- a camera lens is one of the most important aspects of the technical
component of photographic equipment, and fortunately the part that will
depreciate in value the slowest & thus an area which should be
considered when purchasing a new camera - get the best lens that you can
afford that will do the job for you.
- one of the problems confronting many photographers who use dSLRs is the
different requirements of a lens for a cropped sensor dSLR to that of a full
- a full frame dSLR requires consistent sharpness across a 43mm image
circle with minimal vignetting
- most legacy zoom lenses struggle to match the consistent
resolution required for a 16mp full frame dSLR
- for this reason, Nikon are creating new higher resolution lenses
for their full frame dSLRs (their new tilt shift lenses and their
new wide angle zoom) and it can be expected Canon and Sony will
follow suit as not even Canon's L series zooms are likely to be
adequate for the 21mp 1DsMIII.
- a case in point is a comparison of two of the most commonly used
pro 70-200mm lenses designed to cover 35mm film:
- Nikon's AF-S
VR 70-200mm F2.8G appears optimised for cropped sensors as
it is sharper on these than is Canon's on a cropped sensor wide
open, but suffers from more distortion, vignetting, CA and soft
corners on a full frame. This is perhaps not surprising as up
until 2007, Nikon did not have a full frame dSLR.
- Canon's 70-200mm
F2.8L IS appears optimised for medium resolution full frame
and is soft wide open on cropped sensors.
- a cropped sensor dSLR requires even higher spatial resolution but
confined to a smaller image circle (eg. 28mm for a 1.6x crop)
- most legacy zoom lenses struggle to match the central resolution
required for a 10mp APS-C cropped sensor dSLR which has ~175
pixels/mm compared to a Canon 5D of a less demanding 121 pixels/mm.
- one of the reasons I chose the Canon 1DMIII 1.3x crop camera is
that its sensor resolution is ~135pixels/mm, not too high for good
quality legacy lenses while its 1.3x crop removes many of the issues
with vignetting and poor corner performance of full frame lenses.
- for this reason, Olympus created specially designed high
resolution, telecentric lenses for their 2x crop sensors which on a
10mp sensor has 203 pixels/mm.
- see also sensors.
- in general, you get what you pay for as designing complex lenses of high
quality is always a matter of making compromises between:
- cost of production
- build quality
- optical aberrations
- at different focus points, apertures and focal length (if a
- how does the lens' resolution relate to the sensor resolution - is
the lens the bottleneck in the system?
- at small apertures (eg. f/11 or smaller), the laws of physics
(diffraction) is what usually becomes the bottleneck limiting
resolution in any good quality lens
- at wider apertures, it may be the lens:
- it is said that current Canon L series lenses are only
just adequate for the 16.7mp Canon 1Ds Mark II camera but
better lenses will be needed to make the most of a 22mp
sensor of the same size.
- it would be thus reasonable to assume that in resolution
terms, lenses not specifically designed to match digital
sensors are likely to be the resolution bottleneck if sensor
resolution exceeds 139 pixels per mm.
- pixels per mm for various sensors:
- 22mp full frame = 160 pixels per mm
- 16.7mp Canon 1Ds Mark II = 139 pixels per mm
- 12.7mp Canon 5D = 121
- 12.2mp Nikon D2Xs = 181
- 10mp Canon 1D Mark III = 135
- 10mp Canon APS-C = 175
- 10mp Nikon DX = 163
- 10mp Olympus = 203
- 7.4mp Olympus E330 = 174
- BUT if the camera is not on a tripod and the shutter speed
is not fast enough, then camera shake is much, much more likely to be the
bottleneck this is why image stabilisers
can be so important.
- zoom range:
- it is much harder to create great quality wide angle
zooms than telephoto zooms
- furthermore, the longer the range of zoom, the more sacrifices in
other areas one must make
- changing the focal length does not effect the focus - many
modern auto-focus lenses are not parfocal, meaning one has to re-focus
when you change the zoom setting which is not usually a problem in
auto-focus mode but a considerable problem in manual focus mode.
- not such a problem with film but digital sensors have a
thicker "cell" and thus do not tolerate light coming in at
sharp angles which is particularly noticeable when using wide angle
lenses designed for film cameras on digital cameras, especially at wide
open apertures, which results in "purple fringing" due to
chromatic aberration and vignetting. For this reason, Olympus in
particular, has created a new series of lenses especially designed for
digital with telecentricity a major design point.
- circle of illumination:
- the size of the image it projects - this is
why small digital sensor cameras can have smaller lenses at cheaper
prices for similar optical quality, zoom range, etc.
- optical speed:
- ie. the maximum aperture available on the lens
- for moving subjects or when shallow DOF is needed, a faster lens
is better than a slower IS lens
- how pleasant the out of focus highlights appear - this is one
reason why Leica's lenses were so highly sought and why many dislike the
compact telephoto mirror lenses. In general, bokeh is determined by the
shape of the lens aperture diaphragm, the more circular, the better.
- the modern medium to high end digital lenses tend to have more
- flat focal field
- is the plane of focus flat ie. if you take a photo of a 2D object
will the edges be in focus as well as the middle
- this is particularly important for astrophotography and
- flat field brightness:
- how even is the brightness from edge to edge
- lens-camera systems have both:
- internal vignetting which is dependent on the characteristics
of both the lens and film or sensor, and is dependent on focal
length and aperture
- panorama film cameras such as 6x9 usually need a centre
spot ND filter to correct this intrinsic vignetting with
wide angle lenses.
- full frame digital sensors often have substantial
vignetting which can be corrected in RAW processing
- extrinsic vignetting - such as may occur when filters are
stacked and block marginal light paths
- astrophotographers often correct these by taking photos of an
evenly lit plain surface and then using the inverse of this digital
image to subtract from the original image.
- additional functionality:
- auto-focus speed and acoustic noise
- internal focusing - lens size does not change when focusing
- image stabiliser
- built-in ability to minimise effects of camera
- built-in lens hood
- built-in filters - some lenses with large apertures have built-in
- weather/dust-proofing, etc
- perspective control
- ability to correct for converging tops of
buildings, etc by shiftng the lens relative to the "film"
plane - also called "shift lenses"
- ability to change the plane of focus by tilting the lens -
also called tilt-shift lenses
- professionals demanding the highest quality images, still usually prefer
fixed focal length lenses over zoom lenses as they will usually have the
best optical qualities, in particular, contrast, low optical aberrations and
- consumers on the other hand are usually happier to compromise image
quality for the more versatile benefits of zoom lenses.
But which lens to use?
- each lens is optimised for a specific purpose
- let's look at choice of focal length and aperture:
- if you can move in or away from your subject so that the subject
size remains constant in your image, then choice of focal length and
aperture is critical in the final result:
- the longer the focal length:
- the further away from the subject you can be which may be less
intimidating and safer
- the less perspective distortions (a wide angle will exaggerate
size differences of those parts closer to the lens compared with
those further away from the lens)
- one good reason why most portraits are taken with a short
- the narrower the background (ie. perspective is altered) which
can remove distracting backgrounds
- the greater the effects of camera shake and thus the need for
tripod, image stabilisation or faster shutter speed
- although the total DOF actually remains
approximately constant with changing focal length at same aperture, the
longer focal length lens will have more front depth of field
and less rear depth of field.
- background blurriness should remain constant although points
at infinity may be more blurry?
- for action photos with a moving subject coming towards you, a
longer focal length at the same image magnification actually makes
focusing easier as the lens will not need to move through as much of
its focus range and thus auto-focus should be quicker.
- the more distant is the minimum focus distance (usually - but
this depends on lens design)
- the wider the aperture:
- the faster the shutter speed needed for the same exposure or a
lower ISO, or a ND or pola filter
- hence sports photographers prefer f/2.8 telephotos or f/4
- indoor sports photographers prefer a f/1.8-2.0 short
telephoto (NB. the Canon EF 85mm f/1.2 is a bit slow on the
AF for indoor sports)
- the more blurry the background will be (this is dependent
mainly upon aperture and not focal length)
- hence portrait photographers use 85mm f/1.2 or f/1.4
lenses if possible
- the shallower the depth of field
- hence landscape photographers prefer using f/11-22 to
- the bigger and more expensive the lens
- a compromise is often made here on weight for hiking and
travel as well as for budget.
- if you are mainly going to use a lens at f/8, not much
advantage in paying for and carrying a f/1.4 lens when a
f/2.8 will do you very nicely.
- often the more severe the aberrations such as lens flare, loss
of sharpness, coma, purple fringing, etc.
- most lenses are optimised for use at f/5.6-f/11 whereas
diffraction problems impair resolution at f/16-22
- purple fringing is an issue with most lenses on digital
SLRs at apertures wider than f/2 or f/2.8, and this may have
more to do with the microlenses on the sensor than the lens
- a large aperture lens often has a larger rear element
which may cause more internal lens flare on digital cameras
and reduced contrast by light reflecting between it and the
surface of the sensor.
- if you can't move in or away from your subject, then subject image
size and angle of view become important, and this is dependent on focal
What lens kits with image stabilisation to cover 14-400mm
range in 35mm terms:
- Olympus Four Thirds:
- Olympus ZD 7-14mm
- Olympus ZD 12-60mm f/2.8-4.0 SWD
- Olympus ZD 50-200mm f/2.8-3.5 SWD
- Olympus ZD 50mm f/2.0 macro
- this gives the best range, quality for number of lenses, weight, size
and aperture whilst giving IS on the full range
- Canon EOS full frame:
- Canon EF 14mm f/2.8L II (no IS)
- Canon EF 16-35mm F/2.8L II (no IS)
- Canon EF 24-105mm f/4L IS
- or Canon EF 24-70mm f/2.8L (no IS)
- Canon EF 70-200mm f/2.8L IS
- Canon EF 100-400mm f/4.5-5.6L IS
- Canon EF 100mm f/2.8 macro (no IS)
- has the advantage of allowing specialty lenses such as tilt-shift
- Nikon full frame:
- astrophotography is
extremely demanding on lenses, as it requires:
- maximal performance at infinity focus
- well corrected for aberrations as these become very obvious with pin
point objects such as stars
- very high contrast to bring out detail in faint deep sky objects so
that they can be seen against the background
- relatively fast lenses to minimise exposure time - usually require an
aperture diameter of at least 70-80mm, preferably 100mm with a f-ratio
- for this reason, normal camera lenses (even Canon's L series zooms or IS
lenses) usually just
do not cut it for getting the best images of deep sky objects as:
- they are usually not optimised for infinity focus
- have too much glass in them correcting aberrations resulting from need
to focus close or to zoom, resulting in lower contrast & potentially
- if you must use one, avoid a zoom lens and avoid optical IS lenses.
- better options are dedicated refractor telescopes (although these are not
so good for terrestrial photography) such as:
- Takahashi FSQ106
- Most of the refractors will cover a full 35 mm frame.
Mostly they only have to cover a half frame or so. But today the
CCD cameras are getting to be full frame as well. The latest favorite CCD camera of the top
line astrophotographers is the SBIG STL 11000 which is full frame.
It is interesting to note that the best refractors are pressed by these
large chip cameras. In fact SCTs have an even harder time with the
new larger chip cameras.
- SCT telescopes do not usually adequately cover a full 35mm frame.
Amazingly even the 16" f10 SCT has a useful circle of illumination
of only about 26 to 30 mm. This gigantic telescope then does not
cover the chip in the 1Ds MarkII or the SBIG STL 11000.
Testing lens resolution:
- it is a good exercise to test how good your lenses are at different focal
ranges (distance to subject) and different apertures, and for zooms, at
different focal lengths, as this enables you to better choose the best lens
for the job at hand.
- a relatively quick method is to photograph lens resolution charts placed
in the centre and in the corner(s) of the image:
- see John
Chapman's lens testing resources
- print a few copies of the resolution
chart onto A4 sheets and mount on wall with sticky tape or blue tack
- ensure charts are evenly lit with lights at 45deg angle to chart and
keep lighting the same for all tests.
- set camera on tripod so that corner chart is in the corner
- the magnification factor = front of lens to chart in mm / focal length
- take the photo and view zoomed in to determine the smallest triplet of
lines where you can see each line
- check on this table to work out the chart lines per mm for that
|Group \ Pair
- you can then determine lens resolution by multiplying your magnification
factor by the triplet resolution in the table
- given your setup and methods are not likely to be the same as others,
your calculations will not be comparable but they should be able to give
you a good indication of relative resolution between your lenses.
- see my Olympus C8080
- here are some of my examples with subject distance = 2.9m and using
100mm focal length lens (in 35mm terms) with values being for centre / top
right corner (for simplicity I will use magnification factor of 29 for
all, thus ignore the actual values - only use relative values):
|100mm (in 35mm equiv.)
||2600/2600 at f/3.2
|Olympus E330 + 14-45 kit lens
|Olympus E330 + 50mm f/1.4 Zuiko OM
|Olympus E330 + 50mm f/1.8 Zuiko OM
||3200/1750 at f1.8
|Olympus E330 + 50mm f/3.5 Zuiko OM macro
|| 3300/3300 at f3.5
here is the tiny cropped but non-resized top right corner, as
you can see the triplets are clearly visible down to #2 of group
1 (you may need to save it and view at 200%)
|Olympus E330 + 35-105mm Zuiko OM
||3100/3100 at f/3.5
- as you can see, the manual focus OM Zuiko lenses, even when at 2x crop
on the E330, perform very well, much better than the budget kit lens, even
wide open although the f/1.8 lens had problems at the corners which
appears to be due to astigmatism.
- here are some of my examples with subject distance = 7.8m and using
270mm focal length lens (in 35mm terms) with values being for centre / top
right corner (for simplicity I will use magnification factor of 29 for
|270mm (in 35mm equiv.)
|Olympus E330 + 75-150mm Zuiko OM
||2300/2300 at f/4
|Olympus E330 + Vivitar 135mm f/2.3
||2300/2300 at f/2.3
|Olympus E330 + Tamron 135mm f/2.8
- the 75-150mm OM was quite disappointing, while the Vivitar and Tamron
did not seem to focus at infinity and all three appeared low in contrast -
personally I would not recommend these on the Olympus E-series.
Lens mount adapters:
- general info on use of adapters:
- you will always lose any electronic linkage between the lens and
camera body, so forget about shutter priority or autofocus or AF
adjusted auto flash TTL aperture control
- Leica M lenses can be serviced so that lens information will be
transmitted to the forthcoming digital Leica M body to allow image
optimisation (software-based moire reduction) as well as inclusion in
image EXIF data. All M lenses made after July 2006 will have this 6-bit
- lens adapters are available from:
- lens mounts and their lens mount-to-film distances:
||lens mount-to-film distances (mm)
|Olympus digital (FourThirds)
||Four Thirds bayonet
|Canon EOS (EF)
||M42x1 thread screw
||M42x0.75 thread screw
|Contax/Yashica (eg. Carl Zeiss)
- thus, you can see that to focus to infinity, the Olympus / Four Thirds
digital camera bodies, apart from their 2x crop factor, are best suited for use of other lenses (except Leica M/LTM)
whilst the Nikon DSLR's and Leica R bodies are the worst, furthermore, you
cannot mount Nikon F lenses onto Leica R cameras or vice-versa as
differences in the distances is only 0.5mm.
- in fact, the Olympus / Four Thirds are the only digital SLR's able to use
manual focus Minolta lenses - see here
but there is an issue with the design of the E300/E330 that will need
- of course, ideally a full frame digital SLR body would make the best use
of legacy 35mm film lenses and at this stage this leaves the Canon 5D, etc
but this may have its own problems with its over-sized mirror hitting the
rear element of some of these lenses (see super wide).
- if you are using 35mm film still, then there are adapters to fit 35mm SLR
lenses to the Leica M cameras from cameraquest
(see also their article on
Leica M lenses) and in addition, Leica are likely to produce a digital
Leica M body in late 2006.
- conversely, the Olympus OM, Nikon F (including AI-S and AF but not the new
M42, Contax/Yashica and Leica R lenses are the most versatile. The Canon EOS
lenses due to their electronic requirements are generally not suitable for
- Unfortunately this makes the Leica M lenses unusable on DSLRs hence you
probably won't find any adapters for them.
- see http://www.a1.nl/phomepag/markerink/mounts.htm
for more mounts.