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8" f/15 refractor project

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#1 GShaffer

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Posted 09 February 2010 - 05:38 PM

Gathering up materials and parts still....have the lens/cell already. Focuser, 9" rings and 9" tube in route.

Have been considering the dovetail for the rings. Checked and having a custom 1 1/8"x4"x36" made would run me $200.00+shipping

However I can buy a 4 foot piece of 1x4" 6061-T6 bar stock for less than $70.00. I have a 23" standard D type dovetail already. What I am thinking is why not bolt the 23" dovetail I have in the middle of a 48" 1x4" which would still give me room to slide back and forth enough for minor balancing purposes and my saddle is a tip in type so I really dont need the dovetail to run the entire length.

Anyone see any reason this wouldnt work for me? My saddle is 18" long....any major balancing adjustments can always be done by moving the OTA in the rings.

If my thinking is right. I save about $130 bucks and end up with my rings 4 foot apart as opposed to 36" on a 11 or so foot OTA.....should be a fairly substantial system.

Thoughts?

#2 Jim Curry

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Posted 09 February 2010 - 06:38 PM

Sounds pretty substantial. What lens are you using?

Jim

#3 GShaffer

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Posted 09 February 2010 - 07:58 PM

Muffoletto Optical..... It was listed briefly on Astromart a while back. Per an evaluation by D&G they said...

"the objective you sent in was good to 1/10 wave accuracy, with a perfect edge zone. Clear aperture is 7.75", BFL 123 3/8"."

Sounds good anyway :)

BTW Jim, how do you like that NA140? I have one and it is one of my favorites.

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#4 Jim Curry

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Posted 10 February 2010 - 08:53 AM

Herb:
It's one of my favorites, too. (seeing as it's my only :>))

It's my first refractor after a lifetime of Newts. Perfect for wide fields and performs as well as the seeing allows when I want to push the mag.

Jim

#5 Mike I. Jones

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Posted 10 February 2010 - 10:23 AM

I'm not surprised. Muffoletto was a SUPERB optical shop. They made the 24" aperture, 200" EFL collimator primary and 25" aperture BK7 beamsplitter for our camera test station. I tested it once in double pass and the DP wavefront error was on the order of 1/8 wave P-V at HeNe. That was after reflecting off the beamsplitter and primary, transmitting through the beamsplitter to the 24" return flat (1/18 wave RMS, figured by Zygo), back through the beamsplitter, off the primary, reflect off the beamsplitter again and back to focus. Absolutely marvelous optical workmanship.

You have a great objective there with a world-class pedigree.
Mike

#6 Ziggy943

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Posted 10 February 2010 - 11:23 AM

I would consider fixing the tube in the rings, not make it slideable to achieve balance. I put external sliding weights on the 9" tube assembly. They go off and on with one brass screw. You can get a nicely proportioned OTA that way.

You may want to blacken the cell.

Jim mentioned "perfect for wide field." At a 123" FL I don't know about that wide field stuff.

Great project and sounds like from Mike you should have a great lens.

#7 Mike I. Jones

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Posted 10 February 2010 - 12:21 PM

Thought you might be interested in this further bit of history.

The demise of Muffoletto Optical was a major blow to the optical manufacturing industry. According to public records of Muffoletto vs. Melick, October 9, 1987, when C. Verne Muffoletto died on April 29, 1986, he owned 81% of the stock of Muffoletto Optical Co., Inc., having previously given 19% to certain key employees. His will offered "...first right of refusal to purchase the remaining stock of THE MUFFOLETTO OPTICAL COMPANY, INC. to any number or all of the employees of said company. The purchase price shall be the fair market value of the company at the date of my death. If less than all of the shares of said company are purchased under this option and the remaining unpurchased shares constitute a minority interest this option shall lapse and be null and void. The said employees of the company shall have six (6) months from the date of my death to exercise this option to purchase."

The whole thing got very messy, wrapped inextricably around the axle in litigation, and resulted in one of the finest optical shops in history disappearing forever. I don't know where all the optical technicians and equipment dispersed to, but it was a tragedy to lose that company and its capabilities. You should take great pride in owning a Muffoletto objective lens.
Mike

#8 Jim Curry

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Posted 10 February 2010 - 12:43 PM

Oops, we were talking about his last question, how did I like the Vixen 140.

Jim

#9 suburbanskies

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Posted 10 February 2010 - 01:01 PM

It's interesting how this optical shop (and most organizations) revolve around a key person or persons. Once they're gone, the whole shebang just falls apart...

Mark

#10 GShaffer

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Posted 10 February 2010 - 03:53 PM

Shhhhh.....I really dont need to get any more excited about it :) It does sound like I may have a real winner though.

I'm not surprised. Muffoletto was a SUPERB optical shop. They made the 24" aperture, 200" EFL collimator primary and 25" aperture BK7 beamsplitter for our camera test station. I tested it once in double pass and the DP wavefront error was on the order of 1/8 wave P-V at HeNe. That was after reflecting off the beamsplitter and primary, transmitting through the beamsplitter to the 24" return flat (1/18 wave RMS, figured by Zygo), back through the beamsplitter, off the primary, reflect off the beamsplitter again and back to focus. Absolutely marvelous optical workmanship.

You have a great objective there with a world-class pedigree.
Mike



#11 GShaffer

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Posted 10 February 2010 - 03:56 PM

Upon reflection out of what I have scope wise if I had to sell down to one....it would be a hard decision between the FL102 and the NA140....Solely basing it on what I enjoy the most visually I suspect it would be the NA140 that got kept.

Herb:
It's one of my favorites, too. (seeing as it's my only :>))

It's my first refractor after a lifetime of Newts. Perfect for wide fields and performs as well as the seeing allows when I want to push the mag.

Jim



#12 GShaffer

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Posted 10 February 2010 - 04:02 PM

Jim was refering to the NA140 we were discussing regarding widefield viewing....

I have considered it.....and will likely use something like that for EP/Binoviewer balancing.....but will also be mounting a 2nd OTA at times so will need some major movement for that and prefer moving in the rings over adding that much weight on and off......

I would consider fixing the tube in the rings, not make it slideable to achieve balance. I put external sliding weights on the 9" tube assembly. They go off and on with one brass screw. You can get a nicely proportioned OTA that way.

You may want to blacken the cell.

Jim mentioned "perfect for wide field." At a 123" FL I don't know about that wide field stuff.

Great project and sounds like from Mike you should have a great lens.



#13 GShaffer

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Posted 10 February 2010 - 04:04 PM

I read up on some of that in my web searching for info.....it is a shame. From everything I have read and heard they definately turned out some quality stuff in their day. I sure hope it (this one) lives up to the reputation.

Thought you might be interested in this further bit of history.

The demise of Muffoletto Optical was a major blow to the optical manufacturing industry. According to public records of Muffoletto vs. Melick, October 9, 1987, when C. Verne Muffoletto died on April 29, 1986, he owned 81% of the stock of Muffoletto Optical Co., Inc., having previously given 19% to certain key employees. His will offered "...first right of refusal to purchase the remaining stock of THE MUFFOLETTO OPTICAL COMPANY, INC. to any number or all of the employees of said company. The purchase price shall be the fair market value of the company at the date of my death. If less than all of the shares of said company are purchased under this option and the remaining unpurchased shares constitute a minority interest this option shall lapse and be null and void. The said employees of the company shall have six (6) months from the date of my death to exercise this option to purchase."

The whole thing got very messy, wrapped inextricably around the axle in litigation, and resulted in one of the finest optical shops in history disappearing forever. I don't know where all the optical technicians and equipment dispersed to, but it was a tragedy to lose that company and its capabilities. You should take great pride in owning a Muffoletto objective lens.
Mike



#14 rwiederrich

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Posted 10 February 2010 - 05:37 PM

Sounds like it's going to be an awesome scope. Long focus is my favorite.

Keep us posted....Let me know if I can help in any way.

Rob

#15 GShaffer

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Posted 10 February 2010 - 06:27 PM

You have a great objective there with a world-class pedigree.
Mike


It seems you have quite the pedigree yourself Mike. I made the mistake of looking at your profile....your occupation and depth of astro hobby along with your posts lend quite a bit of weight to your comments regarding Muffoletto Optical and the possibilities of this lens......I thank you for your input! Sadly you also got me more excited than I already was, doubly so now that I reviewed your history :)

#16 GShaffer

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Posted 10 February 2010 - 06:46 PM

Ahhh the builder of the Nautilus :).....The green OTA.....Made me think of the Nautilus when I 1st saw the pics a while back for some reason. Very nice setup. I watched the video on your site. Intresting mount too.

Thanks....I am sure there will be questions aplenty before this thing is done :)

Sounds like it's going to be an awesome scope. Long focus is my favorite.

Keep us posted....Let me know if I can help in any way.

Rob



#17 rwiederrich

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Posted 10 February 2010 - 10:26 PM

Ahhh the builder of the Nautilus :).....The green OTA.....Made me think of the Nautilus when I 1st saw the pics a while back for some reason. Very nice setup. I watched the video on your site. Intresting mount too.

Thanks....I am sure there will be questions aplenty before this thing is done :)

Sounds like it's going to be an awesome scope. Long focus is my favorite.

Keep us posted....Let me know if I can help in any way.

Rob


Thanks.....getting the mount retrofitted for my newly finished 10"f/15 will be fun as well.

Again....great project..and don't forget to post lots of pics.... :grin:

Rob

#18 GShaffer

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Posted 11 February 2010 - 08:54 AM

Considing the baffle system for this project.

Given this is my 1st time at this I am looking for advice on this. A few questions based on what I have read up on so far regarding baffling.

To baffle or not to baffle? I believe this one is simply YES :)

How many baffles?....more is better within reason? At least 4 in a OTA of this type? Would 6 be better? or ?

I assume from looking at my other OTA's and from what I have read the apature of the baffles needs to follow the size of the tapering light cone from front to rear?

Should they be evenly spaced along the tube or is there a specfic pattern that works best?

Thanks
Greg

#19 Mike I. Jones

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Posted 11 February 2010 - 09:56 AM

This is a diagram I created years ago that gives the formula for the baffle diameter at any point down the tube. You need to know the back aperture DL (slightly less than the 7.75" front aperture) and back focal length BFL (123.375"), and decide on an unvignetted field width "d" (0.75" to 1" is probably about right). The formula gives the baffle ID "DB" at any point down the tube.

4-5 equally spaced baffles are probably adequate. For your 8" f/15 the first baffle would start about 5-6" back from the objective, and the last baffle would be about 12" forward of your focuser base.

Mike

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#20 Mike I. Jones

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Posted 11 February 2010 - 10:16 AM

This is an easy way to optically inspect how well your baffle design is working. It gives a direct, real image of your telescope exit pupil. Aim your refractor at the daylight sky, hold the second eyepiece over the first as shown, and you should only see the refractor back aperture exit pupil, floating in pure blackness. Any stray light coming down the tube will easily be visible outside the exit pupil. You can turn the refractor to within about 10-20 degrees of the sun for the most stringent testing, but be careful!
Mike

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#21 GShaffer

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Posted 11 February 2010 - 10:23 AM

Thats great info Mike.....Thanks!

#22 rwiederrich

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Posted 11 February 2010 - 04:00 PM

This is a diagram I created years ago that gives the formula for the baffle diameter at any point down the tube. You need to know the back aperture DL (slightly less than the 7.75" front aperture) and back focal length BFL (123.375"), and decide on an unvignetted field width "d" (0.75" to 1" is probably about right). The formula gives the baffle ID "DB" at any point down the tube.

4-5 equally spaced baffles are probably adequate. For your 8" f/15 the first baffle would start about 5-6" back from the objective, and the last baffle would be about 12" forward of your focuser base.

Mike


Mike...you posted this formula and diagram on my website AFTER I designed and built my baffle system for my 10"f/15.

I used 1" field width when I designed my system on the floor of my shop...... :smirk:

I also used 5 baffles along with the baffles within my focuser body. No baffles within the draw tube(over kill I think).

PLus...my thinking is that because the tube is 2" larger then the objective(1 full inch completely around)...I would be able to control stray light better...along with the thermal venting built into each baffle.

Your drawings are extremely helpful.....

Rob

#23 GShaffer

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Posted 12 February 2010 - 05:34 PM

1st set of parallax rings arrived yesterday....AP single speed new style focuser arrived today. Bar stock for the 42" dovetail is in route.

Still searching for some 9 to 9.5" parallax rotating rings.....just missed a set too dang it.....

#24 Mirzam

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Posted 12 February 2010 - 05:58 PM

Why do you want rotating rings? Are these for a large finder or guide scope?

Jim

#25 rwiederrich

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Posted 12 February 2010 - 05:59 PM

1st set of parallax rings arrived yesterday....AP single speed new style focuser arrived today. Bar stock for the 42" dovetail is in route.

Still searching for some 9 to 9.5" parallax rotating rings.....just missed a set too dang it.....



Oooo the toys are comin in.... :bow:

You know...the rain and cloud gods just don't get it when folks like to build their own scopes...so I predict a super first light.... :jump:

Rob






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