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AR152 Mod for Binoviewing

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#1 StarAlert

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Posted 19 July 2020 - 01:54 PM

I recently purchased a new AR152 from Explore Scientific. It’s big and beautiful and the stars are gorgeous... as long as they are dimmer than 2.5 magnitude, that is! I don’t like the focuser, though. When I use my Binoviewer and point the scope above 60o or so, I need to “help” the focuser move in. I’m going to replace it with a Moonlite. I’ve always wanted to try a Moonlite, so now is the time.
 

At the same time, I’m going to cut the tube 45mm in order to use my Binoviewer without a GPC or Barlow. The Moonlight is a 2.5” focuser with a 4.5” draw tube. The stock focuser is a 2” with about a 5” draw tube. It seems to me that I shouldn’t have any issues with cutting off the light cone. The draw tube on the Moonlite will be about 1.25” further in, but it is a half inch wider than the stock draw tube. 

 

Will this be ok? I could probably get away with cutting just 40mm if I need to. 



#2 doctordub

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Posted 19 July 2020 - 03:06 PM

Have you looked into getting a T2 prism diagonal. you may not need to cut your ota.

CS

Jonathan



#3 doctordub

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Posted 19 July 2020 - 03:11 PM

Baader has one with short optical path.

https://agenaastro.c...1c-2456005.html

CS

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#4 StarAlert

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Posted 19 July 2020 - 03:17 PM

I have a t2 prism diagonal. In total, I need a minimum of 220mm of backfocus. I think the AR152 has 180mm. 



#5 Jeff B

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Posted 19 July 2020 - 03:27 PM

StarAlert, good choice and it can be made  to be bino-friendly, but you need to be very careful and choosy as to your parts, specifically the focuser and it's draw tube length.

 

Here is a thread around an ATM project I did recently with the same lens and cell.

 

https://www.cloudyni...omat-ota-build/

 

 

The very first thing I did was to measure the exact focus point of the lens relative to the cell.  For you, when you get the scope, measure the exact amount of focuser in-travel remaining when using your 2" diagonal of choice, 1.25"/2.0" adapter and a standard 1.25" plossl when focusing on a star.

 

I'll dig out my notes, and we can go from there with PM's if you like.

 

Jeff


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#6 junomike

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Posted 19 July 2020 - 03:30 PM

I have a t2 prism diagonal. In total, I need a minimum of 220mm of backfocus. I think the AR152 has 180mm. 

180mm should be enough?

What BV set up are you using that requires 220mm of Back-focus?



#7 StarAlert

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Posted 19 July 2020 - 03:40 PM

180mm should be enough?

What BV set up are you using that requires 220mm of Back-focus?

My Tak 100DL has 223mm of backfocus and I’m able to reach focus with only about 2mm left. 
 

I’m using a Maxbright 2 with T2 Prism diagonal and HD quick connect. 
 

Right now, I’m only able to reach focus in the AR152 with the 1.7x GPC. 



#8 StarAlert

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Posted 19 July 2020 - 03:41 PM

StarAlert, good choice and it can be made  to be bino-friendly, but you need to be very careful and choosy as to your parts, specifically the focuser and it's draw tube length.

 

Here is a thread around an ATM project I did recently with the same lens and cell.

 

https://www.cloudyni...omat-ota-build/

 

 

The very first thing I did was to measure the exact focus point of the lens relative to the cell.  For you, when you get the scope, measure the exact amount of focuser in-travel remaining when using your 2" diagonal of choice, 1.25"/2.0" adapter and a standard 1.25" plossl when focusing on a star.

 

I'll dig out my notes, and we can go from there with PM's if you like.

 

Jeff

I sure will. Thanks. 
I’m ordering the Moonlite tomorrow. 



#9 Jeff B

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Posted 19 July 2020 - 03:50 PM

I sure will. Thanks. 
I’m ordering the Moonlite tomorrow. 

Please hold off on ordering the ML focuser. 

 

I remember considering it, but the I.D of the inlet to the draw tube was too small and overly cramped the fully illuminated FOV.  This scope can give stunning bino-vision views so I really, really recommend doing some math first to maximize you fully illuminated FOV.

 

PM me if you don't mind.

 

Jeff



#10 junomike

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Posted 19 July 2020 - 04:28 PM

My Tak 100DL has 223mm of backfocus and I’m able to reach focus with only about 2mm left. 
 

I’m using a Maxbright 2 with T2 Prism diagonal and HD quick connect. 
 

Right now, I’m only able to reach focus in the AR152 with the 1.7x GPC. 

Doesn't seem right as the Maxbright II is only 110mm.  T2 Prism is approx. 40mm and quick connect maybe 20mm.    

Unless I'm missing something?



#11 StarAlert

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Posted 19 July 2020 - 08:07 PM

Doesn't seem right as the Maxbright II is only 110mm.  T2 Prism is approx. 40mm and quick connect maybe 20mm.    

Unless I'm missing something?

I reach native focus with about 2mm of infocus left on my 100DL. It has 223mm of backfocus. 

 

5670DEFC 7942 425F AE08 F672682AB8C1

 



#12 junomike

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Posted 19 July 2020 - 08:38 PM

I believe you however there's not 9" of optical path so I'm not sure what's going on?



#13 StarAlert

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Posted 20 July 2020 - 10:49 AM

I believe you however there's not 9" of optical path so I'm not sure what's going on?

I think this is what’s going on.
From the end of the draw tube (this is where Tak starts the measurement?) to the diagonal is 55mm.

T2 Diagonal is 38.5mm. 
T2 HD quick connect is about 11mm

MB2 is 110-111mm

All that equals about 215mm. 
The Morpheus 17.5 requires the most backfocus of the Morpheus lineup... 7 or 8mm? 

 

Taking out the two Tak adapters and putting a simple  2” compression ring would save 40-45mm. So maybe 180mm of backfocus is sufficient on the AR152 if it’s measured from the end of the draw tube because it doesn’t have all the adapters. 



#14 junomike

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Posted 20 July 2020 - 05:28 PM

Now that makes sense.

Silly how Tak measures the Back-Focus w/o their OEM adapters though.



#15 StarAlert

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Posted 21 July 2020 - 12:40 PM

Change of plans. Instead of the 2.5” Moonlite, I ordered a 3” Feather Touch with 3.5” draw tube travel. The 3” ID will ensure that the front end of the draw tube won’t cut the light cone off if I need to shorten the OTA. Wayne needs to design and machine the adapter cone for the AR152. Could be a month before I get the focuser. 



#16 PatrickVt

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Posted 21 July 2020 - 01:07 PM

For what it's worth, I prefer the idea of the 3" focuser. 

 

I would also recommend you call Explore Scientific and bounce your plans off of them...  the why's and your thoughts and then ask for their advice.  I know that Kent will direct the questions to their engineering people and get back with you.  I mention this and recommend this for two reasons...  Explore Scientific is very accommodating and they may know something as far as limitations or problems that have not be mentioned here.

 

Patrick  



#17 StarAlert

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Posted 21 July 2020 - 01:25 PM

For what it's worth, I prefer the idea of the 3" focuser. 

 

I would also recommend you call Explore Scientific and bounce your plans off of them...  the why's and your thoughts and then ask for their advice.  I know that Kent will direct the questions to their engineering people and get back with you.  I mention this and recommend this for two reasons...  Explore Scientific is very accommodating and they may know something as far as limitations or problems that have not be mentioned here.

 

Patrick  

I’ve called ES three times already just to get the backfocus info on the this scope. They’re still trying to figure it out. 


Edited by StarAlert, 21 July 2020 - 01:28 PM.

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#18 PatrickVt

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Posted 21 July 2020 - 04:28 PM

Normally, I would say I am shocked by the long wait to get an answer from ES.  Unfortunately, with the pandemic, I think they are mostly working from home and the entire staff might not even be working normal working hours.  It is quite possible that the engineering guy(s) is not around all that much right now so it might require a little time to get accurate info.  Add in coordinating with the people at Starlight who are probably limiting working hours in a different way...  Waiting for info is better than bad info.

 

Out of curiosity, did you speak with Kent?   He often chimes in here when Explore Scientific is mentioned so maybe he'll pop in here shortly.  

 

Patrick



#19 StarAlert

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Posted 21 July 2020 - 05:15 PM

I left a voice mail on Saturday. I called this morning and talked with someone who’s been working at ES for three days. And then he hooked me up with someone else who didn’t know the answer, either. My guess is that I haven’t talked to Kent. 
 

The Starlight is ordered and definitely coming. The only thing I don’t know is if I’ll have to shorten the tube. From what Wayne told me, the SL will be just over 3.5” long. My best measurement of the stock ES focuser is 4 5/8” long. The Starlight may be short enough to get the binoviewer to work at native, but I’m ready to do some surgery on the OTA if needed. 



#20 PatrickVt

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Posted 21 July 2020 - 05:39 PM

Is the 3.5" spec the length to where the focuser tube begins (end of optical tube to beginning of the end of the focuser tube)?  Or, is this the length of the focuser tube only (meaning the total extension of the focuser tube)?  If you are not sure, then some confirmation is needed from Starlight and that might be part of the hold-up if ES is trying to get with Starlight.  Admittedly, I haven't looked at the Starlight website to see if there are more specific diagrams with dimensions available.  

 

Wow...  a new employee at ES...  maybe they are so busy that they can't keep up with demand.  

 

Patrick



#21 StarAlert

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Posted 21 July 2020 - 05:45 PM

The 3.6” spec Wayne gave me is the distance from the end of the OTA to the end of the draw tube fully racked in. 
 

The draw tube travel is another 3.5”. 


Edited by StarAlert, 21 July 2020 - 05:46 PM.

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#22 PatrickVt

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Posted 21 July 2020 - 05:47 PM

Also keep in mind that an adapter of some sort might need to be fit in between the Starlight focuser and the optical tube which will also take up some backfocus space.  

 

To be honest, though, I have very little experience with Starlight.  I have replaced focusers and I hope to someday purchase a Starlight for a bigger project in the works but I don't really have any experience with Starlight just yet.  I'm following this to learn a bit more about how to make this work and the optical distances required.

 

Patrick


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#23 PatrickVt

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Posted 21 July 2020 - 05:49 PM

Oh, okay.  We were writing at the same time.  It seems like you and Starlight have already talked.  Got it now.  Thanks for the clarification.  

 

Patrick



#24 StarAlert

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Posted 21 July 2020 - 05:49 PM

This is what Wayne sent me...

 

“Matt, I just met with my lead machinist and he will draw up the print for the adapter to be as short as possible so that the racked in length will be in the 3.6-3.8" range.“

That’s almost an inch shorter than the stock focuser. 


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#25 StarAlert

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Posted 21 July 2020 - 05:51 PM

Also keep in mind that an adapter of some sort might need to be fit in between the Starlight focuser and the optical tube which will also take up some backfocus space.  

 

To be honest, though, I have very little experience with Starlight.  I have replaced focusers and I hope to someday purchase a Starlight for a bigger project in the works but I don't really have any experience with Starlight just yet.  I'm following this to learn a bit more about how to make this work and the optical distances required.

 

Patrick

I’ll be documenting the whole process right here. Pictures and all. 


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