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Towa .965 focuser extension tube modification

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306 replies to this topic

#126 G.Richard

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Posted 02 December 2014 - 06:17 PM

I have the opposite problem - I think the heavier 17 ga. tube would restore the balance more like the original design. Thanks!!!!

You're right Don. I never thought of how it would improve the center of gravity that way. They are quite a bit heavier and the chrome finish on these tubes is better than the one's I've been getting at Menards. 



#127 Don Taylor

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Posted 02 December 2014 - 06:52 PM

Yup - but I see in one of your pics that you were forward about all you could. So I can understand not wanting a heavier draw tube.

You can see in the pics of the Scope 2515 I posted previously the scope balances (polar axis ) about midway between the eyepiece and objective. With a heavier draw tube I could slide the scope up quite a lot.

#128 G.Richard

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Posted 02 December 2014 - 07:20 PM

Here's a link to the wholesaler where I found these originally Don. You could use their "where to buy" feature to see if there is a plumbing supplier near you that would stock them.  

 

http://www.watts.com...ls.asp?pid=1916



#129 Don Taylor

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Posted 02 December 2014 - 07:49 PM

I got lazy and checked the web - found one online with free shipping. http://www.zoro.com/...6c-001b2166c2c0

 

Guess I'll be making another draw tube!

 

Really, the only think I didn't care for was the thin gauge. This one should be about 2x the thickness and weight.

 

Thanks again!

 

P.S.          Can't believe we've had 129 posts on this thread - all about using plumbing pipes on antique Japanese refractors.  Guess there really was a need for 1.25" adapters for these scopes. 


Edited by Don Taylor, 02 December 2014 - 09:05 PM.


#130 G.Richard

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Posted 02 December 2014 - 08:37 PM

Glad you found one. I think you'll be much more happy with the weight of this one. Tomorrow I'm bring back the 8" 17 gauge for a 8" 20 gauge and I'll also get a 12" 17 gauge. So I'll be making another one too. But I still don't know what end to put on both of these.  It truly is amazing 128 replies (6 pages) and what surprises me the most is 1571 views. I would have never guessed that. Thanks for all you've added to it Don.

I forgot to add that I just spend 30 min. with the 60mm looking at the moon. I used a wide variety of ep's including adding my 2.5X Powermate and had no trouble bring any of them into focus.  So even with the short rack gear focusing won't be an issue. It's an amazing little scope for lunar observing. 


Edited by G.Richard, 02 December 2014 - 08:50 PM.

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#131 catboat

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Posted 03 December 2014 - 03:10 PM

Hats off to all of you for this great thread.   :bow:


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#132 rnabholz

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Posted 03 December 2014 - 07:33 PM

Just a quick follow up and data point to add.

 

I got the Scope Stuff flocking paper, and installed it in the new drawtube.  Very effective at killing the glare that I was worried about.

 

Very pleased with the mod - Thanks everyone who participated in the thread.

 

Mine is the economy version...  :^)

 

1.25 Drawtube mod.jpg


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#133 Don Taylor

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Posted 04 December 2014 - 11:39 AM

I got lazy and checked the web - found one online with free shipping. http://www.zoro.com/...6c-001b2166c2c0

Guess I'll be making another draw tube!

Really, the only think I didn't care for was the thin gauge. This one should be about 2x the thickness and weight.

Thanks again!

P.S. Can't believe we've had 129 posts on this thread - all about using plumbing pipes on antique Japanese refractors. Guess there really was a need for 1.25" adapters for these scopes.

Just received the Zurn 17 gauge extensions. Mine measure 0.0385 wall thickness so I'm guessing brass plumbing gauges are different that the structural steel tube gauges. Guess it doesn't really matter.

Still this will be much greater wall thickness and weight than the Home Depot or ACE parts. Even better is the quality of extension and especially the Chrome seems a lot nicer than the others too and the expanded section is long. I 'm pleased.

Edited to correct thickness measured with .200" ball anvil and micrometer

Edited by Don Taylor, 04 December 2014 - 12:08 PM.

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#134 choran

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Posted 04 December 2014 - 01:38 PM

I went ahead and ordered a couple from the same company, but got the kind with one plain end and one threaded end.  Hope the thread matches my adapter!  We shall see.


Edited by choran, 04 December 2014 - 07:21 PM.


#135 choran

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Posted 04 December 2014 - 07:34 PM

OK, the tubes arrived.  Man, they are quick!  They are definitely beefier at 17 gauge than the Ace 20s, and the thread is the same as the Ace version, so fits my adapter fine.  Whew!  The heavier gauge makes it easier to tap a safety screw if you want, though the 20 takes a 4-40 screw and nut with no issues.  There are upsides and downsides to light and heavy, I'd say.  Light:  Less tendency to slide on its own when scope is pointed up, and less drag on the focuser tube.  Heavy:  Easier to tap, more like the original in feel, and certainly won't have any tendency whatsoever to flex on its own.  I'd say it's 6 of one, half dozen of the other, either works just fine and both are strong enough, I think. The heavy ones have the logo stamped on the threaded end, unfortunately, so using those makes it obvious it's not a stock draw tube when I use my threaded adapter, while with the ACE the threaded end has no company logo. This is nitpicky stuff, though, in the extreme.  Any way you cut it, these all work darned well with no slop at all.  

 

If nothing else this proves that if somebody loses their draw tube, they can get a replacement simply by having one of these internally threaded and it will be perfect.

And, if somebody wants to use 1.25" eyepieces with any of these long-drawtube scopes (Tasco, Sears, SCOPE, Meade, Towa) I think this is definitely a great way to go.

Any other way to make an adapter seems to have no advantages, and one might as well use a blue fireball .965 to 1.25 adapter in a .965 diagonal.  The approach of using the plumbing tubes is the only way that I can see that insures there is no possibility of cutting into the light path while using 1.25" eyepieces.  Thankfully, all these focusers screw off the OTA with no problem, so switching tubes around is no problem whatsoever, which makes it a modification that is 100% reversible in a minute or so.  That I like a lot.


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#136 Don Taylor

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Posted 04 December 2014 - 08:24 PM

Chuck:

You last post sums up my thoughts exactly!
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#137 G.Richard

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Posted 04 December 2014 - 08:26 PM

I'm glad to hear your adapter fits on the new tube. Good analysis on the weight Chuck. It's nice to have the various options with the three different gauges available. I did use the short 17 gauge tube on my 60mm scope because I liked the thicker wall for tapping holes to add the rack gear.  


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#138 aa6ww

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Posted 07 December 2014 - 01:11 AM

Because of this thread, my new TOWA 339 has been an excellent scope right from the start. I like the chrome 1.25" compression ring fitting in chrome, just as it comes from the hardware store. I had the scope out a few nights ago and Jupiter was excellent. Back ground skies around Jupiter and the moon were excellent, no signs at all of flaired lights or gray skies. I flocked the inside of the entire draw tube and as far into the scope itself as I could go on both ends, and with 1.25" TV diagonal and ES eyepieces, the scope is a solid performer. I had it out in my front yard this afternoon on the sidewalk and it drew a constant crowd of people, coming by to look at the sun.
People were even stopping in their cars just to look. The long tube classic lines really looks the part of a real telescope.

Thanks again for the simple but effective way to get a 1.25" diagonal on the back end of these excellent scopes.

... Ralph

Attached Thumbnails

  • 80mm F15 TOWA on GP-DX_close up.jpg

Edited by aa6ww, 07 December 2014 - 03:30 AM.

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#139 G.Richard

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Posted 07 December 2014 - 05:55 AM

Thanks for posting the pic of your beautiful 339 scope Ralph, and I'm glad that the mod worked out well for you. Now I just might have to "steal" your handle idea, I like it.



#140 Joe Cepleur

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Posted 15 December 2014 - 10:24 AM

I've had a hard time keeping up with the longer threads this month, and can see I missed a lot in the last two weeks! Thanks to everyone for solving this problem. I am intrigued with the idea of cutting a 1.25" focuser tube that would work for the diagonal and eyepieces I would actually use, and so shall have to play with the ideas in this thread, with whatever gauge is available at my local hardware store. My thoughts off-hand, for ease in experimenting: Use the plumbing drain's compression fitting at least while experimenting. No harm taking the easy, secure route while finding the best length for the tube. Also, forget the rack for now; just push-pull to focus. Skip the harder mod while testing whether a tube can be cut that both reaches focus and does not collide with the flip mirror in the Jason 313. 

 

Then again, I can think of a fund raiser for the schools in Ohio that would circumvent this entire problem....



#141 Chuck Hards

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Posted 15 December 2014 - 10:59 AM

  The approach of using the plumbing tubes is the only way that I can see that insures there is no possibility of cutting into the light path while using 1.25" eyepieces.  Thankfully, all these focusers screw off the OTA with no problem, so switching tubes around is no problem whatsoever, which makes it a modification that is 100% reversible in a minute or so.  That I like a lot.

 

Well, yes and no.

 

Many scopes have one or two baffles inside the main OTA.  If designed properly, these tube baffles will line-up with the baffle in the drawtube for edge-of-field rays.  Removing the focusing tube stop still leaves the tube baffles which are ultimately what define the light cone.

 

I suspect every scope is different.  Some may have an oversized OTA baffle(s), in which case this mod does increase the circle of 100% illumination.  But in others, the OTA baffle(s) may prevent the oversized focusing tube from adding any more illumination to the field.

 

I've ordered two of the 17g tubes and will give this a try on one of my classic refractors. 


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#142 choran

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Posted 15 December 2014 - 11:26 AM

You're right.  I should have said that this approach is the only one I can see that certainly won't make matters worse in terms to cutting into the light cone.  



#143 Chuck Hards

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Posted 15 December 2014 - 12:06 PM

It's a pretty elegant solution, actually, Chuck.  It avoids custom-machined parts and at least gives one the ability to field a wider light cone than the stock focusing tube permits.  The OTA baffles are just another part of the equation.



#144 Joe Cepleur

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Posted 15 December 2014 - 12:36 PM

Now that's interesting... You're saying that if the baffles in the optical tube restrict the light cone to tightly fit the original 0.965" eyepieces, adding a larger focuser of any size will not enlarge that small light cone (!) ??? Makes perfect sense. Still, it may (or may not!)  be possible to push the baffles forward in the tube, or perhaps the stock baffles were not so tight after all, and would allow a larger field of view by chance, not design. 

 

Another approach would be to use a new type of 0.965"-to-1.25" converter. Rather than have the 0.965" end fit inside the draw tube, let it clamp around the outside. That would at least allow the full inside diameter of the draw tube to be used, and it would avoid having anything new hit the flip mirror in a scope with a reflex finder. 



#145 choran

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Posted 15 December 2014 - 12:43 PM

That's what one of my adapters does--slip fit outside the stock tube, not inside.  Only problem there is you can't really blacken the internal thread on the stock tube with paint or you'll clog it up.



#146 G.Richard

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Posted 15 December 2014 - 12:57 PM

I just happened to find the original site that got me started on this mod. So here's the link to Neil's website so you can read his analysis of the baffle issue with his Meade 300.

 

 http://neilenglish.n...atic-refractor/



#147 Chuck Hards

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Posted 15 December 2014 - 01:05 PM

Now that's interesting... You're saying that if the baffles in the optical tube restrict the light cone to tightly fit the original 0.965" eyepieces, adding a larger focuser of any size will not enlarge that small light cone (!) ??? Makes perfect sense. Still, it may (or may not!)  be possible to push the baffles forward in the tube, or perhaps the stock baffles were not so tight after all, and would allow a larger field of view by chance, not design. 

 

 

 

Joe, all I'm saying is that in a properly designed baffle arrangement, the edges will all fall along the outside of the same cone.  Now, the focuser tube moves, so that baffle can't fulfill this condition most of the time.  It may be oversized to start with, and serve primarily to stifle reflections from inside the focuser tube itself. 

 

But ultimately baffles ahead of the focuser tube are what constrain the light cone once the focuser baffle is removed.  It may not be an issue in some telescopes, it might be in others.  Everyone will have to look through their focuser tube and decide if it's an issue for their telescope.


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#148 Joe Cepleur

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Posted 15 December 2014 - 01:15 PM

A few thoughts after reading the thread about the Meade 300 and Chuck's reply:

 

(1) When using 1.25" accessories and an adapter in a natively 0.965" scope, the draw tube gets pushed in toward the objective. That pushes any baffles in the draw tube toward the objective, worsening any vignetting they may be causing. 

 

(2) Flocking is about as good as baffling, so it's likely safe that all baffles in focusers could be removed. (I'm not saying to remove them from your Astro-Physics or Feathertouch, but it should be okay in most classic refractors.) The flocking would also cover any bare threads. 

 

(3) Upon removing the focuser, a small flashlight could be inserted up the tube. The diameter of the light emitted from the objective will increase as the light moves up the tube. Playing around a bit, it should be possible to derive an educated guess as to whether the internal baffles are (blessedly!) oversized. Playing around further, there would surely be a way to calculate this accurately. 



#149 rnabholz

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Posted 15 December 2014 - 01:33 PM

I can't do the math, so I always draw it when I need to understand these matters.

With these small scopes you can draw it full size, or as I uusually do, to scale using graph paper, start with the diameter of the objective. Then add two converging lines that meet at the focal length.

Measure the diameter of the tube baffle's aperture, and the distance of the baffle from the objective.

Then, on the drawing, draw a line representing the baffle at the measured distance, and simply measure the width of the light cone at the baffle's placement point. If the light cone is smaller than the baffle aperture, no clipping has occurred.

#150 Chuck Hards

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Posted 15 December 2014 - 02:20 PM

Except that the converging lines don't meet at the focal length (focal plane).  The image plane has a real size, it is not zero.  You need to define what the diameter of that circle is, and make sure your baffles allow for it.  If the baffles constrain an image of zero diameter, then you have a circle of 100% illumination of zero.  I usually go for a bare minimum of 1/4" fully illuminated with a long-focus visual scope, but it can be much larger for long-focal length, low-power eyepieces.  If you plan on using 25mm to 30mm eyepieces and want a large fully illuminated field, you can design for a fully illuminated circle of over 1/2".  The tube baffles will need to be adjusted to permit this.




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