Re: Triplet Lens -vs- Doublet Lens

Stuart Heggie <stuart.j.heggie@...>

I would think if you plan to combine the NB data later into a false colour image you’ll have the same problem. If your goal is pure B&W then I’d guess you’d be fine. 


On Fri, Aug 17, 2018 at 12:43 PM acf900gto@... [ap-gto] <ap-gto@...> wrote:

As we know, one of the benefits of a triplet lens is that it brings the three primary colors to a single focus while a doublet lens can only bring two of the primary colors to a common focus.  The third forms a kind of blur circle around the other two.

However, if I am doing narrow band imaging with something like a 5nm band pass Ha filter, I am only bringing a single "color" to a focus.  So, it would seem that it would be possible to do quality narrow band imaging with a good quality ED doublet lens.    A 6" ED doublet refractor is certainly a lot more affordable than a 6" ED triplet!

Is there any reason to believe an Ha image from a doublet would be of lower quality than an Ha image taken with a triplet?


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