different lenses for sinar viewer 5x4 vs 10x8

[brighamr]

hi All

i have a 5x4 sinar bellows viewer which is great
i recently got a spare bellows to enable me to do the same on my 8x10
but it is out of focus when i can see the whole screen
moving close brings it into focus so i guess i need different strength lenses

the 5x4 has about a 2x magnification

i’m sure some of you optical guys know exactly what i need to do or know the basic formula i need to work it out

best

robin

[esearing]

I have never seen an 8x10 reflex viewer. The 4x5 one I have is a mirror at an angle and a magnifier to look through. So You could hold a mirror and wear magnifying eye glasses to do much the same thing under a dark cloth. If you don't need the inversion of the image then magnifying glasses or a magnifying glass/lens will work alone for help with composing.

There are also magnifying sheets up to 3x but the edges will likely be distorted. https://www.amazon.com/8x10-Fresnel-.../dp/B001TLJXJ8

[brighamr]

thanks esearing

to be clear. i’m not using the reflex viewer on either camera
sinar made a lensboard size viewer that had the lenses built in same as the reflex
you attached this to the ground glass with a spare bag bellows and then looked thru

this is the 5x4 version.

[Daniel Unkefer]

I'm using the Binocular Lighthood, and an 8x10 Norma Bag Bellows, right now with my 8x10 Norma. Like you I have to move back and forth to see the frosted glass sharply, with a fresnel attached I can see the whole screen for composition, by flipping the magnifier out of the way. Then flip it back in, and move in closer, to sharply focus the camera.

I know I've seen supplemental magnifying lenses for the Binocular viewer, but I don't see them in my catalogs. Perhaps it's buried in other literature.

What Sinar lists in their literature is their 90s era catalogs is a 4.25 Diopter. I guess that is what comes with it? It's not real clear in the catalogs.

I do remember that the diopters in the bino lighthood were interchangeable and offered in different strengths.............

Also I used black masking tape to hold together the bino magnifier and bag bellows. Very annoying it keeps coming apart!

[brighamr]

Hi Daniel

my sinar plate says +3 diopter on the sticker and says the 4.25 is for near sighted people
I guess I need a less than +3 to focus from further away bu I'm not sure

[Daniel Unkefer]

Hi Robin

Mine says the same, I have confirmed.

Perhaps try wearing different strengths of diopter eyeglasses?

I need to find my 8x10 fresnel.

[reddesert]

Focal length is equal to 1 meter divided by the diopter. So the +3 diopter lens has a focal length of 1000 mm/3 = 333 mm or about 13". That typically means you can hold the magnifier up to about 13" away from the screen and see it, but if you move it further away from the screen, you can't focus (for normal vision).

To get a larger distance and field of view for the 8x10 you need lower diopter number. +1.5 reading glasses would be the logical place to start, +2 might work if you need a bit more magnification.