Question about Fieldvision 114mm Reflector (114 x 114mm) Telescope

7 Answers

Upside down images

OK, I was given a field vision telescope as a gift. model #F700/76. The is a very small operationinstruction manual with it that covers pretty much nothing. Having never had a telescope before, I have no idea why the images I view are upside down. I assume they are not supposed ot be... how does one correct this? Is it missing a lens or am I doing something wrong? HELP!

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  • 9 more comments 
  • Anonymous Nov 15, 2007

    I wanted to use the telescope to look at the city, buildings and near by objects. I was able to see images correctly and then after I cleaned the lens on the telescope I was no longer able to see the images correctly. They appeared up side down!

  • Anonymous Dec 26, 2007

    i see images upside down is that normal

  • Anonymous Dec 26, 2007

    upside down image

  • Anonymous Dec 29, 2007

    I can not get the Barlow lens of my model 60050 to focus. The other smaller lenses focus fine. I have tried zoom in and out using the focusing system, but all I see is a continuous blur. I inspected the Barlow lens to see if it was complete, and noticed that it has one lens towards the tapered end only. Is this how it should be...

  • Anonymous Dec 31, 2007

    HAVING UPSIDE DOWN IMAGES ALSO. SO WHAT "IS" THE SOLUTION?

  • Anonymous Jun 07, 2008

    I have a bushnell voyager that is showing images upside down.

  • kids4 Jul 31, 2008

    My telescope images are upside down and don't know what to do to fix it. This is my first telescope ever and it did not come with instructions.

  • jyurkonis Aug 10, 2008

    just purchased a reflector telescope and everything is upside down. Apparently this happens often. Can you help?

  • Anonymous Sep 06, 2008

    Have a Bushnell Model 78-3650 Telescope and everything is upside down.

    Please help us if you know why.

  • Anonymous Nov 23, 2008

    I have a edu science coated optics DIA.=60mm F=700mm telescope and i too see things upside down why do i?

  • Dean SK
    Dean SK Jan 22, 2013

    IT WILL WORK. Just to follow up with my previous review. The telescope will work if you first locate object during the day with the red beam finder, then find it in the view centre of telescope, return to object finder and re-arrange the red beam to the centre of the object, there are two screws on the side and at the bottom, one is for horizontal and the other is for vertical adjustment, now, look in your telescope again if the object is at the centre. Take it out at night and enjoy the moon. Sadly, Bushnell doesn't explain this in the manual or trouble shooting section, kind of dumd dumb. It took me many frustrated days to work it out.

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ALL telescopes will show the image upside-down. You learn to adjust for this. IF you must, they do make a lens called an "erecting lens" that would flip the image back right-side up.

Posted on Dec 28, 2008

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As we all learned in grade school, telescopes produce an upside down image - it's okay for astronomical use since upside down doesn't matter. If you want an image like you'd see in a pair of binoculars, get an image erector from a telescope accessory store to add to your eyepiece.

Posted on Dec 06, 2006

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When you hold a magnifying glass a few inches away from a page of print, you can see the page enlarged.

Also, when you look at a distant object through the same magnifying glass, you see an upside-down image of the object in front of the lens.

A refracting astronomical telescope makes use of two lenses, one of which works in each of these ways.
The lens in the front of the telescope, called the objective lens, produces an upside-down image of the object one is using the telescope to look at.
The lens near the eye, called the eye lens, acts as an ordinary magnifying glass to magnify that upside-down image.
This is the basic principle of the telescope. Naturally, each of these two elements of the telescope could be made up of several lenses, to combat certain inherent limitations, or aberrations, of lenses with spherical surfaces made out of one kind of glass. However, before considering this, it is important to note that nearly all telescopes contain a third important element with a specific function.
In addition to magnifying or creating an upside-down image, a convex lens can do two other things. When reading a book, you have to hold the magnifying glass away from the page in order for it to magnify. If you set the lens right down on the page, it might as well be a flat piece of glass. (Actually, because of the thickness of the lens itself, it's always a small distance from the page, so it will magnify a little bit.)

If you gradually move further away from something with a magnifying glass, at first it gets magnified more and more, but the quality of the image quickly deteriorates. At a point between where the lens acts as a magnifier, and where it produces an upside-down image of what you are looking at, you will find the whole area of the lens filled with the colors of a very small area of the object you are examining.

When the lens is at this intermediate distance from an object, the object is at or near the focal point of the lens. This is not very useful for examining an object. But if you place the filament of a lamp at the focal point of a lens, then a lens so situated collimates the light from the lamp; rays of light radiating out from the filament are bent by the lens so that they are now moving in parallel, creating a useful beam of light. This is done, for example, inside movie projectors.
Still, we might well look upon this mode of operation as being useless, at least from the perspective of using lenses to look at things. The case of a magnifying glass sitting right on the page you are reading certainly could be called useless as well.
However, the third important element in a telescope is actually functioning in both of these "useless" modes at once, and yet it is performing a very important task.
When you look at a lens that is forming an upside-down image of a distant object, naturally the upside down image doesn't extend beyond the lens. After all, you are looking through the lens to see the object, so all the light from the object that you see has passed through the lens.
But if you move your head, and look at the lens from other angles, you can see that the lens is actually making a larger image than you can see from one place. The upside down image is located in front of the lens, even though the light that makes it up is seen through the lens.
How can you see the whole image?
One way is to put a piece of wax paper or ground glass in the plane on which the image is formed. That way, the light hitting it is diffused in all directions, and so you see some of the light from all the parts of the image.
But this is inefficient, as it doesn't direct all the light involved in a useful direction. And it limits the sharpness of the image, since things that diffuse light do so because of minute irregularities within them, as is obvious in the case of ground glass.
If you place a lens right in the position of the image, so that as far as the image is concerned, it is in the useless position of a magnifying glass lying on a page of print, that lens can, without changing the size of the image, bend the light that makes it up so that more of it goes towards your eye, or the eye lens in the telescope.
The way to make it do this the most effectively is to choose its thickness so that if you look through it to see the objective lens, you find the objective lens has been magnified so that it is everywhere you look. So the objective lens is being magnified by it into a large and blurry image, which is all right, because a telescope is not used to look at its lenses, but to look at things through them.
Thus, both "useless" modes of operation are involved in the function of this third element, the field lens.
A field lens is not essential for a telescope, but it makes the image you see through it brighter, and it improves the telescope's field of view, because with it one is no longer looking through a narrow tunnel defined by the size of the objective lens.
upside down images - telesc.gif Astronomical telescopes may use a large mirror instead to perform the function performed by the objective lens.
The field lens and the eye lens are both contained in the telescope's eyepiece.
Of course, optics aren't just for imaging. Optical principles can also be used in such things as light fixtures. For example, here is an illustration of an old-style automobile headlight that, except for unavoidable real-world imperfections of physical objects, takes all the light from a point source, in every direction, and puts that light in a collimated beam:
lamp.gif The light from a point source can be collimated using a parabolic reflector; part of the mirror behind the point source follows the shape of the paraboloid, and more of it is shown by a dark gray line in the illustration.
A parabolic reflector, however, cannot help with the light which shines forwards from the point source. So, a lens is introduced which collimates that light.
Behind the lens, then, the parabolic reflector is now replaced by a spherical one, so that the light from the point source going directly to the back is reflected back onto the point source, from there to continue in the right direction to be collimated by the lens. Of course, the point source might be itself opaque, or for other reasons disturb the path of light passing through it, but in the real world this can be dealt with by displacing it slightly from the exact focus of the design.
Now we have a design that sends the light going in all directions from a point source into a collimated beam shining forwards. However, one more improvement is possible. Replacing the part of the parabolic reflector lying in front of the point source with a spherical reflector, so that again the light is reflected back on itself, avoids the need for a very large parabolic reflector, reducing the bulk of the assembly.
The lens shown in the diagram does have an unrealistically short focal length in proportion to its diameter. Shrinking the lens, and the spherical portion of the mirror behind it, results in the spherical mirror in front becoming larger; also, using a Fresnel lens allows a lens to be achieved with a fairly high proportion of diameter to focal length.

Posted on Oct 01, 2009

  • Dean SK
    Dean SK Jan 20, 2013

    OK, I don't care all about expalnation. I wat to see thing as is and why it's so hard that there is a debate about it that upside down is normal.

  • Bonnie Ford Sep 06, 2013

    Thank you I would like to have both. In the day I want to use it to look at my property. Is there another lens that you can use to switch the view? Thank you

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Well this is a common complaint amoung ameteur astronomers who have just gone out and bought themselves a reflecting telescope ie the type that uses mirrors. the thing is when the light is gathered it comes in at different angles and goes through a sort of "overtaking" process when it hits the primary mirror then is bounced onto the secondary mirror (this should be aligned at 45 degrees) and then in to the eyepiece. so getting to the point you are not alone and this is what happens in all reflecting scopes and you can correct this with about $10000 US i think this method involves using complicated camera optics but there may be simple eyepieces and filters that you could buy to solve the problem. i don't know how to correct the problem but i know what it is and how to explain it.

kind regards

andrew tucker
astronomy student from
trinity college east perth
perth
western australia
australia

Posted on Oct 01, 2008

  • Dean SK
    Dean SK Jan 20, 2013

    If they telescope in the submarine is upside down, we will never win the war.

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In your telescope kit (I have one as well)there should be 2 long tubes that fits in the eyepiece socket on the telescope. One of these is the erector lense that will flip the images for you. Eben

Posted on Jun 25, 2007

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I have a 78-4502 114mm Reflector Bushnell Telescope - objects are upside down, how can I fix this?

Posted on Aug 16, 2009

  • gridleypete Aug 16, 2009

    How can I correct upside down objects in my Telescope

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Ok, i feel like an idiot! i thought my telescope was broken!

Posted on Dec 15, 2007

  • numpty24 Mar 09, 2011

    u r not alone

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