Aspheric Optics: An Overview - aspheric

 2024-06-21 06:04:01

Definition magnificationin physics

It seems to me that there is a trend to use long telelenses rather than macro lenses or adapters etc. for macro subjects like butterflies and damselflies. This has the advantage of not needing to come close with risk of disturbing the insect. There are some example pictures taken with a telelens in your article, however the magnification (that must be high) is not discussed. I’m using myself a 70-200 mm semi-macro lens at the long end, sometimes combined with an extension tube, but I wonder whether an even longer lens for flying insects would not be more useful. Extension tubes have the disadvantage of getting too close to your living subject.

Thanks for an informative and, to me, unrealised aspect of focus. Does this relate to a situation were a large aperture (eg F5.6) has been used in a far ranging landscape shot, and yet (paradoxically to me) the shot is in focus from front to back? I am confused as to how this can be, because it seems to contradict the rule of smaller aperture = greater depth of field. I am sorry if this turns out to be off subject.

These challenges aren’t easy to overcome, but it’s possible to do it with some effort, and that’s half of what makes macro photography so fun! When you do succeed at getting a sharp photo at extremely high magnifications, it’s very rewarding.

Magnification, also known as reproduction ratio, is a property of a camera lens which describes how closely you’ve focused. Specifically, magnification is the ratio between an object’s size when projected on a camera sensor versus its size in the real world. Magnification is usually written as a ratio, such as 1:2, which is said aloud as “one to two magnification.”

However, if your subject is moving, or you’re shooting handheld, focus stacking is much harder, if not impossible. At that point, the best option is to use a flash while practicing your best close-up focusing technique.

Many dragonfly / butterfly photographers use longer lenses like a 4/300mm because of longer working distance and better background blur, especially for in-flight shots. However, this is more “close-up” than real “macro” with magnifications in the 1:10 to 1:2 or so range.

Photography or image pickup with a video camera has been common in microscopy and thus a clear, sharp image over the entire field of view is increasingly required. Consequently, Plan objective lenses corrected satisfactorily for field curvature aberration are being used as the mainstream. To correct for field curvature aberration, optical design is performed so that Petzval sum becomes 0. However, this aberration correction is more difficult especially for higher-magnification objectives. (This correction is difficult to be compatible with other aberration corrections) An objective lens in which such correction is made features in general powerful concave optical components in the front-end lens group and powerful concave ones in the back-end group.

If you do any macro or close-up photography, you’ll likely come across the term “magnification.” Even outside of macro photography, most camera lenses include their maximum magnification in the list of specs.

At the same time, you’ll notice that a macro lens can (seemingly) capture a more magnified view of your subject when you’re using a crop sensor camera. What gives?

Definemagnificationin microbiology

A special case is when the object is the same size in the real world as its projection on your camera sensor. This is 1:1 magnification, also known as 1x or “life size” magnification. It’s important because 1:1 magnification is considered the standard for macro photography, and most macro lenses at their closest focusing distance will be at 1:1 magnification.

The first one is straightforward. Now that you understand magnification, you can easily figure out whether a particular lens offers enough close focus capabilities for your needs. For example, you may realize that you need a 1:1 macro lens for what you’re photographing, and a lens that advertises itself as macro but only reaches 1:2 won’t be enough.

Magnification can also be written in decimal format. For example, 1:2 magnification could be written as 0.5x magnification (which is found simply by doing 1 ÷ 2). This is how magnification generally appears in a list of a lens’s specifications – 0.3x, 0.14x, 0.22x, and so on. Check out this table to see some examples of lenses and their magnifications:

I'm Spencer Cox, a landscape photographer based in Colorado. I started writing for Photography Life a decade ago, and now I run the website in collaboration with Nasim. I've used nearly every digital camera system under the sun, but for my personal work, I love the slow-paced nature of large format film. You can see more at my personal website and my not-exactly-active Instagram page.

Meanwhile, an objective lens for which the degree of chromatic aberration correction to the secondary spectrum (g ray) is set to medium between Achromat and Apochromat is known as Semiapochromat (or Flulorite).

Most macro lenses tell you their current magnification in the same information window as your focusing distance. For example, on my Nikon 105mm f/2.8 macro, the magnification is visible in the window here:

An objective lens is the most important optical unit that determines the basic performance/function of an optical microscope To provide an optical performance/function optimal for various needs and applications (i.e. the most important performance/function for an optical microscope), a wide variety of objective lenses are available according to the purpose.

I’ve corrected that part of the article to say “if you avoid the cheap ones, this is a good way to increase your magnification.” I think my prior wording was overly negative.

Spencer, you say about close-up filters: “They don’t always have the highest optical quality, so it’s not my top recommendation.” I wonder if you have any experience with Raynox DCR-250. I’m quite happy with its image quality when coupled with my telephoto lens (Nikon AF-P Nikkor 70-300mm f/4.5-5.6E ED VR). Also, unlike some other macro techniques, it gives me the flexibility to change the magnification ratio by zooming in and out with the lens.

Hopefully this article answered your questions about magnification in photography. I’ve also introduced the challenges of getting sharp photos at high magnifications, which you can learn more about in our longer macro photography guide.

If your subject is staying still, you can fix most of these issues by focus stacking from a tripod. Even if you don’t focus stack, simply using a tripod allows you to use longer exposures to negate the darkness of f/16 or f/22. It also makes focusing much easier.

It’s similar to the situation with extreme telephoto photography. When your goal is simply to put the maximum number of pixels on a small or distant subject, a crop sensor with a small pixel pitch works very well.

Magnification definitionmicroscope

The other factor, focal length, works the same way. The further you zoom in, the less depth of field you’ll get. This is how wildlife photographers can get a shallow depth of field despite focusing far away and even using narrow apertures like f/11.

Magnificationof image

Glad you found it useful, Brian! I would need to read up on the technical background behind those specifications before writing an article, but I would consider it if there’s interest. I know what you’re referring to, but I’ve only ever used that specification when comparing how large the viewfinder will seem, among cameras with the same sensor size.

Excellent article! So when compare a 70-200mm f2.8 lens at 100mm and a macro 100mm f2.8 lens, one has to compare at the each’s minimum distance, The 70-200mm f2.8 has min. focus distance at 70cm and the macro has the min distance at 26cm (my case). If you compare both at 70cm in distance from the subject, then the results (depth of field, bokeh) are same, right? But the 70-200 can never focus at 26mm. On the other hand, once move the 100mm macro to its min. at 26cmm, the depth of field is much narrower, that’s why one needs smaller aperture to increase the depth of field, and thus need better lighting. Some people suggest that bring a hand light with you. That’s also why a macro lens mostly at no brighter than f2.8 because you have to reduce it to maybe f5.6 at 26cm anyway. Am I right? I did not pay too much attention to Maximum Magnification until I read your article because I am considering buying a macro lens which is on sale (Canon RF 100mm f2.8). Again. thank you. I have learned a lot.

This is because depth of field shrinks as you zoom in and focus closer. Because magnification can be thought of (and even expressed mathematically) as a combination of focal length and focusing distance, there’s no way around it: High magnifications have low depth of field.

Definitionof totalmagnification

On one hand, magnification doesn’t change at all because of your sensor size. It doesn’t even matter if you have a sensor; magnification is a property of the lens and the lens alone.

If you’re reading this article, chances are you want to find out how to get as much magnification as possible. If the tips above for getting high magnification with your existing lenses aren’t enough, it might be time to get a shiny new lens with even more magnification.

The other context in which magnification matters is in figuring out your depth of field. No matter what lens you have, your depth of field is going to be very shallow at high magnifications, and it falls off dramatically once you’re at 1:1 magnification and greater.

This is helpful knowledge to have on the fly if you don’t have time to chimp. It’s also nice to know beforehand how to deal with certain magnifications – such as using a flash at 1:1 because of those small apertures, or using focus stacking if you get to extreme magnifications like 4:1 or 5:1 to get back depth of field.

Many long zooms like my Canon 100-400II have IQ compromises when used near MFD and there are few long primes with high magnification, good closeup image quality and modest weight and cost. Most recent lenses are either very bright, heavy and expensive primes with relatively long MFD or dim, optically compromised (for closeups) zooms; some exceptions though like Nikon PF lenses.

The only way to increase magnification without resorting to external accessories is to focus closer and closer (or buy a different lens).

Navek, no worries, that’s a good question. Depth of field depends on more than just your aperture. There are also two other factors: focal length and focusing distance.

I just found this article when trying to understand the magnification offered by a non-macro lens. This 100mm full-frame lens. The manufacturer’s (Sony’s) blurb, complete with their colorful verbiage says: “Because one of the main features of this lens is bokeh, it has been provided with a macro ring switch that extends the lens’s range into the macro region where bokeh can be used to great effect. The macro mode provides 1.87 ft (0.57 m) minimum focus with 0.25x maximum magnification, with no compromise in resolution performance.” It is that ” 0.25x maximum magnification” I am trying to understand. I’ve got a pretty good reference for what 1:1 would be, as full frame based on the old 35mm film would be the size of a 35mm slide. I can picture four such rectangles forming a larger rectangle, (2×2)) or a total size 4x any one slide’s image. 4x sure sounds like 25%, but I am unsure that is the correct view. For all I know that 25% might be applied linearly, meaning I need to picture a 4×4 rectangle that covers 16 times the area of the sensor (or a slide image).

Magnification definitionbiology

On top of that, because high magnifications have such a low depth of field, you’ll also need to be shooting at small aperture settings when you focus especially close. This means you’re in for some photos that are dark and blurry – not to mention out of focus, since focusing is also difficult when your depth of field may be just a few millimeters across!

4 types ofmagnification

An optical microscope is used with multiple objectives attached to a part called revolving nosepiece. Commonly, multiple combined objectives with a different magnification are attached to this revolving nosepiece so as to smoothly change magnification from low to high only by revolving the nosepiece. Consequently, a common combination lineup is comprised from among objectives of low magnification (5x, 10x), intermediate magnification (20x, 50x), and high magnification (100x). To obtain a high resolving power particularly at high magnification among these objectives, an immersion objective for observation with a dedicated liquid with a high refractive index such as immersion oil or water charged between the lens end and a specimen is available. Ultra low magnification (1.25x, 2.5x) and ultra high magnification (150x) objectives are also available for the special use.

Axial chromatic aberration correction is divided into three levels of achromat, semiapochromat (fluorite), and apochromat according to the degree of correction. The objective lineup is divided into the popular class to high class with a gradual difference in price. An objective lens for which axial chromatic aberration correction for two colors of C ray (red: 656,3nm) and F ray (blue: 486.1nm) has been made is known as Achromat or achromatic objective. In the case of Achromat, a ray except for the above two colors (generally violet g-ray: 435.8nm) comes into focus on a plane away from the focal plane. This g ray is called a secondary spectrum. An objective lens for which chromatic aberration up to this secondary spectrum has satisfactorily been corrected is known as Apochromat or apochromatic objective. In other words, Apochromat is an objective for which the axial chromatic aberration of three colors (C, F, and g rays) has been corrected. The following figure shows the difference in chromatic aberration correction between Achromat and Apochromat by using the wavefront aberration. This figure proves that Apochromat is corrected for chromatic aberration in wider wavelength range than Achromat is.

Unlike some camera settings like shutter speed or aperture, you don’t really need to be thinking constantly about your magnification if you want to get high quality photos. But that doesn’t mean it’s unimportant.

That said, if you’re not at your lens’s maximum magnification (nor very close to it), large camera sensors still have the same benefits as always.

The purposes of optical microscopes are broadly classified into two; "biological-use" and "industrial-use". Using this classification method, objective lenses are classified into "biological-use" objectives and "industrial-use" objectives. A common specimen in a biological use is fixed in place on the slide glass, sealing it with the cover glass from top. Since a biological-use objective lens is used for observation through this cover glass, optical design is performed in consideration of the cover glass thickness (commonly 0.17mm). Meanwhile, in an industrial use a specimen such as a metallography specimen, semiconductor wafer, and an electronic component is usually observed with nothing covered on it. An industrial-use objective lens is optically designed so as to be optimal for observation without any cover glass between the lens end and a specimen.

High magnifications are a lot of fun to use, but it’s not always easy to get sharp photos once you go beyond a certain point. That’s because you’re not just magnifying your subject at these ultra-close focusing distances; you’re also magnifying things like camera shake and subject motion.

Marcin, that’s a good point. I was thinking back to my negative experiences with a really cheap one, but if you get a good close-up filter, you can get some high quality images. I haven’t used the Raynox, but from sample images I’m seeing online, it looks quite good. I don’t see any of the severe chromatic aberrations that plague some of the cheaper close-up filters. Using it on a zoom to get variable magnification is also a good plan.

A variety of microscopy methods have been developed for optical microscopes according to intended purposes. The dedicated objective lenses to each microscopy method have been developed and are classified according to such a method. For example, "reflected darkfield objective (a circular-zone light path is applied to the periphery of an inner lens)", "Differential Interference Contrast (DIC) objective (the combination of optical properties with a DIC( Nomarski）prism is optimized by reducing lens distortions)", "fluorescence objective (the transmittance in the near-ultraviolet region is improved)", "polarization objective (lens distortions are drastically reduced)", and "phase difference objective (a phase plate is built in) are available.

Magnificationformula

The closer you focus, the larger your magnification will be. Macro lenses routinely go to about 1:1 magnification, although some (such as the Zeiss 100mm f/2 Macro) can only go to 1:2 magnification. A few specialty macro lenses can go beyond 1:1 magnification, such as the Laowa 100mm f/2.8, which can go to 2:1. A popular choice among macro photography enthusiasts is the Canon MP-E 65mm f/2.8, which can go all the way to 5:1 magnification! However, this lens can only shoot macro photos and cannot focus on anything distant from the lens; it’s confined to the focusing range from 1:1 to 5:1 magnification.

What does change, however, is that the coin takes up a greater percentage of the smaller sensor. If you were to make a print of both of these photos and display them at the same size, obviously the coin would be larger on the photo from the aps-c sensor. So, even though the magnification hasn’t changed, the composition has.

In the optical design of microscope objectives, commonly the larger is an N.A. and the higher is a magnification, the more difficult to correct the axial chromatic aberration of a secondary spectrum. In addition to axis chromatic aberration, various aberrations and sine condition must be sufficiently corrected and therefore the correction of the secondary spectrum is far more difficult to be implemented. As the result, a higher-magnification apochromatic objective requires more pieces of lenses for aberration correction. Some objectives consist of more than 15 pieces of lenses. To correct the secondary spectrum satisfactorily, it is effective to use "anomalous dispersion glass" with less chromatic dispersion up to the secondary spectrum for the powerful convex lens among constituting lenses. The typical material of this anomalous dispersion glass is fluorite (CaF2) and has been adopted for apochromatic objectives since a long time ago, irrespective of imperfection in workability. Recently, optical glass with a property very close to the anomalous dispersion of fluorite has been developed and is being used as the mainstream in place of fluorite.

As you can see, the coin’s projection is physically the same size on both sensors. (If it looks larger to you on the aps-c sensor, that’s just an optical illusion; the pixel dimensions are the same.) So, it doesn’t matter what size sensor I put behind the lens – it can’t change the physical size of the projection. The magnification is identical in both cases.

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Nice article Spencer. I particularly had an “aha!” moment when reading that magnification is a property of the lens’ projection, not the size of the sensor behind it.

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Maybe a diagram will clear things up. Here’s how a sample subject (a coin in this example) looks at the same magnification on two different sensor sizes:

Luckily, every manufacturer has at least one dedicated macro lens, which you can get from B&H photo with the following links:

For instance, a 24 megapixel APS-C camera is usually preferable to a 24 megapixel full-frame camera if you need as much detail as possible on a high magnification subject. On the other hand, a 45MP full-frame camera and a 20MP APS-C camera have almost exactly the same pixel density, so neither is preferable to the other for macro.

The best way to get high magnifications is still to use a macro lens, but hopefully this list gave you some good ideas on how to go beyond that. Personally, my favorite of these methods is to use a set of extension tubes combined with a 35mm or 50mm prime.

Alternatively, some lenses may not advertise themselves as macro lenses, even if they have pretty impressive close focusing capabilities. For example, the humble Nikon 18-55mm AF-P kit lens can reach to about 1:2.6 magnification (0.38x), and the Canon 24-70mm f/4 goes even further to 1:1.4 magnification (0.71x). That’s more than you’d get with many so-called “macro” lenses from other manufacturers! With either of these lenses, you could take close-up photos of larger subjects like flowers, lizards, dragonflies, and so on, without spending hundreds of dollars on a dedicated macro lens.

If you don’t mind using accessories to go further, here are some things you can do to get more magnification than your lens natively allows:

All these lenses go to 1:1 magnification or more, and will likely provide enough magnification for almost any application.

Excellent writing. Very easy to understand for almost everybody who has taken his hands on an interchangeable lens camera. It’s concise, and nice to read, thanks.

Would you consider doing a similar article on viewfinder magnification? I can’t wrap my head around the magnification spec of “0.77x” (for example) of modern OVFs & EVFs.

If it helps, you can think about it like this: Shooting with a crop sensor is like cropping an image from a full-frame sensor. In the same way that cropping a photo doesn’t increase magnification, neither does using a crop sensor. But it does make the subject larger in your final image.

Objective lenses are roughly classified basically according to the intended purpose, microscopy method, magnification, and performance (aberration correction). Classification according to the concept of aberration correction among those items is a characteristic way of classification of microscope objectives.

If you know what magnification you’re at, you’ll have a good idea of the depth of field you can get. For example, I know that when I’m at 1:1 magnification, I need to use an aperture of at least f/16 in order to get enough depth of field, and maybe even f/22. By focusing a bit farther back – say, 1:2 magnification – it becomes possible to use f/8 or f/11 instead, for the same depth of field.

The takeaway is that small camera sensors can actually work great for this type of high-magnification macro photography. In fact, if they have smaller pixels than the full frame camera, they’re likely to be at an advantage.

Longer lenses (especially from 400mm or so) have disadvantages too to like lower native magnification, more size/weight that makes tracking fast/erratic flying subjects more difficult. DOF can be so small that it can be impossible to find and focus on the subject before it is out of the frame again. Because of those limitations I prefer a 100-200mm lens for the fastest dragonflies. Longer lenses are nice though when the subject is hovering or gliding.

I’m not surprised that you’re seeing a lot of depth of field when you focus on something far away, even at a medium aperture like f/5.6. The farther you focus, the greater your depth of field becomes. So, you’re correct that it relates to this article, where I say that your depth of field gets very shallow at high magnifications/close focusing distances.

For example, say that you’re doing macro photography, and the object you’re photographing has a projection on your camera sensor which is 1 inch across. If the same object is 2 inches across in the real world, your magnification is 1:2. (It doesn’t matter what units of measurement you use; the important thing is the ratio between the object’s size on your camera sensor compared to its size in the real world.)