Linhof fresnel screen

[absalom1951]

My Linhof Technika's ground glass was dirty so I removed it from the camera so as to get to the inside of the ground glass. I found a fresnel screen. I cleaned both the fresnel screen and the ground glass. Cleaning them really helped tremendously. My question is this-from my reading up on fresnel screens I gather that most of them are outside the ground glass rather than inside of the ground glass. Could this one have been installed incorrectly?

 

[blee1996]

Here is the exact stacking order, starting from the inside of the camera and working outward toward you:

1. Inside of camera (Lens)
2. Ground Glass: Matte (frosted) side facing the lens.
3. Fresnel Lens: Grooved (ring) side facing the ground glass.
4. Outside of camera (You)

 

[Chuck1]

Isn't there a different arrangement for technika iv vs v

 

[tcolgate]

Here is the exact stacking order, starting from the inside of the camera and working outward toward you:

1. Inside of camera (Lens)
2. Ground Glass: Matte (frosted) side facing the lens.
3. Fresnel Lens: Grooved (ring) side facing the ground glass.
4. Outside of camera (You)

I'm not sure that's true for all cameras. I'm sure I've heard of cameras (maybe just MF?), where the fresnel goes on the inside. And on my Ensign Cameo, the matt side of the ground glass is on the "outside" (toward the viewer). The matt side still sits on the film plane though, the bulk of the ground glass is just "inside" the camera.

 

[absalom1951]

Here is the exact stacking order, starting from the inside of the camera and working outward toward you:

1. Inside of camera (Lens)
2. Ground Glass: Matte (frosted) side facing the lens.
3. Fresnel Lens: Grooved (ring) side facing the ground glass.
4. Outside of camera (You)

I have a Technika III. My Fresnel Lens is facing the lens and my Ground Glass is facing the Fresnel Lens. In other words, in my camera 2 and 3 are reversed. If I do try reversing 2 and 3 which will put them in the order suggested above it will alter focusing, by changing the Ground Glass not being in the film plane?

 

[Dan Daniel]

Can you measure the measure the distance from the film surface to front surface plane of film holder, then subtract the thickness of a sheet of film. Compare to the distance from the ground glass surface to the front of screen holder itself. Shuffle materials until you get it focus surface to match film holders.

 

[John Wiegerink]

I'm not sure that's true for all cameras. I'm sure I've heard of cameras (maybe just MF?), where the fresnel goes on the inside. And on my Ensign Cameo, the matt side of the ground glass is on the "outside" (toward the viewer). The matt side still sits on the film plane though, the bulk of the ground glass is just "inside" the camera.

Yes, there are different arrangements for different cameras when it comes to ground glass and fresnel lens. If my old memory is correct when the Chamonix 45N1 first started being imported the ground glass and fresnel were one way and after some time they reversed the order.

 

[absalom1951]

Can you measure the measure the distance from the film surface to front surface plane of film holder, then subtract the thickness of a sheet of film. Compare to the distance from the ground glass surface to the front of screen holder itself. Shuffle materials until you get it focus surface to match film holders.

I can try this. I have a old set of Vernier Calipers. Not to sure how accurate they are. I can probably borrow some calipers though. I wonder if tolerances would be a few thousandths or a few hundredths.

 

[tcolgate]

There's a comment on the large format format suggesting that linhof iii did have a fresnel "forward of the [ground glass]"

"The earlier 45 III backs did not have a fresnel, the later models had one in foreward of the gg, as did the later models until sometime during the Master Technika production it was changed to clips that held it after the ground glass."

Linhof Technika III Fresnel Glass

Dear All I need help. I am not sure about the fresnel glass as technikas have different set ups depending on the age and model of the the camera. I have a linhof lll I beleive (no front tilt) can you tell me where I need to place the fresnel glass. I am so confused! I am even thinking to...

www.largeformatphotography.info

There are also some old posts here on photrio talking about it.

Linhof Technika III Fresnel Glass

Dear All I need help. I am not sure about the fresnel glass as technikas have different set ups depending on the age and model of the the camera. I have a Linhof lll I believe (no front tilt), can you tell me where I need to place the fresnel glass. I am so confused! I am even thinking to...

www.photrio.com

 

[Valmidira]

From a physical standpoint, the optimal position of a Fresnel lens is in front of the ground glass (i.e. between the taking lens and the ground glass), with the grooved side facing the ground glass. This configuration provides more favorable angles of incidence for the light rays entering the Fresnel lens, resulting in improved light distribution and brightness.


The drawback of this arrangement is a shift of the focal plane, which is typically on the order of approximately one third of the Fresnel lens thickness. This value depends on the refractive index of the material from which the Fresnel lens is made. Since Fresnel lenses are commonly manufactured from plastics or resins, this approximation (≈ 1/3 of the thickness) is generally valid in practice.


When the Fresnel lens is placed behind the ground glass, the correct orientation is again with the grooves facing the observer (photographer). In this case, however, no correction of the film plane position is required, since there is no shift of the plane of focus.

 

[Dan Daniel]

I can try this. I have a old set of Vernier Calipers. Not to sure how accurate they are. I can probably borrow some calipers though. I wonder if tolerances would be a few thousandths or a few hundredths.

Ground glass and fresnels are usually around 1.5mm thick. A fine ruler would probably be more than accurate enough.

4 surfaces, so that is what, 8 variations maximum? The only significant issue is the location of the ground glass plane in relation to the film holder film plane. All the rest is gravy.

 

[blee1996]

I learn something every day: did not know that Linhof had other arrangements between ground glass and fresnel lens. I agree with @Dan Daniel that the "location of the ground glass plane in relation to the film holder film plane" is the only thing matters for critical focus.

 

[tcolgate]

"put it back however you found it", is probably a solid starting point though (since it sounds like the original arrangement).

 

[absalom1951]

After reading all replies and links provided in the replies and links in the links. I think for the moment I will do as @tcolgate suggests "put it back however you found it" .In one of the links the person contacted a Christopher Cox who is a member of a Linhof group in facebook. I received a reply from Mr. Cox also. Thanks to all for your replies, they are all valued and appreciated. I'm learning a lot about Fresnel screens

 

[BrianShaw]

What did Mr. Cox advise?

 

[absalom1951]

I can copy and print his reply here, is doing that ethical though?

 

[MattKing]

I can copy and print his reply here, is doing that ethical though?

It is fine if he is okay with your sharing the information.

 

[BrianShaw]

I doubt that 2-party consent is required to share technical information from a private correspondence. Personal information would be different.

 

[MattKing]

I doubt that 2-party consent is required to share technical information from a private correspondence. Personal information would be different.

Speaking generally, @BrianShaw is likely correct, but it is probably easiest to first ask him for agreement about sharing everything, before you decide to pick and choose between parts of the content.

 

[BrianShaw]

Speaking generally, @BrianShaw is likely correct, but it is probably easiest to first ask him for agreement about sharing everything, before you decide to pick and choose between parts of the content.

Spoken like a true risk-averse lawyer or forum moderator. To me, it's now irrelevant... because if the information couldn't be summarized in one's own words than it is likely not understood or not very important. I can either figure it out myself or ask Christopher Cox myself. But it does undermine the cooperative nature of the forum where one should be sharing as much information as they are requesting. No problem, though...

 

[MattKing]

Spoken like a true risk-averse lawyer or forum moderator. To me, it's now irrelevant... because if the information couldn't be summarized in one's own words than it is likely not understood or not very important. I can either figure it out myself or ask Christopher Cox myself. But it does undermine the cooperative nature of the forum where one should be sharing as much information as they are requesting.

I agree.
But my answer may be more Canadian then lawyer or moderator speak.
It is always polite to ask .
I personally tend to include the "request to share" in with my initial contacts with people - that way I often find I get even more cooperation.

 

[absalom1951]

Here's the reply I got from Christopher Cox {Facebook Linhof group}
Hi Tom, in general -if looking from behind the camera like you are taking a photo -it goes in front of the ground glass. It should be slightly less wide than the ground glass and sit on its own ridge seperate than the ridge the ground glass sits. Not all backs have this ridge for the fresnel so… it is possible to sandwich them together but this will move the focus plane which is what you want to avoid. Much later after 1972 they changed it to be held by clips behind the ground glass… you could use these clips with earlier cameras the IV and V but I’m not sure about the III but I’m sure some enterprising person could fit them… placing it aft of the ground glass makes it easier to remove but also more likely to get dirty or scratched.

 

[absalom1951]

I did ask Mr. Cox, was the polite thing to do.

 

[BrianShaw]

Thank you, Tom. That is very useful information.