Rick_It

I have only one scope, and I do pretty much everything with it. Orion Optics VX8L + DIY dobson mount + Nexus II. 25% CO and good optics = good performances on visual hi-res. 200mm + HiLux = good performances for visual DSO. With a EQ6 I could even take some long exposure pictures, but I'm not interested. And with a 3x barlow some serious hi-res imaging. Again, not interested but definitely possible. Set-up time around 4 minutes. What's left? It's not grab&go and I can't take it with me for holidays. But I'm totally in love with that scope, and I have lost all interests for new big scopes. I just want a small APO and a small ALT-AZ push-to mount.

The concept is interesting, but it should be scaled up. A 350mm f5 (70mm lens) with the same body for example.

Sorry Peter, obviously I was not aware that you built professionally binoscopes

Peter, it's up to you (of course). However: 1. If the use is mostrly terrestrial, then there are far better alternatives on the market for straight through units which (i) are rugged enough to be backpacked and light enough to be used hand-held, (ii) provide correct-oriented vision and (iii) are flat-field. Example: APM MS50ED. 2. If the use is mostly astronomical, then 90° degree are far better than straight-through (I can't stress enough the "far better"). In this case it really does not exists ANYTHING in the market comparable to the 50mm ED binoscope you want to build. ANYTHING in term of size and in term of costs (500€ w.r.t 1500€ of APM angled binos). So, whatever it takes, use 90° diagonals, even at the cost of cutting the tube

Hello Peter, if you are willing to machine the structure for a binoscope, I think you can consider to simply cut the tubes, remake the M53 thread and solve once for all the problem of not enough backfocus.

Thanks everybody for all your efforts! I'm very interested in the Baader T2 prism, because I have a 28mm/68° (2" barrell, but a T2 opening is enough) which would provide me 8.6x! I bet this objective is the same as the Celestron Hummingbird 50mm ED. Since the Hummingbird exists also in the 56mm ED version, maybe SW will come out with a 56mm Evoguide with enough backfocus for a standard diagonal. They can use the same tube and focuser, just a different lens cell (the 56mm objective has a 29mm longer focal lenght!).

There is a single screw before the focuser, the first screw after the end of the white tube. What's for? To remove the focuser section? Because, if the focuser section can be removed, then someone with a machine shop can cut about 1cm of tube and solve once for all the diagonal problem. I'm also interested on that scope, but it needs to work with a diagonal. PS: I really cannot understand why SW has not made the tube 1cm shorter and the extension tube 1cm longer.

If I have not miss something, anyone has tried the ED50 with a 90° 1.25 prism diagonal. Those are the diagonals with the shortest optical path. Amici prisms have a very long optical path. To be clear, the Celestron prism diagonal which comes with all SCTs is a very common example of a 90° 1.25 prism diagonal. Baader T2 prism is another example. A barlow should also extract focus a little bit.

Shortest optical path is with a 90° 1.25" prism diagonal. - Celestron 1.25" prism diagonal (it comes with SCTs) - Takahashi 1.25" prism diagonal - Baader T2 prism diagonal - Vixen 1.25" prism diagonal Optical lenght of all of these should be around 60mm. They provides an upright but mirrored image. An erecting prism uses a totally different optical layout; it's generally a 45° diagonal and provides a completely erected (correct orientation) image.

Do not forget to check with which diagonals + eyepiece those finders are compatible! I suspect a prism diagonal (= shorter focus path than a mirror one), even a cheap Celestron one, could work. I would check a 25mm Plossl and also 16/20/24mm ES 68° as they are a good fit to that finder and are quite common eyepieces.

I'm really interested

I'm very tempted, I could use it as a finderscope / widefiled on my dobson and - standalone - when I hike in the alps. Paired with a 90° correct image diagonal, a 16mm/68° eyepiece, a 5mm/60° eyepiece and this ultra lightweight table tripod https://www.amazon.co.uk/Manfrotto-PIXI-2-Section-Mini-Tripod/dp/B0152X16XO/ref=sr_1_1

Indeed, the possibility of using a 45° correct image prism like this one https://www.firstlightoptics.com/diagonals/william-optics-125-45-degree-erecting-prism.html would be very interesting. I think you really have to find out the max backfocus available. People may also think to build a little binoscope using two of these, if a diagonal can be used. So, how large is the widest part of the body? If it is below 60mm, indeed a simple and reasonably cheap ED binoscope can be built.

From Mike's picture: Weight of tripod: 5.6kg for heavy duty AZ-5 tripod, 1.8kg for portable tripod. Payload: 9kg with Heavy-duty tripod, 5kg with portable tripod I guess FLO will sooner or later stock also the version with the heavy-duty tripod.

Hi Mike, 1) Where are the locking nuts? 2) Can you regulate the tension / frictions or the locking nuts just engage/disengage the slow motion?

Thanks John! Don't forget to look also at the Pronto. I like it, it's a good match with a lightweight APO for day/night and travel. Try to find out how large a telescope can be with that mount. If an 80 ED works fine with it, it may be a nice combination. And tells us abouth smoothness of the movements!

Indeed, the tripod IS the limit. On the Skywatcher Italian website, listed as coming soon, there is the AZ5 with the same tripod as the AZ/EQ-5: payload is 9kg. http://www.skywatcher.it/prodotto/montatura-altazimutale-az5/ The webpage say also "fluid movements with friction block".

Roy, agree on the tripod. I made a very solid wood tripod; it made an enormous difference in terms of stability w.r.t. the alluminium one. I was able to use it also at high mags in that way, but not with the standard tripod. Dampening time no more than 2 secs.

Payload for a mount is a combination of weight, diameter and lenght. Just to make an extreme case, a 2mt thin stick could easily be carried by an EQ3.2; a C11, even if it is super-short, can't. You can't compromise on lenght in a long focal fl refractor, but you can save on weight, and that's what Bresser has done. As for the clamps, I do agree, they could be metal made. It does not change a lot for costs and weight. But, I guess, the general idea of Bresser is the one I said: make the 90mm as light and as inexpensive as possible to appeal also to beginner and small mount owner; differentiate instead the 102 making it as best as possible for long fl refractor lovers. To answer a previous question: I would prefer a goto mount with a long focal fl refractor, because the hand knobs tend to get in tricky positions. I know what I'm talking about because I used a lot a TAL100 on a manual EQ3.2

Hi, I had the opportunity to see both refractors in Paris last november. There's a logic behind those scopes and I do not agree that Bresser has "compromised on quality". The 90mm is made to be as light as possible, to be used with EQ3.2 class mounts. The 102mm is the one with better mechanics (expecially the focuser), but you need a sturdier mounts (BARELY an EQ5). Just look at the weights: 2.8kg vs 5.3kg. The 102mm weights almost twice the 90mm! Those are wise choices by Bresser because they differentiate the two scopes and they allow also people with cheap mount to use a long fl refractors. With metal clamps, hexafoc focuser and metal cell no way you could have used the 90mm on your mount. You would have ended up with a scope with a cost and a weight very similar to the 102, thus no reasons to buy it. I also do not worry too much for the plastic lens cell: such long fl tollerates very well slightly miscollimation. Then, it's up to you. Buy a new Exos 2 GOTO with the 102/1350 and you will definitely improve a lot. OR stick with the 90mm and save a lot of money!