Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> ATM, Optics and DIY Forum

Pages: 1
snowcrow
sage


Reged: 10/21/12

Loc: Vermont
ProjectionTV lens as refractor?
      #5627520 - 01/17/13 07:04 AM Attachment (36 downloads)

Some years back I picked up a projection TV lens. It has a focal length of 22" and 4" of clear aperture, making it a f/5.5. The cell contains 4 lenses in 3 groups (2;1;1) with baffles between each group.

I built a make-shift telescope using the cell, a piece of 4" PVC sewer pipe, a cap, and a 2" dob focuser I has kicking around.(picture below) Visually it work great with a 20mm plossl EP, but I havn't tried it yet for AP.

Has anyone here tried this before, and is it worth pursuing?


Post Extras: Print Post   Remind Me!   Notify Moderator  
ed_turco
Pooh-Bah
*****

Reged: 08/29/09

Loc: Lincoln, RI
Re: ProjectionTV lens as refractor? new [Re: snowcrow]
      #5627895 - 01/17/13 11:33 AM

This is better than one of those plastic, (yes, plastic) multi-element TV lenses from the 1980s. What you have is a real glass Besseler opaque projection lens from years ago.

I've tested these and the correction really isn't so hot.

But, at 20x or a little more, you have a dandy RFT.


Post Extras: Print Post   Remind Me!   Notify Moderator  
snowcrow
sage


Reged: 10/21/12

Loc: Vermont
Re: ProjectionTV lens as refractor? new [Re: ed_turco]
      #5627922 - 01/17/13 11:45 AM

I had been looking for another one to maybe make a pair of binoculars.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: ProjectionTV lens as refractor? new [Re: snowcrow]
      #5628159 - 01/17/13 02:06 PM

I have an old rear projection TV and always wondered about those big lenses. I may try this myself sometime.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: ProjectionTV lens as refractor? new [Re: Darren Drake]
      #5628336 - 01/17/13 03:38 PM

Quote:

I have an old rear projection TV and always wondered about those big lenses. I may try this myself sometime.




As many of you probably know, before TeleVue made eyepieces and telescopes, they made projection lenses for large projection screen televisions.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
snowcrow
sage


Reged: 10/21/12

Loc: Vermont
Re: ProjectionTV lens as refractor? new [Re: Jon Isaacs]
      #5628383 - 01/17/13 04:04 PM

Well...that is a bit of trivia I didn't know! The name "TeleVue" kind of gives it away too!

Well if it clear up tonight, I'm going to try an image or two through my new contraption with my EOS 550D. Wish me luck.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ed_turco
Pooh-Bah
*****

Reged: 08/29/09

Loc: Lincoln, RI
Re: ProjectionTV lens as refractor? new [Re: snowcrow]
      #5628783 - 01/17/13 08:02 PM

The rear projection lenses from the 1980s were made of plastic and had its object plane very close to the vidicon.
Later lenses from computer projection units also had this feature, but were made of glass. The correction for telescope use was poor, and it would very difficult to get the object, now actually the image plane and the eyepiece focal plane to coincide.

Opaque projection units are the best of the bunch, but really not that good.


Ed


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Extra information
11 registered and 23 anonymous users are browsing this forum.

Moderator:  ausastronomer, richard7, Starman81 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 679

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics