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Makes me wonder if the diagram is accurate - in lenses of this type it's more conventional to mirror the front surface of the mirrored elements. A design where the light passes through the supporting glass twice is asking for trouble.

The latter (i.e. 2) is to block others from doing the same lens, even though it is not really an invention. Personally I think that is misusing the patent idea. A lot! I guess this is accepted for pragmatic reasons. How else would you block others from just measuring a lens and make a similar one?

The first of these is that you can't use a standard diaphragm aperture system, a problem this Canon patent seems to 'solve' by using a variable density ‘electrochromic’ filter to 'stop down' the lens—although this will obviously not have any impact on depth of field.

We caught up with a few product managers and engineers at Adobe Max, and talked with them about the new features in the company's photo editing suite.

Particularly with a relatively modern camera, like my 6D, which has good high ISO performance, which makes an f/8 lens much more practical than it was with earlier cameras.

Among Canon's non-catadioptric lenses, EF 85mm F1.2L also has a slow AF due to the same problem: its front element is about the same size as a 400mm f/5.6, and it also projects the entire lens assembly for focusing.

I still have a 500mm f8 "Lens" from the 80' that was/is 'revolutionary' (named by his inventor's name, ..must check.. Makovsky or the like) claimed to have no lens at all ! Only (magnifying) mirrors. The lens is not round but like a long light box You have to slightly point downwards for shooting straight :-) A roller to index finger for easy focus and one to thumb for a kind of loose aperture.

It's probably best to think of mirror lenses as pocket telescopes that have been adapted for terrestrial photography. My old Nikkor 300mm AIS f/4.5 refracting lens plus a 1.6X Kenko converter outperforms my 500mm f/8 (≈t/11) Samyang mirror lens, but it's a lot of freight to haul on a hike. A mirror lens is much lighter. The high ISOs and shutter speeds available on today's DSLRs and sansmirror cameras mitigate the vibration problems that bedeviled photographers in the days of slow films.

@photoMEETING,Please, read carefully. I did not say that cat lenses should not have vignetting, distortion and CA but that MY cat lens does not have, or at least does not show noticably, those optical issues. OP's comment seems to imply that cat lenses are worst than many conventional lenses. But my cat lens has less vignetting, distortion and CA than many of the kit lenses I have used...

The picture of the patent show that the big mirror is at the back side of the element, so light passes two times through that element. With todays computerized design and wide choice of glasses this could maybe lead to better correction than old catadioptric designs. My old Sigma 600 which I used at an Olympus OM2, turned out to be quite bad when put on a digital E3... Bokeh is horrible. But for some objects it is not important, the moon for example. I had it for its compactness, for in my backpack.

I used to work for a subsidiary of Canon and we were subject to Canon's rules and procedures. One of them was that each group/department had targets for patent filings (or at the very least, attempted patent submissions). Canon views the number of patent filings as an end goal in itself, often regardless if the patent has any business application (yes, I submitted one as well). While this is a very interesting patent, it says nothing about whether Canon intends to productize this idea.Canon files stuff all the time just because they can.

If Canon can offer its 400mm mirror lens at half or a third of the price of a 400mm refracting lens, and hold tight manufacturing tolerances, there probably will be a significant market for it.

I have a Vivitar series 1 800mm f-11solid cat. I had it in storage in my closet for about 30 years. When I looked at it, the front lens cover which was rubberized plastic had disintegrated. It didn't harm the lens but now I have a tin foil front lens cap. It is not really the greatest telephoto lens but if I have to go out to 1200mm on my APSC camera, this is the ticket.

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They are. I have a 600mm f/8 Sigma manual "cat" in my bag. The practical difference between carrying that and a traditional lens of the same length is a *lot* of weight. As I use it for long shots, the in-focus (non-bokeh) depth is fine.

The problems mentioned are not the main drawback of these lenses.The real problem is the poor image quality of all mirror lenses available for ilc's.In most cases you'd better take a shorter lens (like 70-300) crop it to the same magnification and still have better IQ.Let's hope Canon will surprise us and make it different :)

Compared to traditional coaxial mirror lenses, it has a much smoother bokeh (no central obstruction) and an adjustable iris diaphragm allowing control of the aperture and depth of field.

I'd missed the existence of the Tech art - sounds useful. As you say, it'll probably only be for fine tuning, though. I have an old Nikon TC-16A that does the same trick, and have used it for focus on a manual 500mm f/4. It works (though it's not optically very good) and us fairly fast, but it's not free of frustration.

Canon has announced the latest lens in its EOS VR System. It's intended to be an affordable way for social media content creators to experiment with new media formats.

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The International Photography Hall of Fame and Museum has announced its 2024 class of inductees, a group that includes photographers, visionaries and historians.

> contrast is easy to bump up, with little cost in image quality as long as you’re shooting in RAW with enough bit depth.

Modern autofocusing telephoto lenses are designed so that only a small internal assembly needs to be moved for focusing, allowing quick focusing. In this Canon patent case, though, the huge front two elements are being moved. Any attempt to add a motor to this design is probably going to result in a dog-slow autofocus.

There is no reason to love mirrors in photolenses. Except for prices and dimensions/weight. You (we?) have to 'pay' for that later (low contrast, no way to increase DOF, slow max aperture, weird bokeh).

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The comapny's bringing its latest chips to some of its most popular computers, and making its nano-texture display available on a laptop.

Wouldn’t the image quality relate directly to the degree of aberrations in the mirror surface and curvature? I don’t see why image quality would *theoretically* be worse. Perhaps it’s ‘just’ really difficult to produce a near perfect mirror?

The Katoptaron is somewhat bulky, but much shorter than a straight long focal 500mm lens, thanks to the folded optical path:http://img1.imagilive.com/0515/Katoptaron.PNG

Variable aperture from f/8 to f/32. Apparently there were two models, with MFD of 6.25 and 16 feet, respectively. That 6.25 MFD is pretty close for a 500mm focal length.

Works like a charm with quite a snappy AF. It only supports the center AF point, but hey: it supports AF, unlike any other mirror lens.

No need to talk image quality up on distances where air disturbances limit resolution anyway. Best is still to walk and then use your 35mm :-)

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What’s the best camera for around $1500? These midrange cameras should have capable autofocus systems, lots of direct controls and the latest sensors offering great image quality. We recommend our favorite options.

I have both a Tamron 500mm F8 Adaptall model 55B and a Falcon 800mm F8 DX which is, I think a rebadged Rokinon. I tried them to shoot the Moon with an OM-D E-M10 II. The Falcon produces softer and less detailed images than the Tamron...

Leica has announced the Q3 43, a variant of its full-frame fixed lens compact with a 43mm F2.0 normal lens. We've had the chance to use and test it, to produce an in-depth review.

Lomography claims its new Lomo'Instant Wide Glass camera, which includes a ~35mm full-frame equivalent lens, is great for portraits and editorial shots.

We don't usually test a product for ten years before reviewing it, but after a decade of using the Lowepro Photo Sport 300 AW II on an almost daily basis, Managing Editor Dale Baskin tells us why he loves this pack.

Catadioptric lenses went 'out of style' so-to-speak many years ago, but for a time they offered economical and compact alternatives to standard long telephoto lenses. The optical design of these lenses use mirrors to both 'fold' the optical path and magnify the image coming in, allowing for a far more compact design.

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What’s the best camera for around $2000? This price point gives you access to some of the most all-round capable cameras available. Excellent image quality, powerful autofocus and great looking video are the least you can expect. We've picked the models that really stand out.

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I own three such lenses:A Samyang 300mm f/6.3, very small and light. This is the one I carry on the go. An old Tamron 500 f/8 with Nikon mount that I use with a Mitakon Lens Turbo Nikon F to E mount; the Turbo makes it both faster (about f/5.6) and sharper. This is the one I use most of the time for birds and small animals.A Rokinon 800mm f/8, very difficult to work with that I use for extreme long reach.All are manual focus, which is not a problem for an old timer like me. Bokeh (plenty of it) can be very nice or ugly depending on the background.

Would you mind explaining that? I don't think the laws of physics are in your favour. (Less weight and bulk, yes. Well-blurred-out background, not so obviously.)

I used to think the same until I pondered that this type of design is what is used in the Hubble Telescope and it does very well.

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Mirror lenses can be quite sharp. A friend had a Questar telescope he used for birding and the detail available with it was superb. The only problem he had with the Questar was keeping it in alignment after it was knocked around in the field.

If only Nikon came out with an auto focus version of their last Reflex-Nikkor I'd buy one. Perfect lightweight telephoto and optically the best design out of all the other mirror lenses and even some tele-zooms.

Above $2500 cameras tend to become increasingly specialized, making it difficult to select a 'best' option. We case our eye over the options costing more than $2500 but less than $4000, to find the best all-rounder.

The central obstruction has to be large enough to illuminate the sensor, but as you go up in size the central obstruction doesn't have to keep growing and so you get more clear aperture.

@photomeeting: I'm legitimately entertained that you dug up that meaning of contrast. The Airy rings in photography are on the order of the size of a pixel (this is literally how diffraction limited aperture is defined). A tiny bit more power moving outward into the Airy rings has no effect on global contrast, which is what people mean when they say that a mirror lens has "poor" contrast. The "poor" contrast of mirror lenses is mostly due to lack of anti-reflective coatings. This could be mitigated in a modern mirror lens design, and it has nothing to do with the central obscuration.

Yes, I have, sort of. Modern cameras with IBIS offer the stabilization, also with catadioptic lenses. Autofocus is a system with two main parts, the focus sensor (on or off image sensor) and the motors in the lens. In my case I have a semi-manual focusing stabilized catadioptic lens. The focus sensor is active, but the catadioptic lens lacks the focusing motor. However the focus sensor can withold the shutter until I manually get the subject in focus. At f/8 this works slightly unreliable, but its far better then fully manual focusing.

Because not everybody has the ISO50 and 1/8000 convenience or an unlimited DR to correct for blown up highlights. Situations where this may come in handy are sun photography (sunspots, sunsets), aviation photography, desert landscapes in midday sun etc...

A new Canon lens patent out of Japan has been raising eyebrows around the photo community this week. The patent describes a 400mm F5.6 lens, which wouldn't necessarily be newsworthy... except that it's a catadioptric lens (also known as a 'mirror' or 'reflex' lens).

Once the newness wore off, he didn't use it much It was just too "long", hard to find your subject since just a slight movement would move the scene considerably to a different part of the landscape. Maybe a 400mm version would be more practical, though I should think a conventional 400mm would be just as practical and probably cheaper.

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Previous mirror lenses suffered from all kinds of optical issues. If Canon could get this right it might be a pretty good deal. Mirror lenses were smaller, cheaper and lighter.

I had the Pentax 400-600 mirror zoom - sounded great in theory, but the poor optical quality and bokeh made it of little use.

Having said that, my particular lens isn't super sharp, so the kind of shots I take with it have to work within that constraint. On the other hand, it only cost me a couple hundred dollars. :)

The mirror lens I use is a Tamron adaptall-2 SP 55B 500mm f/8. The first camera I did this with was a Pentax K-5 from 2010. Most Pentax cameras from then support the AF-delayed shutter function.

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Wow, rehashing a lot of the bile you already spilled...I suppose my grandparents aren't interested in buying a train, even if it's a quite nice transportation solution.I also suppose most people would not take the train to visit their next door neigbour.And most trains make quite some noise, a glaring fault.Does that mean that we should jump at the throats of people that use the train in their daily commute? Or that we should lock up the train enthusiasts?We get it: you need to somehow flame here, and you use some pseudo-arguments (mostly debunked) and...Right. BYE.

I have a Samyang 300mm F6.3 catadioptric lens for my Fuji X-E1. It is very difficult to focus since depth of field is very thin, and needs to be used on a sturdy tripod. Also the lens vignettes strongly at the edges. So Canon might have to include optical stabilization as well as autofocus. Has anyone heard of an optically stabilized catadioptric lens?

You can have a folded (porro prism) monocular and attach it in front of a suitable lens.Zeiss once did such a contraption for their Contax fixed lens SLR.It could of course be made as one solid lens and be mounted as any other lens.So why use a catadioptric design for the same effect?

Nice, thanks for the example photos! Correct me if I’m wrong, but there’s no reason a cat lens couldn’t be made just as sharp as a traditional one, right? And contrast is easy to bump up, with little cost in image quality as long as you’re shooting in RAW with enough bit depth. The bokeh thing is certainly a limitation as is the inability to control depth of field, but for telephoto work those aren’t all that important. Long telephoto lenses are huge and heavy and expensive.

Maybe this would be more for video use than stills? Look at all the nature shows that use STUPID long lenses (1000-2000mm). Having something smaller, lighter could be key for some applications.

fluppeteer: My LM-EA7 does OK AF-tuning focus on both my Spiratone 300mm f/5.6 and my Samyang 500mm f/6.3. Both those lenses are fairly light, which is good for the LM-EA7's drive motor (not clear how heavy Canon would make their 400mm f/5.6 lens if they make it). There's also the little benefit that my A7II, A7RII, and A6500 also get to use IBIS to reduce shake.

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US travel/adventure brand Aether Apparel has made a photographer-friendly waxed field jacket in conjunction with Leica. Is that something we need?

In my experience and from what i have read and heard, less elements is better, assuming CA isn't an issue and on mirror lenses it isn't. They do have lower contrast but that's pretty easily fixed in post with very little penalty.

If you want a compact camera that produces great quality photos without the hassle of changing lenses, there are plenty of choices available for every budget. Read on to find out which portable enthusiast compacts are our favorites.

Mirroring the back surface gives you two advantages:1) Extra freedom for the optical designer, as the glass light now goes through (twice) is an extra set of curvature/glass type parameters that can be used for correction (but introduces a little chromatic aberration). This can potentially eliminate one separate lens in the system.2) It protects the mirror coating. With age front coated mirrors can get foggy, or develop spots in humid conditions.

For certain types of photography and certainly video, I can see in-body IS as an advantage. But I've never felt I had a huge need for it. I also wonder how long the actuators last over the long term with constant sensor movement. I could be wrong, but I doubt it's a cheap fix.

As someone who has used long lenses for a while, my 80-400/5.6 stays at f/5.6 and my 300/4 stays at f/4 except in rare circumstances where I need more dof...

I used CAT's long time ago. I never had to use a ND filter, because they had already a max. aperture of only 5.6 / 8. That said, the 'integrated electrochromic variable ND' would't be a big deal.

When the manufacturers say they've created a camera for 'creators' or vloggers, that doesn't mean they've turned their back on photographers.

:-) interesting !!! - ..but it's not him in this case. Sorry I still don't have access to my lens from here. ( I shall even photograph and post it here. If the inventor's name was found -if I remembered it- I could probably find photos of that very particular only-Mirror-"lens" on the web )Thanks !

I will give the name of my cat lens once the OP will give us the names of those that suffer all kinds of optical issues ... ;-)

Con:- fixed at F8: so slow and no DOF control- sometimes really hideous background blur- low contrast. This is however easy to correct in post processing.

A better name for these lenses is Catastrophic. Works fine in a telescope where you don't care about bokeh, but for a telephoto, no thanks

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This week we're taking a look at another batch of accessories, including fun ways to control Photoshop and Lightroom, and some retro-looking gear for the X-M5.

I had a Canon (or Canon adapted) lens of this sort back in the early nineties and while it was OK for well-lit situations - hopeless in low light - the background blur (now known as Bokeh) was not to my tastes at all.If you want to try this type of lens I'd suggest a 3" to 4" Maksutov-Cassegrain telescope such as a Bosma or Celestron. A fair bit bulkier, but typically have reach of between 1000-1500mm. You'd want a finderscope though as, without an eyepiece to compensate the FoV is very narrow and the image pretty dim.

True, and it'll probably still have the same awful f8 maximum aperture, which nowadays will make autofocusing unreliable on all but top end cameras.

Canon's newest, non-extending 70-200mm F2.8 L zoom for RF-mount includes features aimed at both photo and video shooters. It also works with Canon's RF-mount 1.4x and 2x teleconverters.

The exposure adjustment technology could be useful in other lenses, but I'd much prefer to have iso 25, 10,5 expansion options if that were possible with decent quality.

This is definitely an interesting lens if Canon follow through. If they price it well and design it well it could be a very affordable, sharp, compact super tele, donut bokeh aside.

The RF 24mm F1.4 L VCM and RF 50mm F1.4 L VCM are part of Canon's new 'hybrid' series of lenses designed to work with both EOS and Cinema EOS cameras.

Why is there so much light loss? Also, I wonder if modern coatings might mitigate this somewhat. Is it because of the large size of the central obstruction?

You can stop the lens down, get rid of the doughnuts and get greater depth of field by making your own aperture. Make a front lens cap. Cut a circular hole in the cap - off center and the width of the ring of the lens opening.

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5ds plus 200mm f2.8. crop it to 2x equivalent and you have a lightweight 400 5.6 in terms of depth of field. No need for teleconverter and beautiful bokeh. So long as you only need around 10MP you're golden. I do this with a 13MP 5d classic and live with much, much smaller output resolution sometimes. If you want better image quality you're better off with a wider aperture; the magnification these days - imo - is not worthwhile without corresponding wide aperture e.g. 300 /400 f2.8. For greater depth of field shots, you might as well be using a crop sensor (or crop of full frame as described above) unless you're printing billboards....in which case you'll not mind carrying a big white for the better quality.

I didn't find the one I had half bad really; awesome reach and very portable. Not suitable for large prints or cropping which is why you typically see small images from it posted online. What I liked most was the absence of CA and the light falloff. As for an ND filter..found no use for the 4x drop-in that came with the Minolta.

EVERY obstacle in the lightpath causes diffraction and reduces contrast. Every piece of dust, for example. This is especially true for such a huge secondary mirror.

It's certainly an interesting Idea. I never owned a "Cat" back in the day, but a friend of mine did, it was an "off brand" of around 800mm if I recall. It had OK image quality but it was middle of the road sort of graphics..

If it comes to image quality, mirrors (CAT) are a compromise only. I (we?) totally accept that compromises at a 8 meter (diameter!) telescope, but not at a 400mm telephoto lens.

I think this patent is of type 1. The invention is to use variable attenuation in order to accomplish a similar function as an aperture.

"IBIS in a SLR doesn't stabilize the viewfinder" that's true, but the best stabilization of today's cameras is the combination of IBIS and in-lens-stabi. Look at Olympus and Panasonic. I know, they both have electronic viewfinders, but nevertheless they use in-lens stabilization and their systems could even benefit with a reflex viewfinder.

Other advantages of a catadioptric lens design includes very nearly eliminating chromatic aberration and off-axis aberration; but, of course, this kind of lens design doesn't come without its drawbacks.

I love mirror lenses but they are not a tool for getting high resolution images by any means. That doesn't mean they aren't valid for creating art though.

Stopping down with a CAT lens is not that big a deal. Here done quick and dirty. Of course they would supply a nice round cut-out:

@Max Iso:But very low contrast details of the subject (usual problem for telephoto lenses) ends in NO contrast in the image. They become invisible.

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Wouldn't be an electrochromic stepless variable ND filter, integrated either in the lens or in the body, a great feature for videographers who want to shoot with a constant and shallow depth of field ?

A problem though with cat lenses is that while the aperture may be f/5.6, the t-stop is likely about 1-1/2 stops less, so more like T/9 or T/10. So you have the disadvantage, especially significant for long lenses of a slower t-stop, but you still have the very shallow dof which you can't (usually) increase.

Second. The focusing systems on modern day cameras will probably go nuts with them. I guess this would probably be a manual focus only lens.

In my DPR gallery, there are some Moon shots taken with the Tamron SP 500mm F8.0 Adaptall Mirror Lens 55B and an OM-D E-M10 II. I did not find the results "pretty bad" at all. But that is just me...

"Catadioptric lenses do, however, have several drawbacks. [...] Their modulation transfer function shows low contrast at low spatial frequencies."Source: https://en.m.wikipedia.org/wiki/Catadioptric_system

With all the software-based enhancements happening these days (image stacking, distortion correction, red-eye removal, artificial bokeh, etc), I wonder how difficult it would be to correct the donut bokeh in-camera.

In the end, it seems manufacturers (or consumers) decided that the drawbacks of catadioptric lenses were not worth the ultra-compact design. But as more and more photographers seek to lighten their kit, maybe Canon sees an opportunity to bring the 'mirror lens' back into public consciousness.

I'm Back and Yashica launch a digital film module as a full product, nearly a quarter of a century after Silicon Film failed.

Source: I work on ultra-high-contrast imaging on the largest telescopes in the world. Dealing with the consequences of Airy rings caused by a central obstruction and secondary supports is literally what I spend my days doing.

We often read about patents. They create expectations but few come to fruition. Patents are used to block competitors as well as creating marketable IP and if the marketing minions think they can something with it as some stage, it might even go into production,.

Why on earth would you want to decrease the amount of light coming in a lens like this without increasing depth of field? No wildlife photographer says "Gee, if I only had less light, I could make a picture out of this!"

Minolta did that (fast autofocus) years ago with the 500mm f/8 AF Reflex. There was also a Sony version, both in A mount and both no longer in production.

Probably not difficult at all, if these lenses were popular enough for Adobe et al to bother making that feature. You could do it manually without much difficulty but it would be time consuming and tedious.

There is a big advantage to these lenses in that they can be made into very large apertures, and this can overcome the loss of contrast from the central obstruction. An 8" cat is as sharp as a 6" diameter lens, but a heck of a lot cheaper. I've shot photos through a 14" catadioptric scope, and it was amazingly sharp.

Focus is difficult. I was shooting a few months ago, with an old Spiratone 500mm f8 mirror lens, on a Canon 1D MkII. Some of my subjects were coming at me -- specifically, on a zip line cable. All I had to do was pre-focus and blast away at 8fps. Some of those were decent.

It will be interesting to see how they compare. I was surprised to see that it's a 400 F5.6, as they already have an older standard lens version which is still very good, but old. However, it's light weight and easy to carry. These new lenses appear as though they will be large.

It comes down to the accuracy of the mirrors and the traditional lens/lenses. So it's a different process, but certainly there _is_ a process.

As you go up in size, normal lenses get much heavier and more expensive. There is a crossover point where this tech makes a lot more sense. Look at an 11" Celestron Edge for example--amazing focal length, and very sharp. Nobody makes an 11" diameter "normal" (refactor) lens.

I don't think this design is inherently soft, it's just many of the mirror lenses that have been made happen to be cheap and poorly constructed. I have a Celestron C90 cata (maksutov cassegrain) and it's very sharp and was sub $200.

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"A central obstruction has the effect of transferring light from the Airy disk to the diffraction rings. This light transfer causes the image to loose contrast. The bigger the central obstruction , the more contrast that is lost.“Source: http://www.laughton.com/paul/rfo/obs/obs.html

The cat is very compact. It also is almost free from chromatic aberration. It also is kind of cheap. I see some advantages there :)

Hmmmm.... I can't see the point. It's rare that f5.6 - 8 reflex lenses can't be used at base ISO and you need to stop down to reduce excessive exposure. You might in some circumstances want a smaller aperture to get more DOF but this electronic ND filter isn't going to do that for you. The real problems with reflex lenses are 1) modest resolution - good refractors are better - and 2) the dreaded dough-nut bokeh that draws attention to itself and just isn't the way we see the world. Solve that, and you might have a winner......

@photoMEETING,I must apologize. I forgot to take into account that I use my cat lens on cameras with cropped sensors ! This is certainly the reason why vignetting, lateral CA and geometric distortion are barely noticable... I do not have the possibility to check on an FF body...

Nice re-approaching...No matter if it's Canon effort or any other manufacturer...I think that current tech can add a useful low cost touch too...

There do exist off center telescopes. I do think an off center tele lens would be awkward though. And ... I assume the bokeh will not be all that oretty.

Also, be careful with focus and recompose technique: your subject may get out of focus due to the small DOF. I just shoot with the subject in the center and "recompose" afterwards by cropping.

My 500mm Canon FD mirror/reflex lens from many years back has had a new life over the past couple of years, mounted on a Sony A6000. It does a good job, with its 750mm equiv. when I need the extra reach.I certainly would be looking at this lens if it makes it to production.

A faster sensor, improved autofocus and video see Nikon's third-gen mid-range full-framer go toe-to-toe against Canon's EOS R6 II and the Sony a7 IV. We feel its all-round ability lifts it to the top of the pile.

I've tested this between my Soligor 500mm f8 cat and both a 200mm f2.8 prime and a zoom at 200mm f4.8 on its long end. In both cases, I get better IQ and image acuity by cropping a 200mm shot than with the 500mm cat. That said, I the cat has a slight advantage on weight and manual focusing (larger barrel so larger focusing ring, plus it has a finer focusing pitch), so sometimes I prefer it for its rapid shooting times (camera to eye, focus, shoot). But when I need IQ, prime glass rules.

@geekyrocketguy:If this ist true:> I work on ultra-high-contrast imaging on the largest telescopes in the world.you really, really should know better than that:> A tiny bit more power moving outward into the Airy rings has no effect on global contrast.

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Contents · 1 Focal length. 1.1 Derivation using Snell's law · 2 Image formation · 3 Physical optics · 4 References ...

I've owned a couple of the old Nikkor 500mm mirror lenses -- bought the first one in 1986, the only new Nikkor I've ever owned. Image quality could be good in the right conditions, but the basic problem I found was one of steadiness. These lenses are very light for their focal length, and hence very susceptible to shake. I found I had to shoot from a very rigid tripod or put it on a monopod so I could act as an absorber. Maybe newer bodies with stabilization could solve that. https://www.flickr.com/photos/tags/nikkorcreflex500mm

The theme for our November Editors' photo challenge is 'Fog'. Show us your favorite fog photos for a chance to be featured in our winners' gallery later this month. This challenge is open to photos taken at any time.

Resolution on my Samyang 800 is fine. Contrast is down. Works well on my D7000 where its 1600mm. Heavy tripod and remote are mandatory. Skyscapes, landscapes where you want the atmospheric blue as an indicator of dof.

I like mirror lens, it is a low cost solution for wildlife photography as long as you do not need top notch image quality. As far as I know not much has changed in the optical design over the years, I believe only the coating and precision of the mirror improved. There are two best mirror lenses I've ever used, namely Tamron and Russian MTO 3m5ca both 500mm/f8, I particularly like the MTO, it is still available in very reasonable price today. One thing to note on mirror lenses, in particular the Russian made ones, the mirror always mis-aligned and over tighten, caused the focus to shift at the far end, after 'relaxing' the mirror I was able to push further the far end (beyond infinity) so that allowed me to use any screw adapter still remain true infinity focus. Btw Russian mirror lens uses M42 instead of T2 mount which has slightly different pitch, don't force in or you will break the mount !

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Aside from that, the TechArt Pro LM-EA7 can't AF in a very wide range with a mirror lens, but it can use AF to tune approximate manual focus -- which is quite useful with the shallow DoF that mirror lenses have.

Jan 21, 2024 — Applications of Diffraction Gratings · The ship is receding, so the source of the light is moving away from the receiver. · dsinθ=mλ⇒sinθ=λd.

How about an off-center catadioptric lens? Does such a beast exist? Essentially, it would be like a cylindrical section of a normal catadioptric lens plus extra housing for the secondary mirror. The front element of the lens would be off center with respect to the sensor. The advantage is that you wouldn't get the donut bokeh. But maybe instead you'd get some other weird asymmetrical bokeh.

I've long wanted a 450mm f5.6 mirror lens for shooting sports. It would provide a well-blurred-out background, probably comparable to a 400 f2.8 with a lot less weight and bulk.

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Yeah, and an E-mount version would be very welcome, I think. It’s exactly the kind of system where such compactness will be valued.

Yes but the Hubble sensors are 0.6 megapixel. It doesn't take much resolution to satisfy that sensor! Most hubble images are composites of hundreds of seperate images.

I've shot with a couple of different cats, including a little with the Zeiss 1000mm f/5.6, which actually had fairly good contrast (for a cat) and excellent 'sharpness'.

While Max Iso is a bit too far down the supposition lane, he still has a point: even if we, the mirror-lovers, are a tiny fraction of the market, you can bet your... jewels ;) that we are still in the tens of thousands (buyers), too many to ignore.We get it, @photoMEETING has a score to settle, but when a telescope man and evidence from sales go against the crusade for eliminating catadiopter optics...Small and easy thing to check: what do you think it would sell best: a lens like 400DO or a future 400 CAT?

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