It's not a question of buying what someone has, it's buying what I want and works at it's best with the Mobius camera sensor.
@Dashmellow One thing I should say here is that I see some of you guys talking about lenses with 1/1.7" (Diagonal 9.50mm image circle) and 1/1.8" (8.93mm image circle. I have read statements in checking out lens that said these formats were only for certain camera censors and most others that said the MAX sensor circle was for 1/2" sensors which is diagonal of 8.00mm.
It's possible this is only for certain focal length lenses, I'm not sure of the impact because they never said. Must have something to do with the building of the lens with certain components
I don't think they said this for nothing so if you are buying a lens with those formats (larger then 1/2"-- Diagonal of 8.00mm) it might be wise to ask the Manufacture if it has any bearing on what you are using the lens on. So, I guess they would want to know the camera sensor size you are using.
This is a little out of my league so I'll give out a @ call for dashmellow.
@Lola, I'm not really sure what you are getting at here.
As we've talked about, the
image circle is the cross section of the cone of light transmitted by a lens onto a perpendicular target such as film or a digital camera sensor. Basically, every lens, regardless of it's focal length throws a circle of illumination of a particular size depending in its particular design and purpose. Lenses are designed so they will throw an image circle which can accommodate different sensor aspect ratios such as 3:2, 4:3, 16:9, etc., as well as sensors of different sizes. There are all different kinds of lens designs intended for all different kinds of cameras. The field of optical design is highly complex and complicated as it can involve a wide array of variables depending on how any given lens will be used on any given type of camera sensor combination according to how the camera is intended to be used. It becomes even more complicated when you consider factors such as variable focusing, variable apertures and the quirks and characteristics of particular focal lengths. Wide angle lenses tend to throw a larger circle of coverage, for example.
The thing you need to keep in mind is that we are talking about
M12 (S-mount) lenses that we have in our dash cams which are fixed focus and of fixed aperture. That makes it all very simple. All you really need to know when shopping for a lens with the proper coverage is that it will project an image circle that is big enough to cover your particular sensor so that it will not cause vignetting. (Cutting off the corners of your image.) But if the lens you choose happens to project an image that is WAY bigger than the sensor it was specifically designed for, all that will happen is that it will act as if it is providing the greater magnification of a more telephoto lens than if it fit perfectly into the entire circle of coverage because the smaller sensor will only be a smaller section of the circle.
Here's a demonstration image I made:
Imagine that you are looking at the circle of coverage from a lens designed specifically for a 1/2" sensor. (seen in
white)
If you install this same lens on a camera with a 1/3" sensor (seen in
red) it will only record a smaller section of the available circle of coverage onto the smaller sensor, thus providing an image that has more of a telephoto effect.
So, if you were to buy an 8mm focal length lens that is designed for a 1/2" sensor it will act "perhaps" more like a 12mm focal length lens if installed on a camera with a 1/3" sensor. (I'm only guessing at the increased magnification, of course, but it's probably somewhere in the ballpark.)
The telephoto effect demonstrated above can be a very good thing for our purposes because the center portion of a lens's circle of coverage always provides better optical performance than towards the outer edges of the circle. You'll get a sharper, brighter, more optically corrected image with less barrel distortion than it otherwise might have.
Also, since we are seeking faster lenses here with the largest possible aperture, we are much more likely to find larger apertures in shorter focal length lenses (such as
@dirkzelf's ƒ/1.2 - 4mm here) than in longer focal length M12 lenses.
It is no accident or coincidence that you haven't been able to find the super wide aperture 12mm lens you have been looking for.
@Lola, I've been watching you go through this whole lengthy process and I'm really impressed that you are such a ferret for information that you have been going to so much trouble to learn all about this and find what you want. The truth of the matter though is that I think you are making yourself a bit crazy over all this after so much time. To be honest with you I think such things as talking to manufacturers about building you a custom lens is kind of over the top IMHO. The Mobius is a great camera and I love the platform, as you know, but there is a limit to what the Mobius can achieve even with the finest lenses. I recommend finding a decent lens from a reliable vendor on AliExpress. That's the one source that seems to have these specialty lenses available and I'm sure you'll be very happy with it. Personally, after looking around, I'm considering a 6mm ƒ/1.2 StarLight similar to
@dirkzelf's choice. I think it will provide enough of a telephoto for my purposes and it appears so far to be the fastest lens available in a longer focal length. Then again, that varifocal 2.8 mm - 12mm IR lens I've been experimenting with has provided remarkable optical performance, especially considering that it only cost me $7.50. And it's an ƒ/1.4 which isn't too shabby for a 12mm and it's designed specifically for a 1/3" sensor! I'm considering installing an IR-cut filter on it once I'm done with my IR experiments. It might be all I need in a Mobius telephoto? .....or perhaps you too for that matter.