Lens selection for close proximity surface photos

[Danmo]

Good day all,

I am searching for some advice on how I could successfully take photos of a surface that is 5mm away from a CMOS camera sensor.

My ideas so far are;
1.) Find a lens with sub millimeter focal length (0.2mm by my calculations)
2.) Utilize mirrors to increase object distance
3.) Pin hole camera design

I have attached a sketch to illustrate.

 

[sophiecentaur]

Why not increase the object distance and use a longer lens?
And welcome to PF, by the way.

 

[Danmo]

The vertical space allowed for the camera is approx. 15mm.

Oh, and thanks!

 

[sophiecentaur]

The vertical space allowed for the camera is approx. 15mm.

Oh, and thanks!

If you have a space to one side then you could use a 45 degree mirror and a long lens on your sensor. But then, I'm not sure about the usable field there would be. I guess the mirror would need to be curved (convex) and placed at the far side of the subject.

Only you know the actual geometry but I wonder what sort of distortion the arrangement in the diagram will produce - and what masking of the surface there could be, if it's not flat all over. Could there also be a question of available light and depth of focus, whatever system you choose?

A few more sketches are required.

A

 

[Andy Resnick]

Summary:: Lens selection for short object distance

Good day all,

I am searching for some advice on how I could successfully take photos of a surface that is 5mm away from a CMOS camera sensor.

I have attached a sketch to illustrate.

This is going to be a very difficult design challenge, if your diagram is reasonably accurate- a 100mm diameter object placed 5 mm away subtends nearly 86 degrees (170 degree total field of view), so you are likely looking at a fisheye design with all the distortion that implies.

What about a 'door peeper' lens like this:

https://www.grainger.com/product/1H...ucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231

Not sure it will fit your space.

That said, you haven't specified some basic performance aspects: I assume this is visible light imaging, for example. Are there any optical performance requirements regarding throughput or resolution? What about the object illumination- is this a transmission or a reflected light situation?

 

[Danmo]

Thank you both sophiecentaur and Andy Resnick for your input.

Great idea with the door peeper Andy, I will look into this!
And yes, the object will be illuminated by led lighting therefore is a reflected light situation.

 

[Vanadium 50]

I wonder if the fisheye distortion can be (effectively) removed in software.,

 

[alan123hk]

I believe you need to use a macro lens and a macro flash, it is best to use a tripod at the same time.

 

[Tom.G]

I think your idea #2 is the best bet. Use a mirror to relay the image to where-ever the camera fits.

If you have never looked at the workings of a flatbed scanner, find a cheap or junked one and do so. Closest to the object surface there is a flat mirror. From there the path is a series of curved mirrors in a folded light path (3 or 4 mirrors if I recall correctly). The advantage of reflective optics is they don't have to be massive for short focal lengths, also no chromatic aberrations.

Of course a scanner uses a line sensor which is much shorter than the paper width, so the mirrors are curved in only one dimension. It sounds like you need area sensing though, so two-dimensional optics are needed. Anyhow, the optical path is light weight and compact -- just not as compact as you are after.

Is this for a production item or can one (a few) be sacrificed for one-off data collection?

Please keep us updated on you progress.

Cheers,
Tom

 

[Perfidium]

Mobile phone cameras are extremely thin and have increased in there ability to produce good results - May be a way forward

 

[sophiecentaur]

Mobile phone cameras are extremely thin and have increased in there ability to produce good results - May be a way forward

It would make a lot of sense if it were possible. I wonder if the lens may be too integrated for a one-off modification, tho’. The spec details would be important. It might be interesting.

 

[Perfidium]

Or this type of thing for ideas
lots of this sort of thing about in various configs
eBay item number:
353209858759