Fujinon 135 W Focus Shift Problem

[James Hoggard]

I bought a Fujinon 135 W in a Seiko shutter last fall to replace my Caltar 135 in order to increase the image circle for that particular focal length. I have used the Fuji a few times and have noticed that the background in most of the shots gets quite soft, if not simply out of focus. I am focusing and calculating the depth of field and hyperfocal distance by measuring with a tape measure so I think my technique is fine. In fact, I've never seen this problem - with this consistency - until I started using this lens. When I view with the lupe on the ground glass I now make sure to give this lens some leeway by focusing a little further than infinity, but it still gets soft while the foreground is always sharp.

First of all what would cause this problem? I have another older Fujinon lens (90mm) in a Seiko shutter, but it doesn't go soft in the background. Is there something that can be fixed by taking the lens apart - assuming it was someone who knew what he was doing? Or do I just live with it and adjust the focus accordingly? What is a good way to go about finding the actual hyperfocal distance for this lens?

[Jac@stafford.net]

I would wonder if there is a mismatch of front and rear elements.

[EdWorkman]

Am I to understand that you check the focus with a loupe, but actually focus by calculation and measurement?
What happens if you focus with the ground glass?
You say 'focus shift'. To most folks that means the focus changes as one stops down , such as happens with half a Protar.
Do you measure from the node of the lens [ by some adjustment of the measurement] or are you simply using the lens board or front element?

[ic-racer]

If your negatives have the focal point farther away than the ground glass shows, your ground glass is farther from the lens than your film was at the time of exposure.

In my work I prefer to show distand objects sharp and have closer objects get progressively less sharp. Since closer objects are larger, they can be identified without the resolution needed for distant objects. That is a extended way of saying I focus at infinity for most landscape and ignore the 'hyperfocal' prinicple.

[Jim Jones]

Determining depth of field by measurements and calculations is less useful than observing it on the ground glass. An understanding of those calculations is a valuable tool for the technically inclined photographer, but formulae disregard the demands of the subject, the creative interpretation of the photographer, and the final presentation of the image. What one sees on the ground glass relates more directly to the final photograph than mere mathematics. As Ed noted above, some lenses do exhibit focus shift. When using Kodak's fine, but discontinued, High Speed Infra-red film with an IR filter, we had to extend the lens by a small factor which varied with different lens designs. In this instance, we had to rely on that mathematical factor instead of direct ground glass focusing.

[James Hoggard]

Thank you for your replies. As I said, I have not seen this problem in any of my other lenses that I have used over the years. I am a landscape photographer so most of the time I like to have everything in focus, so the hyperfocal distance is very important - hence my annoyance with this lens. Anyway, I'm looking for a way to overcome this problem. Has anyone here actually had to determine how much focus adjustment is necessary for a lens that has a focus shift? I guess is can be different for each f-stop?

[ic-racer]

Another interesting exercise is to compare what we gain and what we lose when we focus at infinity instead of the tried-and-true hyperfocal distance. At the inner limit of the conventional depth-of-field the disk-of-confusion is half the diameter of the lens opening (because the distance to the inner limit of the depth-of-field is one-half the hyperfocal distance). Thus at the inner limit of depth-of-field the most we lose by focusing at infinity is a factor of two in resolution of the subject. On the other hand, for subjects beyond the hyperfocal distance, the story may be quite different. At a subject distance of twice the hyperfocal distance, the disk-of-confusion is equal in size to the lens diameter. At this distance either method gives the same result. At three times the hyperfocal distance, the disk-of-confusion is twice the lens diameter. At four times the hyperfocal distance, it is three times the lens diameter and so on. At ten times the hyperfocal distance, the disk-of-confusion is nine times the lens diameter. Thus, if we are using a good lens, good film, and careful technique, we potentially have a lot to lose in the resolution of distant subjects by focusing the lens at the hyperfocal distance. In practice, by focusing instead at infinity, we will lose a factor of two in subject resolution at the near limit of depth-of-field but gain about a factor of six in the resolution of distant subjects! It’s often worth the trade. Merklinger: THE INS AND OUTS OF FOCUS ISBN 0-9695025-0-8

[toyotadesigner]

'The Ins and outs of focus' is available as a PDF here:

http://www.trenholm.org/hmmerk/TIAOOFe.pdf