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09-30-2012, 06:42 AM   #1
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Wide angle C mount lenses?

Has anyone tried any of the really wide angle C mount lenses?

For example:

CCTV LENS - 2.5MM Wide-Angle Lens C-Lens - Spysonic

Also, has anyone ever seen any adapters for M12 board mount lenses to Pentax Q mount? I believe this lens is a board mount but it would be fun to try on the Q.

COP L017S Mini Lens 1-7mm Ultra Wide Angle Lens Fish Eye View | COP

Thanks,

Shawn

09-30-2012, 07:35 AM   #2
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Be careful with that first one - "CS-mount" has a different (smaller) flange focal distance than C-mount (12.5mm vs. 17.5mm), so the C-mount adapter shown probably has additional glass in it to compensate, further degrading whatever image quality the original lens had. You'd be better off finding (?) a CS-Q mount adapter and using it that way, since the Q has a flange distance of 9.2mm. However, I've never seen a CS to Q adapter but here is an option...

The rule of thumb is that you can adapt a lens with a larger flange focal distance with a simple extension and almost no degradation, but lenses with a smaller native flange distance are next to impossible. Hence the reason you don't see many rangefinder lenses on DSLRs! Going from CS-mount to C-mount to Q would be kinda backwards...

Also, caveat emptor, as this fleabay listing for something quite similar (sold as "C-mount") looks to be CS with the adapter already screwed on... and more than double the price of your original link! A good question for that seller would be "Can this lens be used on a CS-mount camera?" If the answer is "yes, remove the back" then you know you're already looking at a degraded optic.

EDIT: here is a wide-angle option that is very high quality (Computar), if you can find a CS-mount to Q-mount adapter (or make one).

Last edited by panoguy; 09-30-2012 at 07:59 AM.
09-30-2012, 08:14 AM   #3
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"Be careful with that first one - "CS-mount" has a different (smaller) flange focal distance than C-mount (12.5mm vs. 17.5mm), so the C-mount adapter shown probably has additional glass in it to compensate"

I don't think that is the case. If you look at that page the C mount version of that lens is a different lens entirely, it looks as if it is fixed focus.

I have not seen an adapter to go from CS lenses to C cameras. All the adapters I have seen are for C lenses on CS cameras, in that case the adapter is just a 5mm extension ring. Those are also sold as macro rings for C mount lenses.

Shawn
09-30-2012, 09:10 AM   #4
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QuoteOriginally posted by Shawn67 Quote
I don't think that is the case. If you look at that page the C mount version of that lens is a different lens entirely, it looks as if it is fixed focus.
Ah, looks like you're right. That's a really confusing catalog listing!

In any case, if you want decent image quality, I'd suggest looking at modern (which these days means CS-mount and/or "megapixel" labeled) Computar, Jenoptik, or Pentax lenses. If you just want an adaptable wide angle, these no-name brands might produce a good image, but more than likely not. I've used older C-mount and Bolex lenses on a 1.2MP video system, and they were outresolved by that sensor (ie: blurry crap)!


Last edited by panoguy; 09-30-2012 at 09:49 AM.
10-06-2012, 06:38 PM   #5
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My C mount to Pentax Q adapter arrived today. I didn't end up getting it till late at night. I can confirm that the 2.5mm lens linked to above is a C mount and works on the Q. It should work out to be about a 14mm FF FOV. I think the Pentax Fisheye is about 18mm.

The lens is not fixed focus (the front thin element moves) but it is fixed aperture. It does not cover the entire sensor, you get the traditional fisheye circular view. I think it is considerably faster than the Pentax Fisheye. I took a shot of my floor with the 01 Prime wide open at ISO 125 and it center weighted metered to 1/30 of a second. With the 2.5mm lens it metered to 1/13th of a second. In theory it is around f2.8ish.

Should be fun to play around with this lens more, esp. for $23.

BTW, I would not try this lens on other cameras. It projects fairly deeply into the camera and I would be very worried about it interfering with a mechanical shutter... since the Q doesn't have one....

Shawn
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10-06-2012, 07:26 PM   #6
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Wow that looks great for $23! Can't wait to get a Q.
10-07-2012, 09:42 AM   #7
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Shawn67 this looks like an interesting circular fisheye for the Q. Could you post a full size pic or two so we could judge the IQ ?

Also a lil bit of research yielded this lens for $16 at L025F - Fixed Iris Lens C/CS Mount 2.5mm F:1.6 1/3" | COP, USA, Video Surveillance, CCTV Equipment, Camera, Security Products, Surveillance Equipment, Security Camera, Surveillance Camera

Thanks!
10-07-2012, 05:59 PM   #8
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Sure, IQ is interesting on the lens. It seems to do better closer up. It will focus in very tight. On the flowers I was an inch or less away from them and I think it could still focus even closer. As you can see in some of these it does have some CA. I did not try correcting this in LR4 to give a better representation of what the lens is doing itself. I think most of the CA could be removed in LR4. For the same reason these have minimal PP to them.

To focus on these I was using a loupe on the LCD with magnification on the LCD.













If you right click on any of the pictures and view this picture you will see a larger version of the picture that you can zoom in more.

Shawn


Last edited by Shawn67; 10-07-2012 at 06:16 PM.
10-08-2012, 08:51 AM   #9
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wow thanks Shawn! looks like it gives about the same IQ like those add-on fisheye adapters .. ok in the center, pretty bad along the edges.
i do like your closeup shots!! that's it's best application.
10-12-2012, 04:59 PM   #10
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Here is another C mount wide angle option for the Q. These are from a Pentax/Cosmicar 4.8mm f1.8 C mount lens. This is fixed focus lens that is equivalent to about 27mm. Just a couple of test shots at f1.8, 2.8,4 and 5.6 before I lost the light. For street shooters this may be a nice lens. With the adapter the lens is a little longer than the 01 prime but still looks fine on the camera, no worries about focus and the electronic shutter is silent.

Some completely boring shots at different apertures to see how the lens does....
f1.8



f2.8



f4


f5.6



Will try this lens out more this weekend
10-13-2012, 08:16 PM   #11
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Posted a number of shots from the 4.8mm C mount lens at:
https://www.pentaxforums.com/forums/pentax-q/172196-lets-share-shots-q-30.html#post2134234

Shawn
10-20-2012, 09:58 AM   #12
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I ended up picking up a few more C to Q mount adapters.

The adapters are nice as they are two part to allow you to rotate the lens so that the aperture scale is upright. This also allows you to shim a lens if needed. From my testing the Pentax 4.6mm fixed focus lens needs a little shimming on the Q. I ended up taking apart the adapter (3 allen screws) and added 3 small squares of paper from a sticky note between the two pieces of the adapter and reassembled it.

This is a 1:1 comparison (from the center of the lens) in LR4 between the adapter with no shims vs. the adapter shimmed with the paper.



Getting the lens shimmed improved focus all over the lens, objects close up are sharper now too. BTW, the comparison function in the Qs playback menu was really nice is helping me to see the need for the shims in the first place.

Shawn
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