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Binoviewer with 180Mak

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#1 morls

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Posted 29 February 2024 - 04:53 PM

Hi,

Wondering if anyone has experience using binoviewers with a skywatcher 180 Maksutov, f15?

Cheers

Stephen



#2 Illinois

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Posted 01 March 2024 - 07:52 AM

Mine is Orion 180 mak cass. I used William and 1 1/4 “ diagonal and 12 mm eyepieces for 225 power.  Jupiter and Saturn look great at 225 power.  Your skywatcher is same as mine so it should work.  I tried 2 inch and it don’t work so smaller diagonal work! 


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#3 planedriver

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Posted 01 March 2024 - 12:59 PM

Hi,

Wondering if anyone has experience using binoviewers with a skywatcher 180 Maksutov, f15?

Cheers

Stephen

Hi Stephen,

 

I have the SW 180 Mak and use it with two Baader Zooms with a bino - and ever since I use it that way I have never looked back. It will work right from the start due to the massive focuser travel of the Mak however you have to be careful if you want to have optimum performance from the scope. 

 

The Mak has a focal lenght of 2700mm but it is achived with the supplied diagonal - probably with the original 1.25 so we can assume the 2 inch diagonal also sold with the scope will add to that.  

 

Now if you add a bino with it's roughly 100mm lightpath the focal length will be definitely closer to the 3000mm value ( or even more) than to the original 2700.

This will cause aperture loss - meaning the scope will use less light than it could + the mirror is not in the ideally corrected position. To retain the original aperture you need to compensate that with a GPC or barlow or Powermate.

 

What I did was the following - (nothing scientific but rather practical): I have set up the original setup with a 1.25 diagonal + an eyepiece and counted the number of focuser knob turns CCW from stop end to the point of reaching infinity focus - it's about 10 turns. This means the designed mirror position is found around 10 turns of focuser turns - and this corresponds to approx. 2700mm - this is a rough assumption but gives me a good idea how far I am with different setups.

 

Now if you add a bino to the setup with the same eyepiece(s) it means 13+  turns due to the added lightpath.

 

Long story short once I had these numbers I have tried different barlows, Powermate in different positions in the optical train - APM 2.67 barlow on the bino resulted 11 turns , while the 2.5X Powermate in front of the diagonal results 9 turns - so both of these are roughly within one turn of the original 10 - for me perfectly acceptable. 

 

Ususally I use the Powermate as it gives me the option to use an ADC between the diagonal and the bino plus it works at 2X (opposed to the 2.67X) - and actually with this setup the required number of turns for focus is around 9 and a half - so even closer to the 10.

 

So with the Powermate working at around 2X at the widest zoom setting (24mm) the lowest magnification will give be around 225X. For me it's not an issue as for wider fields I use smaller refractors.

 

Andras

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#4 morls

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Posted 02 March 2024 - 09:16 PM

Thanks Andras, a lot of great info there. I'm using a rack and pinion focuser so will need to take this into consideration...

Stephen

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#5 doug mc

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Posted 03 March 2024 - 07:20 PM

I have the 150mm model. If you want to prevent aperture reduction but don't mind a 1.8x power increase, I use the William Optics 1.6x OCS in front of my 1.25 inch diagonal. This particular OCS is not a typical barlow, it is a two group lens system. When screwed into the front of the diagonal it will push the focal plane of your scope all the way too focus position of your eyepieces in a typical standard binoviewer. So little adjustment of focus is needed compared to a single eyepiece in your diagonal. 


Edited by doug mc, 03 March 2024 - 07:22 PM.

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