Advantages of a Built -in vs. Clip-on Fresnel

Does anybody know the advantages/disadvantages of a clip-on fresnel

mounted on the eye side of ground glass(e.g. Sinar) vs a factory

installed fresnel mounted on the lens side of the ground glass(e.g.

Toyo)? I am doing predominantly close tabletop work and would like

all the composing/focusing help I can get. My eyes are not as sharp

as I'd like them to be.

Richard Kagan

I have used a camera with a removable fresnel on the viewer

side of the glass (Wisner), and a camera with a fresnel on the

inside of the camera (Canham), behind the glass. I found the

veiwer-side fresnel relatively distracting in regard to

ground-glass viewing, while the fresnel on the inside of the

camera helps with brightness and focussing, but does not

otherwise produce any noteworthy distractions. I personally

prefer the fresnel on the inside of the camera.

Richard,

 

I have a Sinar with the clip-in fresnel but I tend to use it only for initial composition - generally in dingy churches where you need all the light capturing you can get. When I've set the movements up coarsely (?) I remove the fresnel as I found I was getting unsharp images - I couldn't focus through it properly with my loupe. I've then only got the grain of the g/glass to worry about when focusing. I also think my fresnel has a slight bow on it which doesn't help as it rocks slightly when installed :-(.

 

I don't use swings / tilts much but on the odd occasion I found it more difficult to focus with a double layer of g/glass & fresnel in as you've then got a focus shift / offset to the loupe when going through both layers at an angle. It might be me being hopeless though...

 

At least having a clip-in version means I've got a choice rather than needing a screwdriver each time.

 

One positive side of having a fresnel fastened inside the g/glass - it doesn't drop out / on to the floor / get scratched / lost etc and you don't have to find somewhere safe for it when unclipped :-)

 

Andrew

A fresnel between lens and ground glass will cause curvature of the focal plane. It does not matter how the manufacture adjusts for the fresnel, the curvature will still occur. I can't stand a fresnel. I move my head around to follow the hot spot when focusing.<p>

 

Wisner on fresnels: http://www.wisner.com/viewing.htm

I have a love-hate thing with Fresnels and was lucky enough to have an extra GG back for my camera so one is plain and the other is Fresnel. Not the cheapest solution if you have to buy an extra back but it works well for me.

Linhof, over time, has done it both ways.

 

Old cameras had it underneath the GG. This position helped to protect the delicate

construction from scratches and reduced the need for handling. However users found that

they could not replace it themselves as they might change the correct position of the

focusing plane and that they did not always want to see the magnified grooves when using

a loupe.

 

So Linhof changed the position to the rear which has several benefits. 1: Changing the

fresnel or the gg will not effect the image plane so the user can easily do these changes. 2:

The fresnel can be removed or used at the users whim. 3: The user can experiment with

different gg and fresnel combinations at will. And current fresnel screens can withstand

handling better then the old ones.

I use two focusing frames with an Ebony SV45U.

 

One has a wide-angle fresnel mounted on the viewer's side of the GG, and the other is "plain" (no fresnel). The Ebony permits easy and rapid swapping of the focusing frame.

 

I find that if I use the wide-angle fresnel with a normal to long lens, it is very difficult to see anything. (This combination is much worse than trying to use a wide lens without a fresnel.)

 

When using a wide lens (80mm), the fresnel provides a more even illumination of the the entire frame, which is useful for composition. I do find it more difficult to focus with a loupe on the fresnel, compared to a plain GG. If I am having a lot of difficulty focusing, I switch out the fresnel for the plain GG.

 

 

(I believe the Ebony GG (which is actually plastic) also has a mild fresnel built into it, which is on the lens side. This seems to work well for lenses 110mm and longer, but is not strong enough to be effective for wider lenses.)