Lens distortion measured for several 90-degree lenses.

[nutsey]

I measured the lens distortion (using this method) of 90-degree versions Git2P and 7S action cameras as well as some other popular low-distortion lenses.

Firefly 7S (4.3mm lens):

a=0.0362736
b=-0.098951
c=0.0433648

GitUp Git2P (4.1mm lens):

a=-0.0016663
b=-0.0175647
c=0.0217117

Cheap $10 4.35mm lens:

a=-0.00999378
b=-0.0123347
c=0.0527412

3.87mm lens:

a=0.09937
b=-0.24381
c=0.15197

4.35mm lens:

a=0.0250548
b=-0.0622145
c=-0.00153784

[independent]

Interesting.

I wonder if the firefly lens has moustache or wavey distortion? This kind of distortion is associated with modern lens designs and has been typically more difficult to correct in "post".

[nutsey]

Yes, Firefly's lens shows pretty classic moustache / wavy / complex distortion.

[oldrockfan]

thanks for posting nutsey, any sample pics you can share to see the effects?

[nutsey]

oldrockfan Sure.

7S' wavy moustache:

GIT2P's barrel:

[nutsey]

The a,b and c values can be used with DeBarrel/Defisher Avisynth plugins.

[nutsey]

Just to compare. This is how supercheap variofocal 3Mp 2.8-12mm M12 lens from Aliexpress performs at ~4mm/~70° HFOV.

[oldrockfan]

great pics and sure do show the distortion. Shows what we all probably knew which is low cost lenses are always gong to have some distortion. I am using the digital crop on my T5e but would still like to have a good 90 degree lens for it.

[independent]

This is one of those photos made by the camera in video mode with the 4.1mm lens

My 4.1mm is as sharp a lens as anyone would need. I bought the ($30version) 3.8mm and found not as good. Also, bought a high end 7.2mm lens and found it good. Very difficult to judge focus on the screen however. 3.8mm lens has less distortion than 4.1mm gitup lens by a small amount.

[nutsey]

Could you please post some pics shot with that 7.2mm?

[independent]

7.2mm lens no distortion. 10 glass elements and at least the last two elements are a cemented group.
As you can see it is fairly sharp in the corners. It was the only frame were I got the focus correct. I put the 4.1mm lens back on now and it's not an easy thing to change lenses. It is best to keep a lens to a camera.

As an aside It's a process to process these images from raw because the git2p is not yet supported (the git2 is) by the open source raw converters yet except for libraw (rawspeed, dcraw, and darktable don't yet support the git2p). As we know the jpegs out of these cameras are truly terrible.

Feels about 45mm (35mm eqiv) but is less, around 40mm equivalent when I calculated it. We are shooting these lenses wide open and they have to perform extremely well to be sharp as there is no aperture to stop down and improve the image.

[nutsey]

Seems to be worthy of its $80 price.

[oldrockfan]

nice image quality but not sure eighty dollars is worth it for one of these cameras. I am thinking about trying one of the lower cost lenses. If I can get quality equal to the original just with the different fov... I will feel it was worth it. I've seen several lenses in the $20-$40 range.

[nutsey]

This photo was taken with a custom made attachment lens mounted to the 2.8-12mm M12 lens mentioned above.

[TeriyakiSandals]

care to rank the lenses best to worst?

[nutsey]

Can't do it at the moment as I haven't measured some params like resolution... Moreover each of them has strong and weak points making it hard to say which one is the best.

[TeriyakiSandals]

be sure to post when you do!

[oldrockfan]

I will be watching for the update ranking too. I've been distracted so haven't upgraded my lens yet but want it for Christmas so need to order pretty quickly.

[TeriyakiSandals]

I will be watching for the update ranking too. I've been distracted so haven't upgraded my lens yet but want it for Christmas so need to order pretty quickly.

if it helps, i'm satisfied with the $11 4.35mm from ebay, aliexpress, etc. but this is far from an in-depth review...