Ex-stock delivery of CNC precision polished plano-convex aspherical lenses made of N-BK7, high refractive index S-LAH64 glass or UV fused silica. EKSMA Optics can design and produce custom-tailored aspheres with anti-reflection coatings to suit your particular laser application.

The same issues with aberrations also occur for cylindrical optics, focusing only in one direction. Therefore, instead of true cylindrical lenses, for example, one often uses lenses with a slightly acylindrical surface.

Your work is amazing. Thank you. I’m just starting to educate myself, but it took me a while to find someone I wanted to learn from.

There are also lenses which are at the same time aspheric and achromatic. For example, one can combine a spherical glass lens with an aspheric polymer part. There are even hybrid aspheres, combining refractive and diffractive properties.

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Keep in mind that not all lenses can zoom (change the focal length).  Some lenses are prime, which means they cannot zoom in.  A common lens that cannot zoom (one which you likely own) is a 50mm f/1.8 lens.  It's a fantastic lens, but it cannot zoom in or out.  It's a fixed focal length lens.

We offer custom aspheric lenses. Single point diamond turning and molding capabilities. Available materials: optical glass, Si, Ge, chalcogenide glass, ZnSe.

However, most photographers stick to the standard of the 35mm imaging sensor (full frame).  So if you hear a photographer recommend shooting at 200mm, they probably mean 200mm on a full frame camera.  35mm has long been the standard.  The good news is that you can use some very simple 3rd grade math to know exactly the focal length equivalent on your camera.

In some cases (particularly for polymer-based optical elements, plastic optics), one simply uses molding forms with appropriate shapes, which by their nature do not need to be spherical. Such injection molding and also compression molding processes can be used for cheap mass production, but usually do not with a particularly high optical quality. There are also glass molding techniques with subsequent annealing, leading to higher quality but at higher cost.

Nikon, Fuji, and Sony crop sensor cameras have a 1.5x crop factor.  Canon crop sensor cameras have a 1.6x crop factor.  So if someone recommends a 200mm focal length, you can rightfully ask whether they mean full frame or crop sensor.  However, the focal lengths photographers talk about are usually in full frame.  So you can do some simple math to know what focal length you should use to achieve the same field of view as 200mm on a full frame camera.

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If you're still learning the fundamentals of photography, I really highly recommend you take a minute and read through my photo basics series.  It's a collection of 8 posts I wrote for newer photographers.  It'll walk you through getting a good exposure, how to set your camera up to get crisp sharpness, composition, and more.  Read the photo basics series here.

In some cases, it is sufficient to use standard aspheric lenses or mirrors as are available from various manufacturers on stock. However, aspheric lenses have a number of additional parameters (see above), making it substantially more difficult to find the required combination of properties in stock lenses. Mostly, this is possible only for lenses which are optimized for standard optical tasks, such as collimating a strongly focused beam. In other cases, custom optics have to be used.

The actual measurement of focal length is the distance, in millimeters, between the convergence point and the imaging sensor.  The convergence point is the point at which the light rays combine in the lens.  No worry, though, you'll never need to know that again.  There's no pop quiz at the end.

As aspheric optics allow one to avoid spherical and other aberrations in the first place, they can substantially simplify both the optical design process and the resulting optical designs. This can also lead to a more compact optical systems, which is particularly relevant e.g. for the design of mobile devices. For example, extremely compact camera objectives as required for smartphones must work with a minimum number of optical elements and therefore heavily depend on aspheric optics. The reduced number of optical surface may also be a relevant advantage. Besides because of various complex trade-offs in optical design, by using aspheric elements one can often eliminate certain requirements and finally achieve overall better optical performance.

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I also want to make sure it's clear that you can achieve the same wide angle of view on a crop sensor camera as on a full frame camera just by using a wider lens, so there is no advantage to a full frame camera for landscape photography.  And on the long end, it can be handy to have a crop sensor camera because it makes a 400mm lens turn into a 640mm lens without paying thousands and thousands of dollars on a lens that long.

Spherical optical surfaces are typically not used because they are ideal concerning the optical function – usually they are not –, but only because they are most convenient to manufacture. The usually employed generation process naturally produces spherical surfaces. Note that it is not possible geometrically to obtain non-spherical surfaces with simple grinding; spherical surfaces are the only ones where one can transversely move around the grinding tool while maintaining full contact with the process surface.

Opticallenses

Here, <$z$> is the profile height as a function of the radial coordinate <$h$> (distance from the optical axis). <$K$> is the conic constant, which can be used to obtain certain typical shapes (which may be modified further with the additional terms): Here, <$z$> is the profile height as a function of the radial coordinate <$h$> (distance from the optical axis). <$K$> is the conic constant, which can be used to obtain certain typical shapes (which may be modified further with the additional terms):

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Is it true that when using a crop sensor your 1.8 lens is then doubled to a 3.6? In other words, are your f stops all doubled?

Jim, I have been taking professional pictures for over 10 years and still do not understand “focal length”. I pick the lens in my kit that I know would work best for my needs and shoot. Do I really need to know all this?

After you've taken a picture, almost all cameras will save the focal length information in the metadata of a picture.  So if you want to go back and see what focal length you used to get a certain look, then you can go into the properties of the photo and see that.

When surfaces deviate more profoundly from spherical shapes, e.g. with oscillations, such components are called free-form optics.

I wrote an entire article about how the crop factor affects field of view, which you can read if this isn't quite sinking in yet.

I love this article! Truly excellent and easy to read. I study photography at Chicago Photography Academy and found this extremely helpful.

If you shoot at 20mm and the person you're photographing is 30 meters away, the person will be small (magnification) and you will see a lot of area around the person (field of view).   However, if you zoom in to 300mm, the person will be large in the picture (magnification) and there won't be much scenery on the sides of the model showing in the frame (field of view).

Aspheric lensthorlabs

There is one last thing you need to understand about focal length in order to have the basics under your belt.  Here it is: As focal length increases, the change of the field of view decreases.  As focal length reduces, the change in the field of view increases.  Or in other words, there is an inverse exponential relationship between focal length and the change in field of view.  Clear as mud?

There is no “right” or “wrong” focal length for any given situation.  It's all a matter of personal preference and what you want to capture.  However, there are certainly norms of the focal lengths typically used in different situations.

Some computer-controlled fabrication techniques are well suited for making custom aspherics. In some cases, components which are normally used in spherical form are subject to additional treatment where they are turned into aspherics.

If you have a crop sensor, I recommend you at least have a 35mm or 50mm f/1.8 in your arsenal. Very affordable fast primes.

ThorlabsLens

As you listen to the Improve Photography podcasts each week or watch our Youtube videos, you'll often hear us discussing different focal lengths for different purposes.  In this article, all the examples of focal lengths I've used have been with crop sensor cameras, because that's what most of you will be using on your cameras.

A substantial variety of manufacturing techniques for aspheric optics has been developed in the last couple of decades. Some of them can also be applied to different kinds of mirrors. Some methods are suitable for generating arbitrary freeform surfaces. The choice of fabrication method can depend on various aspects:

The focal length measurement tells the photographer what the angle of view will be.  The angle of view means how wide of an area is visible in the picture.  It also conveys the magnification of far-away objects in the photo.

Wider lenses show more distortion (unnatural bending of objects in a picture–especially around the edges of the frame).  Also, the wider field of view of a wide lens (10 – 18mm) will make objects which are close to the camera seem much larger, and objects further from the camera much smaller.

All of the focal lengths below are the common focal lengths for crop sensor cameras, since the vast majority of the people reading this article will be shooting crop sensor cameras.  These are rough numbers, intended to give you an idea of what focal length you'd want).

It can be a bit confusing as a beginner to understand focal length because there are a few twists and complexities, but I'll do my best to explain it in 5 minutes or less.  I'll start with the most basic information and then build up to the more advanced stuff.  Be sure to read the entire article because there are some cool examples down lower that will help you get the right focal length for when you're taking pictures of people.

asphericlenses中文

Focal length is measured in millimeters, but the measurement is not of the actual physical length of the lens, but rather the magnification properties of the lens.

One last thing to notice, and this one is a bit more advanced, is that the background appears blurrier and blurrier as the focal length increases, despite the camera settings staying the same for all of the shots.  To learn more about that, read my article on the many things that impact depth of field.

If you shoot a crop sensor camera (Nikon D3300, D5500, D7200, or Canon Rebel, 70D, 7D, Fuji XT1, or Sony A6000 just to name a few), then your camera's crop factor will make your camera more zoomed in when compared to full frame cameras at the same focal length.

Edmund Optics offers various aspheric lenses, including CNC polished lenses, infrared lenses with diffraction-limited performance, precision glass molded lenses, color-corrected lenses, condenser lenses and plastic molded lenses.

As optical systems are pushed to be better, faster, and cheaper, it becomes necessary to explore aspheric solutions. Aspherical elements eliminate monochromatic aberrations (e.g. spherical aberration) and improve focusing and collimating accuracy.

The point is that full frame cameras are not capable of shooting any wider or more telephoto than a crop sensor camera.  The difference just means that if the same focal length is selected on the lens, the full frame camera will produce a wider shot.

Note that it is usually neither necessary nor advisable to use aspheric optics throughout in a system. Instead, it is often sufficient to use a single aspheric surface to obtain good control of various types of aberrations. Such a surface may either be close to spherical, but with some specific deviations, or it may not have an own focusing function, only compensating aberrations introduced by other elements (correction plates).

Best photography article I’ve read in quite a while.. I never get clear explanations about focal length but this one explained it in a way I could actually understand… Especially the meaning of “wide” with face portraiture.. THANK YOU!

So suppose I take a picture of a building on a crop sensor camera at 18mm.  If I put the same lens on my full frame camera and shoot at 18mm, the full frame picture will be much wider.  However, I could easily get a 13mm lens and put it on my crop sensor camera to match the exact same field of view as the full frame camera.

Thank you so much for explaining focal length in so much detail! I am a new DSLR owner (crop sensor) so this article was super helpful for me. I was particularly interested to understand what the mm measurement actually means because that just baffled me and I hadn’t found a clear explanation anywhere else. I think I’m probably going to have to keep coming back to this article as I practice to get my head around it all, but thanks for giving me a giant leap forward in my understanding! 🙂

If you understand this principle, it can save you a lot of money on lenses!  When I suggest to newer photographers that they buy a wide-angle landscape photography lens, they sometimes say something like, “Why would I spend $500 on a 10mm lens when my camera already came with an 18mm lens?”  Aside from the optical quality differences, the difference between 10 and 18mm is HUGE and will make a significant difference in how much of a landscape fits into the frame.

Aspheric lensEdmund

You need to understand that point to select a proper focal length for portrait photography.  In the (horrible quality) animated gif above, I took four pictures of my wife from different focal lengths.  After each shot, I STEPPED BACK and zoomed in.  By doing this, her face remains the same size in the picture, but as you can see, the photo looks COMPLETELY different!

Lensirregularity

Fresnellens

In short, the focal length of the lens is the measure of how “zoomed in” your lens is.  Much like looking through binoculars, you may be at 40 mm and be able to see an entire mountain, or zoom in to 400mm and only see one tree on the mountain.

Therefore, more refined manufacturing methods are required to produce aspherical optics. There are adapted grinding processes, also diamond turning techniques, which can work without the mentioned full contact between the work tool and the processed sample. Some of them involve the use of computer-controlled machines (CNC, robotic manufacturing).

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In many cases, refined types of interferometers in combination with suitable computer software are used for such purposes. They allow for the precise assessment of the highest surface accuracies, far below 1 μm or a small fraction of the optical wavelength. Another option is to use 2D or 3D optical profilometers. The latter of are quite flexible method, but usually substantially lower accuracies than interferometry.

All lenses show the focal length right on the lens.  First of all, you'll see the range of the focal length that the lens can achieve in the name of the lens.  If your camera came with an 18-55mm f/3.5-5.6 lens, then you know that the widest your lens can go is 18mm and the most zoomed in your lens can go is 55mm.

Thank you for this interesting article. You mentioned that there is no advantage of full frame sensor over the crop sensor. Now what about shooting in low light and the impact on the noise level ?

As you turn the barrel of your lens to zoom in, you can look at the scale on the end of the lens that connects to the camera to see what specific focal length you are shooting at.

Precision aspheric lenses reduce visual defects and produce clearer images, making them ideal for many applications. In addition, because the surface of an aspheric lens is designed and formed to effectively reduce aberration in specific applications, custom aspheric lenses make flexible solutions to complex problems. At Shanghai Optics, we use two main methods to produce custom aspheric lenses: molding and traditional polishing with the state-of-the-art manufacturing and metrology equipment.

200mm on a full frame camera is the same thing as about 135mm on a crop sensor Nikon camera, because the Nikon has a crop factor of 1.5x.  On a Canon crop sensor camera, however, it would be 125mm.

All this means is that on the wide end of your lens, zooming in 5mm will dramatically impact the field of view (how much scene you can fit into the frame).  However, when you're zoomed in tight, zooming in 5mm will only make a minute difference in how much scene is in the picture.

Using our advertising package, you can display your logo, further below your product description, and these will been seen by many photonics professionals.

Focal length is something that we talk about constantly as we discuss different lenses and styles of photography in our weekly free podcasts.

When on the wide end, you see much more of the backyard around her.  You see the side of the house, all of the fence, and you can't even see the trampoline because she's covering it.  However, as you scoot back, you see much less of the yard (narrower field of view).  Also, notice that the face looks badly distorted when shooting with a wide angle lens up close, but as you scoot back and zoom in, everything looks normal and proportional.

Optical elements and systems also produce other kinds of optical aberrations, such as astigmatism and coma, which can lead to non-ideal performance of focusing or imaging devices. There are sophisticated optical design principles which allow one to minimize different kinds of aberrations of optical systems, even when using only spherical optical elements. However, the number of required optical elements and consequently the number of involved optical surfaces may be substantially increased compared with what would be required just to obtain the basic optical function.

Most lenses and focusing or defocusing mirrors, as used in general optical instruments and in laser technology, have spherical optical surfaces – surfaces which have the shape of a sphere within some extended region. (They can be either convex or concave.) However, some optical elements are also available with non-spherical surfaces and are then called aspheric optics (or sometimes aspherical optics). They exhibit surface profiles which do not have a constant local radius of curvature – often with weaker curvature of parts which are more distant to the optical axis. In most cases, surface profiles are at least rotationally symmetric.

Further, we have many interesting case studies on the same page, with topics mostly in fiber optics. Concrete examples cases, investigated quantatively, often give you much more insight!

Given the following suggested focal lengths for different situations above, what is the ideal distance between the photographer and the subject? I am new into photography, I am sorry for my noob question.

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Further modifications are possible with the coefficients <$K_4$> and higher; due to the high powers in <$h$>, they affect mostly the outer parts of the profile.

However, if you are interested in shooting sports photography and you already have a 250mm lens on a crop sensor camera, it would be mostly worthless to spend $500 on a 300mm lens (assuming the optical quality is the same) because it will barely make a difference in the magnification and field of view.

Please understand that full frame cameras are neither superior nor inferior to crop sensor cameras.  They both have benefits and drawbacks.  I used to shoot a full frame Nikon camera, but ended up switching to a crop sensor Fuji XT1 camera which I'm really enjoying right now.  Don't let anyone tell you that a full frame camera is better.  It's simply different.

excellent tutorial on photography HARMER sir, my good wishes to you. SHASHI KUMAR MOGHE

Now that you've read through this handy cheat sheet of focal lengths for different situations, you should really consider checking out my free lens finder.  It asks you 5 questions about what camera you use and what you want to take pictures of and your budget, and it gives you my personal recommendation of the perfect lens for you.  Find your perfect DSLR lens here.

This is really a great information for beginners. Today I learnt something new and informative. Thanks so much, keep posting.

The essential function of focusing or defocusing optical elements is to cause a radially varying optical phase change. For example, for simple focusing of a laser beam with originally flat wavefronts one would ideally apply a phase change which has a quadratic component with radius (but no higher-order terms); this kind of radial dependence is approximated by an optical element with spherical shape, as long as one stays close to the beam axis. For more extreme positions, so-called spherical aberrations become relevant – particularly for lenses with high numerical aperture. Similar effects occur in imaging applications.

As an alternative to a multi-lens system, Knight Optical offers a wide range of high-quality aspheric optics including fire-polished and plastic aspheric lenses. Custom VIS and IR aspheric lenses are available including diamond turned infrared aspheric lenses, moulded glass aspheric lenses, including with diffraction-limited performance.

AMS Techno­logies offers a broad selection of aspheric optics for applications in the visible (VIS) and infrared (IR) wavebands such as collimation, focusing and coupling of fibers and lasers:

Asphericallens

Note that there are technical challenges not only concerning the fabrication of aspheric surfaces, but also concerning optical metrology. One needs to measure not only simple quantities like focal lengths (i.e., assess radius errors), but also additional parameters of the sag equation (see above). Both the surface accuracy and surface roughness are of interest; the former tells how well an optical service matches the designed shape over larger areas, while roughness is a phenomenon on smaller scales. Different methods are used for quantifying such inaccuracies of optical elements.

Other applications are in optical data storage, fiber optics (e.g. launching laser beams into fibers or fiber collimators) and optical space technology. Depending on the situation, the overall manufacturing cost may even be reduced, despite the higher cost of producing aspherical optical elements. For such reasons, modern software packages for optical design must have extended features concerning aspheric and general freeform optics. In fact, numerical methods are nowadays most often used for aspheric lens design.

Landscape photography (10mm to 18mm) Full body portrait of a person (24 to 45mm) Headshot (55 to 140mm) Night photography (10 to 18mm) Close-up photography or macro photography (70 to 150mm) Wildlife photography (200mm to 850mm) General lens for shooting family and kids (35 to 90mm) Outdoor sports photography (200 to 400mm)