Re: Triplet Lens -vs- Doublet Lens


Stuart Heggie <stuart.j.heggie@...>
 

My comment was specific to combining multiple filter images for a false colour image. Not monochrome. 

Anyway as long as you use a registration package that deals with slight changes in image scale I’m guessing you’d still be okay. 

Stuart

On Fri, Aug 17, 2018 at 4:35 PM George gobrien99@... [ap-gto] <ap-gto@...> wrote:
 

PixInsight has a function called DynamicAlignment for correction of image scale. I suspect the scale change due to slight differences in wavelength would be miniscule, however.

Also, to be clear the refocusing is only necessary when you change NB filters, not for each subframe.

George

From: Stuart Heggie stuart.j.heggie@... [ap-gto]
Sent: Friday, August 17, 2018 3:11 PM


To: ap-gto@...
Subject: Re: [ap-gto] Triplet Lens -vs- Doublet Lens

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

Stuart

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.
 
Regards,
 
George
 
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,
George

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. 

Stuart

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?

Charlie

--
Stuart Heggie
http://www.stuartheggie.com/featured.html


--
Stuart Heggie
http://www.stuartheggie.com/featured.html



Join main@ap-gto.groups.io to automatically receive all group messages.