Cosina CT-20

The Cosina CT-20 was introduced by Cosina in the 1980s as a SLR camera. The Cosina CT-10 was succeeded by this model. The 35mm camera was also available on the market under the name “Petri GX-3.”

Its special features that set it apart from the CT-10 include an integrated self-timer and a dedicated exposure compensation button.

Lens

The Cosina CT-20 is equipped with a Pentax K bayonet mount, a widely used standard that allows the use of a wide range of lenses from different manufacturers.

The specific flange focal distance, i.e., the distance between the lens mount surface and the film plane, is set at 45.44 millimeters.

Although the camera was often offered as a kit with a standard lens, such as a Cosinon-S 50mm f/1.8, the K bayonet allows the user to use lenses with a wide range of focal lengths and apertures, from wide-angle to telephoto lenses.

Focusing is performed manually using the focusing ring on the lens, with a central split-image indicator, surrounded by a microprism ring, in the viewfinder serving as a focusing aid. Correct focus is achieved when the two halves of the split image are precisely aligned and the image in the microprism ring appears clear and flicker-free.

A scale for controlling the depth of field and a distance scale are usually present on the lenses. For infrared photography, a special infrared marking, usually a red line or dot, assists in precise focus adjustment.

The respective aperture and the available filter thread are properties of the lens used, not of the camera itself.

Changing lenses is straightforward: simply press the lens release button on the camera body and then turn the lens counterclockwise.

Exposure Settings

The Cosina CT-20’s exposure metering system is based on TTL (Through The Lens) metering, which uses a silicon photodiode (SPC).

The metering pattern is center-weighted, giving greater weight to the central area of ​​the image field to achieve balanced exposure in most shooting situations.

The camera operates in aperture priority mode, in which the photographer preselects the desired aperture using the lens’s aperture ring, after which the camera’s electronics automatically determine and set the appropriate shutter speed.

The exposure metering range extends from EV 2 to EV 19, based on ASA 100 and a lens with a maximum aperture of f/1.4 to f/22.

The film speed is set manually using a dial and covers a range from ASA 25 to ASA 1600.

The shutter mechanism is a magnetically controlled, vertically moving metal-leaf focal plane shutter, offering shutter speeds from 4 seconds to a rapid 1/1000 of a second, as well as a “B” (Bulb) setting for long exposures, where the shutter remains open as long as the shutter button is held down.

In the viewfinder, light-emitting diodes (LEDs) on the left side indicate the shutter speed selected automatically or the current exposure situation: A green LED indicates a shutter speed range suitable for handheld shooting (approximately 1/30s to 1/1000s), a yellow LED warns of slower shutter speeds (below 1/30s), where a tripod or flash is recommended to avoid camera shake, and a red LED indicates overexposure, suggesting a smaller aperture (higher f-number).

A specific feature of the Cosina CT-20 is the additional exposure compensation button, often labeled with symbols such as ‘+/-‘ or ‘Backlight’. When this button is pressed during the shutter release when shooting with strong backlight, the camera typically extends the exposure time by 1.5 to 2 EV to counteract underexposure of the main subject.

Alternatively, exposure compensation can also be achieved manually by adjusting the ASA setting, for example, by selecting ASA 25 when using ASA 100 film to achieve overexposure by two f-stops.

Flash System

The Cosina CT-20 is equipped with a standard hot shoe with a center contact for triggering. The fastest flash sync speed is set to 1/100 second.

When using third-party flash units or manual flash models, the camera’s mode dial must be set to the “X” position, which permanently sets the shutter speed to 1/100th of a second.

The camera was specifically designed for use with the dedicated Cosina Speedlight Auto-160 and Auto-220 flash units. When one of these flash units is attached, turned on, and the camera’s mode dial is set to “AUTO,” the shutter speed automatically synchronizes to 1/100th of a second as soon as the flash indicates it’s ready to charge. This readiness is also signaled by a red “F” LED in the camera’s viewfinder.

An additional audible signal has been integrated for the CT-20 model: an electronic tone sounds as soon as the dedicated flash indicates it’s ready to fire with the shutter button halfway pressed. The aperture required for correct flash exposure must be manually set on the lens according to the instructions for the respective flash unit.

Additional Features

Beyond its core photographic functions, the Cosina CT-20 offers several useful additional features. It features a connection for a mechanical cable release integrated into the shutter button, a standard tripod thread (1/4 inch) on the bottom, and eyelets for attaching a camera strap.

A frame counter on the top of the camera indicates the number of shots taken and automatically resets to the “S” position when the back is opened. A film memo holder on the back of the camera serves as a practical reminder of the film type loaded.

The Cosina CT-20 expands its functionality with a mechanical self-timer, which offers a delay of approximately ten seconds and is activated by flipping a lever on the front of the camera. During the self-timer’s countdown, a flashing red light on the front indicates its activity, accompanied by an electronic beep. The self-timer mechanism can be canceled at any time by returning the lever before the actual shutter release. Furthermore, the CT-20’s shutter release mechanism is designed as an electrically controlled magnetic switch, allowing for particularly smooth operation.

As already mentioned, the CT-20 also features a useful exposure compensation button for shooting situations with difficult backlighting.

Dimensions and Weight

The body of the Cosina CT-20 measures 133 millimeters in width, 85 millimeters in height, and 48 millimeters in depth. The weight of the camera body alone, without lens and batteries, is 450 grams. These dimensions and the moderate weight contribute to its being considered a comparatively compact and lightweight SLR camera for its era.

Power Supply

Power for the exposure metering system and other electronic functions, such as the LEDs in the viewfinder and, in the CT-20 model, the electronic shutter release and the self-timer beep, is provided by two 1.5-volt button cells.

Compatible battery types include S-76 (eBay / Amazon*), A-76, G-13, or equivalent alkaline manganese (LR44) (eBay / Amazon*) or silver oxide (SR44) cells (eBay / Amazon*).

These batteries are located in a compartment on the bottom of the camera, which can be opened with a coin. The correct polarity is marked on the inside of the battery compartment cover.

A built-in battery check function is included: If the mode switch is set to “AUTO” and the shutter button is lightly pressed, one of the LEDs in the viewfinder should light up to confirm sufficient battery power; if the LED remains dark, the batteries need to be replaced.

It is advisable to change the batteries approximately once a year or remove them if the camera is not to be used for an extended period to prevent possible leakage.

Films for the Cosina CT-20

The Cosina CT-20 is designed for use with standard 35mm film (eBay / Amazon*).

The camera supports films with a sensitivity scale from ASA 25 to ASA 1600, which corresponds to today’s ISO range of 25 to 1600. Automatic detection of film speed using DX coding is not implemented; therefore, the ASA/ISO value of the inserted film must be set manually using the dedicated dial.

Quick Operation Guide

1. Inserting Batteries: Open the battery compartment on the bottom of the camera using a coin and insert two suitable 1.5V batteries (e.g., LR44/SR44), observing the correct polarity. Then carefully close the compartment.
2. Checking Batteries: Set the mode switch to “AUTO,” lightly press the shutter button halfway, and observe whether one of the LEDs in the viewfinder lights up, confirming that the batteries are working.
3. Loading Film: Pull the rewind knob up to unlock and open the camera back. Place the film cartridge in the designated film chamber, carefully pull the film tab up to the take-up spool, and thread the end of the film into the slot or under the clamp on the spool. Make sure the film’s perforations engage correctly with the teeth of the advance wheel.
4. Initialize film advance: Operate the film advance lever and the shutter button several times in succession until both rows of film’s perforations are securely engaged by the advance mechanisms. Then close the camera back.
5. Advance film: Operate the film advance lever and release the shutter button until the frame counter on the top of the camera displays “1.” During the winding process, the rewind knob should rotate counterclockwise, which serves as an indicator for correct film advance.
6. Set the film speed: Set the ASA/ISO value of the loaded film using the film speed dial on the camera.
7. Select the shooting mode: Set the mode dial to “AUTO” for shutter priority, “X” for flash photography (which fixes the shutter speed at 1/100th of a second), or “B” for long exposures, as required.
8. Select the aperture: Set the desired aperture using the aperture ring on the lens.
9. Focus: Look through the viewfinder and turn the focus ring on the lens until the subject is sharp and clear in the split-image indicator or microprism field. appears.
10. Check exposure: Press the shutter button halfway and observe the LED display in the viewfinder. If necessary, adjust the aperture or, on the CT-20, use the backlight button for exposure compensation.
11. Release: Press the shutter button fully to take the picture.
12. Rewind film: After the last exposure of the film has been taken, press the film rewind button located on the bottom of the camera. Then, unfold the small crank on the rewind button and turn it clockwise until you feel less resistance. Then, open the camera back and remove the film cartridge.