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Making a 2" field stop?

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#1 buddy ny

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Posted 18 March 2019 - 01:39 PM

I own some 82° Ep's. I'm not a fan of them, but I like big eye lenses.

I want to stop down a Masumaya 82° 32mm that really has no FS , to say 65°_70° range.  Im a pretty crafty guy & I know most of you are.

Has any one done this to their o

wn EP''s. With "sharp" field edge results

What materials.. Did u do it on a lathe?  Etc..ect



#2 Jon Isaacs

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Posted 18 March 2019 - 01:57 PM

Sharpness of the field stop depends on the proper positioning of the field stop.  it also depends on the observer's eye.  Normally the field stop is placed at the focal plane of the eyepiece and will be sharp for an observer whose eye is naturally focused at infinity.

 

I have made field stops but only for experimental purposes and I used heavy paper.  

 

Jon



#3 buddy ny

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Posted 18 March 2019 - 02:14 PM

Sharpness of the field stop depends on the proper positioning of the field stop.  it also depends on the observer's eye.  Normally the field stop is placed at the focal plane of the eyepiece and will be sharp for an observer whose eye is naturally focused at infinity.

 

I have made field stops but only for experimental purposes and I used heavy paper.  

 

Jon

Thanks Jon

I figure to dial in the field stop. Took that much into consideration , so that it's sharp @ infinity



#4 Sketcher

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Posted 18 March 2019 - 03:14 PM

I've made a few field-stops for various reasons.  My preferred material is thin, black plastic.  Some "For Sale", "No Hunting", etc. plastic signs (at hardware stores) are printed on black plastic.  I use an Exact-o (hobby) knife to cut out the field stop.  Sandpaper will get rid of any colored paints that were used to print whatever message was on the sign (if necessary).  The sandpaper will also roughen the surface, transforming it from glossy to flat.

 

I've made field stops for 2" and for 1.25" eyepieces in this manner.  Sometimes a square or rectangular field-stop is more suitable than a circular field-stop . . .

 

You mentioned specifically 2" eyepieces and large eye-lenses  Standby for a short story:

 

I once had a 2-inch eyepiece (with a very large eye-lens) in the focuser of a reflecting telescope that was being used for some solar observations.  After I finished my observations, I pointed the telescope perpendicular to the sun to prevent the (large) primary mirror from focusing a small, concentrated disk of solar energy onto some flammable surface.  I'm no dummy.  Or so I thought!

 

The eyepiece had a home-made, rectangular, plastic field-stop precisely at the focal-plane of the eyepiece.  I happened to look back and noticed some smoke coming from the long, wood OTA.  A very quick glance at the telescope/eyepiece/sun geometry was all that was needed to determine what had happened.  The eyepiece was pointed at the sun!  The large eye-lens collected enough solar energy, focused it on part of the plastic field-stop, and started melting the field-stop!

 

So, be careful with those large eye-lenses!


Edited by Sketcher, 18 March 2019 - 03:19 PM.


#5 buddy ny

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Posted 18 March 2019 - 03:43 PM

I've made a few field-stops for various reasons.  My preferred material is thin, black plastic.  Some "For Sale", "No Hunting", etc. plastic signs (at hardware stores) are printed on black plastic.  I use an Exact-o (hobby) knife to cut out the field stop.  Sandpaper will get rid of any colored paints that were used to print whatever message was on the sign (if necessary).  The sandpaper will also roughen the surface, transforming it from glossy to flat.

 

I've made field stops for 2" and for 1.25" eyepieces in this manner.  Sometimes a square or rectangular field-stop is more suitable than a circular field-stop . . .

 

You mentioned specifically 2" eyepieces and large eye-lenses  Standby for a short story:

 

I once had a 2-inch eyepiece (with a very large eye-lens) in the focuser of a reflecting telescope that was being used for some solar observations.  After I finished my observations, I pointed the telescope perpendicular to the sun to prevent the (large) primary mirror from focusing a small, concentrated disk of solar energy onto some flammable surface.  I'm no dummy.  Or so I thought!

 

The eyepiece had a home-made, rectangular, plastic field-stop precisely at the focal-plane of the eyepiece.  I happened to look back and noticed some smoke coming from the long, wood OTA.  A very quick glance at the telescope/eyepiece/sun geometry was all that was needed to determine what had happened.  The eyepiece was pointed at the sun!  The large eye-lens collected enough solar energy, focused it on part of the plastic field-stop, and started melting the field-stop!

 

So, be careful with those large eye-lenses!

That had to suck. I can see the sun melting an Plastic F.r

I like your use of materials..i have some on hand.  It'll take me a couple of experiments to get what I want.. 

I don't do Solar with this EP

Thx for the heads up


Edited by buddy ny, 18 March 2019 - 03:45 PM.


#6 AxelB

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Posted 18 March 2019 - 03:53 PM

I posted a question about flocking eyepieces and modifying field stop in the DIY forum this morning. We will see what turns up.

I guess someone will tell me about 3D printing. I have no idea how to generate the drawing to feed such a machine tho...

Edited by AxelB, 18 March 2019 - 03:53 PM.

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#7 SomebodyElseEntirely

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Posted 18 March 2019 - 04:40 PM

I have made a number of field stops over the last few years. I use thin, stiff plastic sheet or metal. Any colour will do — I spay paint the completed field stop flat black. A good circle cutter is all that is required. It must be sharp, because you want a good, clean cut. And you will need to execute a smooth action. I sometimes have to make a few attempts to get an absolutely perfect cut. No big deal — the material is cheap, and the process is not terribly time consuming. The results have been impressive.

 

I would not use paper. I haven't tried it, but I imagine that one would see fibres along the edge. I like my field stop to be a clean, sharp, perfectly formed circle.

 

As to installation in a Masuyama, I'm afraid I can't be much help. I have only installed field stops in eyepieces with built-in focussing mechanisms (ex-military and ex-microscope eyepieces), and the result every time is a sharp field stop.



#8 buddy ny

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Posted 18 March 2019 - 05:00 PM

I have made a number of field stops over the last few years. I use thin, stiff plastic sheet or metal. Any colour will do — I spay paint the completed field stop flat black. A good circle cutter is all that is required. It must be sharp, because you want a good, clean cut. And you will need to execute a smooth action. I sometimes have to make a few attempts to get an absolutely perfect cut. No big deal — the material is cheap, and the process is not terribly time consuming. The results have been impressive.

 

I would not use paper. I haven't tried it, but I imagine that one would see fibres along the edge. I like my field stop to be a clean, sharp, perfectly formed circle.

 

As to installation in a Masuyama, I'm afraid I can't be much help. I have only installed field stops in eyepieces with built-in focussing mechanisms (ex-military and ex-microscope eyepieces), and the result every time is a sharp field stop.

I've taken the Masuyama apart. The Field lens Is held in by chrome barrel. It doesn't have a F.S.. proper.   I'm thinking some thing like a 2"- thin washer with felt on one side ,, cut back a 1/8 from the edge the felt acts as a buffer to the glass . cut back an 1/8 .Leaves a sharp edge

then I got to dial it in ...maybe a shim of Formica

I'm glad to hear u got really good results

I have industrial drill press & a small metal lathe.. Well see.. Thx for the positive note

 

,,



#9 Eddgie

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Posted 20 March 2019 - 07:52 AM

I posted a question about flocking eyepieces and modifying field stop in the DIY forum this morning. We will see what turns up.

I guess someone will tell me about 3D printing. I have no idea how to generate the drawing to feed such a machine tho...

It is easy to make such a drawing.   If you know someone that has a 3D printer and you can describe what you want, PM me and I will sketch it up.

 

Here is the problem I foresee for you though.  In many of these 82 degree eyepieces, the field stop is between the Smyth lens (or whatever the amplification set is) and the main elements. This may present spacing issues. You would have to ensure that you have sufficient space to actually mount the field stop at this point.

 

The thinnest you can really go with a 3D printer due to base adhesion is maybe .5mm or so, but .8mm would be better.

 

Anyway, it sounds like it would be more or less a flat disk with a hole in the center and this is pretty easy to generate and .stl file for. I could do it for you in less than 3 minutes.

 

The .stl file is all that is needed to print it.

 

If you want it printed, I can do that for you as well I suppose.   I would simply need the outside diameter, inside diameter, and thickness.  


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#10 MitchAlsup

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Posted 20 March 2019 - 10:49 AM

I would use 6061T6 plate aluminum 1/8" thick and do most of the work on a mandrel on the lathe. Bore the hole small to fit a mandrel, the turn the outside, and thread if necessary. Then switch mandrels and finish the insides using a high angle taper and remember the flat side of the knife edge goes towards the EP while the tapered side goes towards the primary.

 

Anodize to a medium hard state, and boil in black die for 30 minutes.


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#11 buddy ny

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Posted 20 March 2019 - 11:15 AM

I would use 6061T6 plate aluminum 1/8" thick and do most of the work on a mandrel on the lathe. Bore the hole small to fit a mandrel, the turn the outside, and thread if necessary. Then switch mandrels and finish the insides using a high angle taper and remember the flat side of the knife edge goes towards the EP while the tapered side goes towards the primary.

 

Anodize to a medium hard state, and boil in black die for 30 minutes.

That's a good way to go. I have the tools

I got a guy who does the "home" anodizing

Your steps a sound.

You know your way around a shop



#12 Starman1

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Posted 20 March 2019 - 01:36 PM

It is easy to make such a drawing.   If you know someone that has a 3D printer and you can describe what you want, PM me and I will sketch it up.

 

Here is the problem I foresee for you though.  In many of these 82 degree eyepieces, the field stop is between the Smyth lens (or whatever the amplification set is) and the main elements. This may present spacing issues. You would have to ensure that you have sufficient space to actually mount the field stop at this point.

 

The thinnest you can really go with a 3D printer due to base adhesion is maybe .5mm or so, but .8mm would be better.

 

Anyway, it sounds like it would be more or less a flat disk with a hole in the center and this is pretty easy to generate and .stl file for. I could do it for you in less than 3 minutes.

 

The .stl file is all that is needed to print it.

 

If you want it printed, I can do that for you as well I suppose.   I would simply need the outside diameter, inside diameter, and thickness.  

I think in this case, the field stop is below the field lens in the barrel, so it should be easy to push it in from below.


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#13 AxelB

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Posted 20 March 2019 - 01:43 PM

It is easy to make such a drawing. If you know someone that has a 3D printer and you can describe what you want, PM me and I will sketch it up.

Here is the problem I foresee for you though. In many of these 82 degree eyepieces, the field stop is between the Smyth lens (or whatever the amplification set is) and the main elements. This may present spacing issues. You would have to ensure that you have sufficient space to actually mount the field stop at this point.

The thinnest you can really go with a 3D printer due to base adhesion is maybe .5mm or so, but .8mm would be better.

Anyway, it sounds like it would be more or less a flat disk with a hole in the center and this is pretty easy to generate and .stl file for. I could do it for you in less than 3 minutes.

The .stl file is all that is needed to print it.

If you want it printed, I can do that for you as well I suppose. I would simply need the outside diameter, inside diameter, and thickness.


Wow! Thank you very much. I’ll send you the details by pm.

My need is for a plossl so the field stop location is easily accessible.

#14 dan_h

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Posted 21 March 2019 - 03:26 PM

I would think it should be possible to purchase a step down ring with the outside thread to match the eyepiece barrel thread. The field stop could then be put on the ring and threaded into the exact location needed. 

 

Easy to do and the bulk of the work is in acquiring the ring. 

 

dan


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#15 Starman1

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Posted 21 March 2019 - 04:33 PM

I sold step down rings for years.  They always had a stop on them so they would thread in and stop when the shoulder hit whatever it was being threaded into.

A threaded in field stop would have its entire outer surface threaded and have no shoulder.  That doesn't describe any step-down ring I've seen.


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