Wista SP - Strange Fresnel Lens

[neil poulsen]

I recently purchased a Wista SP 4x5 fields camera, and I'm experiencing a strange effect with the included ground glass. At normal viewing distance (8" or 9"), closing the left eye leaves the left half of the screen dark, and closing the right eye leaves the right half of the screen dark.

The result is that I'm experiencing a disturbing effect, when both eyes are open. I've never encountered this before, and I suspect it has to do with the focal length of an integrated Fresnel lens. (It sure appears to include a Fresnel lens, given the brightness of the image.) Is this strange effect characteristic of these cameras? Unfortunately, the screws are too tight and too small for me to remove the ground glass, and I don't want to risk stripping the Phillips inserts. Otherwise, I could get a better look at the construction of the viewing system.

My guess from a Wista Fiel 4x5 that I have, is that the SP has a two layer affair: one layer being a thin sheet of glass with the grid on it, and a second piece of plastic that may be an integrated Fresnel and matte surface for focusing. So, this raises another question of whether I can use only a Wista product designed for the camera (like Arca Fresnel lenses), or swap in any suitable ground glass/Fresnel combination?

Any suggestions? I look forward to using this camera. But, I sure don't want to deal with this strange effect ongoing.

[Ari]

All Wistas I've used had the same arrangement: a fresnel/GG-in-one, with a clear glass overlay.
It may be that you're using a wide lens, which would block up some of the viewing area at certain angles, which can be annoying.
But I've found that if you use the focusing hood, it's an almost problem-free viewing/focusing experience.
The Wista screen is one of the best I've seen, though not without its drawbacks.

[Bob Salomon]

Wista screens have their names stamped into the bottom edge of the short side of the screen. Does your screen have the Wista name on it?

[neil poulsen]

Wista screens have their names stamped into the bottom edge of the short side of the screen. Does your screen have the Wista name on it?

Yes it does. (Thanks.)

If desired, can one swap the g.g./grid out for another g.g./Fresnel combination? For some cameras, the dimensions are designed for the particular g.g./Fresnel, especially when the Fresnel is between the g.g. and the lens. (e.g. Arca.)

[Bob Salomon]

Yes it does. (Thanks.)

If desired, can one swap the g.g./grid out for another g.g./Fresnel combination? For some cameras, the dimensions are designed for the particular g.g./Fresnel, especially when the Fresnel is between the g.g. and the lens. (e.g. Arca.)

Wista offers both gridded and plain screens and cover glass.

[Doremus Scudder]

Neil,

I have three or four Wistas with factory Fresnel screens. I find that the distance between your eye and the ground glass/Fresnel screen makes a lot of difference in this regard, as does the focal length of the lens you are using. Try and find the optimal viewing distance by moving your head closer and farther from the viewing screen. Ignore being able to focus at this point; the best position may be too close for your eyes to correctly focus. If this is the case, note the approximated distance from eye to screen and then get a pair of reading glasses that allow you to focus easily at that distance. I use 3.5-4 diopter glasses for viewing and then a loupe for fine focusing.

Hope this helps,

Doremus

[IanG]

Neil, I have the same screen on my 45DX and find it the best screens I've used on a 5x4 camera, I rarely need to use a dark cloth and there's no focus hood on the 45DX

I suspect you get the same effect with most backs with fresnel screens, so I just put my 120mm Dagor on my Super Graphic and I get the effect you describe :D Remember the fresnel is there to help improve bightness at the edges and the corners, If you look at a diagram of how a fresnel focusses light you'll see why the effect happens when you look at the screen at an angle.

Ian

[neil poulsen]

I've since seen information suggesting that the focal length of the Fresnel associated with this screen is "long." In fact, if I stand back a couple of feet from the screen, I avoid the effect mentioned above.

But that's quite a distance. I think I'd rather deal with the issue than stand back that far. Overall though, it's a decent screen. Just wish there were a shorter focal length available.

[John Layton]

To gain a bit more clarity on how the focal length of a fresnel lens affects the image as viewed on your ground glass, and, depending on your own lens focal length preferences/priorities, how to choose the best "all around" fresnel lens based on these preferences/priorities, I'd like to suggest that you contact Bill Maxwell (Maxwell Precision Optics).

[neil poulsen]

To gain a bit more clarity on how the focal length of a fresnel lens affects the image as viewed on your ground glass, and, depending on your own lens focal length preferences/priorities, how to choose the best "all around" fresnel lens based on these preferences/priorities, I'd like to suggest that you contact Bill Maxwell (Maxwell Precision Optics).

Great idea. I will do so. Thanks.

[rdeloe]

I stumbled on this thread because I wondered exactly the same thing about the fresnel lens on my "new" Wista 45VX. Previously I used a plain ground glass on a Wisner Technical Field, so it's taking me a while to get used to the fresnel lens on the Wista. From another much older post about fresnel lenses on the forum, I was directed to this page on Ron Wisner's former site (which is still available via the Internet Archive). It helped me understand how fresnel lenses work. Recommended reading. http://web.archive.org/web/20080501175650/http://www.wisner.com/viewing.htm