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06-01-2021, 01:25 AM - 4 Likes   #1
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Pentax Q with linear ultra-wide Theia SL183M 1.8-3mm f1.8 CS mount lens ?



Using my DIY metal CS mount. Though apparently there is a C mount version of this lens too. At itís widest 1.8mm it covers the Q sensor without crop. Can focus to infinity fine and also can focus super close to the front element. Manual aperture slider. I find it odd though, that the image is upside down on the LCD!? Whatís up with that?

Unlike many other wide C and CS lenses, it is nice that this one is not fisheye, but linear instead.

Waiting for an occasion to use this.

https://www.theiatech.com/ultra-wide-lenses

Someone tried this lens on a Q a while back. Video samples.
https://www.youtube.com/playlist?list=PL7gw6kMEMn1rqzImygaaDL18OXbQNRrPn


Last edited by 2old4toys; 06-01-2021 at 02:19 AM.
06-01-2021, 02:57 AM   #2
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Very interesting. That is the problem with the Q bodies - too many quirky lenses to try and just not enough time for them all!
06-01-2021, 05:27 AM - 8 Likes   #3
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Nice lens!

QuoteOriginally posted by 2old4toys Quote
I find it odd though, that the image is upside down on the LCD!? Whatís up with that?
The lens probably includes a relay lens inside it.

Normally a UWA requires lens elements that are extremely close to the sensor. For a lens that goes to a focal length of 1.8mm, the rear element would be significantly less than 1.8mm from the sensor. But that's not possible for C-mount/CS-mount due to the flange focal distance of 17.526 mm and 12.526 mm respectively.

Some UWAs use a retrofocus design to stretch the focusing point of the image further back. But retrofocus has it's limits. A 4X retrofocus (e.g., used to put a 12mm UWA on a 46 mm mount like Pentax K) wouldn't be enough for the Theia. The Theia lens needs something more like a 9 or 10X stretch to be compatible with C-mount.

For a really long stretch, lens designers use a relay lens. In a relay lens, the image from the main lens comes to a focus inside the lens barrel and then the relay lens captures the focused image rays and sends them further on. In doing so, the relay lens inverts the image relative to what the main lens created. For extremely long stretched lenses such as endoscopes and borescopes, the long pipe of the lens has a series of relay lenses.

Last edited by photoptimist; 06-01-2021 at 06:53 AM. Reason: typos
06-01-2021, 05:51 AM - 1 Like   #4
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QuoteOriginally posted by photoptimist Quote

The lens probably includes a relay lens inside it.
I learned something new! Thanks for the clear explanation.

06-01-2021, 06:05 AM   #5
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It would be nice know how it behaves on Q-7 sensor. Given crazy prices on 08 lens nowadays I am in search of manual lens wider than 5 mm.
06-01-2021, 11:09 PM - 1 Like   #6
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QuoteOriginally posted by photoptimist Quote
The lens probably includes a relay lens inside it.
Wow. You know your stuff! Cheers for the fast explanation.
06-12-2021, 08:55 AM - 4 Likes   #7
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Q-S1 with the SL183 is a cctv lens covering 1.8mm to 3mm F1.8 Itís very very wide even when zoomed in. Wider even than the current crop of smartphones with their ultra-wide lenses. At itís widest on a Q-S1, there is vignetting in the corners but next to none in the original Qís smaller sensor.
Softer than the Q 08 lens of course but I love how wide it is, can be had at USD75 if you are lucky.

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07-22-2021, 02:40 AM   #8
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Does anyone have photo with this lens on Q7 on 3mm?
1 Day Ago   #9
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QuoteOriginally posted by cunesk8 Quote
Does anyone have photo with this lens on Q7 on 3mm?
I will do a fresh one for you.

I just picked up a Theia 9mm - 40mm f1.5 that I am playing with now on my Qís. More on that later.

In the mean time, for anyone interested in the Theia optical linear distortion crushing technologiesÖ I found a subjectivity interesting presentation posted a couple of months ago on Vimeo.

This tech has been sent into space!


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