Who made Spiratone lenses for Nikon

Keyword: Spiratone

Part III: Catadioptric photo lenses from 1946 - today.

(part One do you think ...? Find herePart IIhere.)

The findings from Part II lead to the conclusion that for the from the 1950s emerging catadioptric photo lenses were derived from the diverse "catadioptric dialytes" (Brachymediale) already known for astronomical applications, some of which have been known and among them for up to 150 years Maksutov is a special variant.

A brief history of the catadioptric photo lenses:

With the strong emergence of the mirror lens lenses in the 1960-70s, they formed special design features which are usually not found in this form in astronomical telescopes:

a) Apart from the fact that the photo optics are very robust and hermetically sealed, it was also made increasingly dispensed with the hole in the primary mirror! This means that the rays that are thrown back from the secondary mirror no longer reach the camera or film plane through an opening in the main mirror, but rather through a non-mirrored central area of ​​the mirror surface through the glass of the mirror body to step.

This means that the interior of the optics between the two mirrors is hermetically sealed even better. It also means that the central area of ​​the mirror body is also included in the beam path as a refractive lens element. This area then often forms the sub-aperture corrector in the beam path after the secondary mirror together with 1-3 other lenses. It must consist of lens glass of the highest quality, since this area of ​​the main mirror - in the case of a Mangin mirror - is traversed three times by each light beam!

b) It occurs more and more frequently after 1965 Mangin mirror on, which corresponds to the basic configuration of the Hamilton telescope. First there are primary mirrors of the Mangin type, soon also in the secondary mirror or in both positions at the same time or only in the secondary mirror. As we saw above (Hamilton telescope) the Mangin level is already a basic element of the cadadioptric dialyte - As far as I know, it has never been used as a telescope or astro camera on its own.

Image 1: Mangin mirror - Source: Wikipedia - Author: not known - https://creativecommons.org/licenses/by-sa/3.0/

In addition to the effect as an element of the optical calculation, the Mangin mirror provides two further advantages for the photo lens:

  • The micro-surface structure of the reflective mirror surface resting on the polished glass surface is much smoother than a vapor-deposited aluminum layer on its "open" side, which also has to be covered with a transparent protective layer (mostly Si02).
  • The mirror coating is perfectly protected against the ingress of corrosive gases, moisture, etc. and retains its unrestricted effect in the long term. That alone would be a sufficient reason to prefer this type of construction!

c) Photo lenses of catadioptric design require tubular screens to shield against false light around the central beam aperture in the center of the primary mirror (towards the front in the direction of the secondary mirror) or around the secondary mirror (towards the main mirror) to protect the camera from incident stray light. The tube diaphragms and the problem of false light can be clearly seen on the following lens section:

picture 2: Lens cut with Shielding tube covers against "false light" on Olympus Zuiko Reflex 500mm f / 8 (The light entry is on the right in this picture!) - Source: Olympus product description and specification sheet for the lens

This picture clearly shows that without these two diaphragms, rays of light could pass through the ring-shaped aperture opening (right) directly and without reflection on the mirrors onto the center of the main game game and thus also into the camera! A lens hood in front of the lens can only safely prevent this if the lens hood were extremely long - which of course contradicts the lens concept ...

The existence of these tubular diaphragms in the central area has an impact on the so-called obstruction - i.e. the shading of the light rays in the center of the aperture:

In the case of bundles of rays that enter the optics at an angle from the edge of the image field, the tube diaphragms cast a shadow on the main mirror. As a result, the entire annular mirror surface is no longer "active". It is interrupted in the width of the diaphragm tube. With a suitable image structure, this can be seen in the extra-focal aperture ring images of light reflections, as can be seen in the following in the intentionally blurred image of the roof of the house:

Picture 3:Tube aperture shadow"With the extra-focal blurring rings in the edge area with the Olympus OM Zuiko Reflex 500mm f / 8: the small" Packman rings "can be seen at the bottom left and right - the opening points towards the center of the image. - Source: photo dinosaur

d) The size Corrector lens in the light entry aperture always serves as a support structure for the secondary mirror. As described in detail in Part I, the “obstruction” by the secondary mirror in the beam path leads to a reduction in the contrast of the first-order diffraction image. But at least the absence of spiders avoids the diffraction spikes caused by them in the images of a point light source, as they occur in the normal Newton and Cassegrain.

My personal MILESTONES of catadioptric photo lenses (CATs):

Preliminary remark: the classification of certain lenses as "milestones", which I undertake here, is purely SUBJECTIVE and is based on my - limited - knowledge or my experience. I am aware that other photographers and observers may come to slightly different conclusions based on their own experience.

At this point I would like to remind you again that in the 1950s to 70s, compared to "long" telephoto lenses (> 200mm focal length), not only compactness (overall length) and low weight spoke in favor of "CATs", but rather above all the freedom from color errors (chromatic aberration, "CA") - in relation to the price! The first color-pure telecannons with fluoride lenses were already available in the 1970s - but at an extremely high price using a very sensitive material. Few amateur photographers could / would not afford the price. So I am convinced that the “prime” of the catadioptric telephoto lenses was mainly borne by the amateur segment.

At the end of this article I will make some (well-founded) assumptions about why the catadioptric lens design has almost completely disappeared again.

Here is my brief overview of the time scale and the History of closed catadioptric systemsthat were suitable as photo lenses or were specifically built for them.

I also list the basic developments known to me in the timeline, with it the temporal dimension at a glance becomes visible.

I then list photo lenses from my point of view Milestones in the development of such optics represent. This is not a complete one Description of this lens segment! I am currently trying information about all ever delivered To collect Photo-CATs and hope to be able to publish an almost complete list in a few months.

Almost all known catadioptric telephoto lenses were made for the 35mm format expected. A few drew Medium format 6 × 6 or 6 × 7 from: Carl Zeiss Jena mirror lenses 500mm and 1,000mm, Kilfitt 500mm and 1,000mm and Pentax 6 × 7 1,000mm f8 - as far as I know.


Fundamentals-Invention (Astronomy) of Catadioptric dialyte (also "Brachymedial " called) by Hamilton and then a large number of variants and further developments.

Here is the link to Hamilton's GB Patent No. 3781.

Until recently, an Italian company actually delivered Hamilton telescopes / cameras for astronomical purposes (Ceravolo).


Fundamentals invention (astronomy) of Schmidt corrector plate - this resulted in the Schmidt camera and Schmidt-Cassegrain telescope


Fundamentals-Invention (Astronomy) of Maksutov corrector meniscus lens - this resulted in the Maksutov-Cassegrain telescope - but if you look closely it is a special form of the catadioptric dialyte.

from 1945

Maksutov-Cassegrain 3.5 ″ f / 12 telescopes - Delivery of large quantities of the telescope at Soviet schools, built (initially) probably in Novosibirsk. If you want to know what the school telescope looked like, please follow this link for a very compact biography of Maksutov on Prabook. There you can see a picture of D. Maksutov with "his" school telescope in front of him on the desk. With a similar specification it was named in Poland as "PZO"Manufactured and in the GDR by Zeiss as"Telementor". These devices were also sold to the West (as they brought foreign currency!).

It is noteworthy that the motivation to create an extremely robust, durable and low-maintenance telescope for schools led Dimitri Maksutov to the original idea for the meniscus teslescope design. I see an example in that too the pursuit of the common good can lead to excellent innovations!

In this link to "cloudynights.com" I found more interesting photos of the Polish PZO instrument.

from 1954

QUESTAR Maksutov-Cassegrain telescope 3.5 ″ (in Mass production manufactured until today)

Classic Maksutov-Cassegrain, focal length 1280mm f / 14.4 (Specification from 1961) - was and is also supplied as a telescope tube ("Field Model" or "Birder") with an eyepiece or camera connection.

A cult classic in amateur astronomy. But NASA is also said to have procured some ...

Picture 4: Questar 3.5 ″ telescope with dew cap pulled out - source Wikipedia, author: Hmaag - https://creativecommons.org/licenses/by-sa/3.0

from 1936 to the 1960s Years

At least in Germany (Zeiss), Japan (Nikon) and Russia (GOI) and USA (Kodak) large semi-transportable (mostly catadioptric) mirror lenses for military and satellite-based applications were developed. These were exclusively of the Maksutov type and had focal lengths of 1,800mm - 8,200mm. There is a lot of information about this in the overview article by Marco Cavina in this link. After the Second World War, the optics companies were able to rely on this extensive experience in the development of catadioptric interchangeable lenses for single-lens reflex cameras.

before 1958

First Maksutov-Cassegrain telephoto lenses for SLR from LZSO, Soviet Union: MTO 1,000mm f / 10.5 and MTO 500mm f8 - received a gold medal at the EXPO in Brussels in 1958.

I do not know, when exactly this Maksutov-Cassegrain was brought to the photo market. It still has to be under the strict supervision of Dimitri Maksutov himself who lived until 1964. Are there readers who can help?

Image 5a: MTO-500mm f / 8 - Source: photo dinosaur

Image 5b: MTO-1,000mm f / 10 - Source: photo dinosaur

The archaic design and the solid construction led to the optics (until today) being affectionately known by amateurs as "Russian tons"Are designated. Manufacturer names were and are MTO, arsenal, Rubinar. Unfortunately, the quality of the optics was not always constant, which should often have been due to the built-in mirrors. You can find a report on this (Dr. Wolfgang Strickling) here.

1959/1961Nikon after the Russian MTOs, launched its first CAT with ambitious data as early as 1959, the Reflex Nikkor 1,000mm f / 6.3 - and one followed in 1961 Reflex Nikkor 500mm f / 5. From the early 1970s to the 2000s, Nikon continuously offered that "Reflex-Nikkor-Trio" 500 f / 8 + 1,000 f / 11. 2,000 f / 11 at. Many details can be found in the article by Marco Cavina - for lovers of the Italian language! The 2,000mm f11 were therefore all manufactured from 1971 to 1975 in two versions. That explains well enough why you rarely come across the 2,000 CAT in the "wild".

Image 6: Reflex-Nikkor C 500mm f / 8 - Source: photo dinosaur

1961Carl Zeiss Jena

represents the catadioptric "Mirror lens" 500mm f4.0 at the Leipziger Messe (Developed from 1955by Dr. Harry Zöllner, W. Dannenberg. (A short time later a Mirror lens 1,000mm f5.6, the so-called "Stasi cannon", added). The optics are for Medium format 6 x 6 calculated and delivered!

So far, freely accessible representations of lens sections, resolution and MTF curves are not available for these optics. However, there is a fabulous synoptic article by Marco Cavina in which the Jena mirror lens 500mm f / 4.0 and the Mirotar f / 4.5 are described and compared in detail.

Already In 1941, the designers Robert Richter and Hermann Slevogt developed and registered a CAT system (Richter Slevogt telescope) at Zeiss, which is similar to the "Houghton Telescope" (see Part II), which was registered in the UK shortly before. Both groups probably knew nothing about each other during the war.

This Carl Zeiss Jena mirror lens obviously goes back to these developments in 1941.

In his article Cavina expresses the assumption that the optical performance of the Jena lens does not come close to the lens from Zeiss Oberkochen, which was described below and released shortly afterwards, since it was probably developed as an IR long-range lens for shooting on IR black and white film.

In the blog “Zeissmania” (part II) you can find some pictures that the author himself took with the Zeiss Jena 1,000 f / 5.6 (website of the Burgenland amateur astronomers BAA).

1963Zeiss Oberkochen (West)

represents that MIROTAR 500mm f / 4.5 and produces 200 copies for Contarex. Zeiss designers are Helmut Knutti and Alfred Opitz. Later, another small lot will be made especially with the KyoceraContax connection (c / y) manufactured. Several brand new Contarex lenses were (according to Marco Cavina) converted to c / y in the factory. From 1975 supplies Zeiss MIROTAR 1,000mm f5.6 and makes 20 copies. (All mirotars are for 35mm format expected.)

Picture 7: Lens cut of the Zeiss Mirotar 500mm f4.5 - Maksutov design with two correction menisci but no Mangin mirror yet - Source: data sheet from Zeiss

Specification data sheets from Zeiss with lens cuts can be found here and here.

This is a representative of the “Maksutov faction”, still with a pierced primary mirror.

Zeiss does not yet use a Mangin mirror here! For the required large image field of the 35mm format and the large aperture ratio of f / 5.6, a simple Maksutov meniscus is not sufficient as a corrector for the highest demands. For this reason, Zeiss used a second (inverted) and very thick meniscus beforehand - a solution that Maksutov himself had already used for the large MAK astronomical cameras in Chile and the South Caucasus.

The Mirotar 500mm f4.5 is the reference CAT in the small picture area. In Marco Cavina's article, the MTF curve is shown in comparison with other APO lenses and the 500mm f / 8 from Zeiss: it is far superior to all other optics.

before 1964Canon

posed three superlative CATs for the Tokyo Olympics available, which probably did not fit into the amateur photographer sector, but are all the more remarkable:

  • Canon TV-800 f3.8
  • Canon TV-2.000mm f11
  • Canon TV- 5,200mm f14

You read that right - no misprint! I have no idea in what “numbers” Canon manufactured these optics. So they were obviously used for television with Vidicon. Here you can find more information about this in another article by Marco Cavina (in Italian).

1965 - The US photo distributor "Spiratone

begins a Maksutov-Cassegrain lens 500mm f / 8 - manufactured by LZOS in the Soviet Union - to be delivered in the west. It gets very good test results in photo magazines. Later (at least BEFORE 1983) comes a catadioptric mirror lens 300mm f5.6 added.

1965 to 1980 - this is the period

in the EVERYONECamera or lens manufacturer brought out one or more photo CATs.

Within a very short time it was standard that the Original manufacturer (Nikon, Canon, Pentax, Minolta, Yashica) offered at least two CATs in its program: all had a 500mm f / 8 CAT, as well as either 800mm f / 8 (Minolta) or 1,000mm f / 10 or f / 11 on the long end. There were also some 1,200mm and 2,000mm optics on the market. As I said, I'm working on an overview that is as complete as possible. Pentax brought in in addition to its 35mm line Reflex Takumar 1,000mm f / 8 for medium format (the Pentax 67). As far as I know, this was only available at Zeiss Jena and Kilfitt.

Olympus was an exceptionwhere one hesitated around not until 1982 a single but very compact one Zuiko Reflex 500mm f / 8 to bring out (see below).

The Leica CATs "MR-Telyt-R" were Minolta lenses in a Leica design.

The real ones" Third-party lens manufacturers ("3rd party lenses") also reacted very quickly: apparently first and foremost SIGMAwho have favourited very early (date?) a super-bright 500mm f / 4.0 brought out. I found a report from an American photo friend who found this optics in a completely neglected condition and "processed" it with his own standard resources (respect!). Finally he realized that it couldn't have been that bad.

Sigma then brought the largest "zoo" of catadioptric focal lengths onto the market over the decades. Also the rather unusual focal lengths 400mm and 600mm. I once had a 600 Sigma CAT, but it didn't really convince me.

Of course there were too Tokina and Tamron with their own catadioptric designs - although you have to note that the ones that appeared in 1979/81 Tamron 500mm f / 8 and 350mm f / 5.6 came close to the top group of (later!) lenses from Olympus and Zeiss. The Tamron 500 f / 8 CAT was even a little shorter and lighter than the Olympus 500 f / 8 released in 1982. Image and lens cut here on the Adaptall-2 website. With the 350 Tamron, the screw-on lens hood (you must use it!) Is practically as long as the lens itself.

Makinon was another real Japanese lens manufacturer with mostly quite good products.

In Europe / Germany From 1972 onwards there was no longer any serious SLR manufacturer. However, there were still famous third-party lens manufacturers, above all Kilfitt / Zoomar. It's legendary Kilfitt-Zoomar Sports-Reflectar 500mm f / 5.6 (Late 1960s), described in detail here on the Pentaconsix website - and here this 1970 featured Kilfitt / Zoomar Sports-Reflectar 1,000mm f / 8 both calculated for medium format and can also be used on many cameras with the Kilfitt WE adapter system.

A huge number of private labels offered a large number of CAT variants very cheaply. As far as I know, 1965 was the earliest Spiratone, USA (see above) - where you also knew who the manufacturer was (MTO or LZSO in Russia). With the others, I have no idea who the manufacturer could have been. Apart from the aforementioned Spiratone, I am not aware of any that would have attracted attention due to its particularly high optical quality.

1975 VivitarSeries1 Solid CAT 800mm f11 and 600mm f8

Picture 8: Vivitar Series 1 Solid Cat 800mm f / 11 on the Sony A7RIV (without lens hood) - source: fotosaurier

In the early 1970s I read about a newly published Patent from Perkin Elmer via a so-called "Solid Catadioptric Lens"- i.e. a mirror lens lens that should consist of" a single glass cylinder "(possibly read in Herbert Kepler's" Kepler on the SLR "in Modern Photography?):

Picture 9: Sketch from the patent application Perkin Elmer "Solid-Cat" from 1967, issued 1970. Source: U.S. Patent Application US3547525A

This optics should be extremely short - I was thrilled. A few years later I finally found out in “Modern Photography” that this lens was used as a Vivitar Series 1 optics 800mm f / 11 actually appeared on the market.

Fig 10: Lens cut VivitarSeries1 Solid-Cat 800mm f / 11. It's amazingly close to the original design! - Source: Patent Perkin Elmer Patent Patent application

It was immediately clear that I would have to have it at some point - which then took a few years ... The history of the Vivitar Series 1 optics will have to be reported separately at some point. For us, these lenses were a revelation back in the 1970s - and I still own most of them today!

The two solid cats (600mm and 800mm) build extremely short - but are much heavier than the other common CATs on the market.

It wasn't until decades later that I came across the special story of this lens that fascinated me so much. it can be found in the archives of the "SPIE" in the form of an interview with the Lens designer, Juan L. Rayces (1918-2009). This also includes a photo of the designer with his lens on the tripod - on the busy beach! (Probably unthinkable today ...)

Perkin Elmer also supplied copies of this lens under its own brand (and also special versions to NASA).

Fig. 11: Solid Cat version 800mm f / 11 under Perkin-Elmer's own brand - Source: fotosaurier

What really happened under the brand "Vivitar Series 1": production started in 1975 - but was stopped again after 3 monthsbecause Vivitar found it was too expensive for an amateur lens. Therefore, there is actually only a relatively small number of lenses worldwide (although it was heavily advertised at the time - also in Germany).

1978Minolta RF Rokkor 250mm f5.6

Picture 12: Lens cut Minolta RF Rokkor-X 250mm f / 5.6 - Source: Minolta data sheet

In descriptions, the Mangin mirrors are often highlighted as an "innovative step" in themselves - which is not correct if one assumes catadioptric dialyte (from 1814!). Also, the name of a "Rumak", which I have already read, is not really accurate: Rumak would describe a Maksutov type who - named after Rutten as Rutten-Maksutov - does not use the mirrored spot on the back of the meniscus as a secondary mirror, but a Cassegrain secondary mirror mounted on a pedestal on the meniscus. But this look is not a Maksutov type at all.

This look just has an excellent one Brachymedial design - especially taking into account the short focal length and extremely short length of 58mm (without lens hood).

As with all CATs, the use of the lens hood is strongly recommended!

Picture 13: Minolta RFx Rokkor 250mm f / 5.6 (without lens hood) - Source: fotosaurier

Fig. 14:Size comparison between RF Rokkor and a fast normal lens (Olympus OM 50mm f / 1.2 - but this is the most compact of the f / 1.2 normal lenses. My today's Sony GM-50mm f / 1.4 has about 3 to 4 times the volume of the RF Rockor ...) - Source: fotosaurier

The RF-Rokkor 250mm f / 5.6 opened a new focal length segment for catadioptric lenses at the end of the 1970s with a really big hit in every respect - optically as well as geometrically! Maybe it was in the air too? - Immediately the third-party lens manufacturers romped about in this segment, but interestingly, none of the major camera manufacturers followed Minolta in this segment (as far as I know ...). I consider the focal length range (250-350) to be very sensible, since the "average amateur photographer" is easily overwhelmed with the manual focusing of 500 lenses - see my remarks at the end of the article.

The focal length of 250mm was only once “trusted” by one of the third-party lens manufacturers. The product was probably only sold through private labels - known in Germany as “Berolina 250mm f / 5.6”, elsewhere also as “Focal” etc. I don't know who the designer or manufacturer was. The optical quality is rather modest and the optics are also much larger than the RF Rokkor (almost as long as the Olympus Reflex 500mm f / 8).

The other optics were all in the range of 300mm (f / 4.5 to f / 6.3) or 350mm f / 5.6 (Tamron - very good optics!) - there was even a Russian Maksutov type (Rubinar) and an astro manufacturer like Celestron have tried that. The Spiratone brand was also there again (much praised!).

1978/79Celestron (Schmidt-Cass.) 750 f / 6.3 and Questar (MAK) 700mm f / 8

These are attempts from the astro device segment to offer pure photo telephoto lenses (which the Russian MTO had done very well in the past - until today!).

Celestron (1978) was the only thoroughbred Schmidt-Cassegrain lens that was brought to the photo market. It disappeared again from 1986.

The QuestarDevice (1979) was also not long on the market as the "bright Maksutov type".

Picture 15: CAT telephoto lens "Celestron 700" 700mm f / 8 - source: fotosaurier

High quality and superbly built - but the photo market works differently than the “astro niche”.

1982 - Olympus OM Zuiko Reflex 500mm f / 8

Picture 16: The compact Olympus Zuiko Reflex 500mm f / 8 on the "petite" OM4Ti (lens hood inserted) - Source: fotosaurier

I especially highlight this 500 CAT because it has practically no defects - apart from the lack of a tripod connection, which would have contradicted the Olympus concept! Its most noticeable advantage is that excellent image contrastthat makes focusing easy (very sensitive!) - even without the focus magnification on the digital system camera. The picture “jumps” into the sharpness zone. The image structure (“rendering”) - including the background! - very nice. The pull-out lens hood is also very practical.

Picture 17: Example of the beautiful rendering with the Olympus OM Reflex Zuiko 500 f / 8 - Source: fotosaurier

Picture 18: Lens cut Olympus OM Reflex Zuiko 500mm f / 8 (Light entry from the right! - Lens hood pushed in) - Source: Olympus data sheet

Together with the Minolta AF Reflex 500 and the Mirotar 500mm f / 8, which appeared almost 20 years later, it is the best 500 CAT that I know personally and practically. Both mirrors are Mangin mirrors. The most noticeable thing is that ALL optical elements are here in just two groups around the two mirrors are combined! It is that CAT with the lowest number of glass-air surfaces. I suspect this is part of the secret of the superb image contrast.

In my most recent measurements with a Nyquist frequency of the sensor of 3,168 LP / BH I am measuring with the Zuiko-Reflex approx. 1,500 LP / BH (corresponding 125 lines / mm) in the middle of the picture - in the outermost corner at approx. 860 LP / BH. I give the resolution values ​​for 30% contrast (as is usually the case ...) For analog photography at the time, these were the values still exceeded the practical film resolution (especially with ISO 400 films - or even higher ISO values!).

As far as I know, only the Tokina 500mm f / 8 is significantly more compact than this optic - but that plays a league below that in terms of optical quality. The Tamron 500mm f / 8 is also a bit shorter - but you have to screw on a lens hood that is almost as long as the lens itself!

1982/83Vivitar Series 1 450mm f4.5

The dating is certain here: October 1982 the lens was presented at the Photokina in Cologne. As far as I know, it was made for a year from 1983. There is also another one 2-way teleconverter, which is specially calculated for the optics and is connected directly to the T2 thread.

This look has nothing to do with the Vivitar Series 1 "Solid Cat" that were previously delivered!(That had been accepted in isolated cases ...)

This is probably the most exotic catadioptric photo optic (so far) that has actually made it onto the market! - Clearly a case for the "My Crazy Lenses"- soon here in this blog ...

The design comes from the optics design company OPCON Associateswho have favourited the former Perkin-Elmer employee Ellis Betensky Founded in 1969 with two other partners (Melvin Kreitzer and Jacob Moskovich) - and which still exists today (since 1996 without Betensky).

Fig. 19: Vivitar Series 1 450mm f4.5 (Length 150mm - without the lens hood) on the Olympus OM - source: fotosaurier

After an intensive search I finally found the patent for this catadioptric lens: U.S. Patent 4,523,816Registered 1983 for Vivitar. Other than often read is than Inventor Melvin Kreitzer registered and not Ellis Betensky. The pictures "Fig.3 and Fig.4" can be viewed by clicking on "Full Pages" (on the left edge).

Image 20: Rough lens cut sketch from the U.S. Patent 4,523,816 for the Vivitar Series 1 450mm f / 4.5 - Certainly does not correspond in all details to the final manufactured lens - e.g. the thin flat glass plate closing towards the front is missing (see FIG-4) - source: US patent 4523816

The EXOT has four highly innovative features:

a - According to the specification claims, the (very thick!) Front corrector L1 consists of PMMA plastic ("acrylic glass").

b - The corrector L1 has one on the front aspherical surface! ... a kind of "disguised Schmidt plate"?

c - The system has one Inner focusing by shifting the corrector lens group G2. This changes the focal length of the lens in close-up.

d - The front plastic corrector element L1 is on the front of the lens protected by a thin, plane-parallel glass pane(missing in Fig.3 - only indicated in Fig.4 of the patent).

More information about this lens in the article in the series "My Crazy Lenses" soon.

1989Minolta AF Reflex 500mm f / 8

Fig. 21: Minolta AF Reflex 500 on the Sony A7RIV (with lens hood) - source: fotosaurier

Picture 22: Minolta Autofocus 500mm f / 8 - Source Minolta lens specification

Minolta has thus - 4 years after the introduction of the AF-SLR as the first worldwide and to this day the only manufacturer - did something that was actually considered "impossible": function of a reliable one Auto focus at aperture 8! I had the lens on the Dynax 7D and I still use it to this day on the Sony A7RIV (with adapter LAEA4) - it works excellently and very quickly even in low light! The lens was delivered with the Sony A-mount for a long time and is available in almost any quantity and at a reasonable price Japanese used market to obtain - rather rare in Germany and much more expensive than in Japan!). It is also one of my "crazy lenses". (Report will follow in a few weeks!)

The construction used two Mangin mirrors and is similar to the design of the Minolta RF 250mm f / 5.6. In terms of image quality, it is absolutely in the top league - because of the basic focusing difficulties with manually focusing CAT lenses the autofocus is a great qualitative benefit in practice!

I consider it - together with the RF Rokkor 250mm f / 5.6 - to be the D-SLR and mirrorless system camera under today's conditions most useful historical CAT - Can also be used free-hand for "normal everyday photography". The class of manually focusable 500 CATs is otherwise something for the Staiv!

1997Zeiss Mirotar (for Contax c / y) 500mm f8

This is the last relevant 500 CAT (from an original manufacturer)that came on the market - and it's one of the best, which Zeiss has now brought out as a “late-giving birth”. However, one can see from Marco Cavina's MFT curves that it does not come close to the outstanding 500mm f / 4.5 reference lens. (I think: that's not a shame - about 800 grams compete against almost 4 kg ...)

Picture 23: Zeiss Mirotar 500mm f / 8 from 1997 - source: Zeiss data sheet

This lens now has all the features of the "modern" CAT construction: Mangin mirror and non-pierced primary mirror. However, it is no longer a Maksutov type, but one Hamilton construction with sophisticated sub-aperture correctors. The Mangin primary mirror is unusually thick! In addition to an extendable sun visor, the lens had a very slim, rotatable tripod mount - so it was perfect in every way.

Image 24: Zeiss MIROTAR 500mm f / 8 - Source: photo dinosaur

At the beginning of the 2000s, many brand new Mirotar 500mm f / 8 lenses suddenly appeared on offer at a price of 500 EUR (below half the list price)! There was a rumorthat a whole container with these lenses had been stolen - after that it would all have been stolen goods ... Or maybe Zeiss had just made a larger batch in advance and tried to get rid of the goods in good time before the Kyocera-Contax-SLR (2005) was discontinued be - so it found a radical sale instead of? I don't know what really was the reason - but I bought it. I.When compared to the Olympus CAT, I found that both lenses are equally at the top of the field of competitors (at the time with comparison on analog film