16 or 18 mm lens??

Show and tell for your homebrew nv projects. DIY 'Stickies' here too.
The marsh
Posts: 36
Joined: 29 Jan 2013, 21:30
Location: South wales

16 or 18 mm lens??

Post by The marsh » 17 Feb 2013, 21:24

Is it a 16 or 18mm I need to see more of scope view as using a 25mm and only see centre of scope

Gingernutz
Posts: 92
Joined: 01 Mar 2012, 22:54
Location: Louth, Lincolnshire.

Re: 16 or 18 mm lens??

Post by Gingernutz » 17 Feb 2013, 22:05

Most people prefer the 16mm lens. I seem to remember Some Bloke did a comparison drawing of a 16 and a 12 to show the field of view of them both.

terry1001
Posts: 981
Joined: 27 Aug 2012, 09:30
Location: Ipswich, Suffolk

Re: 16 or 18 mm lens??

Post by terry1001 » 17 Feb 2013, 22:15

The marsh wrote:Is it a 16 or 18mm I need to see more of scope view as using a 25mm and only see centre of scope
the 16mm lens will give you a wider field of view, you will get a circular illuminated area with a black surround and effectively lower magnification. If the black area around the lit part is a significant size it will tend to affect the exposure and the central part will be brighter than it should be and may produce white out in some parts. If the whole of the sensor is lit, and there are no or very small black areas, the auto exposure will produce a more balanced image.
Some people prefer the circular view but this requires a higher scope magnification than with a full sensor image for the same size on the monitor. Seeing 'only the centre of the scope' just means you are getting a higher magnification at the monitor. At the end of the day it is a personal choice.

User avatar
some bloke
TRADER MEMBER
Posts: 7544
Joined: 27 Jan 2012, 16:14
Location: Cornwall or Leicester

Re: 16 or 18 mm lens??

Post by some bloke » 18 Feb 2013, 08:20

terry1001 wrote:
The marsh wrote:Is it a 16 or 18mm I need to see more of scope view as using a 25mm and only see centre of scope
the 16mm lens will give you a wider field of view, you will get a circular illuminated area with a black surround and effectively lower magnification. If the black area around the lit part is a significant size it will tend to affect the exposure and the central part will be brighter than it should be and may produce white out in some parts. If the whole of the sensor is lit, and there are no or very small black areas, the auto exposure will produce a more balanced image.
Some people prefer the circular view but this requires a higher scope magnification than with a full sensor image for the same size on the monitor. Seeing 'only the centre of the scope' just means you are getting a higher magnification at the monitor. At the end of the day it is a personal choice.
I wish I could have said all that. Ruddy good balanced answer. :thumbup:

I'd add it also depends on your scope minimum magnification. A 25mm lens would just crop a tiny bit off the image edges at 3 mag scope, a tad more off to about the corners of a 4 mag scope and there is definitely no trace of the scope corners as you approach 5 mag. Lots of guys use 6 mag scopes so you will almost definitely need a 16 mm one for that. If you are using a watec camera it was designed to use a 1/2" format lens although some manage good results with a 1/3" format if lots of light will be used.
Image

User avatar
snoopy
Posts: 2629
Joined: 22 Jun 2012, 23:22
Location: NER NER LOL stoke on trent

Re: 16 or 18 mm lens??

Post by snoopy » 18 Feb 2013, 21:29

1/3 sencor with a 16mm MTV(board cam) lens on 2.5 scope mag is about what i see on 5-6 through just the scope... thats on mine though.
'who is that masked man? its the kemosabby der..the bloody injun tells you every week!'

terry1001
Posts: 981
Joined: 27 Aug 2012, 09:30
Location: Ipswich, Suffolk

Re: 16 or 18 mm lens??

Post by terry1001 » 18 Feb 2013, 22:07

snoopy wrote:1/3 sencor with a 16mm MTV(board cam) lens on 2.5 scope mag is about what i see on 5-6 through just the scope... thats on mine though.
That's about what I would expect, the 16mm lens on a 1/3" sensor gives about 2x mag, the benefit of having the extra magnification on the camera is that you make the most of the scopes light gathering at lower mag. With a larger scope objective you can probably afford to go up a little bit in magnification before performance starts to drop off. Generally you won't notice any dimming of the image because the camera will increase the gain to compensate but you will start to get increased 'noise' and a loss of image quality. My personal preference is to keep the scope at a minimum mag and use a longer focal length lens on the camera, but - as always - each to his own!

User avatar
snoopy
Posts: 2629
Joined: 22 Jun 2012, 23:22
Location: NER NER LOL stoke on trent

Re: 16 or 18 mm lens??

Post by snoopy » 18 Feb 2013, 22:16

Terry? what mag equivelenta for the 1/2 and a lens, 1/3 or 1/2 lens? i'd like about the same as the mtv lens on that scope.
'who is that masked man? its the kemosabby der..the bloody injun tells you every week!'

terry1001
Posts: 981
Joined: 27 Aug 2012, 09:30
Location: Ipswich, Suffolk

Re: 16 or 18 mm lens??

Post by terry1001 » 18 Feb 2013, 23:00

snoopy wrote:Terry? what mag equivelenta for the 1/2 and a lens, 1/3 or 1/2 lens? i'd like about the same as the mtv lens on that scope.
As a rough guide if you take the sensor diagonal measurement which for a 1/2" lens is about 12mm then a lens of that focal length gives about 1x magnification so for 2x you'll want a 25mm lens and a 100mm lens about 4x.
1/3" sensors are about 8mm diagonal so a 16mm lens gives 2x, a 1/4" sensor is 6mm diagonal and a 12mm lens will give 2x.
Unfortunately you can't be sure that the sensors are the size claimed but this is near enough to give a fair idea.

User avatar
snoopy
Posts: 2629
Joined: 22 Jun 2012, 23:22
Location: NER NER LOL stoke on trent

Re: 16 or 18 mm lens??

Post by snoopy » 19 Feb 2013, 01:36

its more of a clue than i had ty
'who is that masked man? its the kemosabby der..the bloody injun tells you every week!'

The marsh
Posts: 36
Joined: 29 Jan 2013, 21:30
Location: South wales

Re: 16 or 18 mm lens??

Post by The marsh » 21 Feb 2013, 23:47

Any idea on best 16mm for watec??

Post Reply