$10 Fresnel for 8x10

[Kevin Crisp]

Drew: Typically, the ground glass stays where it has always been, the Fresnel is behind it (closer to the photographer) with the fine grooves up against the ground glass and the smooth side of the Fresnel facing the photographer. There are some cameras such as the Graphics, which placed the Fresnel in front of the ground glass. I doubt one of these cheapies would work with a Graphic that had somehow lost its original Kodak Fresnel.

My Canham 4X10 had just a ground glass, I added one of these really thin reading Fresnels and the image is much more even and easy to see. The one I have bulges a little on the 10" dimention, but is fine when the loupe is against it to focus.

[ic-racer]

Shen Hao does not sell a fresnel for the 8x10 and they have no groove provision for mounting one in front of the GG.

This screen is a quarter of an inch thick. Mounting it behind the ground glass offers GG protection and the possibility of an installation without any camera modification.

Of about 12 cameras with focus screens I own, 3 have the fresnel behind the GG and the other 9 have it between the lens and GG. The lines of the fresnel are less pronounced when mounted between the lens and GG, but they work just fine when in the other position.

[Wally]

No, it actually goes on the side between the lens and the GG. But to correctly place it, it should not move the GG with respect to the film plane, so a shallow bit of material must be removed from the area that the GG sits in so that when the GG goes back in, it sits where it did before.

If you don't do this, then the GG will be at a different place than the film in the film holder with respect to the lens.

Sometimes you can get away with this if you (a) shoot landscapes (and therefore stop down quite a bit) and (b) you don't need too small a circle of confusion (ie, you're not going to enlarge the image much beyond 2x). In these circumstances you might not notice any loss of apparent sharpness.

But if you shoot portraits, and you focus on the eyes, and don't stop down much, you'll often find that the eyes are a bit soft and the chin whiskers are extremely sharp.

[JoeV]

For my 8x10 box camera project I ended up using the Staples brand Fresnel lens as the ground glass. One side is Fresnel, the other side is blank. I ground the blank side down with a random orbital sander and 320 grit emory into a usable ground glass-like surface, which is oriented in the camera facing the lens. It offers a nice, bright image. The only caveat is the flexibility of the plastic means that for critical focus you don't want to push on the plastic with your loupe, else you'll effect focus accuracy.

~Joe

[Wally]

Shen Hao does not sell a fresnel for the 8x10 and they have no groove provision for mounting one in front of the GG.

This screen is a quarter of an inch thick. Mounting it behind the ground glass offers GG protection and the possibility of an installation without any camera modification.

Of about 12 cameras with focus screens I own, 3 have the fresnel behind the GG and the other 9 have it between the lens and GG. The lines of the fresnel are less pronounced when mounted between the lens and GG, but they work just fine when in the other position.

Do you mount it with the grooves facing toward or away from the ground glass?

I don't have the Shen Hao 8x10, just the lowly 4x5.

In that model, the fresnel gets mounted between the GG and the lens, in it's own little recessed space.

I'm no optics person, just a duffer with a camera, so I defer to the members that described the correct placement of a fresnel in older posts on this site. They said that any mod that changes where the ground glass is must be carefully done as it changes the actual focus point, so one must be careful to place it such that it renders on the ground glass at the same plane as the film when you put the holder in, which (IIRC) is .187 inches from the film holder flange. This measured distance is only valid for a ground glass that does not have a fresnel - if one is added to the optical path, the actual focus point can shift. By how much I don't remember. I assume it's something to do with the fact that the fresnel is bending the light.

It should be an easy enough thing to check for, of course. Just take a pic of a ruler that's at a 15 degree offset from being parallel to the plane of sharp focus, then focus carefully at the 6 inch mark, expose with a fairly wide aperture to accentuate the in-focus area, and develop. See if the six-inch mark is where the film found the smallest circles of confusion.

As for the idea that putting it on the outside, between the photographer and the ground glass was wrong, I may have read that here or been told by my mentor here in San Diego. I can't recall right now, and I'm too sleepy to search the archives tonight.

[IanG]

No, it actually goes on the side between the lens and the GG. But to correctly place it, it should not move the GG with respect to the film plane, so a shallow bit of material must be removed from the area that the GG sits in so that when the GG goes back in, it sits where it did before.

There's no correct place. Some manufacturers use a fresnel behind the screen others in front.

The best is the super screen combination the all in one fresnel and ground glass, Beattie Intenscreen, Maxwell etc, although some manufacturers like Wista, Linhof offer similar screens although there's slight variations in brightness etc, and more importantly cost

I did some tests last years with two 5x4 camera's, and with a good ground glass screen & a fresnel brightness improved significantly over a plain glass screen but didn't quite reach the standard of my Wista combination screen.

Like ic-racer I bought some of the Staples type fresnels and I'm using one for my second 10x8 Agfa Ansco, the first came with a new, boxed Beattie screen

Ian

[Wally]

There's no correct place. Some manufacturers use a fresnel behind the screen others in front.

The best is the super screen combination the all in one fresnel and ground glass, Beattie Intenscreen, Maxwell etc, although some manufacturers like Wista, Linhof offer similar screens although there's slight variations in brightness etc, and more importantly cost

I did some tests last years with two 5x4 camera's, and with a good ground glass screen & a fresnel brightness improved significantly over a plain glass screen but didn't quite reach the standard of my Wista combination screen.

Like ic-racer I bought some of the Staples type fresnels and I'm using one for my second 10x8 Agfa Ansco, the first came with a new, boxed Beattie screen

Ian

Thanks for the update. I stand corrected.


// Wally