Guide: About lens for newbies

[zoossh]

Please do not post in this thread in order to maintain a clean and efficient platform.
Status: Updated till 2009 Jan 18, in progress



Summary:
1. What newbies need to know about DSLR lenses?
1.1 Lenses are separated from the body
1.2 Know what lens mount you need for your camera body.
1.3 Know what is AF, MF and the motors.
1.4 Know whether the lens is suitable for your sensor frame.
1.5 General categorisation of lens by focal length.


2. DSLR lenses nomenclature
2.1 Lens abbreviations
2.2 Introduction to lens nomenclature
2.3 External controls
2.4 Image circle
2.5 Focusing Mechanism
2.6 Material and quality


3. Types of DSLR lenses
3.1 Fisheye
3.2 Ultrawide angle
3.3 Wide angle


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[zoossh]

1. What newbies need to know about DSLR lenses


1.1 Lenses are separated from the body

From the old days we use our film compacts to today we use our new electronic compacts, lenses are always integrated into the body, which together form the camera. On the other hand, some professional camera system can be separated and detached by the end-user into different components, with which they can choose the best of each component they want.

In DSLR, you have the benefit of using such semi-modular components and would be able to expand a plethora of different lens which are optimised for their respective range.

DSLR usually comprise of the following main detachable components.
1. non-inbuilt flash gun
2. pre-lens accessories
3. lens & tubes
4. body
5. batteries
6. storage medium
7. body accessories

When you make a purchase, "body only" means you are only buying the camera body at that price without including any lens, and you need to pay additional price for any lens you wanted to buy separately. "kit" means you are buying a package, which includes the camera body and the basic lens designated by the manufacturer.



1.2 Know what lens mount you need for your camera body.

When a camera body is separated from the lens, the body would have a hole with which a mirror can be seen, and that is the single reflex mirror (SLR) that gives the name of the camera type. Surrounding that hole is a circumferential metallic ring called the mount, which means the lens can be mounted on it.

On the back (rear) of the lens, you will see the last glass element of the lens, and surrounding it is again a ring protruding out. That is called the fittings, and it should fit the mount. However, most people called the fittings and the mount as single term - lens mount.

After you have purchased your camera body, you need to get lenses that can fit on the body based on this mount. This is the same when you check out what power plug you need to bring so that you can fit them into a socket when you go overseas. They must be able to fit not just physically, but the electronic compatibility also ensues ability
1. to meter correctly,
2. to control the aperture ring and
3. to autofocus correctly.

Different brands would have different designs of the connection between the mount on the body and the fittings on the lens. There are various technical reasons, but one of them is to lock the consumers to their initial investments of the lens so that they would stay with the same bodies form the same company. Each brand may have different generations of its mounts, but usually keep to one mount at a time.

Newer lens today of the same mount system are usually completely compatible but if you intend to buy older lenses, you will need to check the electronic compatibility. Of cos, those who are checking out the classic lenses are probably veterans who do not need to read this guide.

Current popular mount systems include

1. Nikon F mount: Nikon and Fujifilm brand bodies
2. Canon EOS mount: Canon brand bodies
3. Sony Alpha mount: Sony, Konica-Minolta brand bodies
4. Pentax K mount: Pentax, Samsung brand bodies
5. 4/3 mount: Olympus, Panasonic, Leica brand bodies

The naming convention or nomenclature gets complicated because there is such things called 3rd party, which means they manufacture parts that can be attached to and serve other parts of many other brands. So you need to know that there may be differences betweens the parts, as below,

[Brand of camera body] + [Type of body mount and subtype] vs [Type of lens fitting and subtype] + [Brand of lens]
Nikon body + Nikon F-mount vs Nikon F-mount fitting + Nikkor lens
Fujifilm body + Nikon F-mount vs Nikon F-mount fitting + Sigma lens
Fujifilm body + Nikon F-mount vs Nikon F-mount fitting + Sigma lens
Samsung body + Pentax K-mount vs Pentax K-mount fitting + Sigma lens
Sigma body + Sigma SA mount vs Sigma SA mount fitting + Sigma lens

As can be seen, the mount and fitting must be of the same type, and the brands of the body and lens most of the time follow the brand of the mount, but exceptions can be seen as above.

For 3rd party lens manufacturers, they may produce the same lens with different mounts. For example, Tokina 11-16mm f/2.8 lens only comes commercially available as Nikon and Canon mount, so Sony, Pentax, Olympus and other users would not be able to use this lens.

Sometimes there may be adaptors that would allow a different fitting to be attached via the adaptor to a different mount, however, they may not offer the electronic compatibility. Such adaptors are few, specific and expensive for obvious reasons.

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[zoossh]

1. What newbies need to know about DSLR lenses


1.3 Know what is AF, MF and the motors.

AF is autofocus. MF is manual focus.

Manual focus means that you need to use your hand to manually turn the focusing ring on the lens in order to focus properly.

Auto focus means that there is a complex system that allows the camera to automatically focused at a certain point according to the setting you set, by the simple action of half-press of the shutter release button.

AF requires a motor to do the mechanism of focusing, which can be in the body or in the lens.

It is an non issue in Canon bodies without in-body motor as most of their lenses have in-built motor. 3rd party lens made with canon mount also has in-built motor in order to make the AF work.

For Nikon bodies, currently D40, D40x and D60 are moves by Nikon that removes the in-body motor. However, only some lenses have in-built motor titled as AF-S (autofocus silent wave motor) which can be used on these smaller cheaper motorless bodies. These AF-S lenses are more expensive then the older AF-D lenses. If you use those non-AF-S motorless lens on the motorless bodies, they will still work but without autofocusing. You need to manually focus. 3rd party lens made with nikon mount are also not always made with motor. Sigma HSM (HyperSonic Motor) lenses is an option though.

There is no need to worry about both the body and the lens each having the motor. The lens motor will be used and is faster and more accurate.



1.4 Know whether the lens is suitable for your sensor frame.

After ensuring that the lens mount is compatible physically (usually proprietary brand to brand), and that the electronic fittings between the lens and the body works to give you aperture control, metering and autofocusing (or if you dun mind doing manual focusing without autometering), the next thing is to see if the lens's opening is big enough to cover the sensor image frame.

Most of us in the past couple years do not need to worry about that as the larger frame camera models are just out of affordability for us, but as the full frame models are pricing downwards and if the trend continues, it may well very soon be affordable to those richer newbies who are willing to spend on full frame models for their 1st DSLR. As of early 2009, Nikon and Canon sells their cheaper full frame models at about S$3000. And Sony has also joined the competition.

Try to imagine a round shaped cookie dough and a rectangular shaped cookie cutter.
The round cookie dough is the glass in the lens, of which its cross sectional dimension is called the image circle. The rectangular cookie cutter is the sensor in the camera body.

The cookie dough contains the contents of your image. Everytime you capture an image through the lens onto the sensor, is like cutting the round dough with a rectangular cutter. If you have a large dough, the smaller cutter applied on it will be able to carve out a rectangular piece out of the dough, that is the resultant image. If you have a dough that is smaller, the cutter can cut out most of the dough, but some part of the cutter may not be filled with the dough.

Similarly, the diagonal dimension of the rectangular sensor must be within the diameter of the image circle. If not, areas of the sensor that is not covered by the image circle will be black. You may be able to capture an image, but the image will always have dark concave corners.

Currently, full frame refers to the same size of the old 135 film used, which is 36 x 24mm. Most DSLR these days come at sizes that is smaller than that and is fairly close to the smaller film format of APS-C, and adopted this name although the sizes varies from brands to brands.

All older DSLR lens model share the same image circle size as the film SLR lens. In order to make lens smaller, lighter and faster to focus, and since the larger image circle is not required in the DSLR with APS-C size equivalent sensors, the image circle is reduced in these lens, that produce a proper rectangular image only on such sensors, but not on the older film SLR or on the newer full frame DSLR.

These lenses include
. DX: (Nikkor) Digital Exclusive
. DC: (Sigma) Digital Compact
. Di II: (Tamron) Digitally Integrated II. (Di is full frame while Di II lenses are meant only for APS-C size sensor)
. DT: (Minolta-Konica-Sony) Digital Technology
. EF-S: (Canon) Electro-Focus short back focus

Pentax, Samsung, Fujifilm and the 4/3 sensor family (Olympus, Panasonic, Leica) does not have full frame.

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[zoossh]

1. What newbies need to know about DSLR lenses


1.5 General categorisation of lens by focal length

Focal length remains the key determinant of categorisation of lens.

First of all, compatibility of physical contact and functional contact needs to be determined, that means
1. the camera body mount and the lens rear fitting can physically hold together without damaging any physical component of either the body or the lens, very much determined by the brand and type of mount/fittings as described above.
2. whether the lens have electronic components that enables coupling of metering, aperture control and focusing of the lens with inputs/outputs via the body. Those without such electronic components, especially with autofocusing, are regarded as manual focus lens or film lens. Depending on the era of the lens, compatibility of such couplings varies accordingly, e.g. some old lens can meter and control aperture but cannot autofocus.
3. whether the lens have an inbuilt motor for autofocusing when motor in the camera body is excluded, such as that in the Canon and the sub-entry levels of Nikon, e.g. D40, D40x and D60.

Put it simply, before focal length is discussed, DSLR lens can be broadly divided into MF (manual focus) or AF (auto focus) lens.

After the compatibility issue is out, everything seems to revolve around focal length, which primary determines magnification and reach, which in turns affect composition and working distance.

Broad categories include
1. Prime (fixed single focal length) versus Zoom (a range of focal length)
2. Low versus high power zoom (the span of the range of focal length)
3. Deviation from standard focal length, on one end wide, and the other end tele.
4. Minimal focusing distance which is affected by the focal length and the image distance.

As such the focal length and its range is always described in all lenses, and with which we can understand pt 1 to pt 3 from it directly. Pt 4 is often described as a separate value that we need to look at its specification directly as it is also affected by the image distance and cannot be judged alone by the focal length. Maximum aperture is the 2nd most important factor after focal length and is also always reflected in the nomenclature of all lenses. It determines the maximum light capturing ability. Special lens are adopted on other special features for special subjects, which will be described further below.

Focal length determines how much angle and how much magnification according to the size of your subject, the desired framing proportions at your standing position (distance from subject) accordingly. Note that the first two factors are equipment factors (angle of view, magnification factor) whereas the other three are subject and user factors, again illustrating that the user is not everything.

* the categorisation is arbitrarily grouped according to the focal length range that is often commerically available.

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[zoossh]

2. DSLR lenses nomenclature


2.1 Lens abbreviations

Frequently Used Acronyms in ClubSNAP
Patrick Murphy Studio's abbreviations used in lens names
Nikkor Lens Information by Thom Hogan
Nikkor Lenses Glossary
Canon Glossary
Sigma Lenses Overview
Tamron Digital FAQ
Tokina Optical Technology
Minolta AF
Dyxum lens glossary

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[zoossh]

2. DSLR lenses nomenclature


2.2 Introduction to lens nomenclature

This portion is a bit complicated as different companies have different descriptions and abbreviations. The common portion however is as below.

[Brand] [Mount type] [focal range] [maximum aperture at shortest and longest focal length]

e.g. Sigma (Nikon F-mount) 12-24mm F4.5-5.6 EX DG ASPHERICAL HSM (ignore the latter portion first)
it is hence maximum aperture size of f/4.5 at 12mm and maximum aperture size of f/5.6 at 24mm
usually the mount type is not mentioned in the description, but on purchase, the retailer will almost always ask you.

If there is no range given, it means either a prime lens with only 1 focal length, or it has a uniform maximum aperture throughout all its focal length range


Lens focal length nomenclature
If only a single figure is given, e.g. Nikkor 50mm f/1.8 AF D, it means it is a prime non-zoom lens that have only 1 focal length with only 1 constant angle of view. Composition varies only by movement of subject or photographer.

If a range is given, e.g. Nikkor 18-200mm f/3.5-5.6 AF-S G VRII, it means it is a zoom lens that can change the focal length and angle of view.


Lens aperture size nomenclature
As described above, the maximum aperture size at a given maximum and minimum focal length is given, whereas the minimum aperture size is not given.

Apparently a prime lens with a fixed focal length will only have a single maximum aperture size. In the case of a zoom lens, it may have a single value or two values. Two values are designated to the maximum aperture size respectively at the maximum and minimum focal length, and this is called variable aperture. If the maximum aperture size remain unchanged at both the maximum and minimum focal length, i.e. having only 1 single value, it is called a constant aperture.


Other lens features with standard nomenclature
I have classified the rest of the references under these features (check the lens abbreviations for more information)

1. image circle
A full image circle is required for a full size digital sensor or film body. A modern lens with a full image circle is compatible for both full or smaller size digital sensors, but is more expensive and heavier. Smaller image circle for smaller sized sensors however can give rise to lighter and smaller designs, but is not compatible with the full size digital sensor or film body in the way that it will only cover the peripheries.

2. focusing mechanism
Modern lens should have autofocusing, mostly available with lens motor which is faster than the body motor. Short minimal focusing distance is required for macrophotography.
- availability of autofocusing, either from body or lens motor
- availability of lens motor
- movement mechanisms of the elements and the barrel
- minimal focusing distance, whether short or normal

3. material
Basically adopted to reduce the susceptibility of digital sensor which at this point of time is still not so sensitive to light falling onto the sensor at an angle, especially on the peripheries. Also due to increased number of elements, the likelihood of reflections between the elements within the lens is increased too, thereby requiring better coatings and glass qualities.
- special coating
- glass shape
- glass quality
- build quality

4. what kind of controls it has on the exterior body

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[zoossh]

2. DSLR lenses nomenclature


2.3 External controls

This refer to the way how a lens include information and control of aperture, focal length, focusing distance, may also derive some abbreviation, e.g. D (Nikkor) refer to distance information (usually with aperture ring), whereas G (Nikkor) refer to lack of aperture ring.

Basically the rings and switches on a lens are quite limited, unlike the body. Depending on brands, turning of ring in a clockwise or anticlockwise fashion may derive different effects.

The ring that will always be there is the focusing ring. Basically it does manual focusing. A switch such as M/A mode (Manual Focusing and Autofocusing switch) will mean that you can disable and enable autofocusing on the lens.

Next is the zoom ring, which of cos always exists on zoom (variable focal length) lenses, and never exist on (single focal length) prime lenses.

Lastly is the aperture ring, which nowadays have been taken away from some of the lens, thereby meaning that aperture size can only be regulated on the camera body and effected on the lens.


With regards to Nikkor lenses, there is abbreviation to such lenses with different controls,

D: Distance information (Nikkor), available in D-type and G-type lenses, or Distance integration (Minolta)
helps to relay subject-to-camera distance information to AF-capable bodies, thereby supporting electronic calculations in focusing, metering and flash.

G: Genesis designation (Nikkor), refering to newer G-type Nikkor lenses where the physical aperture ring is removed and its function replaced by selection on the camera body. Do note D-type Nikkor lenses does have an aperture ring. Further information on AF-D and AF-G Nikkor lenses are available here from Grays of Westminster Glossary.

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[zoossh]

2. DSLR lenses nomenclature


2.4 Image circle

Smaller image circle
This group of lens is often termed “for digital only”. The image circle is large enough only for an APS-C size sensor (about 24mm x 16mm) at its widest aperture size throughout its range. If used on film, or a full-size (35mm equivalent) or closed to full size sensor, light will not adequately cover the entire film/sensor area thereby giving severe physical vignette. However, these formats makes for more compact and lighter construction at a cheaper price.

The confusing part is manufacturers termed their lens with special coating that make the light more coincident on the sensor as “for digital”, which is different from the compatibility issue.

. DX: (Nikkor) Digital Exclusive
. DC: (Sigma) Digital Compact
. Di II: (Tamron) Digitally Integrated, with additional coatings to reduce reflections off the sensor chip. Unlike Di, Di II lenses are meant only for APS-C size sensor.
. DT: (Minolta-Konica-Sony) Digital Technology

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[zoossh]

2. DSLR lenses nomenclature


2.5 Focusing Mechanism

The ability to do autofocusing basically differentiated between traditional and modern lenses.

. AF: Autofocusing
. MF: Manual focusing
. MP-E: Canon designation for manual focus macro lens
. EF: Electronic Focus (Canon; also refer to its lens mount)



Focusing Mechanism: In-lenses Motor
Basically refer to special ultrasonic motor for autofocusing, supposedly faster and less noisy. And is required if the camera body has no motor, e.g. Nikon D40

. AF-S: (Nikkor) Autofocusing with Silent Wave Motor
. SWM: (Nikkor) Silent Wave Motor
. xi: (Minolta-Konica-Sony) Motorized Zoom
. SSM: (Minolta-Konica-Sony) SuperSonic Motor
. USM: (Canon) Ultrasonic Motor
. HSM: (Sigma) HyperSonic Motor
. MSM or M-HSM: (Sigma) Micro HyperSonic Motor



Focusing Mechanism: Handshake & vibration reduction
Reduces vibration by 1-2 stops, allowing slight improvement over borderline cases
. VR: Nikon Vibration Reduction
. VC: Tamron Vibration Compensation
. IS: Canon Image Stabilisation
. SSS: Sony Super Steady Shot
. OS: Sigma Optical Stabilizer
. SR: Pentax Shake Reduction



Focusing Mechanism: Rear focusing
Only the rear lens group moves for focusing, thereby making autofocusing smoother & faster.

. RF: Rear Focusing (Nikkor & Sigma)
. IRF: Internal Rear Focus System (Tokina)



Focusing Mechanism: Constant barrel length
Only the inner lens group or groups moves and hence the outer lens barrel does not extend or rotate during focusing, thereby allows for a more compact, lightweight construction as well as a closer focusing distance with faster focusing & improved handling over a shorter length. As the filter thread and barrel does not rotate, it reduces difficult handling of circular polariser and graduated filters.

. IF: (Nikkor & Tokina)Internal Focusing
. IF: (Sigma) Inner Focus, does not extend outer barrel
. HF: (Sigma) Helical Focusing, does not rotate outer barrel



Focusing Mechanism: short minimal focusing distance, aka macro
Lens that can focus closeup; specifically, the size of an object focused on the film or sensor is close to the same size as the actual object
. Micro: Macro (Nikkor)

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[zoossh]

2. DSLR lenses nomenclature


2.6 Material and quality

Material: Coating of glasses
usually meant to reduce reflections, flare, ghosting, chromatic aberration and vignetting, especially effective for lenses with a large number of elements, e.g. zoom, on digital sensors

. SIC: (Nikkor) Super Integrated Coating
. N: (Nikkor) Nano Crystal Coat , features ultra-fine crystallized particles of nano size (one nanometer equals one millionth of a mm).
. DG: (Sigma) Designed for digital
. Di & Di II: (Tamron) Digitally Integrated
. MC: Multi-coating (Tokina)



Material: Special elements shape
Aspherical lens elements are particularly useful in correcting the distortion in wideangle lenses, and also contributes to a lighter and smaller lens design.

. ASP: Aspherical lens elements
. ASL: Aspherical lens elements (Tokina)



Material: Special elements contents
Glass with low dispersion minimized chromatic aberration (image and color dispersion that occurs when light rays of varying wavelengths pass through optical glass) and gives better focusing of colors, which is often a problem with conventionally designed wide-angle lenses.

. ASPH: (Leica) Aspherical
. APO: (Sigma, Minolta-Konica-Sony, Leica) Apochromatic
. AD: (Tokina) Anomalous Dispersion
. LD: (Tamron and Promaster) Low-Dispersion glass
. ED: (Nikkor) Extra-low Dispersion
. SD: (Tokina)Super low Dispersion glass
. SLD: (Sigma) Super Low Dispersion glass
. UD: (Canon) Ultra-low dispersion glass
. HLD: (Tokina) low dispersion glass with higher refractive index
. XR: (Tamron and Promaster) Extra Refractive index glass



Premium series labelling
Basically refer to higher end models, with special glass/elements, good build/finish, better optical quality.

L: (Canon) Luxury Low Distortion, with ultra-low and super low dispersion glass, fluorite elements & aspherical elements
EX: (Sigma) Excellence, with good exterior finishing and build with better optical quality.
SP: (Tamron) Super Performance
AT-X & AT-X Pro: (Tokina) Advanced Technology-Extra
G: (Minolta-Konica-Sony) Gold



Others
CRC: Close-Range Correction system (Nikkor), adopts independent movement of each lens group, & improves picture quality at close focusing distances, thereby increasing the focusing range.

DF: Dual Focus mechanism (Sigma), disengages the linkage between the internal focusing mechanism and outer focusing ring when the focusing ring is moved to the AF position. This provides easier & precise handling, since the focusing ring does not rotate during autofocusing. The wide focusing ring also enables easy & accurate manual focusing.

DC: Defocus-image Control technology (Nikkor). By rotating this ring, it allows control of spherical aberration in the foreground or background and create a rounded out-of-focus blur ideal for portrait photography.

STF: (Minolta-Konica-Sony) Smooth Transtition Focus, contains a special element which makes transitions between in and out of focus areas very smooth. This gives a Bokeh of the highest quality.

DO: Multi-Layer Diffractive Optical Element (Canon), which substitutes a thin diffraction grating for a thicker internal lens. Quoted from kirbic from dpchallenge, as opposed to refraction which is the way a curved lens bends light, diffractive optics, as the name implies, rely on diffraction to bend light. Typically one element is the lens is diffractive, and it enables a smaller, lighter lens for a given focal length. Further information here.

RS: (Minolta) Restyled (aka "New"), aesthetic changes, and possible faster focus or addition of D feature.

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[zoossh]

3. Types of DSLR lenses


3.1 Fisheye

Although fisheye has additional features than an ultrawide angle lens and can be regarded as a lens with special features, it is discussed here as its ultra-ultra wide angle and corresponding short focal length is a determinant along the focal length spectrum.

Fisheye lens refers to lens where barrel distortion that comes with its ultrawide angle is the INTENDED effect. It is often extremely wide-angled and close to 180 degrees angle of view, possibly able to capture your foot if you have your foot slightly forward, tilting the camera slightly down and not checking through the viewfinder. The focal length is often less than 10mm, nonetheless the angle of view is still a combined effect of the actual focal length and the sensor size, unless we are talking about corrected focal length equivalent to 35mm aspects. Putting on camera bodies of different sensor sizes, the angle of view changes and the effect changes.

The novelty of the fisheye effect can quickly run out without careful selection of subjects and composition. Often fisheye pictures that failed is because of a person's normal senstivity to composition can be affected by infamiliarity to the distortion. Things that is obvious in normal wide angle shots becomes less obvious when composing in fisheye at the time of capture. Without a central object of interest in sufficiently large proportion, which is easily the case as wide angle pictures makes everything small, the compositional impact will fail. It is like taking of an eye with a large pupil and having all the details in it (good composition), versus having an eye with all the white sclera and a small black pupil in it (bad composition).

Situations used for fisheye is plenty perhaps, as I have not acquired a fisheye lens to experiment. I'm pretty sure with the distortion, a lot of creativity can be explored and I would not be able to think of them now. Some commonly seen situations used for fisheye, is a little extension of the ultrawide angle that i more commonly used, and that includes

1. exaggeration of a central subject that is very near (animals head, and safety first when attempting such acts)
2. broad landscape with exaggeration of horizon.
3. indoor with enclosed space
4. subjects that runs harmoniously with similar spherical shapes to the fisheyes (existing domes, curves, burst fireworks that is rounded)


There are two types of fisheye lens.

1. Circular fisheye: 180 degrees angle of view, where the image does not fill the whole frame but simply the middle surrounded by black (similar to APS-C sized lens paired with larger sensors, but with the distortion)
1. Diagonal fisheye: extreme barrel distortion around the edges, but the image fill the whole frame.

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[zoossh]

3. Types of DSLR lenses


3.2 Ultrawide angle

* the categorisation is arbitrarily grouped according to the focal length range that is often commerically available.


Nomenclature
This category of digital lens come into place after modern DSLRs adopt a smaller sensor size, as such many focal length now becomes more tele on the new bodies using the same old lens. With a 1.5x crop factor, a 24mm (wide) becomes 36mm (mid wide) and a 35mm (mid wide) becomes 50mm (standard). The previous wide angle lens now loses the wider end of the wide angle, and started from the mid wide portion onwards. New digital lens are thus invented to cover the wider end of the previous wide angle, as well as a portion that is really wide, called the ultrawide angle.

As there is no objective definition to the angles, it is determined by two things, by what is commerically available, and secondly by what you can subjectively set as a cut off. The current ultrawide angle lens are mainly between 10-24mm which on 1.5x crop factor becomes 15-36mm. As for personal subjective cut off, I notice more distortion and apparent differential sizes of near-far items at around 14mm and below on my 1.5x crop factor Nikon D50, which is about 21mm on 35mm equivalents.


Form
One might notice the longer the focal length, the longer and bigger the lens is. However, ultrawide angle lenses also appear large. This is as quoted from wikipedia (2007 Nov 24), the mirror box "prevents lenses from having rear elements closer to the film or sensor to be mounted" and "this means that simple designs for wide angle lenses cannot be used. Instead, larger and more complex retrofocus designs are required."


Application
The use of ultrawide angles are used for various purposes, which is usually done NEAR to the subject.

1. need to encompass many separate activities or details on a horizon.
- for panaromic crop of human activities
- for landscape with vertical details, e.g. mountains, with which the wide angle requirement is determined by how far you are from the subject. If you are really very far away from the subject, such as mountain ranges where you are standing like a few kilometres off, very often wide angles itself are sufficient and in some cases, isolation with longer focal lengths may be applied instead.

2. need to cover a broad cluster of activities or subjects in an enclosed space
- small exhibition rooms through a window
- indoor with limited space, group photos (distortion would be apparent if it is too wide)
- ultrawide angle is very useful but beyond a certain threshold, distortion becomes very bad and is not nice for faces near the periphery, the less wide end of a ultrawide angle lens is thus better applied if the space constrain allows
- once out into the streets and alleys, there is often a little more space to move around, thus a conventional wide angle to standard focal length lens (with 1.5x crop factor bodies) are better suited for this purpose instead of ultrawide.

3. need to cover a tall or big structure very near to you
- usually on buildings where one hope to capture the roof to the bottom, usually a chapel or something, about 2 floor high
- you may be able to move to the farthest end, on a road opposite this building, often with your back against the building that is opposite your subject.
- distortion especially of converging verticals is acceptable, and can gives good effect depending on your taste. failing which the only other option is to invest in a tilt shift lens or to move to a floor that is directly opposite to the centre of the building.

4. to emphasize size differences between near far effect
- it can be applied on many things, such as the face of an animal. it can achieve very comical effects, and less suitable for solemn subjects, e.g. human portraits.
- the application on sports, provided safety is ensured, when being very near to the subject, can bring drama to the activity.


Choices

Nikon F mount
14mm f/2.8D Nikkor AF, ED FX
14-24mm f/2.8G Nikkor AF-S, ED FX
12-24mm f/4.5-5.6, Sigma DG HSM, EX ASPHERICAL FX
12-24mm f/4G Nikkor DX AF-S, IF-ED
10-16mm f/2.8 Tokina DX AF, AT-X 116 Pro
12-24mm f/4 Tokina DX II AF, AT-X 124 Pro
10-20mm f/4-5.6, Sigma DC HSM, EX
11-18mm f/4.5-5.6, Tamron Di-II AF, LD Aspherical IF SP
10-24mm F/3.5-4.5, Tamron Di-II AF-built in motor, LD Aspherical IF SP

For good reviews for nikon mount ultrawide angle zooms, one can read the following,
Kenrockwell: Very directional guide to lost souls.
Nikonians : More objective guide to more experienced users.

Canon EF mount
14mm f/2.8L II Canon EF USM FF
12-24mm f/4.5-5.6, Sigma DG HSM, EX ASPHERICAL FF
10-22mm f/3.5-4.5, Canon EF-S USM
10-16mm f/2.8, Tokina DX AF, AT-X 116 Pro
12-24mm f/4 Tokina DX II AF, AT-X 124 Pro
10-20mm f/4-5.6, Sigma DC HSM, EX
11-18mm f/4.5-5.6, Tamron Di-II AF, LD Aspherical IF SP

Sony-Konica-Minolta A mount
12-24mm f/4.5-5.6, Sigma DG AF, EX ASPHERICAL FF
11-18mm f/4.5-5.6 Sony DT
10-20mm f/4-5.6 Sigma DC HSM, EX
11-18mm f/4.5-5.6 Tamron Di-II AF, LD Aspherical IF SP

Pentax K mount
12-24mm f/4.5-5.6 Sigma DG AF, EX ASPHERICAL FF
14mm f/2.8 Pentax
14mm f/2.8 Pentax DA
15mm f/4 Pentax DA, ED AL Limited
10-17mm f/3.5-4.5 Pentax
12-24mm f/4 Pentax
12-24mm f/4 Pentax DA, smc ED AL IF
10-20mm f/4-5.6 Sigma DC HSM, EX

Four-third mount
Four third . org
7-14mm f/4 Zuiko Digital ED (35mm equivalent: 14-28mm, 1.5x equivalent: 10-19mm)
9-18mm f/4-5/6 Zuiko Digital ED (35mm equivalent: 18-36mm, 1.5x equivalent: 12-24mm)
11-22mm f/2.8-3.5 Zuiko Digital (35mm equivalent: 22-44mm, 1.5x equivalent: 15-30mm)
10-20mm f/4-5.6 Sigma DC HSM, EX



Issues
Problems with ultrawide angle is of cos due to the fact of its extreme optics
1. Due to its difficult optics which is a long story, ultrawide zooms are large and heavy, yet difficult to give very good optic quality as compared to the wide and standard focal lenths.
2. There is a higher likelihood of barrel distortion as well as converging verticals when pushed to extreme.
3. Faces are distorted at the peripheries and presented a main source of visual disturbance to some as human face are one of the most familiar recognisable subject that is least tolerant to distortion.
4. Light fall off may occur towards the peripheral due to difficult optics.
5. Ultrawide are more prone to physical vignetting, which depends on the thickness of the extension, which are usually in the form of extra screw on filters and cokin rectangular filters. As a rough guide for me, a normal thickness UV filter + a single slot cokin holder will physical vignette at 12mm and below, and clear safely off the shadows at the corners from 14mm onwards.
6. Ultrawide emphasize the uneven polarisation even more, when the sun is on one side of the sky near or within the frame.
7. Ultrawide brings in a lot of horizontal details which test one's judgement on composition.
8. Ultrawide can make things really small. If there is a lack of vertical interest, an ultrawide landscape can be boring, flat and undramatic, with a large empty sky, large empty foreground and tiny subjects at the horizon.

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[zoossh]

3. Types of DSLR lenses


3.3 Wide angle

* the categorisation is arbitrarily grouped according to the focal length range that is often commerically available.


Nomenclature
At 1.5-1.6x crop factor for most half-frame or APS-C size sensors, most wide angle lens starts from 17-18mm, which is about 26mm onwards at 35mm equivalents.


Application
Wide angle lens lack the extreme features of the ultrawide, but is still needed to be relatively near the subject.

It is often included within the range of a kit lens, and at the wider end of 18mm at 1.5x crop factor gives you an angle of 77 degrees, which is slightly less than 90 degrees which you can easily estimate by putting your arms out and perpendicular at each other. This should comfortably include a few person a few metres from you, or a store from you, or a door from you. If you step back to maybe 3-5m away from subject, you can include more.

It can emphasize a nearby large object using its widest end, but not as much as the ultrawide, and can be used in a mid size room like our HDB kitchen but not in the toilet. It is hardly enough to cover a tall building at close distance though, which would require a ultra-wide angle. If you use wide angle lens from 18mm onwards, you probably need to shoot from across a road to include the whole building.

As already noted, the usefulness of the wide angle is already a little limiting, so it almost becomes the minimum requisite of all travel lens, as the next focal range starting from 35mm at 1.5x crop factor onwards will only allow you to capture within 45 degrees of view.

The tele end of these lenses starting from 18mm varies, and so will not be covered here.


Choices
Choices are plenty and varies in terms of power. For Nikon, it can be 17-35mm, 18-55mm, 18-70mm, 18-135mm to 18-200mm, or for Tamron, up to 18-250mm.

Powers is measured by the number of times the shortest focal length is multiplied. So 36mm = 2x 18mm.
17-35mm (2x),
18-55mm (3x),
18-70mm (4x),
18-135mm (8x),
18-200mm (11x)
18-250mm (14x).

Generally, the longer the tele end, the larger, longer and heavier is the lens, so it weighs both for and against travel, which is to be versatile and to be light. The optic quality usually drops with increasing power. Generally, those less than 5x power seems to be better rated.

And of cos, the maximum aperture usually decreases with longer focal length, or if not, will require a larger lens with better glass. Apart from the power, these lens are also separated by their maximum aperture.

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