Diopters

[Carl Hall]

The PME5 prism that came with my 500cm has a "+1D" diopter in it, which means it's completely blurry when I look through it. I'm trying to get hold of a 0 or "neutral" diopter but I'll be damned if I can find anything anywhere! No websites that I can find sell them at all, and there's none on ebay (current auctions or even in previously sold items).

Am I right in saying that a 0 diopter is essentially a plain piece of glass? If so does anyone know of anywhere that can supply such a thing if I give them the diameter and thickness?

This had been driving me crazy over the last 2-3 days so if anyone has any ideas you'll make me a very happy person

Cheers!

 

[kendo1]

I'm sure I saw this mentioned somewhere.
Anyway, quick look: https://books.google.co.uk/books?id...&q=hasselblad diopter correction lens&f=false

Wex photographic do some correction lenses.

 

[skysh4rk]

The PME5 prism that came with my 500cm has a "+1D" diopter in it, which means it's completely blurry when I look through it. I'm trying to get hold of a 0 or "neutral" diopter but I'll be damned if I can find anything anywhere! No websites that I can find sell them at all, and there's none on ebay (current auctions or even in previously sold items).

Am I right in saying that a 0 diopter is essentially a plain piece of glass? If so does anyone know of anywhere that can supply such a thing if I give them the diameter and thickness?

This had been driving me crazy over the last 2-3 days so if anyone has any ideas you'll make me a very happy person

Cheers!

Unlike with waist level finders, some prisms don't necessarily need a 0 dioptre. Can you not just take the +1 off the Hasselblad prism?

Edit: Nope, I think you can disregard what I've said. It seems there is definitely a zero dioptre for that prism.

 

[Carl Hall]

I'm sure I saw this mentioned somewhere.

Anyway, quick look: https://books.google.co.uk/books?id...a87Z3FxwIVw9kaCh3VVwln#v=onepage&q=hasselblad diopter correction lens&f=false


Wex photographic do some correction lenses.

Cheers for the link the PME5 doesn't have the eye lens where you can twist the lens to set it to your own required value, just a screw in type where you replace the actual glass part for another.

That book that you linked to looks incredibly useful, might have to see if I can get a hard copy from somewhere or a pdf online!

 

[Carl Hall]

Unlike with waist level finders, prisms don't necessarily need a 0 dioptre. Can you not just take the +1 off the Hasselblad prism?

You can unscrew it yes, but then you're just left with hole in the end of the prism, and you're kinda just looking at a small reflection in a mirror down the en. Not sure if I've described that very well but it's pretty difficult to use without one and I bet all sorts of crap would get inside lol

 

[skysh4rk]

You can unscrew it yes, but then you're just left with hole in the end of the prism, and you're kinda just looking at a small reflection in a mirror down the en. Not sure if I've described that very well but it's pretty difficult to use without one and I bet all sorts of crap would get inside lol

Yeah, I just watched a video on youtube that showed that. It's likely going to be hard tracking down a zero dioptre on its own, as I'd imagine most people would have been replacing those with other dioptres, not buying them.

 

[skysh4rk]

You can unscrew it yes, but then you're just left with hole in the end of the prism, and you're kinda just looking at a small reflection in a mirror down the en. Not sure if I've described that very well but it's pretty difficult to use without one and I bet all sorts of crap would get inside lol

Are you sure that the finder originally came with a zero dioptre? The standard dioptre on the Bronica GS1 prism, for instance, is -1.5.

 

[kendo1]

I've heard of people grinding down reading glasses to fit to get their required dioptre.
I see no reason why this could not be done with a 'neutral' lens (piece of glass!). Might be worth having a word with an optician.

 

[droj]

You can unscrew it yes, but then you're just left with hole in the end of the prism, and you're kinda just looking at a small reflection in a mirror down the en.

Which implies that a zero dioptre ain't the answer? So proceed cautiously to avoid wasting time & effort. First establish the baseline, let's call it "camera neutral" (Google what your camera's supplied with by default), then factor in your eyesight correction requirement (if you have one?). The baseline is different across makes and models, which aids the confusion ...

 

[Steve Smith]

What will a flat piece of glass do which fresh air will not?


Steve.

 

[steveo_mcg]

Don't you want some dioptre to magnify the image? The pop up lens in the RB67 wlf has a fairly strong lens to help fine focus.

 

[Carl Hall]

Yeah, I just watched a video on youtube that showed that. It's likely going to be hard tracking down a zero dioptre on its own, as I'd imagine most people would have been replacing those with other dioptres, not buying them.

Yeah I think that's going to be the biggest problem, it's a well known fact that fillies can't sell things as easily as they can buy them

Are you sure that the finder originally came with a zero dioptre? The standard dioptre on the Bronica GS1 prism, for instance, is -1.5.

Which implies that a zero dioptre ain't the answer? So proceed cautiously to avoid wasting time & effort. First establish the baseline, let's call it "camera neutral" (Google what your camera's supplied with by default), then factor in your eyesight correction requirement (if you have one?). The baseline is different across makes and models, which aids the confusion ...

Yeah I've read this elsewhere too but then without any diopter (I mean, dioptre!) The image in the mirror reflection is pin sharp which just adds to my confusion. Been trying to find out what the default one is but I'm struggling to find out anywhere. Wonder if Hasselblad will tell me if I email them?

 

[Carl Hall]

What will a flat piece of glass do which fresh air will not?


Steve.

I was thinking it would just seal the prism somewhat. Obviously it wouldn't help magnify the image but it'll keep dust and crud out

Don't you want some dioptre to magnify the image? The pop up lens in the RB67 wlf has a fairly strong lens to help fine focus.

What correlation is there between dioptre and magnification? Like my glasses are -2 but when I wear them nothing is magnified through them as such

 

[Steve Smith]

What correlation is there between dioptre and magnification? Like my glasses are -2 but when I wear them nothing is magnified through them as such

Only positive Dioptres magnify.

The focal length in metres is 1 divided by the Dioptre value. e.g. a 1000mm lens is 1 Dioptre, 500mm lens is 2 Dioptre, etc.

A positive Dioptre lens converges light. e.g. a 1 Dioptre lens will focus parallel beams of light to a focal point 1 metre away.

Dioptres are useful when adding lots of lens elements. So if you had three elements next to each other which had focal lengths of 1000mm, 333mm and 250mm, how would you work out the combined focal length of the group?

Easy. Convert to Dioptres and add them all together.

In my example, the lenses are 1, 3 and 4 Dioptres which add to make 8. This translates to 0.125 of a metre or 125mm focal length (ignoring the variance which spacing between elements will add).

Obviously, if there is a negative Dioptre diverging lens in there, its value is subtracted.

Like my glasses are -2 but when I wear them nothing is magnified through them as such

You are short sighted which means that the lens in your eyes focus to a point in front (or short of) the retina. To compensate, your glasses have a negative, diverging lens. This counters the lens in the eye which is too converging and gives you correct focus.

The combined lens consisting of glasses lens and eye lens becomes the value the eye lens on its own should have been.

I wish my eyes were as good. My contact lenses are -9 and -10 Dioptres!


Steve.