K-3 Super 16 viewfinder modification is done

[Eugene Zagidullin]

The camera came to me converted to S16 by replacing the gate and the lens flange. The frame behind the viewfinder eyepiece was also missing. To complete the conversion I decided to modify the viewfinder as well by installing a bigger ground glass. The original ground glass is a part of a TTL beam splitter prism assembly with a convex lens glued on top. In my modification some degree of magnification is sacrificed by removing this assembly together with the lens. All work is done using just Dremel and files. Everything is spray painted black with some PVC tape for masking. 

 

[Dom Jaeger]

Seems like an interesting project. 

In the interests of assisting you, are you aware that the ground glass image needs to match the film plane within hundredths of a mm in order for it to be accurate for focussing?

I can’t tell exactly how you mounted the larger ground glass but if the ground surface facing the mirror is not exactly where the previous ground glass surface was positioned you will not have accurate reflex focussing. With a zoom you may notice the focus drifts as you zoom out. The camera flange depth needs to be accurate too of course, which often isn’t checked with DIY S16 conversions.

Camera techs normally set ground glass depth using a collimator and a calibrated test lens. My experience with K3s is that the ground glass position is not easily adjusted.

 

[Eugene Zagidullin]

8 hours ago, Dom Jaeger said:

Seems like an interesting project. 

In the interests of assisting you, are you aware that the ground glass image needs to match the film plane within hundredths of a mm in order for it to be accurate for focussing?

I can’t tell exactly how you mounted the larger ground glass but if the ground surface facing the mirror is not exactly where the previous ground glass surface was positioned you will not have accurate reflex focussing. With a zoom you may notice the focus drifts as you zoom out. The camera flange depth needs to be accurate too of course, which often isn’t checked with DIY S16 conversions.

Camera techs normally set ground glass depth using a collimator and a calibrated test lens. My experience with K3s is that the ground glass position is not easily adjusted.

 

I used the original prism as a reference to set the glass perfectly perpendicular. Regarding the focusing plane the mount has enough free play for final adjustment. I plan to do it with a reference lens on infinity.