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Is it possible to add a lens in front of another lens to make it a telephoto lens?

I have a few "fisheye" adapters that I can put in front of any lens to take a fisheye photo, but I wonder is the same technique can make a lens a longer focal length lens (on cameras where the lens cannot be removed).

Edit: the question originally asked for "zoom", but based on comments, the question is really about increasing the focal length.

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  • What camera? These attachments can be camera-specific for compact cameras.
    – xenoid
    Aug 7 at 7:02
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    Do you actually mean a zoom lens - one with variable focal length - or do you actually just mean telephoto - a longer yet still fixed focal length, making things 'nearer & bigger'?
    – Tetsujin
    Aug 7 at 7:07
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    Sorry-telephoto Aug 7 at 8:04
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Is it possible to add a lens in front of another lens to make it a zoom lens?

While I'm sure it's optically possible to convert a prime into a zoom, I have not seen any conversion lenses that do so. There are variable teleconverters that attach to the mount of some lenses, but they come in multiple pieces that are combined to provide different magnification levels. (They don't zoom.)

If you just want access to different focal lengths, without zoom cabability, there are screw-on auxiliary lenses you could look at. Common conversion factors include 0.5x, 0.8x, 1.4x, and 2x. However, they would produce severe vignetting if used with medium formats because most are made for 35mm or smaller formats. Even when used with their intended format, image quality is often poor unless the conversion lens was made to be paired with a specific taking lens.

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  • Thank you. I might have worded my question wrong, but yes, I do not need to zoom, just to change the focal length of the lens with an add-on. What would I be looking for exactly, name wise? Aug 7 at 5:58
  • You can search for conversion lens.
    – xiota
    Aug 7 at 11:54
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Sure. These things do exist when they're practical.

For example, there are lots of telephoto lenses for cell phone cameras, and a very few of them are even non-fixed-length lenses. They stink on ice optically, they reduce the camera's light gathering to the point that they're problematic in a lot of environments, and they're nearly impossible to hold because the lens weighs more than the device it is attached to and there's too much flex between the cell phone and the lens, but they do exist.

But for a camera with a larger lens, it is probably not practical. Bear in mind that for even a lens the size of those on a typical point-and-shoot camera, the amount of weight you'd be adding to the lens would be considerable even for a 2x increase in reach, much less for enough of a telephoto magnification to be worth doing. Think "three pound lens on a 3 ounce camera" and you get the picture.

So anything is possible, but that doesn't mean you should. :-)

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  • Thanks. Could you add any kind of practical pointers to what lenses I can add to a 6x6 or 6x4.5 medium format camera (like a zeiss ikon or holga etc) ? I don’t mind B-pose or tripod or heavy setups. Thanks Aug 7 at 0:30
  • The lens thread size is what matters, not the camera size. Search for telephoto attachments for a specific lens thread size.
    – dgatwood
    Aug 7 at 1:06
  • Those types of auxiliary lenses usually convert from one focal length to another. I have not seen one that converts primes into zooms.
    – xiota
    Aug 7 at 4:10
  • Correct. I haven't seen anything with a zoom larger than about a 12x zoom for a cell phone. They're just not practical to build at that size, and there's almost no market for it.
    – dgatwood
    Aug 7 at 17:25
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It is theoretically possible, but not advisable. The lens manufacturer would have spent a lot of time and effort researching the correct lens groups to match so that you have the best optical design at that focal length and price point. Anything you place in front of the lens will lower the light transmission, and most likely also lower the image quality. You could place hyper expensive optical elements in front of the camera, but unless those lens elements were manufactured for your camera, in order to correct minor faults in your lens, you will still come out with lower I.Q(image quality, not intelligence quotient) than before.

I once tried one such attachment(on a smartphone). It was a waste of money. The reason you can get away with using a fisheye adapter is coz fisheye lenses cause so much distortion and change the perspective so exaggeratedly that you don't generally notice the reduction in IQ.

Adding a lens/optical elements to the front of your lens to make it a zoom lens or increase the focal length will just be a waste of time. Trust me, I experimented doing just that. When I was a student and had just gotten in to photography and was strapped for cash, I tried various combinations of multiple lens designs(using a lens on another lens, using a focussing screen and magnifying that image using another lens, using extension tubes on the second lens to magnify the image circle of the first lens and a whole lotta other dexter's laboratory stuff) for getting a focal length advantage.

IT JUST DOESN'T WORK.

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  • Ok then I might just look for a very light (maybe from an old camera) 80-100mm lens for medium format (that clears 6x4.5) Aug 7 at 8:12
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You state "camera whose lens cannot be removed": that is a compact camera. What you are looking for is called a teleconverter by manufacturers. Wikipedia calls it a "teleside converter" in contrast to "tele converters" (or tele extenders) which are typically between lens and body.

They usually don't make a lot of sense with modern cameras which often have sensor resolutions already squeezing out what the optics can hope to deliver. In particular cheap third-party add-ons tend to lose more optical resolution than they gain in magnification, meaning that cropping will deliver a more detailed image than adding the converter. Older compact cameras often have dedicated optional converters by the manufacturer themselves, including options in the camera supporting them that may change focus distance display, EXIF data, and image stabilisation strength.

They tend to consist of two groups of optical elements spaced significantly apart and maintain the aperture number of the principal lens.

Modern compacts tend to have such complicated optical recipes and high resolution that even those higher quality converters for older compact cameras tend to give mixed results at best.

Typical focal length extension factors are 1.4× and 1.7×. Cheap aftermarket converters are not just typically low quality but also tend to severely overspecify the magnification factor.

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Afocal to the rescue:

Using ordinary binoculars, you can hand-hold your fixed lens camera so that it replaces your eye. This is called the "afocal" position.

Camera lenses are converging lenses. In other words, light rays from objects traverse the camera lens. The camera lens causes these rays to alter their direction of travel. Their new path causes them to converge to a point downstream from the lens. A measurement of this back-focus distance is approximately the focal length.

Binoculars / telescopes force the light rays to exit the eyepiece as bundles of parallel rays. In other words they do not come to a focus (afocal). The human eye peers through. Light rays from distant objects naturally arrive at our eye as parallel bundles.

The binocular / telescope placed before a camera lens simulates the view we humans experience. You can use fixed or zoom binoculars. This lash-up is awkward but works. Try it -- you will like the view (image to photograph).

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  • I used to do that as a kid with my terrestrial telescope and a canon IXUS 60 point and shoot. It was fun to do as a kid, the I.Q was also not to shabby(The IXUS 60's IQ was not great to begin with, so not much degradation was noticeable). However, the O.P. was asking that for a Medium/large format camera. I'm not sure the exit pupil of any pair of binos is that large in order to allow him to have a clear FOV. He will only be able to capture the centre dot and everything around will be black. Aug 8 at 17:06

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