triplet or doublet apo ??

[Thales]

Hi all

I've searched here for discussions/reviews of f/6-ish 80mm-ish Apos and found interesting ideas about what to go for.  One discussion put the SW Equinox doublet ahead of a triplet as it would be less bothersome with focussing for visual purposes  etc.. (Not sure I followed everything though).

Anyways, I was looking at no accessory OTAs: the ES triplet ( c. £440, tube minus everything); the Equinox doublet (c £520) and the TS Optics triplet (simlar price to the Equinox I think).

I already have a 5" achromat which I'm happy with for the things it's good at, but I definitely see the advantages in something I can

- easily transport, take with me on trips - mainly for visual purposes

- use generally for widefield views - again visual,

- get good access to the EP when on an equatorial when scope is getting near the zenith

- easily attach to my camera tripod when travelling

- probably start imaging with (ie prime lens, as opposed to afocal etc) later on at some point

I suppose any of the 3 would be good for that? Then comes the choosing, the differences between them firrstly being in the glass (ES uses Hoya FC007; SW FPL-53 and Schott """on selected models"""??? implying not all exmples use that - seems weird, pot luck?; and TS has the FPL-53, but doesn't say what else)  Just to say as well I've no experience with any of these glasses.

So, any particular reasons for going for the Equinox since the triplets are either the same price or cheaper?

Many thanks for your thoughts!

Jeff

[ChrisLX200]

Hmm, can't offer specific opinion on your alternatives. I can say the Equinox (which I have) is a very nice little scope for visual, and at a pinch not half bad for imaging. The thing about APO Doublets (ED doublets) is that for visual use they are excellent when in focus at which point they show little or no colour fringing even on bright subjects. Either side of focus they will tend to show violet or magenta fringing. For imaging though, the camera is far more picky and it will pick up what the eye does not see. So star bloating on the blue channel may be apparent (for example). You really need a triplet design to correct fully for chromatic abberations but, having said that, some excellent doublet design will indeed out-perform an inferior triplet, just having an extra slice of glass in there is no guarantee of better performance. So for visual use then yes, almost certainly a doublet design will be perfect, but for imaging you would have to be much more careful about what you buy.

ChrisH

[Thales]

 just having an extra slice of glass in there is no guarantee of better performance. So for visual use then yes, almost certainly a doublet design will be perfect, but for imaging you would have to be much more careful about what you buy.

ChrisH

Thanks a lot Chris, that is very helpful (and very clear!) - I guess I am much more oriented to visual at the moment and flatteners/reducers etc. sound a bit of a bother until you're fully into imaging.  TS say their triplet is routinely used for observing - though I can't find reviews of it; and the ES triplet doesn't have too much in the way of reviews..so the Equinox is risng to the top of the bucket list!  Thanks for your views. Jeff