ALPR: anyone have a 100mm lens they like?

[cam235]

Due to the number of burglaries in my neighborhood lately, I want to keep a record of cars passing by. Because of a bend in the road, I have a view directly along it from one corner of my house, but depending on how tall the nearby parked cars are, plus other obstructions limiting my camera elevation, plates may be visible only when they are 250 to 300 feet away. I have an "IR Cannon" illuminator that is actually good enough for that distance (for reflective plates; nothing else) and I've got a Dahua 4MP HF5421E that I like (especially the remote manual focus feature). The trick is the lens.

I have tried two CS-mount varifocal lenses: a pricey Theia 9-40mm and a cheap noname 6-60mm. Both lenses show legible plates by eye (day & night) with the 40mm giving better detail and brighter image despite the shorter length. Even with careful focusing, neither one is optimal for reliable ALPR operation at that distance.
Theia Technologies CS-Mount 9 to 40mm Telephoto Day/Night SL940A
Vari-focal Lens CS Auto Iris 6-60mm for CCTV Security Surveillance Camera | eBay

So... I have a few lenses that don't quite work. Can anyone suggest one that will? I see 100mm lenses such as the one below, but I worry it will be dark and blurry like my 6-60.
8 - 100 mm CCTV Camera CS mount Lens, auto iris, varifocal, mega pixel! MO08100G | eBay

 

[cam235]

It is curious... I have now tried to order three different kinds of CS-mount 100mm lens from three separate suppliers (ebay, Amazon, and B&H Photo in New York). In each case, after several days, the vendor replied that the supposedly in-stock lens is either simply not available, or backordered with no ETA. As if the product doesn't really exist. Looks like the way to get that kind of reach is with a PTZ camera with 20x lens.

 

[Kawboy12R]

I've seen adapters for CS mount to DSLR-type lenses before. A box camera with a Canon 75-300mm lens on it is seriously badass. I don't remember where the adapter came from though.

 

[cam235]

Thanks- yes, I do have a Canon EF - CS lens mount adaptor from ebay. I tested a Sigma 70mm macro and it works, I was just hoping to avoid using a big heavy expensive DSLR lens, and I also wanted a lens with auto-iris the IP cam could control. But maybe the DSLR lens is my only real option at this point.

EDIT: Would love to find a decent 100mm lens for DSLR "cheap", but haven't seen them under $400 new. I see an old used Canon FD 100mm macro for $65, maybe that's an option.

 

[Kawboy12R]

Seems to me that the old film Canon stuff doesn't work with newer EOS Rebel stuff so would be available cheap used. But yeah, apart from size the auto iris problem might present the most complications.

 

[cam235]

In case anyone else needs a long lens: I finally got one, and can confirm this particular model works pretty well on the 4 MP Dahua box camera for reading plates at 250-300 feet.
SPECO TECHNOLOGIES VF5100DC 5-100mm Auto Iris Lens CS Mount
Amazon.com : SPECO TECHNOLOGIES VF5100DC 5-100mm Auto Iris Lens CS Mount : Surveillance Camera Lenses : Camera & Photo

That lens is good enough for OpenALPR to get a correct read from 250 feet with 94% confidence level (assuming the plate frame doesn't touch the numbers, as many CA plates tend to)

 

[nayr]

sweet, thats what I was hoping.. post up some samples pls.. thats really good for such a distance.

 

[cam235]

Sure, I will post some. I want to actually set up a plate at a known distance. With such a long lens looking along the road, as a random car drives it is hard to tell exactly how far away it is. One thing I can say is you definitely need to refocus morning & evening, because the 850nm IR and visible focus points are different (I was spoiled before with my IR-compensated Theia 40mm).

Hmm... even with refocus, this lens may actually work better at night, than during the day, due to chromatic aberration. When all of your light is only one wavelength (eg. 850nm) focus looks better. Just morning now; likely will do better during daytime when the lens is more stopped down.

 

[cam235]

So far I am happier with this lens at night, than during the day, but I'll see if I can focus it better this weekend. Here are a few shots using the 5-100mm Speco zoom lens at the long end, on the Dahua 4MP box camera. The night shot is a 1:1 crop where I am holding the plate at a distance of 310 feet from the camera (IR illuminator also right next to the camera). There are three small reflective tape squares below the plate, spaced 6" apart on centers. The two daytime photos of the school bus are at (very approximately) 200 and 300 feet away.

 

[bp2008]

Nice results. Does that lens auto-focus? I'm guessing not since you said you need to refocus it twice a day.

I think a good PTZ would be easier to work with (20-30x zoom + autofocus + long range powerful IR built in). Better if they would build one without the pan and tilt parts to make it cheaper and more compact, though. If I recall, most 20x PTZs are close to or beyond 100mm focal length at the far end of their zoom.

 

[cam235]

Absolutely a good PTZ would be easier. First thing I tried was a Sunba mini-PTZ with lens to 94mm and the hardware was OK but firmware very poor. No manual exposure! night images totally overexposed. Also cannot view horizon, about five or ten degrees short. Awkward to mount the thing tilted to compensate. Don't want to pay for a good quality 25x PTZ. Also they are a bit large & obtrusive.

My Speco lens does not autofocus, but the Dahua box cam can move its sensor to focus with remote command. For example with my setup, this command:
http://myuser:mypass@192.168.1.46/cgi-bin/devVideoInput.cgi?action=adjustFocus&focus=0.07&zoom=0
is about the right focus setting for daytime. If I use "&zoom=1" then it does an autofocus adjustment but that locks onto the nearby tree branch at the edge of frame, so that's no good.

 

[bp2008]

Ah, yes, now that you mention it my Dahua PTZs have a heck of a time autofocusing on the thing I want when there is something closer like that tree branch. And at night I am lucky if they focus on anything at all if it isn't very brightly lit when the focusing is happening. I guess you'd still need to automate manual focus changes even with a PTZ.

 

[nayr]

yeah unless he mounts a license plate out there on a permanent fixture auto-focus wont work at night with exposure so high it cant see anything..

though presets usually include a focus setting so they can auto-focus faster; so if you turn off autofocus you could use presets instead of API commands w/a PTZ

What shutter speed you looking at? That tree is a bitch; chainsaw? lol heh

 

[cam235]

Right now I use a shutter speed of 1/500 during the day and 1/120 at night. The one good thing about the view under the trees is it's almost exactly along the road. Also that's a T junction just before the house at the end, so there's a limit to how fast cars will go. Result is hardly any motion blur with 1/120 so it's good enough in this case.

 

[nayr]

turn on WDR, start off low and work your way up.. with them shadows your gonna need it and it'll probably let you crank it up to 1/1000 in day.

im running over 2x that but im half the distance; you may need even more IR at night to run higher; mebe dual cannons.. reducing noise/gain is the best way to increase reading accuracy.

 

[cam235]

Thanks for the tip @nayr about WDR. I enabled that and a setting of 25 makes the picture low-contrast, but ALPR seems to like it just fine. Here's a car somewhere around 200 or 250 ft. Since then I've backed off the WDR settings to 18.

 

[cam235]

UPDATE! I just tried a Canon EF 100mm f/2 lens I happened to have on the shelf, obviously big & heavy but holy cow it's so much better, there is no comparison. No need to stop it down; even wide open the image is crisp. From 250 feet I can read a dealership phone number printed along the edge of a license plate frame.

The main drawback is, um... the price: Amazon.com : Canon EF 100mm f/2 USM Lens : Camera Lenses : Camera & Photo

Back in the day I remember people claiming the other Canon full-frame DSLR choice in this focal length (Canon EF 100mm f/2.8 Macro) is sharper than this one, so maybe you can find a deal on this lens used. Seems like a waste to be using a full-frame DSLR lens on a 1/3" sensor camera, but I wasn't using it otherwise.

 

[tangent]

So you just happened to have some sort of EF to CS mount adapter? Or are you just looking through a DSLR?

Good optics make a big difference. The canon lens obviously contains a bunch of auto focus hardware that wouldn't do any good mounted to a box camera part of the reason for the price.

 

[cam235]

Yes, I also had a Canon EF to CS mount adaptor handy. they are around $15 on ebay.
Canon EOS EF EFs lens to C Mount Film Movie Bolex Video Camera CCTV Adapter Ring | eBay

It's a pretty righteous lens for the little box camera, but the mount has held up to the weight, so far.



If I didn't have the Canon handy, I might have tried something like Amazon.com : Nikon 100mm f/2.8 series E AIS manual focus lens : Camera & Photo together with Camera Adapter For Nikon F Mount Lens To 16mm C Mount Film Movie Adapter | eBay

 

[cam235]

I put the previously shown test plate in the trunk of my car, left the lid up and drove down the street. This image is a 1:1 crop with Dahua 4MP and the Canon EF 100/2 lens, at a distance between 250 and 300 feet.


You can see by the fuzziness of the taillights how far apart the 850nm and visible-light focus settings with this lens are (of course, the Canon EF lenses were never intended for IR). In my case, using the HTTP API "action=adjustFocus" I need to set focus=0.19 for daytime and focus=0.37 at night.

BTW, the Speco CS-mount 5-100mm lens was usable at night, it's just during the day that it had veiling glare, low contrast and blur issues. The Canon EF image is really clear and detailed during the day. For example, this delivery truck is between 200 and 250 feet away.