Make your own bifocal diopter!

Huss · Aug 13, 2020

I have a Pentax SuperA that has small LCD exposure numbers in the viewfinder (at the bottom). They were blurry as my eyes are not what they were. Even though what I was focusing on was sharp.
I bought a +2 diopter to see if that would help. That made the numbers sharp, but now the image was slightly blurry! So I bought a glass cutting tool from the hardware shop ($5), and cut away the top 2/3 of the diopter. To do that I took the glass out of the plastic holder.
Now I can see the numbers clearly, and I can see what I need to focus on! Hey presto, bifocal diopter!

Paul Howell · Aug 13, 2020

Nice hack.

jgoody · Aug 13, 2020

Slick!!

CMoore · Aug 13, 2020

Huss said:
I have a Pentax SuperA that has small LCD exposure numbers in the viewfinder (at the bottom). They were blurry as my eyes are not what they were. Even though what I was focusing on was sharp.
I bought a +2 diopter to see if that would help. That made the numbers sharp, but now the image was slightly blurry! So I bought a glass cutting tool from the hardware shop ($5), and cut away the top 2/3 of the diopter. To do that I took the glass out of the plastic holder.
Now I can see the numbers clearly, and I can see what I need to focus on! Hey presto, bifocal diopter!

Going to be a few weeks before another member will "Out-Clever" you on this bit of ingenuity.

AgX · Aug 13, 2020

A good solution, but I wonder wjhy the LCD display is out of focus in first instance.

ic-racer · Aug 13, 2020

AgX said:
A good solution, but I wonder wjhy the LCD display is out of focus in first instance.

I have cameras like that (the numbers don't appear to be at the same focal point as the focus screen). My theory was that the simple viewfinder optics are not flat field. One might need a viewfinder with six elements for a perfectly corrected field.

AgX · Aug 13, 2020

The eyepiece must be flat field. Otherwise there at least would be unsharp corners at the groundglass image.

Huss · Aug 13, 2020

AgX said:
The eyepiece must be flat field. Otherwise there at least would be unsharp corners at the groundglass

The Pentax diopter is not flat, but curved.

ic-racer · Aug 13, 2020

AgX said:
The eyepiece must be flat field. Otherwise there at least would be unsharp corners at the groundglass

True. On second thought it may be the human eye's horrible chromatic aberration. My worst camera with this issue is Rolleiflex 3003 with LED readout. The red light is horribly out of focus in my eye.

AgX · Aug 14, 2020

Huss said:
The Pentax diopter is not flat, but curved.

The term flat field does not refer to the shape of an optical element, but to its focal plane.

Huss · Aug 14, 2020

AgX said:
The term flat field does not refer to the shape of an optical element, but to its focal plane.

Then I guess Pentax curves that diopter to maintain the flat field!

Make your own bifocal diopter!

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