Image Enlarger.

An enlarger is a specific kind of transparency projector that is used to develop photographic prints from transparencies or negatives on film or glass.

Construction:

An enlarger consists of a light source—typically an incandescent light bulb—shining equally through a condenser or translucent screen, a container for the transparency or negative, and a specific lens for projection. A film holder, which houses a developed and exposed photographic transparency or negative, directs the light.
Prints made with an enlarger are called enlargements. However, some commercial enlargers include an integrated dark box and can be used in a room with light. Enlargers are frequently used in a darkroom, a closed space from which extraneous light can be eliminated.

Enlarger physical arrangements:

The head of the majority of modern enlargers is vertically mounted, pointing downward, and may be moved up and down to change the size of the image that is projected onto the machine's base, or a work table if it is wall-mounted.
A horizontal enlarger is composed of a trestle, the head of which is placed on crossbars between two or more posts for added support. A horizontal enlarger structure is used when high-quality, large-format enlargements are required, such as when photos are taken from an aircraft for mapping and taxation purposes. [Citation necessary]
Baseboard, enlarger head, elevation knob, filter holder, negative carrier, glass plate, focus knob, girder scale, timer, bellows, and housing lift are all parts of the enlarger.

Image enlargement limits:

The grain size of the negative, the sharpness (accuracy) of both the camera and projector lenses, the picture blur brought on by subject motion, and camera shake during the exposure will all affect the degree of enlargement that is practical (independent of the enlarger structure).
Consideration is given to the finished product's desired viewing distance. For instance, a 12 x 18 cm (approximately 5 by 7 inch) print from a particular negative might be adequate for a scrapbook when viewed at 50 cm (20 inches), but insufficiently detailed when hung on a hallway wall at the same distance in an A4 print, even though it could be used at a larger 120 x 180 cm (ten times larger) on a billboard when viewed no closer.

Advantages:

• It is easy to adjust the local contrast and density of different areas of the print. As the amount of light exposing the paper changes, the image density will fluctuate in various places. A mask with a hole can be used to add more light, which will darken the areas with more exposure, while "dodging" is the process of limiting the total amount of exposure to a zone, which will brighten the areas with less exposure. The tool is constantly moving to prevent a sharp edge at the region boundary. Using these techniques, it is possible to substantially change the mood or focus of a photographic print.
• Additionally, by overlaying the print with a hand-cut mask, exposing it, and then exposing it once again with a fresh negative using the inverse of that mask, you can produce composite images like those by Jerry Uelsmann. With modern digital picture editing software, this is far more challenging to accomplish successfully than it was with traditional photographic techniques.