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Are we overlooking the obvious?

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#51 CrazyPanda

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Posted 11 June 2019 - 07:32 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

Two things jump out at me here:

The tone, obviously, but also the contrast. The contrast of the straight-through shot is better IMO. The lines in the beadboard are a bit darker and more clear. The image with the diagonal just has the appearance of a slight haze to it, which may also explain why it's visible in the black areas of the image, too. Of course, differences in camera angle and many other factors might be causing this.

I'd like to see a series of images of each setup to see if there is any variation, or if what we're seeing here is consistent. If both the tone and this "haze" is consistent, then I would say that this diagonal is problematic compared to the straight-through view.

 

These daylight comparisons I think are useful, and it would be good to see the same experiment on other diagonals as well.


Edited by CrazyPanda, 11 June 2019 - 07:38 PM.

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#52 25585

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Posted 11 June 2019 - 07:47 PM

Daylight photos comparing mirror with prism will be different to some extent due to UV possibly? 


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#53 Procyon

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Posted 11 June 2019 - 08:22 PM

Definitely the interior tubing reflections concerning the black tones. Since I have the scope set up near the back patio door, I snapped a few pictures with my cell phone, nothing fancy though, without an eyepiece, diagonal was upside down. I need to get a phone attachment for the scope. Left pictures on both samples are with the diagonal attached to the telescope. I took some shots around 7:30pm but since my whites are indoors it probably won't change much of the toning. These pictures were taken at 7:55pm eastern.

 

11" SCT, 2" Baader Dielectric Mirror Diagonal. Patio door was left open :/) Looking at my pics, it would have helped if I had focused, but was curious about the whites. grin.gif They look very ok. Contrast on some colors may be slightly off? I don't have any buildings or neighbors visible from my backyard to try this with an eyepiece. The bar is the patio door 5 feet away and the trees are 60 feet away. 

 

Untitled.jpg

 

ged.jpg


Edited by Procyon, 12 June 2019 - 05:36 PM.


#54 Procyon

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Posted 11 June 2019 - 10:01 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.

I think this is very true, camera settings are a big possibility for all kinds of misleadings. I was reminded of this very quickly by accidentally clicking on pro picture view w/Galaxy S8. 

 

But than again, wouldn't both show the same since the settings remained the same? 


Edited by Procyon, 11 June 2019 - 10:17 PM.


#55 rockethead26

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Posted 11 June 2019 - 10:59 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.

Unfortunately as you get closer to sunset, the light gets warmer, not cooler.


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#56 Procyon

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Posted 11 June 2019 - 11:12 PM

Unfortunately as you get closer to sunset, the light gets warmer, not cooler.

True, thought the warmer picture was taken later, or was just speaking in general that it would affect tone. Nice thinking to check time on pics I meant. 



#57 RichardHennig

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Posted 12 June 2019 - 09:47 AM

I think this is very true, camera settings are a big possibility for all kinds of misleadings. I was reminded of this very quickly by accidentally clicking on pro picture view w/Galaxy S8.

But than again, wouldn't both show the same since the settings remained the same?


To compare color tones of images, we need to ensure that the clever camera algorithms do not alter the weights and balance of different color channels, which is what the default automatic white balance does.

If you can either change the setting to either a fixed temperature, or daylight, or record the image in a RAW setting, then the color balance is preserved and allows accurate comparisons.

Edited by RichardHennig, 12 June 2019 - 09:58 AM.

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#58 csrlice12

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Posted 12 June 2019 - 10:07 AM

Is it live, or is it Memorex....or maybe the building is 50 shades of beige.


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#59 bobhen

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Posted 12 June 2019 - 02:05 PM

I’ll just comment on the 2” diagonals that I have now.

 

Astro-Physics. I have (2)
Stellarvue
Astro-Tech

 

The best is the Astro-Physics. Under close scrutiny, the other 2 just don’t fair as well. I don’t use the other 2, there’s no point.

 

Bob


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#60 25585

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Posted 12 June 2019 - 02:48 PM

Which 1.25" mirror diagonal would be good for F6 refractors also including bino?  I only have a Tak prism in that size.



#61 Starman1

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Posted 12 June 2019 - 03:04 PM

You want something 2" for ability to handle the weight, and something strongly-constructed, like TeleVue, Astrophysics, etc.

With TeleVue, you also have the choice of dielectric coatings or enhanced aluminum.


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#62 Astrojensen

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Posted 12 June 2019 - 03:36 PM

 

Which 1.25" mirror diagonal would be good for F6 refractors also including bino?

 

I have a Baader T2 prism diagonal, which I use with my heavy Zeiss binoviewer. Mine's a prism, but there's a mirror version, too. It's only slightly bigger than a normal 1.25" diagonal, but MUCH more solidly constructed. You can configure it to either 1.25" or 2" nosepiece and there's various eyepiece adapters to choose from. 

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 12 June 2019 - 03:38 PM.

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#63 Procyon

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Posted 12 June 2019 - 05:13 PM

A T2 or Zeiss 1.25" with a 1.25" Clicklock is excellent. If Refractors take Visual Backs or VB's, maybe look for one that is very well constructed also, even if you have to give up, or rather add another 5-10mm of optical path. Binoviewers can easily flip with the slightest touch at some point, with heavier eyepieces, especially if the VB is ultra short. 


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#64 turtle86

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Posted 12 June 2019 - 08:23 PM

I’ll just comment on the 2” diagonals that I have now.

 

Astro-Physics. I have (2)
Stellarvue
Astro-Tech

 

The best is the Astro-Physics. Under close scrutiny, the other 2 just don’t fair as well. I don’t use the other 2, there’s no point.

 

Bob

 

The Astro-Physics diagonal is a work of art.  The Astro-Tech is very good for the money, but the Astro-Physics is in a different league altogether.


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#65 turtle86

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Posted 12 June 2019 - 08:59 PM

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

I frequently use a beach chair when lying on my back to observe with binoculars.  It’s a very relaxing way to observe but as you say it’s impractical with a telescope.

 

No doubt that theoretically a view without a diagonal is going to be purer than a view with one, especially one that is mediocre or worse.  But practically comfort really does count for something, especially if I’m doing a long observing session.  I just don’t think it’s worth it to contort myself to observe without a diagonal, and I suspect that with a good one the only thing I’m going to miss is lower back pain.


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#66 russell23

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Posted 12 June 2019 - 09:25 PM

Which 1.25" mirror diagonal would be good for F6 refractors also including bino?  I only have a Tak prism in that size.

I like my Baader 1.25” prism.  


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#67 BGazing

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Posted 13 June 2019 - 07:37 AM

With planets so low...perhaps I might finally try observing sans diagonal. Silver lining?


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#68 Astrojensen

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Posted 13 June 2019 - 11:01 AM

No doubt that theoretically a view without a diagonal is going to be purer than a view with one, especially one that is mediocre or worse.  But practically comfort really does count for something, especially if I’m doing a long observing session.  I just don’t think it’s worth it to contort myself to observe without a diagonal, and I suspect that with a good one the only thing I’m going to miss is lower back pain.

Absolutely true. Comfort at the eyepiece is critically important, in my opinion. You simply see more, if you're relaxed. 

 

But I wish people (and manufacturers) would pay more attention to diagonal quality. We see threads about eyepiece quality every single day, but only extremely few about diagonal quality. This despite that we've seen hard evidence in this thread that diagonals have a FAR wider quality spread than eyepieces do. 

 

 

Clear skies!
Thomas, Denmark


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#69 Astrojensen

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Posted 13 June 2019 - 11:04 AM

With planets so low...perhaps I might finally try observing sans diagonal. Silver lining?

Heh! I like your thinking, but the poor seeing at the low altitude is likely going to make the effort futile. Been there, done that.

 

 

Clear skies!
Thomas, Denmark


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#70 leonard

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Posted 13 June 2019 - 11:21 AM

Hello ,

 

 

 

                  Has there ever been an adjustable diagonal , as a secondary mirror can be in a newtonian telescope ?

I have not seen anything like that , have you ?



#71 turtle86

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Posted 13 June 2019 - 11:34 AM

Absolutely true. Comfort at the eyepiece is critically important, in my opinion. You simply see more, if you're relaxed. 

 

But I wish people (and manufacturers) would pay more attention to diagonal quality. We see threads about eyepiece quality every single day, but only extremely few about diagonal quality. This despite that we've seen hard evidence in this thread that diagonals have a FAR wider quality spread than eyepieces do. 

 

 

Clear skies!
Thomas, Denmark

 

I think lack of comfort itself is too often overlooked.  It is why I gave up on Pentax XO's.  Great eyepieces, but they were so uncomfortable for me to use that I came to conclude that they interfered with what I was viewing. 

 

By similar token, I find observing without a diagonal to be sufficiently uncomfortable to interfere with the view.  It's only comfortable if the object is very low in the sky, but who wants to observe objects that are only 10-20 degrees above the horizon?  (I make a special exception for Omega Centauri and Centaurus A, but that's about it!  grin.gif)  So I think a diagonal is a virtual must, even though theoretically it can never improve the view. The challenge is to find the diagonal that compromises the view the least.

 

I agree that the diagonal tends to get overlooked in discussions about tiny differences between various eyepieces, and that in a general sense the diagonal needs more consideration and scrutiny.  Though there is a lot less information out there on diagonals as opposed to eyepieces (and telescope objectives and mirrors for that matter), at least we have a general idea of which are some of the better ones.  Your Baader prism diagonal sounds excellent and I don't think most people could go too wrong with Astro-Physics or TeleVue, other than the hit to their wallet.


Edited by turtle86, 13 June 2019 - 11:36 AM.

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#72 TOMDEY

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Posted 13 June 2019 - 12:15 PM

Hello ,

Has there ever been an adjustable diagonal , as a secondary mirror can be in a newtonian telescope ?

I have not seen anything like that , have you ?

I bought a new Antares 2MDC Adjustable Star Diagonal about seven years ago. Unfortunately, as received, BNIB, it was way out of alignment, and the three screws could not bring it in. Either the angle was way off or the lateral axis was far displaced. Here's the problem: It takes four degrees of freedom to align the input to output axes. (lateral x, lateral y, theta x, theta y). But three screws provide only... three! Add to that the confines of a too-small cavity, and the mirror in there is likely to bump into something --- which is the fatal defect in mine. The coating is also defective: Marked "Dielectric 99%", but measures 89%. That pretty much turned me off to adjustable diagonals. I decided it would just be far far better to make it right in the first place, so the user would have confidence to simply use it and get on with life. My Astrophysics PMDMAX and Lumicon LumiBrite are the only two (of fifteen!) that measured superior re' all requirements... and are the ones I use!    Tom


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#73 nicoledoula

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Posted 13 June 2019 - 12:20 PM

Diagonals add another element to the optical chain and are unnecessary (except for comfort reasons). Very few articles about diagonals being out of alignment makes this whole thread kind of pointless. Of course some are better than others but that's been argued ad nauseum as well. "Illusions"? LOL The Japanese might not be as tough as they used to be. Maybe they learned the image wasn't degraded as much as they believed. Bottom line: diagonals are an unnecessary part of an optical chain which CAN degrade images if not up to snuff. I suppose we have to test them all (in quantities) in order to make any other statements about "which is best". 



#74 Starman1

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Posted 13 June 2019 - 12:33 PM

Hello ,

 

 

 

                  Has there ever been an adjustable diagonal , as a secondary mirror can be in a newtonian telescope ?

I have not seen anything like that , have you ?

Yes.  Through the years there have been many star diagonals with collimation screws on the exterior.

It has been a dying thing, though, and it's rare to find one today.

Antares and Scopestuff.com used to sell them, but both are discontinued.

 

You could do it on your own with a bit of time, a drill, and a tap.


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#75 Procyon

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Posted 13 June 2019 - 01:29 PM

I'd like to take 10 of the best diagonals, point them towards a distant white and black object in the day, and see which ones have the most neutral whites and darkest blacks. Would that help with anything or no point really? Unless Bill's already done this.

Edited by Procyon, 13 June 2019 - 02:16 PM.

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