Two cams with 12mm lens, but VERY different FOV. Why?

[Fastb]

I had a 4MP cam with a 12mm fixed lens watching my driveway. I was pleased with the FOV, but wanted better nighttime images.

I decided to change it out for a 2MP Starlight varifocal,, 2.7mm to 12mm. I figured I’d probably set it to 12mm, for an identical FOV.

I mounted the Starlight in the exact same position as the 12mm fixed cam. However, the FOV is very different. Why? Details below.



IPC-HFW5231E-Z - Starlight varifocal

IPC-HFW5231E-Z | Dahua Technology - Dahua Technology





The varifocal lens is 2.7mm ~12mm. In the pic below, the cam is fully zoomed in, ie: 12mm.







IPC-HFW4431M-I2 - 12mm fixed focus.

This fixed lens camera is available in 3.6mm, 6mm, 8mm, and 12mm.

Aliexpress.com : Buy Dahua Stellar camera DH IPC HFW4431M I2 replace IPC HFW4431D&IP HFW4421D 4MP POE IR80M CCTV camera IPC HFW4431M I2 with bracket from Reliable cctv camera suppliers on Shop1282343 Store



This pic is from the 12mm model.




Q: Why is the FOV so very different?
I bought the 12mm from aliexpress, maybe I received a 16mm lens? I bought my Starlight from Andy.

More info: When surfing into both cameras, the cam's web interface header says "Dahua", unlike some of my other cams. The header on those web interfaces simply says "IP Camera". So I don't think the 12mm fixed cam is a cheap knockoff, with a cheap lens that gives the wrong FOV.

Q: Why is the FOV so very different?

Thanks for any info or hunches,
Fastb

 

[Philip Gonzales]

I had a 4MP cam with a 12mm fixed lens watching my driveway. I was pleased with the FOV, but wanted better nighttime images.

I decided to change it out for a 2MP Starlight varifocal,, 2.7mm to 12mm. I figured I’d probably set it to 12mm, for an identical FOV.

I mounted the Starlight in the exact same position as the 12mm fixed cam. However, the FOV is very different. Why? Details below.



IPC-HFW5231E-Z - Starlight varifocal

IPC-HFW5231E-Z | Dahua Technology - Dahua Technology

View attachment 23205



The varifocal lens is 2.7mm ~12mm. In the pic below, the cam is fully zoomed in, ie: 12mm.

View attachment 23206





IPC-HFW4431M-I2 - 12mm fixed focus.

This fixed lens camera is available in 3.6mm, 6mm, 8mm, and 12mm.

Aliexpress.com : Buy Dahua Stellar camera DH IPC HFW4431M I2 replace IPC HFW4431D&IP HFW4421D 4MP POE IR80M CCTV camera IPC HFW4431M I2 with bracket from Reliable cctv camera suppliers on Shop1282343 Store

View attachment 23207

This pic is from the 12mm model.

View attachment 23208


Q: Why is the FOV so very different?
I bought the 12mm from aliexpress, maybe I received a 16mm lens? I bought my Starlight from Andy.

More info: When surfing into both cameras, the cam's web interface header says "Dahua", unlike some of my other cams. The header on those web interfaces simply says "IP Camera". So I don't think the 12mm fixed cam is a cheap knockoff, with a cheap lens that gives the wrong FOV.

Q: Why is the FOV so very different?

Thanks for any info or hunches,
Fastb

Is the sensor size the same on both cams?

 

[Fastb]

For the Starlight, it's a larger sensor (which helps with nightime performance) Sensor: 1/2.8” 2Megapixel progressive scan STARVIS™ CMOS
For the fixed 12mm cam, the spec says: Image Sensor : 1/3'' 4 Megapixel progressive scan CMOS.

In a past life, I bought cam lenses for surveillance cams, to change FOV. When buying the lens, the size of the sensor mattered in lens selection. You don't use a lens for 1/4" sensor with a cam with 1/3" sensor for example. The lens would project the image onto a 1/4" area, wasting the outer pixels of the 1/3" sensor.

So the lens must be matched to sensor size, or: a) pixels are wasted, or b) the lens projects an image that overlaps the side of the sensor....

Fastb

 

[Fastb]

@Philip Gonzales asked about sensor size. I initially didn’t think that was a factor. After all, the sensor (size) and lens are a system, right?

And in the past, when I put a lens for a ¼” sensor onto a camera with a 1/3” sensor, the corners of the image were blackened. Similar to the effect you see in movies, when showing what the actor sees through a telescope, eg:



So lenses and sensors are paired for compatibility, right?

But Philip’s comment made me think more about it. So I went to the IPVM Camera Calculator, ie: IPVM Camera Calculator V3

I entered the info for a 12mm lens, with the subject distance of 75ft. Then I changed the Imager size (1/3” and 1/2.8” ) See blue circles, below.

The calculator shows the different a) Horizontal FoV and b) the width of the FOV at 75 ft. See red circles below.

The Starlight horizontal FOV increases by 6 degrees – approx 25%!






Very interesting! And it shows why a varifocal is beneficial – because picking a fixed lens size can be tricky!
Another observation: Using a varifocal (with 1/2.8 inch sensor) to decide on lens size of a less expensive fixed lens camera (likely with a 1/3" sensor) may not give the intended results....

Fastb

 

[Philip Gonzales]

@Philip Gonzales asked about sensor size. I initially didn’t think that was a factor. After all, the sensor (size) and lens are a system, right?

And in the past, when I put a lens for a ¼” sensor onto a camera with a 1/3” sensor, the corners of the image were blackened. Similar to the effect you see in movies, when showing what the actor sees through a telescope, eg:

View attachment 23217

So lenses and sensors are paired for compatibility, right?

But Philip’s comment made me think more about it. So I went to the IPVM Camera Calculator, ie: IPVM Camera Calculator V3

I entered the info for a 12mm lens, with the subject distance of 75ft. Then I changed the Imager size (1/3” and 1/2.8” ) See blue circles, below.

The calculator shows the different a) Horizontal FoV and b) the width of the FOV at 75 ft. See red circles below.

The Starlight horizontal FOV increases by 6 degrees – approx 25%!

View attachment 23218

View attachment 23219


Very interesting! And it shows why a varifocal is beneficial – because picking a fixed lens size can be tricky!
Another observation: Using a varifocal (with 1/2.8 inch sensor) to decide on lens size of a less expensive fixed lens camera (likely with a 1/3" sensor) may not give the intended results....

Fastb

Yeah, I'm no expert but I dabbled a little in photography and I remember something like a 35mm lens on a crop sensor camera is roughly equivalent to a 50mm lens on a full frame sensor camera. Same thing with 50mm lens on a crop sensor vs a 75mm on a full frame sensor. It has been a while so forgive me if my terminology is a little off.

Also I ready @nayr 's post on the ultra starlight camera that mentioned sensor size and focal length in the first post.

Dahua Ultra Starlight Varifocal Bullet (IPC-HFW8232E-Z)

 

[Fastb]

Point well made. Excellent reference to nay's previous post. As usual, nayr was spot on.

In the post you referenced, nayr said:
"Don't let the 16mm optics fool you, due to the larger sensor size these is very close in FOV's to the 1/2.8" @ 12mm.. this camera will not get you any more zoom than the Eco Starlights."

Philip, thanks for your help. Someday i hope to not be wet behind the ears. Maybe just damp, lol!

 

[Philip Gonzales]

Point well made. Excellent reference to nay's previous post. As usual, nayr was spot on.

In the post you referenced, nayr said:
"Don't let the 16mm optics fool you, due to the larger sensor size these is very close in FOV's to the 1/2.8" @ 12mm.. this camera will not get you any more zoom than the Eco Starlights."

Philip, thanks for your help. Someday i hope to not be wet behind the ears. Maybe just damp, lol!

You're welcome. I still have a lot to learn myself. I think if we knew everything already then this wouldn't be as fun.

 

[Kawboy12R]

Also, please note that the PPF calculations for 1/2.8" sensors on the IPVM.com/calculator are broken and have been for a while. You are better off to use the calculations for 1/2.7" sensors when you want the ones for 1/2.8".

To see for yourself, put in the numbers for any cam/lens and then step the imager size down from 1/3", 1/2.8", 1/2.7", 1/2.5". Notice anything funny about the PPF numbers and the FOV for 1/2.8"? They're way off. More like 1/2" numbers. If you step from 1/2.5" to 1/2.7" you "zoom in" a bit. The same should happen when you step from 1/2.7" to 1/2.8" but you don't. You zoom way out.

I reported this glitch to @john-ipvm a number of times a year or more ago with no acknowledgement and it hasn't been fixed so you'll have to continue using the workaround.

You'd think that with the 1/2.8" sensor size becoming very popular that it would be embarrassing to 1) not notice it in-house, and 2) not fix it or even acknowledge when users report that it's broken. I can't be the only one that's noticed and reported this.

 

[crc2004]

Also, please note that the PPF calculations for 1/2.8" sensors on the IPVM.com/calculator are broken and have been for a while. You are better off to use the calculations for 1/2.7" sensors when you want the ones for 1/2.8".

To see for yourself, put in the numbers for any cam/lens and then step the imager size down from 1/3", 1/2.8", 1/2.7", 1/2.5". Notice anything funny about the PPF numbers and the FOV for 1/2.8"? They're way off. More like 1/2" numbers. If you step from 1/2.5" to 1/2.7" you "zoom in" a bit. The same should happen when you step from 1/2.7" to 1/2.8" but you don't. You zoom way out.

I reported this glitch to @john-ipvm a number of times a year or more ago with no acknowledgement and it hasn't been fixed so you'll have to continue using the workaround.

You'd think that with the 1/2.8" sensor size becoming very popular that it would be embarrassing to 1) not notice it in-house, and 2) not fix it or even acknowledge when users report that it's broken. I can't be the only one that's noticed and reported this.

Having a broken calculator is much worse than having no calculator at all. I hope too many people didn't buy the wrong camera because of this defect.

 

[fenderman]

Having a broken calculator is much worse than having no calculator at all. I hope too many people didn't buy the wrong camera because of this defect.

oh the horror...they will survive....

 

[Kawboy12R]

Exactly. I wasn't completely surprised that I didn't get a personal reply, but I am frankly a bit astonished that it has gone unfixed for this long.

 

[wopi82]

It's all about sensor size and so called focal length multiplier or crop factor. What Philip Gonzales is referring to, is a APSC sensor format, which has a crop factor of 1.5 and 1.6 depending on camera brand. Focal length of a lens is given in a full frame format. So if you mount a 20mm lens on FF camera, you'll get 20mm. But if you mount it on a APSC camera, you'll get 30mm equivalent for Nikon and 32mm equivalent for Canon. A 1/2.8" sensor has a crop factor around 6.6, so a 3.6mm lens will give approx. 24mm equivalent. A 1/3" sensor has a crop factor 7.2. Interestingly, the new Dahua IPC-HF8835F is equipped with micro four thirds sensor which has been announced by Sony only a few months ago. 4/3" sensor has a crop factor of 2. Its area is 225 sq. mm compared with 17 sq. mm of 1/3" sensor. The image quality from this camera will be far far better than present Starvis Ultra models. This sensor is also capable of capturing two different exposures at the same time, so WDR will be free of any artefacts. For more info about sensor sizes, I encourage to visit this page: Digital Camera Sensor Sizes: How it Influences Your Photography It's a great source of knowledge about digital photograph in a nutshell.