Re: Triplet Lens -vs- Doublet Lens

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

George, I was thinking the same thing. The image scale changes very slightly.  


On Fri, Aug 17, 2018 at 3:07 PM George george@... [ap-gto] <ap-gto@...> wrote:

Remember…since you are refocusing for each image the image scale is changing.






George Whitney

Astro-Physics, Inc.

Phone:  815-282-1513

Email:  george@...


From: ap-gto@... [mailto:ap-gto@...]
Sent: Friday, August 17, 2018 1:47 PM
To: ap-gto@...
Subject: RE: [ap-gto] Triplet Lens -vs- Doublet Lens



I don’t mean to butt-in, but I think Charlie is on to something. Each NB image will have been focused independently. There would be no chromatic aberration because each set of images will be in focus, albeit on what would have been different focal planes. Registering and combining the images would seem to work fine.

I think this makes sense, coming from an old physicist.

Clear skies,

From: Stuart Heggie stuart.j.heggie@... [ap-gto]
Sent: Friday, August 17, 2018 2:08 PM
To: ap-gto@...
Subject: Re: [ap-gto] Triplet Lens -vs- Doublet Lens

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?


Stuart Heggie

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