Focus Shift when Enlarging.

Making your print in the darkroom
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RoganJosh
Posts: 194
Joined: 29 Aug 2012, 11:26

Focus Shift when Enlarging.

Postby RoganJosh » 26 Jan 2015, 14:12

Any experts on front of lens filter diffraction? I recently tried using a combination of filters on the same print when enlarging b&w negs, which to my surprise created a double image. Strangely enough I never noticed this when using a low contrast filter, only a high contrast filter (possibly because the double image stands out more..?).

Should I be placing the filter behind the lens (between the light source and the lens) instead of in-front of the lens (between the lens and the paper)?

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Maris
Posts: 513
Joined: 27 Jul 2012, 16:02
Location: Noosa

Re: Focus Shift when Enlarging.

Postby Maris » 27 Jan 2015, 13:12

I've checked and double checked below the lens contrast filters and have never found a downside. I use good enlarging lenses (Fujinon, Rodenstock, Nikkor) that can image every grain of a negative on to gelatin-silver paper. When I add a contrast filter (any of them from -1 to 5+) I'm still imaging every grain in every negative. The only times I've had double images were due to bumping the enlarger head between above-the-lens filter changes or if a negative "popped" in the negative carrier during the exposure. And yes, high contrast filters accentuate any defects in a negative/enlarger/lens/filter.

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RoganJosh
Posts: 194
Joined: 29 Aug 2012, 11:26

Re: Focus Shift when Enlarging.

Postby RoganJosh » 27 Jan 2015, 13:25

Ok cheers Maris. Maybe I am slightly bumping the enlarger when exchanging filters. It would explain the inconsistencies between different filters.


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