An unexpected optic: reversed Pentax Q 03 Fish-eye

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Thagomizer
Posts: 46
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

An unexpected optic: reversed Pentax Q 03 Fish-eye

Post by Thagomizer »

Hi all;

Having reversed SLR lenses (prime and zoom), and movie camera lenses for macro shooting, I have wondered, on and off, about reversing the Pentax Q 03 Fish-eye, https://www.pentaxforums.com/lensreview ... h-Eye.html, figuring that its short (3.2mm) focal length would produce even higher magnification than anything I'd yet tried reversing. I'd toyed with the idea for a while. Holding one up to my eye and looking through it in reverse, however, it was VERY dark. I really couldn't make out anything using this quick inspection method, so I didn't bother trying it for quite some time.

Eventually, curiousity got the better of me. So, I got a hold of one. I attached it to my Pentax KP using a 49mm reverse adapter, a 37-49mm step up ring, and some masking tape around the front barrel of the lens to keep it snug in the step up ring. No extension is necessary to get the image circle to fill the APS-C frame. (I don't know what would happen with full frame, though.)

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Working distance is very short. Horizontal field of view is less than 2mm on the APS-C sensor. Image below shows the space between a pair of millimeter marks on a metal ruler.

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Not that I'm any great judge of these things, but there seems to be little, if any, CA in the shots it produces. Sharpness in 100% crops isn't outstanding, but my test procedures aren't nearly as rigourous as most other members whose lens testing work I see on the forums here. Someone with better technique might be able to wring more IQ out of this lens than I can. These are also just single shots, so the tiny sliver of in focus image plane (of whatever quality) is buried within out of focus stuff in front of and beyond the plane of focus. Somebody using this for a stack would undoubtedly get more out of it than I can.

Here are some more images I took with it.

Knurled ring from the lens shown in the camera mount/working distance image above:

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Laser printed price tag toner droplets:

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Business card:

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Painted numeral from a camera lens barrel:

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And some less flat subjects. Whole wheat bread:

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Shield bug eye. Please pardon the dust!

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Here's a link to a thread on the Pentax Forums where I talk about this, including more images: https://www.pentaxforums.com/forums/136 ... ost4907222

Anyone who's already got this might want to try this out for themselves; buying one to play with wouldn't cost much.

Scarodactyl
Posts: 417
Joined: Sat Apr 14, 2018 10:26 am

Post by Scarodactyl »

Nice results, thanks for sharing this! Any chance of some 100% crops, just to get down to brass tacks/pixels?

Thagomizer
Posts: 46
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Post by Thagomizer »

Here you go! Results at 100% aren't anything to write home about.

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I still have to try out using this lens as the front element of an ultra wide macro relay lens. I'm hoping it will give better IQ than the cheap M12 board lenses I've seen used for this application. We'll see....

RobertOToole
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Joined: Thu Jan 17, 2013 9:34 pm
Location: United States
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Post by RobertOToole »

Interesting, I've always wondered about these little Pentax lenses, and you tried the fish-eye!

The downsized images good, the 100% crops don't hold up but thats okay.

Thanks for sharing the results.

Robert

Thagomizer
Posts: 46
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Post by Thagomizer »

RobertOToole wrote:Interesting, I've always wondered about these little Pentax lenses, and you tried the fish-eye!

The downsized images good, the 100% crops don't hold up but thats okay.

Thanks for sharing the results.

Robert
You're welcome! I was hoping for more, but you can't win 'em all. Next step is to try building a macro relay lens using it as the front end. I know I won't be expecting miracles with the 03, but I'm thinking that WA macro isn't quite as demanding as the high magnification workout I put it through.

Lou Jost
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Location: Ecuador
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Post by Lou Jost »

That was a fun experiment!

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