Fresnel lens orientation

[jmccl@yahoo.com]

Should the "grooved" surface be facing the taking lens or should it be facing the viewing glass?

Thanks for your help.

Jim

 

[BrianShaw]

What camera. Graflex seems different from others.

 

[shutterfinger]

The ribbed side of the fresnel faces/touches the ground glass regardless of which side of the ground glass you put it.
IF the camera was not designed for a fresnel to be in front of the ground glass and the fresnel is mounted on the bosses the ground glass mounts on then the back will need machining to put the plane of focus on the ground glass in sync with the film plane.

 

[DREW WILEY]

I oriented my fresnel to the trashcan. Well, not literally; it's stored away somewhere. It came with the camera; and the first significant improvement I made was to remove it.

 

[jmccl@yahoo.com]

What camera. Graflex seems different from others.

Deardprff 8x10

 

[jmccl@yahoo.com]

The ribbed side of the fresnel faces/touches the ground glass regardless of which side of the ground glass you put it.
IF the camera was not designed for a fresnel to be in front of the ground glass and the fresnel is mounted on the bosses the ground glass mounts on then the back will need machining to put the plane of focus on the ground glass in sync with the film plane.

Hmmm. I never considered that the fresnel should go on the "outside", but I can see that by putting it on the "inside" I just moved the viewing plane away from the film plane. Will the fresnel brighten the image if it is placed on the "outside". The camera is a Deardorff 8x10.

 

[shutterfinger]

Sinar uses a clip in fresnel that fits over the ground glass and is removable.
If you put the fresnel in front of your ground glass and moved the position of the ground glass then it is no longer at the film plane.
A fresnel does not brighten a ground glass, it smooths out the bright spots/areas allowing one to see into the deep shadows easier.
1. remove the back from the camera with a film holder inserted into the back with a piece of scrap film installed and darkslide removed.
2. lay a straight edge across the back ensuring it lays on an edge that is of equal height on both sides.
3. measure from the straight edge to the surface of the film with the film flat against the film holder. This can be a tooth pick taped to the straight edge.
4. measure at several positions.
5. remove the film holder and install the ground glass.
6. measure to the ground glass ground side as you did with the film in the film holder.
7. Shim the ground glass so that the ground side is the same distance as the surface of the film in a film holder. Paper can be used for shim stock. Different weights of paper are different thicknesses.
8. A fresnel mounted in front of the ground glass that does not move the position of the ground glass will not adversely affect film plane focus. (others may disagree)
9. A fresnel mounted in front of the ground glass that moves the ground glass position must be adjusted for the optical focal length of the fresnel to retain correct film plane focus.

 

[AgX]

If the fresnel lens is mounted betweeen standard and ground glass and if there is a mounting flange at the fresnel lens of different thickness than the actual lens, thus yielding a different spacing depending on orientation, then it matters. In all other cases not.

(With other lenses as for instance a meniscus the orientation has influence on the location of the focal point as well as the image quality.)

 

[Ian Grant]

8. A fresnel mounted in front of the ground glass that does not move the position of the ground glass will not adversely affect film plane focus. (others may disagree)
9. A fresnel mounted in front of the ground glass that moves the ground glass position must be adjusted for the optical focal length of the fresnel to retain correct film plane focus.

If point 8 was correct then, manufacturers would allow a fresnel to be clipped on the inside, however the fresnel is a lens so the screen position need to move back approx 1/3 to 1/2 the thickness of the fresnel to maintain optimum focus. Of course the ground glass holder may also need to be modified to allow for part of the thickness of the fresnel. It's enough to be critical at wider apertures so rear fitting is better when the back hasn't been made to take a fresnel under the ground glass to fit on the outside, that's what I did with my Crown Graphic.

The fresnel will need to be rear fitted on the Deardorff. I'm sure you've come across a few Crown & Speed Graphics where the Fresnel's been incorrectly placed, I have here in the UK.

I oriented my fresnel to the trashcan. Well, not literally; it's stored away somewhere. It came with the camera; and the first significant improvement I made was to remove it.

Some like a fresnel others don't also screen and fresnel qualities vary a lot. A fresnel's not so good when focussing with a loupe but screen brightness can make focussing so much easier and snappier with one.

Ian

 

[BrianShaw]

Screen brightness is over-rated. My personal opinion. With the exception of the factory-installed Graflex fresnel (Graflite, I think the call it), I’ve tried several fresnel on my Cambo and done the same as Drew.

 

[Ian Grant]

Screen brightness is over-rated. My personal opinion. With the exception of the factory-installed Graflex fresnel (Graflite, I think the call it), I’ve tried several fresnel on my Cambo and done the same as Drew.

When you're out in the field working hand held or even quickly with a tripod screen brightness makes a huge difference to ease of focusing.

Screen brightness starts with the GG screen itself, the original Graflex screens are quite poor a better screen can add 2 stops apparent (and measurable) brightness which is very significant. Add a fresnel and you get to 3 stops increase in overall brightness.

Perhaps I;m spoilt because the screen in my Wista 45DX is so good I rarely need to use a dark cloth, it's the original Wista combination screen, so I expect something as close a possible with my other cameras where possible. My Super Graphic and Pacemaker Speed Graphic are about 1/2 a stop less than the Wista in terms of screen brightness both have new screens but the original Graflex fresnels. The Crown Graphic with an external Chinese fresnel is just as bright as te other Galex cameras.

When you put a Crown Graphic and original screen and 150mm f4.5 lens alongside a Wista 45DX and 150mm f5.6 lens, as I did, you realise what a startling difference brightness makes to ease and speed of use and also more accurate precise focusing. A better screen makes the biggest difference, the fresnel makes the screen less directional when composing and focusing. If you spend sometime under a dark-cloth composing etc a fresnel os less important and maybe a hinderance.

With my main 10x8 camera I was lucky it came with a new Beattie Intenscreen so it's very easy to focus and nice and bright.

I restore & repair quite a few cameras and also make and fit a lot of screens each year so want the best on terms of brightness and ease of focussing, as so the people I do work for.

Ian

 

[shutterfinger]

With the exception of the factory-installed Graflex fresnel (Graflite, I think the call it)

Its called Ektalite Field Screen.
Crown and Speed Graphic ground glass and fresnel can be improved by removing them, washing in warm water, applying dish soap directly to the gg/fresnel surface, rubbing with finger tips only (gently) then rinsing under running water with a final rinse in a weak PhotoFlo solution, then standing on edge to dry or drying with a clean lint free cloth.

I mounted a fresnel in front of the gg on a Meridian 45B without displacing the gg and it did not affect focus.

 

[BrianShaw]

Thanks... I knew that but had a complete brain phart.

Graflite = flash.

 

[BrianShaw]

I hear ya, Ian... perhaps I’m spoiled too.

But, honestly, I often get my best images by looking at the scene, getting it “roughly framed”, and exposing properly rather than spending excruciating efforts to frame and focus exactly “perfectly “.

We all have our ways, needs, and criteria I guess.

 

[Ian Grant]

Crown and Speed Graphic ground glass and fresnel can be improved by removing them, washing in warm water, applying dish soap directly to the gg/fresnel surface, rubbing with finger tips only (gently) then rinsing under running water with a final rinse in a weak PhotoFlo solution, then standing on edge to dry or drying with a clean lint free cloth.

I mounted a fresnel in front of the gg on a Meridian 45B without displacing the gg and it did not affect focus.

Cleaning isn't enough to make a significant difference, it'll help with a fresnel but not the GG unless it's very dirty. I make a lot of screens every year the (over a hundred) 2 stops difference was between a very clean Graflex screen and a new screen.

Ian

 

[DREW WILEY]

Brian, how on earth can you emphasize exposing properly but not focusing properly, or thoughtfully composing? What's the point? The thing I hate about fresnels are all those danged lines that make acute focus a headache to begin with. I've never had a problem focusing due to low light, and most of the lenses I now carry are in the f/9 max aperture range. Sometimes the real problem is the type of grind on the groundglass.

 

[BrianShaw]

Brian, how on earth can you emphasize exposing properly but not focusing properly, or thoughtfully composing? What's the point? The thing I hate about fresnels are all those danged lines that make acute focus a headache to begin with. I've never had a problem focusing due to low light, and most of the lenses I now carry are in the f/9 max aperture range. Sometimes the real problem is the type of grind on the groundglass.

Excellent point... I forgot to write that word in the proper context. It’s been a rough day.

What I meant to say is that focus is needed but I don’t struggle like I read some folks do with 10x loupes Etc.

Call me a hack, but I check focus... I just don’t slave over it. Come to think about it... I don’t slave over exposure either. I guess I am a hack!

Even my dimmest GG is bright enough to focus without the need for a fresnel. I’m lucky, I guess. But that might be changing as the cataracts are getting bad enough that I’m noticing them

 

[DREW WILEY]

A 10X loupe is likely to just show you a lot of grind pattern on the glass, anyway. It's apt to be counterproductive to achieving fine focus. Cataracts are now becoming a middle-aged epidemic due to so much computer use. I'm retired now, so don't have to use a computer for hours a day;
but my reading glasses for computer use, which I'm wearing right now, have a special amber coating to slow down incipient cataracts. Mine are all still tiny and affect only peripheral vision when something bright happens to hit one and I see zig-zags flashing in that eye for up to 20 minutes at a time. Sunglasses outdoors. Doesn't affect photography are darkroom work.

 

[jmccl@yahoo.com]

Thanks everyone for your response. I removed my new fresnel from the inside of the GG and I just held it up to the GG on the outside. Wow, what a difference in brightness. For now I'll just fiddle with the GG and learn about focusing. When I get more comfortable there, I'll add the fresnel and see if that is the way for me.

Thanks again. This is all a first for me so I will likely be posting more questions as I get further into this 8x10 world.