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  #1  
Old 13th February 2009, 11:18 AM
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Default Wista Focus Screen Orientation

Hi All,
I have a Wista DX III that I bought second hand about 12 months ago.
I have not been totally happy with sharpness even in landscapes but recently I did some still life shots that were decidedly fuzzy even though I used a loupe to focus. The lens was a 150 mm Symmar S that gave sharp images on my Arca Swiss monorail.
Last night I was reading up on film holders and now understand that the 'standard' depth is 5 mm with a small tolerance. I checked my focus screen and it is 5 mm from the camera back face BUT to the Fresnel side not the ground side. I understand that you focus on the ground side of the screen. That would put it out by the thickness of the screen. I have checked the Arca Swiss screen position and the ground side faces the lens and is 5 mm from the camera mating face.
Looking closely at the screws holding the screen in place it looks like they have been removed at some stage, small scratches on them and one missing.
I am now wondering if the ground glass has been out at some stage and replaced the wrong way round by the previous owner.
If anybody has one of these cameras, or anything similar, can you please tell me if the ground glass side or the Fresnel side faces the lens?
I think I know the answer but would like confirmation before I get out the screwdriver.
Any comments or help appreciated.
Bill
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Old 13th February 2009, 11:51 AM
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Bill, for critical focusing the ground glass screen should face the lens. Any fresnel lenses should then be placed on top of the focusing screen. There is usually a glass protector over the fresnel making a 'sandwich' of three screens.
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Old 13th February 2009, 01:21 PM
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Thanks Trevor, that is the conclusion I had come to.
My screen appears to be the ground surface on one side with the Fresnel on the other all in one piece. If (when) I turn it over the Fresnel will be exposed and subject to possible damage. I was wondering if a piece of unexposed but processed film may act as protection. Better that than fuzzy images.
It will be done this afternoon.
Bill
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Old 13th February 2009, 02:04 PM
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It is more common to have the Fresnel on the outside, on the viewers side of the ground glass, but some cameras have the Fresnel on the lens side of the glass. The whole assembly is offset to allow for the focus shift.

If your screen assembly is a combined unit and the raised edges of the Fresnel are on the "outside" - i.e. not against the glass, then I suspect the Fresnel part should indeed be on the inside, facing the lens. It is however possible that it is intended to be used Fresnel side out, but with a protective glass cover to protect the Fresnel lens ridges - I have heard of that idea being used too...

Hopefully someone with a Wista can chime in and put us all out of our misery.

[Addendum: just found an advert for a "4x5 Protective Plain Top Glass for Fresnel Focusing Screen - A replacement 4x5 plain top glass for the Wista fresnel focusing screen." so it looks like the latter idea is probably the case - you are missing the cover glass. ]
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Old 13th February 2009, 02:36 PM
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Thanks Bob.
I have turned the screen over and placed a piece of film over the Fresnel for now until I have found if it works. It looks as though in the long run I may need a cover glass. There is not much room under the clips for it though.
Another thought is to contact the importer and ask them. I believe it is Teamwork.
I have taken 2 shots of a sheet of newspaper one each way for the screen. To the eye they look the same but I have found that negatives have looked sharp before and when they get under the enlarger that's when the problems show. They are currently drying so I will get them into the enlarger tonight or tomorrow.
Of course it could be the enlarging lens.........!
Bill
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Old 13th February 2009, 06:00 PM
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Just had a look at the negatives in the enlarger. Although they look similar to the naked eye when enlarged to 16" x 20" the difference is quite marked. Under my Peak focus finder it is obvious which is which. So another excuse gone for unsharp images!
Bill
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Old 13th February 2009, 06:02 PM
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No matter which side the fresnel lies, the GG is invariably towards the lens. On my Speed Graphic the fresnel had been placed lens-side with the GG surface of the glass facing the lens, but on my wooden Wista back the GG still faced the lens but any fresnel (there wasn't one) would have been on the outside.

One piece GG-fresnel lenses place the GG towards the lens and might have a glass cover sheet, but the chances of the fresnel getting scratched should in any case be low. Very thin clear acrylic sheet might work as well as thin glass, and be easier to fit.
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Old 13th February 2009, 07:00 PM
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Thanks Sandeha.
I noticed you had contributed to a similar discussion on another site and was hoping for your advice.
Bill
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Old 15th February 2009, 01:58 PM
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Just to round this off I have scanned a couple of small sections of the negatives before and after turning the screen. Newsprint is not the sharpest of mediums anyway but it does show the difference.

Click on the thumbnail for a larger image.

Click image for larger version

Name:	Before.jpg
Views:	274
Size:	91.8 KB
ID:	144
Before turning

Click image for larger version

Name:	After.jpg
Views:	254
Size:	114.7 KB
ID:	145
After turning


Bill
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Old 15th February 2009, 03:00 PM
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Bill, what a difference! I opened both attachments in a new window so was able to compare them side by side.

Just goes to show how easy it is to get the screen the wrong way round.
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