Pentax Q with linear ultra-wide Theia SL183M 1.8-3mm f1.8 CS mount lens ?

2old4toys · 06-01-2021, 01:25 AM - **4 Likes**

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Using my DIY metal CS mount. Though apparently there is a C mount version of this lens too. At it’s 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!? What’s 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.

**PJ1** · 06-01-2021, 02:57 AM

Very interesting. That is the problem with the Q bodies - too many quirky lenses to try and just not enough time for them all!

photoptimist · 06-01-2021, 05:27 AM - **8 Likes**

Nice lens!

Originally posted by 2old4toys

I find it odd though, that the image is upside down on the LCD!? What’s 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.

**UncleVanya** · 06-01-2021, 05:51 AM - **1 Like**

Originally posted by photoptimist

The lens probably includes a relay lens inside it.

I learned something new! Thanks for the clear explanation.

**jumbleview** · 06-01-2021, 06:05 AM

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.

2old4toys · 06-01-2021, 11:09 PM - **1 Like**

Originally posted by photoptimist

The lens probably includes a relay lens inside it.

Wow. You know your stuff! Cheers for the fast explanation.

2old4toys · 06-12-2021, 08:55 AM - **4 Likes**

Q-S1 with the SL183 is a cctv lens covering 1.8mm to 3mm F1.8 It’s very very wide even when zoomed in. Wider even than the current crop of smartphones with their ultra-wide lenses. At it’s widest on a Q-S1, there is vignetting in the corners but next to none in the original Q’s 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.

Attached Images

View Picture EXIF

View Picture EXIF

cunesk8 · 07-22-2021, 02:40 AM

Does anyone have photo with this lens on Q7 on 3mm?

2old4toys · 07-29-2021, 04:29 AM

Originally posted by cunesk8

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 Q’s. More on that later.

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

This tech has been sent into space!

reh321 · 08-10-2021, 08:33 AM

Originally posted by 2old4toys

I will do a fresh one for you.

Where did you get this lens?
How much does it cost?

2old4toys · 08-10-2021, 07:14 PM - **1 Like**

Originally posted by reh321

Where did you get this lens?
How much does it cost?

EBay USA from seller e-uturn
I paid 65USD before shipping, though I think I was pretty darned lucky to land one for that price.

Edit* Looks like he still has a few left, see if you can negotiate a lower price

https://www.ebay.co.uk/itm/THEIA-SL183M-CS-Lens-1-8-3MM-F1-8-Pro-4K-Manual-I...-127632-2357-0

Adding my pic from same location at dusk which I like better than the earlier one I attached here.

Hi @cunesk8 I have PM’d you a photo taken with this lens at 3mm on a QS-1 which is same sensor size as a Q7. I don’t have a Q7 myself (yet…)

**spiffariffic** · 09-22-2021, 09:20 PM

Hmmmmmmm. This is very cool but I am very, VERY much not handy enough to cobble together my own mount. I'd manage to ram a screwdriver through the camera somehow. Or a hand.

Could I use a CS to C adapter on this and then a regular C adapter on the Q? The CS to C adapters exist and are cheap.

06-01-2021, 01:25 AM - 4 Likes	#1
2old4toys Pentaxian Join Date: Jan 2018 Posts: 391	Pentax Q with linear ultra-wide Theia SL183M 1.8-3mm f1.8 CS mount lens ? Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here. Using my DIY metal CS mount. Though apparently there is a C mount version of this lens too. At it’s 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!? What’s 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, 05:27 AM - 8 Likes	#3
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,123	Nice lens! Originally posted by 2old4toys I find it odd though, that the image is upside down on the LCD!? What’s 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

07-29-2021, 04:29 AM	#9
2old4toys Pentaxian Join Date: Jan 2018 Posts: 391 Original Poster	Originally posted by cunesk8 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 Q’s. More on that later. In the mean time, for anyone interested in the Theia optical linear distortion crushing technologies… I found a subjectivity interesting presentation posted a couple of months ago on Vimeo. This tech has been sent into space! Vimeo

08-10-2021, 07:14 PM - 1 Like	#11
2old4toys Pentaxian Join Date: Jan 2018 Posts: 391 Original Poster	Originally posted by reh321 Where did you get this lens? How much does it cost? EBay USA from seller e-uturn I paid 65USD before shipping, though I think I was pretty darned lucky to land one for that price. Edit* Looks like he still has a few left, see if you can negotiate a lower price https://www.ebay.co.uk/itm/THEIA-SL183M-CS-Lens-1-8-3MM-F1-8-Pro-4K-Manual-I...-127632-2357-0 Adding my pic from same location at dusk which I like better than the earlier one I attached here. Hi @cunesk8 I have PM’d you a photo taken with this lens at 3mm on a QS-1 which is same sensor size as a Q7. I don’t have a Q7 myself (yet…) Last edited by 2old4toys; 08-10-2021 at 07:38 PM.

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06-01-2021, 02:57 AM	#2
PJ1 Loyal Site Supporter Join Date: Jul 2012 Location: Toowoomba, Australia Photos: Gallery \| Albums Posts: 5,484	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, 05:51 AM - 1 Like	#4
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,403	Originally posted by photoptimist 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
jumbleview Site Supporter Join Date: May 2012 Location: Concord, CA Posts: 1,069	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
2old4toys Pentaxian Join Date: Jan 2018 Posts: 391 Original Poster	Originally posted by photoptimist The lens probably includes a relay lens inside it. Wow. You know your stuff! Cheers for the fast explanation.

07-22-2021, 02:40 AM	#8
cunesk8 New Member Join Date: Jun 2009 Location: orlová CZech republic Photos: Gallery Posts: 27	Does anyone have photo with this lens on Q7 on 3mm?

08-10-2021, 08:33 AM	#10
reh321 Pentaxian Join Date: Nov 2014 Location: South Bend, IN, USA Photos: Gallery \| Albums Posts: 23,180	Originally posted by 2old4toys I will do a fresh one for you. Where did you get this lens? How much does it cost?

09-22-2021, 09:20 PM	#12
spiffariffic Site Supporter Join Date: Sep 2021 Location: Tucson, AZ Posts: 13	Hmmmmmmm. This is very cool but I am very, VERY much not handy enough to cobble together my own mount. I'd manage to ram a screwdriver through the camera somehow. Or a hand. Could I use a CS to C adapter on this and then a regular C adapter on the Q? The CS to C adapters exist and are cheap.