Andrew_B

What are the pros and cons of R&P versus Crayford? I've got a 2" Crayford FTF on the way but I didn't see a R&P option in that size - not that it matters and I'm sure either would be more than good enough for my needs.

I second the suggestion of a modded mirrorless camera. You can pick them up secondhand for very little money compared to what a dedicated astro camera would cost. I got a full spectrum converted 24MP Fuji for just £180 and the performance is very respectable even when shooting narrowband.

Tak doublets have a pretty devoted following and a 5" fluorite doublet would probably sell in reasonable numbers, not least because just about everything else available at the high end in that aperture range are triplets, quadruplets, and whatever else aimed at the imager. Astrophotography drives most of the market but there's still a decent number of visual observers or people who do both and enjoy the convenience of a fast-cooling and lightweight scope. I've just had a look at an old Tak advert from 1990 and the FC-125S was selling for £5,400 back then which is the equivalent of over £12,500 today. Even high end astro gear is far cheaper than it used to be.

I've used both vaseline and candle wax to grease threads and they worked well enough. The reason I chose them was because they were immediately available and I know what's in them so there shouldn't be any nasty surprises and they ought to be relatively easy to remove if they end up in the wrong place. Stuff like molybdenum disulphide grease or graphite grease might do the job well but if they get on your hands and then on your clothes or furniture then it's going to make a mess.

If a scope gets you out observing and you enjoy it then it doesn't matter what it cost or how close it gets to optical perfection. I suspect that people who spend their time worrying about what they can't see because of the limitations of their scope will never be satisfied with what they can see.

Using a wide air space can give better correction with a given pair of elements so that might be an option, but it would mean a larger and heavier scope that might be a bit more prone to losing collimation. That said, the old FS-series were a lot bigger and heavier than their equivalent modern FC-series scopes so perhaps a lightweight but highly corrected 125mm doublet could be a viable option.

It's okay I could appreciate the humour. 😁 Like you say there's so many factors involved like presence and size of an obstruction, cool down time, convenience of different designs, local seeing, etc, etc that what counts as a good scope will vary enormously from person to person. Sometimes people get a bit too focused on judging things in terms of easy to compare numbers rather than more qualitative factors and want a single easy answer about what's "best" that they can apply universally.

I think I must have read that info somewhere on telescope-optics.net and this page has the formula for the minimum focal ratio at which a spherical mirror gives acceptable performance as the cube root of 90.15 multiplied by the diameter in inches. For a 6" mirror this would be F8.15 so a spherical F8 optic should be close enough to be good but I'd imagine they'd parabolise it anyway.

I bet that's a really impressive planetary scope and a good 6" F8 mirror is easy to make and apparently should give decent performance even if it's left with a spherical figure. Mind you, you couldn't pay me to own a Newtonian, they're just not my cup of tea.

LZOS provide test reports because they're a contractor selling components to a third party. They're not doing it for the benefit of the end user even if the people buying the completed scopes do love those Strehl numbers. Even publicising the minimum tolerance isn't straightforward. Is it referring to peak monochromatic Strehl or minimum across the entire visual spectrum and how much difference would it make in the real world anyway? Ultimately a good test report is worth nothing if you don't like the view through the scope and I don't need a test report to tell me whether I can see false colour or if my scope delivers a perfect star test.

That's annoying. I was sure that was for the right camera and it was one of the first results when I searched for reviews of the 485C model. The perils of skim reading! I notice the 462 uses 2.9 micron pixels and has very similar characteristics - perhaps the same basic pixel architecture so the 485 might in practice be like a scaled up version of the 462.

QHY launched their version using the same chip earlier this year as the QHY5III485C. Only found this one review but it's better than nothing!

The starburst glow (or sausage glow since I like that name!) doesn't seem to be a problem with DSLRs so presumably cameras based on the sensors from consumer cameras should be free of that glow compared to those based on chips intended for machine vision and surveillance cameras. Not wishing to derail the thread but does anyone have a link to a good guide for how to do things like calibration frames etc to deal with amp glow and fixed pattern noise in lower cost CMOS cameras? I want to try some deep sky imaging with my little ASI178MM (only used it as a guide camera so far) but the workflow is clearly rather different to what I'm used to.

Is you triplet using an oil-spaced lens?

Only produced in small numbers as well. They look superbly made to the point of being over-engineered although the weight does kind of remove one of the big selling points of having a high quality doublet in the first place. In theory one of their scopes would be an option for the OP but waiting times and no availability secondhand pretty much rules them out.

You should drop Tak a line about wanting a larger fluorite doublet. I'm sure they're aware that there's demand for one but more evidence of that can't hurt and even the biggest companies do pay attention to customer feedback - I once emailed Apple about overly aggressive noise reduction algorithms in their smartphone cameras and they came back to me about it asking for more information and example images.

Looks like it's an FC-100DC with a Starlight 2.5" Feather Touch focuser. Hadn't realised just how compact it is compared to the TSA-120!

That's a fantastic looking scope although looks like it must weigh a ton! What design is it using to have 4 elements? Is it a flatfield Petzval or something else?

The TSA-120 would tick a lot of boxes although it's obviously at the lower end of your aperture range and may not be a big enough step up from your current FC-100. Never had the pleasure of using one myself but I know some of the members here own or have owned one. Stepping up to the TOA-130 would get you optics that are about as good as it gets but you'd have to find one on the secondhand market to be within your budget. An APM/LZOS scope might be an option but it would be the same situation as the TOA-130 of you needing to find a pre-owned example.

@johninderby - just wanted to let you know that I picked up a cheap but surprisingly solid Svbony dovetail saddle that does the job brilliantly, so thanks again for your help. My ADM dovetail was ever so slightly too wide to fit it though so I took a file to the saddle and after removing probably less than a mm of metal it's now a perfect fit.

That looks a really good setup - nice and secure with loads of protective padding around everything. As far as I can tell the Peli 1525 should be okay for carry on luggage on most mainstream flights with exceptions possibly if you were travelling by light aircraft somewhere. It was other makes of similar style cases that seemed to have loads of models that were almost the right size but which would be a bit too deep or too long for me to be confident that they'd be allowed onboard. Peli cases aren't cheap but when I think about the cost of what's going inside I'm not as bothered about paying a bit more to keep it all safe. I wouldn't just use it for holidays either because I'd take it with me when I wanted a little scope to use while I was out doing some astrophotography from a dark site. I ended up laying an outline of the internal dimensions of the case on the floor and then experimenting with different configurations of scope and accessories to see if I could fit a useful setup in the one piece of luggage and that showed it would do the job nicely.

That's a good idea. Even expensive foam is a lot cheaper than a new case. If I was taking a scope abroad I'd probably have it and a few accessories in its own carry-on case and then put the mount and anything else that was fairly rugged in with my clothes in a checked bag.

That orange case is smart looking and not a bad price. Less likely to fall over it in the dark than a black case as well. I've also been looking for a travel case for my little scope and the Peli 1525 seems to be the best option but it's quite pricey. It's surprising how many protective cases are almost carry-on sized but are ever so slightly too big in one dimension.

WD40 was never designed to be a lubricant. From the outset it was a corrosion-prevention compound for the aerospace industry that was first used by Convair to protect the thin stainless steel skin of the Atlas ICBM!

That's good to know. I've got an Astro Essentials 20mm Plossl which gives a great view in my 60mm and I wanted something a bit lower power that wasn't too big and kept to a 1.25" fitting. Doesn't seem much point pairing a tiny lightweight scope with a huge heavy eyepiece! Low power eyepieces give a lovely 3D view with that scope so I'm looking forward to trying it out. For £23 including delivery I'm not expecting spectacular performance, but simple eyepiece designs like Plossls seem to be fairly decent even when they're cheap.