globular

I read somewhere that Patrick Moore's formula for limiting magnitude puts a 130mm at about 13.1 - so you must have close to perfect optical train, viewing conditions and good eyes - better eyes than Patrick at least. 🤣 The same formula gives mag 14.0 for an 8" - but I'd imagine, as an SCT with a central obstruction, it will be slightly dimmer in reality? Definitely worth a go though. edit: my secondary is 2.5" so I'd expect a limiting mag equivalent to an aperture of 2 * root( sqr (8" / 2) - sqr (2.5" / 2) ) = 7.6" ... which is mag 13.9. So not that much dimmer!

Nice report John. Sounds like a fun night. I too had my telescope out for the first time in what seems like a lifetime. Your description of your Jupiter observing mirrors mine. Best detail was at 180x although it looked lovely in different ways in a host of different EPs. Two broad brown belts with numerous thinner ones of exactly the colours you describe. My wife was particularly taken by the grey one she picked out after lingering at the eyepiece longer than I've ever known her to. (Her bad back usually limits her to quick glimpses at a time). We both had our best views of Jupiter yet and a thoroughly enjoyable hour dedicated to it. Wife went to bed when we lost Jupiter to the trees and I had another hour touring various globular and open clusters - many of which I've made a note to return to with my sketchpad - and some planetary nebulae. Thoroughly enjoyable. Saturn, sadly, remained hidden by trees on this occasion. I did view the lovely blue Neptune - only the colour giving away that it was not just another star. I didn't try for it's moon.... but now I know it's possible I'll give it a go next time. I suspect my 8" might not be enough though??

I did think I could collimate for the binoviewer and then add an extension into the light path for cyclops viewing... similar to your locking the mirror idea. But I soon decided against it. 2125mm F/10.5 is where you should be using an 8" EdgeHD and I just can't bring myself to deviate too far from this optimal position. I'll keep this thread going with my progress.

Thanks Mark. Great to hear from a user of the linear binos. Which brand did you get? Is it the TS Optics one? There was some chatter in another place that the 'cheaper' ones suffer more with reflection than the more expensive Orion one. "I tried the $399 model. Sent it back. Bought the Orion. Less reflections and spurious color." Not sure if there is in fact any technical differences between the different brands.... I understand they are all built in the same factory.... I'd have thought it's just the branding that's different. I am really tempted by this binoviewer.... avoiding moving the primary a long way to focus being it's biggest draw. However I suspect this design would be better in a shorter focal length telescope than mine.... where the 17mm field stop will not be as restricting as it would be for for me. The maximum TFOV I'd get with them is 0.45 degrees. And the biggest exit pupil 1.9mm. And if I can't look at bright stuff either because of reflections.... well it all seems a little too compromised. <shrug>

Most diagonals allow the eyepiece holder to be screwed off; And baader make lots of threads for their clicklocks. This means you can keep your Tak prism but with a more robust and undercut friendly holder.

Thanks Jetstream I found a few of his threads. There is one where he painstakingly measures all combinations of different visual backs and diagonal, with and without binoviewer. Good to see his measurements give the same as my formulaic theoretical approach. And another where he lists all his baader accessories that he accumulated in search of the shorted path possible for use with binoviewers. Looks like he got it working but only by keeping everything as short as possible. In other words I suspect he could tell the difference if things were too long.

My SCT came perfect from the factory and has stayed that way since - I check it regularly but have never needed to tinker. I don't intend to start now for a binoviewer - but would like to give one a try.

When these scopes are collimated everything is optimised at that primary mirror position (i.e. the position during collimation). Focusing different EPs, Binoviewers, Cameras, etc, is achieved by moving the primary mirror and things start moving away from optimal. Most EPs, even when not par focal, don't require that large a change of focus; so you don't notice any difference. Add something to the light path that significantly moves the focal plane and you might start to notice. A (conventional) binoviewer falls into this category. The new(ish) linear binoviewers don't. What I don't know.... hence this thread..... is how bad it is in reality. I suspect / hope it's not that bad. I certainly won't be fiddling with my collimation to fix it - so if it's bad I won't use one. (or maybe I'll try a linear one).

Thanks @jetstream. It looks a lovely instrument and I like the power switch and the filter slider option too. It's a bit expensive though. I would definitely have to have tried something else first to make sure I get on with binoviewers before laying out over £1200. Also, while they do a SCT 'version', I think this is simply a minimised light path option (with their own diagonal and connectors) rather than something that prevents the need for lots of inward focus movement (and hence large primary mirror movement). Indeed their own FAQs state: "The collimating of your SCT must be done with the binoviewer in place if the best possible images are to be produced. This is because the primary mirror of your SCT must be moved toward the secondary convex mirror (negative) in order to push the focal out of the exit aperture of the tube assembly in order to reach focus with the binoviewer/eyepieces. I have seen a very big difference in the quality of planetary images after fine tuning the collimation of our company's Celestron SCT with a Denk Binoviewer in place. The reality is that the scope becomes a different instrument when switching from single eyepieces to binoviewer usage. This must not be ignored if you want the best images possible with the binoviewer setup." I don't want to have to collimate my SCT when switching between cyclops and binoviewers! This issue is not just with the Denkmeier, of course. Nearly all binoviewers will require significant primary mirror movement to achieve focus. All except the Bresser Binoviewer Deluxe, which, if I'm reading their claims correctly, do not move the focal point when inserted into any telescope. So my perfectly collimated scope in cyclops mode will also be optimal for binoviewing. And no big mirror movements mean no added spherical aberration (thanks @Louis D for confirming this). I just don't know what the Bresser glass is doing to achieve this.... is it really going to achieve this without introducing aberrations itself? It feels too good to be true. Anyone know how they've done it? I'd love to hear from anyone with one.... whatever scope they use it in. @Knighty2112 have you had first light with yours yet?

I’m contemplating trying binoviewers and I have a SCT. Great, I’ll have none of the focusing issues often reported with binoviewers; there is lots of focus travel in my SCT. But wait. If I take the baader maxbright mark II as an example; this has a light path of 110mm. And adding light path to a SCT adds focal length. So my F/10.6 is going to be a F/12.3 when binoviewing. Boring maths bit: * 8” EdgeHD has published fl of 2032 and F ratio F/10 * But this figure is only obtained when using the stock visual back and diagonal that celestron fitted to their original C8s - light path of which was 103.4mm * With the EdgeHD stock diagonal (light path 137mm) the fl is actually 2032 + 3.1 x (137 - 103.4) = 2136.3 and so it’s really F/10.5 * I have a clicklock visual back and a 2” prism diagonal with combined light path of 143.4; so I have fl 2156 or F/10.6. * adding binoviewers with extra 110mm of light path will add 3.1 x 110 = 341mm to focal length; so fl is 2497 or F/12.3 Now, I could seek out a 1.25” diagonal when using the binoviewers. So I could save maybe 50mm light path. This puts me at 2497 - 3.1 x 50 = 2342 fl or F/11.5. Still a lot different to my cyclops configuration. But then so what? Does the F ratio moving a bit really matter? I can just pick different fl EPs to get the magnification I want, right? Or will it do other nasty things too? The larger focus movements required will move the primary mirror a lot closer to the secondary… that doesn’t sound good in terms of contrast or aberrations? Will that spoil the benefits of binoviewers? Does the Bresser Binoviewer Deluxe solve these issues? (If they really are issues?) This binoviewer claims; “Thanks to the newly patented optical system you can get into focus with any telescope. Since the BRESSER BinoViewer Deluxe does not require any additional light path (back focus), it can be used with any telescope - including Newtonians and short focus refracting telescopes, which traditionally suffered when using standard binoviewers. No light path corrector or similar accessory is necessary. If a standard 1.25'' eyepiece can be focused, the binoviewer will also work. The eyepiece focal length and field of view size of the eyepieces used are fully retained” Maybe this is the binoviewer I should try in my SCT? Anyone already tried it? Sorry for the long post. Hopefully some of you will have got this far and can put me straight on any mistakes in my logic and / or on the workability of binoviewers in SCTs.

It is in Wayback Machine under "http://www.schlatter.org:80/Dad/Astronomy/collimate.htm" It looked like this in February 2020: https://web.archive.org/web/20200223041214/http://www.schlatter.org:80/Dad/Astronomy/collimate.htm

Isn't that just bigger... needed for the size of telescope.... rather than better, per se, as an optical design or construction?

BroadBand Anti-Reflective "Broadband anti-reflective (BBAR) coatings consist of multiple layers, alternating between a high index material and a low index material. The layers are deposited on the substrate via electron-beam deposition. The thickness of the layers is optimized to produce destructive interference between reflected waves and constructive interference between transmitted waves. This results in an optic that has enhanced performance within a specified wavelength band as well as minimal internal reflections (ghosting). "

Do bits go green then?

Very nice! I’m not jealous. My clouds are lovely too.

Clicklock clamps are very good - but they are quite bulky and you might have focus travel issues with some eyepieces. The Explore Scientific one is not such a nice clamp but is better at not using up so much focus travel. In reality I suspect it will depend on the actual thread you have and availability of the ES as to which way to go.

Explore Scientific make a 3" diagonal that comes with a 3" to 2" reducer..... https://www.bresser.de/en/Astronomy/Accessories/EXPLORE-SCIENTIFIC-Star-Diagonal-Mirror-76-2mm-3.html But a quick search and I can't see that they sell just the reducer on their own..... might be worth asking them (or Bresser) if they can get you one.

good luck and measure carefully - there are all sorts of very similar looking but frustratingly different ones to catch you out.

There will usually be some sort of thread on your 3" focuser... and you get a 2" holder that screws into that. e.g. https://www.firstlightoptics.com/adapters/baader-clicklock-m75a-x-1-for-feather-touch-3-focusers.html

Wonderful report. Thanks for sharing your mesmerising session. May be add a Nagler 2-4 zoom to your case ready for the next perfect night?

I'm actually learning a lot about SkySafari functionality while collating these dark nebula targets into observing lists.... 🤣

Your write-up of this is legendary.

I suspect the only horses head I'll see round these parts are in the fields down the lane.

Nicely done I like doing open clusters but mine end up scruffy I've added this list to my list of lists Thanks for the tip off.

Your starsense will automatically do the (step 3) star align for you... so you don't need to manually find stars you know the names of. You do need to make sure your starsense camera is aligned with your telescope though.... but this is a one off job (provided you don't remove the camera between sessions).