Peter Drew

I could buy a 4" Tak tomorrow if one is available, but I won't and probably never will. Not that I doubt whether the Tak is one of the best available but because I already have a good 4" Vixen Fluorite. Given my age and the conditions I "observe" in, there would not be the difference in performance to me that would justify the price. As it happens, I very rarely use the Vixen, why?, because to use it I have to take a tripod, mount and the Vixen outside and set it up to do so. By contrast I can just switch on a dome mounted 16" SCT which carries a SW 150ED as a finder/alternative view telescope. 🙂

I sold mine for £200. 🙂

Yes, why do astrophotography when someone else can do it for us. 🙂

I've never bothered to completely flock a tube but I have always flat blacked the secondary edge and any shiny part of the drawtube that projects inwards. The most effective antireflection mod that I have found is to apply a flat back area on a white tube opposite to the eye not in use whilst observing. This prevents a light area seen by this eye merging with the view of the observing eye. 🙂

One of 6 that form part of one of my observatories. 🙂

A basic "Todmorden" pier is essentially a 600x600x50 paving slab and a couple of standard hollow building blocks. The items are bolted together with 12mm stainless steel screwed rod. A hole drilled in the top of the top block will allow bolting through to the base of the EQ mount. A piece of tubing equal to the largest diameter of the EQ base will spread the load. Images on other threads. 🙂

I've had one for several years and like it. It seems to give similar views to other single TV plossls. I use it mainly for collimating telescopes as most of my telescopes are too long focus for the high power even the 6mm setting would produce for average visual use 🙂

A "Todmorden" pier will cost around £50. 🙂

One of my pair, manual drive.

I would prefer my Tal1's over any other current Newtonians of similar size. 🙂

Very nice, looks like new. I have a couple that could do with a similar treatment. 🙂

I would also suspect the original filter. To me, it looks far too stressed which would easily distort its performance. Baader film should guarantee a good result. 🙂

Best plan! 🙂

I can't help feeling that this is similar to shining a torch on to an aluminised surface which always makes things look worse than they are. If the views using the Quark are as good as described then the unit probably falls within the manufacture's entry level parameters. 🙂

If the misalignment is gross I would expect the extrafocal rings to be skewed to one side. To be honest, I've corrected alignments where the centres had been 1cm out and not noticed a significant improvement to the performance. Some objective designs are more sensitive in this respect. 🙂

I didn't see it but the description seems typical of a flare. 🙂

What's not sharp with pic #1 ? 🙂

I've not actually used one but I have the optical set from one for which I've built my own OTA. I haven't had chance to use it yet as its mount is still a work in progress. I believe they were available in F4-F16 and F5-F20 configurations, mine is the latter. Either will have David Hinds A quality optics so as good as it gets. They have reasonably large secondary obstructions and together with the difficulty of including baffles that don't vignet results in a brighter sky background than would be seen in the equivalent refractor or Newtonian. Their strengths, in the era they were made and sold, were compactness and the very long focal lengths ideal for lunar and planetary photography. Also worth determining if it is a Classical Cassegrain or a Dall-Kirkham Cassegrain, mine is the D-K. 🙂

I think Orion UK will charge it as a diagonal with a minor axis the same as your mirror diameter. The Hilux is good but pricey. 🙂

My 30" Dob base is made of MDF which has a good native finish to it. Well painted, it has survived for at least 25 years. 🙂

Yes Nicos, I was aware of the sub divisions of disappointment of the objective in question. I suppose it boils down to what constitutes a "lemon". In the CN thread, the purchaser reported exceptional planetary performance, besting his Zambuto 10" Newtonian, his concern was fringing at the limb of the planet, that's the sort of lemon I could cope with although like the purchaser I would be miffed by the results provided by the DPAC having paid a high premium for better. I would love a 180mm triplet with a good figure in red as my main interest these days is Ha solar for which I use a 150mm Istar achromat. I hope the CN thread can continue to the point of resolution of the issue as this will be of importance to amateur astronomy. 🙂

I spent much of yesterday reading the CN thread from the start, I could hardly keep up with the expansion! CN threads of this nature are always entertaining as they expose a lot of "thin skin" but the focus of this thread has important implications for the suppliers of optics to the amateur astronomer. The telescope at the heart of the controversy is not a lemon, it tested near perfect in red which would be beneficial in some applications. Where things went wrong was the implication that the telescope was of exceptional quality suitable for the expectation of the purchaser to suit his visual interest which would have been better achieved if tested in green light. I think that the inevitable rise in the interest in DPAC testing will tend to keep manufacturers on their toes, but like all methods of optical testing it will take experience before stringent results can be obtained. I suspect that DPAC will be a great tool to differentiate between good and poor for most interested amateurs, finer nuances are likely to be outweighed by real life observing conditions. My interest has certainly been piqued and I have an 8" master flat. 🙂

If it has been metal to metal binding there should be some witness marks on the mating surfaces. 🙂

Defocusing a star to show the doughnut either side of focus is used to examine the correction and/or other defects rather tan collimation. A nicely concentric large defocused image can often collapse into a less than perfect image near the point of focus. You need enough magnification to reveal the "Poisson Spot", a small star like appearance in the almost focused image. The centring of this with minute tweaks of adjustment will give the best available performance. 🙂