A Few Projects

Show and tell for your homebrew nv projects. DIY 'Stickies' here too.
lightmesser
Posts: 467
Joined: 09 Jan 2014, 01:19
Location: Eastern Europe

Re: A Few Projects

Postby lightmesser » 07 Jan 2018, 21:01

Very nice :)

Trackerman
Posts: 85
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Postby Trackerman » 16 Jan 2018, 18:47

folks

just for information..
I received this 16m lens by post today.
https://www.ebay.co.uk/itm/Replacement- ... SwY~laByPZ

and its definitely WAY BRIGHTER than the standard 16mm cctv lens.

I cant explain in words, but it's just amazing to see the difference.

No question about it.

Note its a C-mount and needs to be 1cm (+- 0.2cm) away from the camera ccd, I printed a m12 to C adapter, but you may need something else depending on your camera fitting.

this is what I mean by standard 16mm lens by the way...
https://www.ebay.co.uk/itm/2-8mm-3-6mm- ... PKXObioIrw
Last edited by Trackerman on 16 Jan 2018, 19:04, edited 2 times in total.

Trackerman
Posts: 85
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Postby Trackerman » 16 Jan 2018, 18:58

Image

Image

superslack
Posts: 66
Joined: 08 Feb 2016, 23:58
Location: Virginia

Re: A Few Projects

Postby superslack » 16 Jan 2018, 19:35

Thanks for the tip on the lens. What is the diameter of the objective lens? I'm curious to compare to my m12 lens I got here https://www.bhphotovideo.com/c/product/ ... Mount.html

Trackerman
Posts: 85
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Postby Trackerman » 16 Jan 2018, 21:55

Super slack, the objective lens measure 9.5mm and the exit lens measures 9mm

What does the bhphoto lens measure ?

Trackerman
Posts: 85
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Postby Trackerman » 16 Jan 2018, 22:16

I suspect the bhphoto lens has wider glass.

Pity bhphoto charge crazy shipping to Ireland.

So I've ordered one of these
https://rover.ebay.com/rover/0/0/0?mpre ... 2456241776

It looks to have a wider objective lens.

phoenix
BRUCE ALMIGHTY
Posts: 4497
Joined: 09 May 2012, 14:40
Location: Aberdeen

Re: A Few Projects

Postby phoenix » 16 Jan 2018, 22:47

if the focal length of the lens is 16mm and the diameter of the objective is 9.5mm then the aperture (f number) of the lens is 16/9.5 = 1.68
Lots of lenses claiming to be f 1.2 simply aren't
The quality of glass and construction have a lot to do with how bright the final image looks

Cheers

Bruce
LAND ROVER - THE WORLD'S WORST 4X4 BY FAR

Trackerman
Posts: 85
Joined: 30 Oct 2017, 19:22
Location: ireland

Re: A Few Projects

Postby Trackerman » 16 Jan 2018, 23:11

Cheers Bruce,
That's good to know..
It means my old lens was f 2.8 and my new one is f1.7
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 f2.8 ! It's sooo dark.

I read that each f stop on a camera is a doubling of light.
F1.0, f1.4, f2.0, f2.8 , f4.0 etc each is half the light of the previous.
So going from f2.8 to f1.7 is three times more light (f1.7 is middle between f1.4 and f2.0)
That explains my experience above, three times more light is a massive improvement in anyone's book.

Wonder what the bhphoto lens measures ?
It's claimed to be f1.2 so the objective should be 13mm or so ...

phoenix
BRUCE ALMIGHTY
Posts: 4497
Joined: 09 May 2012, 14:40
Location: Aberdeen

Re: A Few Projects

Postby phoenix » 17 Jan 2018, 00:37

You're correct about the doubling (or halving) the amount of light passing through a lens with each full f stop
The amount of light passing through a lens depends on the surface area where the light enters the lens (the objective) and surface area is related the square of the diameter (pi r squared and all that)
In an f 1.0 lens, the diameter of the lens is equal to it's focal length, and if the amount of light entering the lens is reduced by half, the the area of the lens is reduced by half.
Reducing the area by half means reducing the diameter by the square root of 2 which just happens to be 1.4
Therefore a lens with an aperture of f 1.4 will pass half the amount of light that a lens with an aperture of f1.0 will pass
Similarly an f 2.0 lens will pass 1/4 the light of an f 1.0 lens (the square root of 4 is 2)
An f2.8 lens will pass 1/8 the light of an f 1.0 lens (the square root of 8 is 2.8)
etc, etc

Cheers

Bruce
LAND ROVER - THE WORLD'S WORST 4X4 BY FAR

superslack
Posts: 66
Joined: 08 Feb 2016, 23:58
Location: Virginia

Re: A Few Projects

Postby superslack » 17 Jan 2018, 01:54

The bhphoto lens is 16mm diameter. I measured it and it is also shown on the marshall electronics lens drawing.


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