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I'm looking at an ad for a used Canon 1200mm f/5.6L EF USM Autofocus Lens where they are asking $180,000. Yes, that's not a typo.

I don't get it.

I'm an amateur astronomer and I know I can buy a killer 1200m refractor for well less than $180k. What makes this so expensive? I know that a good refractor only has a triplet (or a doublet) as the objective and a small, but complex, eyepiece. The Canon lens has 13 elements, 2 of which are flourite.

This isn't about this particular lens, and this question may well be better for an astronomy forum

But why are camera lens so much more expensive than refractor telescopes?

Michael C
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Paul Cezanne
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  • Save money, buy this used NASA lens! $33.5k on eBay. http://petapixel.com/2015/04/27/massive-2540mm-f8-nasa-lens-shows-up-on-ebay/ – Michael H. Apr 29 '15 at 03:35

5 Answers5

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  • Rarity. There were only approximately 20 of these now out of production lenses ever made. When they were in production they sold for about $90,000 (US). Due to the time needed to grow the large fluorite crystal used in the 3rd element of the lens, once ordered they took about 18 months to produce.

  • Autofocus Capability. These lenses include auto focus capability. Moving focus elements as large and heavy as this requires mechanisms that are both robust and extremely precise. Moving them fast enough to be used to photograph sporting events means they must also be very powerful.

  • Maximum Aperture The EF 1200mm f/5.6 L requires an entrance pupil of 214mm (8.4 inches). A 1200mm f/8 telescope needs only a 150mm wide objective. When you compare the areas of a 214mm circle to that of a 150mm circle, you see that it takes at least twice as much material to create a lens 214mm wide compared to 150mm wide. And that is before you consider that the larger lens element must also be thicker in the center to maintain the same amount of curvature on the surfaces.

  • Optical Image Quality While things like coma and chromatic aberration are expected at the edges of the field of view of a large refracting telescope, they are not as acceptable in a camera lens. And the larger the diameter of a lens is, the more correction must be applied to obtain the same image quality. This requires more elements in the lens, and these additional elements are almost always made of exotic materials with a higher refractive index and lower mass density than normal optical glass. They must also be precisely shaped to almost insane tolerances to perform as designed.

  • Image Circle Diameter A telescope need only to cast an image circle the size of a human eye's pupil: approximately 8mm in diameter. A camera lens intended for use with a Full frame camera must cast an image circle approximately 44mm in diameter.

  • Minimum Focus Distance Many telescopes are designed to focus only at longer distances, some even only at infinity. Camera lenses such as the EF 1200mm f/5.6 L can focus at infinity but are expected to focus at shorter distances as well.

Michael C
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    Why then not use a reflecting telescope instead of such a camera lens? – Count Iblis Apr 28 '15 at 02:27
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    @CountIblis Those exist too. They're known as reflex lenses. There's everything from a not uncommon 500mm f/8 which is under $100, to the Nikkor 2000mm f/11 which makes you wonder if you should call it a telescope or a camera lens. –  Apr 28 '15 at 02:45
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    An important difference that you can get into the optics bit - the block diagram for the 1200mm f/5.6 shows 13 elements in 10 groups, two of which are fluorite. A 1200mm f/6 telescope has 2 elements. That is a significant difference in the amount of glass. –  Apr 28 '15 at 02:55
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    The reason for the difference in number of elements is that a telescope is designed only to focus at infinity, while a camera lens has to be able to focus at a range of distances. – 2012rcampion Apr 28 '15 at 03:26
  • Yeah it's mostly #4, many more elements and a much more sophisticated optical design to reduce aberrations in the corners of the image. You can spend $180,000 on a telescope, however. – Matt Grum Apr 28 '15 at 07:33
  • I guess the aperture of the telescope cannot be changed? Consider adding that to your excellent post if it is true. – null Apr 28 '15 at 07:43
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    I also read that the bokeh of a refractor telescope looks horrible, as a result of its construction. Like this: https://upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Catadioptric_system_bokeh_christmas_tree_lights.jpg/650px-Catadioptric_system_bokeh_christmas_tree_lights.jpg – Erwin Bolwidt Apr 28 '15 at 08:10
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    Don't forget things like coatings to increase transmissivity etc. and preventing to get light into the wrong paths. Telescopes are used in the dark where light from the wrong direction is no problem, and you can easily compensate the bad light performance of beginner telescopes by longer exposures. – PlasmaHH Apr 28 '15 at 08:56
  • Great answer! My guess is that the need for close focusing means that you need many elements and that's what causes the materials cost to be so high. Then when you throw autofocus in the mix... – Paul Cezanne Apr 28 '15 at 09:47
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    @ErwinBolwidt that's from a design that has a mirror in the center to make it more compact while allowing for a large aperture and long focal length. Schmidt/Maksutov-Cassegrains are the telescopes that look like paint cans/buckets. From the outside a refracting telescope looks a lot like a telephoto lens. – Dan Is Fiddling By Firelight Apr 28 '15 at 13:07
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    @ErwinBolwidt that's not a refractor - that's a reflector. The center disk is from the mirror in the center. Note that bokeh (out of focus) isn't a concern for telescopes as they're all focused at infinity for all practical purposes and aren't used to take pictures of things closer than a few hundred thousand miles (unless you're trying to photograph the ISS). –  Apr 28 '15 at 20:11
  • @DanNeely though note that most long lenses for cameras are indeed telephoto lens design where the physical length of the lens system is shorter than the focal length. This means we don't have things that are absurdly long. My 80-400mm lens is physically 203mm long. That means more glass and a more complex design and more expensive than a 400mm long refractor telescope. An 800mm f/5.6 is 461mm long (I'd hate to see it at 800mm long). –  Apr 28 '15 at 21:50
  • @null You can change the aperture of a refractor by simply masking part of the entrance pupil. Such rings are widely available for use when viewing bright objects such as the moon. – Michael C Apr 29 '15 at 02:35
  • @Michael then this is comparable to AF. – null Apr 29 '15 at 07:26
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    Changing the entrance pupil does not affect the point of focus in the slightest... – Michael C Apr 29 '15 at 08:29
  • @MichaelT You'd never use them as macro lenses; but near focus for most telescopes is 20-30 feet on the small end to maybe a few hundred feet for some really big ones. In particular, smaller telescopes and spotting scopes used by birders/etc use the same type of optics. The most important difference being that a spotting scope will generally be paired with a correct image diagonal (or an erecting prism if looking strait through); while for astronomical use the prism is either dropped entirely or a design that leaves the image mirrored is used to maximize light transmission. – Dan Is Fiddling By Firelight Apr 29 '15 at 14:15
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    @DanNeely which is comparable with 500mm lenses (a 500mm f/8 without special attention had a closest focus distance of 4m). The 2000mm f/11 had a closest focus of 18m. Though this really depends on application and constraints. A two element lens would be unacceptable for quality for a photographic lens, but would be acceptable for a spotting scope. This means more elements to correct the image for photographic quality. –  Apr 29 '15 at 14:31
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    #5 assumes that amateur astronomers don't do imaging. This is completely and utterly false, and astrophotography is one of the hobby's biggest draws. It's also the most expensive and the most frustrating, but pretty pictures taken by amateurs definitely draws people in. – Ernie Apr 29 '15 at 18:17
  • "The reason for the difference in number of elements is that a telescope is designed only to focus at infinity, while a camera lens has to be able to focus at a range of distances." No, the reason is that as you increase the number of elements, the more light you lose. All astronomers (amateur or professional) are working with very dim subjects that can't be improved with better lighting. As such aperture trumps nearly everything else, and the less glass there is in the optical path, the better. – Ernie Apr 29 '15 at 18:29
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    @Ernie "Imaging" is one thing when it can be spread out over several hours and hundreds of exposures that are then stacked and corrected for things such as CA and coma in post. It is an entirely different thing when it must be done at 1/1000 second or even faster for one frame. Especially when the specific lens in question was designed and introduced for use with film cameras, where correcting CA and other aberrations was much more difficult than with digital imaging. – Michael C Nov 16 '15 at 11:33
  • @Ernie #5 does not assume that amateur astronomers don't do imaging or care about things such as CA and coma. It might assume that such astronomers would prefer to use less expensive designs better suited to such things, such as Newtonian or catadioptric designs that use shaped mirrors as their primary objectives, than use more expensive refracting designs that are not as well suited. – Michael C Nov 20 '15 at 17:51
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Michael Clark missed one important point in his otherwise correct answer:

  • Physical vs. Optical length Think about what the 1200mm really mean. This is the focal length. This normally means that the distance from the center of the lenses to the place where the image forms is 1200mm. (Yes 1.2 meters!) On your telescope I guess that you pretty much see these 1200 millimeters as the telescope is around 1.2 meters in length. On your Canon you're probably not carrying a lens that is 1.2 meters long. The lens in question is 83.6 centimeters. This significant shortening of the physical dimensions can be achieved by optical elements, most probably the ones with fluorite.
user23573
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  • I think that the Zeiss 1700mm f/4 for medium format (?!?! nice image circle though) may be nearly 2 meters long. Its also a bit more expensive than the 1200mm f/5.6. –  Apr 28 '15 at 20:15
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    You don't need fluorite to make a lens shorter than it's focal length (telephoto), there are many telephotos at much lower price points. Fluorite reduces chromatic aberrations. – Matt Grum Apr 29 '15 at 08:36
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    @MattGrum, I half-way agree on your first point, you don't need fluorite to shorten your lenses. It's not primarily the price and fluorite will not "magically" reduce chromatic aberration. For both, the length of your lens and chromatic correction (and a bunch of other properties) you need a very careful and balanced selection of different glass materials. Fluorite just adds another option in that equation. "Photography is always the search for the best tradeoff." – user23573 Apr 29 '15 at 09:09
  • @MichaelT, Unfortunately there are no physical dimensions for this monster available. But interpolating from the images I've found and looking at the images from exhibitions, I would assume that the whole thing is just about 1.3 meters long. So, there is some optical shortening done on that one. Additionally this lens is for medium format which is usually quite a different caliber when it comes to the price. – user23573 Apr 29 '15 at 09:19
  • @BogdanWilli very true. The Nikon 400mm f/2.8 is 368mm. The Nikon 1200-1700mm is similarly huge. The telephoto design comes with a trade off that includes less light and with such monsters the telephoto design is less desirable, though there is still some shorting to avoid it being too big and expensive (more glass needed, but not as big - the tradeoff). –  Apr 29 '15 at 09:25
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    @BogdanWilli "fluorite will not "magically" reduce chromatic aberration" actually it will, but it's not magic - it's physics, fluorite is a low dispersion material which means different frequencies of light spread out less when passing through, so it will reduce chromatic aberrations compared to a similar element of standard optical glass. – Matt Grum Apr 29 '15 at 09:35
  • @MattGrum Sorry, you miss this point completely. The chromatic aberration is not corrected or "minimized" by using more materials which have "less of a dispersion". You correct it as follows: Use a high density glass convex lens in combination with a lower density glass concave lens. See Wikipedia about Achromat and Apochromat. Your term "standard optical glass" in reality is a catalog of different glass types with different optical characteristics. IMHO this discussion is worth a question in itself. – user23573 Apr 29 '15 at 11:53
  • When fluorite is used, it is for superior CA correction (as the low density concave lens) and has nothing to do with reducing the physical length of the lens. Canon Super Telephoto lenses use fluorite elements. Their Nikon counterparts do not. Yet the long lenses for both manufacturers are pretty close in length for the same focal lengths (apart from lenses that use Diffractive Optics). – Michael C Nov 16 '15 at 11:03
  • The reason telescopes don't use fluorite is that CA is less of a concern for the objective lens elements since most eyepieces only use light from the center of the image cast by the objective. If a wide field of view is desired then the CA correction that can be done via the eyepiece is normally deemed sufficient. – Michael C Nov 16 '15 at 11:07
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Different tools for different jobs. A telescope is for looking at objects with the naked eye, a camera lens is for recording high resolution images.

It is acceptable for a telescope to have large distortions around the edges and nobody much cares about colour correctness. This makes it simple (cheap) to make the lenses which are good enough to do the job. Now add the sheer size of the optics required to get an f-stop of 5.6 from a 1200mm focus length.

---- edit to correct the edits ---

A 1200mm telescope is for looking at Stars, a 1200mm f/5.6 lens is for looking at Celebrities. If you expect to sell a picture of Venus then you really don't want it to look like a picture of Jupiter. If you expect to sell it for over $30,000 then it had better look like Venus.

Paul Smith
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  • @NickM, I know you thought you were trying to help, but you have it utterly backwards. Viewing stars requires the ability to detect the presence or absence of light, nothing more. That is why they can be use much lower quality optics then lens used to view people. The naked eye is the most descerning optical instrument we know of, not the least – Paul Smith Apr 28 '15 at 20:42
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    I disagree completely. Astronomers are very concerned about distortions, and to some extent color correctness. – Paul Cezanne Apr 28 '15 at 22:41
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    The 1200mm refractor telescope is that of a backyard astronomer rather than a professional. The backyard astronomer is much less concerned about these issues than a professional... and a reflector has much less (to no) issue with distortion and chromatic aberration (a mirror reflects all frequencies of light (that it reflects) equally). There really aren't that many refractors in professional use anymore. –  Apr 29 '15 at 13:34
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    GAAAAAH! Absolutely not! There are plenty of amateur astronomers out there willing to pay $10,000 for their OTAs alone, plus accessories like application-specific cameras (which can run for nearly as much, if not more), computers, and software for image processing. On top of that, there are at least a dozen pro-am astronomers in the world who sell their photos to fund their hobby (Jack Newton comes immediately to mind, look him up). Your assertion is born of ignorance, and is paramount to saying that photographers never need to use anything more expensive than a cellphone camera. – Ernie Apr 29 '15 at 18:11
  • @Ernie - It is not clear who you are railing against, so the charge of ignorance becomes difficult. Also no one has suggested photographers do not require quality? Perhaps you have misinterpreted what I said to imply that I think astronomers do not require quality, but I didn't say that. I just said that the quality they require, and are happy to pay a lot for, does not compare to that required of celebrity publications. Jack Newtons pictures are pretty, but do not compare to Hubbles, do they? – Paul Smith May 07 '15 at 16:46
  • @Ernie, when the Canon 1200mm f/5.6 L was designed for the FD mount in 1984 (and then adapted to the newer EF mount in the early 1990s), most amateur astronomers were not paying anywhere near $10K for their OTA! And digital imaging and processing for astronomy back then was pretty much the domain of government funded astronomy programs! One reason that the 1200mm f/5.6 is no longer produced is that advances in digital imaging for photography has made the need for such a lens obsolete. – Michael C Nov 16 '15 at 11:38
  • @MichaelClark: and what's that got to do with amateur astronomy being OK with large spherical aberrations and poor colour correction? People who do astrophotography for any period of time at all (ie, those who don't quickly give up in frustration from poor equipment, and are willing to spend more) do care about these things. The difference between now than then is that many advances in lens design and production has made such high-quality lenses cheaper. It's not because people didn't care. – Ernie Nov 20 '15 at 17:33
  • @Ernie Before the digital imaging revolution of the past two decades most backyard astronomers were much more concerned with viewing than with imaging. Those who were more concerned with imaging (via film) used reflector types of telescope designs, rather than refractors. But mirror/reflector lenses that are suitable for astrophotography, where the shape/quality of bokeh is not a concern, are not as suitable for long focal length photography, where the shape and quality of bokeh is a primary concern. And a medium sized Dobsonian, or even a typical 1200mm Matsukov-Cassegrain is too big. – Michael C Nov 20 '15 at 17:43
  • ... to be used to photograph Olympic sports! – Michael C Nov 20 '15 at 17:54
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Astronomers use reflectors mostly but are indeed interested in accuracy.

The lens in question is much faster than a telescope.

Adrian Midgley
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  • I can buy a 10" f3.9 reflector for under $1,000. – Paul Cezanne Apr 29 '15 at 09:48
  • The f-number used to describe a telescope doesn't describe the same thing the f-number used to describe a camera lens does. With a telescope it is an indication of maximum field of view. With a camera lens it is an indication of maximum light gathering capability. For the telescope, the light gathering capability is indicated by the diameter of the objective lens. – Michael C Nov 16 '15 at 11:11
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Part of the reason is doubtless that professional photographers earn more money than professional astronomers, and so can be milked a bit more for their cash.

Score: +5 Funny

Nicholas Shanks
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  • I very much doubt that. Optics is complicated. It's more to the effect that the price tag of this item reflects the high costs of research and the small number of people who have any need or desire for it. This increases the price because there is no economy of scale for mass production. – Ernie Apr 29 '15 at 18:03
  • I used to be a professional photographer. I can tell from my personal experience that this absolutely not the case. It's the same short-circuited assumption as the following: All footballers are incredibly rich, see what Ronaldo earns! – user23573 Apr 30 '15 at 06:32
  • @BogdanWilli It's funny because (a) it's true, professional astronomers don't get paid, and (b) geez, lighten up, it's a joke. – Nicholas Shanks Apr 30 '15 at 10:38
  • @Ernie You have too much serious in your reply. – Nicholas Shanks Apr 30 '15 at 10:39
  • @Nicholas See it this way: It's not so funny for me, it's the reason why I am no more a professional photographer. A profession I really liked. Nevertheless I've at least tried to reply with a joke. – user23573 Apr 30 '15 at 12:29