ED v triplet

[earth titan]

Probably a question with no concise answer, but here goes anyway.

I currently have a good achromat. Not too bad for visual work nut it suffers when it comes to imaging. I've upgraded all of my other scopes and this is the last to be done. I will be looking for a travel / imaging combination, so fairly fast.

I see a lot of ED scopes, which I understand are mainly doublets, varying from relatively low pricing to very high.

Then there are triplets, true APOs as I understand it. There seem to be some lower price triplets which are mid the range of ED pricing.

Are there distinct advantages of a triplet which will warrant additional costs for a good one?

Recommendations appreciated, with links to photos taken with them appreciated.

[ollypenrice]

I wouldn't choose an instrument on its lens format or glass type but only on its performance.

I've had a 'cheap' triplet, the Meade 127, and can compare it with a premium triplet, the TEC140. Discounting the aperture difference, the difference at the EP is, frankly, slight. In imaging the main difference appears in the stars, which suffered some blue bloat in the Meade and were significantly larger. I imaged the Whale in both and the galaxy was similar from both scopes. I doubt there would be much in it between the similarly priced Meade 127 triplet and the SW 120 doublet.

So many things contribute to the final result that just saying 'triplets beat doublets' is unlikely to be helpful. At a fixed price a doublet can have more spent on the two lenses that it does have and construction and collimation are easier/cheaper. But does that mean that it will be better, or the same as, or worse than the triplet? The only way to find out is to try them.

If you have the good fortune to own, say, a TeleVue or Tak doublet you will smile as you read that doublets can't compete...

Olly

[Mark Scott]

Achro.....Normally lots of colour fringing on bright objects.

Ed (semi-Apo).....Very well corrected lens to most show little or no colour fringing.

Triplet (true Apo)....Should be fully corrected, so no colour fringing.

The only problem with the list is there are a lot of exceptions to the rule. What one may see another may not?

Most manufacturers use the same lens mating for doublets and triplets, FPL-51; in triplets this is fine as it's the triplet lens configuration that eliminates false colour. But Sky-Watcher uses the Fpl-53 configuration for its doublets which still continue to get great recommendations/reviews. If I'm honest, that was the deciding factor when I came to choose an 80mm doublet.

:)

[michael.h.f.wilkinson]

I got a fairly cheap APM triplet mainly because it is faster than most doublets. It is a touch easier to get good correction on a fast triplet than on a similar speed doublet.