A filter is called such because it selects (“filters”) components of light, and either absorbs them or transmits them.  For instance, a yellow filter will absorb blue and transmit green and red light.  That is also the reason why it looks yellow.  A filter will absorb its complementary colour and transmit everything else.

Filters are/were commonly used in BW to achieve some contrast in the grey rendering of objects in colour. A panchromatic (all colour sensitive) BW film will render a red object and a green object -if they are of the same luminance- as equal shades of grey.  Using a red filter will let all the reflected red light in and block blues and greens- thus contrast separation is achieved by rendering the red object as light grey and the greens as dark grey in the monochrome picture.

To illustrate this principle, take a look at the following pictures:

1. The Original Scene as Seen in Colour:

2. Shot on BW, Without any Filter: Grey-rendering of hues (note the reds and the blues)

3. Through a Yellow Filter:  Yellow filters have sometimes been called “Cloud Filters”
 

4. Through an Orange Filter:  Contrast between coloured objects, particularly blue/green and red/orange is more pronounced.

5. Through a Deep Red Filter:  More dramatic skies, -darkened blue skies- darkened greens.

6. Through a Blue Filter: Mimicks the effect of the old colour-blind plates from the XIX century.

Note: Skies will darken only when they are truly clear and blue.  Hazy skies, cloudy and grey weather will not show the effect well.

Red and Orange, as well as Deep Yellow Filters will often render skins pallid and sometimes give a ghostly, drained-of-blood appearance to people and portraits.

Green filters are used to achieve a healthy, tanned look (green darkens reds) with people subjects outdoors. A green filter will also darken skies.

Related Posts:

• What Lens Hood to Use for Industar or Jupiter Lenses?
• HOW NOT TO DESTROY YOUR FED AND ZORKI (A Basic Primer)
• (Extreme!) Closeups with a Rangefinder Camera
• Entering from the Bottom: Loading a Leica Properly. (also for FED, Zorki, and Canon RF cameras)

Two types of Soviet-made hoods for these lenses can be found: round and rectangular. 

The rectangular version can only be used for certain types of Jupiter and Industar lenses.  These would be the Jupiter made until the 1960s, and were usually with white aluminium barrels.  These lenses did not have rotating fronts.   Later Jupiter (and Industar?) lenses made from the 1970s onwards  would have rotating fronts.  A rectangular hood would rotate as the lens is focused and would result in various degrees of vignetting.

The round version is for the later Jupiter lenses. Usually these are the black Jupiters.  They should also be the type used for Jupiter lenses on Kiev cameras.  A round hood will always have the same orientation when the lens rotates during focusing so vignetting can never be a problem.

The hoods (diameter 36mm) for collapsible Industar will also fit Elmar lenses.  They are deep enough even for use with Elmar 9 cm lenses.  On a 50mm, they can be too long. 

This hood can easily be DIY’ed with a piece of blackened cardboard tube.  3 cm deep and 36mm wide, no tapering necessary.  This would be good enough in cutting stray light.

These hoods can cause viewfinder blockage.  However an accessory finder can be used.  The finder in this case will be high enough to clear the hood.  With long lenses, extra finders are used anyway.

**rectangular hood courtesy of Jefjac

Related Posts:

• Filter Basics for Black and White Photography
• HOW NOT TO DESTROY YOUR FED AND ZORKI (A Basic Primer)
• (Extreme!) Closeups with a Rangefinder Camera
• Entering from the Bottom: Loading a Leica Properly. (also for FED, Zorki, and Canon RF cameras)