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Ground Glass and Fresnel

 
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tim brakemeier



Joined: 08 Jun 2007
Posts: 7
Location: Eichwalde/Germany

PostPosted: Tue Jun 12, 2007 12:39 pm    Post subject: Ground Glass and Fresnel Reply with quote

Hi,
after solving the problem with my Shutter (thanks again Charles!) I am trying to fix the next problem at my Auto 4X5 Super D - the focus.
Even when I am 100% sure that the focus is correct on the ground glas I´ll get negatives out of focus.
I guess the groundglas is not adjusted well. I took out the ground glass to clean it and realized that its made out of the groud glas and a fresnel. This two were sticked together with black tape. But I am not sure if they were put together in the right oder.
I think it must be like this, ground glas with the focussing side towards the mirror and on top of this the fresnel.
On the other hand, somewhere I read, that on the Graflex the fresnel is below the ground glas.
What is the right order?
thanks
Tim
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45PSS



Joined: 28 Sep 2001
Posts: 3210
Location: Mid Peninsula, Ca.

PostPosted: Tue Jun 12, 2007 9:28 pm    Post subject: Reply with quote

Wash Ektalite Screen (graflex speak for fresnel) and ground glass in warm water with dish soap and your fingers. Rub the ektalite screen ribbed side with the ribs only, not across. Rince with clean water and then in a PhotoFlo bath and allow to air dry. Handle by the edges only once cleaned.

Reassemble as follows:
Ektalite screen flat side toward the reflex mirror/lens; ribbed side toward view hood.
Ground glass ground side to ektalite ribbed side; ground glass smooth side to view hood. (standard Graflex Corp. layout on their cameras)
Charles
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PhG



Joined: 11 Jul 2007
Posts: 11
Location: Paris (France)

PostPosted: Thu Jul 19, 2007 4:53 pm    Post subject: Reply with quote

What do you mean by "smooth side"? The "milky" one?
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Philippe Grunchec
http://philippe.grunchec-photographe.over-blog.com/
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45PSS



Joined: 28 Sep 2001
Posts: 3210
Location: Mid Peninsula, Ca.

PostPosted: Fri Jul 20, 2007 12:24 am    Post subject: Reply with quote

milky=ground
smooth as in plain glass.
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pv17vv



Joined: 22 Dec 2001
Posts: 255
Location: The Ardennes, Belgium

PostPosted: Mon Jul 23, 2007 5:09 am    Post subject: Reply with quote

Quote:
What is the Proper Placement of  the Fresnel? One subject which comes up often is the correct position of the fresnel lens. In years past, several arrangements have been used, including placing the fresnel behind the ground glass, in front of the ground glass, and incorporated into a ground glass made of plastic. However, there is only one correct arrangement. The ground glass surface should face the camera lens, and the fresnel is placed behind it, on the outside of the camera, toward the photographer. The textured surface of the fresnel should be placed against the ground glass. There is a particular reason for this arrangement. In manufacturing cameras and film holders, one overriding concern is the correct position of the focal surfaces of the respective parts. In the film holder this is the position of the septum, against which the film rests, and in the camera this is the position of the diffusion surface, or ground side of the ground glass upon which one focuses the camera. Nothing is more important than the proper registration and agreement of these two elements. If the fresnel were placed in front of the ground glass, interposed between the lens and the ground glass surface, even if it were still physically in the same position occupied by the film plane, a lack of registration can occur.


Courtesy Ron Wisner.

mfG aus Belgien.

Georges
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45PSS



Joined: 28 Sep 2001
Posts: 3210
Location: Mid Peninsula, Ca.

PostPosted: Mon Jul 23, 2007 6:37 am    Post subject: Reply with quote

Georges,
That is Ron Wisner's opinion and /or view on the subject. Graflex Corp. used the Ektalite Field Screen in front of the gg and positioned the sandwich so that the gg optical focal plane was at the film plane and therefore if a Graflex Corp. camera has its gg or Ektalite Field Screen replaced or removed then the optical difference in focal plane/film plane must be delt with. Graflex's placement of the Ektalite Field Screen in front of the ground glass is just as correct as Ron's placing it behind the ground glass and if this were a Wisner or Sinar or other board then I would call it a fresnel and state that it should be placed behind the ground glass as that is the way those cameras are designed. The purpose of a Ektalite Field Screen/Fresnel is to even out the image on the ground glass so that one can see in the deep shadows and not have hot spots to contend with when focusing/composing. I have both Graflex Corp. and Sinar cameras and notice no real difference in everday use. Go to www.Photo.net and do a search for Ron Wisner and read all the complaints about him and how he runs his camera business, real eye opener.
Charles
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pv17vv



Joined: 22 Dec 2001
Posts: 255
Location: The Ardennes, Belgium

PostPosted: Tue Jul 24, 2007 5:09 pm    Post subject: Reply with quote

Quote:
Graflex Corp. used the Ektalite Field Screen in front of the gg and positioned the sandwich so that the gg optical focal plane was at the film plane


Thanks for claryfying this particular point, Charles.

Now was Ektalite installed on ALL new Graflex cameras, or was it an option ???

Georges
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45PSS



Joined: 28 Sep 2001
Posts: 3210
Location: Mid Peninsula, Ca.

PostPosted: Tue Jul 24, 2007 11:11 pm    Post subject: Reply with quote

Quote:
Now was Ektalite installed on ALL new Graflex cameras, or was it an option ???

No, all cameras were not supplied with an ektalite field screen. It was standard on 3x4 and 4x5 Pacemakers with graflok back, Super Graphics, and 3x4 and 4x5 Super D Graflex where it is called ektalite field lens. The ektalite field screen was optional on 2x3 Pacemakers and Century Graphics and the other models of Graflex SLR cameras. An older Graphic retrofited with a Graflok back would have the ektalite field screen.
Reference: Graphic Graflex Photography 11th Edition, 1958.
Charles
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JoePhoto



Joined: 13 Oct 2001
Posts: 74
Location: New England

PostPosted: Mon Mar 14, 2011 9:20 pm    Post subject: Reply with quote

I hope people don't start messing up the pronuciation of Fresnel ( fray-NELL) by saying "frezznell" like they did with the English word forte (properly pronounced FORT not FORTAY). I've actually heard landscaping contractors pronounce the word LOAM as LOOM. Just something that tics me off when it comes from supposedly educated people.
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Henry



Joined: 09 May 2001
Posts: 1439
Location: Allentown, Pennsylvania

PostPosted: Tue Mar 15, 2011 12:40 am    Post subject: Reply with quote

One problem, aside from the optical (focus) one, with placing the fresnel toward the back of the camera, is that the smooth surface, being plastic, is bound to get scratched if you focus with a loupe. I mounted my fresnel on my Century by cutting it so that there are four tabs that fit in the corner notches of the focussing frame, IOW, in the same plane where the ground glass formerly was; the gg goes behind the fresnel (i.e., closest to the photographer), with the ground side against the smooth side of the fresnel.
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