Making an RDP (Red's Double Plossl) Telescope Eyepiece

In this clip we show you how to create a large, high-quality 2" telescope eyepiece of the RDP (Red's Double Plossl) design-from disassembling the binoculars, to arranging the lenses, to attaching them together with a 2" barrel to make the finished ocular.
For more information about making your own eyepieces, feel free to join our DIY Facebook group, where instructions on this and related subjects are pinned at the top of the group:
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[@littlesunny63]

I feel privileged to be the 1st to comment here. Well done embracing the KZbin video stuff. Your project has meant a great deal to so many. Thank you for the kindness you give being so generous my friend.

[@Nanu.Padilla]

I got an 18mm and a diagonal from Mr. Red Henry when I was starting out in this hobby. Thank you, again, for helping so many of us in this amazing hobby!

[@bradvietjeastronomy2872]

Excellent video, Red! I’d like to see how you incorporate the eyepieces, or combinations of 50-, 35-, and 25mm objectives. Those little 25 mm binoculars are nearly worthless anyway, so making eyepieces from them might be their highest calling😉

[@maplebridge48]

Yes. The first sample eyepiece I show in the video (at about 1:15) was made from four 25mm objectives, and ones I show after it used various combinations of 35mm, 40mm, and 50mm objectives..

[@TheStevecas9860]

I have made many following Reds instructions but I now pretty them up by encasing the four lenses in a 54mm diameter Polished Aluminum tubing capped off with the 50mm dust covers and they look very professional!

[@moone27]

They do indeed! Great job!

[@mediocrefunkybeat]

Thank you, Red. I'm just gathering the parts for an eyepiece based on 10x50s. I'm in the UK and have 50mm steel tube, which is the perfect size. As you said, 2-inch (50.8mm) isn't quite right. I had a quick go at a rough assembly this afternoon to get the idea and it's ridiculously easy to make the eyepiece in this video. I'm waiting for the second pair of binoculars but getting the first pair ready is exactly how you describe. I'm very excited at the result. I have a feeling this may turn into something of an addiction...

[@SterremanWillie]

Wow! Amazing! I happen to be busy renavating a 16-inch SCT telescope tube that became surplus at a professional observatory for which I need low power, wide angle eyepieces. Guess what I'll be sourcing very soon? I'm also an ATM from South-Africa and can guess that you were either referring to Chris Stewart or Johan Smit! Thanks for sharing your accumulate wisdom with us. Love your music too!

[@TheStevecas9860]

I,m giving one away to a fellow astronomer today 01/05/2024 so he can experience the amazing views of the eyepiece and pass it on to others how to build it from Red's instructions!

[@greedypaul6343]

Red sent me ome of his freebies. Epic piece that quickly became my favorite. Soon as I get back into building again, I'll be doing as Red does

[@gilga999]

This is blowing my mind! Amazing build!

[@HeyApos]

Thanks a lot for this great idea and very well made video. Just one comment: some superglues will adhere gases, which will go onto the glass surface make them blind. And if superglue gets onto the glass surface, you will never be able to remove it. I got a bino adapter here, where the person superglued some parts near the prism and ruined the optical surface - very sad. So it's fine to use superglue, but be VERY careful, it will not come in touch with the optics. Again, thanks a lot. I will take a deeper look into the channel and facebook group :-)

[@TheNobbynoonar]

Hello from England Mr Red. Just found your video by chance. Truly inspirational! I’ve been a keen amateur astronomer for over 50 years. I’ve got several pairs of binocular lenses that I knew would come in handy one day (spares from previous projects) It never occurred to me that I could make my own telescope eyepieces with them. I’m definitely going to have a go at this. Thank you very much for such an interesting and informative post. Clear skies.

[@leobeat66]

Excellent!. I just have one broken bino...Is there anything good to do with it for an eyepiece?

[@TheStevecas9860]

Yes, use the oculars to make telescope eyepieces but to use the main objectives you need four lenses!

[@lucasmorawetz4934]

How much apperent field of view does the big one have

[@ryanastroman9846]

I'm glad your making these videos, Red. I've made a few of your RDP's and even started experimenting and getting some cool results.

[@davidrojas7940]

Amazing video, I have to try it. Thanks for sharing.

[@RoysVideos]

Hi red! Thanks for the great video. Totally new to astronomy and ive jumped in head first with a zhumell z12. Now Im on the hunt for eyepieces! Hard to find these binoculars at decent prices now. If you happen stance to have any freebies Id be willing to donate! Thanks again for the educational video!

[@TheStevecas9860]

Great instructions. Red how do you determine the focal lenght of eyepieces?

[@elijahmerrill9045]

Also wondering that.

[@TheHarmonicOscillator]

Measuring the effective focal length (EFL) in a compound lens is tricky, because the principal planes are embedded inside the eyepiece. One way is to mount it on a telescope and start by carefully measuring the magnification of the objective element + eyepiece system. Here’s how: The mag is equal to the entrance pupil diameter (EPD) divided by the exit pupil diameter (XPD). Or M = EPD / XPD. For a Newtonian, you can usually assume that the EPD is located at the primary mirror, so its clear aperture diameter is the EPD. The XPD is an image of the EPD that appears as a sharp circle of light suspended in air at the eye relief distance from the eye lens of the eyepiece. Project that circle onto a screen and measure the XPD. The mag of the telescope is equal to the ratio of the objective EFL divided by the eyepiece EFL. M = OEFL / EEFL If you don’t know the objective EFL, reflect a distant light source off the primary mirror and measure the distance between the surface of the mirror to image. Make sure the light source is at least ten times the length of the telescope tube away from the primary mirror. The eyepiece EFL equals the objective EFL divided by the mag. EEFL = OEFL / M I hope this is clear. I’ll attach a link to an article with another method that looks interesting, perhaps easier, but I haven’t tried it. www.jim-easterbrook.me.uk/astro/ep/method/

[@TheStevecas9860]

@@TheHarmonicOscillator That totally went over my head?

[@michaelaldan6969]

Another from SA here...nicely explained, I have modded scopes before but never made an eyepiece...great stuff, joined your facebook page

[@TheStevecas9860]

So far I have made 30 50mm and a half dozen 40mm I find the closer you get the lenses together you get the wider field of view but if you space them longer you get more magnification. these eyepieces give amazing eye relief

[@leobeat66]

Since I have just one broken bino I´m thinking about a SINGLE Possl,,,Should it work?

[@ohmythatsweird]

How can I do this if my telescope uses 1.25" . Somebody please tell me if I can.

[@bbdudeyt]

wow, a perfect project for this winter! thank you!!

[@kevingodwin3827]

Does the glass of one lens touch the others glass? Is the distance apart important? What is the spacing between all the 4 glass lens? The same?

[@reflactor]

This video is simply fantastic. Precisely what KZbin was made for. Thanks for the details, Red!

[@markwhalebone751]

Excellent tutorial Red.

[@robertsonsid]

Will 35mm binoculars work for 1.25in eyepieces? What is the advantage of Double Plossl over a Plossl? Great video.

[@redhenry7012]

Sure. Four 35 mm binocular objectives will make about a 37mm or 38mm focal length eyepiece. Using binocular objectives, it is necessary to make a "double" Plössl, since two lenses by themselves do not have a short enough focal length.

[@mynameisben123]

Doesn’t the distance between the lenses really matter a lot? Ie, the arbitrary distance between them that results from their mechanical construction, might result in an optical design that doesn’t do what you want?

[@kaibroeking9968]

Hi, This is a really neat idea! However, you do have to be a bit careful with the superglue: it tends to gas out and may lay a bit of a fog on surfaces. I learned this the hard way :) Luckily, superglue comes off with acetone (put it on a cotton ball and dab the area repeatedly). As long as the glue stays on the outside of the lens housings and you do not use it excessively, you should be alright.

[@TheStevecas9860]

I agree I had the same issue but use epoxy or just use insulation tape to connect them together but use epoxy for the barrel!

[@MrKA1961]

what is the exact distance between the lenses?

[@lars-andersbrnn6927]

wow! i have like 50 uncollimated binoculars laying around.. and this is reusing in a good way, glad i didn't throw them away😊

[@ChrisHenryVideos]

🎯

[@maxromano2262]

Great video. I'm kicking myself for giving away so many old binoculars over the years. 😄 That's okay. There's always old ones floating around out there. Can't wait to try this. I have a couple of two inch eyepiece barrels on hand already.

[@Herbybandit]

This is a brilliant idea which I am definitely going to try. Thank you Red. A word of warning on cyonacrylate glue (super glue) as it sets it gives off fumes which can leave a horrible mist like residue on glass or plastic, be sure not to get any near the lenses.

[@TheHarmonicOscillator]

I’m looking at a used 2” 21-mm Ethos on eBay now. 21-mm is the longest Ethos Televue sells. The price with shipping is $850. Your South African friend made a good deal!

[@TheStevecas9860]

For the standard 1.25 eyepieces, you can use vacuum cleaner metal hosing they fit perfectly

[@TheStevecas9860]

After gluing the 4 lenses use Black insulation tape and stretch it tight around them it look visualy pleasing but more importantly keeps it all in alighment

[@vicamaral]

You sir are AMAZING, JUST LOVE dyi lens.

[@martinlagrange8821]

This blew my brains out - I'm going to have to make some monsters !

[@TheStevecas9860]

You wont belive the view in any telescope

[@martinlagrange8821]

@@TheStevecas9860 The binocular eyepieces are exceptional - even on an f/10 system, there are stars clear to the edge of the field. On an f/5 RFT, there are stars in focus appearing to hang in space beyond the edge of the eyepiece, all crisp with no coma. They are inexpensive, mind-blowing eyepieces. The big ones I am making as soon as I have another pair of 7 or 10x50's bought second hand.

[@TheStevecas9860]

You can use the retaining rings as spacers and you can glue a few together!

[@IvanIvanov-hg4hj]

Hello Sir! Do the binoculars have to be 7x50? Can an eyepiece be made from 20x50 binoculars and will it be of higher magnification?

[@MrKA1961]

These binoculars usually have a focal length of about 180 mm. But if your binos are 20x50 and the objective lenses have a longer focal length you can still make them and get a good eyepiece from them but with slightly longer focal distance. So, they will work even better with Schmitt Cassegrains or Mak-Cassegrains which have a very long focal distance. This will provide an excellent field of view for those scopes.

[@winstoneaton4468]

I am fairly new to stargazing and have spent a little $$ on eyepieces for my 8" dobsonian . I came across your channel and put it into practice. I have made 4 different eyepieces of various mm. I will never buy another eyepiece. The background is dark. Flat across the field. Wide views. Great eye relief. I have to say that you have given me a great new way of seeing the wonders out there. Also, doing it yourself gives you me a very satisfying feeling. I even made a 40mm and it works great. Thanks for the information. Winston.

[@TheStevecas9860]

So glad Red has given us the knowledge to build these eyepieces and the joy it gives!

[@rubictan5626]

Hi Red I have a scope where focuser was1.25 inch. If eyepiece made was from a 50 mm objective lens, How could it be fitted or inserted to a scope with 1.25 inch focuser?

[@redhenry7012]

I would make a smaller, shorter-focal-length eyepiece of the same design to go on a 1.25" barrel. I have made quite a few of these smaller ones. For example, four 35mm binocular objectives will make about a 37mm or 38mm focal length eyepiece with about a 50° field of view, and four 30mm lenses I bought from Surplus Shack made a 29mm eyepiece with about 60° field of view. And these eyepieces still have the excellent image correction of the larger ones.

[@dulcimoredan]

Thank you sir.