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Are we overlooking the obvious?

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#26 Starman81

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Posted 11 June 2019 - 10:40 AM

In some testing unrelated to diagonals, I came upon a surprising difference. While taking pictures of a daytime scene with and without a diagonal, the difference is very apparent!

 

This picture below is without a diagonal, straight through a 40mm Plossl eyepiece in an ST 80. Don't pay attention to the vignetting present. Observe the tone of the image. 

 

 

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#27 Starman81

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Posted 11 June 2019 - 10:43 AM

Now with the same setup, taken a few minutes earlier, the only difference is that a high-quality 2" dielectric diagonal is used.

 

Both pictures taken with a cameraphone with exact same settings (HDR, f/1.8, 4.51mm, ISO3).

 

Looks like the diagonal is casting a very warm tone to the image, doesn't it? 

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#28 Sarkikos

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Posted 11 June 2019 - 10:47 AM

Now with the same setup, taken a few minutes earlier, the only difference is that a high-quality 2" dielectric diagonal is used.

 

Both pictures taken with a cameraphone with exact same settings (HDR, f/1.8, 4.51mm, ISO3).

 

Looks like the diagonal is casting a very warm tone to the image, doesn't it? 

Yes.  What is the diagonal?

 

Mike


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#29 russell23

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Posted 11 June 2019 - 10:48 AM

yes.  Interesting.



#30 Starman81

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Posted 11 June 2019 - 10:54 AM

Yes.  What is the diagonal?

 

Mike

 

Baader ClickLock Dielectric!

 

Optical setup with the diagonal: 

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#31 Starman81

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Posted 11 June 2019 - 10:57 AM

Optical setup without the diagonal:

 

In both setups there is a TV 40PL and the same 2" 0.5x focal reducer. Filter wheel was empty; just testing if it would come to focus. Some might ask: what kind of insane type of testing was this? Surely these are not usable optical configurations... NV is the answer. It goes by different rules! 

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#32 Starman81

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Posted 11 June 2019 - 11:00 AM

One variable in this informal 'experiment' is the level of sunlight from minute-to-minute, but I don't think that is a factor here as there is not an apparent difference in sunlight. The tone difference is too much to account for between the two setups by any small variation in sunlight, in my opinion. 


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#33 Deep13

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Posted 11 June 2019 - 01:06 PM

Yup, diagonal quality is important and often ignored. My 5" f/12 refractor has a TV Everbrite mostly because the Denk 2 binoviewer is designed for it. I understand that high quality prism or mirrored diagonals might be a bit better optically.

I'm mostly a Newt guy, and my scopes either have Discovery diagonals from 2000-2005 or Antares, which are all really good.

#34 Procyon

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Posted 11 June 2019 - 01:15 PM

Great, now we have to look for neutral toned diagonals? lol.gif troll.gif mellow.png huh.png wacko.png blink.png unsure.png



#35 Procyon

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Posted 11 June 2019 - 01:20 PM

I placed them next to each other, hope you don't mind, any reason why the blacks on the right side picture appear more faded or lighter?

 

Untitled.jpg


Edited by Procyon, 11 June 2019 - 01:21 PM.

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#36 Astrojensen

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Posted 11 June 2019 - 01:25 PM

I placed them next to each other, hope you don't mind, any reason why the blacks on the right side picture appear more faded or lighter?

 

attachicon.gif Untitled.jpg

Micro-scatter spreading light all across the image, decreasing contrast? 

 

 

Clear skies!
Thomas, Denmark



#37 Starman1

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Posted 11 June 2019 - 01:26 PM

I placed them next to each other, hope you don't mind, any reason why the blacks on the right side picture appear more faded or lighter?

 

attachicon.gif Untitled.jpg

Maybe slight differences in focus.


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#38 Starman81

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Posted 11 June 2019 - 01:48 PM

I placed them next to each other, hope you don't mind, any reason why the blacks on the right side picture appear more faded or lighter?

 

attachicon.gif Untitled.jpg

 

Thanks for that!

 

I'm not quite sure about the shading of blacks between the two pictures being different...

 

What I do know is that with this Baader Clicklock diagonal, I have had some superb Jupiter and Saturn views (while used with my SW 120ED and Delos eyepieces). That would fit the narrative of warm-toned optics enhancing Jupiter observations, right? Saturn, I think observers are split on whether they would favor warm or cool tone, if they had to choose.

 

I am not a critical lunar observer, so if it warmed the image of the Moon noticeably, it's totally possible that I could have missed it.

 

Warm/cool tone is just one of the performance characteristics of a diagonal. I was surprised to see this unintended difference in the pictures (for which my real intent was to measure TFOV with different setups). I am sure that some you photogs could do a much better job with a controlled experiment indoors, using software to give us some hard numbers... Take it for what its worth--a thought-starter.


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#39 Starman1

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Posted 11 June 2019 - 02:08 PM

Looks like a slight difference in TFOV and, perhaps, magnification.


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#40 Astrojensen

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Posted 11 June 2019 - 02:13 PM

Looks like a slight difference in TFOV and, perhaps, magnification.

But should that have such a dramatic effect on color tone? 

 

Now I'll need to compare my different diagonals next time the Moon is high in the sky. 

 

 

Clear skies!
Thomas, Denmark


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#41 rockethead26

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Posted 11 June 2019 - 02:52 PM

I placed them next to each other, hope you don't mind, any reason why the blacks on the right side picture appear more faded or lighter?

 

attachicon.gif Untitled.jpg

Which pic is actually closest to the real scene in tone? A thin layer of high clouds in front of the Sun can impart a bluish cast to a photo. The bluish one also looks like it received less light during the exposure which may also be indicative of a high, thin cloud layer. Otherwise I cannot explain why the warm rendition, with the diagonal used received more light with the same exposure settings.


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#42 nicoledoula

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Posted 11 June 2019 - 03:04 PM

Japanese amateurs generally don't use diagonals. Extra clarity wasn't the reason diagonals were designed, comfort was the reason. Figuring out comfortable ways to view straight through is the challenge. The extra optical component can only hinder the view, not improve it.  

 

Which pic is actually closest to the real scene in tone? A thin layer of high clouds in front of the Sun can impart a bluish cast to a photo. The bluish one also looks like it received less light during the exposure which may also be indicative of a high, thin cloud layer. Otherwise I cannot explain why the warm rendition, with the diagonal used received more light with the same exposure settings.

"received more" SCATTERED light



#43 Starman81

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Posted 11 June 2019 - 03:12 PM

Which pic is actually closest to the real scene in tone? A thin layer of high clouds in front of the Sun can impart a bluish cast to a photo. The bluish one also looks like it received less light during the exposure which may also be indicative of a high, thin cloud layer. Otherwise I cannot explain why the warm rendition, with the diagonal used received more light with the same exposure settings.

 

Closest to the real scene in tone? Hmmm... Tough to say to now, a month later, if I'm being honest. 

 

Just some other notes for the sleuths out there... The patio in the picture is west-facing and the warm toned picture was taken at 7:00pm and the cooler tone picture was taken at 7:30pm. Local sunset time was 8:49pm that day (May 16th).


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#44 RichardHennig

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Posted 11 June 2019 - 03:21 PM

I am wondering if this difference in color tone could originate in the in-camera automatic white balance? Most phone cameras will determine the white balance based on the overall picture. As you notice, the picture is framed differently and due to the mirror upside down. I would not be surprised if this simply results in a different white balance setting.

If your phone has a mode to fix the color temperature instead of the standard auto white balance setting, it would be easier to compare the results.

My phone certainly has resulted in dramatic color shifts by simply different framing of a picture.
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#45 Astrojensen

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Posted 11 June 2019 - 03:47 PM

Japanese amateurs generally don't use diagonals. 

I'm fairly sure that's mostly a thing of the past. I found some pictures from star parties in Japan and they use diagonals on their refractors and cassegrains just as much as we do. 

 

Sorry if that broke some illusions. grin.gif

 

https://astro365.exb...18_19352155.jpg

 

https://astro365.exb...718_1935124.jpg

 

 

Clear skies!
Thomas, Denmark


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#46 BGazing

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Posted 11 June 2019 - 03:58 PM

I use the Baader BBHS silver in the T-2 configuration.  Bill P. has reviewed the 2" on this site.

That one is a beauty. Compared it to APM prism and it was chalk and cheese, we switched both back and forth in C8 and refractors and BBHS was clearly the best. Differences between BBHS and Baader dielectric are subtler, but there...on planets and moon.


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#47 Starman1

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Posted 11 June 2019 - 05:08 PM

But should that have such a dramatic effect on color tone? 

 

Now I'll need to compare my different diagonals next time the Moon is high in the sky. 

 

 

Clear skies!
Thomas, Denmark

No, I was merely explaining the reason why dark lines might have been a bit less distinct in one image than in the other.

In my phone, I can drag a point in the picture to whatever in the scene I want the camera to focus best on.

If the camera in the phone focuses on a different part of the frame in each image, that could easily account for subtle differences in focus

and the distinctness of dark lines.


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#48 Sarkikos

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Posted 11 June 2019 - 05:23 PM

Japanese amateurs generally don't use diagonals. Extra clarity wasn't the reason diagonals were designed, comfort was the reason. Figuring out comfortable ways to view straight through is the challenge. The extra optical component can only hinder the view, not improve it.  

There are no comfortable - and convenient - ways to view straight through unless you are pointing near the horizon.  Do we really want to lie on our backs?  Well, that might work for small binoculars, but it's kind of impractical for telescopes.

 

Convenience, practicality and comfort do count for something.  I'm not giving up my diagonals.  I am trying to use better ones.

 

Mike


Edited by Sarkikos, 11 June 2019 - 05:24 PM.

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#49 Procyon

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Posted 11 June 2019 - 06:15 PM

The patio in the picture is west-facing and the warm toned picture was taken at 7:00pm and the cooler tone picture was taken at 7:30pm. Local sunset time was 8:49pm that day (May 16th).

Nice thinking. It may or may not have been a big factor. But 30 minutes in time difference nearing sundown should affect the picture tone somewhat I'd think. What if every diagonal we try this on, ends up looking like that though, lol.

Will it mean straight through has less glass interference, or?

Can ED glass be used in mirror diagonals or prisms?

Edited by Procyon, 11 June 2019 - 06:17 PM.


#50 Starman1

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Posted 11 June 2019 - 06:26 PM

Nice thinking. It may or may not have been a big factor. But 30 minutes in time difference nearing sundown should affect the picture tone somewhat I'd think. What if every diagonal we try this on, ends up looking like that though, lol.

Will it mean straight through has less glass interference, or?

Can ED glass be used in mirror diagonals or prisms?

ED glass would be pointless in a mirror, and prisms are usually BK-7 glass.




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