Binocular Rebuild 2

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Conversion of a 7x50 binocular to an 18x90 binocular The 50mm objectives of a vintage 7x50 binocular were replaced with 90mm objectives. This resulted in an 18x90 binocular with a 5mm exit pupil and a 2.8degree Tfov. Views are “comfortable” and the effort, in my opinion, resulted in a fine terrestrial binocular. The total cost was about $300 and, of course, there is little or no resale value to show for the effort. Prior to starting, check with Surplus Shed for the availability of the 90mm D. / 500mm Fl. objectives. http://www.surplusshed.com/pages/category/achromats_4.html Here is the path I took. Obtain, as pictured, an identical binocular. Do not substitute http://www.shopgoodwill.com/search/SearchKey.asp? itemTitle=binoculars&catid=0&sellerID=all&closed=no&minPrice=&maxPrice=&sortBy=ite mEndTime&SortOrder=a&showthumbs=on http://shop.ebay.com/items/__selsi- binoculars_W0QQLHQ5fAuctionZ1QQ_nkwZselsiQ20binocularsQQQ5ftrkparmsZ39Q253A2Q257C6 6Q253A2Q257C65Q253A1QQ_dmdZ1QQ_fromfsbZQQ_sopZ1QQ_trksidZp3286Q2ec0Q2em14QQ_vcZ1 This vintage Selsi is commonly available for under $25 shipped. Selsi Lightweight Amber Coated Luminous 7X50 Field 7.1 degrees binocular In addition, it is strongly recommended to obtain and review a copy of “Choosing, Using & Repairing Binoculars” by J. W. Seyfried.

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New life for vintage Binoculars

Transcript of Binocular Rebuild 2

Page 1: Binocular Rebuild 2

Conversion of a 7x50 binocular to an 18x90 binocularThe 50mm objectives of a vintage 7x50 binocular were replaced with 90mm objectives. This resulted in an 18x90 binocular with a 5mm exit pupil and a 2.8degree Tfov. Views are “comfortable” and the effort, in my opinion, resulted in a fine terrestrial binocular. The total cost was about $300 and, of course, there is little or no resale value to show for the effort. Prior to starting, check with Surplus Shed for the availability of the 90mm D. / 500mm Fl. objectives.

http://www.surplusshed.com/pages/category/achromats_4.html

Here is the path I took.Obtain, as pictured, an identical binocular. Do not substitute

http://www.shopgoodwill.com/search/SearchKey.asp?itemTitle=binoculars&catid=0&sellerID=all&closed=no&minPrice=&maxPrice=&sortBy=itemEndTime&SortOrder=a&showthumbs=on

http://shop.ebay.com/items/__selsi-binoculars_W0QQLHQ5fAuctionZ1QQ_nkwZselsiQ20binocularsQQQ5ftrkparmsZ39Q253A2Q257C66Q253A2Q257C65Q253A1QQ_dmdZ1QQ_fromfsbZQQ_sopZ1QQ_trksidZp3286Q2ec0Q2em14QQ_vcZ1

This vintage Selsi is commonly available for under $25 shipped.

Selsi Lightweight Amber Coated Luminous 7X50 Field 7.1 degrees binocular

In addition, it is strongly recommended to obtain and review a copy of “Choosing, Using & Repairing Binoculars” by J. W. Seyfried.http://www.universityoptics.com/books.html

Ensure that your Selsi functions as intended. The images should be clear, crisp, bright and, most important, merged. The mechanics should be smooth and firm. If not then follow the instructions in Mr. Seyfried’s book and return the Selsi to its original condition. This is not difficult if you work slowly, cautiously and gently. When you are satisfied with the operation of the Selsi remove their objectives assemblies. (Remove the retaining rings with a spanner wrench. As an alternative, notch the side of a small metal paint scraper with a Dremel cut off wheel so that the notched metal inserts into and just spans the retaining ring. Then firmly push into the retaining ring slots and twist.)

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Now- as pictured, the 58mm (male) ends of the 58mm to 55mm macro coupler rings (see parts list #1) are threaded into the empty binocular objective cells. The 55mm (male) end protrudes. (The choice of this particular Selsi is based, in part, upon compatibility with the macro coupler ring 58mm threads.)

Next - not pictured, the 72mm. to 55mm. step down rings (see parts list #2) are threaded onto the protruding 55mm.end of the macro coupler ring

– as pictured, the internal 3in. ends of 4in. to 3in. PVC schedule 20 reducers were enlarged using a Dremel with a sanding attachment (about 2mm.removed) to just accept press fitted 82mm to 72mm. step down rings (see parts list #3) which were then carefully and squarely epoxied (sp?) in place

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- After the epoxy sets, the 4in. to 3in. PVC schedule 20 reducers were threaded onto the 72mm. to 55 mm. steps down rings.

The 90mm D. / 500mm Fl. Surplus Shed plastic objective cell is an excellent press fit for 4in. schedule 20 PVC pipe. The PVC snaps into place with a firm press fit. To take advantage of this fit disassembly of the cell is required. Two strap wrenches are used with a slow, gentle and firm torque to separate, without breakage, the adhesive binding the plastic retaining ring. Once the glass is removed, the two original objective element spacers are replaced with three and the objectives, relative to the cell, are then reversed – the crown element faces out to the world. Ensure that the glass is set to the alignment marks. In addition, prior to reassembly glare should be reduced by applying flat black paint to all offending surfaces.

– The 4in. schedule 20 tubes were cut, by trial and error, to proper length using a 12in miter saw. Start at about 300cm of length and slowly work your way down. The finalized tubes were then fastened to the reducers with 3 bolts/nuts (rather than solvent welded) set 120degrees apart and, for the last time, the objectives were snapped into place. Ensure that the finalized tube ends are squared off.

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Do not fret; at this point the images should not merge. Disassemble the finalized binocular and reduce glare on all offending internal surfaces with flat back paint and or flocking and or baffles (24.4mm image size). Prior to reassembly apply and work in a thin film of synthetic grease to all threaded surfaces. Reassemble but do not over tighten.

As pictured - cut a 1/2in plastic plate so that it overhangs and protects both the binocular sides and the objectives. Slots are routed to accept 90mm mounting rings (see parts list #4). In addition, slots are routed to accept nuts/bolts to support the binocular front end. Place one nut, on the bolt, below the plate and a second nut, on the bolt, above the plate. Drill the plate, down the centerline, at the binocular balance point and tightly screw in a brass wood insert that will accept a standard monopod or tripod fitting.

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Insert the binocular into the mounting rings. Adjust the binocular to your IPD and firmly tighten the mounting rings to the plate. Allow some play in the ring clamps and slowly rotate the PVC objective tubes until the images accurately merge. This is trial and error and should be done with care and without excess. It is, of course, preferable to rotate the objective cell and or adjust the front end support bolts rather than rotating the PVC objective tubes.

If, upon immediately looking into the eyepieces, the images are not merged or if after removing your eyes readjustment is required then the above procedure should be repeated. There is no reason to be subject to the discomfort of eyestrain.

If all fails then disassemble the Selsi and reseat the prisms and or reseat the Selsi objective tubes (bell housing)

Your views should provide a comfortable solid 70% sweet spot with slight but noticeable distortion beyond that. A 28mm eyepiece in an f/5.5 hand tweaked terrestrial binocular does perform.

Consider, as a next project to achieve higher magnification, using a wide field 7x35 (beware not to wide) good/high quality vintage binocular.

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Parts list:

#1 - 58mm (male) to 55mm (male) macro coupler ring

http://www.bhphotovideo.com/bnh/controller/home?ci=0&shs=macro+coupler&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=jsp%2Fproductlist.jsp&A=search&Q=*&bhs=t&Go.x=20&Go.y=7B&H # GBMC5558 - $7.95 each

#2 - 72mm (male) to 55mm (female) step down rings

http://www.bhphotovideo.com/c/shop/0/Stepping_Adapter_Rings.html/shs/step+down+ring/mnp/0.0/mxp/0.0/sortDrop/Price%3A+Low+to+High/pn/3B&H # GBSDR7255 - $9.95 each

#3 - 82mm (male) to 72mm (female) step down rings

http://www.bhphotovideo.com/c/shop/0/Step_Down_Rings.html/shs/step+down+ring/mnp/0.0/mxp/0.0/sortDrop/Price%3A+Low+to+High/pn/6B&H # GBSDR8272 - $19.95 each

#4 - Antares Cradle Rings – 88mm – 90mm

http://www.agenaastro.com/3-5-Antares-Cradle-Rings-p/pama-an-cr3.5.htm$34 / pair

90mm D. 500mm Fl. objective

http://www.surplusshed.com/pages/category/achromats_4.html$60 each

10 feet - 4in. schedule 20 PVC sewer (drain) pipeHome Depot - $10

4in. to 3in. PVC schedule 20 reducersHome Depot - $2.50 each

The above information is copyrighted © by William C. Blunk and Howard Rose Nov. 10, 2008 for individual use only and may not be copied for other than individual use or distributed, either for free or sold, without permission.