Our lab is using a Zeiss 20X water immersion lens (Item no.: 421452-9800-000) in a custom light-sheet microscope, and I was trying to perform some simulations of the point spread function (PSF).
I searched for the patent of this lens, and potentially found something relevant at the German patent office (Application No. 10 2005 051 025.6). In this patent, Table 3 describes a 20X water-immersion objective lens with a 1.0 NA and 2.149 mm working distance. I’m copying this table here for your reference:
I have used the ZOS-API to populate this data into OpticStudio (code below) to potentially avoid copy/paste mistakes. Then, I made the following changes to my file (that I will also attach to my post):
- Thickness of Surface 0: 2.149 mm (the working distance)
- Material of Surface 0: SEAWATER
- Aperture Type: Object Space NA (dummy STOP on Surface 1)
- Aperture Value: 1.0
- Telecentric Object Space
- Afocal Image Space
- 3 Fields, uniform Object Height along Y between 0.0 and 0.2 mm
- F, d, C (Visible) wavelength preset
And this is the result:
My problem is that the OPD Fan shows huge differences, above 50 waves, and the main aberration seem to be spherical. I was told long time ago that Zeiss used to balance some of the objective lens aberrations on the tube lens in a way that you’d have to buy both lenses from them (you couldn’t just get the objective lens and buy your tube lens elsewhere). But even if that were the case, I suspect I’m making a mistake somewhere. I also know that SEAWATER might not be the material that they used in the patent, but they also don’t specify which one they used. On the plus side, it seems that the STOP is located before the last doublet, or at least that’s where the rays seem constricted.
In the patent, they also show different tube lens design to be used with the objective lenses. I believe Table 4 is the corresponding tube lens, but when I use it, it gets even worst, so I thought it would be easier to troubleshoot the objective lens alone first.
Does anybody have any idea what I might be doing wrong, and how I could improve this design?
Thank you for your help and take care,
PS: its not polished, but for those interested this is the code I used after pasting the Patent data into a text file and correcting some abnormalities with whitespaces appearing before some minus signs
# Open text file
patent_text = open(filepath)
# Read every line in the text file
patent_text = patent_text.read().splitlines()
# Insert surfaces at index (surfaces appear before the specified surface)
insert_surface = 2
# Create a Model Glass solve
Surface_1 = TheSystem.LDE.GetSurfaceAt(1)
ModelGlass_Solve = Surface_1.MaterialCell.CreateSolveType(ZOSAPI.Editors.SolveType.MaterialModel)._S_MaterialModel
# Loop over every line and modify the OpticStudio file
for line in patent_text:
# Split the data at every line (or surface)
patent_surface_data = line.split()
# Insert new surface
surface = TheSystem.LDE.InsertNewSurfaceAt(insert_surface)
# Change surface radius
surface.Radius = float(patent_surface_data)
# Change surface thickness
surface.Thickness = float(patent_surface_data)
# Change surface material
# Change Model Glass parameters
ModelGlass_Solve.IndexNd = float(patent_surface_data)
ModelGlass_Solve.AbbeVd = float(patent_surface_data)
# Apply solve
# Update insert surface index
insert_surface += 1
I can’t see any problems in what you’ve done. I checked the LDE against the patent -- looks right. I optimized the lens with the first airspace (working distance) variable -- the OPD reduced to 10 waves, still terrible. Wondering if it could be for a 160mm tube, I optimized for a focal image space with front and back airspaces variable -- the optimum air spaces were inconsistent with a valid tube length and the OPD still terrible.
Perhaps the prescription give in the patent isn’t correct.
Thank you for taking the time to double-check what I did. It seems like I’m not completely crazy yet. I will try some of the other embodiements described in the patent and keep the post updated.
I don’t think my answer should be marked as best just yet, or the question marked as solved.
In my mind, you are such a figure in the field that I didn’t think about it when I got your answer. I don’t seem to be able to un-solve the questeion yet though. Perhaps
@Sandrine Auriol can do it?
No worries, David. I didn’t realize it was you that marked it solved. I’ve never known how that happened. As for me, I’m not so sure! Now if it was an answer from Mark . . . .
I doubt this is the main issue but have you tried to figure out which actual materials are being used by Zeiss?
I think the Model Index formula OpticStudio uses breaks down for some of the surfaces, especially S2 (nd=1.597, vd=35.0) which is extremely far off the standard glass map line and S4/S6/S10/S12 which have an Abbe above 80 (from the Help Files...”The Abbe number also is limited to the range of roughly 20 to 80”).
Patent literature is a minefield, and I have little confidence in the data presented. I really doubt the glass data in particular...specifying just two of the three model glass parameters is naughty but it gets past the patent examiners.
If you do cntl-Z on the model glasses OpticStudio will find the nearest equivalent from the currently loaded glass catalog(s) with any template attached. I’d then try a Hammer with the radii and thicknesses fixed and the glasses set to substitute...worth a try.
Thank you for the great suggestions! I was clearly too optimistic when I finally found the patent. I will definitely play around with the materials and see if it leads anywhere. I’ll keep this post updated!
I’ll toss a few thoughts into the ring…
First, I also agree with Michael and Mark that the limited model glass specification (just index and Abbe number, with no partial dispersion) is likely part of the problem. Note that the patent actually lists ne and Ve (not the more conventional nd and Vd) -- not sure if that will matter too much if you are going to Hammer on the glass choice anyway.
Second, it may very well be the case that the tube lens called out in the patent is needed to have the entire optical path work properly. I wouldn’t necessarily assume that the objective design by itself can be glass-tweaked to become diffraction limited. I would try both together with glass optimization. If that works, then a next step could be separate optimization.
Lastly, I think patent designs often try to obfuscate the details, not so much that the patent has a problem getting through examination, but enough so that a direct copy of the design doesn’t work very well. If I were going to try and hide some details, then the glass specification (or lack thereof) is obvious low-hanging fruit, but so is the number of significant digits for values in the parameter table. Rounding values to lower precision may also be part of the problem.
I removed the “Best answer” tick.
And thanks again for all the suggestions. It really shows the strength of this community. I’ve tried to incorporate all that was discussed into the file I’m sharing with this reply.
And this is the result:
I’m attaching my file for reference. This is definitely much better than what I could ever come up with before. For the most off-axis field, the Strehl ratio comes at about 0.7.
Can I ask you if there is something else you’d try, such as varying the thicknesses, to refine this design? I’m already quite happy about it and I think I can run my tests, but I’m just oblivious as to whether this is close to the “intended” design or not.
Thanks for all the help again, and I wish you a great week,
That’s excellent work David.
If your goal is to get as close as you can to the Zeiss implementation then that’s probably as good as it gets. If you just want the best possible performance, you can continue to refine the design.
Personally, I use patent designs as starting points for further optimization for all the reasons we’ve discussed.
My goal is to get relatively close to the Zeiss implementation, and as you said, I’ll probably stop here. My next step is to study the point spread function through a simulated specimen. Although those specimen are fairly transparent, I suspect a significant difference in refractive index with the surrounding immersion medium, and I’m curious to visualize it in my simulations.
It’s hard to pick a best answer, everybody has been really helpful. I strongly suggest whoever is reading this to go through the topic in its entirety.
Thanks all again, and take care,
@David.Nguyen ! I’ll have a chat with Allie as we don’t have any specific locations for such files but that could be interesting indeed! I’ll get back to you.