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Question about Tasco Specialty 56TN (200 x 50mm) Telescope

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Lense, objective need a 50 mm objective lens for a tasco 3 B brass telescope. focal length apparently is 14 inches.

Posted by t d taylor on


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Here's the link to the manual if you need it; http://www.tasco.com/products/manuals/specialty_30076150.pdf call; 1-800-423-3537 and they will be able to tell you how to get a replacement OL Hope this helps :)

Posted on Apr 04, 2007


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About my tasco 46-060675 D=60mm F=900mm come with 3 eye lense 1(sr4mm) 2 (k10MM) 3(k25MM) and two tube 1(1.5x erecting eyepiece) 2 (3xbarlow lense

The different eyepieces are to give different magnifications. This is worked out by dividing the focal length of the telescope, f = 900, by that of the EP. So the 25 mm Kellner (that is the type of optics in the EP) will give 900 / 25 = 36 times magnification.

The erecting eyepiece is used for terrestrial viewing. Normally with an astro telescope everything is upside down as that does not matter when looking at a star. So when you want to look through someone's bedroom window you use this.

A Barlow lens is an add-on magnifier. If you add this onto any EP (it normally fits between the EP and the scope) it will increase magnification x 3.

There is a practical limit to what any scope will deliver, governed by its aperture (the size of the front lens) and for your scope this will be about x 120 magnification. Beyond that the image becomes too dim and fuzzy. This means that your 4 mm eyepiece ( x 225 magnification) won't be much use. It will be hard to find the object you are trying to observe, it will be hard to focus, and the image will wobble around. Nor is your barlow lens much use either I fear.

You might consider another eyepiece around 18 mm to give a nice spread. A Plossl type is good. If you get serious about astronomy, I think you will immediately want a better scope after using the Tasco.

What lenses for Jupiter

You have asked a loaded question like "what size is a grey suit".

You need the focal length of the telescope divided by the size of the lens. Say 700 mm divided by 12.5 mm = 56 power. That said how close do you want to get to it? And how steady is your telescope?

Which lens is more powerful..a 10mm or a 20mm?

A 10 mm. If you know the focal length of your scope, divide that by the focal length of the eyepiece, and the answer is the magnification you will get. However bear in mind when viewing astro objects, a very high magnification will degrade the image sharpness, and make the object hard to get on centre. Most experienced amateur astronomers use a medium power eyepiece at most.

What does F=900mm and D=4.5 actually mean? Also the lens you look through is an H=15mm? Where can I find replacements or new lenses etc?

F900 is the focal length of your telescope. (achieves focus in 900mm) D=4.5 means you have a 4.5 inch mirror An H15mm is a Huygens 15mm eyepiece. Very old and, by now, poor design. magnification is fl of scope/ fl of eyepiece
900/15= 60x power. 4.5in mirror = (50x per inch aperture maximum magnification) 225x max power (on a perfect night)
To get replacement eyepieces first you must measure the diameter of your focal tube. Eyepieces come in 3 sizes .965in (on cheaper scopes) 1.25in (most popular) and 2in.( mostly higher end scopes) If you have a .965in focal tube, you are limited in your choices. Antares makes some .965 plossl eyepieces also surplus shed has some inexpensive eyepieces. Or, if you want to spend the money , get a .965 to 1.25 adapter. This way you can buy 1.25in eyepieces and they will serve you well when you upgrade to a better telescope.
1.25 eyepieces are available all over the internet.

Purchased a tasco 675 luminova telescope and the front lens was missing. Where can i get one from?

I assume you mean the eyepiece. This telescope uses 1.25 inch eyepieces. Maximum magnification is 400x on a perfect seeing night.
I would start with a 20mm plossl which would give you 33x. Enough to see the moon and Jupiter/Saturn. If you get interested, then buy more eyepieces and most important a moon (neutral density) filter.
telescope focal length (675)/ eyepiece focal length = magnification
Good places for eyepieces are Ebay, Astronomics, Smart Astronomy

I have a tasco galaxsee 14-114375. when i look through the high powered eye peice i can never find the object. i can see colours if i look at buildings and such, but if i try to see a star its just black....

1. Your finder is not properly aligned with the telescope. Therefore you are not looking at what the finder is looking at.
2. Max. power of the scope is 250x (if everything was perfect and it ain't) 375x like they say on the box is a LIE!
Tasco eyepieces are junk and you may be suffering from eyepiece "blackout" magnification = 500(focal length)/ eyepiece focal length

I am wondering how good you should be able to see images through a bushnell skytour 78-9960 telescope i can see the moon good but all the planets are really small and cant tell them from stars really. i...

No -- just remember that your scope is only 60mm wide. This is almost the same size lens as a pair of 10x50mm binoculars. About the most usable magnification for any telescope is 50 times aperture. So your scope is probably around 120 power. Yes I know the box said 500 power or 675 power or some number that you can never achieve in that size telescope.

All objects in the sky are very small because they are very far away. It does not look like the PHOTOS taken by the Hubble Space telescope.

Read my tips on my profile page.

Clear Skies- and read these:



Lost lens to bushnell 18-1561

I have a similar problem with my Bushnell 18-1650!

As you can see below, the plastic thing that holds the lens snapped off from the telescope's diagonal, and is now lost along with the eyepieces. This is a childhood scope I'm trying to rescue!

Should I:
1) glue a new eyepiece straight onto the diagonal
2) buy a new diagonal AND eyepiece
Or do I need to just buy a new telescope?

Thanks in advance.


I dont know how to use my barlow lens

I use a barlow lens quite a bit with my telescope. It is usually inserted before the diagonal if you use one or before the eyepiece if you don't. The barlow lens for your telescope will double the power of the eyepiece used.

However, despite what the manufacturer claims for your telescope things will look quite poorly if you try to view at 180 power. Generally you'll get the best images by using 50x for each inch of your objective lens. For example, your telescope has a 50mm lens. That's roughly 2 inches. 2 inches times 50x gives you a maximum useful power of 100x. Depending on the viewing conditions you may be able to exceed this or not even reach it. Things will look blurry and dim when you try to use too much power.

Your power or magnification is calculated by dividing your telescope focal length which is 360 mm by the eyepiece focal length. You have two eyepieces with focal lengths of 4mm and 20mm. If we divide 360mm by 20mm we get 18 power. If you add a barlow to that you get 36 power. Dividing 360mm by 4mm (no barlow) we get 90 power. That would be your maximum useful power.

Therefore, you should be able to used the 20mm eyepiece with or without the barlow but the 4mm should only be used without the barlow.

I hope all of the math wasn't confusing.


Problem with objective lens

This is an air separated doublet (invented in the 1700s). Each lens element is made of a different type of glass to reduce false color. So if you get it back together wrong you will notice the bad image. Look at the edges of the elements the thinner one usually goes in front. The concave surface of the rear element should also face front. With the plastic separation ring in place the convex surface of the front element should not come into contact with the rear element's concave surface. It shouldn't rock, there should be about 1mm air separation between them. On shorter focal length refractors (under 500mm) the front surface of the front element has less concavity that the rear surface. On longer focal lengths they are about the same. All I can say is try this and if the image isn't that great flip the front element and try it that way. And don't feel too bad we've all learned the hard way to mark the edges of the elements as we take them out. HTH
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