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Ground Glass Focus Way Off From RF & Scale

 
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Velostiraptar



Joined: 20 Jul 2020
Posts: 6

PostPosted: Sun Jul 26, 2020 4:13 am    Post subject: Ground Glass Focus Way Off From RF & Scale Reply with quote

Hi, I just received my first Graflex, a 2x3 Crown. Seller described as ‘user ready’ with Wollensak 90mm 4.5 lens, ground glass back, ‘calibrated’ RF, and graflok rollfilm back. Following the manual, I popped it open and drew the front standard out to the infinity stops. The bellows seemed kind of drawn out far for infinity perhaps so I checked and sure enough the GG image is focused to just a few feet away while the scale and coincident RF image indicate infinity. So much for ‘user ready’!

Can I fix this? Also what the heck? Seems like maybe this camera was ‘calibrated’ for a different lens. From the dust on the rails it looks like no one had adjusted the stops for a long time. Do the standard 105 lenses have a much longer register (or flange focal distance? Am I using the right term here? ‘Distance from film at infinity‘ is what I mean) than the 90s?
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45PSS



Joined: 28 Sep 2001
Posts: 3874
Location: Mid Peninsula, Ca.

PostPosted: Sun Jul 26, 2020 5:50 am    Post subject: Reply with quote

Being you have a 2x3 Crown it has a side Rangefinder.
Kalart was the most common but a few Hugo Meyer do exists on Graflex Graphic cameras.

Now your camera was likely set up for a 101mm or 105mm lens and someone stuck a 90mm on it to make it complete. Focus scales were matched to a specific lens.
Lens are rarely their marked focal length. They are usually within 3mm either side of the nominal marking. The greater the divergence from the nominal value marked on the lens the greater the error at distance from infinity even if infinity is the same for both lens. A scale for a 101 that optically measured 99.5mm and a 101mm lens that optically measures 102mm the scale error will occur at 12 to 15 feet while a 101mm that optically measures 101.2mm will be off at 8 feet (roughly). The same holds true for a rangefinder calibrated for a lens.
The distance from the rear nodal point of the lens to the film plane is called the back focus. The rear nodal point of lens used on these cameras is at or near the aperture/shutter blades.

Loosen the screws on the infinity stops so that the stops move easily on the yoke. Use a jewelers screwdriver or similar.
With the camera on a sturdy tripod move the yoke forward from fully retracted .040 ± .010 inch and set the focus lock. With the lens wide open and the shutter open on T or locked open on B with a cable release. Focus the lens on an infinity target at least 5000 feet away on the ground glass using a good loupe. Lock the front standard. Measure from the ends of the yoke to the front standard on both sides. When both sides are the same distance from the end of the yoke and infinity is in sharp focus with the standard locked slide the infinity stops up to the front standard and tighten the front screw on both. (the stops must be in the up position) Unlock the front standard, slide it back, tighten the rear screws on the infinity stops, slide the front standard to the infinity stops, lock and verify that infinity is in sharp focus.
Next calibrate the rangefinder to the lens. The instructions are here https://graflex.org/speed-graphic/kalart-adjustment.html and a better copy of the Kalart manual is available at https://drive.google.com/file/d/0B1sPJkp-Mdghc0FwQkRuWEhFZEE/view?usp=sharing

The factory service manual for your Crown is https://graflex.org/manuals/23-Pacemaker-Speed-and-Crown-Graphic.pdf
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Velostiraptar



Joined: 20 Jul 2020
Posts: 6

PostPosted: Mon Jul 27, 2020 12:37 pm    Post subject: Reply with quote

Thank you for the detailed instructions and the document links. Fortunately there is a person in my area with a small business specializing in vintage camera repair, so I have a fallback if my RF calibration attempt fails.

Does anyone have a hack for aligning the stops to keep the front standard parallel? Something easily made or bought that fits on the yoke to guide the stops? I get the feeling my chances of avoiding inadvertent swing are pretty low if I just eyeball it.
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William Hallett



Joined: 07 Jan 2012
Posts: 69

PostPosted: Mon Jul 27, 2020 1:13 pm    Post subject: Reply with quote

You need a small machinist's square - put the stock against one of the rails, and use the blade to line up the tabs of the infinity stops with one another. You will have move the track forward a bit so that the side braces do not foul the square.
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45PSS



Joined: 28 Sep 2001
Posts: 3874
Location: Mid Peninsula, Ca.

PostPosted: Mon Jul 27, 2020 6:37 pm    Post subject: Reply with quote

https://www.ebay.com/itm/6-Inch-Digital-Vernier-Caliper-150mm-Stainless-Steel-Micrometer-Electronic-Tool/254581768431?hash=item3b464180ef:g:~BcAAOSw739evj8j
I use a caliper but the rounded edges of the standard can be challenging.
A stainless steel ruler will work also.
https://www.ebay.com/itm/iGaging-SAE-ruler-rule-stainless-steel-8ths-to-64th-inch-precision-machinest-4R/143513726896?hash=item216a15afb0:g:9CgAAOSwSKBeLhr3
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