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APM 140 - Switch 2.5" for 3.7" Focuser

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#1 troy6666

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Posted 23 June 2019 - 11:41 AM

Hello all:

 

I want to switch my 2.5" for the 3.7" focuser.  I wanted to order it from APM, but I was told the baffles were different so they can't be switched.  This really doesn't make much sense to me since the telescope is available with either focuser, and I doubt there is any difference between the OTAs.

 

Does anyone know if this is a direct switch, or is a different adapter needed to make the connection to the OTA?

 

Thanks much



#2 aa6ww

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Posted 24 June 2019 - 02:47 AM

I seriously doubt there is a baffle difference. I have the APM 152ED with the big focuser and its rock solid. It even holds my 9mm 120 deg ES Eyepiece very steady, and thats a beast of an eyepiece.

 

...Ralph



#3 ris242

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Posted 24 June 2019 - 01:02 PM

I seriously doubt there is a baffle difference. I have the APM 152ED with the big focuser and its rock solid. It even holds my 9mm 120 deg ES Eyepiece very steady, and thats a beast of an eyepiece.

 

...Ralph

 

 

Try the 30mm 100 deg. 4x the beast lol.gif



#4 Artimus183

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Posted 07 November 2019 - 09:40 PM

Try the 30mm 100 deg. 4x the beast lol.gif

Noob question perhaps, but I assume the 3.7" can actually take it (its a 3" barrel) with the proper adapter while the 2.5" couldn't? 



#5 junomike

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Posted 08 November 2019 - 08:05 AM

Noob question perhaps, but I assume the 3.7" can actually take it (its a 3" barrel) with the proper adapter while the 2.5" couldn't? 

Technically that is correct however I'm not sure the 3.7" will fully illuminate the light cone.  Most likely it would.


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#6 junomike

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Posted 08 November 2019 - 01:22 PM

Just received a PM from Markus.

Turns out the OTA's are different lengths with the 3.7" OTA being shorter so adding a 3.7" Focuser to an OTA originally shipped with a 2.7" will shorten the back-focus.

Also, the baffles are different so the 2.7" OTA has a smaller fully illuminated FOV (as I was worried about).


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#7 Artimus183

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Posted 09 November 2019 - 12:44 AM

Technically that is correct however I'm not sure the 3.7" will fully illuminate the light cone.  Most likely it would.

Thanks for letting me know. Hadn't considered the light cone..

 

Asking because I'm planning going for the 140 w/ 3.7" even though I plan to do Visual. Just sounds like a better, overall more flexible part (at a cost obv.). Would you agree, or are there negatives about a bigger focuser?

 

Art


Edited by Artimus183, 09 November 2019 - 02:34 AM.

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#8 junomike

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Posted 09 November 2019 - 09:21 AM

Thanks for letting me know. Hadn't considered the light cone..

 

Asking because I'm planning going for the 140 w/ 3.7" even though I plan to do Visual. Just sounds like a better, overall more flexible part (at a cost obv.). Would you agree, or are there negatives about a bigger focuser?

 

Art

I'd go the 3.7" version even if some consider it overkill.  I hate being limited and if you ever consider using EP's with larger field stops then 46mm, you'll be ready.

Also, IME the large the focuser the less stress it has  when lifting the same weight as a smaller (equally made) focuser.


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#9 dscarpa

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Posted 09 November 2019 - 03:41 PM

  I recently got a Vixen130ED SS with a Moonlite that's heavy duty and might fit your scope if the 2.5" R&P doesn't work out. I suspect the 2.5" R&P on my CM 90 III is similar to the APM and I've been very happy with it so far.  As a 66 year old visual observer and one who carries all his scopes around on their mounts I prefer the lighter weight of a 2.5" on my refractors. I've never had a problem with them  or the Crayfords on my SCTs handling the 20 ES100 and 31 ES82 which are my heaviest eyepieces. David 




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