at bright lights directly). Now turn On the camera (don't look at its screen!). Take off glasses (if you use tem). Get the ruler in one hand and camera in another. Press the ruler (numbers out and down) to your eyebrows, and open eyes wide (look into the camera against dark background). Smile and make a shot of your face with flash. You should get something like this: 😃 Then it should be easy to estimate your dilated pupil size on the image (if not, you will have to wait another 20 minutes in the dark, so take it seriously). In theory, you could achieve 6mm pupil size if perfectly dark adapted and even better (all eyes are different but older eyes are less flexible). But in high light pollution it will shrink back just from looking through the EP, so being a bit conservative on that pupil size is beneficial in two ways: you keep the light narrower prolonging un-vignetted view and also bumping the zoom which is in turn darkening your view, preserving your darkness adaptation for longer. The math rule I have described above is trying to ensure that ALL the lights your mirror (or objective lens) is focusing is transferred by the eyepiece through the pupil opening to your retina in most efficient way, so the EP is not limiting the light energy your brain perceiving by shrinking the light beam. But the darkness adaptation is an independent and much more important factor.

I'm sure you will find that information shortly, Paul. Meanwhile I'd like to comment on your approach a little bit to give you some third party perspective. I believe that a 12" and even 16" Dobs aren't really "Large Aperture" Dobs. Thus, there is no truly appealing reason to hunt for a "Portable" design specifically unless the goal is the air travel as well, as a truss like those Sumerinas can be folded really compact to pass airlines restrictions easily. But that contradicts with your desire to have a mobile instrument which is ready to observe "out of the box". All trusses, especially "ultralights" will require you to tediously assemble it every time and then collimate it. They are flimsy mechanically and not well protected from elements. Thus you will surely need additional accessories to make a bare truss more tolerant to the field abuse and addon equipment support. Their design's primary goal is to collapse to a "carry-on or checked luggage" size. Thus there are a lot of engineering compromises and sacrifices for that goal. Not sure why you are concerned about the weight and a split weight while planning to travel by a large SUV (maybe fuel efficiency?), but if you look at the weight, the assembled Alkaid12 is 16.5kg. My z12 is 38kg. But Alkaid's rocker and base are tiny compared to z12, so I can speculate that 90% of the Alkaid's weight is in the OTA (~15kg, surely it has a different composition, so that 15 kg is the rocker/base/mirrors boxes and struts separate, but you got the idea). My z12 OTA weight is 20 kg. So the hand carry difference is just 5 kg! z12 rocker and base module is around the same weight (18 kg) as well. So I would in a snap sacrifice the second trip to/from the car with that weight for the clear benefit of instant telescope assembly/take-down, which I'm enjoying with my z12 solid OTA for over a decade already vs any same size "easy to setup" truss which will require many small pieces assembling in the field often in the dark. I'm just coming out of the car with the base in the hand and EPs pack on the back, finding the open level spot, drop it there, return to the car for the OTA, carry it in both hands (by comfortable wide spaced rope handles) to the site, drop it into the base, and immediately start observing. The solid OTA also means that your collimation will stay intact for a very long time, even after a rough rural road ride. I'm enjoying it all the night and in the morning just dropping back the OTA, then the base (already too tired to care about some truss disassembling). Ready to drive home or drop down the dark tent and take a nap (by the way, my dark tent is popup as well, no poles or stakes to fiddle with, just unzip, drop to the ground so it can unfold itself, throw-in the self-inflating pad, then sleeping bag, and you are cozy. A bit heavy, yes due to springs in all seams, not for backpacking, but it's ready to roll instantly). Very time efficient as well, as I don't have to plan arriving before dark to have time for setup in the day-light and can tear-down before dusk to hit the road before the traffic starts stacking up. Above - my 2002 trunk, base on the left, OTA in the cradle on the right. What "base bulk"? It's the trunk space divider! "Awkward carry"? Just remove the nonsense eyepieces holder on the side and it behaves as a briefcase in your right hand (base forward). The SW Flextube is heavier than solid steel OTA by about 2 kilos for 12". It might be appealing for small cars, but with the SUV a full OTA or collapsible doesn't matter (for you it is). I'm driving small SUV (Subaru Forester). z12 was fitting perfectly in 2002 model with the front seat moved forward. In 2018 model even that is not needed. To make things even easier I built this ultimate solution for it (cradle above). So on a developed campground (paved) I'm simply removing the cradle as a drawer, mounting the base on top and rolling it to the observing spot (usually a huge open day-use parking lot empty at night) that's a single easy stroll (just don't forget the backpack with accessories). On a rural site it's not needed as I'm usually setting up right behind the car.

Thank you for the details. So, it looks like you are observing bending forward, like looking into the microscope. Thus the mount is sitting rather low. In that case even for a 10"+ SCT OTA it is most convenient to have a tallest riser you could get, so you can transition from the EP view to the straight-through pointer simply rising your head up. That would also provide a better background view to look for your target star unobstructed with the OTA and the fork. I would install it centered on the farther end of the OTA to avoid bumping into it when observing and to allow pointing close to Zenith as the long stalk will overhang the base enough to get the view under it. Also, as you are not likely planning on learning any advanced Telrad pointing techniques like the TPM (having the GoTo), going to have it far from your eyes (parallax issue is negligent), and don't really need it anywhere after the star alignment (dark adaptation is not there yet to care about) you can save the weight, bulk, and the take-down time (possibly some dough as well) by opting for a simple RDF instead of the Telrad. I would recommend cheap reflex gun sights like this one: Large window, adjustable brightness, Alt/Az reticle option, easy to wipe dew. The price is on par with Telrad though (I bought mine on eBay a long while ago for just $5). There are risers for the picatinny rail as well. And most are far cheaper than astronomy risers. Just look in Airsoft guns "section", not in real guns To make sighting on the far end of the OTA easier, I'd recommend placing a sticker on the near side marking the position to line up the eye with the RDF mirror ring so you could find the dot in the mirror easier. You can put it closer to amend the latter, but these sights have some parallax (especially if your own eyesight is not 20/20), so too close sighting might reveal it.

Hey Don. I have the E3.7-SC already, and I bet you have already shipped the APM30 to me maybe just minutes ago So I will have almost exactly that set completed this week thanks to you, otherwise I would be saving for the TV N31 until summer and then for the Paracorr till next winter (click on the image to see my current collection with that 30mm already included). On a side note, the E3.7-SC is an ultimate planetary EP for a Dob. It allows me to watch the planet transit from edge to edge for almost a minute with no distortions due to the field curvature and surely without shaking due to the manual guiding.

An alternative suggestion: get a 3D printer instead. A single 1kg spool of PLA filament would allow you to make hundreds of nice looking ready to use eyepieces of infinite complexity to play with just off the top of your head (after you master a suitable CAD app). A used printer could be found for $100 (as a small printer like 15x15cm is easy to find cheap when people eventually upgrading to a larger volume). Or you could make one, as parts are dirt cheap on eBay/Ali. A spool of filament is $15.

TV Ethos 17mm with my 12". Somehow its 88x 100 deg wide AFOV window having a hypnotizing effect on me. Sometimes I'm just aimlessly wandering the Milky Way gas clouds with it for hours (even without NBs). It's giving me a lightspeed warping between stars sensation.

You forgot to clearly state your instrument and mount models (you can add its description to your forum signature, see mine below? Or if you don't know at least make a photo of it and attach to the post). Without that it's hard to judge which (or if) Telrad riser would be more beneficial in your situation and most of advice will be just guessing. In general, however, the riser or not depends on your pointing and observing flow. So in fact in addition to the above you need to answer the following as well: Are you using the EP diagonal? How you are pointing your SCT to invisible objects (e.g. Galaxies)? Are you sitting or standing when pointing? What about when observing? How you are storing your SCT when done observing? Depending on your answers certain recommendations might be irrelevant.

You want stacking. 8m is a nonsense with the 200mm. I'm getting stars down to 9.5m with the 1.2mm (!) smartphone aperture at 10 seconds (10-12) shots stacked: http://fo.kukarin.com/storage/originals/83/f9/m97crop.jpg

I guess the 130P is the "Heritage"? They have a well know flaw in the stock RDF shoe. It's not parallel to the optical axis, so an arbitrary RDF may not have enough vertical adjustments freedom to be aligned with the EP view.