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Pacemaker 4x5 / Fresnel Questions.

 
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Brandonium



Joined: 30 Mar 2016
Posts: 6
Location: Helena, AL

PostPosted: Tue Apr 12, 2016 6:34 pm    Post subject: Pacemaker 4x5 / Fresnel Questions. Reply with quote

Hi all,

I've been working on my Pacemaker Speed Graphic (SN: 900870). I have the top mounted rangefinder and graflok back. It appears as though I have the ektalite fresnel lens between the ground glass and the lens. I've been looking into replacing this and already have a quote from Steve Hopf on a ground glass replacement but there are some concerns that don't seem to get addressed the more I search and read about the fresnel.

First, does a replacement fresnel not exist or is one not able to get a replacement one that is 1/8" thick (the thickness of mine)? It seems like every conversation goes to shimming and measuring but if my combo is correct then why not just measure what you have? I shouldn't have to worry about shimming should I? I've been contemplating contacting Bill Maxwell to see what he can offer.

Secondly, my ground glass is also measured out at a 1/8" thickness and 100x122mm in overall size. I'll most probably go with the borosilicate setup over the fresnel if I can get my hands on one cut to the right size.

Thirdly, I keep seeing that certain focal lengths benefit from certain fresnel lenses. I will be running two focal lengths for the most part. The 178mm Aero-Ektar and the 203mm Dallmeyer Pentac. Any concerns here?

Here is an image of my exact setup:

http://i.ebayimg.com/images/g/PtMAAOSwQjNW-rhp/s-l1600.jpg

Any input would be much appreciated.

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45PSS



Joined: 28 Sep 2001
Posts: 3839
Location: Mid Peninsula, Ca.

PostPosted: Tue Apr 12, 2016 7:22 pm    Post subject: Reply with quote

Graflex Cameras were laid out with an engineers ruler therefore the cameras and components are measured in tenths, hundredths, and thousands of an inch.

Newer products are thinner due to improved manufacturing techniques or better materials.

The only reason I can see to replace a ground glass/ ektalite field screen is if it is scratched to the point of affecting focus. To properly clean a ground glass and ektalite field screen remove them from the camera then wash them in warm water with dish detergent. I use running water and Dawn. I wash one side at a time then rinse thoroughly then rinse in a weak PhotoFlo bath, then stand on edge to dry. With the ektalite field screen rub the ribbed side in the direction of the ribs only, never across them. Use your finger tips only to rub either the ground glass or fresnel. Normal increase in brightness is up to two stops depending on how much buildup was on the pair. The groves on later Graphics fresnels were finer than they were on the early release versions.

The focus panel of a ektalite field screen equipped camera is milled .020 to .030 deeper than a non ektalite field screen camera. The ektalite field screen was introduced around 1951. It was fully discussed in the past and I do not remember the exact measurement. Finding a NOS ektalite field screen will be difficult to impossible. Brass or aluminum shim stock would be the best when using new. You not only have to contend with the thickness but the optical quality of the new fresnel. The current setup has the ground glass set back 1/2 the optical distance of the fresnel if I remember correctly.

Ektalite field screen is the Graflex term for fresnel.

The correct assembly order is the fresnel with the ribbed side facing the rear of the camera then the ground glass with the ground side facing the fresnel/front of the camera.

900870 is near the middle of an order of 2000 cameras listed at the end of September 1954 making it an early production 1955 version. If you need a service manual for your camera it is available here
http://www.southbristolviews.com/pics/Graphic/manual-pdf/servicemanual.pdf
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