[ivanvernon]

I received my 6x7 55-100 yesterday and quickly took a couple of test shots out the backyard. I also compared it with the same composition at the same settings with the 645 80-160 zoom and both at 100mm. The time between the two test shots was as quick as I could swap lenses on the 645z, I am fairly fast at swapping lenses. At first I did my customary pixel peeping and found that the 55-100 is indeed a bit sharper than the 80-160, but only marginally sharper. Also keep in mind these are handheld shots, so I would call it a preliminary observation.

However, when I got my head out of the pixels, I saw something I have never seen before. The mountains in the background show a lot more detail, I'm tempted to say, yet both showed the same detail, just with the 55-100 the detail is much more pronounced. I tried to recreate the same effect with the 80-160 in post, but could not get even close. This is a first time revelation for me to see the dramatic difference between two high-end lenses and the one outperforming the other to this extent.

If any of you had observed the same kind of difference with lenses, please share, because as I've said this is a very new and very pleasant discovery. Perhaps the veil has been lifted for me for the first time.

Here are the two pictures. I cropped out the foreground to bring attention to the mountain. BTW, I saw the same "popping" effect in other areas of the same picture, especially the greens with high contrast. The jpgs uploaded with this message dulled the difference somewhat compared to what I saw on my screen.

The first picture is the 80-160 and the second is the 55-100

Thanks for sharing this. The differences clearly favor the 67/55-100. I really like this lens.

[kaseki]

I received my 6x7 55-100 yesterday and quickly took a couple of test shots out the backyard. I also compared it with the same composition at the same settings with the 645 80-160 zoom and both at 100mm. The time between the two test shots was as quick as I could swap lenses on the 645z, I am fairly fast at swapping lenses. At first I did my customary pixel peeping and found that the 55-100 is indeed a bit sharper than the 80-160, but only marginally sharper. Also keep in mind these are handheld shots, so I would call it a preliminary observation.

However, when I got my head out of the pixels, I saw something I have never seen before. The mountains in the background show a lot more detail, I'm tempted to say, yet both showed the same detail, just with the 55-100 the detail is much more pronounced. I tried to recreate the same effect with the 80-160 in post, but could not get even close. This is a first time revelation for me to see the dramatic difference between two high-end lenses and the one outperforming the other to this extent.

If any of you had observed the same kind of difference with lenses, please share, because as I've said this is a very new and very pleasant discovery. Perhaps the veil has been lifted for me for the first time.

Here are the two pictures. I cropped out the foreground to bring attention to the mountain. BTW, I saw the same "popping" effect in other areas of the same picture, especially the greens with high contrast. The jpgs uploaded with this message dulled the difference somewhat compared to what I saw on my screen.

The first picture is the 80-160 and the second is the 55-100

If I didn't know about the quick lens change, I would have at a glance believed that the aerosol level changed between images. What I see on the 80-160 lens assembly image is either contrast degradation due to lens surface haze, or a different power spectral density (PSD) function causing the high-frequency contrast to degrade at a bit lower frequency than for the 55-100. The improved mountain detail on the 55-100 looks to me to also be true of the closer window details, leaving a light scatter due to aerosols argument in the dust.

[texandrews]

I received my 6x7 55-100 yesterday and quickly took a couple of test shots out the backyard. I also compared it with the same composition at the same settings with the 645 80-160 zoom and both at 100mm. The time between the two test shots was as quick as I could swap lenses on the 645z, I am fairly fast at swapping lenses. At first I did my customary pixel peeping and found that the 55-100 is indeed a bit sharper than the 80-160, but only marginally sharper. Also keep in mind these are handheld shots, so I would call it a preliminary observation.

However, when I got my head out of the pixels, I saw something I have never seen before. The mountains in the background show a lot more detail, I'm tempted to say, yet both showed the same detail, just with the 55-100 the detail is much more pronounced. I tried to recreate the same effect with the 80-160 in post, but could not get even close. This is a first time revelation for me to see the dramatic difference between two high-end lenses and the one outperforming the other to this extent.

If any of you had observed the same kind of difference with lenses, please share, because as I've said this is a very new and very pleasant discovery. Perhaps the veil has been lifted for me for the first time.

Here are the two pictures. I cropped out the foreground to bring attention to the mountain. BTW, I saw the same "popping" effect in other areas of the same picture, especially the greens with high contrast. The jpgs uploaded with this message dulled the difference somewhat compared to what I saw on my screen.

The first picture is the 80-160 and the second is the 55-100

Well....that's a surprise. # 2 definitely has more clarity imo.

[RICHARD L.]

Slightly higher contrast and better U.V. management, maybe ...

Regards

[RICHARD L.]

Both pictures were taken handheld and @ f/11. The first image was taken just before sundown at 55 mm FL and the second one at sunset at 100 mm FL. Both are quite sharp with great color and contrast. Only drawbacks are the weight and the fact you must never forget to focus precisely. Colors seem to be on the cool side (bluish) though.

P.S. I had to slightly crop the first picture of the flour mill, so the proportions of the frame appear a little different (sorry).

[Ed Hurst]

Milford Sound May 2018 - Missing travelling...

Z and 28 -45

Absolutely smashing shots from Fiordland, Paul. I keep meaning to go back there, but haven't managed to get around to it since having kids. It's definitely a priority as soon as I can, and your wonderful shots have only further stoked the fires!

[TDvN57]

If I didn't know about the quick lens change, I would have at a glance believed that the aerosol level changed between images. What I see on the 80-160 lens assembly image is either contrast degradation due to lens surface haze, or a different power spectral density (PSD) function causing the high-frequency contrast to degrade at a bit lower frequency than for the 55-100. The improved mountain detail on the 55-100 looks to me to also be true of the closer window details, leaving a light scatter due to aerosols argument in the dust.

Thanks for the technical explanation, I will run some more tests when time permits with this in mind. But first I need to research more about the details in your explanation.

I did find Ed Hurst's caution about getting focus right to be spot-on, thanks Ed. I have a split focus screen in my 645z which makes the near to mid range a little easier. For objects at abt 100m distance I found the focus to be close to infinity on the focus ring and very sensitive to get right. A small touch and the focus is out.

[Ed Hurst]

Thanks for the technical explanation, I will run some more tests when time permits with this in mind. But first I need to research more about the details in your explanation.

I did find Ed Hurst's caution about getting focus right to be spot-on, thanks Ed. I have a split focus screen in my 645z which makes the near to mid range a little easier. For objects at abt 100m distance I found the focus to be close to infinity on the focus ring and very sensitive to get right. A small touch and the focus is out.

Glad to have been of some help, Theuns! I did find it to be a challenge, but it's a lens that hugely rewards care in this department... At first, I achieved a low-ish success rate with the lens and was beginning to doubt its potential before discovering what the problem was...

[TDvN57]

What I see on the 80-160 lens assembly image is either contrast degradation due to lens surface haze, or a different power spectral density (PSD) function causing the high-frequency contrast to degrade at a bit lower frequency than for the 55-100.

I did a bit of reading on power spectral density and it appears that each lens, or perhaps lens batches or even perhaps types will have their own PSD characteristics.

This brings a totally new variable into the selection of lenses. I doubt that any lens manufacturer would publish this data and a calibrated measurement of each lens does not seem practical.

I wonder if the comparison between the f stop and t-stop values might be a layman's check to come to the same conclusion as a full psd analysis. I know these are two totally different issues, but sometimes some unrelated characteristics very in unison with others under similar conditions. Or perhaps best yet is just take a picture and compare to a known reference. :-)

Kaseki, any thoughts on this?

[RICHARD L.]

Test of my old 67 Pentax 55-100 mm f/4.5 zoom on a digital 645Z. Results are overwhelming : very sharp when correctly focused, no flare, no ghosting, excellent contrast but somewhat cold color rendition (less warm than current 645 lenses).

[mattb123]

One from this morning. Fall foliage is just getting going here.
645D & FA 80-160

[StephenMerola]

Nice shot Matt. Great colors.

[mattb123]

Nice shot Matt. Great colors.

Thanks! I'm hoping they stick around for a little while. I have some shots planned before they fall!

[kaseki]

I did a bit of reading on power spectral density and it appears that each lens, or perhaps lens batches or even perhaps types will have their own PSD characteristics.

This brings a totally new variable into the selection of lenses. I doubt that any lens manufacturer would publish this data and a calibrated measurement of each lens does not seem practical.

I wonder if the comparison between the f stop and t-stop values might be a layman's check to come to the same conclusion as a full psd analysis. I know these are two totally different issues, but sometimes some unrelated characteristics very in unison with others under similar conditions. Or perhaps best yet is just take a picture and compare to a known reference. :-)

Kaseki, any thoughts on this?

I let some EE drift into OE. It would be better to think in terms of modulation transfer function MTF, which is a non-statistical (deterministic) measure of the same thing. The EE PSD has an abscissa of cycles per second, or radians per second; the MTF (at the focal plane) abscissa is cycles per mm. One can download from Kodak, for example, the MTF (by color) of films such a Portra. One can read up on MTF of spatial filtering, such as the array we are sensing with -- a sinc-squared function, as I recall. There is an MTF equation for diffraction. There is an MTF for the lens assembly that certainly varies with zoom and f/no. The lens assembly MTF can be measured with a decent optical bench, a Nikon autocollimator, and a focal plane microscope, for example. What I was trying to hint at was there are a lot of differently shaped MTF functions that pass the value 0.5 at the same spatial frequency, so they appear to have the same nominal bandwidth, but may yield images of varying character. This is also true of the 90% and the 10% points.

The product of the MTF functions is the overall MTF of the entire image chain. Camera processing and post processing can further modify the overall MTF shape.

Sometimes magazines make such measurements and report them. I recall such a source in Germany that reported on film scanners, and maybe other things.

For a technical description, the lowest price unused source I can think of, besides the Internet, is Edward O'Neill's Introduction to Statistical Optics, reprinted by -- who else -- Dover Books.

A less hairy, or maybe equally hairy but less grad student level would be the likely out-of-print Digital Image Processing, by Wm. Pratt.

As I recall, T-stop is just F-stop with transmission included. Unless the effect in the images is due to a lot of internal scattering, I wouldn't expect the T-stop differences between lens assemblies to inform us much about high spatial frequency resolution.

On top of all this, it occurs to me that auto focus systems (including one's eyes and brain) might maximize contrast in different ways that could move focus from where the finest detail contrast is maximized to where some other spatial frequency contrast is maximized. And this effect could be MTF shape dependent.

[tuco]

A blast from the past. Some shots during the Son Of Pitch race.
Pentax 6x7, 67 200/4

The running leg of the course.
TX 6043 Gen Trix-X





After a leg of running with the wind, the contestants drop their spinnakers, raise their head sails, round the mark and get a tuned airfoil shape set on the main/head sails going as fast as possible.

PXP 6057 Gen Plus-X