leonardcastro
journeyman
Reged: 01/24/08
Posts: 5
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Does anyone know of a way to turn an ETX60 into an ETX70 or 80? It seems as though you could just unscrew the 60mm objective and replace it with a 70 or 80mm lens set.
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Veridian
sage
Reged: 07/17/06
Posts: 478
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Leonard,
This is the question I am asking myself as well. Thanks for posting this.
There are 80mm lens sets available through Surplus Shed and perhaps even in the short focal length needed to fit this tube. Although, I don't think their coatings will be quite as nice.
Mark J.D.
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leonardcastro
journeyman
Reged: 01/24/08
Posts: 5
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Thanks for the info. I checked Surplus Shed and they do have 80mm lenses. I am a bit leery though. The ETX uses 2 lenses (concave & convex) together. I don't think Meade sells parts. Maybe if someone has spare ETX parts I'd be willing to purchase them.
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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The Surplus Shed 80mm/400mm lens cell is a friction fit over the 60mm BB tube end. All one needs to do is remove the 60mm lens and retaining ring, fit the cell over the tube, check collimation, then lock it in place with a few spots of super glue. I just did this with a Walmart Etx-60. Now it is a Etx-80. Lynn
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radsdad
super member
Reged: 11/05/06
Posts: 116
Loc: Southern California
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How does it work, Lynn? Any pictures of the finished project?
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Meade ETX-125AT UHTC and ETX-60AT
Zhumell 20x80 Supergiant Binoculars
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scopes_r_us
super member
Reged: 01/14/05
Posts: 113
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I would be interested in hearing more about this lens mod.
Please provide a link to the lenses used.
Does the 60mm lens just unscrew?
Have you star tested this arraignment?
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nytecam
Postmaster
Reged: 08/20/05
Posts: 5997
Loc: London UK
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Quote:
Does the 60mm lens just unscrew?
My ETX-70 stripdown webpage provides details for lens mounting.
I'd be interested in the end result of this conversion but have doubts about its value - other than an ATM project. The ratio of improvement from 60mm to 80mm aperture is 80*2 /60*2 or ~60% more light grasp assuming the replacment OG has a similar transmission bearing in mind the Meade simple 2-element coated objective has, I suspect, a good transmission and may be superior to multi-element lenses sourced elsewhere. There will be a very slight improvement in scope magnification [via the same eyepieces], resolution and limiting mag - all things being equal. Good luck in your project 
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Nytecam 51N 0.1W
Meade 30cm LX200+ETX-70+e-finder+C8+Ha+CaK PSTs SBIG SGS+homebuilt spectrographs
Starlight SXVF_M9+Lodestar CCDs/Canon 300D DSLR/Hitachi HD+Disgo Video Fun cams
My observatory build-ETX-70 imaging-my videos
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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I will post some pix this p.m. Az time. Lynn
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Rainbow
professor emeritus
Reged: 08/27/04
Posts: 662
Loc: Norfolk, UK
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I would imagine that at f5 the CA would be pretty nasty
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Meade ETX 90 UHTC, 497 Autostar, 884 tripod, right angle finder.
CALIBRATE MOTORS and TRAIN DRIVES!
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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Here are some shots of the converted etx-60
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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More
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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60mm lens, retaining ring and threaded cap
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gaz-in
sage
Reged: 12/17/07
Posts: 470
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Interesting...a couple questions...
1) Once you removed the 60mm lens, did the Surplushed assembly friction fit inside or outside the tube?
2) Did the dew shield for the ETx-60 still fit? If not where did you get the dew shield?
3) What process/tools did you use to assure the lens assembly was in proper alignment before super glueing down?
Thanks so much...I am very interested in trying this mod....
Dan
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gaz-in
sage
Reged: 12/17/07
Posts: 470
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Sorry...one more question...is this the lens assembly you used?
http://www.surplusshed.com/pages/item/l2196.html
Thanks
Dan
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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Hi Dan, This is a simple project, but collimating is sort of hard to explain. Here I'll give a try.1. The Surplus Shed lens cell fits over the sliding part of the ota. If you seat the cell so the back end of the cell is flush with the silver part of the tube (the very end of the tube is black) then the collimation is close.2.No. I have some tubing I cut to length and added some velcro to the inside to make fit.3.You use a cheshire eyepiece to collimate a refractor. When you look thru the cheshire with the lens cap on the objective you see reflections from all four optical surfaces of the objective. The idea is to adjust the cells so all the reflection are concentric. Much simpler than it sounds.Yes, that is the lens I used in my scope. By the way, my lens and cell are pretty shabby looking because I have used it in other projects. Lynn
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Veridian
sage
Reged: 07/17/06
Posts: 478
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Wow, Lynn, this is amazing! Good job and thanks for the photos also. 
What's the color like on the brighter targets?
Mark J.D.
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Veridian
sage
Reged: 07/17/06
Posts: 478
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Hi Lynn,
I was going to ask if there is any problem having enough focus travel, but then I realized that the 60mm has a 350mm f/l and this 80mm 'SS' lens has a 400mm f/l. It looks like the 'SS' lens extends about 50mm further, so this should be just about right then.
In another thread, John Carruthers pointed out that the 2 pc. sliding tube focus design can cause some drooping when reaching full extension. Do you feel the added weight of the 'SS' lens & cell, and now a longer sliding tube, will exaggerate this? In other words, do you think this will cause some collimation troubles for you when focus is on the 'long end'?
*****
Mark J.D.
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Lynnrb
member
Reged: 01/01/08
Posts: 54
Loc: Phoenix, Az
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Mark, The scope still has about 1" more of out focus when focus a infinity, about the same as the 60mm. This scope is going to have about the same C.A as the etx-70, both are f/5. The S.S. lens is an air spaced achromat where the 60mm is a cemented lens. I believe the air spaced can be better corrected, in theory anyway.
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scopes_r_us
super member
Reged: 01/14/05
Posts: 113
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Quote:
Wow, Lynn, this is amazing! Good job and thanks for the photos also.
What's the color like on the brighter targets?
I too would like to hear of the star testing.
Thanks
Mark J.D.
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nytecam
Postmaster
Reged: 08/20/05
Posts: 5997
Loc: London UK
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Quote:
Sorry...one more question...is this the lens assembly you used?
http://www.surplusshed.com/pages/item/l2196.html
Thanks Dan
I might have to eat-my-own-words - looks like the perfect and inexpensive swap
--------------------
Nytecam 51N 0.1W
Meade 30cm LX200+ETX-70+e-finder+C8+Ha+CaK PSTs SBIG SGS+homebuilt spectrographs
Starlight SXVF_M9+Lodestar CCDs/Canon 300D DSLR/Hitachi HD+Disgo Video Fun cams
My observatory build-ETX-70 imaging-my videos
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