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Comment by throwanem | Hacker News Reader

I bet medium-format 1:1 macro lenses are spendy, though.

Only if they're fast. Slow objectives would get by with lenses from e.g. regular eyeglasses arbitrary-aspheric production lines. It only gets expensive (>1000$) when you need fancy glass elements (or manage to waste a lot of money on inefficient R&D... computers are really good these days, and at least for fixed-focus prime lenses (you want 1:1, right?) the parameter space is fairly small.

I can highly recommend [0] for some reading on how simple optics can be if you can optimize aspherics for a fixed focus. Just to state the obvious: two identical infinity-focused objectives can be placed with the infinity-corrected sides looking straight towards another, for a physically long 1:1 macro "lens".

I wonder if there is a decent topology for a decently-high-NA reflective objective in the 1:1 to 1:10 (object:sensor) magnification range. And also whether some of those topologies would cope with a (sensor-sized) reflective spatial light modulator (LCoS/DLP would seem most practically relevant) in place of the sensor.

I still get that mouth-watering imagination when thinking about direct digital (maskless) photolithography, as the flexibility is enormous, especially regarding rapid prototyping of highly integrated circuits (350 nm is the limit for single-patterning using aluminium-coated MEMS modulators (aka TI's DLP technology), due to the UV reflectivity drop below 400 nm and thermal limits of the MEMS device).

[0]: https://www.telescope-optics.net/

The back to back infinity-focussed objective set up works nicely with 2 sets of cheap infinity microscope objectives 2x or 4x back to back in a thorlabs tube. Paired lenses cancel out a lot of aberrations (but not all of them). I use this setup regularly for fairly close up, highly planar projective work. For 'low magnifications' say 2:1 and up the Edmunds 2X, 0.15 NA, Ultra Compact Objective has decent price/performance, but this is for sensors in the 1/1.8 - 1" range. If you come up with a nice, planar, cheapish 1:1 design for large sensors, drop me a line. (Disclaimer - not an optics person, but peered into the fascinating rabbit hole)

What numerical aperture and image circle are we talking about? 0.15 NA leaves a lot on the table (at least 0.6 NA objectives can be had for still-decent prices).

But I'd probably look at a Zeiss Planar style design.

In general, a 3/5-element design (achromat/apochromat) should do the trick I think, provided you have access to arbitrary aspherics. And in case you can accept a shift in focal length with wavelength (like monochromatic photolithography would), a single symmetric element should be up to the task, unless I'm missing something.

Thanks, we are pretty low budget. Image circles are in the 1/3", 2/3" range and we are looking at patterns with say 5 to 50 um pitch on a flat planar object, monochromatic, we control illumination, standard 3.45 um pixels (so 1k to 5kish). We have a decent small design with two elements (good planarity, ok resolving and ok ish depth of field are what we care about). But we also sometimes look at larger frame (aps-c and up) and are also interested in smaller (eg VGA Omnivision type tiny module but with a decent planar macro lens e.g. f= 4 or 6mm, for 0.5 or 1x mag would be interesting). We do imager based metrology at the sub um and nm level

Yeah, sounds like a normal https://en.wikipedia.org/wiki/Double-Gauss_lens from BK7 or so should do the trick. You'd have significant chromatic abberation, but with monochromatic illumination that's not a problem.

This would just be 4 normal lenses, afaik. And you should be able to reach around 100 mm image circle I guess with the low NA you get away with at that relatively low resolution.

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