Cooke TTH 12.37" F8 RVP Soft Focus Portrait Lens

RVP Soft Focus Lens 8x10 Large Format Photography by Tim LaytonRVP Soft Focus Lens 8x10 Large Format Photography by Tim Layton "The Taylor, Taylor and Hobson lens, Rapid View and Portrait (later simply known as the R.V.P. as identified on the lens barrel itself) originated before 1885 and consisted of a simple combination meniscus set well behind the aperture blades.

I searched for this lens for a very long time and I was super excited when I was able to locate such a clean and beautiful copy.  

It was merely a landscape lens normally working at F/16 opened up to F/8. This introduced or rather increased the spherical aberration and the curvature of field, and the definition was by no means even, being very much sharper in the center than around the edges.

It was the first soft focus objective used by Clarence White; it was also used by Alfred Stieglitz at some time in his career as well.  Knowing that I am using the same exact lens as Alfred Stieglitz is pretty exciting to me. 

In 1913 it was rebranded as the Cooke Achromatic Portrait Lens. Except for the improved quality of the glass and the working aperture, the R.V.P. was nearly identical to Charles Chevalier’s achromatic French Landscape Lens F/15, of 1839, one of the earliest lenses designed specifically for photography.

This general landscape lens design was in production for nearly a century and was in wide use in 1900 and Kühn believed it was the model for Smith’s lens." - THE SOFT-FOCUS LENS AND ANGLO-AMERICAN PICTORIALISM, William Russell Young, III

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Cooke TTH 12.37 Inch F8 RVP Portrait LensCooke TTH 12.37 Inch F8 RVP Portrait Lens Before the Cooke Portrait lens, there was the Taylor Taylor & Hobson (TTH) RVP (Rapid View Portrait) lens, later renamed the Cooke Achromatic.

This lens is rare today and particularly good for landscape and group photos thanks to a bit more depth of field than the softer Cooke Series II lens.  I own both lenses and I love them both for different reasons. 

The RVP lens has an ethereal glow and nice even bokeh like other Cookes and covers 8x10 at portrait distances.

The Taylor Taylor & Hobson Rapid View Portrait (R.V.P.) is the grandfather of a lot of soft-focus meniscus lenses from the 1910s - 1920s such as the Cooke Achromatic Portrait, the Karl Struss Pictorial, the Pinkham & Smith Semi-Achromat, the Bausch & Lomb Portrait Plastigmat, and even the Kodak 305 and 405 Portrait lenses. Clarence White and Alfred Stieglitz among others used the RVP for their Pictorialist photographs.

 The R.V.P. has a long barrel, with an achromatic doublet meniscus in the rear. The front holds only the iris, at F8 or sometimes mentioned at F7.5. The workmanship on all TTH lenses is of the highest quality, with deep, precise engraving, the patented "exactly three turns to remove" flange, and a glowing brass lacquer so hard their lenses usually look 50 years younger than they are.

But the RVP was made in the 1880s, not the 1920s, much earlier than the second wave of soft-focus enthusiasts. For a decade or more, this was the lens to use if you wanted soft focus. Earlier photographers experimented with opened up landscape lenses or shot "slightly out of focus" conventional lenses. Actually, in the 1800s a "view lens" meant a landscape lens, and the Rapid View (RV) was TTH's version, at F11. At some point, they realized that opening up the lens to F8 would give a softness that was conducive for portraits. Thus, the Rapid View Portrait (R.V.P.) was born.

The story is that in 1913 TTH/Cooke was requested to remake the R.V.P. because a new generation of photographers wanted a lens like the first Pictorialists used. So they brought out the Cooke Achromatic Portrait Lens F7.5. If you compare them, they are identical to the RVP except for the engraving. A couple of years later Karl Struss and Smith started making similar lenses, and the rest is history.

Cooke TTH RVP F8 19th Century Soft Focus Lens by Tim LaytonCooke TTH RVP F8 19th Century Soft Focus Lens by Tim Layton "While the Cooke Portrait Anastigmat line of lenses was the main soft focus product by TT&H, in 1911, they also produced the now, rarely seen, Cooke Achromatic Portrait Lens. This lens was basically a copy of an older lens sold by TT&H, known as the Rapid View and Portrait Lens which was a combination of meniscus lens with a good amount of spherical aberration left in the design.

In the 1911 issue of The Photographic Times writes, "The Taylor, Taylor, Hobson Company of New York have placed on the market a single Achromatic lens known as the Cooke Achromatic Portrait lens. This is really the old Rapid View and Portrait lens made twenty years ago by Taylor & Hobson, of Leicester, England, and known then as the R. V. P.

For many years the lens has been used by artists like Mrs. Kasebier, Clarence White, and Alfred Stieglitz, and has been preferred by them to the modern anastigmat. It has been marketed as the result of numerous inquiries that have been received for a lens of that type. Whoever expects sharp definition will be disappointed, but the photographer who desires softness and roundness coupled with line modeling and a true perspective will be both astonished and delighted.

RVP Soft Focus Lens 8x10 Large Format Photography by Tim LaytonRVP Soft Focus Lens 8x10 Large Format Photography by Tim Layton Each Cooke achromatic portrait lens is furnished in an English sole-leather carrying case and shows the same fine workmanship that characterizes Cooke anastigmats. The lenses work with a full aperture of F7.5. Full particulars will be mailed on request by the Taylor-Hobson Co., 1135 Broadway, New York."

The Photo-Miniature magazine of February 1912 remarks, "The Taylor-Hobson Co., 1135 Broadway, New York, have placed on the market a single achromatic lens known as the Cooke Achromatic Portrait lens. This is really the old Rapid View and Portrait lens made twenty years ago by Taylor & Hobson, of Leicester, England, which has been used by artists such as Gertrude Kasebier, Clarence White and Alfred Stieglitz, in preference to the modern anastigmat, for certain sorts of pictorial photography. It is noteworthy for its softness of definition, roundness, and plasticity of modeling, with an accuracy of drawing which is particularly pleasing in portraiture. Those who seek these qualities in their work, and do not demand extreme speed or sharp definition, will be pleased with the performance of this lens." -Antique & Classic Camera Website


8x10 Large Format Contact Prints

Cooke Series II @ F4.5 Contact Print by Tim LaytonCooke Series II @ F4.5 Contact Print by Tim Layton I used my Chamonix 8x10 large format view camera loaded with Arista EDU Ultra 100 B&W film rated at EI 80 and tray developed in hand mixed D23.  

For this first print, I wanted to expose the image wide open at F8 to experience the full soft focus effect of this lens for still life images.  As you will see below, I also took the lens out for some landscapes. 

I focused on the lens of the 5x7 vintage camera in the scene to ensure the center of the image was sharp, relatively speaking with a soft focus lens. 

I absolutely love the RVP lens wide open at F8.  I instantly feel like I am an 19th century photographer in the Pictorialism period.  I feel like making "art" with this lens and have zero desire to document a subject. 

Cooke RVP at F8 by Tim LaytonCooke RVP at F8 by Tim Layton

In this second print, I wanted to stop down the lens to F22 and see what the print would look.  I was wondering what would happen to the magical soft focus effect and how that might change the mood of the print. 

As with the first print, I used my Chamonix 8x10 large format view camera loaded with Arista EDU Ultra 100 (Fomapan 100) B&W film rated at EI 80 and tray developed in hand mixed D23.

As you can see in the second print at F22, the feeling and mood of the print is considerably different. It is still "soft" as compared to contemporary optics, but it is much sharper at F22 than it is wide open at F8. 

I contact printed these prints from the original 8x10 film negative as you will notice the film notch and edges of the film on the prints. All of the prints are straight prints on Ilford MGIV RC paper using a number 2.5 variable contrast filter and no dodging or burning. I used a hand mixed version of the D72 formula for development. 

Cooke RVP @ F8 by Tim LaytonCooke RVP @ F8 by Tim Layton

In this third print, I wanted to head out into the field and stop the RVP wide open in all its glory at F8 and see how this looks as compared to the studio still life prints.

Notice the natural vignetting and fall off on the print when focused at infinity as opposed to closer subjects.  I actually expected this to happen because this lens was made as a soft focus portrait lens and not to be used for infinity subjects.  Also, the actual coverage area for this lens is 6 1/2 x 8 1/2 and I am using it on my 8x10 camera. 

As with the the other prints, I used my Chamonix 8x10 large format view camera loaded with Arista EDU Ultra 100 (Fomapan 100) B&W film rated at EI 80 and tray developed in hand mixed D23.

I think this scene and the resulting print are a great match because it has a vintage/Victorian-era feel to it. 
Cooke RVP @ F8 by Tim LaytonCooke RVP @ F8 by Tim Layton

THOUGHTS & ANALYSIS

Cooke Series II F4.5 Contact Print Exposure by Tim LaytonCooke Series II F4.5 Contact Print Exposure by Tim Layton As you can see from the prints above, it is possible to create a lot of different moods with this incredible lens.  It really is up to your creative mind of how to use the lens. 

I plan to always shoot the lens wide open in all its soft focus glory no matter what the subject is because I have lots of sharp lenses.  When I want an ethereal soft focus or Victorian-era type of mood, this lens will be the one that I grab. 

If you are a portrait photographer, I would think this lens would be like gold.  The closest that I get to portraits is wildlife.  While I will not be able to to create original negatives of wildlife with this lens on my 8x10, I can however use it when I am making enlarged negatives in my copy camera which could be an interesting twist.  I typically use my Nikon F6 with the latest Nikon Telephoto glass for wildlife to create the 35mm negatives and then I either make smaller enlargements from the 35mm or make enlarged negatives for making big prints or contact prints. 

I contact printed these prints from the original 8x10 film negative as you will notice the film notch and edges of the film on the prints. All of the prints are straight prints on Ilford MGIV RC paper using a number 2.5 variable contrast filter and no dodging or burning. I used a hand mixed version of the D72 formula for development. 

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HISTORY OF THE COOKE LENS

The properties of light and its behavior in glass have been a constraint for lens makers ever since the first optics were made. The ability of glass to bend light is known as refraction.

Glass types that are able to bend the light for effectively are known as high refractive index glass.  Glass will also separate light into its component wavelengths (as seen in a prism). This is commonly referred to as dispersion. Glass types that cause less chromatic aberration are known as low, extra-low, and ultra-low dispersion glass.

A "perfect" lens would focus all wavelengths of light from all areas of the glass into the same flat plane of focus. When a lens fails to do this it is known to have an aberration. Chromatic aberration is when the different wavelengths of light do not meet at the same point. If different parts of the glass fail to focus the light to the same point it is known as spherical aberration. When the plane of focus is curved rather than flat it is known as astigmatism

Cooke TTH RVP F8 19th Century Soft Focus Lens by Tim LaytonCooke TTH RVP F8 19th Century Soft Focus Lens by Tim Layton Early on lens makers were limited to two types of glass: sodium lime (crown), and lead crystal (flint). Photography’s first lens, the Wollaston meniscus of 1804, was a simple single element lens made of flint glass.

Chevalier improved on the design by adding an element of Crown glass that was designed to cancel out some of the dispersion (chromatic aberration) found in the Wollaston meniscus. This was known as the achromatic doublet (1829). 

The photography processes of the time required a lot of light. The maximum aperture of the Chevalier was F/16 so it was a very “slow” lens that required long exposure times.

In 1840, the mathematician Joseph Petzval came up with a new much faster design. The Petzval lens consisted of 4-elements, with a cemented achromat in the front and an air-spaced achromat behind the aperture. The result was a "fast" lens with a maximum aperture of 3.8.

RVP Soft Focus Lens at Rocky Creek Falls by Tim LaytonRVP Soft Focus Lens at Rocky Creek Falls by Tim Layton The faster exposures allowed for portraits to be taken with the lens so it became known as the first portrait lens. The lens was very sharp in the center of the image but it suffered from a highly curved field of focus (astigmatism). 

In the 1890s, Ernst Abbe and Otto Schott invented new types of optical glass which quickly led to new breakthroughs in lens design. The first lenses with complete correction of field curvature came into the market. First was the Zeiss Protar (1890), followed by the Goerz Dagor (1892), and the Cooke Triplet (1893). These were known as Anastigmat lenses because they were free of astigmatism. The Anastigmats were hugely successful and quickly replaced the majority of earlier lens designs.

THE COOKE LENS TODAY

Cooke TTH RVP F8 19th Century Soft Focus Lens by Tim LaytonCooke TTH RVP F8 19th Century Soft Focus Lens by Tim Layton There is now a resurgence in older styles of photography. Many find that the sharp contrasty look of modern lenses and digital cameras lacks the “character” of older classic lens types or the processes associated with analog photography. There is a growing number of photographers who use wet plates instead of film, or digital camera sensors, to obtain a more unique "classic" look. Many refer to the look of lenses that were used back in the days of 1930's Hollywood glamor and noir style photographers.


The Cooke Series II, also known as the Cooke Triplet, has become a favorite of many photographers today. The character is very different from the Petzval-type lenses which are also popular. The curved depth of field of the Petzval lens produces images that are very sharp in the center but have a soft-and-swirly look toward the edges.

In contrast, the Cooke lens has almost no curvature of field. The “proper” English portrait lens, the Cooke renders everything in a very even and balanced way. Curvature of the field remains flat and consistent throughout the entire image circle. The transition to out of focus is very smooth, and the background itself has very nice blur qualities (bokeh).

The out of focus areas have a very rounded and smooth look. The background is tranquil free of distractions. It is a lens that is designed to be used at large apertures.

Depth of field is shorter with larger apertures, and many prefer to use the lens "wide open" for Artistic selective-focus photography. Wide-open, it is sharp like a knife blade, and going from that rapidly to a smooth and melty background is “what it is about”.

Cooke TTH RVP F8 19th Century Soft Focus Lens by Tim LaytonCooke TTH RVP F8 19th Century Soft Focus Lens by Tim Layton There is so much “eye candy” in a Cooke image. Every part of the image is pleasing. Areas where in and out of focus objects meet really pop with an almost stereoscopic 3d look.

While visible “slow” transitions from in and out focus are equally amazing. A simple picture with a line of trees, fence posts, or even a wall becomes work of art by the fascinating way the Cooke renders the transition to out of focus.  

There is something about the sharp and smooth. And the Cooke has smoothness...The gradations present in the background are very rich and buttery. The out of focus objects are smoothed over evenly without geometric distortion. The flatness of field remains in the out focus areas; it does matter if an object is near the center or the corners as long as it is the same distance behind the focus the effect is the same.
Cooke also produces lenses for Hollywood with the same Cooke look that dates back to the Cooke Triplet (series II). Cooke cinema lenses are very well regarded and also quite expensive (~$30,000 new).
For those who prefer less than “knife” sharpness, the Cooke lens features a sliding element based, soft-focus feature. By turning the dial, the edge is taken off the image giving a more subdued diffused look. The literature states that this is done through the use of spherical aberration and that this also adds more depth to an image.

The name of the Cooke Series II can be somewhat misleading in that sold series III, IV, V and VI lens but the other lens models were sold concurrently to the series II and are not later “improved versions” of the Cooke lens. The series II was Cooke’s most premium portrait lens and had the largest aperture sizes. The other series were lighter, more economical, and sold for group portraits... Where one would already stop down for depth of field. Series II is the one you want.

Behind The Scenes Vintage Large Format Lenses by Tim LaytonBehind The Scenes Vintage Large Format Lenses by Tim Layton WHAT IS A SOFT FOCUS LENS? 

A soft focus lens is a type of lens that is designed to produce a soft but sharp image that combines a distinct, finely-defined, inner image core with a warm out-reaching glow. This is different from conventional lenses which are either sharp and in-focus or out-of-focus and blurry.

 A true soft focus lens is actually both in and out of focus at the same time. Form and detail are not lost, but instead, are combined with a warm halo that is produced from the multiple levels of out of focus light. The effect is different from a Gaussian blur layer in that the effect varies through the focus range of the image.

With a soft focus lens the transition between in focus areas and the background is improved and the background itself is enhanced with better gradation, shape, and a stepless “circle of confusion”. In addition, the local and global contrast of the entire image is softened enhanced in the most complex way.

Light is spread into from the highlights into the midtones and shadows in varying degrees based on proximity, focus, and the strength of the highlights. There is a growing appreciation and the desire, among a portion of fine art photographers to explore the artistic and creative value in the unique way the soft focus and other classic lenses interpret the word. The characteristics of soft-focus lenses vary and some are very rare and highly sought after adding a level of prestige to owning certain prized optics. 

Behind The Scenes Vintage Large Format Lenses by Tim LaytonBehind The Scenes Vintage Large Format Lenses by Tim Layton Soft focus lenses vary widely in optical configurations and the principles behind each lens’s unique characteristics. Most of the “character” comes from the careful incorporation of just the right amount of one more optical aberrations.

An Optical aberration is the term describes are different types of technical “flaws” or “optical imperfections” in the lens. The attempt of the majority of modern lens design is to reduce “optical aberrations” to create sharper, clearer, more detailed, and accurate images. However early on in the evolution of lens design, the question was asked if more accuracy actually produced better more meaningful images. A number of lens designers experimented with “controlled imperfection” to look for a “better-than-accurate” view of the world. And so the soft focus lens came into being introducing with it a romanticized dreamy version of the world with more emphasis on depth, form, and the interaction of light rather than pure unadulterated detail. 

Soft focus photography became very popular with the rise of Hollywood glamour photography in the 1920s. Significant early photographers who were known to have some point used a soft focus lens include Holland Day, Alvin Langdon Coburn, Edward Weston, Nicola Perscheid, Karl Struss, George Hurrell, and Ansel Adams. Soft focus lenses and filters have been used sparingly in the mainstream from the ’20s until now. Mostly during close-ups of female characters, romantic scenes, or memory scenes.  

WHAT MAKES A LENS "SOFT FOCUS?"

Almost (if not) all Soft focus lenses use a degree of chromatic and/or spherical aberration to achieve an effect where a portion of the image is both and out of focus at the same time.

This creates a soft but sharp effect with the in focus areas produces sharp details and with the addition of a warm graduated glow formed from the out of focus light.

The first soft-focus lenses relied primarily on chromatic aberrations to produce a soft image.

CHROMATIC ABERRATION

Behind The Scenes Vintage Large Format Lenses by Tim LaytonBehind The Scenes Vintage Large Format Lenses by Tim Layton Chromatic aberration is a term for when one or more bands of the visible spectrum have a slightly different focal length than the others. In color photography, this can often be seen as color fringing and is generally a sign of poor optics. The best modern lens types use special glass to reduces the dispersion of the optical spectrum to produce an Apochromatic lens.  

However with black and white film sometimes chromatic aberration can add a nice photogenic soft focus effect. If each color has a different focal length you always have a section that is out of focus creating the simultaneous in and out of focus effect. With a soft focus lens based on chromatic aberration, you must use black and white film and the effect will react differently to the based on its own spectral response. Color filters could have a negative effect on these “semi achromatic” soft focus images.

There is also an issue where there is often a perceived difference in focal length between the image on the ground glass “visual focus” and the “chemical focus”  of the negative. This is due to the spectral differences between the black and white film used and the human visual system.  

SPHERICAL ABERRATION

Cooke Series II @ F4.5 Contact Print by Tim LaytonCooke Series II @ F4.5 Contact Print by Tim Layton This occurs - when the light that travels through the edge of a lens, focuses on a different point than the light that travels through the center of the lens. Imagine a “multifocal” lens with each aperture being a different focal length.

This is a spherical aberration. With the right amount of spherical aberration, you can have sections of the image that both in and out of focus at the same time creating a wonderful soft focus effect.

Many soft focus lenses used only spherical aberration to achieve their softness while allowed for more consistent results with more film types and bring together “visual” and “chemical” focus. 

FROM A TECHNICAL ASPECT

RVP Soft Focus Lens 8x10 Large Format Photography by Tim LaytonRVP Soft Focus Lens 8x10 Large Format Photography by Tim Layton Despite their age, old soft focus lenses have great value today as powerful tools of photography. From a technical aspect some of the qualities of a nice soft focus lens and modern large format film cannot be matched with digital capture.

The level of detail present in the core of a soft focus image varies for design to design but all soft focus images have one thing in common extraordinary smooth linear or non-linear gradations.

The optically produced glow and smoothness of present around the highlights and out of focus areas are perfectly stepless and analog, it is not limited by diffraction, bit depth, pixel sizes, or optical sharpness. The gradations out resolve even the best of today's black and white films.

Cooke Series II @ F4.5 Contact Print by Tim LaytonCooke Series II @ F4.5 Contact Print by Tim Layton When you think about it, one can easily understand how the extra pixels and “film real-estate” of large format produces higher quality images with older soft focus lenses just as it does with modern sharp glass.

The quality and integrity of the scan and printing system used is not lost when using a 100-year-old soft focus lens. Film images can be scanned using high-resolution 16-bit Creo or Drum based scanners at very high resolutions and printed in large sizes to show that “gradation detail” not present in digital capture. Black and white darkroom and contact prints also have very good technical qualities. 

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WHY USE A SOFT FOCUS LENS?

RVP Soft Focus Lens 8x10 Large Format Photography by Tim LaytonRVP Soft Focus Lens 8x10 Large Format Photography by Tim Layton Soft focus photography is very different than most of the modern photography. Having the ability to take an ultra-sharp snapshot of the world alone does not create art. It's not about what is the sharpest lens with the highest modular transfer function or which back has the highest pixel count. The goal of photography as an art form is to create an emotional reaction inside the viewer of the image. Subject, composition, meaning, and style are essential components of artistic vision. The great photographers of the past did not have access to today's modern digital camera technology and we continue to marvel and react to their work. 

Soft focus photography allows one to take a step back and to explore photography in a new way. It adds something magical and timeless. Finding new ways to utilize and explore the unique attributes of high character lenses can be very rewarding. The soft focus style does not work for every image but when it does work it is amazing. In the right hands, a soft focus lens can be used to produce an image of exception complexity and nuance.

The effect of a soft lens can bring a certain harmony, balance, and emotion to an image. The subject is revealed in sharply defined form and detail surrounded in a wondrous and magical glowing luminous veil; an ethereal lightness. Depth is enhanced. There is a mellow blending of reality and imagination as the clearly defined melts away in a kind and gentle transition into the soft and tranquil background. Contrast is also enhanced. There is something magical about the combination of sharp details, a delicate transition to out of focus, and gradations that sensationally smooth, rich, and creamy. It is like the lens takes you away to an almost enchanted realm.

Cooke Series II Variable Soft Focus Lens by Tim LaytonCooke Series II Variable Soft Focus Lens by Tim Layton In the soft focus world each once lonely spot, or pixel, becomes a glorious beacon of light. With the power, if bright enough, to shine across neighboring areas affecting the surrounding pixels and area. Individual bright spots combine to form highlights but with true luminosity; a communal brightness, that can spill into the deepest shadows adding harmony and balance to the image. 

The effect is not content-aware but is truly content dependent. Lighting can be re-imagined. In general, soft focus lenses will have lower contrast but the contrast is also very unique and complex. Global and local contrast are both affected most elegantly; as light is spread from the highlights into the mid-tones and shadows it does so in varying degrees based on proximity, focus, and the luminosity of the highlights.

One must visualize the effect of light spillover on the image and learn to incorporate the spillover into an image and use the flare from a highlight to brighten a cave or shadow region.

Cooke Series II Variable Soft Focus Lens by Tim LaytonCooke Series II Variable Soft Focus Lens by Tim Layton Lone highlight details can be given a little more oomph but can also get blown out surrounding light sources. A spot meter can help out tremendously with the exposure and lighting of soft focus images. 

As humans; our mind focuses on something and our eyes follow. When looking at printed images what is the effect the choice of focus on the mind? How does separating a subject from its surrounds affect our opinion of the subject? How can context be changed by the choice of a lens? 

An attribute of Bokeh; “Blur Disc’s” and the “circle of confusion”

Maybe you have seen in a movie or photograph where a light is out of focus and shows up as a polygon. What you are looking at is often referred to as the "blur disc" or "circle of confusion". What a spot of light is out (behind) of focus it spreads to form a disc.

It might be better to use the term "blur disc" then "circle of confusion" as a "circle of confusion" is a more general term for describing any part of the cone of light that is created behind a spot.

The smallest focus point is known as the circle of least confusion. Often a larger circle is acceptable depending on the size of the sensor or resolution capabilities (and desired print magnification) of the film.

Arista.EDU Ultra 100 Negative With Cooke Series II F4.5 Variable Soft Focus Lens by Tim LaytonArista.EDU Ultra 100 Negative With Cooke Series II F4.5 Variable Soft Focus Lens by Tim Layton As long as the circle of confusion fits within a pixel it will show up as being in focus to that pixel. The size of the circle of least confusion is integral to many mathematical formulas for determining exact depth of field. Too many, the circle of confusion translates to a single spot or pixel in a print. When photographers talk about the circle of confusion as an attribute of the visible out of focus they are talking about a much larger circle that is further out of focus. Both are circles of confusion, and to reduce confusion, I feel it is better to use the term “blur disc” in reference to a part of the cone of focus that is large enough to be clearly identified as being out of focus yet retains some shape or form.

The shape of the Blur Disc is determined by a number of factors; the number of blades on the aperture, for example, determines the number of sides on a polygonal disc pattern. A lens with a rounder aperture is said to have a rounder "blur disc". The transition from the center of a circular blur disc to the edge varies dramatically from different lens designs.

Cooke TTH RVP F8 19th Century Soft Focus Lens by Tim LaytonCooke TTH RVP F8 19th Century Soft Focus Lens by Tim Layton * A "perfect" "neutral" or "good" blur disc has no or very little gradation and small out of pinpoint highlight shows up as an evenly light circle with a hard edge. The type of blur disc is associated with modern Apochromatically and Spherically "correct" lens designs

* "Negative" or "bad" blur disc's have a visually unappealing "doughnut" light pattern; light is distributed more heavily toward the outer edges then it is in the center. The result can be visually distracting.

* The "Positive", "ideal", or "Best" blur discs have a smooth step-free gradation with the center being the brightest point. The look is generally accepted as being the most visually attractive. The out of focus areas on a lens of this type of having smoothest gradations and fewest distractions (sharp edges, doughnut artifacts) of these three basic blur disc types. Figures are smoothed but are more generally recognizable then with the other two main disc types.

Cooke TTH RVP F8 19th Century Soft Focus Lens by Tim LaytonCooke TTH RVP F8 19th Century Soft Focus Lens by Tim Layton In order to produce this type of disc blur, the Light needs spread out from the center at an unequal rate so that the brightest point of light is at the center and a smooth gradation radiates outward with no sharp edges. Remember.... the light near the center of the disc is closer to being in focus than the light near the edge.

The most common way portrait lenses go about creating an ideal "blur disc" is to carefully introduce spherical aberration (a term used to describe a change in focal length throughout the aperture range). The idea is that the center parts of the lens would be closer to being in focus while the outer parts will spread out more do to being further from being in focus.

Some lenses have a curved depth of field that can distort the shape of the "blur disc" depending on the spots' location in reference to the center of the lens image circle.

Color fringing and reflective ghosts are negative things that can appear in the "blur disc" on poor quality lenses.

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