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By Michele Scotti
Hi everybody - I'm humbled that some of you are following the thread on the 800mm telescope. I thought it was worth starting a sub-topic specifically related to the mirror making.
So as the works on the mount got halted by the lockdown we had some time to virtually meet-up and discuss the optics for this project.
The onset was pretty straightforward with an 'if we are doing this we are making the mirror'. And that sorts out the make vs buy, I suppose.
As of now, the only two things decided so far are the diameter -at 800mm- and the f/3.3 - of course we can accommodate some variance.
Some aspects of the making are pretty unchartered territories for our club so I'd like to seek some good advice from anybody in terms of direct experience or rather point us at some resources/threads.
Back-ground: to make it short, our senior member had three 500mm f/5 done years ago. He did of course faster optics up to f/3 among many other mirrors - I actually never asked him how many, uh! He has always worked with full tool and has no experience with slumped glass. Btw we do have some experience in slumping glass but -weirdly enough- not in machining.
During our initial discussions we boiled the scenarios down to 3:
float glass, 35/40mm thickness considering 15mm of sagitta. This is a thermal challenge with its big outward mass, it's going to make the machining more of a challenge and the stabilization time longer float glass, 25mm (which seems more of a commercially available), slumped. Trading the thermal challenge with the slumping borosilicate, 25mm, slumped. Tbh this is just a better version of the previous point at a cost that is not prohibitive
What are the sources of glass in Europe for thickness over the bog standard 25mm?
Disclaimer: this is surely an ambitious endeavor and by no means we are underestimating that. Not only the bigger diameter is a step-up; the fast optics is a challenge too.
To start with we have some questions about slumped glass. It looks like an attractive, modern approach to mirrors that exceed a given diameter. I think I saw already some threads specifically about the slumping itself - that's golden.
However it's the grinding/finishing/parabolizing that is puzzling us. Are there specific techniques or is it the same as the flat back glass?
Also, how do you support the mirror? Would a support that replicates the telescope mirror cage be appropriate - a 27-point in our case? Or is it a matter to build a concave support that holds the back of the mirror? How accurate/solid should that support be?
Any experience out there??
I reckon that's enough as a start - thanks everybody in advance for your contribution.
Stay safe! Michele
So, I have been testing three different kind of lasers, each one is supposed to be the "best" in each category or what you want to call it, the hotech and HG is almost the same, but whit the difference in how you lock it down.
The Catseye is very different in how it works.
I made a Youtube video of my thoughts
What do you think? which one do you use?
Hi guys, firstly - sorry if this is posted in the wrong place.
I've just ordered a Canon 600D to start doing some astrophotography and it arrives tomorrow - I'm stoked. I've been wanting to get into astrophotography for a while now and I'm so happy to finally be pulling the trigger.
The last item on my shopping list is a solid beginner telescope which would couple well with my Canon 600D. The research I've done is all pointing towards a newtonian reflector.
My primary goal here is to take some pictures of stars and planets with the Canon 600D attached to the telescope. I've been looking at the Sky-Watcher 114/900 as it's relatively cheap, which I think is great for someone just starting off - but was wondering what your opinions were seeing as you've all been through this before. Do you have any other recommendations? I'd like to keep my budget up to £300, and that's stretching it really.
Thanks for taking the time to help!
Hi, I am trying to collimate my astrpgraph, a TS N-AG10 with a Hotech 2" self centering laser and I am having some questions of the clamping procedure.
Each time i am trying to tighten the collar so that the laser would tighten up in the focuser, the laser dot is quite far off the earlier spot the laser hit.
I have sience bought a Howie Glatter 2" laser, when i adjust the secondary so that the laser dot hit exactly in the center of the primary dot and change laser to the hotech, the laser dot is about 4-5mm off, if I release the Hotech laser and re-tighten it, the dot will hit somewhere else.
I can not just trust the hotech laser - has anyone else experienced the same thing?
*Both of the lasers is collimated itself at 5 meters distance with the dots not moving at all.
By Gary Shaw
I just acquired a 200mm F4 newtonian from TS Optics which I'll use primarily for Electronic Assisted Observing with several ZWO cmos cameras.
My challenge is that my current scope is an F3.6 schmidt newtonian so I have no experience with coma correctors or spacers/adaptors in the optical train. TS tells me that I need 55mm from the coma corrector (TSGPU) to the sensor. They provided 40 mm of various adaptors and spaces and I guess I get the remaining 15mm from the camera housing itself - as shown in the attached image. The threads on several of the adaptors(see notes) are bad so those pieces need to be replaced but, once that's fixed, I have four questions for this community:
1. ...is this odd assortment of parts and pieces typically how one goes about achieving the required 55mm dimension from the Coma Corrector to the camera sensor? Just seems that there must be a simpler, and sturdier way to do this without having to use 4-5 separate parts.
2. Once all the adaptors add up to the correct dimension and are attached to the Coma Corrector, where does one locate the whole assembly(with coma corrector) in the focuser draw tube? Is it a matter of trial and error?
3. If one did not care about viewing peripheral stars looking a bit like comets and didn't, therefore, use the coma corrector, would any of these adaptor/spacers be needed to bring the camera to focus so one could observe using, say, Sharpcap 3.2 Pro or other software?
4. If I were to use a filter or two, where would these best be located in the lineup and do they work with the various threads and adaptors?
Apologies for my lack of experience and thank you for any help you can provide me in understanding how to observe and image with coma correctors