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Correct Image or star diagonal viewing?

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#1 25585



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Posted 09 November 2018 - 02:12 PM

As most Moon maps are NSEW, and the moon is terrain, who uses correct image to view the moon as for binoculars and spotting scopes etc?

Edited by 25585, 09 November 2018 - 02:13 PM.

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#2 coopman


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Posted 09 November 2018 - 02:32 PM

The correct image diagonals degrade the image quality. Use a normal non-correct image diagonal.
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#3 photoracer18



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Posted 09 November 2018 - 03:33 PM

Ditto against CE diagonals also.
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#4 burb scope

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Posted 09 November 2018 - 03:40 PM

There is a mirror-reversed version as well as a regular version  of the Hatfield Photographic Lunar Atlas to match your view.

#5 Aleko



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Posted 18 November 2018 - 11:56 AM

The correct image diagonals degrade the image quality. Use a normal non-correct image diagonal.

Depends on the diagonal.  The hi-end (and hi-cost) Baader Amici Prism Diagonal gives an outstanding image. 


When using a lunar Atlas, I'll use the correct image Baader Amici. When just scanning around, I'll leave my normal (reversed) diagonal in.  My only complaint when using the Amici on the moon is that I always end up trying to move the scope in the wrong direction, since I'm so used to the normal diagonal. But that's my fault, not the diagonal's. 



#6 erin


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Posted 18 November 2018 - 05:23 PM

Okay, I am going to venture out and say that I enjoy using the CI prism on the moon. I certainly would not say whether it is better than a star diagonal, but I do not see image degradation, and I like that I am seeing it like the naked eye view or the binocular view I am so used to. I just don’t see the difference.


Please don’t throw the rotten tomatoes my way!

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#7 Sketcher


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Posted 07 December 2018 - 03:36 PM

I have some correct-image diagonals.  I've never thought about using one when observing the moon.  But since the topic has surfaced, I'm thinking that a 90-degree CID would have real benefits when sharing views with those less accustomed to the rotated and/or flipped images that many of us have grown accustomed to.


I mostly use refractors -- with conventional diagonals, so my lunar views are usually mirror-reversed.  Most of my lunar charts/atlases are correct-image, though I also have the mirrored and correct versions of the S&T Moon Maps.  Over time, I've learned to easily recognize the many 'familiar' lunar features regardless of the image orientation.


Yet, there are times when some confusion becomes possible.  Under such circumstances, I'll sketch a quick full-moon 'finder-chart' on which I'll indicate ("X" marks the spot!) the where-abouts on the moon of my sketched feature(s) -- making the task of later matching the sketch with mapped (and labeled) features less confusing.  But most of the time this isn't a necessary measure for me to take.  (I almost never take a moon map/atlas outside with me.)


Most (of the 'major') lunar features are unique enough that they can be readily identified (via their unique features, appearance, and/or location) regardless of the image orientation.  So I've never considered using a CID for my lunar observations.

#8 barbie


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Posted 07 December 2018 - 11:49 PM

I use high end prism and mirror diagonals and image orientation is simply not an issue for me.  Image quality IS, however, and I've found that a good diagonal is well worth the money and can be used for many years down the road no matter which scope(s) you're using at any given period of time.

#9 Kunama


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Posted 09 December 2018 - 03:21 PM

Correct image in a binoscope watching.gif

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#10 Joe Eiers

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Posted 15 December 2018 - 03:32 AM

  With the software that's out there I tend to just stick with standard diagonals.  It's such an easy matter to flip the image and display on the screen whatever format  you desire.   Just another option.

  As far as high quality diagonals, I agree with above, but to be honest with you I can't see the difference between an average diagonal and a "perfect" one.  Most folks agree that differences in diagonals is pretty subjective if you look at the posts out there.

  Just my 1.5 cents.


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#11 Jon Isaacs

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Posted 15 December 2018 - 11:05 AM

Correct image diagonals use Amici/roof prisms which split the light into two paths and then rejoin them.  The split in the mirror causes a diffraction spike on bright stars . 


There is also the question of phase coatings.  The two light paths result is different phases and better roof prism binoculars use phase coatings to correct this as it otherwise results in a loss of contrast. 




I am not seeing that the Baader correct image diagonal is phase coated. 





#12 ShaulaB



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Posted 15 December 2018 - 11:13 AM

Once upon a time, people learned the mental gymnastics required to go from a direct image chart to the finder or telescope orientation. In the age of electronics, your Sky Safari or whatever app can adjust the view to whatever is desired. Were we smarter back in the day? No, not really.
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#13 JoeInMN


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Posted 19 December 2018 - 08:43 PM

Has anyone ever tried this: Take two good quality star diagonals; remove the eyepiece holder from one and the barrel from the other; stick the housings together so that the first one reflects to one side and the second one upward. This would give a correct-but-rotated effect similar to that of a Newtonian. You could just daisy-chain them intact; the amputations are just to shorten the path as much as possible. I imagine a lot of focusers wouldn't have enough travel anyway. I don't have the parts to try it myself...

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