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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 31 Dec 2009 (Thursday) 21:07
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The Official Shoot the Moon Thread

 
aezoss
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Post edited over 2 years ago by aezoss.
     
Feb 15, 2016 22:14 |  #3556

Sky-Watcher 127mm Maksutov Cassegrain.

Edit: updated image.

Lee


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aezoss
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Post edited over 2 years ago by aezoss. (2 edits in all)
     
Feb 15, 2016 23:30 |  #3557

Astro-Tech AT72ED + 2x Barlow + 1.25" diagonal.

Edit: updated image.

Lee


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Celestron
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Feb 16, 2016 08:56 |  #3558

Very hard to get CA out of images of the moon without an APO scope and just about any camera lens . Moon is way too bright an object . Myself I prefer a brighter looking moon image than this . It is clear and focus looks good tho .




  
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aezoss
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Feb 16, 2016 13:27 |  #3559

Celestron wrote in post #17900405 (external link)
Very hard to get CA out of images of the moon without an APO scope and just about any camera lens . Moon is way too bright an object . Myself I prefer a brighter looking moon image than this . It is clear and focus looks good tho .

You're right, these two are underexposed. I'll rework them. An APO's on the wish list. Thanks for the feedback.

Lee




  
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Inspeqtor
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Feb 17, 2016 00:20 |  #3560

Celestron wrote in post #17900405 (external link)
Very hard to get CA out of images of the moon without an APO scope and just about any camera lens . Moon is way too bright an object . Myself I prefer a brighter looking moon image than this . It is clear and focus looks good tho .

What is an APO scope? Is it possible to connect them to a camera?


Charles
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aezoss
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Feb 17, 2016 02:45 |  #3561

Inspeqtor wrote in post #17901486 (external link)
What is an APO scope? Is it possible to connect them to a camera?

There are two main types of refracting telescopes; achromatic and apochromatic. Apos generally provide better CA/SA correction than achromats. Apos may have exotic glass, more lens elements, more complex construction and cost (much) more than equivalently sized achromats.

"ED" scopes split the difference. Better correction than an achromat. Less expensive than an apo.

Starizona has a short overview here (external link).

No problem interfacing a DSLR with most apos.

Lee




  
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Inspeqtor
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Feb 17, 2016 08:29 |  #3562

aezoss wrote in post #17901536 (external link)
Inspeqtor wrote in post #17901486 (external link)
What is an APO scope? Is it possible to connect them to a camera?

There are two main types of refracting telescopes; achromatic and apochromatic. Apos generally provide better CA/SA correction than achromats. Apos may have exotic glass, more lens elements, more complex construction and cost (much) more than equivalently sized achromats.

"ED" scopes split the difference. Better correction than an achromat. Less expensive than an apo.

Starizona has a short overview here (external link).

No problem interfacing a DSLR with most apos.

Lee

Thank you :-)


Charles
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TCampbell
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Feb 17, 2016 13:00 as a reply to  @ aezoss's post |  #3563

There's a huge difference between an achromatic refractor and an apochromatic refractor.

They "look" very similar on the outside... but the optics are vastly different.

If you use a simple magnifying loupe and look at at printed text on a white paper, you'll notice that while the center seems nicely magnified, something strange is happening around the edges... the "black & white" print seems to be bleeding color... with red and blue fringing coming out of the text.

This is because the "white" light is actually a combination of all the color in the spectrum and the edges of the lens are curved and are behaving like a prism -- splitting light into its constituent wavelengths. What's actually happening is the "red", "green", and "blue" wavelengths of light aren't actually focusing at the same distance and they also aren't all the same size. Blue light bends more then red. This effect is called "chromatic aberration".

To correct for this problem, an achromatic refractor adds a single lens element except instead of the typical convex lens shape, the send element has a concave surface that stacks against the first lens element. The two are put together in a configuration called an "achromatic doublet". The purpose of the 2nd lens element isn't to magnify anything... it's job is to attempt to reverse the chromatic aberration problem created by the first lens element.

While it does a decent job, it's not perfect -- and if you check the edges of the field of view with an achromatic refractor, you'll notice the stars near the edges of your field of view show a bit of color fringing (the "white" stars are just slightly diverging into a smear where the colors aren't quite converging perfectly.)

If you are doing visual astronomy, then you'll more than likely have your object of interest in the center of the field of view and as long as it's in the center it will probably look pretty good.

But if you are intending to do imaging, then your resulting images will show that color bleeding problem along the edges and corners.

There's a better optical configuration called an apochromatic triplet. In addition to adding a third optical element and chaining the configuration, usually the grade of optical "glass" is also significantly better and they tend to use some form of low-dispersion glass.

Not all apochromatic scopes use a triplet configuration. There are some slightly lower cost APOs that use a 2 element design (these are sometimes called "semi-APO" scopes. They use better "extra low dispersion" (aka "ED") glass.) There are also some higher end APOs that use a quad-element design.

Astro-imagers use the apochromatic designs because it means they get a sharp field free of CA from corner to corner.

The only down-side of an APO is that they tend to cost significantly more. A $1000 would be a very low price for an APO. They're typically several thousand dollars for just the optical tube -- no mount.

If you do a comparison looking through an achromatic and an apochromatic scope side-by-side... the difference is significant.




  
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Celestron
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Feb 17, 2016 21:34 |  #3564

That's a long explanation TCCambel but spot on. I could not have explained it that well. Well done !




  
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sandwedge
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Feb 17, 2016 22:52 |  #3565

IMAGE: https://dougmoon.smugmug.com/Planes/i-Vxj7Rzr/0/XL/Plane%2002172016-213-XL.jpg
IMAGE LINK: https://dougmoon.smugm​ug.com …72016-213-XL.jpg&lb=1&s=A  (external link) on Smugmug

http://www.flickr.com/​photos/63710159@N07/ (external link)
http://www.DougMoon.sm​ugmug.com (external link)
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Inspeqtor
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Feb 17, 2016 23:06 |  #3566

Oh WOW! That is really GREAT!!!!!!!!!


Charles
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sandwedge
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Feb 17, 2016 23:20 |  #3567

Inspeqtor wrote in post #17902801 (external link)
Oh WOW! That is really GREAT!!!!!!!!!

Thanks!


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http://www.DougMoon.sm​ugmug.com (external link)
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PeteD
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Feb 18, 2016 19:15 |  #3568

Tonight's with a light crop


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Feb 18, 2016 19:16 |  #3569

y19mike77 wrote in post #17872364 (external link)
thumbnail
Hosted photo: posted by y19mike77 in
./showthread.php?p=178​72364&i=i89964041
forum: Astronomy & Celestial

This one looks like Death Star


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Feb 18, 2016 19:17 |  #3570

sandwedge wrote in post #17877349 (external link)
Not real happy with the results, but at least I'm getting good at being at the right spot at the right time. International Space Station lunar transit, 1/29/16.

Used a 2x tc on a Sigma 150-600. I'm thinking I'll try it without the tc next time, as I had to bump the ISO to 2000 to compensate for the f/13. Combine that with loss of IQ and I'm not sure it is worth it. Also, there weren't perfect conditions - the Moon was at 52 degrees altitude at the time (meaning more atmosphere to shoot through and the ISS is farther away than during a more vertical pass). Also. the solar panels are more at an angle.



QUOTED IMAGE
IMAGE LINK: https://dougmoon.smugm​ug.com …2016-5703-XL.jpg&lb=1&s=A  (external link) on Smugmug

QUOTED IMAGE
IMAGE LINK: https://dougmoon.smugm​ug.com …2016-5704-XL.jpg&lb=1&s=A  (external link) on Smugmug





QUOTED IMAGE
IMAGE LINK: https://dougmoon.smugm​ug.com …2016-5705-XL.jpg&lb=1&s=A  (external link) on Smugmug

I saw it heading that way tonight. Got ready and lost it in the sky


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The Official Shoot the Moon Thread
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