Fresnel screen direction

[norly]

Hello everyone.
I just wanted to ask if it is me that's the problem.

Ive been using a plastic Fresnel for many years, but Ive always had it with the uneven side towards me (where I put the Loupe). Now i read that its actually wrong.

I moved it around so that the flat side is towards me, but it was much better before. Now I have to be much more straight in front of the glas, otherwise I get sharp falloff patterns (circles) on the sides.

I never had any problems with sharpness or similar using the fresnel in the wrong direction.

Any reasons why I should go back to the former installation?

[Tin Can]

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My answer is

Depends

[norly]

Thanks. Nice feature, but none of those gave the answer I wanted... Just wanted to know if anyone else prefer the "frosty" side of the fresnel.

[Alan9940]

I've always heard that the rough side should face the lens (ergo, smooth side toward you) and that the fresnel should sit on top of the ground glass. I only have one 4x5 with a fresnel installed and that's the way it's on the camera. No issues with focusing or any other concerns. And, yes, it's normal that the view becomes quite a bit darker as you move off the center axis of the fresnel.

[John Layton]

If the fresnel field in question features a ground/frosted focussing surface on one side - then this is an "all in one" focus screen/fresnel field...and, assuming that the film back of the camera in question is designed (or has been adjusted) to use with such a screen - or with a plain (non fresnel incorporated) ground glass, for that matter, then the focussing (non fresnel) surface must face the lens, and the fresnel field must face the back of the camera. As the plastic fresnel field is somewhat delicate - it is advisable to place a protective glass on top of the fresnel field. In addition to being protective this glass may or may not feature grid lines.

To correctly install a two-piece (focussing screen and separate fresnel field) into the above mentioned film back - the frosted/ground (focussing) surface must also, as above, face the lens, and this piece must be installed first…followed by the fresnel field, which can face in either direction. Highly recommended in this setup is the presence of yet a third piece, placed in back of the plastic fresnel field…of a protective piece of glass.

On the other hand, to correctly install a two-piece (focussing screen and separate fresnel field) into a film back which has been designed (or adjusted) only for use with such separate pieces…then the fresnel field must be placed into the film/focussing back first (with the fresnel surface facing backwards), followed by the ground glass, with the ground (focussing) surface facing forward. Seeing as the ground glass piece is, well, glass…no extra “protective” piece needs to be added to this.

Considering the above mentioned specifics, it is not all that uncommon for folks who are unaware of them, and who seek to “upgrade” a focussing screen for whatever reason…to purchase, and then install, the "wrong" component(s) and then to experience focussing inaccuracies.

[norly]

Kind of interesting thou that Ive been using it wrong side out, so to speak for 15 years of professional work and never realised it. I must say that I find it easier to se the whole image when looking at the (edit:) uneven side. When Im using the loupe, its same same but the (Edit:) Uneen side gives a much more even image. that can be viewed from more angles...

but it seems like Im quite alone about this... :)


To clarify:
I got the following setup since 15 years. Lens then Viewing glas then a Linhof fresnel (flat side towards viewing glas).

[Tin Can]

If it's not broke don't fix it

[John Layton]

Norly...please refine your earlier statement - that you'd been using the screen with the "uneven" side towards you. Would this be the side with all of the concentric circles...or the "frosted, matte surface" side? Which?

If the "frosted, matte surface" (focussing side), has indeed been set towards the lens, and you've been realizing accurate focus...then you're probably fine, even though, as you mention, the image might seem more "even" with the frosted side facing towards you.

Depending on the design/manufacture(er) of the fresnel screen, those circles can be distracting!

[norly]

Sorry. Ive had the uneven side towards me. Got a bit confused there about how to describe it... With the concentric circles...


Anyway, Ill keep it like this. But its interesting that I am the only one who finds that side better to look at. Its extremely enjoying when you flip the fresnel since i have to keep the head perfectly aligned, or I will lose vision on the sides of the screen. This works much better on the uneven side.

[John Layton]

I would recommend that you think about obtaining a piece of glass (either plain or with a grid) which would be installed on top of your current plastic fresnel - as a protector...also acting as a good "landing surface" for a loupe.

Years ago...I had a wonderful Linhof Technikardan - complete with their "Super Screen" plastic fresnel/focus screen. Thing is, this screen (which I used with no glass protector) was supported by four (adjustable) contact surfaces (design flaw in my book) - and if I was not careful, the screen would deflect with any amount of pressure from a focussing loupe...not exactly great for accurate focus!