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Baader Maxbright II. daytime observation

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#1 szjozso

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Posted 05 February 2025 - 07:45 PM

Hi All!

 

I like nature observation and contrail spotting. I tried to use my MB II but the light path my Amici prism  is too long, so I can't get focus in my 66/400 ed scope .

My Baader zenit prism with 1,25 GPC  is fine, but I don't like seeing the left and right sides reversed. This is disturbing, especially observing aircrafts.

There is a Baader Amici prism for Maxbright I. (https://www.baader-p...-corrector.html)

I asked the support if it is suitable to the MB II. They don't recommend, because it was designed for the MB I and the smaller prisms cause vignetting.

Does anyone have experience with it? Or do you have any other sugggestions? 

Thank you for reply in advance.



#2 Finbarius

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Posted 05 February 2025 - 09:08 PM

Hi there, and welcome.

 

The claim that the Baader 45° Maxbright amici prism 1¼", with inbuilt 2x gpc, is not recommended or suitable for the MBII is very surprising.

I use it with my MBII, especially in my 60mm Tak, the FOA-60Q (60/900) or without the Q module (60/630 - but balancing can be a challenge). So my usual setups are slower than yours, which will have some effect.

 

The usual 90° Zenith prism I use otherwise has a clear aperture of 25.5mm, while this 45° amici has 25mm, that is only 0.5mm smaller, so I see no reason why it should be a problem. Vignetting does occur with longer eyepieces such as my 32mm 1¼" plossl, but I've not found this a real problem. I do prefer a slightly shorter length eyepiece with smaller field stop that avoids this. So, my other eyepieces that work very well in my set up are 25mm (aFoV 42°, field stop 17.4mm), 21mm (66°, 24.5mm), 16mm (85°, field stop 23.5mm).

 

Hope this helps.


Edited by Finbarius, 05 February 2025 - 09:11 PM.


#3 szjozso

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Posted 05 February 2025 - 10:36 PM

Hi Szputnik!

 

Thank you for the reply. I use 18 mm BCO, 25 mm plössl, and 32 mm plössl eyepieces, so with the first two would work fine. 

I might order the prism, I hope it will work well.

 

Thanks again.



#4 Finbarius

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Posted 09 February 2025 - 01:49 AM

I need to correct the record: I made a mistake in my post.

 

The clear aperture in my usual prism for celestial viewing, a Baader Zenith 90°, is 32mm, not 25.5mm. It is the MB2 itself that has 25.5mm, which is close to the MB 45° amici prism's 25mm.

 

In the Baader info page, the first question, in 2018, was about this MB amici prism's suitability for use with the Mark V (asked in 2018) - and the answer there was that they did not recommend that particular combination. The second question, in 2021, lacks some detail, but their answer does state that this prism was "made especially for the old Maxbright bino-viewer", which could give the impression that it is not suited for the MB2. I then wondered about the differences between that original MB and the MB 2, and found this CN thread where Eddgie gives the relevant info - the prism of the MB2 is larger, 25.5mm v. 23mm. Eddgie made the point that only some eyepieces would reveal the differences, and that also fits with my experience, with the point I made remaining true: the MB2 and MB 45° prism do work nicely together, but it does depend on the eyepiece and the viewer's tolerance for vignetting in the lowest powers or widest fields. Anyway, I hope you enjoy it when you receive it.



#5 ABQJeff

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Posted 09 February 2025 - 02:11 AM

I use my MBII with a 90 degree amici all the time  Lots of options.  I use Baader T2 astro amici and an Omegon 90 degree amici.  Note you will need a stronger GPC than 1.25x to get focus.   Get the 1.7x and 2.6x to give you options.  Barlow or Powermate can work as well, but don’t suppress prism effects.  My Quarks have built in 4.3x focal extenders.



#6 szjozso

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Posted 09 February 2025 - 02:11 PM

Hello
I also have a 45-degree zenith prism. (similar to this: https://www.omegon.e...i-prism/p,44697). There is also a noname 90 degrees. I put a 2x Barlow lens in the filter thread, but I couldn't get the focus on any of them. Is there another way I could try?
By the way, I plan to get the 2.6 GPC as well. If I put that in MB 2, would I get the focus? In this case, the Baader Amici prism might not even be needed. What do you think?
Thank you very much.



#7 Spikey131

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Posted 09 February 2025 - 04:35 PM

The Maxbright 2 manual shows their T2 Amici prism as an option.  The light path of this prism is 48mm, 9mm longer than their “Zeiss” T2 prism. 
 

The light path for the 1.25, 1.7 and 2.6 Baader GPC is -30, -65, and -120mm, respectively.  So if you had a Baader T2 Zeiss prism, and it reached focus with the 1.25 GPC, you would know that the Baader Amici would reach focus with the 1.7 GPC.

 

Unfortunately, our friends at Omegon do not report their light path specs.  And Barlows behave differently depending upon where they are placed.  I believe that if you placed a Barlow on the nosepiece of the binoviewers, it would reach focus.  But I don’t know if that diagonal could handle the weight and leverage.



#8 Eddgie

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Posted 11 February 2025 - 09:51 AM

 

The light path for the 1.25, 1.7 and 2.6 Baader GPC is -30, -65, and -120mm, respectively.  

 

This must be in context of having the GPC placed in front of the diagonal, yes? These are not the figures for when it is used behind the diagonal.  These sound off though, and I have never seen this spec posted. Were these measured directly, or synthesized?



#9 Eddgie

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Posted 11 February 2025 - 10:43 AM

 

 

 

 

 

Before I go further, it is important to say that at f/6, all standard binoviewers made today will vignette the light path

 

At some point though, what happens if that if the aperture is too small, the vignetting turns into aperture reduction and this is much more concerning than vignetting, which is always present in modern standard binoviewers. 

 

 

Hi there, and welcome.

 

The claim that the Baader 45° Maxbright amici prism 1¼", with inbuilt 2x gpc, is not recommended or suitable for the MBII is very surprising.

I use it with my MBII, especially in my 60mm Tak, the FOA-60Q (60/900) or without the Q module (60/630 - but balancing can be a challenge). So my usual setups are slower than yours, which will have some effect.

 

 

 

I agree with Finbarius. If this was a non-amplified diagonal, I would be concerned about vignetting and maybe even aperture loss, but once you put the 2x into the diagonal, this concern goes away.

 

Here is the way it works.  When the light enters the binoviewer, it passes through a 25.5mm opening and it travels 110mm to the focal plane (assuming the field stop is at the top of the eyepiece holder). 

 

This means that a 25.5mm cone of light enters the system (no GPC or Barlow). This cone will converge at a rate of 1mm for every multiple of the focal length that it travels.  If the system is f/6, this means that to travel 110mm, the cone will be reduce in diameter by 18.3mm by the time it reaches the focal plane. The fully illuminated field will be reduced to (25.5 - 18.3 =) 7.2mm in diameter. Outside of this circle, there will be vignetting, but all standard binoviewers do this (vignette), and the amount of vignetting is not enough to be easily seen unless the system is very fast (though at f/6, someone that is sensitive to vignetting will see it when using very low power eyepieces with wide field stops).  

Let's see what happens with the 2X.  I think the aperture is about 21mm or so and I am assuming that the GPC is ahead of the prism, but I don't know this.  It does not matter though because here, I am simply trying to show the behavior of the system. So, if the light cone is 21mm at entry, the light cone changes to f/12 when it enters the diagonal.

 

In this case with the f/12 light cone, given a 30mm light path in the diagonal and a 110mm light path of the BV, that cone will start converging at a loss of 1mm of fully illuminated field for every multiple of f/12.  That means that the cone will be reduced by 11.6mm over the path from the 21mm aperture of the BV to the focal plane.  If the aperture started at 21mm, and it is reduced by 11.6mm, at the focal plane, the fully illuminated field will be 9.4mm (21mm - 11.6mm =) or 2.2mm wider than the system used without the a GPC. 

 

Running the numbers with the 1.25x GPC between a standard diagonal and the binoviewer, the figures would be that the system is turned into f/7.5.  Here, the light cone enters into the 110mm BV and loses 15.17mm so arrives at the focal plane 10.6mm in diameter so using the Amici in the link above would cause a bit more vignetting, but the difference in a fully illumined circle difference of 1.2mm, would be almost impossible to see (2x diagonal vs 1.25x GPC at the BV entry).

 

Here is a simpler comparison. I run my 130mm f/7 Apo without a GPC (when not observing planets or double stars) and the fully illuminated field is 9.8mm, and even at f/7, as sensitive as I am to vignetting, the field appears to be visually free of any vignetting. It is there, but it is just not enough to see.   At f/12, the vignetting falloff would be gentler than at f/7.5, and my guess would be that no observer on earth would be able to detect the slight differences between using the 2x diagonal and the 1.25x GPC. 

 

(f/6 is pushing it, and I would always recommend using a GPC, Powermate, or Barlow in front of any kind of prism diagonal or a Barlow for a refractor this fast.) 

 

As for the Amici, I have not used one that did not show aberration on bright stars, but for non-point sources, this will not be visible, though it does very slightly lower contrast. For terrestrial or daytime use, the aberration does not do enough damage to be of any concern, but the aesthetic damage on stars can make it a show stopper for many. 

 

It is important to note though that I do not have the actual figures for this diagonal, but Baader says the "inner diameter) is 25mm, so if that means the front aperture, my numbers are very conservative being based on 21mm, so if that is indeed the correct figure, the fully illuminated circle would be 4mm larger than the example, meaning that it would be bigger than even when using the 1.25" GPC. 

 

The convergence of the light cone is just basic geometry, and it can be applied to many things, but it is particularly good to know when trying to understand binoviewer behavior. 



#10 Finbarius

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Posted 12 February 2025 - 11:50 PM

… Here is the way it works. …

The convergence of the light cone is just basic geometry, and it can be applied to many things, but it is particularly good to know when trying to understand binoviewer behavior. 

Thanks Eddgie for the extra info and analysis. Related, often discussions on eyepieces in CN lack the important context of the scope's f/ratio, and many negative pronouncements are made about particular eyepieces without indicating how well suited they were to the scopes. It would be useful if manufacturers indicated the type of scope or range of f/ratios an eyepiece was designed for. Hence, I love my Masuyama 85° 16mm in the various slow FOA-60Q configurations, but maybe not (haven't tried) in my f/4.7 newt.

 

Back on the 45° possibilities for the MB2, even Baader only gives the optical path of the MB 45° prism as "variable", perhaps because the nose is rather long and it need not be seated all the way into the clamp - useful if extra optical length proves necessary. While various Amici prisms are possible, the advantage of the Baader MB 45° is its compactness (see photo below) if you have a suitable 1¼" eyepiece clamp in place. I use a Baader clicklock clamp with added Quick Change dovetail; the QC ring is already on my FOA-60. But a disadvantage with the MB 45° can be that it is fiddly to add and remove: I often struggle to get the nearly invisible (looks like a) spacer ring out of the collar so the provided key tool can be used to attach and to remove it - and must remember to return it otherwise the collar will not tighten on diagonals. Of course you can leave the collar on as it is used for both the MB 45° and the T2 prisms, but my scopes are set up for the quick changers so I only use the collar for this MB 45° prism. And when I do, I really enjoy it.

 

MB2 MB45amici


#11 Spikey131

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Posted 20 February 2025 - 08:32 PM

This must be in context of having the GPC placed in front of the diagonal, yes? These are not the figures for when it is used behind the diagonal.  These sound off though, and I have never seen this spec posted. Were these measured directly, or synthesized?

Loads of data here:  https://www.baader-p...-maxbright.html

 

This appears to be in the context of installing the GPC behind the diagonal, since that is the only way they advise.

 

I took no measurements, since I was relying on Baader’s website.




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