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View Full Version : Focus screen foulup - I think



Bob McCarthy
27-May-2006, 15:24
Just located and purchased a technika 2000. It was advertised to come with a beattie screen. Price was Ok and it was advertised to be like new. Got the camera and it was pretty much as advertized.

Made a new friend who has offered to help get me started. Wonderful gentleman who is very generous with information and advice. On our first meeting face to face, he handed me a new fuji 180 (on board) so I could try out the camera. Thats rare in today society

I am minimally familiar with LF, but have extensive experience in photography (both 35mm and MF). Something with the screen is wrong. The screen appears to bow with any pressure(from placing loupe). On closer examination, there is only one screen, it is brightish on one side, somewhat frosty with grid on the other. Using a soft cleaning cloth, I can feel a very fine fresnel on the rear surface facing me. The film plane is obviously not accurate as it is bowed in normal position and is flexable. All that is in the camera is the plastic screen. Am I missing the ground glass screen? Seems so but I don't have any experience with LF viewing systems.

There are two silver hold down clips on each side of the current gg (?) , unused at present. What do I need to do to get the situation repaired?

No wonder the guy sold the camera, lousy focus. may be a blessing is disguise.

Thanks for any advice,

Bob

robc
27-May-2006, 16:02
take a look at this thread

http://www.largeformatphotography.info/forum/showthread.php?t=16221&highlight=linhof+gg

it sounds like the GG has been replaced with a fresnel.

The GG should be where your fresnel is and the fresnel fitted on the outside under the clips. The frosted side of the gg should be on the lens side.

Capocheny
27-May-2006, 16:13
Bob,

From what I can remember of the Master Technika I had awhile back... the screen definitely did NOT bow when a focusing loupe was put onto it.

IMHO, it does sound like you're missing the ground glass... and if that's what it is, then it won't cost you all that much to get a replacement. I'd think it would be readily available from the distributor.

I'm sure if Bob S. is around... he'll most likely wade in on your question.

.

Rob,

Even if the ground glass has been replaced with a fresnel screen... are they THAT flexible such that it'll bow when you try to focus on it? I could be mistaken but I wouldn't think so. :>|

I have a fresnel on my Sinar and it's quite stiff... no bowing whatsoever. :)

Cheers

Bill_1856
27-May-2006, 16:51
The plastic screen should have been backed with a plain (or grid) piece of glass, which is apparently missing on yours. Get one from Beattie. Also, the plastic focusing/fresnel screen should have been shimmed to match the depth of 4x5 cut film holders. You may need to have that done by an expert (Marflex, Grimes, Ritter, etc). Hang in there -- it's a wonderful camera.

Michael S. Briggs
27-May-2006, 17:26
I've never had one, but from reading other postings, I think that the Beattie screen is an integral screen that combines a frosted surface and Fresnel lens into one piece of plastic. or maybe with a protective clear plastic overlay. This seems to match your description of the screen on your camera. So you are probably not missing anything. But it is a problem if your screen is not flat by more than a several thounsandths of an inch when you focus.

The two holding clips in the center are for attaching accesories such as a viewing bellows. The long metal clips are what holds the screen in place, with four screws holding the clips in place. There is nothing wrong with the two clips in the center flopping about.

Since the screen is bent, you might want to replace it with a conventional ground glass, or a ground glass plus plastic Fresnel combination. The Linhof-brand ground glass isn't outragously priced, or you can purchase some other brand. I prefer to use just a ground glass, but many photographers like to add a Fresnel. In my opinion the best way to install a ground glass plus Fresnel is ground glass towards lens, Fresnel closer to photographer. If the frosted surface if your current screen is laying on the positioning shims, and since your describe the Fresnel as closer to the photographer, you should be able to just install a plain ground glass by laying it onto the positioning shims, frosted surface towards the lens. But its probably an excellent idea to test the focus afterwards, or perhaps have the workd done by a repair placed (listed by Bill G.) in case the focus is somehow misadjusted.

Here are some past discussions: http://www.largeformatphotography.info/forum/showthread.php?t=17024, http://www.largeformatphotography.info/forum/showthread.php?t=14933, http://www.largeformatphotography.info/forum/showthread.php?t=12526 and http://www.largeformatphotography.info/forum/showthread.php?t=9396

Bob McCarthy
27-May-2006, 17:47
The plastic screen is definately bowed in by maybe 1/8 to 1/4 inch. It is held in (and maybe shimmed?) on the two short dimensions. The long dimension across (landscape) is definately bowed in towards the lens and can be moved more with modest pressure. If it were stacked over a glass GG I would guess it would conform to glass underneath. I'm trying to reach the original owner to see if he recalls anything, the original gg maybe in his possession.

I am concerned about calibration (?), and don't have a clue how to prove up good adjustment.

Thanks for your help.

Bob

JimL
27-May-2006, 18:31
As Bill said, you're missing the backing glass which protects the fresnel grooves. It sounds like your screen is either warped or is clamped into the gg frame wrong, causing it to bow. It would be best to remove the screen to see where the warp is coming from or (if you're not comfortable with DIY) send it to a repair person.

KenM
27-May-2006, 19:17
Sound like you're describing a Linhof Superscreen - I had one on my Master Tech, and was amazed at how bowed the screen was - I fail to understand why a $4500 camera has a piece of crap plastic GG/fresnel - brutal. In the end, I removed it and replaced it with a Satin Snow GG - it's certainly not as bright, but I at least know it's perfectly flat (checked with a depth gauge).

As was mentioned above, there should have been a gridded glass protector placed over the superscreen - since that's missing, I would either replace it, or get rid of the Superscreen and replace it with a plain GG.

If I were to replace it with a Fresnel-type GG, I would probably go with a Maxwell screen. I'll be sure to have a spare hour or so when I phone in the order :D

Brian Ellis
27-May-2006, 19:32
I had a Beattie screen on my Master Technika for a while. It didn't bow but it wasn't especially good either. Having spent what you must have spent to buy a Master 2000 I'd suggest that you forget the Beattie, spring for another $250 and get a Maxwell. That's what I did. It's a substantial improvement over every other type of screen I've owned (with the possible exception of the BosScreen, it's better than the BosScreen I think but not by as wide a margin as the others)and I've owned most of them at one time or another.

Michael S. Briggs
27-May-2006, 20:00
The plastic screen is definately bowed in by maybe 1/8 to 1/4 inch. It is held in (and maybe shimmed?) on the two short dimensions. The long dimension across (landscape) is definately bowed in towards the lens and can be moved more with modest pressure. If it were stacked over a glass GG I would guess it would conform to glass underneath. I'm trying to reach the original owner to see if he recalls anything, the original gg maybe in his possession.

I am concerned about calibration (?), and don't have a clue how to prove up good adjustment.

Thanks for your help.

Bob


If the screen is bowed this much, it needs to be replaced. The mounting method sounds correct. If you remove the clips by removing the four screws, you will find two metal strips which positon the screen. These aren't exactly shims, since the position position is adjusted by turning the screws on which these strips rest. Buy probably this won't be necessary.

Some of the links that I provided in my previous answer suggest photographic tests of the focus accuracy. If you are unsure of your ability to implement these tests, then send the camera to one of the repair places suggested above.

This screen isn't meant to be stacked over a ground glass. The frosted surface is integral to the screen that you have, so it shouldn't be put on top of a ground glass with its own frosted surface. What may be missing is a clear protective sheet that goes between the integral screen, with its combinded frosted surface and Fresnel, and the photographer. At one time the US distributor for Linhof supplied Super Screens for Linhof cameras. I don't think that these were a Linhof factory product -- probably that were Beattie screens. I think I remember previous complaints of them bending.

1/8 inch bow or more is definitely defective. So replace your screen. You can buy a Linhof ground glass from B&H or other suppliers, a Satin Snow, various generies on ebay, and see if you like these. Or you can try the Maxwell. Since the screen you have has its frosted surface facing the lens, probably you can make a straightforward replacement. Just don't make a replacement in which a Fresnel is in front of the frosted surface (this would require adjusting the focus). But without knowing the history of what has been done to the camera and examining the camera, we can't be sure, so either you should test the focus accuracy with your new screen or have a repair person install the new screen or check the camera for you.

Bob McCarthy
28-May-2006, 05:12
I live in the Dallas /Ft Worth area, is there anyone local to me who is capable of evaluation/repair of the problem?

From what I've gathered the boss is temp sensitive. Texas is pretty hot in summer!!

I'm going to disassemble the unit today. Maybe it's mounted incorrectly. The question then comes down to, does it require a glass or not? It does have a frosted surface, it has a bright surface (micro fresnel surface). It does not appear to conform to the assembly instructions on the vendor page.

Bob

robc
28-May-2006, 05:47
You need to get it checked by someone who knows what they are doing!

At each end of the gg there is a thin metal strip each of which is held on by two screws. Removing those screws will release the GG (or beattie screen in your case).
When you remove the screen you will find four little metal strips, one at each corner, which the GG should rest on. Those little strips each have a hole in the centre. There is a very fine screw on the opposite side of the back which protudes through the back and onto which the little strips are placed with the screw end in the hole.
The strips will probably fall off when you take the GG off. The strips are not shims. They are rest plates. Height is adjusted by turning the screws from the other side.
If the screws have never been adjusted then you will probably not be able to see the slot of the screw from the other side because when the back is new it will have been set and black paint will cover the end of the screws. If you can see the slot clearly with a loupe then someone has probably adjusted them at some time. You will need a fine watch makers screwdriver to adjust them if you take the plunge. If they have not been adjusted then leave them alone.

The four little rest plates are not absolutely flat on my back and all slightly bent so in theory they should go back in original positions and orientation. But since someone has been playing with your back I doubt that was done because until you have disassembled the unit you don't know that. In other words, after reassembly you need to check position of GG and adjust if necessary, by means of turning the screws.

The frosted side of the glass rests on those four plates and the plane of the frosted glass is where your film plane should be. i.e. where a filmholder WITH FILM IN IT should be. Depth to GG frosted surface should be the same as depth to film in film holder.

There is a standard for film depth but what is more important is making sure that film depth is the same as GG depth regardless of what the standard is. Therefore, first work out the average depth of your film in your film holders and second set the GG to the same depth. If that conforms to the standard, fine, if it doesn't, don't worry about it. Having all filmholders of same make and vintage helps greatly with this.

N.B. because of the way the GG fits the camera, any make of GG which fits should not need height adjustment if screws have not been altered and rest plates are fitted in exact same position as original settings. But until you check depth you won't be sure about that...

Linhof way of using a fresnel is to use a normal GG and then place a fresnel on outside of GG under two clips.

Good luck.

Bob Salomon
28-May-2006, 06:21
'The two holding clips in the center are for attaching accesories such as a viewing bellows. "

No, those are the clips to hold the Linhof fresnel screen, nothing else is mounted there.

Michael S. Briggs
28-May-2006, 09:03
......

The question then comes down to, does it require a glass or not? It does have a frosted surface, it has a bright surface (micro fresnel surface).

..........
Bob

I answered this in my second answer, of timestamp 03:00.

Bowed Linhof SuperScreens are a common but not universal problem. Ken mentioned his experience above. Other discussions that mention problems: http://www.largeformatphotography.info/forum/showthread.php?t=3515, http://www.largeformatphotography.info/forum/showthread.php?t=8400,
http://www.largeformatphotography.info/forum/showthread.php?t=9715
and http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=003AeW. There are assertions that the problem is related to an early version, or leaving off the cover sheet, or if leaving off extra shims along the long side, or from hot temperatures.

Yours is wrapped, for whatever reason. I'd replace it, so why worry about details of how it is installed? The only detail to check is whether the frosted surface is facing the lens and resting on the metail strips that RobC and I have described. If so, you can probably simply lay a replacement screen onto the strips, with its frosted surface on the strips, facing the lens. If you can't find a local repair place and don't want to ship the camera, try a photographic test of the focus accuracy, as described in some of the previous links that I gave.

The principal is that you can switch between screens if the frosted surface stays in the same position with nothing in front of it. So if the focus is currently correct on your camera and the frosted surface of the screen faces the lens and rests on the metal strips, you can replace the screen with a glass ground glass. It's that simple. If the current screen doesnt have the frosted surface this way or someone has misadjusted the focus, then the focus would need to be adjusted.

Bob McCarthy
29-May-2006, 04:28
I did take the screen off the camera and found all as you discribed. The adjusting screws were still painted over. The plastic screen has taken a warped set, thought it appeared to be a somewhat different amount (lessor) off the camera.

The screen itself when laid back into position seemed to be somewhat undersized upon examination. The long dimension did not fully cover the metal feet when the screen was centered into position. Maybe 1/3 (or a little more) of the silver feet was exposed.

Since the screen has taken a set, this one is trashed. I had a suggestion to apply heat and will try that as a temporary fix.

The camera is definately misfocusing using the picket fence/polaroid test, but that may be a good sign as I would expect it to, if the screen was bowed.

Maxwell, Boss, or Linhof?

Bob

robc
29-May-2006, 05:41
I think I would be tempted to get a satin snow and then if that was not bright enough I would put a fresnel on top of it...

KenM
29-May-2006, 08:30
If you have the time and access to a drill press and a very flat surface, you can make one of these: http://www.acanadianplace.com/images/depth-gauge.jpg. Took me about an hour to make it. I used it to make a minor adjustment to my back on my MT. I also had the chance to use this tool on a brand-new just-out-of-the-box MT 2000, and I found that my back was closer to spec - ok, by 0.001", but still! :D

It also works to check your film holders. It's handy tool, and not that expensive tomake either. The dial indicator is about $20 or so, and I already had the plex. Even so, you could get a big enough piece of plex for about $10-$20 (or even less) to make the jig.

The only thing I need to add to it is a couple of small screw hooks to the left and right of the dial indicator, so I can stretch an elastic over it to hold the dial indicator down. While it was nice and snug to begin with, it's loosened up over time, so it needs to be held down.

Regarding construction, once you've glued everything toegether, lap the bottom of the plex on a flat surface to ensure that it's flat. I had a very heavy piece of granite that I use for sharpening my chisels that worked very well for this.

You can also buy a depth micrometer, but these are quite expensive. I have one, but it only has a 4" base, so I can only use it to measure the corners.

Bob McCarthy
31-May-2006, 06:56
I want to thank all who responded to my original post. I'm appreciative to all for the sharing of information and experience to this rookie in LF. I have much to learn, but am energized by the opportunity. I hope I can reciprocate at some point.

BTW, I am going to start with a new Linhof ground glass, and go from there. Should get it this weekend.

Bob

robc
3-Jun-2006, 06:25
Just took delivery of a couple of MIDI SHEET MAGNIFIER's from

http://www.magnifyingglasses.co.uk/acatalog/Online_Catalogue_Page___Sheet_Magnifiers_8.html

focal length seems to be about 100/150mm and boy do they make a big difference on my Linhof GG with reflex viewer. And at only £3.00 each I saved myself £92 on the Linhof item.

Sure they are cheap plastic but there is no focus shift when I put the fresnel on and its so much brighter. They are about 1mm thick. Dimensions were only 95mm on the short side but the long side needed to be trimmed at boths ends by about 8mm to fit.

Recommended!