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Masuyama 32mm 85* field stop - we’re is it located ?

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#1 vkhastro1

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Posted 18 September 2020 - 11:00 AM

I have a Baader MPCC and am trying to get the correct 55 mm spacing from the field stop.

Unfortunately there is no field stop for the Masuyama 32mm 85* eyepiece.

I look at the lower eye lens through the silver coloured eyepiece barrel and there is no built in field stop.

 

I have the correct spacing for my Pentax XW eyepieces in 1.25” mode (from the Baader MPCC instruction manual).

I can focus the Pentax eyepiece, lock the focus position. Add spacers (trial and error) until I achieve the approximate best focus position.

Any other options?

 

Any help would be appreciated.

 

 

 



#2 SeattleScott

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Posted 18 September 2020 - 11:12 AM

I guess the first question is why are you using a MPCC with the 32mm 85? Seems like you would only use the MPCC if you were using a fast newt. The 32/85 is really for long focal ratio scopes, like F10 as a bare minimum from what I understand.

Scott

#3 Astrojensen

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Posted 18 September 2020 - 11:22 AM

Per the Ohi Optical homepage, all Masuyama eyepieces have the focal plane exactly at the transition between the lower and upper barrels.

 

http://www.ohi-optic...o.jp/base2.html

 

 

Clear skies!
Thomas, Denmark


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#4 vkhastro1

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Posted 18 September 2020 - 12:02 PM

I guess the first question is why are you using a MPCC with the 32mm 85? Seems like you would only use the MPCC if you were using a fast newt. The 32/85 is really for long focal ratio scopes, like F10 as a bare minimum from what I understand.

Scott

The 32mm Masuyama 85* works well but not perfectly in my Altair 102ED f/11 refractor.

 

I also have a Skywatcher 130PDS f/5 Newtonian OTA.

Because of the 2” dual rate focuser configuration requiring the use of a 2” extender, a TV Paracorr cannot be used - tried it, definitely a no-go.

I have an 2” APM 30mm UFF (with no coma correction) that works very well in this scope.

Just trying to squeeze some extra FOV using the Masuyama eyepiece as well as utilizing it in several different types of scopes.


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#5 Thomas_M44

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Posted 18 September 2020 - 12:11 PM

I guess the first question is why are you using a MPCC with the 32mm 85? Seems like you would only use the MPCC if you were using a fast newt. The 32/85 is really for long focal ratio scopes, like F10 as a bare minimum from what I understand.

Scott

 

It's interesting to note that William Paolini  (BillP) and others have found the 32mm Masuyama quite pleasing even in scopes of modest f-ratio of f/6 and below.  Going faster than about f/8, the Masuyamas will show progressively more astigmatism in the outter field, but nonetheless the clean FOV remains comfortably large and the contrast, clarity and color rendition are superb.

 

Despite the outter-field abberations at faster f-ratios, BillP stated he much enjoyed the 32mm Masuyama even in an f/4.7 10" Dobsonian.

 

So yes, true, to have the entire 85-degrees of AFOV sharp to the edge, the Masuyamas need a slower f-ratio scope, and f/10 is a good rule.  Nonetheless, there is plenty of crisp unaberrated central field to enjoy in even considerably faster scopes.

 

There are always Naglers, if one wants sharpness to the edge of the FOV in fast scopes with an 80-ish degree AFOV eyepiece.

 

Here's an informative thread on the 32mm Masuyama:

 

https://www.cloudyni...l=35mm masuyama



#6 vkhastro1

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Posted 18 September 2020 - 01:14 PM

Per the Ohi Optical homepage, all Masuyama eyepieces have the focal plane exactly at the transition between the lower and upper barrels.

 

http://www.ohi-optic...o.jp/base2.html

 

 

Clear skies!
Thomas, Denmark

Thanks Thomas.

Did a daytime test.

Focused on a 300 metre distant tree.

Used the Pentax XW20 + MPCC spacing combo, locked focus.

Used the MPCC with Masuyama 32mm with 14mm spacer, yielding ~ the optimial 55mm focal distance.

Exactly in focus.

 

However the 130PDS requires a 2” extender to reach focus.

The internal lip of the extender restricts the insertion of the Baader MPCC/eyepiece combo into the 2” focuser.

As a result the focuser has to be racked in all the way to reach focus. 

The focuser tube comes within an inch of the 2ndary mirror.

It blocks out a large portion of the primary mirror.

This option is not feasible.

 

The only option is to unthread the eyepiece set screw black holder on the aluminium 2” focuser tube.

Fabricate a custom 2” extension that will thread on to the 2” focuser tube and be thread on the opposite end to reaccept the black 2” eyepiece set screw holder.

An expensive option.

 

Looks like the APM 30mm UFF will be the best least expensive option.

I do have a TV 31mm Nagler type V and will give it a try but it much heavier than the APM 30mm UFF.



#7 DRodrigues

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Posted 17 October 2020 - 05:54 PM

Is it possible to remove the 2" barrel of the ep?

If so, the ep thread is SC?

Just remembered if this ep could replace my TS 30 at my binoviewer  https://www.cloudyni...ith-125-binovs/...



#8 helpwanted

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Posted 17 October 2020 - 06:24 PM

I’m happy with my 32m in my f8 Tak



#9 rowdy388

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Posted 17 October 2020 - 08:30 PM

 

Looks like the APM 30mm UFF will be the best least expensive option.

I do have a TV 31mm Nagler type V and will give it a try but it much heavier than the APM 30mm UFF.

I also have the 32mm Masuyama and 31NT5. I use the Masuyama (almost always with a nebula filter)

much more than the Nagler mostly because of the weight.



#10 skullpin

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Posted 18 October 2020 - 04:12 PM

The barrel unscrews. The field stop is in the barrel and is just a slight ridge machined directly in the barrel.

 

Keith

 

Is it possible to remove the 2" barrel of the ep?

If so, the ep thread is SC?

Just remembered if this ep could replace my TS 30 at my binoviewer  https://www.cloudyni...ith-125-binovs/...




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