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Mirrorless Pro-Class Cameras with Interchangeable Lenses Sony A7, A7R and similar high end cameras that can serve as the sole cameras on Pro-event assignments.

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  #1  
Old February 2nd, 2018, 09:22 AM
Asher Kelman Asher Kelman is offline
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Default Adapting Fine Vintage Lenses!

We are used to the wonderful flexibility of Sony A7 series cameras being able to take most any lenses you own, and that has been a blessing to so many of us.

I myself have saved Pentax, Leica, Canon FD and assorted other great lenses and adapted them successfully to the A7R.

Today I have the Fuji GFX camera and just one f4.0 32-64mm lens.

So I purchased a Contax/Yashica adapter by Fotodiox. If fits perfectly and I can now any C/Y lens.

Here I started with the "Anniversary" 28mm f 2.0 lens and tried it first, hand hold at night in the Eaterly restaurant balcony in Century City, where the salmon is the freshest and delciously cooked!

A packed table of happy celebrating women adjacent to us needed a group picture so I, of course stood up and took that phone so they could all be in the picture.

It turned out they were all from Manahattan Beach, further south from Los Angeles and knew my "Puff of Wind Sculpture" and so we made friends! They have been close for decades, playing tennis together and sharing good times with their growing families.

Then I snapped some quick shots with the contax 28 mm. I cannot remember what setting, but I beleive it was at 5.6, pretty wide open for a MF camera.

The illumination was so uniform all over the field, so I had to burn in the corners and edges a tad to get the result below. No sharpening applied.





Asher Kelman: The Tennis Players

Fuji GFX 50S
Fotodiox C/Y - GFX Adapter
Contax Anniversary 28mm 2.0
1/13 sec, ISO 1600
Corners "burnt in" CC PS 2018



For 1/13 second this is acceptable!

I need to test it with daylight too, with smaller aperture and more reasonable shutter speed!

Enjoy


Asher
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  #2  
Old February 3rd, 2018, 12:32 AM
Asher Kelman Asher Kelman is offline
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Let me qualify this salute to a vintage lens, the superb Contax 28mm 2.8, "Anniversary edition. Using it in poor light hand held with no flash is not the best way of leveraging this lens nor of doing photography. Frankly, in poor light, with manual focus one should better use a cell phone as one will get more keepers snapping away.

If one has the time to carefully focus and support the camera, the pictures will be rewarding.

However, walking around a in poor light and taking grab shots as I would with an AF lens, my success rate 10% at best.

So don't get carried away by my romanatacism towards MF vintage lenses for photographing in the worst light.

Asher
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  #3  
Old February 3rd, 2018, 02:26 PM
Stephen Sepan Stephen Sepan is offline
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Cool Medium Format manual-focus lenses

I took a turn at using a number of Mamiya 645 (Sekor C) and Pentax 6x7 lenses on my FF and crop-sensor cameras (adapted) in addition to their native film bodies.
As you indicate, it works best with patience and discipline (and a tripod ;-) ) but it sure can be rewarding when it works out.
I have since sold the MF film bodies, and some of the lenses, but kept a few to play with on my Nikons.

Steve
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Old March 26th, 2018, 03:26 PM
Dr Klaus Schmitt Dr Klaus Schmitt is offline
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Congrats Asher,
I'm ogeling the GFX50 too, but unfurtunately quite afew lenses I have won't deliver the needed image circle....hmmm
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  #5  
Old March 26th, 2018, 06:49 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Dr Klaus Schmitt View Post
Congrats Asher,
I'm ogeling the GFX50 too, but unfurtunately quite afew lenses I have won't deliver the needed image circle....hmmm
Any suggestions for vintage lenses able to match the 50MP and the coming 100MP update reportedly coming this year.

I getting doesn’t bother me unless I am atritching or photographing something that has to be entirely uniform, such as a work of art.

I wonder how I could adapt my Cooke PS945 4x5 229mm lens? Has its own shutter!

I guess I would need bellows! Well there’s an adapter available for 4x5 cameras with a Graok back, so it’s doable! The 35mm camera equivalent field of view would be about 188mm! But we would only use a fraction of that real estate!

Asher
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  #6  
Old March 27th, 2018, 06:48 AM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
We are used to the wonderful flexibility of Sony A7 series cameras being able to take most any lenses you own, and that has been a blessing to so many of us.

I myself have saved Pentax, Leica, Canon FD and assorted other great lenses and adapted them successfully to the A7R.

Today I have the Fuji GFX camera and just one f4.0 32-64mm lens.

So I purchased a Contax/Yashica adapter by Fotodiox. If fits perfectly and I can now any C/Y lens.

Here I started with the "Anniversary" 28mm f 2.0 lens and tried it first, hand hold at night in the Eaterly restaurant balcony in Century City, where the salmon is the freshest and delciously cooked!

A packed table of happy celebrating women adjacent to us needed a group picture so I, of course stood up and took that phone so they could all be in the picture.

It turned out they were all from Manahattan Beach, further south from Los Angeles and knew my "Puff of Wind Sculpture" and so we made friends! They have been close for decades, playing tennis together and sharing good times with their growing families.

Then I snapped some quick shots with the contax 28 mm. I cannot remember what setting, but I beleive it was at 5.6, pretty wide open for a MF camera.

The illumination was so uniform all over the field, so I had to burn in the corners and edges a tad to get the result below. No sharpening applied.
A charming shot!

Indeed the ever so slight burning in of the corners seems very apt here.

By the way, I have for some while wanted to commend you for the very nice way you often place the shooting data below the image caption. The typeface size and color are just right.

Still, compared to your mention in the following post, it is not clear if the maximum aperture of this vintage lens is [f/]2.0 or [f/]2.8.

Best regards,

Doug
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  #7  
Old March 27th, 2018, 06:54 AM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

you say:
Quote:
Originally Posted by Asher Kelman View Post
I wonder how I could adapt my Cooke PS945 4x5 229mm lens? Has its own shutter! . . . The 35mm camera equivalent field of view would be about 188mm! But we would only use a fraction of that real estate!
I don't understand the part I have highlighted in blue. Are you saying that a field of view of ff35e 188 mm is too large to embrace your imagined subjects, so you would often crop the images significantly? Or what?

Best regards,

Doug
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  #8  
Old March 27th, 2018, 01:52 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Doug Kerr View Post
Hi, Asher,

you say:

43.8mm x 32.9mm
I don't understand the part I have highlighted in blue. Are you saying that a field of view of ff35e 188 mm is too large to embrace your imagined subjects, so you would often crop the images significantly? Or what?

Best regards,

Doug
The recordable portion of the actual “field of view“ of any lens mounted on a 4x5 camera is limited to a maximum of the fixed area of 4x5”. That maximum is achievable today only by use of a sheet of 4x5 film and then that it turn is much larger than the sensor area of the Fuji GFX camera.

The sensor size here is just 43.8mm x 32.9mm, 1441.02 sq mm, or 2.23 sq inches. That is just 2.23/20 of the real estate of image in the film plane 4x5 camera!!

Stopped down, the lens is very sharp. Wide open, f4, I believe, the periphery lens glass brings in light to focus in a way that adds the flourish of angels glow to an ultra sharp image. Even then, some of that quality might be lost as the more peripheral light, (from the outer part of the lens mounted on the front of the 4x5 camera body), is going to be obstructed, in part, by the throat of the camera lens mount, which forms the mouth of a recess at the depth of which is the smaller GFX sensor. So to some extent, there’s a penumbra caused by the recess walls. This will rob the edges of the GFX sensor more than the center. So we might see less of the gentle “dust of angels” and the special “soft focus” magic of the bespoke Cooke PS945 lens.

Asher
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  #9  
Old March 27th, 2018, 02:27 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
The recordable portion of the actual “field of view“ of any lens mounted on a 4x5 camera is limited to a maximum of the fixed area of 4x5”. That maximum is achievable today only by use of a sheet of 4x5 film and then that it turn is much larger than the sensor area of the Fuji GFX camera.
So you mean that you will only be using part of the image circle generated by that lens. Of course. But the size of that image circle is not is not a corollary to that lens' focal length, or of the field of view that focal length gives for any given frame size (not larger than its image circle).

Quote:
The sensor size here is just 43.8mm x 32.9mm, 1441.02 sq mm, or 2.23 sq inches. That is just 2.23/20 of the real estate of image in the film plane 4x5 camera!!
Sure.

Quote:
Stopped down, the lens is very sharp. Wide open, f4, I believe, the periphery lens glass brings in light to focus in a way that adds the flourish of angels glow to an ultra sharp image. Even then, some of that quality might be lost as the more peripheral light, (from the outer part of the lens mounted on the front of the 4x5 camera body), is going to be obstructed, in part, by the throat of the camera lens mount, which forms the mouth of a recess at the depth of which is the smaller GFX sensor. So to some extent, there’s a penumbra caused by the recess walls. This will rob the edges of the GFX sensor more than the center. So we might see less of the gentle “dust of angels” and the special “soft focus” magic of the bespoke Cooke PS945 lens.
Interesting.

Thanks.

Best regards,

Doug
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  #10  
Old March 27th, 2018, 02:56 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Doug Kerr View Post
Hi, Asher,


So you mean that you will only be using part of the image circle generated by that lens. Of course. But the size of that image circle is not is not a corollary to that lens' focal length, or of the field of view that focal length gives for any given frame size (not larger than its image circle).



Sure.



Interesting.

Thanks.

Best regards,

Doug

Yes, I tried to read to my wife, my explanation to you and her eyes glazed over, well before I got past mention of the sensor size in mmm!

So you did very well reading it all!

Asher
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  #11  
Old March 27th, 2018, 02:58 PM
Jerome Marot Jerome Marot is offline
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Quote:
Originally Posted by Asher Kelman View Post
Stopped down, the lens is very sharp. Wide open, f4, I believe, the periphery lens glass brings in light to focus in a way that adds the flourish of angels glow to an ultra sharp image. Even then, some of that quality might be lost as the more peripheral light, (from the outer part of the lens mounted on the front of the 4x5 camera body), is going to be obstructed, in part, by the throat of the camera lens mount, which forms the mouth of a recess at the depth of which is the smaller GFX sensor.
We are talking about a 229mm focal length lens of symmetrical design, 4 elements, f/4.5. The GX lens mount is not going to matter.
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  #12  
Old March 27th, 2018, 04:06 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
We are talking about a 229mm focal length lens of symmetrical design, 4 elements, f/4.5. The GX lens mount is not going to matter.
Jerome, are you saying that the glow effect when the entire surface of the lens is used wide open, is not derived from the extra light from the lens perimeter?

It is my understanding that it is designed to have sharp focus from the center glass and the edge glass provides the glow.

If we drop the sensor down a tube, then the penumbra caused by the walls of the sink hole should preferential y block the light from the edges of the lens.

Where might I be in error?

Asher
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  #13  
Old March 27th, 2018, 10:56 PM
Jerome Marot Jerome Marot is offline
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Quote:
Originally Posted by Asher Kelman View Post
Jerome, are you saying that the glow effect when the entire surface of the lens is used wide open, is not derived from the extra light from the lens perimeter?

It is my understanding that it is designed to have sharp focus from the center glass and the edge glass provides the glow.

If we drop the sensor down a tube, then the penumbra caused by the walls of the sink hole should preferential y block the light from the edges of the lens.

Where might I be in error?
The "tube" is actually pretty short and does not prevent the sensor to view the edges of the lens.
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  #14  
Old March 27th, 2018, 11:41 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
The "tube" is actually pretty short and does not prevent the sensor to view the edges of the lens.
Well, Jerome,

I have a lot of experience using my Canon Eos camera on a shift attachment for the 4x5 camera and there are major penumbra issues from the walls of the “tube” at the bottom of which the Eos sensor sits.

This penumbra effect is very significant and each peripheral plfrane has to have the dark shadow area cropped before stitching.

Is there some reason why it would be so different on the Fuji GFX?

For sure, with a single frame centered in the image plane of the 4x5 there would be trivial penumbra!

The GFX May have well somewhat less penumbra than the Eos, but I am sure it will be very signicant at the sides of the 4x5 field.

Asher
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  #15  
Old March 28th, 2018, 02:03 AM
Jerome Marot Jerome Marot is offline
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If you shift, you increase the possibility of penumbra. You did not say you inteded to shift on the GFX.
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  #16  
Old March 28th, 2018, 11:22 AM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post

If we drop the sensor down a tube, then the penumbra caused by the walls of the sink hole should preferential y block the light from the edges of the lens.

Where might I be in error?
If the interior of the tube is cylindrical, it is not the walls of the tube that might block peripheral rays but rather its mouth (the wall around the entrance of the "tunnel").



The item labeled "throat" of course represents the "tube" under discussion, in an ideal form.

This blocking is more prominent for image points farther from the center of the image (for example, blocking of the rays shown in red vs. of those shown in blue).

Best regards,

Doug
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  #17  
Old March 28th, 2018, 12:45 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
If you shift, you increase the possibility of penumbra. You did not say you inteded to shift on the GFX.
Jerome,

Consider, even if you do not shift, there will be a punumbra as the Large Format lens, at full aperture, has a greater active diameter than the small GFX sensor, which, by the way, is recessed and so the throat edges block some rays.

Asher
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  #18  
Old March 28th, 2018, 02:22 PM
Jerome Marot Jerome Marot is offline
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Quote:
Originally Posted by Doug Kerr View Post

Nice drawing of mechanical vignetting but, in reality, the tube is 8 times shorter than the sensor-lens distance. Lens is a 229mm focal length and register distance is 26,7 mm. Mount diameter is 65mm, which is wider than the lens aperture.

Quote:
Originally Posted by Asher Kelman View Post
Consider, even if you do not shift, there will be a punumbra as the Large Format lens, at full aperture, has a greater active diameter than the small GFX sensor
The lens is at 229mm distance from the sensor and its aperture diameter is 51mm (derived from the f/4.5 aperture), which is about the same size as the sensor (55mm). Besides, what you were interested is spherical aberration (the so-called "glow" effect) and that is indeed a consequence of peripheral rays but is not really changed by obstructions at the sensor side.
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  #19  
Old March 28th, 2018, 02:36 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
Nice drawing of mechanical vignetting but, in reality, the tube is 8 times shorter than the sensor-lens distance. Lens is a 229mm focal length and register distance is 26,7 mm. Mount diameter is 65mm, which is wider than the lens aperture.



The lens is at 229mm distance from the sensor and its aperture diameter is 51mm (derived from the f/4.5 aperture), which is about the same size as the sensor (55mm). Besides, what you were interested is spherical aberration (the so-called "glow" effect) and that is indeed a consequence of peripheral rays but is not really changed by obstructions at the sensor side.
Jerome,

Thanks for your insight. Could you apply your thoughts to use of an Eos camera instead, (with the same lens), as I know that causes dark shadows at the periphery of the 4x5 field!

Asher
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  #20  
Old March 28th, 2018, 03:01 PM
Jerome Marot Jerome Marot is offline
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Quote:
Originally Posted by Asher Kelman View Post
Thanks for your insight. Could you apply your thoughts to use of an Eos camera instead, (with the same lens), as I know that causes dark shadows at the periphery of the 4x5 field!
I suppose you mean "at the periphery of the 24x36mm field". Quite simply, the tube is narrower and longer. Or the adapter for mounting the EOS on the view camera is poorly designed, that also happens.
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  #21  
Old March 28th, 2018, 03:37 PM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
I suppose you mean "at the periphery of the 24x36mm field". Quite simply, the tube is narrower and longer........
Thanks Jerome,

Yes those points are true, but let’s put the Eos sensor at the sides of the 4x5 film plane. That is where gross totally dark shadows appear in the last 3 lateral shifts away from the center of the 4x5 film plane.

From this experience, I would expect to have similar issues with the GFX.

There are available sliding adapters for Eos, which I already have, and coming soon in stock, hopefully, for the GFX too.

The solution for the Eos on 4x5 is to have more overlapping shots and crop away the underexposed edges as needed.

Asher
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  #22  
Old March 28th, 2018, 10:57 PM
Jerome Marot Jerome Marot is offline
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Quote:
Originally Posted by Asher Kelman View Post
Yes those points are true, but let’s put the Eos sensor at the sides of the 4x5 film plane. That is where gross totally dark shadows appear in the last 3 lateral shifts away from the center of the 4x5 film plane.
Certainly. I said earlier "If you shift, you increase the possibility of penumbra. You did not say you intended to shift on the GFX."

What are we discussing in this thread? I thought we were discussing the 229mm f/4.5 large format lens mounted without shift on a GFX and that you feared that the "glow" from spherical aberration would be influenced by the "tube" formed by the GFX mount. If you want to discuss the effect of other combinations, which ones do you have in mind?
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  #23  
Old March 29th, 2018, 01:23 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
Certainly. I said earlier "If you shift, you increase the possibility of penumbra. You did not say you intended to shift on the GFX."

What are we discussing in this thread? I thought we were discussing the 229mm f/4.5 large format lens mounted without shift on a GFX and that you feared that the "glow" from spherical aberration would be influenced by the "tube" formed by the GFX mount. If you want to discuss the effect of other combinations, which ones do you have in mind?
Exactly, Jerome!

Yes, talking of existence of shadows at edges doesn’t tell us about the “glow” the lens is noted for. We consider it valuable but I guess it can also be called an aberration like the whirls and bubbles of wide open OOF bokeh! But I do not know the optical design basics that leads to this Cooke famous glow!

I can deal with simple “vignetting” or edge shadows, but I wondered what would happen to the glow?

If someone knows the optics that cause this, then that would be interesting to be able to predict the effect! I did not look for that effect with the Canon mounted, as I was doing table top still life. But I need to try this with bright window light, (as soon as I can get the GFX adapter), and a portrait where one expects this effect.

Asher
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  #24  
Old March 29th, 2018, 08:41 AM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
Yes, talking of existence of shadows at edges doesn’t tell us about the “glow” the lens is noted for. We consider it valuable but I guess it can also be called an aberration . . .
In fact, it is the result of an aberration, spherical aberration, in fact.

Any simple lens with the usual spherical surfaces exhibits this aberration. It prevents the generation of "sharp" images by preventing the rays from a point on the object that pass through different portions of the lens from ever coming together at a singular point. Much of the complexity of multi-element lenses is to minimize it.

But of course it can also be appreciated, even "cultivated", for work in which a certain kind of departure from complete "sharpness" is artistically desired.

Now, how this comes about in the lens design under discussion I don't know (others here are better equipped to discuss this than I).

Best regards,

Doug
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  #25  
Old March 29th, 2018, 10:03 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Doug Kerr View Post
Hi, Asher,



In fact, it is the result of an aberration, spherical aberration, in fact.

Any simple lens with the usual spherical surfaces exhibits this aberration. It prevents the generation of "sharp" images by preventing the rays from a point on the object that pass through different portions of the lens from ever coming together at a singular point. Much of the complexity of multi-element lenses is to minimize it.

But of course it can also be appreciated, even "cultivated", for work in which a certain kind of departure from complete "sharpness" is artistically desired.

Now, how this comes about in the lens design under discussion I don't know (others here are better equipped to discuss this than I).

Best regards,

Doug


Thanks Doug!

What I understood was that the lens stopped down is excedingly sharp, but that the edges contribute a crafted set of de-focus glow in addition, like the gentle brush of angels!

Or simply, there’s an angel assigned to each Cooke PS945 lens and she deftly adds her splash of glowing dust whenever the lens is used full open!

Asher
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  #26  
Old March 29th, 2018, 10:34 AM
Jerome Marot Jerome Marot is offline
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Actually, I noted that the "glow" is the effect of spherical aberration, see e.g. message #18...

The cooke PS945 lens is supposed to be "4 elements in 2 air-spaced doublets". This is not the historical cooke portrait lens, which used 3 elements:


but would probably be based on a double Gauss design. The double Gauss design has normally little spherical aberration, but that aberration can be increased by departing from the standard design, of course. It is known to have some residual oblique spherical aberration, which may be what the cooke PS945 uses for peripheral fuzz.

Spherical aberration can be used for pictorial effects, so some lenses (like the original "cooke portrait lens" above) intentionally added some. I actually own a lens, the Minolta 100mm soft focus, for which spherical aberration can be varied for dreamy effects.

Spherical aberration increases with aperture, so it can be reduced by simply stoping down, which is what the cooke PS945 suggests.

The photographic effect of spherical aberration is, in a nutshell, to add a second defocussed image mixed with the main sharp image. One can actually do that with photoshop and a get similar effect. The "glow" corresponds to the defocussed image. There are a few other benefits: spherical aberration will appear to increase depth of field and may improve bokeh. All these effects made that aberration sought after by pictorialists at the turn of last century.

The problem with modern cameras is that their sensors are far too tiny (even the GFX!). The effects of spherical aberration are relatively easy to use on large formats, less so on smaller formats. It is extremely difficult not to overdo the effect on small formats. Last but not least, your PS945 lens appears to be optimized for large format, with aberrations that are optimal at the edge of a large format negative, which is far outside your smaller sensor.
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  #27  
Old March 29th, 2018, 11:16 AM
Asher Kelman Asher Kelman is offline
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Quote:
Originally Posted by Jerome Marot View Post
Actually, I noted that the "glow" is the effect of spherical aberration, see e.g. message #18...

The cooke PS945 lens is supposed to be "4 elements in 2 air-spaced doublets". This is not the historical cooke portrait lens, which used 3 elements:


but would probably be based on a double Gauss design. The double Gauss design has normally little spherical aberration, but that aberration can be increased by departing from the standard design, of course. It is known to have some residual oblique spherical aberration, which may be what the Cooke PS945 uses for peripheral fuzz.

Spherical aberration can be used for pictorial effects, so some lenses (like the original "cooke portrait lens" above) intentionally added some. I actually own a lens, the Minolta 100mm soft focus, for which spherical aberration can be varied for dreamy effects.

Spherical aberration increases with aperture, so it can be reduced by simply stoping down, which is what the cooke PS945 suggests.

The photographic effect of spherical aberration is, in a nutshell, to add a second defocussed image mixed with the main sharp image. One can actually do that with photoshop and a get similar effect. The "glow" corresponds to the defocussed image. There are a few other benefits: spherical aberration will appear to increase depth of field and may improve bokeh. All these effects made that aberration sought after by pictorialists at the turn of last century.

The problem with modern cameras is that their sensors are far too tiny (even the GFX!). The effects of spherical aberration are relatively easy to use on large formats, less so on smaller formats. It is extremely difficult not to overdo the effect on small formats. Last but not least, your PS945 lens appears to be optimized for large format, with aberrations that are optimal at the edge of a large format negative, which is far outside your smaller sensor.
Jerome,

Great! Our lines of thought meet and you believe that I may have trouble finding the glow in the center with a single frame on the GFX sensor. That is what I feared! But I will test that, as now I have a clearer set of question to organize into a shoot when I get the equipment which has been promised but not yet is stock, AFAIK!

Back to the forbears of the modern Cooke PS945. It is based on the English Company hinted at in the letters “PS”, namely “Pinkham & Smith”. The lens in particular is the now rare highly sought after Pinkham & Smith Visual Quality Series IV #2 portrait lens. Cooke made their new lens to come apart and accommodate a “modern” Copal shutter with a flash synch connection!

Asher
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Old March 29th, 2018, 11:30 AM
Asher Kelman Asher Kelman is offline
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Jerome, Doug and others,


Here is a video by Eddie Gunks on the observable build of the Pinkham & Smith Visual Quality lens series IV used as the model for the Cooke PS 945 f4.5.

Also, of more interest here are pictures from such treasured original P&S vintage lenses!

Enjoy!

Asher
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Old March 29th, 2018, 02:46 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post

What I understood was that the lens stopped down is excedingly sharp, but that the edges contribute a crafted set of de-focus glow in addition, like the gentle brush of angels!
Well, in fact, the deleterious effect of the "classical" spherical aberration (which we get in ample degree just by using a simple lens with spherical surfaces) increases as we try to increase exposure by introducing into the game rays traveling through the lens at greater and greater distances from the optical axis.

Basically, in a lens uncorrected (or even incompletely corrected) for spherical aberration, as we consider the rays from a point on the object entering the lens farther and farther away from the optical axis, they converge in space closer and closer to the lens compared to the convergence of rays entering the lens near the optical axis, which we think of as "ideal" behavior. (Perversely, those entering the lens at the optical axis do not converge at all, so we must deal "in the limit".)

Thus, the phenomenon can be ameliorated by "stopping down".

Now of course, just as not all bokeh (for a given set of shooting parameters) "looks the same", various ways of executing (incomplete) correction for spherical aberration can have a substantial effect on the appearance of the artifacts of the residual spherical aberration, and although I'm not at all familiar with the field, I'm sure there has been a great deal of work to play this instrument to produce the effects that one or another subcamp will see as "desirable".

It is of course lovely to metaphorically think that these more and more errant rays can be employed as glowing dust on their brushes by angels (preferably with large breasts).

Best regards,

Doug
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Old March 29th, 2018, 03:09 PM
Jerome Marot Jerome Marot is offline
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Not quite the same, but this is a picture taken with the Minolta 100mm Soft Focus lens, to show the effect of increased spherical aberration:


On that particular lens, there is a slider to increase or decrease spherical aberration, to give a "soft focus" effect.
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