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Vintage Tasco 60mm - variable powers - ?

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#1 m1618

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Posted 12 October 2013 - 08:28 AM

Please help me identify this Tasco and figure out what to do about this variable powers thing.

It basically pulls out to manually vary the eyepiece. I just ordered one of those 0.965 to 1.25 diagonals. How do I go about using it? As in...do I take out that inner tube? How? Or leave it?

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#2 fjs

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Posted 12 October 2013 - 11:38 AM

I have a 40mm Tasco that operates under the same principal (I assume). If so, a part of the variable powers eyepiece is an image erector lens in the assembly. This erector also acts to extend the focal length of the objective. The result of removing that piece would necessitate cutting some length from the tube. There would also likely be the need to cut some length of tube for the diagonal.

#3 Stargoat

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Posted 12 October 2013 - 01:41 PM

Looks like you have the Tasco 5VTE based on the focuser name tag. Since there is no Reg No on the tag, it is pre 1963. Up to 1960, the scope was called the 40 Power 5TE and the name tag stated 40 X 60mm.

Stephen

#4 BarabinoSr

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Posted 12 October 2013 - 02:26 PM

The 60mm Tasco 5VTE is primarily configured for terrestrial use and has very limited astronomical capacity erect image because of the many elements in the optical train . You can view luna , the sun (project the image onto a piece of paper! (Dont look at the sun through this or ANY scope with out proper eye protection) and Jupiter Venus Saturn. The eyepiece is part of a sliding lens system that consists of eyepiece ,fixed lens , and an element attached opposite the eyepiece inside the tube. The movement of the draw tube to various positions ( ie;15X,30X 45X and 60X yields the listed magnifications. Adding a star diagonal to a scope in this configuration will not work. Note that the eyepiece is threaded to the focuser drawtube. Gary

#5 m1618

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Posted 13 October 2013 - 05:50 PM

thank you that was very informative! I managed to take it apart and remove those elements in the train. If I were to cut the tube a few inches...would I then be able to reach focus? As if some short tube wide field refractor??

The primary lens on this scope look like they are in excellent condition. Would like to somehow use a diagonal for it and 1.25" eyepieces and not just terrestrial.

#6 apfever

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Posted 13 October 2013 - 09:14 PM

Hi m1618,

This is called a hijacking. This is where your string is strongly referenced, but still led astray in a nice way.
Pictured is my 5VTE which is what you have an early version of. This shows what the label morphed into. Next to it is my Monolux which is identical in size and function.

Yes, you can do what you want. You can do anything with enough modifications. However, you are making quite a few and some major ones such as shortening the tube to compensate for ripping out some guts of a vintage scope. Actually, its a fairly cheap scope and I would say tinker away and have fun. I simply enjoy colorfull rhetoric.

I was planning on making sure my Monolux if fully set, then parting out the 5VTE for FREEEEE if there was a FREEEE/Wanted/Needed string here. Actually, I'm lying now. Parting is secondary. First I would try to see if J.I. would want this for his 5VTE shelf job. I don't care if this goes to another one or if another one comes here, as long as something nice is created that can then be DONATED (J.I. is an expert at that). The last 60mm I donated went to the Cub Scouts. Remaining parts could then be offered for free if they could be offered for free.

My Selsi is labeled 40 X60. It is also a fixed eyepiece draw tube with a transfer lens in it.

Thank you for your free time reading this.

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#7 apfever

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Posted 13 October 2013 - 09:18 PM

better label shot.
Though ugly as a one eyed......well ughly, it is not dented or gouged and is complete with the original mount that is just as functional and just as totally ugly.

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#8 roscoe

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Posted 14 October 2013 - 07:14 AM

I was given a 5VTE with the eyepiece missing, and dismantled it and cut it down, and figured out a way to attach a .965 diagonal to it to make sort of a spotting scope or perhaps a finder for a future larger scope.
Here it is with the first (cheap) 45 diagonal I had on it......
The images weren't that good, I later got and tried a better 45 diag, without much better results, and also temporarily added a piece of tube to lengthen it so I could try a stright-thru view with an EP, and no better then, either
One of these days, I'm going to build a ronchi tester and see if I can tweak the objective a bit in hopes of an improvement, but my advice is to try the objective out with an EP in some sort of temporary setup before you put a bunch of time into it.....
Russ

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#9 BarabinoSr

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Posted 14 October 2013 - 09:10 AM

One of our classic friends, Preston, has done some work with converting one of these into a short focus rich field scope. Perhaps he will chime in . I believe the focal length of the average objective in one of these is about 430mm. I have a couple of these- the TASCO 55VTE (Circle T), which has all of the magnifications of their 5VTE but comes with a finder and goes up to 90X. Two others I have ,a Selsi(also Circle T-[Towa]) version and one, Holmar racks through 60X. Of the three, the 55VTE and the Selsi have cemented objectives ,but the unlabeled Holmar is unique in that its objective is air-spaced. I also had a Selsi version , grey tube back in the early 70's .I took all the internal lenses out and added a concave element inside the drawtube itself- experimental but it worked . When the drawtube was racked out I got about 120x , and limited FOV of about 40 degrees. Used that arrangement to look at Mars in 1971 when it was at closest approach. So you do have some options.

#10 Preston Smith

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Posted 14 October 2013 - 12:02 PM

Hi M1618,

Gary is correct, I have worked on quite a few of these scopes. The original intent of these telescopes is very noteworthy. It was to provide a basic telescope with magnification capability but all contained in one instrument. It would be very convenient to take along on an outing or a trip and not have to worry about eyepieces and diagonals. It's internal optic design gave the viewer the ability to observe terestrial objects.

Alas, the telescope market back then had little room for profit so there were a lot of compromises when making this type of telescope. The objectives made for ths type of scope were good for terrestrial observing but not usually the best for astronomical observing.

Roscoe did a very good job describing what he did to convert the scope to a traditional focuser and diagonal scope. The first thing you would have to do is determine the actual focal length of the objective. The easiest way to do this is to unscrew the objective lens cell from the telescope. Place a piece of white paper on the ground. Align the objective so that the sun shines through it onto the paper. Move the objective up and down until the sun becomes a small, sharp-edged sphere. That is the focal point of the objective. Use a metric tape measure to measure the distance from the paper to the back of the objective. That will be the true focal length of your objective lens.

After that, you would want to mount your abjective on a small stick (zip ties will hold it in place) and then point the objective toward a terestrial object - something like a telephone pole or a flag pole. Then use an eyepiece inserted inside a diagonal and align it with the stick and the objective. try to bring the object into focus while looking through the eyepiece. Mark on the stick where the vertical edge of the diagonal is. It will be less than the focal length of your objective. That will help you determine the total length of your tube and focuser to reach focus (with that eyepiece).

You can afix a diagonal onto the focus tube but you'll have to find a diagonal that has matching threads - and you'll probably have to use Locktite Red to keep the focuser from loosening. But realize that the inside tube diameter on these type of focusers is probably smaller than it should be and may cut off (vignette) part of the image.

Bottom line, it's a lot of work to convert one of these scopes to make it into a regular astronomical scope - and there is a high probability that the objective lens may not give you optimum viewing.

However, converting one of these telesocpes into a finder for a larger telescope is a very worthwhile project.

My recommendation is to keep the scope as it is. The challenge would be to use it to its maximum capability and let us know how it performs! :jump:

I've attached a picture of a small 40mm variable telescope and focuser that I converted to a finder. I cut down the length of the focuser tube and the rack to limit vignetting. It was a lot of work but I have a fully focusing 40mm finder that looks cool and matches the paint scheme of the main telescope! ;)

Best Regards!

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#11 m1618

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Posted 14 October 2013 - 10:10 PM

:bow: <- not in some idolatrous way

You have quite the collection sir on flikr!
I did end up ordering a diagonal...but as others have suggested as well, I'll try it outside the tube first.

Interestingly enough I found some etch just where the focal length would have been and pencil marks just below the line so I suspect the previous owner was just at the chop saw before he pulled the plug on it. :grin:

#12 roscoe

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Posted 14 October 2013 - 10:15 PM

Mine is a Tasco, and has an air-spaced objective, which is why I plan to ronchi test it, to see if rotating the crown will improve the image.

Both 45 degree diagonals I have tried on it have had short threaded stubs that .965 OD metal tubes screwed onto, so both got the 'back' end of the threaded ring, that's on the end of the non-sliding part of the focuser drawtube, JB Weld epoxied onto the stub (I think I had to file the threads down some for that to work)
It makes an ok-enough daytime scope, and the 45 diagonal yields a correct image, but there's definitely some chromatic effect to the image.......but an attempted view of jupiter was not-so-special.
But, as Preston says, they were built to a price point, and I'm sure there was variation in the objective quality, perhaps mine was just a dud. Yours is still worth messing with, just in case you got a near-perfect one.
R

#13 roscoe

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Posted 14 October 2013 - 10:17 PM

I just reread your initial post, I took the sliding tube right out, as well as whatever lens or lenses (don't remember) that were in the focuser tube.

#14 Preston Smith

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Posted 15 October 2013 - 10:36 PM

:bow: <- not in some idolatrous way

You have quite the collection sir on flikr!
I did end up ordering a diagonal...but as others have suggested as well, I'll try it outside the tube first.

Interestingly enough I found some etch just where the focal length would have been and pencil marks just below the line so I suspect the previous owner was just at the chop saw before he pulled the plug on it. :grin:


In just a few years I'm sure your collection will exceed mine! :roflmao:

This is an addictive hobby and there are still many scopes hiding in cellars, attics and sheds waiting to be rediscovered!

Very interesting about the pencil marks on your scope. Looks like the scope is a survivor. ;)

#15 m1618

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Posted 16 October 2013 - 02:52 AM

For closure and full circle, here's what I ended up doing.
I took out the inline erector/barlow and kept the tail eyepiece after cleaning it. Turns out that the diagonal I ordered prior to me posting on this forum (and many advising that it would not fit) sure enough, it didn't fit. Only 12" of the tube is left...and still without a diagonal.

First light just a while ago. Reaction? Sort of like binocular views. Color is actually great! No red/blue on the moon. Surprised. Wondering though, stars have coma?(blurred glow) and the moon had a ghost too. Is that spherical aberration? Enter some aberration lingo here.

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#16 BarabinoSr

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Posted 16 October 2013 - 05:41 PM

It would be a good idea to flock or blacken the inside of that drawtube first. It's very shiny inside there. I recommend that you get a small can of flat black spray paint, remove the eyepiece and spray the inside of that tube just enough to eliminate the glare, and give that a day or so to dry .Before spraying wrap up the outside of that tube and focuser body with paper and tape so that it will stay looking good. That will reduce greatly the internal reflections you're seeing.
You said that the stars appear like "blurred glows"in your scope, which suggest to me that you may not be achieving perfect focus. Are they perfectly round or distorted and are you using the thread on eyepiece ?:question:
Also , have you ever removed the objective from its cell ? Aberration could be caused by a few things. Is the objective seated properly in its cell? An improperly seated lens like that will certainly show distorted views. It's possible that it was placed back in its cell backwards. Let us know what you can find out!! G:cool:

#17 David E

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Posted 16 October 2013 - 07:55 PM

Wondering though, stars have coma?(blurred glow) and the moon had a ghost too. Is that spherical aberration? Enter some aberration lingo here.


That glow and ghosting is neither coma nor spherical aberration. Admittedly not an optical expert here but it sounds to me like the lens might have poor polishing and/or poor coatings. Ghosting is usually from the eyepiece, not the objective. However it could be a Littrow achromat doublet as these have been known to cause a ghost image. For daytime use, that ghost image probably would only be seen as a loss of contrast. Or, it could be someone in the past took out the elements of the objective to clean them and put them back in wrong.

#18 Preston Smith

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Posted 16 October 2013 - 08:09 PM

If all you kept was the tail eyepiece then is there only one lens in it?

#19 m1618

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Posted 16 October 2013 - 11:24 PM

I'm happy to report this scope is now working! Thank you all. Turns out that the lenses were not seated properly. Almost pinpoint stars and moon was crisp! This has been a rewarding experience especially with all the CN folks. Thank you all!

I also found out that the inside had already been flocked...so whoever had this scope before definitely tinkered with it as well. So there's just a few more things I would like to try. I just ordered a 60mm Meade focuser that accepts the 1.25 eyepieces and I might have to have the tube end professionally cut because I suspect the focuser is not seated perfectly thus the slightly imperfect pinpoints. Imagine I used a tiny hand saw and stayed up late night whereas a chop saw would have done that in seconds. Sigh, I see why my wife shakes her head.

#20 David E

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Posted 17 October 2013 - 04:16 AM

Fantastic! When you get done you are going to have a really nice astronomical refractor.






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