Wednesday, October 18, 2017

Optical vs Filter "softness"

As I'm still somewhat obsessed with the topic of "softness" and trying to learn what I can, I thought I'd take a look at comparing the optical "softness" rendered by the Pentax 85mm f2.2 SMC Soft to the Nikon Nikkor 50mm f/1.8 AiS and 85mm f/1.8 K pre-Ai with two Nikkor soft filters numbers 1 and 2.

Here is the comparison (as always, follow the link, find the all sizes images, and look at this at 100 percent to see everything there is to see).  Please note that the second to last comparison should read "... Nikkor Soft 1".  The comparison will make more sense.

Pentax Soft and Nikkor Soft Filters

What I see is that the Nikon lenses with the Nikkor soft filters simply add softness to the image, just as we would expect.  The number 2 Soft filter is, again as expected, gives a stronger softness than the number 1 filter.  In terms of softness, the number 2 filter more closely approximates the Pentax lens when both lenses are shot wide open.

It may not be entirely clear by looking at the above comparisons that the Pentax 85mm f/2.2 SMC Soft distorts the image in ways that the Nikkors deliberately avoid.  I should, however, be clear that changes in the aperture affects the "sharpness" of the subject focused on to a greater degree than it does out of focus areas around the edges.

Further, as previously noted, the depth of field of the Pentax lens does not appear to change with aperture changes.  This behaviour is dramatically different from the Nikon lenses where the depth of field changes as the aperture changes.  This difference in depth of field behaviour should be clear in the above comparison.

To illustrate what I mean when I say the Pentax lens distorts the scene, here are two photographs that show the difference between the Pentax 85mm f/2.2 SMC Soft and the Nikon Nikkor 85mm f/1.8 K pre-Ai with a Nikkor number 2 Soft filter mounted on the front.  The level of "softness" is similar, but the way the images are rendered are very different.

Nikon Nikkor 85mm K f/1.8 Soft Filter #2
Nikon Nikkor 85mm f/1.8 K pre-Ai at f/1.8
with Nikkor #2 Soft filter

Pentax 85mm Soft f/2.2
Pentax 85mm f/2.2 SMC Soft at f/2.2

Wednesday, October 11, 2017

Out of Focus Rendition ~ a quick look at a few Nikkors and one Sony

Before the Strange Beasty Pentax 85mm f/2.2 Soft landed on my doorstep, I took a look at the out of focus rendition (OFFR) of various lenses that I have on hand.

Here is the incredibly boring but sufficient to the task scene.  It was taken with a Nikon Nikkor 85mm f/1.8 K pre-Ai shot wide open.

Nikon Nikkor 85mm f/1.8 K

Here is the comparison (follow the link and head to the files to select the largest, and then view it at 100 percent to clearly see what I will describe in just a moment).  All lenses were shot wide open.

Bokeh Studies

Organizing my comments by ranking these lenses from doughnut shaped OOFR to the smoothest -

  • Nikon Nikkor 50mm f/2 H pre-Ai
    [huge gap in OOFR]
  • Nikon Nikkor 50mm f/1.8 AiS
  • Nikon E-series 75-150mm f/3.5 AiS
  • Nikon Micro-Nikkor 55mm f/3.5 pre-Ai
  • Nikon Nikkor 135mm f/3.5 AiS
  • Nikon Nikkor 135mm f/2.8 pre-Ai
  • Sony 50mm f/1.8 SEL OSS
  • Nikon Nikkor 85mm f/1.8 K pre-Ai
  • Nikon Nikkor 105mm f/2.5 AiS
Looking at the old double gauss 50mm f/2 H OOFR I see what a Zeiss whitepaper on optical design described as over-corrected rendition.  Before I say the OOFR is "horrible" I would like to note that some people love the soap-bubble rendition.  Recently a manufacturer started selling lenses that deliberately give this effect, so who am I to judge?

What's interesting to me is that the more current implementation Nikon Nikkor 50mm f/1.8 AiS gives a much smoother OOFR (hence the previous note about a "huge gap in OOFR").  Looking at cross section diagrams of the two lenses (the f/2 vs the f/1.8) I see the classic double gauss implementation.  They look to be identical and I would've thought their performance to be more comparable, yet it's clearly not.

Further, if I'm correct in thinking about the cross section diagrams of the other lenses I compared here, all but one (the 75-150 E-series zoom) are in one form or another derivative double gauss designs.

If the goal is to find lenses that give smooth OOFR (that is to say, lenses that melt the OOFRs into creamy smoothness), then all but one (the Nikkor 50mm f/2 H) meet the criteria of "goodness".  The standout of the short, "standard" focal length lenses is the 50mm f/1.8 AiS.  It's OOFR is the best of any 50mm lens I've ever owned.  This one is a "keeper."

One surprise is the performance of the Micro-Nikkor 55mm f/3.5.  Yes, the aperture is somewhat small at f/3.5 so the depth of field is not razor thin when shot wide open.  Yet the OOFR is creamy smooth.  It's really quite interesting to see and might be very usable for shooting portraits where the nose and eyes are in focus.

Another surprise is the 75-150mm f/3.5 E-series zoom.  I read somewhere that this lens used to be a favorite of fashion photographers back in the day.  It was considered a "sleeper" lens, and I can see why.  This is a great lens for OOFR at _all_ apertures.  I don't understand it.  The aperture blades do not form a circle, yet the OOFR remains creamy and smooth all the way down thru f/11.  I'm not convinced Nikon designed the lens this way (it's cheap and not otherwise widely regarded), but the effect is clear.

The sharpest lens in the group when shot wide open is the 135mm f/3.5 Nikon Nikkor AiS.  Period.  There are not enough superlatives to explain just how brilliant the lens is.  The OOFR, however, is not quite as buttery-smooth as it's sister the f/2.8 135mm Q.

Stuck in the middle of all these Nikkors is a little Sony 50mm f/1.8 SEL OSS.  The link has disappeared, but there was a page out on the 'net that showed the Sony to be the equal of new Leica lenses.  Well, it's true (in my experience, at least).  The OFFR, too, is really quite outstanding.  For portraiture on APS-C Sony mirrorless this lens is a "keeper."

The 85mm f/1.8 K gives very nice OOFR and lightly "swirls" the background (ala Petzval).  I would've claimed it the winner in my OOFR comparison except for one lens.  And that lens is the 105mm f/2.5 AiS.  It is the smoothest-butteriest (how's that for making up  new words?) OOFR lens I currently own.  It's reputation appears to be well founded.

Prices on old manual focus lenses seem to be dropping.  Perhaps the market is finally saturated with lenses, new and old?  In any event, to stock up on optics to perform this comparison cost me very little.  The 50mm f/2 and f/1.8 lenses are commonly found for between 25Euro and 50Euro.  The 75-150mm E-Series, the 135mm f/3.5, and the 80-200mm f/4.5 lens (not compared here) were _all_ picked up in mint condition off eBay for around 40Euro each.  The 105mm f/2.5 AiS came as a trade for an 85mm f/1.8 H I had and cost me nothing.  The 135mm f/2.8 was very kindly given to me by a friend who picked up a Zeiss 135mm f/2.

In the end, this comparison is about finding many great lenses with wonderful OOFR, while, at the same time, costing next to nothing.

Monday, October 09, 2017

The Case of the Curious Optical Effect...

Something strange happened on the way to experiencing "softness" nirvana.  I've stumbled across an optical effect that I can't explain.

In optical designs I'm familiar with, "depth of field" increases as an aperture size is decreased (stopped down, as it were).  That's the commonly expected effect and is partly why lenses often come with aperture controls.

After looking at Jim Galli's soft focus large format images and thinking about how I might achieve similar effects in APS-C digital without returning to large format film, I stumbled across a small Pentax 85mm f/2.2 Soft in a Nikon F mount.  I'd never seen this lens in Nikon F, so I picked it up for not a huge sum of money.

Today I performed a quick comparison between the Pentax and my Nikon Nikkor 85mm f/1.8 K pre-Ai.  I was looking forward to shooting the Soft wide open and controlling the depth of field by stopping the aperture down a bit.

Looking at the comparisons and after the noting that the spherical aberrations decrease with aperture size (as expected), I noticed that the circle of confusion (said another way, the out of focus rendition) did not seem to change with the aperture.

What's going on here?  I have a mystery on my hands.  Perhaps one of my readers can help explain the optical effect?

Pentax 85mm f/2.2 Soft, Nikkor 85mm f/1.8 K Comparison

Here is a Nikkor "control" image where the 85mm f/1.8 K was shot wide open.

Nikon Nikkor 85mm f/1.8 K

Here is the Pentax 85mm f/2.2 Soft at f/2.2.  As you scroll through the images, look at the "size" of the out of focus bright area situated between the green plant in the center and the red flower just to the right.  You can also look at the "size" of the leaves in the background (upper left region).

Pentax 85mm Soft at f/2.2

Here is the Pentax 85mm f/2.2 Soft at f/2.8.

Pentax 85mm Soft at f/2.8

Here is the Pentax 85mm f/2.2 Soft at f/4.

Pentax 85mm Soft at f4

Here is the Pentax 85mm f/2.2 Soft at f/5.6.

Pentax 85mm Soft at f5.6