Originally posted by mmbrombe I decided to clean up some dust that was becoming noticeable when using the K-70 viewfinder. I used a very soft cloth and VERY LIGHTLY rubbed the mirror and pentaprism surfaces.
The underside of the pentaprism is normally not exposed for you to clean. The line you see is likely a scratch on the underside of the focusing screen.
First rule of camera cleaning for amateurs:
Use extreme care with or better yet, do not touch the mirror.
The surface of the mirror is VERY fragile and abrades very easily. Scratches may affect both the viewfinder image as well as AF performance. Rubbing with a cloth or similar may also affect mirror alignment with serious consequences for AF performance. Replacement requires the skills of a repair technician ($$$). Remove dust with a puff of air from a bulb-type blower.
Second rule of camera cleaning for amateurs:
Never touch the surface of the focusing screen unless you are absolutely sure you are prepared to replace it.
The focus screen is made out of plastic and the micro-textured underside is very fragile. Do not touch. Do not use devices or products designed for lens cleaning on the screen. Remove dust with a puff of air from a bulb-type blower.
Third rule of camera cleaning for amateurs:
Never use canned or compressed air on your camera.
Assuming the line is a scratch, the screen is user-replaceable and costs about $35 for the Pentax-brand replacement. Doing the replacement requires a special tool to set the screen, steady hands, good eyesight, and attention to keeping the work area dust free while doing the transplant. Removal of dust from the area between the focus screen and the underside of the pentaprism can be difficult. A repair shop can also replace the screen for a nominal charge.
You may also choose to leave well enough alone. I have a couple of old film cameras whose screens are marred. Parts are unavailable, so I live with it.
Steve
Last edited by stevebrot; 07-08-2017 at 02:51 PM.