Shen Hao & Fresnel

[Harold Wingo]

I have recently acquired a 4X5 Shen Hao with Ebony Fresnel. It came shipped with the Fresnel on top of the GG, i.e., the Fresnel is next to the eye when viewing. Additionally, the Fresnel's rough side (textured side) too is next to the eye.

1. Should the Fresnel be behind GG?

2. If the Fresnel is not to be behind glass then should the textured side of the Fresnel be next to the eye?

After using the loupe against the Fresnel, I have found marks on the textured side from the loupe! This doesn't seem right.

I also own a Sinar and the Fresnel IS used on the outside of the glass but the Fresnel's smooth side is next to the eye, meaning the textured side is facing the GG.

Badger Graphics has stated the Fresnel needs to be behind glass yet another source is of the opinion that the camera is designed for the image to form on GG and if the Fresnel is placed between GG and film, the image will be out of focus on film because of the additional thickness that's present between film and GG.

Thought I would throw this out for opinions.

Harold

 

[coriana6jp]

On all the LF cameras I have owned that had a Fresnel, it was always mounted behind the glass(IE between the where the film holder goes and GG.. That being said, I have read articles which state its better its better the other way.

The best thing to do is try it both ones and check the sharpness very very closely on a couple of negatives. I have read and seen the even though it looks sharp on the GG, there is occasionally a subtle in focus which affects the film.

Best thing to do is give it a try, sorry its not more help.

Gary

 

[Jerry Thirsty]

The GG on the Shen Hao is mounted from the back of the wood frame (back meaning from the back of the camera, not from the inside of the camera), so its' front surface is pressed against the wood. Therefore, if you put the fresnel in behind it, the GG is still against the wood, meaning that its' position has not changed. If you were to take the GG out, put the fresnel in front of it, and then put the GG back the GG would be shifted backward by the thickness of the fresnel, presumably messing up the focusing to some degree.

It shouldn't matter which side of the fresnel is facing which direction; it's basically a lens, and it directs light the same way regardless which direction it passes through. I'm playing with one of the full page magnifiers here at my desk, projecting an image of the overhead light onto the desk and the only difference I see when I flip it over is that the focal length seems to be a bit shorter on one side than the other.

As fas as I know, all fresnels are made from plastic, so they are prone to scratching (presumably if they were glass you would also have to worry about breaking off the tops of the ridges). Maybe try putting some tape around the bottom of the loupe to give some cushioning?

 

[Curt]

The largest fresnel lenses are in lighthouses and are made of glass.

 

[David A. Goldfarb]

On most LF cameras, the fresnel goes on the outside (between the gg and your eye) with the concentric circles facing in. On some, the back is designed with the fresnel in mind, so it can go between the gg and the lens. If you put it in the wrong place, the gg will be out of register.

 

[chrisofwlp]

It doesn't matter what side of the GG the Fresnel is on. I have a 4x5 with the fresnel on the inside, and recently i installed one on the "outside" of my 8x10.
what matters is Where the GG is, so that your focal plane remains in the same location.

all the fresnal does is reflect light back towards your eye as or after the light has passed through the gg.