The PhotonsToPhotos Optical Bench

A forum to ask questions, post setups, and generally discuss anything having to do with photomacrography and photomicroscopy.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

bclaff
Posts: 7
Joined: Thu Feb 09, 2023 1:35 pm
Location: Near Boston USA

The PhotonsToPhotos Optical Bench

Post by bclaff »

Rather than side-track at least two other threads I am starting a thread regarding the PhotonsToPhotos Optical Bench.

The Optical Bench is a 2D ray tracer that handles most rotationally symmetrical lenses.
It does not currently handle Diffractive Optical Elements (DOEs).

The primary function of the Optical Bench is educational and screen shots are used heavily in the PhotonsToPhotos Optics Primer.

But the Optical Bench has practical uses and some of those relate to close up photography.

There are over 8000 optical prescriptions in the Optical Bench but I recommand sticking with the approximately 1100 that are in the Optical Bench Hub.
The Hub contains likely or closely related optical prescriptions for production lenses.

The optical prescriptions come from examples in patents. Those examples rarely have complete information.
For example element diameters are not often given and the aperture stop (diaphragm) is often omitted.

Group motion is never specified so the Focus and Zoom capability in the Optical Bench is interpolation between known states.

Be aware that pupils are rarely flat. Pupil magnification is reported on the optical axis.
You may get a very different value by dividing P'D by PD as reported on the Positions line.

At other than Infinity Numeric Aperture (NA) is computed from the angle the marginal ray makes with the image side focus point.
Then f# is computed from NA.

I'm sure there are other caveats so this thread is a good place to ask.

rjlittlefield
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Re: The PhotonsToPhotos Optical Bench

Post by rjlittlefield »

Bill, welcome aboard. It's really nice to have the author of that great tool chime in!
bclaff wrote:
Thu Feb 09, 2023 2:28 pm
At other than Infinity Numeric Aperture (NA) is computed from the angle the marginal ray makes with the image side focus point.
Then f# is computed from NA.
I'm curious: why is infinity handled differently? It seems like tracing the marginal rays and doing the same calculation works for infinity also.

--Rik

bclaff
Posts: 7
Joined: Thu Feb 09, 2023 1:35 pm
Location: Near Boston USA

Re: The PhotonsToPhotos Optical Bench

Post by bclaff »

rjlittlefield wrote:
Thu Feb 09, 2023 2:56 pm
bclaff wrote:
Thu Feb 09, 2023 2:28 pm
At other than Infinity Numeric Aperture (NA) is computed from the angle the marginal ray makes with the image side focus point.
Then f# is computed from NA.
I'm curious: why is infinity handled differently? It seems like tracing the marginal rays and doing the same calculation works for infinity also.
I think that f#=1/(2*NA) depends on a well corrected lens and we can't always count on that.
So while I thought that the best approach for other than Infinity I chose to use the object side entrance pupil diameter and measured focal length when Magnification is zero.
I also suspect this is better behaved for a wide variety of lenses.
FWIW, diaphragm diameter (AD on the Positions line) is rarely provided. I compute that by ray tracing for the specified focal length and f#.

bbobby
Posts: 67
Joined: Sat Jan 15, 2022 12:40 pm
Location: Indianapolis, IN

Re: The PhotonsToPhotos Optical Bench

Post by bbobby »

Just yesterday I was checking your website to see if my measurements are roughly the same with what you got in your data base. The particular lens I am testing in the moment is Canon EF 180mm f3.5 L Macro... Canon never updated it and I was wondering why and decided to investigate further... anyway, I see in the list 2 Canon lenses, so my question is what exactly is "Canon 180mm f/3.5 IF macro" - some prototype?
180 list.png
Also I see on your home page this:
Data is measured from raw files taken to my specifications and contributed by people from around the world.
If you are willing to help please email me for further information.
Maybe you can share what files you need? In my testing I am on my 2nd copy (out of 4 or 5) and I am using for the tests Canon 5DS R, Sony A7r4 and Olympus E-M1 Mark II and I do not mind taking few additional pictures and send you the RAW files... I am sure some other people will do the same... I can also email, of course, if you cannot share the information here...

rjlittlefield
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Re: The PhotonsToPhotos Optical Bench

Post by rjlittlefield »

bclaff wrote:
Thu Feb 09, 2023 3:13 pm
FWIW, diaphragm diameter (AD on the Positions line) is rarely provided. I compute that by ray tracing for the specified focal length and f#.
Ah! So now I'm intensely curious...

I own a Canon lens that I have always seen described as "EF 100mm f/2.8L Macro IS USM", for example at https://www.usa.canon.com/shop/p/ef-100 ... cro-is-usm .

I have always assumed that this is the same lens the Optical Bench calls "Canon 100mm f/2.92 IF os macro (Canon EF100mm f2.8L Macro IS USM".

If not computed on the basis of the optical design, where does the f/2.92 come from?

--Rik

bclaff
Posts: 7
Joined: Thu Feb 09, 2023 1:35 pm
Location: Near Boston USA

Re: The PhotonsToPhotos Optical Bench

Post by bclaff »

bbobby wrote:
Thu Feb 09, 2023 3:46 pm
Just yesterday I was checking your website to see if my measurements are roughly the same with what you got in your data base. The particular lens I am testing in the moment is Canon EF 180mm f3.5 L Macro... Canon never updated it and I was wondering why and decided to investigate further... anyway, I see in the list 2 Canon lenses, so my question is what exactly is "Canon 180mm f/3.5 IF macro" - some prototype?
180 list.png
There are many many optical prescriptions given in patents as examples to illustrate the patent claim. Most are never produced even as prototypes.
In that list it's only a production lens is the produced lens name is shown in parentheses.
bbobby wrote:
Thu Feb 09, 2023 3:46 pm
Also I see on your home page this:
Data is measured from raw files taken to my specifications and contributed by people from around the world.
If you are willing to help please email me for further information.
Maybe you can share what files you need? In my testing I am on my 2nd copy (out of 4 or 5) and I am using for the tests Canon 5DS R, Sony A7r4 and Olympus E-M1 Mark II and I do not mind taking few additional pictures and send you the RAW files... I am sure some other people will do the same... I can also email, of course, if you cannot share the information here...
PhotonsToPhotos is probably best known for sensor testing.
If you have a camera that is not already listed (for example in the Photographic Dynamic Range chart) then I'd be interested in gathering data.

bclaff
Posts: 7
Joined: Thu Feb 09, 2023 1:35 pm
Location: Near Boston USA

Re: The PhotonsToPhotos Optical Bench

Post by bclaff »

rjlittlefield wrote:
Thu Feb 09, 2023 3:52 pm
Ah! So now I'm intensely curious...

I own a Canon lens that I have always seen described as "EF 100mm f/2.8L Macro IS USM", for example at https://www.usa.canon.com/shop/p/ef-100 ... cro-is-usm .

I have always assumed that this is the same lens the Optical Bench calls "Canon 100mm f/2.92 IF os macro (Canon EF100mm f2.8L Macro IS USM".

If not computed on the basis of the optical design, where does the f/2.92 come from?
Values on the Specified line (eg. that 2.92) come from the patent. In this case US 7,864,451 Example 1
US7864451B2snip.png
Here are some more details:
US7864451B2values.png
From Specified 100mm / 2.92 = 34.25mm (rounded)
AD of 26.920mm was computed so that PD is 34.25mm (see Positions line)
The ray tracer measured focal length of 100mm and f# of 2.92 (see Measured line)
In this case things worked out quite well.

bclaff
Posts: 7
Joined: Thu Feb 09, 2023 1:35 pm
Location: Near Boston USA

The PhotonsToPhotos Optical Bench Figures

Post by bclaff »

There is a subtle but important difference between the Optical Bench and the Optical Bench Hub
The background figure for the Optical Bench is the patent Figure. For example Canon EF100mm f2.8L Macro IS USM (Optical Bench)
snip.png
But here is the Canon EF100mm f2.8L Macro IS USM (Optical Bench Hub)
snap.png
Note that this background figure is from Canon.
Furthermore, sometime the Hub version is tweaked for aperture stop placement, flare stops, etc.
Generally the Hub is preferred for production lenses.

rjlittlefield
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Re: The PhotonsToPhotos Optical Bench

Post by rjlittlefield »

bclaff wrote:
Thu Feb 09, 2023 5:47 pm
From Specified 100mm / 2.92 = 34.25mm (rounded)
AD of 26.920mm was computed so that PD is 34.25mm (see Positions line)
The ray tracer measured focal length of 100mm and f# of 2.92 (see Measured line)
In this case things worked out quite well.
OK, I think I understand. Because the aperture diameter is not specified for many designs, you take the f# from the patent application as an input, and use that to infer what the aperture diameter must be. Then you use the aperture diameter plus ray-tracing to figure out the NA and effective f# for other conditions. If the lens is well corrected, then if you measured NA in the infinity configuration, you should find that NA=1/(2*f#). That would be an interesting cross-check, particularly if for some reason the calculation did not match the measurement.

For this particular lens, the patent itself does specify the aperture diameter, as line 15 (Stop) in the table on page 18/20 of the PDF HERE. The aperture diameter listed in the patent is "26.92", which matches Really nicely with your computed value of 26.920 . As you say, in this case things worked out quite well!

I am still a little puzzled by what it means to say that "The ray tracer measured ... f# of 2.92 (see Measured line)".

If that means the ray tracer found the angles of the marginal rays and the listed f# was computed from those angles, then you've already done the cross-check and in fact NA was computed in the infinity case even though it was not printed out.

What am I missing in this thinking?

--Rik

bclaff
Posts: 7
Joined: Thu Feb 09, 2023 1:35 pm
Location: Near Boston USA

Re: The PhotonsToPhotos Optical Bench

Post by bclaff »

rjlittlefield wrote:
Thu Feb 09, 2023 6:57 pm
bclaff wrote:
Thu Feb 09, 2023 5:47 pm
From Specified 100mm / 2.92 = 34.25mm (rounded)
AD of 26.920mm was computed so that PD is 34.25mm (see Positions line)
The ray tracer measured focal length of 100mm and f# of 2.92 (see Measured line)
In this case things worked out quite well.
OK, I think I understand. Because the aperture diameter is not specified for many designs, you take the f# from the patent application as an input, and use that to infer what the aperture diameter must be. Then you use the aperture diameter plus ray-tracing to figure out the NA and effective f# for other conditions. If the lens is well corrected, then if you measured the NA in the infinity configuration, you should find that NA=1/(2*f#). That would be an interesting cross-check, particularly if for some reason the calculation did not match the measurement.

For this particular lens, the patent itself does specify the aperture diameter, as line 15 (Stop) in the table on page 18/20 of the PDF HERE. The aperture diameter listed in the patent is "26.92", which matches Really nicely with your computed value of 26.920 . As you say, in this case things worked out quite well!

I am still a little puzzled by what it means to say that "The ray tracer measured ... f# of 2.92 (see Measured line)".

If that means the ray tracer found the angles of the marginal rays and the listed f# was computed from those angles, then you've already done the cross-check and in fact NA was computed in the infinity case even though it was not printed out.

What am I missing in this thinking?

--Rik
In this case, because the patent specified the effective diameter of the stop I used that instead of solving with ray tracing.
So perhaps this wasn't the ideal example.
As it turns out the optical prescription doesn't quite do f/2.92 because the effective diameter of surface 12 (and maybe 13 and 14) is insufficient.
However, to two decimal places it works out.

The ray tracer measures the focal length and also PD. (Actually everything on the Measured line (duh))
The "exact" measurements give 99.99574843204789mm / 34.24588174999998mm = 2.9199349913671866 :D

I don't perform the cross-check you suggest.

rjlittlefield
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Re: The PhotonsToPhotos Optical Bench

Post by rjlittlefield »

Just repeating what I think I'm hearing...

So, f# on the "Measured" line is always calculated from ray-tracing measurements, but at infinity it's a different calculation, FL/PD, where for other cases it is 1/(2*NA).

Thanks for your patience!

--Rik

bclaff
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Location: Near Boston USA

Re: The PhotonsToPhotos Optical Bench

Post by bclaff »

rjlittlefield wrote:
Thu Feb 09, 2023 8:31 pm
Just repeating what I think I'm hearing...

So, f# on the "Measured" line is always calculated from ray-tracing measurements, but at infinity it's a different calculation, FL/PD, where for other cases it is 1/(2*NA).
Correct. You got it.
rjlittlefield wrote:
Thu Feb 09, 2023 8:31 pm
Thanks for your patience!
No problem. I started the thread to clarify things. This dialog is just what I had in mind.

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