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Screen glas discussions
- Thread starter martin-f5
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- Dec 19, 2017
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Martin, I make screens quite regularly a new plain screen may well be quite a bit brighter towards the edges and corners. I wrote something about this on APUG around 2007.
I have a Crwn Graphic I leave in Turekey and had it on a tripod alongside my Wista with similar results. However the Wista screen is a combination screen with built in fresnel. I fitted a new plain screen to the Crown Graphic and it was significantly brighter, later I added a fresnel to the rear.
You have to be careful adding a fresnel (or removing one can affect the focus register. In fact Chamonix had this problem when they added a fresnel under the GG screen and hadn't ealised the GG frame holder needed modifying. A friend had one from the first batch and at wide apertures his portraits weren't sharp, Chamonix did resolve the issue quite quickly and replace the backs that was around 10 years ago.
Sinar and Linhof have removable fresnels these fit behind the GG screens (viewer side) so the fresnel lens doesn't affect the focus.
I've serviced a couple of Speed Graphics and found one had a fresnel added incorrectly, the other had a fresnel removed, neither focussed correctly. One issue with PAcemaker Graphics is the GG frame casting is the same number regardless of whether for no fresnel, or for one, they needed machining differently to allow for some of the fresnel thickness.
When I added a fresnel to my Crown Graphic it was on the outside of the GG I had to shim the retaing clips so the viewfinder hood would clip in place. Once done I was olnly around 1/3 to a 1/2 stop dimmer than the Wista but you can't better a combination screen, but the back has to have been made to take one.
A good new GG screen can add around 2 stops brightness towards the edges add the fresnell and it another stop, a new screen has less effect on central brightness but there can be a slight improvement, a fresnel has no effect on central brightness.
Ian
I have a Crwn Graphic I leave in Turekey and had it on a tripod alongside my Wista with similar results. However the Wista screen is a combination screen with built in fresnel. I fitted a new plain screen to the Crown Graphic and it was significantly brighter, later I added a fresnel to the rear.
You have to be careful adding a fresnel (or removing one can affect the focus register. In fact Chamonix had this problem when they added a fresnel under the GG screen and hadn't ealised the GG frame holder needed modifying. A friend had one from the first batch and at wide apertures his portraits weren't sharp, Chamonix did resolve the issue quite quickly and replace the backs that was around 10 years ago.
Sinar and Linhof have removable fresnels these fit behind the GG screens (viewer side) so the fresnel lens doesn't affect the focus.
I've serviced a couple of Speed Graphics and found one had a fresnel added incorrectly, the other had a fresnel removed, neither focussed correctly. One issue with PAcemaker Graphics is the GG frame casting is the same number regardless of whether for no fresnel, or for one, they needed machining differently to allow for some of the fresnel thickness.
When I added a fresnel to my Crown Graphic it was on the outside of the GG I had to shim the retaing clips so the viewfinder hood would clip in place. Once done I was olnly around 1/3 to a 1/2 stop dimmer than the Wista but you can't better a combination screen, but the back has to have been made to take one.
A good new GG screen can add around 2 stops brightness towards the edges add the fresnell and it another stop, a new screen has less effect on central brightness but there can be a slight improvement, a fresnel has no effect on central brightness.
Ian
- Joined
- Sep 22, 2017
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- 300
Until today I had a Chamonix, it's sold now, but the results I got with the Chamonix were perfect in focus, never had issues.
I now had to replace the screen because of selling the Chamonix.
Oh my dear what are I'm doing...
But I really do love the Linhof, it's bulky and heavy twice the times of a Chamonix.
The new owner will be very happy with her.
Anyway, I asked Maxwell for a screen glass and we wanted 570 $ which is quite a lot.
I also have seen some on Ebay but well, buying one from Linhof will help them to make money.
Close-up focusing on a screen with fresnel is a little bit tricky but with a ruler on the subject helps a lot.
I now had to replace the screen because of selling the Chamonix.
Oh my dear what are I'm doing...But I really do love the Linhof, it's bulky and heavy twice the times of a Chamonix.
The new owner will be very happy with her.
Anyway, I asked Maxwell for a screen glass and we wanted 570 $ which is quite a lot.
I also have seen some on Ebay but well, buying one from Linhof will help them to make money.
Close-up focusing on a screen with fresnel is a little bit tricky but with a ruler on the subject helps a lot.
- Joined
- Dec 19, 2017
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I have a Beattie Intenscreen fitted to my 10x8 Agfa Ansco Commercial View, makes focussing very easy. Morco have 5x4 Beattie screen at £170, not bad when they were £236 in 2004 They did make one to fit 5x4 Linhofs but you'd need to check with Morco if they have one suitable
My Beattie screen came new and unused still in its box with the camera, I hadn't expected it so it was a bonus particularly as it would cost about the same as the camera if I'd bought one new.
Ian
They did make one to fit 5x4 Linhofs but you'd need to check with Morco if they have one suitableMy Beattie screen came new and unused still in its box with the camera, I hadn't expected it so it was a bonus particularly as it would cost about the same as the camera if I'd bought one new.
Ian
The difference between old Linhof and recent Chamonix is indeed striking!
I heard from users that when using e.g. a Maxwell screen on a Linhof camera, the focus point may need to be readjusted.
Advantage of a Linhof screen on a Linhof cam is that no such readjustment is necessary.
Recent Linhof screens are rather bright btw.:
I heard from users that when using e.g. a Maxwell screen on a Linhof camera, the focus point may need to be readjusted.
Advantage of a Linhof screen on a Linhof cam is that no such readjustment is necessary.
Recent Linhof screens are rather bright btw.:
One thing that never seems to be mentioned with brighter screens is that they don't increase the amount of light at all. They are condenser lenses and focus the available light from the screen to a single spectator point. If your eye is at that critical point, the screen, and particularly the edges, do appear much brighter. Off-axis, the screen appears darker and on the most efficient screens can seem to switch off altogether. It can even be significantly dimmer for the other eye. With movements, this spectator point moves and can be difficult to locate, particularly with wide lenses. It becomes literally a pain in the neck.
Ideally, the focal length of the fresnel should be paired with the focal length of the lens. With long lenses a fresnel seems unnecessary. I switched to a less efficient screen because of all this.
This is not to deny that some screens, of any kind, are better-made than others.
There are other factors too. A coarser grind looks brighter but a finer grind is better for revealing detail. The actual surface shape of the grind may have an effect, too, but I don't really know. I seem to recall 35mm cameras claiming to have "laser-etched" screens. Laser-etching may offer delicate control of the micro-contours.
Other members of the forum may know more...
Ideally, the focal length of the fresnel should be paired with the focal length of the lens. With long lenses a fresnel seems unnecessary. I switched to a less efficient screen because of all this.
This is not to deny that some screens, of any kind, are better-made than others.
There are other factors too. A coarser grind looks brighter but a finer grind is better for revealing detail. The actual surface shape of the grind may have an effect, too, but I don't really know. I seem to recall 35mm cameras claiming to have "laser-etched" screens. Laser-etching may offer delicate control of the micro-contours.
Other members of the forum may know more...
- Joined
- Dec 19, 2017
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- 2,712
Good explanation of how a fesnel works David. When I began making screens I did a lot of testing aa measuring, comparative tests as well as with a spot meter, I picked up some tips from Dave Parker who used to make satin Snow screens. The smallest I've made was for a 6x4.5 N&G Baby Sybil, followed by a few for TLR's where people have wanted a brighter screen but not wanted a modern Acrylic screen.
Ian
Ian
A
Anthony
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Making a ground glass view screen is easy - I use 400 grit carbide, water from a spray bottle, and a 1/4" 3x3" platen for the grinding. The 400 grit works well for a view camera. Even with slow Goertz lenses in dim light, I can delineate plenty of detail (with magnifying eyeglasses).
Rinse, dry, and check - often I need to touch up edges and corners. With practice you'll only need 2 inspections and you're done.
Refinements:
1. With a tabletop belt sander and a 100 grit belt, I sand the edges and corners of the view screens. You can brace a portable belt sander too and use that. Wear gloves the first few times - very little pressure is needed. Makes the glass safer and more pleasant to handle. You can also do it by hand with a hardwood sanding block - wrap the sandpaper around it.
I don't cut the 1/4 glass for the grinding platen - I let the glass shop do that. they'll usually sand it for you too.
2. I use the flat corian kitchen countertop. One spray on the countertop. Put about 4-8 sheets of newsprint down. Another short spray. Put the glass down and it won't move. Peel up and discard the old sheet each time you rinse and check the glass.
3. When you're ready to grind a screen, take a permanent marker and write the word "UP" - backwards - on one side. Cover this with masking tape - it'll wear off otherwise. This side goes down and you grind the other side. As you rinse and dry to check your work, it's easy to mistake which side you're grinding.
Lastly - I'm not the most tolerant or endlessly patient sort for this kind of thing. I save that for creative work, yeah? So if I do this, anyone can do it. On Christmas Eve, I made 2 8x10 view screens for a Calumet 8x10 while my wife wrapped presents and my daughter watched episodes of "The Office." I dislike that show intensely.
Carry on.
Rinse, dry, and check - often I need to touch up edges and corners. With practice you'll only need 2 inspections and you're done.
Refinements:
1. With a tabletop belt sander and a 100 grit belt, I sand the edges and corners of the view screens. You can brace a portable belt sander too and use that. Wear gloves the first few times - very little pressure is needed. Makes the glass safer and more pleasant to handle. You can also do it by hand with a hardwood sanding block - wrap the sandpaper around it.
I don't cut the 1/4 glass for the grinding platen - I let the glass shop do that. they'll usually sand it for you too.
2. I use the flat corian kitchen countertop. One spray on the countertop. Put about 4-8 sheets of newsprint down. Another short spray. Put the glass down and it won't move. Peel up and discard the old sheet each time you rinse and check the glass.
3. When you're ready to grind a screen, take a permanent marker and write the word "UP" - backwards - on one side. Cover this with masking tape - it'll wear off otherwise. This side goes down and you grind the other side. As you rinse and dry to check your work, it's easy to mistake which side you're grinding.
Lastly - I'm not the most tolerant or endlessly patient sort for this kind of thing. I save that for creative work, yeah? So if I do this, anyone can do it. On Christmas Eve, I made 2 8x10 view screens for a Calumet 8x10 while my wife wrapped presents and my daughter watched episodes of "The Office." I dislike that show intensely.
Carry on.