Filters & Holders.

The Bower Filter Kit came with three lens filters in the set, a UV (Ultra Violet) filter which serves to limit the effect of UV rays, a F-DL (Fluorescent Light) filter which counters the green cast created when photographing a subject that is illuminated with fluorescent lights and a P.L (Polarising) filter which comprises of two rings that can be turned to darken or lighten the image, very similar to putting a pair of sunglasses on the lens to cut out glare.
This particular set is designed to fit lenses with a 62mm diameter thread with a 0.75mm pitch. There are three commonly used pitches of thread depending on the diameter of the ring 0.5 mm, 0.75 mm or 1.0 mm. The most common ring diameters available are 30.5mm, 37mm, 40.5mm, 43mm, 46mm, 49mm, 52mm, 55mm, 58mm, 62mm, 67mm, 72mm, 77mm, 82mm, 86mm, 95mm, 112mm and 127mm.
The set came in a felt lined box that is partitioned for each filter to keep them clean and protect them from scratches or damage, costing $80 in the USA it equated to around £40 with the exchange rate at the time making each lens filter less than £15 each.
Not only do these filters perform a specific filter effect they also protect the lens from damage, better to damage a £15 filter rather than a £300 lens!

The Cokin A-series filter holder is part of the Cokin modular filter system and is used to hold filters for different effects in front of the lens. The A-series holder can hold up to three 66mm x 72mm A-series filters, a single 70mm diameter A-series filter or combination of both in the slots provided! The Cokin A-series holder can be rotated on the lens adapter ring so filters can be aligned for different effects.
The Cokin A-series filter holder comprises of a rear facing adapter ring slot plus three forward facing slots for rectangular filters and one narrow slot for a rotational round filter, (such as a Polariser or Galaxy Diffractor filter). The narrow slot is also used to house the cover that protects the lens acting as an alternative to the lens cap. This saves removing the Cokin A-series filter holder when it is not in use. By using a Cokin A-series filter holder a single set of filters can be used on many different size lenses by simply changing the adapter ring, this significantly cuts down the amount of different size filters that would have had to have been carried for each different size lens.
Cokin make four different sized versions of the modular filter system.
A-series ("Amateur", 66mm), P-series ("Professional", 83mm), X-Pro, ("Professional," 130mm) and Z-Pro, ("Professional", 100mm).
X-Pro and Z-Pro are designed for larger cameras!

If you are using the Cokin modular filter system you are going to need an adapter ring to fit the Cokin filter adapter to the front of the lens. The Cokin adapter rings make use of the filter mounting thread that is found as standard on the front of the lens, the diameter and pitch of the Cokin adapter ring is important! If the wrong adapter ring is used the thread could be damaged. The diameter of the lens thread should be easy to find out as it is usually marked on the lens itself the pitch however could be one of three, 0.5mm, 0.75mm or 1.0mm although generally the diameter of the lens will have a standard pitch for that diameter.
The size of the adapter ring will also depend on what series of the Cokin modular filter system you are using. The A-series filter system will cover a lens from 30.5mm up to 62mm in diameter but may produce some problems with wide angle lenses. The P-series filter system will cover a lens from 42mm up to 82mm in diameter which is better suited for wide angle lenses of smaller diameters but could still cause problems on larger diameter wide angle lenses. The X-Pro and Z-Pro filter systems are designed for larger format cameras not generally suited to 35mm standard format SLR or DSLR cameras!

This Cokin A124 tobacco filter measures 66mm x 72mm and is designed to fit with the Cokin A-series filter system. The letter preceding the number found on the filter refers to the system series it is to be used with, the number itself refers to the type of filter effect.
There are five Cokin tobacco coloured graduated filters available A124, A125, A125F, A125L and A125S each with slight differences...
A124 - Graduated tobacco filter reduces the light by 1 stop.
A125 - Graduated tobacco filter reduces the light by 3 stops.
A125F - The graduation extends to cover the entire filter, reduces the light by 3 stops.
A125L - Feathers the tobacco color more gently and graduates to clear, reduces the light by 1 stop.
A125S - The graduation extends to 3/4 of the filter, reduces the light by 3 stops.
These filters are mainly used to give an unnatural tobacco color to the sky, giving a landscape a more dramatic effect. Used up-side down it can intensify the colour of sands on the beach.

The proper name for this filter is Diffractor Galaxy and the example shown has a series number of A042 denoting it is for use with the Cokin A-series filter system. There are three filters available that give a similar result with regards to the rainbow coloured effect. The A040 Diffractor Cosmos, A041 Diffractor Universe and The A042 Diffractor Galaxy.
The Diffractor Galaxy filter has loads of engraved prismatic grooves that like a prism, diffract the light into its spectral colors, but without distorting the image this gives a sort of rainbow colour effect to any bright light source present in the image.
The filter is designed with notches around the diameter so it can be rotated within the filter adapter, the notches acting as a thumbwheel.

Filter Effect Example Pictures:

The Diffractor Galaxy filter causes a rainbow effect to occur at any light source found in the picture.

This A061 Soft Focus filter has a clear spot in the center which has no filter effect. The surrounding area is more cloudy to slightly diffuse or smudge the image in these areas. The A061 Soft Focus filter is colorless with a diffuser effect, (there are other coloured filters giving the same effect available). This means that the subject in the center of the photograph is reproduced clearly while the surrounding area of the photograph is changed to draw the eye to the centre of the photograph. This filter is commonly used for portrait photographs.
Filters with numbers A060 and A061 are generally for lenses with a focal length range between 50 and 250 mm.
Filters with numbers A070 and A071 are generally for wide angle lenses with a focal length range between 20 and 40 mm.

These Cokin Close Up Lenses work really well on digital cameras and are ideal if you are into close up photography but can't afford expensive macro lenses. The lenses are no substitute for macro accessories such as extension rings or bellows units but they do allow you to take closer than normal photographs. One of their main advantages is that they do not block any light and only adjust the image working ratio whilst increasing the working range of standard and telephoto lenses.
One of the drawbacks is the need to be more accurate with your focusing, some auto focus lenses may struggle to cope with the close up lenses and may have to be focused manually. A fairly high ƒ number is also preferable to increase the depth of field to keep the images in focus, probably anything from ƒ8 upwards.

The filters included in the set are:
A101 Close up +1 Dioptre.
A102 Close up +2 Dioptre.
A103 Close up +3 Dioptre.
(What is a Dioptre? Use this link for the Wikipedia explanation).