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Pacemaker w Pentac lens

 
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rickcollins



Joined: 23 Aug 2017
Posts: 14
Location: Victoria

PostPosted: Sat Dec 15, 2018 7:48 pm    Post subject: Pacemaker w Pentac lens Reply with quote

I just purchased a very nice Pacemaker and I have attached an 8" Pentac 2.9 lens with a JoLo mount. So far so good.
However, I am attempting to calibrate the focus and establish some solid points on a scale on the rail.
I am finding I am having to rack out the lens nearly all the way to the end of the rail as a starting point.
Is this the norm?
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45PSS



Joined: 28 Sep 2001
Posts: 3757
Location: Mid Peninsula, Ca.

PostPosted: Sat Dec 15, 2018 8:53 pm    Post subject: Reply with quote

1 inch=25.4mm; 25.4*8=203.2
Large format lens back focus is usually close to or slightly less than the lens focal length.
Pacemaker infinity point is rails fully retracted then forward .040 .010 inch but the previous Speed setting of fully retracted can be used if you don't want to focus past infinity.

With the rails set to the infinity position pull the front standard out until an infinity at least 5000 feet away is in sharp focus on the ground glass.

A 203mm/8inch lens should focus infinity 3/4 the length of the rails/bellows.
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Dan Fromm



Joined: 14 May 2001
Posts: 2039
Location: New Jersey

PostPosted: Sun Dec 16, 2018 3:46 pm    Post subject: Reply with quote

The mount adapter holds the lens entirely in front of the front standard, adds considerable extension.

The lens focal length is defined as the distance from the rear nodal point to the film plane when the lens is focused to infinity. The rear nodal point is close to the diaphragm.

And there you are, unable to focus much closer than very far away because the adapter has eaten the space needed.
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rickcollins



Joined: 23 Aug 2017
Posts: 14
Location: Victoria

PostPosted: Mon Dec 17, 2018 12:58 am    Post subject: Reply with quote

Thank you. All set now.
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