Cake

Now that is a really interesting idea. I wasn't too keen on any attempt to modify the tube itself, as it's my only telescope at the moment and I don't want to do silly things to it, but aside from having it manufactured this has no downsides. Considering the OTA does have decent 4" lens, retrofitting it with a decent focuser would still be cheaper that getting a new 4" goto refractor, even if it's after getting a big newtonian dob.

That's a backup plan, yeah. I'm just still hoping to be able to get full mileage out of this one, though. Note that's that exactly what I did, I posted all the dimensions in the OP. The problem is that so far finding the focuser flange dimensions is exeedingly difficult and this telescope won't just take them as standard, hence this thread. You are absolutely right that the focusers are expensive. Most cost more than I paid for the telescope in the first place, goto mount included. As for the OTA, the rest of it is reasonably decent and they just seem to have really cheaped out on the focuser (and the red dot which mounts to it). That seems to be the main thing Meade went on to improve in the NG models because from reviews in seems that those focusers are pretty much the same as skywatcher ones, the rest of the OTA and the goto stand are fairly similar to mine. I guess I'll just try to improve this focuser as much as possible and maybe diy motorise it, and save the money for a 10" dob.

Is this what you mean? https://www.firstlightoptics.com/skywatcher-focusers/dual-speed-2-crayford-focuser-for-sky-watcher-refractors.htm Because that's the problem, it seems to go inside the tube, mine slides over it. But if FLO offers advice, that's great to hear. EDIT: Looked it up, this website actually provides dimensions https://www.365astronomy.com/dual-speed-2-inch-crayford-focuser-for-skywatcher-refractor-telescopes.html This focuser cannot be mounted on my telescope without extensive modification.

I have an old (not NG) Meade StarNavigator 102. The focuser on it is rubbish even by my complete newbie standards, as it's plastic-on-plastic, rough sliding (no space for teflon skids or such) rack-and-pinion. Shakes the entire telescope when used. I have taken it apart, cleaned it up and lubed it up. I know I can attach some extensions to the wheels to improve it somewhat, but that's a half-measure that I want to only leave as a last-ditch option if nothing else is worth the expense. The problem is, I don't know whether I can get a better focuser which would fit instead of it, as this one slides over the tube and none I've seen online do. To make things a bit easier, I'm attaching some photos and here's some dimesions: Outer tube - outer diameter 94mm, inner 90mm, 2mm wall 4mm gap Inner insert - outer 82mm, inner 70mm, 6mm wall All screw holes 12mm form the end of the tube For good measure, the inner side of the focuser collar is 93-4mm (duh), and the actual tube is 55mm. If there is no easy replacement, would I at all be able to mount an affordable motor (because I won't spend a lot of money on THIS focuser) like the Skywatcher one on the underside, as per photos?

I've checked where I've read that again, it was actually 3x the Dawes limit, which now seems less suprising than it seemed to me.

Interestingly, when researching this I've seen someone mention another rule of thumb which is "3 pixels per arcsec on the sensor" (which you can calculate based on this http://plato.acadiau.ca/courses/phys/1513/optics.htm), and if you calculate both, they do seem to be more or less equivalent in my particular case. For a 3um pixel and 102mm aperture, that's an ~f/18, so just slightly longer than the five times. EDIT: I've checked again, it's 3x pixel per Dawes limit.

Thank you for your replies Thanks, that's the kind of stuff that isn't obvious from just theory. I think the seeing and my use of the telescope are the most important factors here. I'm thinking of prime focus as an improvement on EP projection to a smartphone, no more no less. I'm not an avid astrophotographer hunting for the best viewing conditions, so sub-optimal seeing will be the limiting factor. I needed to know the physical limits of the telescope so that I wouldn't exceed them, I don't need to push them. I'm not willing to splash out on even mid-range equipment at this moment. My whole setup (the telescope with it's standard bits plus a cheap 4mm plossl) have cost me only £160, a decent camera and ADC would likely double or triple that. So I'm willing to spend £40 more on a cheap camera and something on a half-decent barlow, but I don't think of imaging planets as priority enough for more. Alternatively, I might not spend anything more and stick to EP projection if a cheap prime focus camera is just too poor of a tool. I would like to hear your opinion on that. Is smartphone on a EP (I currently have a 25mm and 9mm 40deg afov whatevers that came with the telescope and a 4mm/48deg afov plossl) better than a cheap prime focus camera, like the SVBONY 105? EDIT: I specifically mean the quality of the image, as I did go to https://astronomy.tools/calculators/field_of_view/ to comapare the possible fields of view as in the attached pictures. Yeah, I don't mind a barlow, but if I can avoid getting an ADC, that's awesome.

Hi all, I'm very new to astronomy as a whole and need someone with practical experience to tell me whether I actually understand the theory. I've recently bought on the cheap an old Meade StarNavigator 102 refractor, 102mm/800mm (not NG, as reviewed here). It's physically in good condition and I'm happy with what it is, but I understand it will have limitations and I'm just not sure if I actually know what they really are. Specifically when it comes to imaging the planets. I've read up a bit about how prime focus photography works and from what I gather this 800mm focal length telescope with no Barlow will give a 0.77 asec/pix image on a 3um size pixel camera (I'm specifically thinking of the SVBONY 105 because it's cheap, I'm on a budget and I care more about learning how it works before I start spending real money). On the other hand, I believe I understand that the absolute physical limit of resolution for this telescope is its Dawes limit, which (assuming Wikipedia isn't lying to me) would come out to ~1.14 arcsec. In other words, each pixel apparently already catches the telescope's smallest resolvable detail? Do I undertand correctly that adding a barlow of any power would not have any more effect on the amount of detail than simply cropping the image, i.e. just make it bigger? Altough I imagine that the more pixels per arcsec, the better the signal/noise ratio of what is being captured, but that's a tangential issue.