Setup for 1-2x at 300mm working distance?

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bokemon
Posts: 20
Joined: Sun Jan 16, 2022 6:06 pm
Location: Silicon Valley, CA

Setup for 1-2x at 300mm working distance?

Post by bokemon »

Hello folks,
I have an application to do live-view imaging at 1-2x magnification with as good resolution as possible and working distance of around 300mm. Since this will look thru glass of a few mm worth, it might limit the NA to around 0.2 or so before spherical aberrations start to kick in. (No, this is not the same as my other project utilizing Mitutoyo objectives at 5x and 10x)

What is the best setup or equipment to use for this? Is it just some camera lens, or is there more specialized equipment that doesn't cost > $1k? I think for 1x mag at 300mm, that means you need a 300mm focal length lens? I looked a bit at the "machine vision" C mount lenses, but they only go up to around 100mm. Yeah, you can use a sensor with small pixels, but I'm more worried if the lenses are of poor quality, since they all seem to be specc'd in terms of megapixels...

I already tested a setup using just an Olympus EM10ii camera (micro 4/3) with the "fantastic plastic" 40-150mm zoom lens plus a Raynox DCR150 in front. The Raynox is a little too powerful and limits the maximum focus distance to 200mm, but ok whatever, I can try a different close-up adapter. Anyway, this setup seemed to work relatively well and the nice thing is that the camera has an HDMI output that plugs straight into a monitor, so there's no need for a computer. I calculated out that given the sensor pixel size of 4um, the pixel resolution at the sample was around 5.5 um, and so it could image a 50 um grid very cleanly. Could not do the 10um grid, tho. Next I tried the same setup, but with my Panasonic 100-300mm lens. That could somewhat image the 10 um grid, but the image quality was clearly worse than "diffraction limited", and so I blame the lens. Maybe I get some old school manual 300mm prime? (And obviously not the BIG F4 ones since this setup needs to be reasonably compact)

I haven't tested with a piece of glass yet, but I assume if it causes problems, I would have to stop down the aperture. But would I be better off doing that via a front aperture stop instead of the aperture control in the lens itself, which is near the mount?

lothman
Posts: 951
Joined: Sat Feb 14, 2009 7:00 am
Location: Stuttgart/Germany

Re: Setup for 1-2x at 300mm working distance?

Post by lothman »

if you want a high NA and a large working distance then the lens diameter has to be big, see how much bigger the Mitutoyos are compared to "normal" microscope lenses with smaller working distance.

http://www.lmscope.com/en/Aufloesungsve ... pe_en.html

If there is a macro Lens with NA 0.2 and WD >300mm it will be for sure higher than 1k$ and big and heavy.

So a quality closeup lens on a quality tele lens seems the way to go. This will also keep you AF and automatic aperture.
Last edited by lothman on Fri Sep 16, 2022 11:54 am, edited 1 time in total.

Scarodactyl
Posts: 1616
Joined: Sat Apr 14, 2018 10:26 am

Re: Setup for 1-2x at 300mm working distance?

Post by Scarodactyl »

You could use a 300mm surgucal objective on a 100-300mm zoom lens focused at infinity. They are much like a closeup lens but somewhat nicer I suspe t. I use a 400mm on a 70-210 for jewelry photography and like it.
You can get one for like 100 bucks https://www.ebay.com/itm/185384590806
Last edited by Scarodactyl on Fri Sep 16, 2022 2:37 pm, edited 1 time in total.

JKT
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Joined: Fri Oct 28, 2011 9:29 am
Location: Finland
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Re: Setup for 1-2x at 300mm working distance?

Post by JKT »

Your NA is going to be considerably lower. NA=0.2 would equal f/2.45 if I'm not mistaken. For 300mm working distance that would require 122mm diameter from the front lens.

Fortunately you are not likely to need that NA. APS-C sensor with 32 MP would need about NA=0.12 for practically max resolution and FF sensor with 45 MP would need roughly NA=0.085. The first would take 70mm front lens and the second 50 mm front lens. Naturally you'd need rear lens that can handle those sizes as well.

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