Mobius Telephoto Dashcam

[Dashmellow]

F stop is focal length divided by diameter so judging from the pictures the 8mm and 12mm would be about f1.2

The question is how sharp these actually are, which you can only discover by trying them. I ordered the kit so I'll report back on whether they suck

It doesn't work like that, nor could you determine the ƒ-number of a lens simply "judging" from a photo of it.

The f-stop number is a ratio of the focal length of the lens to the diameter of the entrance pupil (effective aperture).

 

[Deleted member 37895]

It doesn't work like that, nor could you determine the ƒ-number of a lens simply "judging" from a photo of it.

The f-stop number is a ratio of the focal length of the lens to the diameter of the entrance pupil (effective aperture).

As far as I know, these lenses all use the entire diameter of the lens as the entrance pupil-- there's no iris

 

[Dashmellow]

As far as I know, these lenses all use the entire diameter of the lens as the entrance pupil-- there's no iris

OK, so what are the front lens element diameters of each of these lenses that you are using to calculate the ƒ-number you claim they have?

Also, have you confirmed whether these lenses include an installed IR-cut filter? That's another piece of vital information omitted by the seller. Fact is that as standard "CCTV" lenses they are highly unlikely to include IR-cut filters, so once they arrive you'll need to deal with that if you want normal color balance in your dash cam videos.

 

[Deleted member 37895]

OK, so what are the front lens element diameters of each of these lenses that you are using to calculate the ƒ-number you claim they have?

Also, have you confirmed whether these lenses include an installed IR-cut filter? That's another piece of vital information omitted by the seller. Fact is that as standard "CCTV" lenses they are highly unlikely to include IR-cut filters, so once they arrive you'll need to deal with that if you want normal color balance in your dash cam videos.

Look at the thread diameter-- 12mm. From that you can estimate the lens diameters

You can buy IR cut filters in these packs https://www.amazon.com/gp/B015R07LPO

 

[Dashmellow]

Look at the thread diameter-- 12mm. From that you can estimate the lens diameters

You can buy IR cut filters in these packs https://www.amazon.com/gp/B015R07LPO

Again, it doesn't work like that.

As far as I know, these lenses all use the entire diameter of the lens as the entrance pupil-- there's no iris

Just because an M12 lens doesn't have an iris doesn't mean it doesn't have an aperture. Take a good look through the front of any M12 lens and you will see the entrance pupil. The entrance pupil is not the same as the diameter of the front glass element although there is a mathematical relationship between the two. You can't "estimate" effective aperture because even a small miscalculation will make a huge difference in how much light can pass through the lens. This kind of thing would require precise measurements, assuming it would even be possible. Guessing or estimating won't work. Certainly, your previous statement that, "judging from the pictures the 8mm and 12mm would be about f1.2" is not only impossible to do but also your conclusion is highly unlikely.

Each ƒ/stop in photographic nomenclature allows twice the amount of light to reach the sensor as the previous (smaller) full stop.

Standard full ƒ-stop values are - 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64

Half ƒ/stop values are 1, 1.2, 1.4, 1.7, 2, 2.4, 2.8, 3.3, 4, 4.8, 5.6, 6.7, 8, 9.5, 11, 13, 16, 19, 22

With each number to the next, the aperture decreases to half its size, allowing 50% less light through the lens (1 stop). So, the difference between say ƒ/1.2 and ƒ/1.4 is a half a stop which is significant. So again, guessing or estimating these numbers accurately enough is not possible.

 

[Deleted member 37895]

Again, it doesn't work like that.



Just because an M12 lens doesn't have an iris doesn't mean it doesn't have an aperture. Take a good look through the front of any M12 lens and you will see the entrance pupil. The entrance pupil is not the same as the diameter of the front glass element although there is a mathematical relationship between the two. You can't "estimate" effective aperture because even a small miscalculation will make a huge difference in how much light can pass through the lens. This kind of thing would require precise measurements, assuming it would even be possible. Guessing or estimating won't work. Certainly, your previous statement that, "judging from the pictures the 8mm and 12mm would be about f1.2" is not only impossible to do but also your conclusion is highly unlikely.

Each ƒ/stop in photographic nomenclature allows twice the amount of light to reach the sensor as the previous (smaller) full stop.

Standard full ƒ-stop values are - 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64

Half ƒ/stop values are 1, 1.2, 1.4, 1.7, 2, 2.4, 2.8, 3.3, 4, 4.8, 5.6, 6.7, 8, 9.5, 11, 13, 16, 19, 22

With each number to the next, the aperture decreases to half its size, allowing 50% less light through the lens (1 stop). So, the difference between say ƒ/1.2 and ƒ/1.4 is a half a stop which is significant. So again, guessing or estimating these numbers accurately enough is not possible.

Yes it's true, we can't know for certain, and we can't with the ones where the number is given either. The best you can do is have faith in a Chinese seller of a Chinese product from a Chinese factory, or just try these things and see which ones work best. Unfortunately, even then we don't know the next purchase we make is the same product, because the supply chain is so obscure. I have the same complaint about security DVRs and cameras, no one really knows what is what and troubleshooting them is very difficult as a result

 

[Dashmellow]

Yes it's true, we can't know for certain, and we can't with the ones where the number is given either. The best you can do is have faith in a Chinese seller of a Chinese product from a Chinese factory, or just try these things and see which ones work best. Unfortunately, even then we don't know the next purchase we make is the same product, because the supply chain is so obscure. I have the same complaint about security DVRs and cameras, no one really knows what is what and troubleshooting them is very difficult as a result

I disagree. It depends on where you buy. The supplier of these lenses you bought on Amazon provides virtually no information about them. The same is basically true for that 16mm lens you purchased. You don't know what is going to show up in your mailbox. It's your privilege to engage in a crap shoot if you wish but I prefer to buy lenses from a supplier who will provide a range of specifications along with information about how the lens is constructed. Domestic vendors of specialty lenses such as Peau Productions will provide everything you need to know to make a knowledgeable purchase as do many of the better Chinese vendors . There are basic things one would want to know so the lens will meet your requirements. For example, I would not buy a lens not knowing if it were made of metal or plastic or whether the lens elements themselves are glass or plastic. I would not buy from a vendor who doesn't provide the aperture number or the rest of the basics.

Treeye, the supplier of the 4mm and 6mm lenses we've all been talking about here provides a fairly full range of accurate specifications for the lenses they sell and the ones I received from them have proven to be of excellent quality and certainly match the listed specs. And when there was an issue with my purchase they did a terrific job making things right. I'll stick with sellers like them. I don't believe the supply chain to be quite so obscure as you seem to think it is and I have no reason to question any of their numbers either. These are legitimate Chinese businesses offering decent quality goods to a variety of customers, whether it be individuals, or OEMs. It's when you buy no-name products from vendors who won't even clarify what they are actually selling that you'll run into issues with obscure supply chains, etc. It's true that there is a lot of junk out there and the Chinese market is flooded with goods of dubious origin but not every vendor is like that. Just choose your vendor wisely.

For the 6mm lens Treeye provides the following info:
metal/glass
focal length-6.0mm
aperture - ƒ/1.2
image format coverage - 1/2.5"
BFL 5.66mm (back focal length - in air)
MBF 5.01mm (minimum back focus - physical)
M.O.D .3 meters (minimum object distance)

The factory/distributor producing this particular lens offers additional info:

FOV (D×H×V) 75.5°×58°×41.7° (1/2.5" version - others available)
Optical Distortion -20%
Dimension Φ14×31.8mm
Max Image Circle Φ7.2
Weight 10g
Operating Temperature -20~+60 centigrade degrees

 

[Deleted member 37895]

I got the lenses I ordered on Amazon. They definitely don't have IR filters, but I did order that set of filters. I glued one to the 12mm lens with silicone around the edges and I'm letting it cure overnight. For now I'm using the 6mm without an IR filter the image you get is kind of cool. I took some screenshots in webcam mode and those are the ones that appear the most pink, because I think there's no adjustment going on in the hardware. Those pictures the ones without timestamps. Some things look very different. For example my laptop bag is dark blue, but the nylon and the plastic patches show up as light and dark respectively. Something interesting I discovered is all my car windows block infrared, as the pink tinge and bright foliage are gone when looking through the glass.

You were right Dashmellow, the apertures on these lenses are small. They seem to all be about f 3

 

[Dashmellow]

I got the lenses I ordered on Amazon. They definitely don't have IR filters, but I did order that set of filters. I glued one to the 12mm lens with silicone around the edges and I'm letting it cure overnight. For now I'm using the 6mm without an IR filter the image you get is kind of cool. I took some screenshots in webcam mode and those are the ones that appear the most pink, because I think there's no adjustment going on in the hardware. Those pictures the ones without timestamps. Some things look very different. For example my laptop bag is dark blue, but the nylon and the plastic patches show up as light and dark respectively. Something interesting I discovered is all my car windows block infrared, as the pink tinge and bright foliage are gone when looking through the glass.

You were right Dashmellow, the apertures on these lenses are small. They seem to all be about f 3

It's interesting that your car has IR blocking glass. It really changes the whole equation for using lenses with no IR-cut filters. It would be interesting to see what effects you may or may not get at different times of day or night.

As for gluing the filters on using silicone sealant or adhesive, I hope that works out OK without damaging the lens or filter. Most silicones release copious amounts of acetic acid fumes during cure (which is why it smells like vinegar) and in a similar way that ethyl cyanoacrylate (super glue) releases fumes that can damage lenses and filters, so too can silcone sealants. You'll know by tomorrow. If anything gets damaged more likely it will be the dichroic filter, I think. Maybe it'll be ok?

You might enjoy playing around with some of the RGB settings with these lenses like I did in my Varifocal IR lens thread. Some of the settings I used in the first mSetup screen shot would be a good starting point.

 

[TCK81]

As for gluing the filters on using silicone sealant or adhesive, I hope that works out OK without damaging the lens or filter.

What adhesive would you recommend?

 

[Dashmellow]

What adhesive would you recommend?

Lens manufacturers use special UV cured optical cements but they are expensive and hard to find in small enough quantities to be practical enough for people like us who only may need to attach a few filters onto a few lenses. The professional optical cements also require specialized curing equipment.

There's specialized stuff like this available in small quantities. - https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=196

Professionally, companies like Edmund Optical supply a variety of optical adhesives and other required gear.- https://www.edmundoptics.com/lab-production/adhesives/

For just gluing one of two IR-cut filters to the rear of an M12 lens I think some of this UV cement (as seen on TV ) might do the trick at a modest price and it comes with a little UV light source. I have some but I haven't tried it yet, so I wouldn't call it a recommendation at this point. I don't yet know if this stuff is at all suitable for using around delicate optical surfaces and if it is I think the challenge will be in applying it properly without having it bleed or run onto the lens or filter. I plan on trying it on some old crappy dash cam lenses first to get a feel for how well it works. I'll report back on how it goes.

https://www.amazon.com/gp/B01M2733NK

https://www.amazon.com/gp/B06VWVHP5N

 

[TCK81]

Lens manufacturers use special UV cured optical cements but they are expensive and hard to find in small enough quantities to be practical enough for people like us who only may need to attach a few filters onto a few lenses.

That is what I gathered from my research and it isn't cost effective. I've read people using 2 part epoxy. I wonder if hot glue would work but would be somewhat challenging for the small space.

 

[Dashmellow]

That is what I gathered from my research and it isn't cost effective. I've read people using 2 part epoxy. I wonder if hot glue would work but would be somewhat challenging for the small space.

I considered using hot glue but abandoned the idea because the IR filter will be attached to the rear of the lens right near the CMOS sensor which gets pretty hot itself. Combined with the other heat generated by the camera as well as being in a hot car I think the hot glue will fail as soon as it heats up again.

 

[TCK81]

I considered using hot glue but abandoned the idea because the IR filter will be attached to the rear of the lens right near the CMOS sensor which gets pretty hot itself. Combined with the other heat generated by the camera as well as being in a hot car I think the hot glue will fail as soon as it heats up again.

Loctite® Stik'n Seal® Extreme Conditions looks like it may be a good candidate. I shall start a thread instead of derailing this one.

 

[Dashmellow]

Loctite® Stik'n Seal® Extreme Conditions looks like it may be a good candidate. I shall start a thread instead of derailing this one.

What makes you think this stuff would be ok around delicate lens surfaces? According to the data sheet on the link you provided it is combustible, an eye irritant, requires gloves for proper handling because of skin sensitivity and it emits toxic fumes. This "sounds" like something you wouldn't want anywhere near delicate coated lens surfaces or dichroic filters. The point of using UV cured optical cement is that it is for the most part inert. At this point, I think the 5 dollar UV glue on Amazon seems the best bet so far.

 

[TCK81]

What makes you think this stuff would be ok around delicate lens surfaces? According to the data sheet on the link you provided it is combustible, an eye irritant, requires gloves for proper handling because of skin sensitivity and it emits toxic fumes. This "sounds" like something you wouldn't want anywhere near delicate coated lens surfaces or dichroic filters. The point of using UV cured optical cement is that it is for the most part inert. At this point, I think the 5 dollar UV glue on Amazon seems the best bet so far.

Other than flammability the MSDS health hazards and precautions of optical adhesive are the same (at least the Milbond brand I referenced). It looks like methanol is the volatile component of the Loctite product that gives way to the flammability and health hazards. Methanol is a recommended solvent to use for cleaning optics so if none of the other chemicals in the product are harmful to the optics I believe it's a very good option.

Optical adhesive has a fairly tight operating temperature (Norland Products has some rated -15°C (5°F) to 60°C (140°F), some will expand the operating temperature range if aged, and there is one (83H) that is recommended from -150°C (-238°F) to +150°C (302°F) which would definitely work!) so I wonder what is typically used for our dash cams lenses?

I don't know if the UV glue pen will handle the operating temperatures that the camera will experience (I can't find any technical documents). I guess there's only one way to find out though... I started a post where we all can discuss this further.

 

[Dashmellow]

Other than flammability the MSDS health hazards and precautions of optical adhesive are the same (at least the Milbond brand I referenced). It looks like methanol is the volatile component of the Loctite product that gives way to the flammability and health hazards. Methanol is a recommended solvent to use for cleaning optics so if none of the other chemicals in the product are harmful to the optics I believe it's a very good option.

So, methanol is the "only" volatile, hazardous ingredient in the Loctite Extreme glue you recommend that may have potential for damaging the lens or filters or cause a health issue? What about the Trimethoxyvinylsilane, (Methoxycarbonyl)aminomethyl trimethoxy silane, or 1,8-Diazabicyclo[5.4.0]undec-7-ene?

"If none of the other chemicals in the product are harmful to the optics it's a very good option" as you put it seems a rather big "if", if you ask me.

I'm very skeptical that this stuff would be a very good choice for our purposes but perhaps you might like to try it and report back to us.

http://henkelconsumerinfo.com/produ...S&LANG=EN&COUNTRY=US&VKORG=3450&MATNR=1360784

Optical adhesive has a fairly tight operating temperature (Norland Products has some rated -15°C (5°F) to 60°C (140°F), some will expand the operating temperature range if aged, and there is one (83H) that is recommended from -150°C (-238°F) to +150°C (302°F) which would definitely work!) so I wonder what is typically used for our dash cams lenses?

That product (Norland 83H) costs 50 dollars per one ounce bottle and so, like all the other commercially available optical cements is why it is not worth considering or even discussing for our purposes unless we have money to burn to mount one or two filters to any of these low cost lenses. What is "typically used for our dash cams lenses" is likely some similar commercial optical cement but it is done in a factory setting where the cost of the product and the equipment for properly applying and curing it is part of the cost of doing business on a manufacturing scale.

 

[Deleted member 37895]

My silicone tube says it releases methanol and ammonia but those are both volatile chemicals, they shouldn't deposit on any surfaces

 

[Radius8]

You could also set it under an incandescent table lamp as a gentle source of heat in order to "bake" out as much of the volatiles as possible before you mount the lens.

I agree with Dashmellow, use caution when dealing with optics. It would probably not take much to coat the sensor with some off-gazed substance and degrade resolution. Think of the nasty, cloudy deposit on the inside of your windshield due to volatiles from the plastic parts in the car.

 

[Dashmellow]

My silicone tube says it releases methanol and ammonia but those are both volatile chemicals, they shouldn't deposit on any surfaces

IR-cut filters are dichroic filters made by depositing thin films of materials on optical glass in a specialized vacuum chamber. The resulting surface is very delicate and that is why they are always installed inside a camera where they are protected. Ammonia fumes are corrosive and it is "possible" that these vapors may interact with the chemicals on the surface of the dichroic IR-cut filters (or coated lenses) thereby causing damage without depositing anything. When super glue causes fogging of lens surfaces or filters the same thing is happening. It's the chemical vapors causing a reaction that creates the fogging, not anything being deposited. Whether it be acetic acid fumes or ammonia fumes I think caution is advised.