looking for lens with externally controllable focus (and fixed focal distance)

[Dobias]

Hello,
for an industrial application I am looking for a lens (for a Dalsa Piranha [line scan camera]). The camera is fixed above a conveyor belt and takes pictures of the objects running beneath it. Right now I am using an AF Nikkor 50mm 1:1,8D.
For a new project the depth of field has to be bigger. The objects are between 1mm and 160mm high. They are nearly cuboids. Even with very much light and maximized camera gain I can not close the Aperture enough to get everything sharp.
So I would like to try it with a lens, whose focus can be set with electrical signals. The object hight is measured by an appropriate sensor located 200mm upstream. I would like to avoid reverse engineering some proprietary protocol of some camera manufactor.
Is there something with an open interface? It would be great if the hardware could survive 100000 to 1000000 repetitions of changing the focus. I think that the internal motor of a lens will do its job more reliable than a hypothetical contruction with a fan belt or something like this.
Do you have an idea for me?
Dobias

 

[Big Mike]

Moving the lens further away will increase the DOF....as long as you don't use a longer focal length.

I assume you are using a Digital SLR camera. You might consider trying a camera with a smaller sensor, as that will most likely result in a deeper DOF.

 

[analog.universe]

How much light is very much? With appropriate strobes you should be able to shoot fine at f/22... even at base sensor gain. I'm not aware of any lens that allows anything but a camera body to electronically control focus unfortunately. But I also suspect that a lighting setup would be cheaper and easier to implement than a new lens anyway? How far did you actually push the aperture before you ran out of light?

 

[Helen B]

The best person to ask is the person who designed your system, or to Dalsa for recommendations for third-party equiment.

Do you want to focus solely on the nearest part of the object or do you need some depth of field for shaped objects? What distance are you shooting at?

You can get lenses that have standard external gearing that meshes to off-the-shelf focus motors and they can be controlled by laser rangefinders.

 

[mjhoward]

I have a few questions first... Is your Dalsa C-Mount? What sensor size and what resolution? There are many Motor Driven C-Mount lenses available that you can connect to some Digital I/O to drive the focus direction, etc. The problem is that most of them are designed for low resolution sensors and may perform poorly if you have a megapixel or higher sensor. You could also use a Canon DSLR... you can control the focus of the lens attached to it through the EDSDK (along with every other function of the camera, including live view).

 

[Helen B]

I think the Piranhas all have a trilinear sensor 2048 or 4096 pixels wide - either 26 mm or 41 mm long (roughly) - but the OP should confirm which Piranha he or she has. It's probably too wide for most C-mount lenses, if the entire sensor width is used (OP to confirm).

 

[unpopular]

^^ is there anything you don't know?!

What purpose is this imaging system? Are you measuring stuff? What kind of resolution do you need?

You may want to consult with Edmund Optics customer service.

Contact Us - Edmund Optics

And what the heck kind of business are you in, teeny tiny boxes?

 

[analog.universe]

^^ is there anything you don't know?!

This is always what's going through my head when I see Helen post.

 

[unpopular]

She's got to be the smartest person here by far, and I love how whenever she scolds some know-it-all type she signs the post:

Best,

Helen

Which is just awesome.

 

[mjhoward]

I think the Piranhas all have a trilinear sensor 2048 or 4096 pixels wide - either 26 mm or 41 mm long (roughly) - but the OP should confirm which Piranha he or she has. It's probably too wide for most C-mount lenses, if the entire sensor width is used (OP to confirm).

If this is true then it's almost definitely not a C-Mount lens. I think the largest image circle I've seen produced for a C-mount was about 23mm diagonally and that is along the lines of m4/3's format which has a 17.3mm width (21.6mm diag.). I can't imagine Dalsa designing their bodies for a mount where heavy vignetting was intentional/unavoidable. I've had experience with some machine vision cameras (mostly by IDS) but they have been between 1/3" and 2/3" and were all C-mount. I know of several companies that make motor driven lenses (zoom, focus, and iris) for this mount, but I'd have to look into options for a different mount. Using the EDSDK for Canon camera bodies is still a good alternative (depending on the environment). The SDK is easy to work with and having readily available COTS parts is always a plus. Nikon also offers an SDK but I've not used it so I can't comment on the functionality they provide.

 

[unpopular]

I really think Edmund Optics is the way to go. If all else fails, they can fabricate the lens to specification.

 

[Dobias]

@Big Mike: I'm not using a DSLR. It's a line scan camera. Digital camera - Wikipedia, the free encyclopedia
@analog.universe: With 16 fluorescent tubes I can only open the aperture to 2.8. With passive cooled LED line light to 8 (still not enough). The camera has to execute over 8000 line triggers per second.
@Helen B: The camera has about 600mm distance to the belt and it would be enough to just be sharp at the maximum height of the object.
@mjhoward: At the moment I am using a F-mount. From first glance, these SDKs looks like they are only for controlling a whole camera, not just a lens. But I will have a second look.
@unpopular: It's for image an barcode recognition. I would like to use a version of the camera with 4096 pixels per line (trilinear). And yes, it's all about teeny tiny boxes.

I will see what I can find out at Edmund Optic. Thanks for all the input guys. :thumbup: