A Few Projects

Show and tell for your homebrew nv projects. DIY 'Stickies' here too.
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MrNewbie
Posts: 297
Joined: 22 Dec 2012, 21:28
Location: Grafton, Ohio USA

Re: A Few Projects

Post by MrNewbie » 17 Jan 2018, 05:05

This is a bit of a tech reading about lenses, But I found it interesting and even learned something.

https://www.cctv-information.co.uk/i/Li ... ugh_Lenses


That lens, does not look all that great. Just about ANY CCTV or C/CS mount will blow the standard M12 16mm lens away.

Any of these will do even better.
https://www.ebay.com/sch/i.html?_from=R ... 2&_sacat=0

Once again you will say...

"These don't seem much different on paper but in testing in dark conditions it's a huge difference.
I could never go back to o the f1.7 ! It's sooo dark."

Stick with the 1/2", it makes a difference..1/2 is better than 1/3


ps...up your M12 to ccctv make to thingiverse or post

Trackerman
Posts: 127
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Post by Trackerman » 17 Jan 2018, 07:26

Cheers Bruce, good info there.

Super slack, it sure does show 16mm, that would imply the lens is f1.0 but they actually claim f1.2 (less)
Either way it's a fine lens, pity we can't get it here easily.


Me newbie, I'll post the files to thingiverse later today and share the link here .

Cheers lads
Tracker

Trackerman
Posts: 127
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Post by Trackerman » 17 Jan 2018, 09:09

As promised.... link to thingiverse M12 to C-Mount adapter

https://www.thingiverse.com/thing:2759814

I made two versions, one straight and one with collar for press fitting into a case etc.

note: the c-lens is press fit into the adapter... I can't make threads that small in 3D print!!!
but press fit is just fine, nice and snug.

cheers

T

summer-blue
Posts: 45
Joined: 07 May 2015, 23:06
Location: ca

Re: A Few Projects

Post by summer-blue » 17 Jan 2018, 22:00

superslack wrote:The bhphoto lens is 16mm diameter. I measured it and it is also shown on the marshall electronics lens drawing.
To calculate the F number, don't measure the object lens diameter. Instead, you need entrance pupil diameter. F number=Focal length/Entrance pupil.
Looking into the lens from the object lens side and use a ruler to estimate the size. Keep you eye as far as possible and ruler as close to the lens as possible. For a M12 cctv lens, it's impossible to have an entrance pupil that big.

summer-blue
Posts: 45
Joined: 07 May 2015, 23:06
Location: ca

Re: A Few Projects

Post by summer-blue » 17 Jan 2018, 22:08

Sorry, I should't say impossible, just hard to imaging. ;)

superslack
Posts: 78
Joined: 08 Feb 2016, 23:58
Location: Virginia

Re: A Few Projects

Post by superslack » 17 Jan 2018, 22:57

Thanks MrNewbie for that link. I found it extremely informative. I never considered the fact that a lens configured for sensor larger than what I'm using would put less light on the sensor than if the lens was configured for the sensor size being used.

Summer-blues

I measured the entrance pupil on the 16mm BH Photo lens, where and adjustable aperture would be, and it was about 9mm. The exit lens was just under 6mm.

I measured the same on the Treeye 25mm "F1.2". The objective lens was 14.5mm and the entrance pupil was about 11.5mm. The exit lens was about 9mm.

Trackerman
Posts: 127
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Post by Trackerman » 17 Jan 2018, 23:03

Good point sumnerblue, that explains a few things.
Now I see it's not the diameter of the front glass but rather it's the diameter of the tunnel through the lens, this is what determines light transmission.

I'll need to re-measure my lenses with this in mind.

Cheets

T

Trackerman
Posts: 127
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Post by Trackerman » 17 Jan 2018, 23:18

Hi super slack, so by the new dimension you provide it would seem the bhphoto 16mm lens is 16/9= f1.7
I suspect it's hard to get an accurate measurement by hand and eye plus the lens distortion can fool the eye so I'd have to give Marshal the benefit of doubt and say it's most likely f1.2 as they claim.

Interesting that my cheapo c-mount lens still measures 9mm wide when I measured the narrowest part of the light tunnel. But the front glass is no where as big as the marshal glass.

Anyway ... The main point is that the nasty little 16mm lens only has 5mm of tunnel ... Making it 16/5 = f3.2 which is even worse than I thought ...

superslack
Posts: 78
Joined: 08 Feb 2016, 23:58
Location: Virginia

Re: A Few Projects

Post by superslack » 18 Jan 2018, 01:36

I need to spend more money on lenses now :thumbdown:

I measured my M12 to C mount adapter and the through hole is about 9.2mm. The night wolf has a 1/2: mccd which has an 8mm diagonal dimension and the night eagle has a 1/1.8 sensor which has a 8.93mm diagonal. I assume the light is collimated when exiting the lens so this won't have too much effect when using the adapter.

lightmesser showed a picture on another forum demonstrating Chinese sellers have no idea what they are selling. So I need to make sure I know what I am buying and guesstimate off the pictures what size and format the lens is.

Trackerman
Posts: 127
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Post by Trackerman » 19 Jan 2018, 19:42

I went and measured my Canon L lenses (expensive glass) and none of them came out as claimed, all were below the calculated f-stop by about 1/2 an f-stop or so...
Now I don't doubt cannon for 1 second, so I suspect the basic science lets us down when we measure using the eye through a front lens which distorts the image.
I reckon we need to allow for another 10% to 25% in the 'observed' aperture vs the actual aperture within the lens itself.

If I allow for this then the canon L-glass comes out spot on... perhaps we need to allow for this in our CCTV lenses also.

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