Where can I purchase a cheap Fresnel screen for my Mamiya 7 custom built Viewer?

[Giovanna]

Hello everyone at Photrio : )

I am trying to design and build a custom made reflex viewer for my Mamiya 7.

In the 90º viewer I am designing, the Fresnel+GG combo will sit in the back of the camera, right where the film frame sits. I certainly need to have a Fresnel lens in front of the GG because I have noticed, viewing the image on the fiber optic glass of my NPC Pola back, that already with a not so wide focal as the 65mm lens, there too much darkness around the center spot, even at the widest aperture.

I would prefer that this thread does not become a discussion related to why one need such a device. For the sake a duly explanation, in any case, I will just say that at times one need to accomplish a critical composition which is impossible to achieve through the rangefinder viewer.

I would truly appreciate if someone could point me in the right direction on where to purchase a custom cut Fresnel screen.


Thank you for your help and have a nice weekend !

 

[Dan Daniel]

Cheap? Go to a bookstore and ask them for magnifiers, the flat sheet kind. Thin flexible plastic sheets with fresnel patterns molded in. Usually $3-8 USD here. Easy to trim to size. You'll be able to see the center point of the fresnel and can work from there. Here's the idea on US Amazon-
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=magnifier+sheet

You can contact this guy and ask for a price. I know that he isn't Maxwell Screen-level expensive (who will be happy to make you one for $2-300 plus) but more expensive than the things above.
http://lensn2shutter.com/fresnels.html

Fresnel screens are made from molded plastic. They can be cut and shaped easily. Score and snap, trim on a band saw, laser cutter. So pretty well any screen you see listed on Ebay or such can be cut down for your purposes.

 

[Ian Grant]

Helix sell a small magnifying fresnel, I've used one on my Home-made 6x7 view camera, it needs to be the eye side of the ground glass screen. Dirt cheap £2.11 inc postage on ebay, but works OK the actual fresnel part is 8,5cmm wide but about 5,5cm wide then plain plastic. It's enough to make a huge difference when focussing.

Ian

 

[jim10219]

Cheap? Go to a bookstore and ask them for magnifiers, the flat sheet kind. Thin flexible plastic sheets with fresnel patterns molded in. Usually $3-8 USD here. Easy to trim to size. You'll be able to see the center point of the fresnel and can work from there. Here's the idea on US Amazon-
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=magnifier+sheet

You can contact this guy and ask for a price. I know that he isn't Maxwell Screen-level expensive (who will be happy to make you one for $2-300 plus) but more expensive than the things above.
http://lensn2shutter.com/fresnels.html

Fresnel screens are made from molded plastic. They can be cut and shaped easily. Score and snap, trim on a band saw, laser cutter. So pretty well any screen you see listed on Ebay or such can be cut down for your purposes.

I have one of these I made for my 4x5 Speed Graphic. It works fairly well, though it's no magic bullet. Honestly, I just need to replace that ground glass. It seems about 4 stops dimmer than my next dimmest ground glass. But the homemade Fresnel takes it from unusable to barely usable for wide angle lenses, so it was worth the $10.

Hell, an afternoon of melting plastic and starting fires in the hot summer sun with it before I cut it down was worth $10!

 

[EdSawyer]

Ideally the fresnel needs to be matched (focal-length-wise) to the lens(es) that are going to be used.

That said, probably the easiest way to get a nice fresnel/GG of the right size and relatively correct focal length would be to cannibalize the one from the 6x7 ground glass back that was made for the RZ67, to be used with tilt-shift gear. It's a really nice focusing screen, and already the right size.

Another option might be just use a (cut-down?) focus screen from an RZ67, they are about 7x7cm, with a metal frame, but the actual fresnel/screen is plastic I believe.

-Ed

 

[Giovanna]

Cheap? Go to a bookstore and ask them for magnifiers, the flat sheet kind. Thin flexible plastic sheets with fresnel patterns molded in. Usually $3-8 USD here. Easy to trim to size. You'll be able to see the center point of the fresnel and can work from there. Here's the idea on US Amazon-
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=magnifier+sheet

You can contact this guy and ask for a price. I know that he isn't Maxwell Screen-level expensive (who will be happy to make you one for $2-300 plus) but more expensive than the things above.
http://lensn2shutter.com/fresnels.html

Fresnel screens are made from molded plastic. They can be cut and shaped easily. Score and snap, trim on a band saw, laser cutter. So pretty well any screen you see listed on Ebay or such can be cut down for your purposes.

Thank you Dan, I appreciate your suggestions !

 

[Giovanna]

Ideally the fresnel needs to be matched (focal-length-wise) to the lens(es) that are going to be used.

That said, probably the easiest way to get a nice fresnel/GG of the right size and relatively correct focal length would be to cannibalize the one from the 6x7 ground glass back that was made for the RZ67, to be used with tilt-shift gear. It's a really nice focusing screen, and already the right size.

Another option might be just use a (cut-down?) focus screen from an RZ67, they are about 7x7cm, with a metal frame, but the actual fresnel/screen is plastic I believe.

-Ed

Hello Ed, thank you for your suggestions. I think I might need some more clarifications from you. I found several Mamiya RZ screens, even close to where I am. Like this one for example:

https://www.ebay.it/itm/MAMIYA-RZ-S...742840?hash=item1ed2540df8:g:Sb8AAOSwdSRZ83RG

I am not too sure, however, that these type of screens do have a fresnel, either "incorporated" in the GG, or as a second layer in the metal frame that contains them. Are you sure about that?

If you are right, I think that might be the easiest solution, as long as I find a way to cut them without breaking them.
Thank you so much,

 

[EdSawyer]

The cross-hair screen probably wont' have a fresnel built in, but the other types generally do. They will have fresnel built into the screen, in many cases. I haven't taken one apart, so they may be one piece or may be 2 - but in any case they definitely could serve the purpose for your needs.

The actual item I was referring to above is the special ground-glass back for the RZ67, to be used with their tilt-shift stuff. The GG/Fresnel can easily be removed from this. I have one of these, there's 6 small screws that hold the screen/GG in place.

https://www.ebay.com/itm/Mamiya-RZ-...-ADAPTER-BACK-SHIFT-TILT-ADAPTER/321942487174

 

[Dan Daniel]

The Mamiya screen is one piece, with fresnel pattern molded on one side and ground glass on the other side. Two clips unscrew and the plastic screen with glass protective cover falls out easily.

You need to put the ground glass side at the film plane. The plastic is hard but can be cut with a knife using repeated (and repeated/repeated/repeated....) scoring. Protect the usable surfaces when doing this. Then wet sand the edges smooth with medium-fine grit sandpaper.

A fine-toothed band saw will also cut it, or a laser cutter.