Fresnell lens

Huub · Apr 17, 2013

A few weeks ago i had a sad accident with my old anf faithfull Toyo, that served me well for over 15 years. It topled down from a small hill and landed sideways on a stone. Tripod and lens were unharmed, camera total loss: dented and bend house, front standard had broken off and the viewing screen had shattered into pieces...

Luckely for me i had a good insurance on the camera and for the money i got back i decided to buy a ShenHao HZX45 II-A. I have been working with this new ca,eraa couple of times now and it handles so much easier then the old Toyo. Especially I am very pleased with the viewing screen: so much easier to focus. It realy snaps in, where the old Toyo always seemed to be a bit blurry. You had to focus very carefully to put the plane of focus where you wanted it.

As to further improve the ease of focussing with the ShenHao i bought myself an additional fresnell lens. As this fresnell lens came without a manual it leaves me with the question on how to put in the camera: should the smooth side be towards the viewing screen or towards the lens panel side of the camera? Both options seem to be possible.

I hope the fresnell lens will improve the brightness of the viewing screen when using wide angles, as is stated generally. But are there also disadvantages to using it, except for the few grams it will add to the weight of the camera? And if so: why hasn't every camera such a fresnell lens as a standard?

AgX · Apr 17, 2013

In general:
The orientation does not matter. As long as the fresnel lens is positioned back of the groundglas, at the photographer's side.
For protecting the lens surface mounting the plain side of the fresnel lens towards the photographer is advisable.

EDIT:

should the smooth side be towards the viewing screen or towards the lens panel side of the camera? Both options seem to be possible.

That would mean you you are considering installing the fresnel in front of the lerns.
In general: No.
Unless the camera is designed this way.

In case there are rebates or such at a fresnel, the proprietory mounting should be used as different mounting could change position of the ground surface of the ground glass too.

Basically the focal lenght of the fresnel lens must be chosen with the focal lenght or rather the exit angle of the taking lens in mind. But to my knowledge this ist not done in LF photography.

Rudolf Karachun · Apr 17, 2013

Remove ground glass, by unscrewing two metal holders. Install Fresnel lens first, with grounded side looking toward you, put ground glass on the top of the Fresnel exactly same way as it was before, screw back metal holders. The Shen-Hao has a special spot for the Fresnel lens. You will see how the Fresnel will fit in its place after the ground glass removed.

Dan Fromm · Apr 17, 2013

Rudolf Karachun said:
Remove ground glass, by unscrewing two metal holders. Install Fresnel lens first, with grounded side looking toward you, put ground glass on the top of the Fresnel exactly same way as it was before, screw back metal holders. The Shen-Hao has a special spot for the Fresnel lens. You will see how the Fresnel will fit in its place after the ground glass removed.

NO NO NO!

If you follow these directions the ground glass will be out of register with the film plane. When adding a fresnel to a back that didn't come with one, the fresnel must go between the ground glass and the photographer.

bobwysiwyg · Apr 17, 2013

Dan Fromm said:
NO NO NO!

If you follow these directions the ground glass will be out of register with the film plane. When adding a fresnel to a back that didn't come with one, the fresnel must go between the ground glass and the photographer.

Now I'm confused. Per the ViewCameraStore in reference to the Shen Hao Fresnel they sell for the 4x5..

"Easy to install.

The screen drops in under the ground glass."

AgX · Apr 17, 2013

A lens placed in front of the ground glass will move the focal plane.
In case this is taken care of with reference to the position of the film plane, thus in the construction of the camera, that should work.

bobwysiwyg · Apr 17, 2013

AgX said:
A lens placed in front of the ground glass will move the focal plane.
In case this is taken care of with reference to the position of the film plane, thus in the construction of the camera, that should work.

Could you elaborate? I'm having a dense day. It would seem you can't have it both ways. If placed between the GG and the lens it moves the GG back some no matter what??

BrianShaw · Apr 17, 2013

You can't have it both ways. Either the focus panel/system was designed to have the fresnel in front of the GG or not.

bobwysiwyg · Apr 17, 2013

Brian, pretty much what I thought. This suggests the ViewCameraStore instructions are incorrect? and the Fresnel should be mounted between the GG and the photographer's eye?

BrianShaw · Apr 17, 2013

I'd stop right now and dial the phone (if ViewCamera Store has a phone number) if I were you. What you read on ViewCamera store can be read etiehr way. If the focus panel was designed with a recess for fresnel under the GG then it seems like Rudolf could be right. If not, then Dan could be right.

Rudolf Karachun · Apr 17, 2013

Dear Bobwysiwyg, if you like to do it right way, just follow my instructions as it shown above. I have a ShenHao and I used to install Fresnel on this camera few times. If you have a Fresnel directly made for the Shen Hao you will be ok. The kind of problems as Dan Fromm mention above may happens if the camera not disigned for the Fresnel at all, ore if the fickness of the Fresnel lens are bigger than required for that particular camera. But as i said above, Shen Hao has a spot for the fresnel and camera designed for the fresnel, they just sell it separatelly as an option, and if yours Fresnel made directly for the ShenHao the lens will fit in its spot with out affecting the ground glass position. This is the right way to go.
Thanks.

E. von Hoegh · Apr 17, 2013

BrianShaw said:
I'd stop right now and dial the phone (if ViewCamera Store has a phone number) if I were you. What you read on ViewCamera store can be read etiehr way. If the focus panel was designed with a recess for fresnel under the GG then it seems like Rudolf could be right. If not, then Dan could be right.

And AGx is right, too. A Fresnel is optically about 2/3 it's physical thickness. I do not use a Fresnel on either of my view cameras for this and other reasons.

Dan Fromm · Apr 17, 2013

Only a malicious SOB would deliver a focusing panel designed for a fresnel without the fresnel. If the focusing panel is designed for a fresnel and the fresnel isn't there, the ground glass will be out of register with the film plane.

Rudolf, you can't have it both ways. Either the OP was screwed when it bought its camera or it was screwed when it bought its fresnel.

I learned all this the hard way. I shoot Pacemaker Graphics with Graflok backs. When the Graflok back was introduced the fresnel was optional; when installed it was mounted in front of the ground glass. Graflok focusing panels (from Graflex Inc.) made to use a fresnel and those made to be used without a fresnel have the same casting numbers. In both types, the ground glass rides on bosses; the bosses in focusing panels modified to use a fresnel are milled down to keep the ground glass in register with the film plane.

Guess who put an aftermarket fresnel in front of a Graphic's GG? Interestingly, the instructions that came with the fresnel said to mount it in front of (on the lens side of) the ground glass.

By the way, at one time a chinese view camera -- I thought 4x5 Chamonix, not Shen Hao -- was routinely delivered with the ground glass out of register with the film plane. Stupid design error that was eventually corrected after many complaints from buyers.

bobwysiwyg · Apr 17, 2013

Perhaps I will give them a call. I currently have a Shen Hao 4x5 which I've had for a few years. I did installed a Fresnel (not specific to the camera) about two years ago and liked the fact that it brightened things up quite a bit. At my age, every little bit helps. Current mounting arrangement is original GG set in the recess with the GG surface facing the lens. The Fresnel is then placed on top of that with the concentric surface facing the smooth side of the GG. I just removed both to examine the recess again. I see nothing that would accommodate putting the Fresnel between the GG and the lens without moving the focus point/film plain. So, barring any additional information I get from a phone call, it seems to me the current order and arrangement is how it would have to be on my Shen Hao. Perhaps later modes were designed differently to accommodate the Fresnel in front of the GG? :confused:

Rudolf Karachun · Apr 17, 2013

Dear Dan, I'm sure you probably learned and know much more than me. But I just know my camera, and it happens to be a Shen-Hao, and I know how it was designed. Maybe you right about the manufacturer, how designed the camera with Fresnel and sells it as an option, but I'm not a manufacturer, I'm a user and I have to follow manufacturer. And if manufacturer wants me to pay more for the Fresnel, I pay more, because I want to have Fresnel on my camera. The question was about how to install Fresnel on the Shen-Hao, and I gave the detailed answer, and even more, gave some explanations to the others why it is this way and not the other because the camera has a place where the Fresnel shall go. I don’t see that anybody except me gave the same detailed answer or even mention that he knows that particular camera and how it’s made. I did best what I can. All other posts in that treat are just about general camera design and construction and knowledge of all of us. And we all are right, we all know that the ground glass shall not to be moved if we like to have a sharp pictures. And believe me or not it will not be moved, because the Shen-Hao designed this way. To follow my recommendation or not this is another question and let the person why ask the question decided. I just did my best. Thank you.

Dan Fromm · Apr 17, 2013

Rudolf, if the fresnel must be present and mounted in front of the GG then its absence is a problem. The GG can't be in register with the film plane with the fresnel in front of the GG and without a fresnel.

BrianShaw · Apr 17, 2013

E. von Hoegh said:
And AGx is right, too. A Fresnel is optically about 2/3 it's physical thickness. I do not use a Fresnel on either of my view cameras for this and other reasons.

Yes, I don't like them either. Tried one on a view camera but didn't like it one bit. No real advantage and seemed to make viewing GG with loupe more difficult. I only use on on a Graphic which was originally designed and delivered with one... and that is mostly because, due to the design of that camera's back, if I remove it my GG will be out of register with the film plane.

Rudolf Karachun · Apr 17, 2013

Ok. Let me be more detailed. Usually the wooden frame where the ground glass go, has shoulders from four sides on which the ground glass slipping. The Shen-Hao designed the way that just two shoulders from two opposite sides of the frame supporting the ground glass. The other two shoulders from other two opposite sides of the wooden frame a made dipper, and there is a gap approximately 2mm. between the shoulder and the ground glass. These two shoulders made dipper in purpose to support the Fresnel. The Fresnel itself, if it is made especially for the Shen –Hao has fickness and cut to the size to slip on these two deeper shoulders, and not on the other two witch supporting the ground glass. This way when the Fresnel inserted, the ground glass stays on the same position as without Fresnel.

Ian Grant · Apr 17, 2013

There's two separate issue here. Some backs have a recess under the ground glass for a fresnel this means the fresnel itself doesn't alter the position of the glass, any shift in focus is relative to the depth of the fresnel rings rather than the overall thickness of the fresnel. There may need to be a thin shim when no fresnel is used.

However where a fresnnel moves the ground glass in a back not designed for a fresnel then the focus is altered and as Dan says in that case the fresnel should be on the rear of the Groundglass - pohotographer side. Where a back is designed to have a fresnle sandwiched on the inside of a fresnel (no specific recess) then when the fresnel is removed there needs to be quite a thick shim a touich less than the fresnels thickness.

Ian

E. von Hoegh · Apr 17, 2013

BrianShaw said:
Yes, I don't like them either. Tried one on a view camera but didn't like it one bit. No real advantage and seemed to make viewing GG with loupe more difficult. I only use on on a Graphic which was originally designed and delivered with one... and that is mostly because, due to the design of that camera's back, if I remove it my GG will be out of register with the film plane.

My first LF camera was my Linhof STIV, which came with a Linhof Super Screen installed. The original GG was in the Super Screen box. I hadn't even made any photos with it before I removed the %&$@* Super Screen, gave it away, and replaced the original GG. It hasn't moved since.

Huub · Apr 17, 2013

Thanks everyone for the reactions.

Rudolf is right about how my ShenHao is constructed: the back has a provision for putting in a fresnell before the ground glass, without changing the register of the ground glass. The fresnel I bought seem to fit perfectly before the ground glas of the camera when checked with a caliper. What i wanted to ask is how I should position the fresnel: with the plain side towards the ground glass or towards the lens?

My second question is what the disadvantage are of using a fresnel lens: some people seem to find it harder to focus the lens. Are there any other disadvantage sin using the fresnel i should aware of?

Huub · Apr 17, 2013

Thanks everyone for the reactions.

Rudolf is right about how my ShenHao is constructed: the back has a provision for putting in a fresnell before the ground glass, without changing the register of the ground glass. The fresnel I bought seem to fit perfectly before the ground glas of the camera when checked with a caliper. What i wanted to ask is how I should position the fresnel: with the plain side towards the ground glass or towards the lens?

My second question is what the disadvantage are of using a fresnel lens: some people seem to find it harder to focus the lens. Are there any other disadvantage sin using the fresnel i should aware of?

Rudolf Karachun · Apr 17, 2013

Fresnel concentric surface shall face the ground glass. Fresnel will help you to see things more brighter. I dont see any disadvantages in using it. May be some other do, but not me.

shutterfinger · Apr 17, 2013

Grooved side of the fresnel should face the ground glass.
A fresnel eliminates hot spots and opens up the shadows making the overall scene lower contrast than it really is.
The rings of the fresnel can make seeing the fine detail of a scene harder to see when using a loupe on the ground glass depending on how fine the rings are on the fresnel and how well you can "see".

I had a Meridian 45B. I bought a reading fresnel from Office Max. I cut the fresnel down to fit the ground glass opening of the camera. Upon removing the ground glass I discovered the fresnel would fit between the frame and bosses for the ground glass without moving the ground glass position. After modifying the edges and assembling I checked the focus with a loupe from infinity to a few feet and no shift in focus.

TheFlyingCamera · Apr 17, 2013

I installed a fresnel in my old Shen Hao HZX-45AT-II. It was a Canham Fresnel/GG combo, purchased IIRC from The View Camera Store. I put the fresnel in front of the ground glass, and never had a problem with focus being off.

Fresnell lens

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