Set your Pentax camera to manual function if it comes with an automatic function. All digital Pentax cameras come with an automatic function, but this function will not communicate with a manual lens, so it will be impossible to use. Similarly, 35mm cameras will not allow you to use the automatic function with a manual lens.
Load the film into your camera if you are using a 35mm Pentax. Set the ISO rating to correspond with the ISO rating of the film. If you are using a digital camera, set the ISO rating to correspond to the type of lighting situation that you are in. For instance, exposures in bright sunlight can use a lower ISO, like 100 or 200, while darker situations or scenarios with a lot of movement should use a faster ISO, such as 800 or 1600.
Place your camera on a tripod if you are shooting in a low lighting situation at a longer exposure time with no flash. This will help you avoid a blurriness and promote a crisp, detailed photograph.
Open the aperture on the manual lens all the way up and then adjust the focus of the image using the manual focus dial.
Set the ISO on your light meter to match the ISO of your film or your camera setting and take a light meter reading. Adjust the aperture on the camera to match the aperture setting obtained by the light meter reading.
Press and release the "Exposure" button to take your photograph.