DaveS

Many thanks for your replies guys. Lots to think about, but pushing me towards the "buy" button as I've seen nothing that could be a deal breaker for me.

I'll weigh my imaging train, but it shouldn't be too heavy.

As a note, I've been running my rig with the WO 0.8 F/R IV and binning 1x1.

I'm seeing enough from this little jewel to give me a hankering, especially at the price, something I could buy on spec, so to speak.

So what are the gotchas?

OK, it needs collimating, but how bad is it? I remember collimating my old 8" newt,which was a pain and it was f/8 to boot, not f/5. Am I really going to have to collimate before every session? If yes, and it's going to take an hour or so then forget it, there isn't that much imaging time to waste, especially during the week when I turn in at 10.30.

Star spikes I'm aware of, just have to decide how much I dislike them, and If I can live with them.

How bad is the focuser? I know it's a crayford and thus suspect as it doesn't have the robustness of a R&P. The crayford on my Meg 90 is a disaster as it cannot pull the camera in on its own. I have to give it a push. If the Skywatcher is anything like that then I'd have to replace it, and a Feathertouch is 21/2 time the price of the bare OTA  .

I'll need a coma corrector obviously, and I think I'd go for the Baader given the comments I've seen re: the Skywatcher one.

So it could go from cheap 'n' cheerful to quite serious very quickly, and I just want to know what I'd be letting myself in for.

On my retirement list then. When I downsize I should have funds for a serious astrophotography rig.

Looks like it could be used on an Astrotrac......

So are we looking at Tak price levels?

Can't afford one yet, but when I retire.....

Good lord, over a year between last posts.

Never mind, that's a rather tasty image, sharp stars into the corners. I'm assuming that's with the 550D?

Have to mildly disagree with adding diffraction spikes to a refractor image, but each to their own I suppose.

This is turning out to be a terrible year for the death of Great Ones.

R.I.P Sir Patrick. You got me interested in astronomy, and will be sorely missed.

Yes, all glasses are now supposed to be ROHS compliant, which means no more heavy lead flints! Fluorite is very fragile, also it has a much larger coeficiant of expansion than glass which makes the mounting of the elements that much harder, FL will also change with temp. When Canon use Fluorite in theit "L" lenses, the element is always well buried in the optical train.

Fluorite will degrade over time, though I suspect that such factors as chemical purity and crystal defects (Or lack of) will have an effect. Nineteenth century fluorite microscope objectives are now all unusable due to crystal degredation, even an early-mid twentyth century objective that I have (A Cooke x45 na 0.95 oil) is no longer as transparent as it was when made.

Cheers We've probably got the marketing types to blame for the confusion!

I understand (Sort-of) the UD ED LD SLD etc glasses from Geofrey Crawley's optical dissections in the Amateur Photographer lens tests, though it's been a long time since I did any even half-way serious reading on the subject of optical design.

Dave

I'm still a little confused, since fluorite isn't a glass, it's pure (Or should be!) crystaline Calcium Fluoride, the only "grades" would relate to chemical purity and absence of crystal imperfections (Dislocations etc). I do remember reading about Fluoride glasses some time ago, but they were regarded as a bit "flakey" compared to bog-standard crown / flint types. times may have changes since then of course .

(Not directed ant anyone in particular)...there is a tendency among non-chemists to confuse eg "fluorite / fluoride" and eg "silicon / silicone" (The number of times I've heard of "silicon implants" ouch! a bit hard (unless you're a Borg ) )

Dave

This is one for the optics buffs.

Getting back into astronomy after 20++ years I realise a lot has changed! especialy the rise of the Triplet Apo telescope.

Re-reading J. B. Sedgwick "Amateur Astronomer's Handbook" I was reminded of the venerable Cooke Photovisual Triplet, and how (By definition) only a triplet design can be truly "Apochromatic", I was wondering whether these new Apo 'scopes are derived from the Cooke design, or are they enteirly new.

I realise that massive strides have been made in optical glass formulation with low and anomalous dispertion types. Incidentluy I'm a little confused by the reference to "Fluorite Glass" in some ads, since Fluorite is, of course, crystaline (And horribly expensive).

Hope someone can enlighten me.

Dave