For the opportunity to review MS MTO-11 10/1000 Many thanks to Alexander Gradovsky.
TTX MTO-11 10/1000
Focal length: 1000 mm
Aperture: F / 10
Filter Diameter: 120 mm
Optical design: 3 lenses, 2 mirrors, 5 elements and 3 groups
Mounting: replaceable, in this case "H" (similarity PRE AI without iris control for Nikon)
There are several options for the MTO-11 10/1000 lens. This review presents precisely the MTO-11 MS 10/1000 1983 model year, Lytkarinsky Optical Glass Plant... There is also the "CA" option, as well as different MC and non-MC lenses, and a somewhat similar lens MTO 1000A 10.5 / 1100. Strange but both versions MTO-11 10/1000 SA (letter A is indicated) and MTO-11 10/1000 (without the letter A) can have an interchangeable shank.
The lens has a very large (huge) focus ring, which rotates all 360 degrees, from 8 meters to infinity. In fact, the lens has infinity race и run towards MDF less than 8 meters. Focusing is very smooth, when focusing, the front of the lens travels only 1 cm forward. Infinity begins after 200m on the focus distance scale.
DOF Aperture and Scale
MS MTO-11 10/1000 not has iris control rings and does not have DOF. The aperture is always in the same value and can not be changed, such is the design of the lens
The lens has a wonderful telescopic hood, which helps him a bit to improve images in side and backlight. The whole lens is made very soundly, like a piece of metal pipe. A very useful property of the MTO-11 10/1000 MC is two types of tripod sockets - wide and narrow. The narrow socket fits modern tripods. And also, the protrusion with slots is duplicated on the lens with a shift of 90 degrees, which allows you to use the lens in both landscape and portrait orientation of the camera. This is really a very good design. The front lens (meniscus) is simply huge - 120mm. In the kit, the lens comes with several filters (just huge) and a nice black case for transportation. The disadvantage is the front cover, which simply puts on and does not snap into the thread of the front lens, the cover often flies off the lens by itself.
Second life on the figure
The MTO 10 \ 1000A lens received a real second life on digital SLR cameras, and the scope of its use has expanded significantly on the central brake cylinder. The lens gained great opportunities due to the ability of modern CZK to shoot at very high ISO. It decreases very much excerptat which you can shoot on the lens, which allows you to “freeze” fast-changing scenes during the day. Usually, MTO 10 \ 1000 was used for highly static scenes where long excerptswhich were the only solution to combat the small aperture of the lens. So, at MTO 10/1000 it was popular as an astronomical lens, on which the moon and stars were shot. It was very difficult to shoot a more or less scene in the afternoon with rapidly changing details in the frame. For example, on a sunny day, using a film with ISO 100 due to the fixed aperture of the lens, excerpt should be 1 \ 100. To shoot during the day, you need a very strong tripod to avoid movement. In those days, even a film with an ISO 800 value was quite difficult to find, because the problem of stirring was very, very serious. Using on modern cameras short excerpts from 1 \ 1000 to 1 \ 4000 with an MTO 10 \ 1000A lens and high ISO values, you can not be afraid for lubrication, using a monopod, which greatly increases the mobility of the lens.
Mirror lenses are said to have a much lower effective aperture than indicated. This is due to the fact that when calculating the value of the number F, the front compensating mirror, which is not taken into account in the calculations, is not taken into account. Therefore, the real diaphragm of MS MTO-11 10/1000 has a value of the order of F / 16.0. If you have any information about this, I will be grateful for the informative link in the comments.
How to shoot on modern cameras and MS MTO-11 10/1000?
The lens of the MTO-11 10/1000 has interchangeable shank (back). Unfortunately, in the name of the lens there is no letter “A”, which is responsible for this possibility, because you just need to know. Interchangeable shank can be chosen as you like. For the Nikon system, I used KP-A \ N, as a result I got a lens with a native mount for Nikon. You can read how to use old lenses on Nikon in the section Soviet optics. For the Canon system, the easiest way is to use two adapters: KP-A \ 42 + M42-Canon EOS, in more detail in the section old lenses at canon.
Personally, I managed to shoot on the MTO-11 10/1000 MC holding the lens in my hands, using the automatic ISO up to 6400 and the minimum shutter speed from 1 \ 1000 to 1 \ 4000, though I had to use sharpness to get into sharpness bracketing focus and make inhuman efforts to hold the lens in his hands. So I got pictures of nature in motion, for example, fly of butterfly, which earlier, in the era of film cameras, it was very, very difficult to do on the MTO-11 10/1000. Of course, taking a tripod is much easier.
Attention 1: when used on modern Nikon central control centers, confirmation with a green dot does not work, and the electronic range finder does not work either. You can focus in Live View mode only with a tripod, and the tripod must be very, very strong. Using flimsy tripods and Live View, the picture on the display will “twitch” very much, which causes inconvenience and makes you nervous. Take off hand in Live View does not work. Taking off the hands, the lens will respond to any of your movements, even heartbeats will be displayed in the viewfinder with light jerks of the image. I do not see any possibility at all to use the lens with my hands. Personally, I managed to run with the MTO-11 10/1000 MC without a tripod for exactly 30 minutes, after which I was no longer glad that I had got out into the wild.
Attention 2: due to its size and weight, the lens can break the camera mount, therefore, it is strongly recommended to hold the lens itself with the camera on it (it will not work otherwise). Also, due to the size, the possibility of grabbing the handle of the camera is lost and access to the buttons that are on the left and right of the mount is lost. It’s very unusual that you can’t take the camera by the handle. Pressing the shutter button in this state is not very convenient. But, on the other hand, the lens does not catch the flash on my Nikon D40, D80 (precisely verified). In general, MC MTO-11 10/1000 is contraindicated for girls photographers.
The lens gives quite normal image quality, slightly contrasting, but for a digital camera this is not a problem. Contrast falls under strong side and back light. Sharpness is average, but sufficient for normal shooting. Most importantly, there is no chromatic aberration, distortion and vignetting and a unique bokeh in the form of bagels.
Sample photos on the cropped CZK
All filmed on APS-C Nikon D200 DX, untreated, on-camera JPEG L, in image processing mode VI. Reduced size to 1600 * 1200 and imprinted data from EXIF. On camera with crop factor 1.5h EGF is 1500mm (one and a half meters of focal length). All removed from a monopod.
Examples of photos on a full frame (Full Frame)
All filmed on APS Nikon D700 FX, no processing, on-camera JPEG L, image processing mode VI. Reduced size to 1600 * 1200 and imprinted data from EXIF. Everything is removed from the tripod and from the hands.
Catalog modern brand lenses 'Zenitar' и 'Helios' can look at this link.
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MS MTO-11 10/1000 unusual vintage super fix telephoto. It is difficult to use, the lens is very small aperture, but the MTO-11 10/1000 MC is interesting for its ability to shoot remote objects and interesting bagel-shaped bokeh.
Material prepared Arkady Shapoval. Training/Consultations | Youtube | Facebook | Instagram | Twitter | Telegram | Assistance of the Armed Forces
I had this TV set in Soviet times. Filmed with Zenit-18. Great lens. There is really one big BUT. I don’t know under what circumstances two men were filmed here in the summer, but at a long distance you will not get such a picture. The farther you take, the more visible heat flows from the ground. I tried to take ground photographs in the summer (Petropavlovsk-Kamchatsky) from the dock where the ship was standing, to the shore, objects on it (people, buildings ...), this is about a couple of kilometers, nothing interesting came out. The updrafts spoiled everything.
For unnecessary sold it. I did not find application then.
Look at shutter speed and sensitivity. Probably for good reason she was bullied on a sunny day.
This is very true noticed.
But the decision is elementary - shoot more shots. 1 out of 50 is likely to be great and 40 to be married.
There is nothing surprising in the photograph you are talking about.
Distortions from heat fluxes depend on:
* From the distance to the object. The farther the more distortion.
* From cloud cover. In the presence of clouds comes to a minimum.
* From the surface of the earth - the asphalt road will show just mirages, and the grass and especially water will be much less.
* From how long the Sun appeared. If only because of the clouds peeped out
* From the time of day. In the morning, until the earth has warmed up, everything is fine.
30 years have passed since Soviet times ended, and the time has come!
Here's some advice on how to shoot so that the turbulence doesn't distort the pictures! Set the shutter speed to at least a second, and adjust so that the exposure is correct. Set the photosensitivity to 100 (or less), remember the filters included, they will darken the image. You can twist them together. If it's still not dark enough, wait for the evening.
Here's how it goes:
I plan to use for VIDEO. So even the dynamics of space appear. Times are not right. You can make movies.
That's right, to remove the ground from him is such a thing. It's a TELESCOPE.
it is dark for a telescope
Come on? Telescopes like Maksutov-Cassegrain are generally f / 13 usually.
In Chinese telescopes, the lens diameter - (light transmission coefficient) is even worse. MS MTO-11CA has at least 116 mm. The price is dumbfounding 87-250 tr.
Greetings. Is it possible to install this device on the Nikon D7000? I tried to put the 630th, but rested against the beak of the built-in flash
I support the question !! help with advice please !!
I put it on canoon D600 using the MS K-1 2X CONVERTER https://radojuva.com/2015/05/mc-konverter-k-1-2x/ perfectly installs and does not interfere with flash
Guys, this lens has an “A” shank, which means that it protrudes at least 12 mm to the landing plane.
The first photo of this article shows just very well from the side that Nikon normally stood on it.
What is wrong with you?
Maybe you confused the name of the lens?
Send a photo “as you did not get up”.
Well, it will be an extremely intimate photo. In addition, everyone did not get up for various reasons (age, not beautiful, tired, ...)
No sex. Just the reasons and ask to send - "How did not get up", and not "what."
N-mount adapter or K2. for all types of cameras. Adjustment to infinity will have to be done independently. Even two cameras of the same brand and type differ in the rear working segment.
Replacement T-mount + pairing ring with your camera.
Lens MC MTO 1000-11CA can be installed on Nikon 7000 without any problems. Through an adapter M42x1-bayonet Nikon F. At the same time focusing at infinity is maintained. The distance from the "beak" of the flash to the lens is 5-7 mm.
You can screw a thin extension ring between the lens and the camera. just allows you to slightly push the device and the flash will not rest. while the focus range is still working
through the macro rings)
When installing the adapter, the rear structure is lengthened. Nothing interferes, though you need to reach the button for fixing the bayonet position. As for the weight of the lens, we mount it not for the camera, but for the lens. The best option is to attach a #4mm curved aluminum connector between the camera and the lens. We get a more durable design for shock and vibration. To zoom in on an object, you can use macro rings, it's better than a teleconverter.
Thank you so much for your articles! I'd like to see a review on MTOM Leningrad.
its sharpness is satisfactory, but the depth of field is simply nonexistent, zero! centimeter - maximum!
Unfortunately, this is true for all SLR lenses, and even telephoto ones, but you can stop the aperture there. When shooting VIDEO, it's not so important - one object enters, another exits.
Hello, did you compare this lens with compact super zoom cameras like the Canon Powershot SX50 SH? Or maybe there is some opinion on this? Personally, I tend to compact, because it is easier
Yes, here you can not compare. When the lens operates at infinity, the rule is simple: the larger the sensor, the higher the resolution, the smaller the sensor, the lighter the optics.
Thank you, but I want specifics; I do not have a full understanding. Let’s say I take a picture on Sony A7 plus this MTO 1000 and then I compress the picture to 10 megapixels. And I’m also shooting a zoomcompact, after which they also reduce the photo to 10mp. What will be the final difference in the pictures?
Read for example: https://radojuva.com/2014/01/future-1-21-gigapixel/
The final difference is that the resolution of the matrix (MP) does not determine the resolution of the lens-matrix system. And on a snarled picture with Sonya, more details will be visible than from the compact.
More M/pic allows for further computer processing. Draw what is not there. The quality of the optics - separately. The quality of the receiver (CMOS matrix) separately. Everything is important.
The more m/pic, the more opportunities for point processing of the object in parts. At 3-5 m/pic, there are large squares on the stretch. Processing is not possible. The future belongs to the large format of 13x18 cm, high-aperture, overall, glass lenses. It is good to get into the large intestine or even much deeper with a miniature camera.
https://www.youtube.com/watch?v=VX8Qbbzn6Vo MTO 1000-AM TEST (HD 1080p)
Comparison video "MTO 1000-AM" on DSLR Canon 700D and "superzuma" Panasonic HC-V700 26x
I recently “reanimated” a Rubinar 10-1000 postojus not to use obscenities, but b… how much shit I removed from the lens this is not… ..ts I list 1e d). what a moron you need to be so that the shank is attached to 1 micro screw size 0.5 mm. and when the focusing is screwed several times with a pressure force of about 3 kg or more, the micro screw simply breaks (I corrected) 2homno the same, but on the focusing ring only 3 micro screws that endure the load even more, but break off, (fixed), applied silicone, everything turned out correctly and the temperature balance is not an obstacle (no bends) when changing temperatures with an estimated margin from min-40 to +50 and there is no obstacle to disassembling the ring .3) d. The question is why a hood is needed, yeah well, so that the side set does not interfere, but not in this lens only, it only degrades the quality very much. It's just that the walls inside the hood glow at any time, which means that it is transmitted to the front lens, that is, there is dust on it from any situation, and not a little usual too, everything just starts to shine on the lens, which is correct - we don't see it, and the image doesn't always. the contrast is lost (corrected) pasted black velvet and problems 0-l 4) they are afraid to glue in the tail with velvet, in vain - it's just nonsense, 1 velvet attracts dust in the tail, absorbs 99% of the reflected rays Is this bad, we take the skoc and just all the crap we collect and connect it with naleplin on scoche. and again become like a “black hole” 5) I dreamed about 10 years ago to put a microcircuit (board) from a native lens BUT, profiled in the camera, the camera must write “correction data AVAILABLE. 6) I had a disadvantage with Bainet fix, you check on your fotik they are (macro-backlash). Only autofocus lenses can have backlash, but not here. There should not be more than one hundred square meters in diameter and in the pin in the hole (latch). (eliminated) grinded at the factory and adjusted, it was difficult to combine the hole with the diameter play, it was easier to clean it. Material brass. And the last adjustment to infinity is a slave segment. Calzo №2 + 2mm = and the infinity at close range coincided with 1% sharpness, that is, on the moon. It is convenient to shoot without hovering to infinity, which is not.
General Result, - 1) sharpness you quickly focus due to the absence of backlash in 100%, 2) maximum contrast due to “01%” reflection, 3) the board for sharpness gives a focus signal exactly because he thinks “his” lens 4) c ..Y no, because the profile works great and in “cool” programs you can't clean it up with a package, since the vignette is manifested in different ways everywhere and overexposures and sub-highlights will be visible, and if there are hundreds of frames, that's f..s with pictures. but here everything is clearly PLEASANT to watch, you already know how it looks. 5) the focus sensor and in the evening does not work badly, only you can not trust the camera, the camera thinks that it is shooting in a poorly lit object and the profile works fine, after all, and the aperture is 11-10 to .. I took pictures from my hands at minus 15 tested and the dynamics is weak from the hands the focus sensor of the cash register works.6) Abberation “0” l (rainbow coyma) Here is a camera without fail not lower than the class of canon 5 mark 3 in sensitivity should be the same and better, or with a matreya stub. I took pictures on average from 10 -000 ISO so that the shutter speed was preferably no longer than 25, but it all depends on the hands. From a tripod I SHOOTED at 000 meters 1000 / 4s- (vyd) the result of macro sharpness - papixel “feeling” 0 and 3 units, a micro hair is coolly visible and this is from 100 meters. in prtsen.-m 400% magnification, notice not 4,5% magnification. I do not believe, but this is a fantasy of our optics (LENS). and the tripod acquired a road tripod with it, you can direct it online with an increase of 700 times, the tripod also brought the mind, but a little bit, the legs became easier to walk from dry ground (trampled down) the head of the Chinese metal without backlash is bumpy and low spherical, the manfroto gave it to a friend, and took it from him Chinese, it works more logically (easier) and lower landing is better, Sechas I want to develop and implement a remote focus, it is already possible to focus on sharpness with operational shooting so that you can focus no more than 100 seconds while I think. pictures in cloudy weather on average 10mb 5 arafe up to 10-10mb now not sun yet
You’ll forgive me in Russian 3- for that I wised up in this part of the introduction, for a very long time
Yuri, you don't have three in Russian. Do not lie. A stake would be a compliment to your diary. But the general idea is generally clear. There are indeed plenty of jambs in Rubinars. As the hero of the film "Nicknamed the Beast" said, "There is a lot of shit in life, but you have to live." So we live - we fix these jambs as best we can.
An example of filming the moon MTO1000 on a Sony a57 with the kenko 2x teleconverter
An example of filming the moon MTO1000 on a Sony a57 with the kenko 2x teleconverter
Interestingly, what will happen if it is also used with a 2x converter?
Focal 2000, aperture 20. Focusing will even be difficult.
By wire relative hole. All told you correctly, optically it is less than the specified 1:10
1:10 is the ratio of the diameter of the front lens to the focal length, but the secondary meniscus mirror blocks part of the light flux. It’s easy to count. Consider the total area of the input lens, subtract the area of the mirror from it. The result will be the actual optical area of the pupil of the lens, based on which the equivalent diameter value can be calculated. I once remeasured for 500mm. there more than a half-stop loss happened. 1000mm should be less. Build building, I will measure for 500 and for 1000. I have these lenses lying somewhere under the table
I bought myself this glass. I am waiting for it when it arrives. I have such a question, I have never found how much it cost in Soviet times. In the eighties I did not meet him not only in stores, but also on my hands. It would be interesting to correlate its cost. At that time I earned 126 rubles a month.
MTO-11 - 325 rubles for a certain period
Prices for all lenses in the photo in the USSR (year unknown):
56 rubles - Jupiter 11
100 rubles - Jupiter 37 MC
100 rubles - Zenitar
120 rubles - Kaleinar 5N
140 rubles - Jupiter 21M
200 rubles - MS ZM-5SA
210 rubles - Telear N
270 rub - world 38B
320 rubles - Jupiter 36B
325 rubles - MTO 11
350 rub - Mir 26B
450 rubles - Granite 11N
550 rubles - Kaleinar 3V
Around 1985, he bought Jupiter 37A for 50 rubles. But this is in the commission.
and there are two versions - the MS was twice as expensive.
This is a 37A MS, but used.
For 2022 - 75-350 thousand rubles. (Korean counterpart).
For 2023, the price is from 9500 - 15000 rubles. There are more expensive ones, but we don't take them. When purchasing, take a lens with a later year of manufacture 1988-1993. There is a hole on the meniscus lens. in which the optical system is built - it is convenient for cleaning.
Thank you very much. It seems to be a trifle but I wanted to find out and did not find it. I can’t wait when it comes. We found a nest of a large horned owl with a friend, she just hatched the second egg, I have Sigma 150-500, after cropping along the long side, the picture is only 1000 pixels It turns out. My friend Kenon has 80-400 liters, plus a teleconverter 1.4 of the native fourth series. The quality of the lens kills in the trash. It's good that I remembered about this monster. To shoot the nest from a tripod, it's the most. It's cheap and cheerful.
Something your site does not load for a long time, writes “waiting for a response from cse.google.com ...”
Sometimes there are problems, we'll figure it out, thanks for notifying
And at least somewhere, at least a hint, from what distance and what size the object is. And that is what I am looking for and cannot find anywhere. For me, this amazingly beautiful article makes no sense ...
It depends on which camera is attached behind. FR is written. The problem is not very clear
Oh, you touched me! Sometimes it is useful to reread school textbooks. You need to read: Algebra. section: Trigonometry, paragraph about tangent and arctangent.
The most complete information on reflex lenses is:
We go. We are looking for, for example: “Angular field of view vertically”.
For the 1000/10 lens (as with the MTO-11. The fact that the name is different does not matter here) this parameter = _1,38 °_.
(Do not forget that this is for a full frame 24x36! For other cameras, you need to take into account the crop factor.)
We take the tangent of this angle - Tg(_1,38°_) = _0,024_. Let's divide the unit by this value: 1/0,024 = _41,5_. This means that with an F = 1000 mm lens, with its field of view angle of 1,38 °, at a distance of 41,5 m, exactly one meter will fit vertically into the frame.
If you want to photograph a company of standing people, roughly speaking, 2 m tall, then what we got for 1 m must be multiplied by 2.
So: 41,5 * 2 = 83 m. Move back to these 83 m and take pictures of people in full growth.
If you have a crop camera (for example, with crop factor = 1,5), then multiply these 83 m by the crop: 83 * 1,5 = 124,5 m. You need to move back to 125 m.
I hope it is clear.
If you want to photograph a person not with a horizontal frame, as it is by default, which is not difficult to guess from the same table, but with a vertical one, then the horizontal part of the frame becomes vertical, and vice versa (vertical - horizontal). So you go to that table, follow the link, and look for “Angular field of view horizontally” and repeat what I wrote above.
Read the block of Dmitry Eftiveev, there are ready-made computer conversions of the aperture.
I tried it on different Nikons. Cameras with a resolution higher than 12 MP, this lens does not pull. Strange, but Nikon D2Xs gave a much better result with this lens than Nikon D300s.
The filter is thinner than the D300.
This has already been written about:
And although they are both DX, that is, cropped ...
Thanks, I thought so. Tomorrow I'll take it again. I liked it very much. At the same time I will shoot on D7500 with Sigma 150-600
The lens, of course, leaves much to be desired, but SLR lenses for 2022 cost 75 thousand 300 thousand rubles. and more and without a guarantee of using optical glasses there, like the Lytkarino plant.
The advantage is the ability to make a hood from the factory supply. 1. Unscrew the front, moving part of the rotation and remove the hood. 2. Unscrew the fastening ring from the green filter, remove the glass filter. 3. We slightly bore the standard hood with a dremel for felt before inserting the filter into the hood. 4 Temporarily seal with epoxy (slightly). 5 Finally fix with screws M2 with a head in the pot. 6. Outside, glue the hood with porous rubber or polyurethane 3-8 mm thick. 7. In order not to slip hands, we glue it with black non-woven material for greenhouses. 8. Finishing coloring KUDO KU-1102 on the outside, KU-2003 on the inside, can be powdered with black copier powder using a squirrel brush, but so that it does not shine. The difference in heights on the construct freed from the hood is also sealed with porous black material coated with non-woven material. Grease is replaced with frost-resistant HUSKEY COOLUBE 65. +55…-65'C. I tired you, Sorry. more firstname.lastname@example.org
Why ruin the lens?
The built-in hood is great and a big plus for the lens.
No one usually carries an external hood with them - where to PUT another cylinder in addition to a bulky lens.
If you want, for some unknown reason, just an additional external hood (but why?), then you can order it to be turned by a turner. Moreover, it can be made of two parts, one of the pipe and the second, a flange, from a suitable round timber or a thick plate.
You can generally glue the outer hood out of paper with epoxy, and due to the thickness make it stronger than the thin built-in one. Only all and the built-in suits.
The hood has a thin wall. It cannot be pulled out. It can be made from a tin can, but there is a lot of hassle. Modern cameras allow you to correct the spectrum, so regular filters are not needed. The use of a lens hood filter ring is justified. The hood lengthens by 3-4 cm. This is a lot. The threaded hood does not dangle, unlike the retractable one. When preparing for an open-air shoot, there is no time to assemble and disassemble, especially in the cold in winter. Drag on yourself as it is and at the end of the shooting, take your legs away with hardened hands that do not bend. I bought Chinese suitcases-trolleys on wheels as a wardrobe trunk. There are big ones there. Price 1200 rub. Seal the back wall of the suitcase from the inside with plywood.
so this or the nikon 1000mm?
And how will people or animals be in the frame from a distance of 400 meters? Very small if you use crop 1.6? Where can I find examples of pictures indicating the real distance to the object in meters and kilometers ...
but Buddha doesn’t allow you to take a calculator and calculate?
Are you kidding?) What are 400 meters? Even if you close your eyes to the dustiness of the air and air currents (which will inevitably spoil the picture), with 400m a person will take about 1/4 of the height of the horizontal orientation frame. Have you presented the faces of small animals?))
To calculate the luminosity, remember the formula
Aperture = 1/(Entrance Pupil Diameter : Focal Length)
In MTO, not the entire entrance diameter is used, so we calculate the equivalent of the diameter, for which we subtract the area covered by the auxiliary (secondary) mirror from the entrance pupil area.
From the result obtained, it is easy to determine the equivalent diameter.
2) Area difference S=πD^2-πd^2/4 , where D is the inlet diameter, d is the diameter of the secondary mirror.
3) Equivalent diameter Deqv =√(D^2-d^2)
We take the data for calculation from the optical scheme:
Aperture \u1d 101,3952 / ( 1000: 9,862) \uXNUMXd XNUMX
So 9,8 is about 10.
These are calculations for the input meniscus.
in the area difference formula before the slash - the numerator of the fraction, after the slash (division sign) - the denominator.
A particularly valuable note.
You need to understand one simple thing. This is not a lens, this is a mirror-lens telescope of the Maksutov system, to which an interchangeable shank was simply attached. Therefore, in principle, there is no diaphragm in it. Well, all further reasoning is just as for a telescope.
Any lens has an aperture diaphragm, even if it is constant)))