- Jul 16, 2016
- Reaction score
- United States
- Dash Cam
- Mobius, A119
What you said made good sense also, I never considered the internal reflection situation, that's a really good point to consider, Does the 9.5mm filter fit a little loose when you drop it down the barrel to the lens element? Reason for asking, wondering if a 10mm would go down the barrel with out any hangups?It's a bummer that Bangood sent the 2MP lens instead of the 3MP but in all likelihood I think you won't notice any significant difference in the results.
It's also unfortunate that Banggood is so vague and unreliable about which lens they actually ship out. Many people, including me received the 3MP lens regardless of which one they order so it seemed like that would be the case going forward. Now it seems they just ship out whichever one they happen to have in stock. I was aware that you can buy these varifocal lenses from many other sources but I wish I had known at the time I bought mine that they are widely available at such very low prices from other sources than Banggood, including many variants. These varifocals are primarily used in CCTV cameras (which is why they don't include IR-cut filters) and that's why they are so common. In fact, recently when I tore down an old vandal dome type CCTV camera I've had kicking around I found an almost identical varifocal lens inside, except that it was 2.8-10mm with a smaller maximum aperture.
If anyone is interested in buying one of these M12 Varifocals at a good price it looks AliExpress is the place to go. Dozens of vendors, including Treeye sell them.
As for mounting the IR-cut filter, the ones I ordered are 9.5mm in diameter and therefore too small to be mounted on the rear of the threaded tube at the back of the lens barrel. I do plan to see if I can mount the IR filter directly behind the recessed rear optical element of the lens on the lip deep inside the tube. Mounting the IR-cut filter close to the rear element avoids any internal reflections inside the lens barrel. If you mount the filter at the back of the lens barrel tube recessed 6mm away from the rear lens element, there is a risk that light traveling through the lens may bounce off the IR filter back towards the lens and cause a loss of image contrast. You could certainly try it though, it won't hurt anything and it might work OK. Experimentation is one of the fun and educational things about DIY.