What do the lens size mean?

[coolxal 0]

I have a camera with a 1/3" sensor (Dahua HDB-3200C).

 

I'm looking for some wider angle lenses and the two that I found says 1/2.5" and 1/2.7"

 

The size of the lens and the type of screw are all correct, can I use either of these lens?

[ssmith10pn 0]

If your camera has a 1/3" sensor then it needs a lens the same size or bigger.

1/2" is bigger than 1/3" so your good.

[buellwinkle 0]

You probably already know this, but make sure the lens has an IR coating like the factory lens, most do not.

[MaxIcon 0]

To expand on BW's comment:

 

This camera has the IR filter built in to the lens, not as a separate component like many cams. If you put in a lens without the IR filter, your colors will be off.

 

Many lenses are labeled IR. This usually means they're IR corrected, not IR blocking; that is, they pass IR through and it focuses at about the same point as white light, so you're in focus with both IR and white light on day/night switching cameras.

 

You want an IR blocking lens. These are a lot less common.

 

Also, when you use a lens made for a larger sensor, you don't get the same field of view as the same size lens for your sensor. A 3mm lens for a 1/2" sensor will give you a smaller field of view than a 3mm lens for a 1/3" sensor.

 

1/3" is 0.33". A 1/2.5" (0.4") will give you a smaller FOV than a 1/2.7 (0.37") lens, which will give you a smaller FOV than a 1/3" lens. Each lens will give the same approximate view in different size circles of light, so your 0.33" sensor sitting in a 0.4" image will lose more of the image around the edges.

 

Also, these sizes aren't the actual sized of the sensors, but that's a whole 'nother post.

[coolxal 0]

To expand on BW's comment:

 

This camera has the IR filter built in to the lens, not as a separate component like many cams. If you put in a lens without the IR filter, your colors will be off.

 

Many lenses are labeled IR. This usually means they're IR corrected, not IR blocking; that is, they pass IR through and it focuses at about the same point as white light, so you're in focus with both IR and white light on day/night switching cameras.

 

You want an IR blocking lens. These are a lot less common.

 

Also, when you use a lens made for a larger sensor, you don't get the same field of view as the same size lens for your sensor. A 3mm lens for a 1/2" sensor will give you a smaller field of view than a 3mm lens for a 1/3" sensor.

 

1/3" is 0.33". A 1/2.5" (0.4") will give you a smaller FOV than a 1/2.7 (0.37") lens, which will give you a smaller FOV than a 1/3" lens. Each lens will give the same approximate view in different size circles of light, so your 0.33" sensor sitting in a 0.4" image will lose more of the image around the edges.

 

Also, these sizes aren't the actual sized of the sensors, but that's a whole 'nother post.

 

Thanks MaxIcon, I asked the guy whose thread you linked me to and he said he got the lens off AliExpress. The previous lens I bought had very off colours but the specs matched so I wasn't sure this time.

 

So will the 1/2.7" 2.8mm lens still give me a wider angle than a 1/3" 3.6mm lens?

 

The two I'm looking at are this and this. The lens with 1/2.7" says 109 degree angle and the one that says 1/2.5" says 114 degree angle. So which one would give me a wider view?

[MaxIcon 0]

Those questions are hard to answer accurately, because M12 lens vendors have flexible standards. Generally, you can't trust any of those numbers to be very precise.

 

Also, both of those lenses appear to be IR corrected, not IR blocking, so your colors will be off with them.

 

The 1/2.7" 2.8mm lens will pretty definitely give a wider angle than the 1/3" 3.6mm. Scaling for the different sensor sizes makes it look like it would be about a 3.1mm equivalent on a 1/3" sensor, but this is a pretty rough guess. The 1/2.5" lens looks like it would scale to about 3.3mm equivalent.

 

The only way to be sure is to buy and try!

[joseph.chen0312 0]

The specifications has lsited you can pick up f=2.8/F2.0 Fixed lens. You better check with your supplier.

[coolxal 0]

So I finally received the lens from the seller on AliExpress.

 

I got the 1/2.7" version. The colors look good and the angle is much wider now. I am quite satisfied.

 

I however just realized that the default lens that came with the camera is 1/2.5"... does that mean the 1/2.5" size was the compatible size and it would've been wider?