Blur Radius vs Blur Falloff ~ Steinheil Auto-Cassaron 50mm f/2.8

A friend pointed me to the Steinheil Auto-Cassaron 50mm f/2.8.  It's a Cooke triplet first element focusing 35mm SLR m42 mount lens and it's rather special.  It positively glows at all apertures and all subject distances.  These first element focusers can work magic by gently introducing optical imperfections as the first and second element distance changes.

Here's how to read the following graphs. Please keep in mind that these are for Full Frame digital.  APS-C is slightly different, as we may see in future posts.

 

 

Comments ~

The lens is soft overlaying sharpness.  At all apertures.  This seems to be Steinheil's design tendency.  

ISCO (the budget design house of Jos Schneider), Schacht, Roeschlein, Staeble, and of course Zeiss by comparison, are contrastier than Steinheil from wide open.

The Steinheil 45mm f/2.8 Cassarit and 135mm f/4.5 Cassar all show similar levels of softness that veil over a distinct sharpness.  Because of the rendition I feel Steinheil can be quite useful for working small format digital into early Pictorialist-like images. 

At this point I'm finding I have many good options from which to choose.  German.  Japanese.  Cooke triplet.  Zeiss tessar.  Steinheil Antiplanet (I have a Staeble 85mm that is of this formula).  All of these are good in one way or another.  I just have to work with them to see where I can go from here. 

Blur Radius vs Blur Falloff ~ Ricoh Riconar 55mm f/2.2

The first first element focusing lens I stumbled on was a Ricoh Riconar 55mm f/2.8 four element 4 group design lens.  It's a strange beasty in terms of lens design, but these seem eminently useful for soft focus work near wide open.    Stopped down the lens is as sharp as anything in the Toy Bin.  Versatility is strong in this one.

Since this is a Pentax K-mount I can't use the first element separation to manage softness level the way I do the m42 thread mount Cosina, Steinheil, and ISCO lenses.  I don't have a helicoid for K-mount.  However, at wide apertures there are plenty of optical imperfections no matter the focus distance.

Here's how to read the following graphs. Please keep in mind that these are for Full Frame digital.  APS-C is slightly different, as we may see in future posts.

 

 

Comments ~

To me it's interesting to see how aperture effects blur.  Bare lens or filtered, aperture can help manage softness levels.

Many of the Ricoh lens/filter combinations are well within old brass-era soft focus lens ranges.  This helps explain why, intuitively, I've felt this was a good Soft Focus lens on Full Frame digital formats.

While there may never be one lens "to rule them all", this little Ricoh seems well up to the task. 

Blur Radius vs Blur Falloff ~ Nikon Nikkor 85mm f/2 Ai

The following is on the heals of looking at another very well corrected, very sharp lens, the ISCO Westromat 50mm f/1.9.  My sweet little Nikon Nikkor 85mm f/2 is a unit focusing ernostar 5 element, 5 group formula lens and is the subject of today's investigation.

Reading the Minolta Portrayer filter instruction manual led me to understand that longer lenses (85mm to 135mm) could respond better to certain kinds of filtration. 

Here's how to read the following graph. 

 

Comments ~

There are several lens/filter combinations that fall into the old brass soft focus lens blur ranges.  This is rather exciting to see and it makes me wonder if soft focus filter designers knew/know more about their craft than I've in the past given them credit for?

One aspect of using a well-corrected lens for soft focus work is that the edges of the field may behave differently than they did in early optics.  

However, as is carefully noted in many journals and writings of the day, including  Biblioteque de la Revue de Photographie -  L. de Pulligny - C. Puyo "Objectifs d'Artiste Practique et Theorie des Objectifs et Teleobjectifs Anachromatique" - Biblioteque national de France (BnF), longer lenses were often the focal lengths of choice to very specifically avoid field edge aberrations at wide apertures (ie: portraiture).

In fact, the only photographer I know of who has succeeded, to my way of thinking, of leveraging field edge problems to outstanding effect is Alex Timmons.  Which means the Nikkor 85mm may be just perfect when used with soft focus filters in the more traditional way.  The time has come for me to validate this in the "real" world.

Blur Radius vs Blur Falloff ~ ISCO Westromat 50mm f/1.9

The ISCO Westromat 50mm f/1.9 is a unit focusing plasmat 6 element, 4 group formula lens. 

I've been looking at adapting certain kinds of somewhat difficult to find lenses to miniature format for soft focus work in using the first and second element separation control of the focusing ring to manage softness level.  However, I also have quite a stack of unit focusing normal 35mm SLR style lenses, and the brilliant little ISCO Westromat is one of them.  

While I am "on a roll" what better time to check two things about unit focusers with regards to potential soft focus work.  First, look at the bare lens wide open (I expect it to be sharp - it takes a lot to design a "bad" lens).  Second, look at what the effect of the filters might be on a very well corrected, sharp, not-at-all-bad lens.

Here's how to read the following graph. 

 

Comments ~

Only the Westromat/Nikon Nikkor Soft 1 combination falls within one of the two old soft focus lens zones.  All other combinations give varying blur radii outside of the old brass lens softness.

Looking at the Blur Falloff tells me that this will give a "fat" blur rendition (40% to 50% luminance measured half way between the leading and trailing edges of blur), even as the Blur Radii measured small compared with first element focusing lenses.  Wherefore I expect this lens used with Soft Focus Filters to deliver a different from Pictorialist softness "look." 

I'll have to spend some time with the ISCO Westromat to see how it behaves in the "real world." It may be just another excellent, sharp, boring 'ol 50mm plasmat that is indistinguishable from fully modern AF.  If that turns out to be the case, there'd be nothing wrong with that, right?

Blur Radius vs Blur Falloff ~ ISCO Iscotar 50mm f/2.8

The ISCO Iscotar 50mm f/2.8 is a Cooke formula, first element focusing, triplet lens.  I'm adapting these kinds of lenses to miniature format for soft focus work by using the first and second element separation control of the focusing ring to manage softness level.  Mated to a helicoid and setting the softness level on the focusing ring, the helicoid is used to effectuate the focus itself.

To show how first and second element separation effects softness level, I graphed Blur Radius against Blur Falloff.  Further, to control highlight "softness", I added a number of different Soft Focus filters to the investigation see to what degree they do their job. 

Here's how to read the following graphs. 

 

Comments ~

These illustrate how the focus ring on the ISCO 50mm can effect the level of softness in an image.  And we can see how Soft Focus filters add softness over the base optics.

Cooke triplets are bog simple, but very well corrected lenses.  I wondered if the German 35mm SLR triplets were derived from the same detailed design specifications, but they are not.  The ISCO is contrasty where the Steinheil is lower contrast but sharper.  

There are other German Cooke triplets, but they are unit focusers and it might be difficult to adapt them to soft focus work.  At this point I'm unable to find any Japanese Cooke triplets.  The closest I can find in first element focusers are tessar formula lenses (such as the Cosina 55mm f/2.8).  If someone knows of a cheap Japanese triplet first element focuser let me know, please.

Blur Radius vs Blur Falloff ~ Cosina Cosinon 55mm f/2.8

The Cosina Cosinon 55mm f/2.8 is a tessar formula, first element focusing lens.  I'm trying to adapt is to miniature format soft focus work by using the first and second element separation control of the focusing ring to manage softness level.  Mated to a helicoid and setting the softness level on the focusing ring, the helicoid is used to effectuate the focus itself.

To show how first and second element separation effects softness level, I graphed Blur Radius against Blur Falloff.  Further, to control highlight "softness", I added a number of different Soft Focus filters to the investigation see to what degree they do their job. 

Here's how to read the following graphs. 

Comments ~

It should be easy to see how the focus ring on the Cosina 55mm can effect the level of softness in an image.  And it should be easy to see how Soft Focus filters add softness over the base optics.

While not shown here, but illustrated earlier, the Cosina tessar formula lens is better corrected for closer focused subjects when the lens is shot wide open.  Stopped down, infinity cleans up nicely. 

I believe this proves the concept of using first element focusing lenses on miniature formats in Soft Focus work.

Soft Focus Photography ~ Visualizing Blur Radius vs Blur Dropoff Measurements

I realize that a lot of what I've written about Soft Focus lenses and filters is diagnostic and perhaps difficult to grasp.  So I went back and measured the rate of falloff and plotted it against blur radius to see if I can't illustrate better what I'm finding.

How to read the graph ~

X axis = Blur Radius - as a percentage of the width of an image

Y axis = Blur Falloff = Luminance Value Measured 1/2 way between leading and trailing edges of blur with potential values of 0 to 255

The smaller the Blur Radius (X axis) the sharper an image will be.  The higher the Blur Radius, the softer an image will be.

The higher the Blur Falloff value (Y axis) the "thicker" blur will look.  The lower the Blur Falloff value the sharper the underlying image will be with a more subtle overlaying veil of softness.

I've included two regions in yellow.  These illustrate the approximate ranges of "softness" achieved by early 1800's/1900's Soft Focus lenses for large format plate and film.

How I came up with these ranges is important.  First, I calculated the blur radius of chromatic aberration of several lenses using the formula found in Biblioteque de la Revue de Photographie -  L. de Pulligny - C. Puyo "Objectifs d'Artiste Practique et Theorie des Objectifs et Teleobjectifs Anachromatique".  

Then I inspected and measure the blur radius of early Pictorialist images.  I found that the Dallmeyer Bergheim Models 1 and 3 are, indeed, quite soft.  Other lenses, such as Pinkham Smith, Darlot, Wollensak, etc appear to return half the blur radius of the earlier Dallmeyer-Bergheim, so I broke my ranges of softness of lenses into two.

Old Soft Focus lenses would vary their levels of softness using focal length, aperture, and/or marginal light controls (such as those found on Heinrich Kuhn's Tiffenbuilder/Imagon and Mamiya RB 150mm SF).  So exact Blur Radius is variable.  Additionally, without being able to inspect old lenses directly, I'm unable to measure Blur Falloff.  Hence the use of these rather vague approximations.  

However, I surmise that the amount of blur seen in early prints was pleasing to practitioners and therefore useful to measure and understand as a target for adapting miniature format lenses and filters in the present time.

I keep in mind, in addition to all the above, that this look at image softness fails to include flare, astigmatism, coma, emulsion and print technologies and techniques.  In this way, adapting miniature format lenses and filters to the Pictorialist Task may, at best, be an approximation of the original style and, really, can only be a First Step.  It's my hope that considering Blur Radius and Blur Falloff may yet prove to have been a useful starting point. 

Here's what a graph looks like.  In future blog posts I will present what I've measured for specific lens, first element separation (where applicable), and Soft Focus filters.