Focusing Soft Focus Lenses

[eddie]

Holy Moly Ken. I hope you didn't give it back! That's gorgeous.

I'm afraid I did

That lens has the MoJo big-time.

I think he may have worn it out!

Seriously though, Great images ken

[uphereinmytree]

I have limited experience, but am finding that my imagon 12" on 8x10 has a very sharp center that moves around with front tilts and swings and makes it hard to use movements as one might with a sharp anastigmat. Left swing moves the sharpest part to the right on the ground glass but doesnt really bring other areas into equally sharp focus as I expect. Keep in mind these are outdoor scenes and not portraits. Am I just blind or should I expect different physics with a meniscus doublet compared to a new anastigmat?

[jp]

Soft focus lenses generally aren't for wide angle use. You're probably seeing the plane of focus getting curved as it goes outside it's "coverage". Learn to use that feature or use smaller film with that lens.

[Mark Sawyer]

I have limited experience, but am finding that my imagon 12" on 8x10 has a very sharp center that moves around with front tilts and swings and makes it hard to use movements as one might with a sharp anastigmat. Left swing moves the sharpest part to the right on the ground glass but doesnt really bring other areas into equally sharp focus as I expect. Keep in mind these are outdoor scenes and not portraits. Am I just blind or should I expect different physics with a meniscus doublet compared to a new anastigmat?

The 12 inch Imagon "illuminates" 8x10, but it was made and recommended for 5x7. There might be times when you want to move that center spot of best focus off center a slight amount, but other than that, I'd recommend using rear swings and tilts for adjusting the plane of focus.

[tgtaylor]

I'm not an expert on SF lenses - I have only 3: 2 Pentax and 1 Vertitar - but found the Pentax focusing method for the 120mm 67 lens the best. Here it is copied from a 2005 post on photo.net: https://www.photo.net/discuss/thread...s-lens.194721/

The second part of the article is written by photographer Kimio Tanaka. He includes the following statement: "The soft focus effect is almost nil around f/8 and depiction becomes as sharp as regular lenses over the aperture range f/11-22." Later, under the heading "How to focus with Pentax Soft lens", he writes: "The focus tends to be a little behind the in-focus point. In other words, the actual point of focus on the film plane is a bit behind the best focus point even if you focus on the focusing screen of the camera. Its principle is a little complicated but, in short, the human eye is dazzled by the flare of the soft-focus lens. Critical focusing is an unexpectedly indispensable factor in the use of a soft-focus lens. If it is not fully focused, a flare-combined picture is not attractive".

Tanaka then goes on to describe three ways to achieve best focus: "The easiest way is the use of correction lines engraved on the lens barrel. As the focus point differs with the aperture stops, stop down the aperture to the desired stop for taking pictures. Be sure to use a matte portion of the focusing screen. Then, turn the focusing ring to the correction line indicator. (The diagram here shows two white correction lines, the left one labelled "resolution weighted", the right one, nearest the orange standard line, labelled "contrast weighted".) The other way is to stop down the aperture to f/11 (the finder field will be a bit dark) and then return to the working aperture which should be within a range of f/3.5 to f/5.6. I myself like this method best and I used it all through the picture-taking this time. Still another way is to find out the focus point at which the contours of the subject image are the sharpest. The sharpest point inside the flare makes the focusing difficult."

The 2 white "correction" lines correspond to extending the bellows out 1 "tad" or 2 "tads" on the LF camera. The way I use it is to stop down until the subject is in sharp focus and determine the point of focus, stop-down until desired softness is achieved, focus on the focus point, and then apply the desired correction.

Thomas

[Mark Sawyer]

I'm not an expert on SF lenses - I have only 3: 2 Pentax and 1 Vertitar - but found the Pentax focusing method for the 120mm 67 lens the best. Here it is copied from a 2005 post on photo.net:

The second part of the article is written by photographer Kimio Tanaka. He includes the following statement: "The soft focus effect is almost nil around f/8 and depiction becomes as sharp as regular lenses over the aperture range f/11-22." Later, under the heading "How to focus with Pentax Soft lens", he writes: "The focus tends to be a little behind the in-focus point. In other words, the actual point of focus on the film plane is a bit behind the best focus point even if you focus on the focusing screen of the camera. Its principle is a little complicated but, in short, the human eye is dazzled by the flare of the soft-focus lens. Critical focusing is an unexpectedly indispensable factor in the use of a soft-focus lens. If it is not fully focused, a flare-combined picture is not attractive".

Tanaka then goes on to describe three ways to achieve best focus: "The easiest way is the use of correction lines engraved on the lens barrel. As the focus point differs with the aperture stops, stop down the aperture to the desired stop for taking pictures. Be sure to use a matte portion of the focusing screen. Then, turn the focusing ring to the correction line indicator. (The diagram here shows two white correction lines, the left one labelled "resolution weighted", the right one, nearest the orange standard line, labelled "contrast weighted".) The other way is to stop down the aperture to f/11 (the finder field will be a bit dark) and then return to the working aperture which should be within a range of f/3.5 to f/5.6. I myself like this method best and I used it all through the picture-taking this time. Still another way is to find out the focus point at which the contours of the subject image are the sharpest. The sharpest point inside the flare makes the focusing difficult."

The 2 white lines correspond to extending the bellows out 1 "tad" or 2 "tads" on the LF camera. The way I use it is to stop down until the subject is in sharp focus and determine the point of focus, stop-down until desired softness is achieved, and then focus on the focus point.

Thomas

With panchromatic film, the focus is where the focus looks like it is. And I think Tanaka is confusing "flare" with spherical aberration, two completely different phenomena. Flare should be almost eliminated in coated lenses like the Pentax and Veritar, and on single-cell cemented doublets and single menisci, as there are no internal air-glass surfaces to reflect the flare.

I think a lot of confusion over focusing soft lenses comes from the focus shift as you stop down. Soft lenses that work through spherical aberration have a spread depth of field, (that's what they were originally designed for, not the soft pictorial effect), and closing the aperture shifts the plane of dominant focus as light from the outer periphery of the spherical lens is blocked. The simplest rule-of-thumb is just "use panchromatic film, and focus at the taking aperture. What you see is what you get."

[tgtaylor]

With panchromatic film, the focus is where the focus looks like it is. And I think Tanaka is confusing "flare" with spherical aberration, two completely different phenomena. Flare should be almost eliminated in coated lenses like the Pentax and Veritar...The simplest rule-of-thumb is just "use panchromatic film, and focus at the taking aperture. What you see is what you get."

Focusing at the taking aperture is what Pentax recommends for this lens but as an alternative suggests the method set-out at the end of Tanaka's 2d paragraph above : "The other way..." Pentax goes on to say that using that method gets you close to the true focus point.


Thomas

[Mark Sawyer]

Pentax goes on to say that using that method gets you close to the true focus point.

The true focus point is pretty subjective when different areas of the lens are focusing the same point on different focal planes.