What do add-on lenses do?
What do the lens numbers mean?
Can I still use autofocus?
What is vignetting and how can I avoid it?
How are the lenses attached?
Lens (and filter) thread sizes
Focal lengths compared
What do add-on lenses do?
Since the zoom lenses that are built-in to the camcorder cannot be removed, then the additional lenses that you can buy are strictly speaking lens convertors. This is because they fix to the end of the existing built-in lens and change its range in some way. The lenses are all rated in terms of their magnification factor. Anything rated at greater than a 1 Times (1X) is considered a telephoto, and anything rated at less than a 1X is a wide angle. A wide angle will increase your field of view (you can see more in the viewfinder), a telephoto will decrease your field of view (the image is enlarged, as if you were closer to it).
Generally, wide angle lenses are useful for filming indoors (or for particular scenic shots outdoors), and telephoto lenses are useful for when you can't get close enough to your subject to fill the viewfinder (sport, wildlife, etc). top
What do the lens numbers mean?
All video camcorders have a zoom lens built-in as
standard. Depending upon the particular model, this lens will have a rating of anything
from say 6X (6 times) to 12X or even more. There are considerable differences between
various makes and models of camcorders in terms of where their zooms start and end.
To find a common point of reference for each model, it is easiest to think of the
widest possible wide angle setting on you current camcorder as being 1X or '1 times'.
It then follows that a 6X zoom will enlarge that image in the viewfinder by 6 times.
If, for example, a camcorder which has a zoom range of 1X to 8X were to have a 2.0X
lens convertor attached, then its new telephoto range would be from 2X to 16X. Similarly,
if the same camcorder were to have a 0.5X wide angle convertor attached to it, then
the maximum area viewed would be twice as great as before, and its zoom range would
then be changed to 0.5X to 4X.Bear in mind that the magnification factors of most add-on lenses are based on the degree of change in visible area, not on the linear (horizontal and vertical) changes. For example, if a camcorder was focused on an image 6m wide by 4m high (ie of area 24m2) which completely filled the frame, then fitting a 2.0X telephoto lens would reduce that area of the image which filled the frame to 12m2, half what it was, or approximately 4.2m wide by 2.8m high (see diagram).
Anything less than a 0.5X, for instance a 0.38X, is classed as a super wide angle or 'fish-eye' convertor. These give an extremely wide field of view and although the effect can be dramatic, any verticals in the picture (telegraph poles, door frames etc) can appear somewhat bent out of shape. top
Can I still use autofocus?
Yes - the autofocus mechanism of the camcorder should not be affected by fitting a lens (or a filter), unless your camera has an infra-red autofocus system. In this case, when using an additional convertor lens you will have to switch to manual focus. top
What is vignetting and how can I avoid it?
Vignetting (pronounced Vin-yet-ing) or 'tunnel effect' can sometimes occur when a lens has been attached and the camcorder's zoom is set towards the wide angle end of its range. What can happen is that the camcorder attempts to look through the side of the lens body, with the end result that the corners of the picture appear dark, or in extreme cases the effect can be like looking through a drainpipe.
To avoid or minimise vignetting, there are two general rules which apply, dependent upon the lens:
Wide Angle: Try to ensure that the lens thread size is a direct match for the camcorder, i.e. if possible avoid stepping rings. If you have to use stepping rings then make sure that they are step-up, ie. the camcorder thread is smaller than the lens thread.
Telephoto : Generally speaking, you can usually use a small percentage of your zoom range before vignetting becomes noticeable, but this becomes less and less the greater the lens factor. Lenses at 1.5X don't usually vignette. At 2X, some do and some don't and at above 2X most will vignette at the wide angle setting. As you would normally be using it only at the tele end of the zoom range then step up and step down rings can be used without any problems. top
How are the lenses attached?
All camcorders have a screw thread which is on the inside front edge of the lens. Lens convertors simply screw onto this. The thread size will be of a specific diameter in millimetres. The actual thread size is sometimes printed around the lens barrel on the inside or outside front edge (see below). Failing this it is usually contained in the technical data section in the handbook. It is most commonly referred to as filter size, as this is indeed the same place that filters are attached. top
Lens (and filter) thread sizes
Around the edge of the lens barrel on your camcorder there is usually some printed information. If you see the diameter symbol (a circle with a slash through it) followed by a number (eg D37), then this number is the thread diameter in mm you need to know when ordering and connecting filters and lenses. Two numbers connected by a squiggle (tilde), eg 23~43mm, is the focal length of the zoom lens, not its diameter. top
Focal lengths compared
|
35mm stills camera |
Camcorder with 1/4in CCD |
Camcorder with 1/3in CCD |
Camcorder with 1/2in CCD |
Camcorder with 2/3in CCD |
|
| Wide angle settings |
28mm |
2.9mm |
3.9mm |
5.8mm |
7.8mm |
|
35mm |
3.6mm |
4.8mm |
7.2mm |
9.6mm |
|
|
40mm |
4.1mm |
5.5mm |
8.2mm |
11.0mm |
|
|
50mm |
5.2mm |
6.9mm |
10.4mm |
13.8mm |
|
|
60mm |
6.2mm |
8.3mm |
12.4mm |
16.6mm |
|
| Telephoto settings |
200mm |
21mm |
28mm |
42mm |
56mm |
|
300mm |
31mm |
41mm |
62mm |
82mm |
|
|
400mm |
42mm |
55mm |
82mm |
110mm |
|
|
500mm |
52mm |
68mm |
104mm |
138mm |
|
|
600mm |
62mm |
83mm |
124mm |
166mm |
|
|
800mm |
84mm |
110mm |
164mm |
220mm |