What's so special about 85mm?

[xpatUSA]

I was looking at µ4/3 lenses and noticed a Nocticron lens of 42.5 focal length which seemed a peculiar number to me, accustomed as I am to whole numbers of mm for lens focal lengths. Then I realized that the so-called "crop factor" of 2 makes that equivalent to 85mm in 135 format.

But in the world of µ4/3, focal lengths of 42 and 45mm are quite common and 42 times 2 is, after all, 84mm - so again I ask, what's so special about that "missing" 1mm that the 0.5mm in µ4/3 makes such a can't-do-without-it difference?

I do realize that the effective focal length (i.e. marked plus extension) is a variable far outweighing a mere 1mm in 85 - which only goes to pique my pedantic curiosity even further ...

[Manfred M]

Ted - It's all about marketing and nothing more. Just like anything else, there are fashions in photography. Basic "rule" is that wider aperture lenses tend to introduce more distortion, especially when shot close to the subjects vs long focal length lenses that tend to produce a flatter, less distorted view.

50 years ago, the standard portrait lens for 35mm film was the 135mm lens. It gave a nice distortion free image, but was a bit flat looking for some folks.

Some 30 years ago, people were shooting portraits at 105mm in addition to the 135. A few daring soles were shooting at 90mm, which gave a bit more dimension to the images. I guess I'm old fashioned, but I still like the 135mm and 105mm look; partially because they let the photographer stand a bit further way and not so much in the face of the subject. Some people prefer the photographer not being in their face. The 105mm has been around since the 1950s.

About 15+ years ago, the 105 started falling fall out of favour and people started doing portraits with the 85mm lens. The f/1.2 and f/1.4 lenses with their shallow DoF became very popular with portrait photographers and that continues to this day. They give a bit more dimensionality to the image. The Panasonic / Leica Nocticron is a f/1.2 lens so with the 2x crop factor gives a similar DoF as an f/2 lens on a FF body. At that focal length, that extra 0.5 mm focal length makes no practical difference, The marketing folks obviously want to tell people they are using a FF equivalent of the 85mm lens and nothing more.

PS - I'm seeing more and more portrait photographers slipping in the 50mm lens for portraiture. This is driven, no doubt, by the distorted cell phone images we see everywhere.

[xpatUSA]

Thanks, Manfred.

Not being a Portrait shooter, I found the potted history most helpful.

This is driven, no doubt, by the distorted cell phone images we see everywhere.

Excellent!

[billtils]

... Not being a Portrait shooter, I found the potted history most helpful...

Many of lenses marketed as "Macro" fall into the "Portrait" focal length range too.

[Manfred M]

Many of lenses marketed as "Macro" fall into the "Portrait" focal length range too.

Agreed Bill, but the main difference is that macro lenses tend to have smaller maximum apertures, so you can't get that shallow DoF many portrait photographers look for. If you don't care about that, I agree, the macro lenses can be used to take excellent portraits.

[xpatUSA]

While we are talking about the suitability of lenses for portraiture, I understand that macro lenses tend to have a flat field.

On the other hand, I found this while discussing "swirly bokeh" elsewhere:

"Talking of which, the Petzval provides good center sharpness before fading out to a strong swirly bokeh effect at the edges. Interestingly, this narrow depth of field effect is accentuated in the Petzval due to a curved rather than flat field of focus – further contributing to the circular form of the bokeh and making it an excellent choice as a portrait lens." (my bold)

https://ehabphotography.com/swirly-b...you-need-them/

Not sure which way it curves.

[xpatUSA]

So, if I understand all correctly, it's not just the odd-numbered 85mm that gets divided exactly by two for m4/3. In other words, I should be able to find a 52.5mm or a 67.5mm lens and so forth ...

... and I just now did!

https://www.ebay.com/p/99732190

https://www.ebay.com/itm/251054408424

Not m4/3 though but it doesn't really matter I guess ...

... as to the original post ... "engage search-engine before opening mouth" refers.

[Manfred M]

While we are talking about the suitability of lenses for portraiture, I understand that macro lenses tend to have a flat field.

On the other hand, I found this while discussing "swirly bokeh" elsewhere:

"Talking of which, the Petzval provides good center sharpness before fading out to a strong swirly bokeh effect at the edges. Interestingly, this narrow depth of field effect is accentuated in the Petzval due to a curved rather than flat field of focus – further contributing to the circular form of the bokeh and making it an excellent choice as a portrait lens." (my bold)

https://ehabphotography.com/swirly-b...you-need-them/

Not sure which way it curves.

This all deals with personal taste and directions in photography. The Petzval lens was developed in the 1840s and Lomo and Lensbaby produce updated versions of this lens. I know some folks that love the "bubble bokeh" that the East German Meyer Optik company produced and are using them on modern cameras.

I personally do not particularly like either effect, but know others that do. That's where personal taste comes in.

[xpatUSA]

This all deals with personal taste and directions in photography. The Petzval lens was developed in the 1840s and Lomo and Lensbaby produce updated versions of this lens. I know some folks that love the "bubble bokeh" that the East German Meyer Optik company produced and are using them on modern cameras.

I personally do not particularly like either effect, but know others that do. That's where personal taste comes in.

Thanks.

What about the field of focus? Flat or curved for portraiture, which is "better"? Or is that also a matter of taste?

[Manfred M]

Thanks.

What about the field of focus? Flat or curved for portraiture, which is "better"? Or is that also a matter of taste?

I have never had anyone discuss this issue, but when you think about it, the human figure is hardly "flat", so getting a good reproduction of it does not require a flat field of focus and in fact, I would theoretically be a disadvantage. I would suggest that the same would be true for most macro work.

Flat filed of focus lenses are important for devices like film projectors. Enlarger lenses would benefit from a flat field of focus as well. The only time a flat field of focus is important would be if one is photographing a flat object (reproducing a page of a book, for example). Even this is not 100% correct; my Leica Pradolux shipped with a lens that was designed to compensate for the curvature of a slide that would distort when heated by the high intensity light from the projector bulb.

[rpcrowe]

Agreed Bill, but the main difference is that macro lenses tend to have smaller maximum apertures, so you can't get that shallow DoF many portrait photographers look for. If you don't care about that, I agree, the macro lenses can be used to take excellent portraits.

I tend to use smaller apertures for indoor/studio portraits than I do with outdoor shots because I can usually control the background when shooting indoors, especially in a studio. Sometimes, outdoors, I want to eliminate a background when it is not particularly flattering.

BTW: I almost always use smaller apertures when shooting portraits of dogs indoors or out - because I want to get the dog's head generally in focus.

An important facet of a portrait lens is its ability to produce pleasing bokeh so that the OOF area of the image don't compete with the subject for the attention of the viewer. The number and curvature of the aperture blades can have a lot to do with the bokeh when you are shooting stopped down but, I have not noticed a great difference between a lens with say 9-rounded blades and a lens with fewer blades that are not rounded when you are shooting at the maximum aperture of the lenses.

Finally - at the risk of sounding racist (which I am not) I have noticed that shorter focal lengths (like 50-55mm on a full frame sensor) can be quite flattering to some Asian faces...

[pendennis]

For head and shoulder portraits, I usually went with a lens which had a focal length of 105mm (in 35mm format). That yields about 2x times the film diagonal. However, that was only a starting guideline. The subject always drove the focal length of the lens. A person with a longish nose, got no real benefit from a focal length such as 85-105mm. A woman, especially in her late 40's, to early 50's can be very self-conscious about her nose, many times thinking it was unattractive. The same goes for younger women who think their shortish noses are too short, too "pixie-ish"; those women were served best with a shorter focal length of 85mm, or less.

As an example - I used to do "before" and "after" photographs for a lady who sold Mary Kay cosmetics. She had parties where women would allow me to take their before and after photos. The before photos tended to have straight-on lighting, but the after usually turned into glamor shots.

A lady who was in her early 50's told me she had an ugly nose, and hadn't had a portrait done since high school. I took her aside, and advised that I could fix that with no problem. I guaranteed a beautiful portrait, or I would give her the negatives and prints, and she could destroy them if she liked. I was using an RB67, and I chose a 250mm lens (135mm in35mm). The longer focal length provided some image compression, and I also set the lights a bit lower, to move the shadow of her nose up a bit. The literal first words after seeing the results was, "What happened to my long nose?"

The result was the sale of a 16x20 portrait, and a number of 8x10's, 5x7's, and wallets. A few months later, I dropped in on her, and the 16x20 was prominently displayed in her den.

The selection of lenses for portraits is never set in stone.

[xpatUSA]

I would like to point out that the original post did not mention portraiture. For example, I also shoot tree trunk burls and other 3D objects like cars or buildings; only a few flat objects as a matter of fact.

So, it can be said these various lenses are simply exhibiting the rules of perspective (distortion) by forcing a change of shooting distance (for equal framing).

From that point of view, I agree with Manfred that a millimeter difference in focal length is generally insignificant.

[xpatUSA]

Originally Posted by xpatUSA What about the field of focus? Flat or curved for portraiture, which is "better"? Or is that also a matter of taste?

I have never had anyone discuss this issue, but when you think about it, the human figure is hardly "flat", so getting a good reproduction of it does not require a flat field of focus and in fact, I would theoretically be a disadvantage. I would suggest that the same would be true for most macro work.

I brought up the field of focus because the Petzval design has a much-lauded curvature whereas macro lenses as mentioned by Bill tend more to flat fields. Hence my question.

[Manfred M]

The Petzval is an ancient design and most of the out of focus effects are at the peripheral areas of the image circle and these effects are most noticeable when shot wide open or just stopped down. Shoot at smaller apertures and the swirling effects go away. The aim is to get the face sharp and other areas get soft and have strange out of focus patterns.

If you want to look at another strange portrait lens, look up the 90mm f/2.2 Leitz Thambar that was introduced in the mid-1930s. If you are feeling rich, the going price for one is in the order of $USD 6000. It makes the modern Lomo produced Petzvals look like a steal.

https://www.dpreview.com/samples/930...ar-m-90mm-f2-2

What both of these lenses have is a very 3-D look to the images that they produce. One commonly identified issue with the modern high resolution lenses with their 15+ elements is that some of the subtlety and dimensionality is lost in the name of sharpness. The less intense areas can get lost in spite of modern glass and anti-reflection coatings. This explains some of the popularity of old glass. These lenses may not be as sharp as modern ones, but they have interesting character.