Pentax Focusing Aids
An SLR camera features two very different light paths, depending on the position of its mirror. In the normal viewing state of a horizontally-held camera, the mirror lies diagonally, and reflects the light gathered by the lens onto the focusing screen. The screen is a thin piece of plastic that lies in the horizontal plane, and the image is reversed left-to-right. Above the focusing screen most cameras feature a viewfinder — an additional system of optics that reverses the image to its correct orientation and allows the photographer to look forward (through the viewfinder) instead of down (onto the screen). In the picture-taking state, the mirror is flipped up, away from the light path, and the image is formed directly on the film. Because of the fundamental laws of optics, the film image is left-to-right and upside-down reversed.
When the mirror is in its "down" position, the distance between the lens and the focusing screen is equal to the distance between the lens and the film when the mirror is up. Because of this, when the image on the viewing screen is in focus, it is also in focus on the film plane, and the ability of the photographer to clearly see that image is crucial, and affects the resulting photograph in a very fundamental way.
All devices listed below lie on the path between the lens and the photographer’s, and therefore all take part in that very important role of image composition and focusing.
At this time the LX is the only Pentax camera that features interchangeable viewfinders.
Interchangeable Focusing Screens
There are various focusing screens available for most middle- and high-end Pentax cameras. Unfortunately only the “pro-oriented” bodies allow the photographer to change the screens himself. The other bodies need to be taken to a qualified technitian.
The viewfinder attachments (eye-cups, magnifiers, refconverters, etc.) that were designed specifically for the M42 Pentax bodies carried the suffix "-S" (probably standing for "screw-mount"). When Pentax introduced the K-series K-mount bodies, they kept the viewfinder attachment slot unchanged. They did, however, change the external design of the viewfinder accessories a little bit, and changed the name suffix from "-S" to "-K". However, to stress the fact that the accessories are fully compatible with each-other, for some items the suffix was completely dropped while for others "-KS" was used. So, if we take a hypothetical viewfinder accessory VA, its name could be Va, VA-S, VA-K, or VA-KS, and it will fit every M42 Pentax body and every K-series K-mount body.
With the introduction of the M-series K-mount bodies, the frames of the viewfinder openings became a bit larger and all viewfinder accessories were redesigned accordingly. The names of these newer accessories (incompatible with the earlier bodies) received the suffixes "-M" and later on "-A". Fortunately, the design of the viewfinder frame has not been altered since the M bodies, so all "-M" and "-A" accessories fit all newer bodies.
The following viewfinder attachments exist:
An eyecup prevents light from entering the viewfinder from around the eye of the photographer. This eliminates extraneous reflections and prevents the light meter from being affected. There are K and M versions available.
Eyepiece Correction Lenses
These SMC-coated devices change the diopter rating of the viewfinder. There are eight lenses to fit the K-bodies (-5 to +3 diopters, in 1 diopter steps) and seven for the M bodies (-5 to +2 diopters, in 1 diopter steps).
A magnifier is used for precise focusing. It clips on the eyepiece and provides 2X magnification of the central portion of the frame. It can also be flipped up for viewing of the entire frame.
Magnifier-M is specifically designed for the M-, A-, and P-series bodies, while Magnifier-F (and the identical Magnifier-FB) are targeted towards the SF and MZ/ZX bodies. However, like discussed previously, these devices are be freely interchangeable among all M-series-and-newer bodies.
A refconverter is a right-angle finder. It attaches to the viewfinder eyepiece and allows viewing while looking down instead of straight through. This is very useful when the camera is close to the ground.
- (The basic) refconverter shows an image that is vertically correct but laterally reversed. This makes it inconvenient to view numbers, and while it fits all K-series bodies, it is recommended for use only with the K1000 and KM.
- refconverter-II keeps the image vertically and horizontally correct. It fits all K-series bodies.
- refconverter-M shows a correct image and in addition has a built-in 2X magnifier that is activated via a sliding switch. It fits all K-mount bodies except the K-series.
- refconverter-A is identical to refconverter-M, except for a slightly broader “field of view” so as to show the LCDs below the viewfinder in the Program-series bodies.