short distance camera module design

[tig]

Hi forum,

I hope I'm in the right place.

Recently I started an interesting project. One of the important part in this project is the very short distance image capturing.

The device which I design should be able to take an image of the object with the size L=100 mm, W=40 mm.
The distance of the object from the camera lens should be ~10-30 mm. Actually the device size is ~50 mm that's why I choose that object distance.

I spend a lot of time to understand how to choose correct sensors and lenses but I'm confused.

There are a lot of lens calculators in the internet. I used them to calculate the parameters of lenses suitable for me.

But, when I tried to find the lenses with calculated parameters I found that the (minimal object distance, working distance or minimal focus distance) mentioned in the specifications are very big.

Ether I don't understand what is the working distance or the calculators missing something.

So here I'm confused.

Could you please point me to the right direction?

Thank you very much.

[chauncey]

tig...your question is a "field of view" question, I think.
You want to shoot an object that is 100mm wide and a 10-30mm focusing distance...right?
The only lenses that will allow you to get that close to your subject are macro lenses.

As an example...this image is using a 35mm sensor camera, a 180mm macro lens with a 2x TC,
making it 360mm, and extension tubes to allow a closer than normal focusing distance.



That 12mm wide image would be 24mm wide without the 2X tele-converter...removing the extension
tubes would require putting more distance between the camera and the subject, like up to 18 inches.

It all depends on your camera sensor size and your macro lens selection.
What do you have?

[Inkanyezi]

There are a few cameras made for medical professions, as endoscopes, and also cameras for dentists, to take images inside the mouth, which can do what you are asking for.

You are asking for a very wide angle at a very short distance. There are no normal camera lenses that get that close, although adaptions could be made with very short focal length wide angle lenses.

The cheapest cameras that can be used for the purpose are the camera modules for cellphones.

[loosecanon]

Canon used to sell a 35mm and a 20mm lens to be used with a bellows - hence no focus mechanism. These special lenses slope to a very narrow front to allow the subject to be lighted. They allow very large magnification with a wider angle lens. They were originally designed for copying film frames.

[tig]

Thank you very much.

Actually the cheapest solution is to design my own camera module which I'm going to do.
The simplest way is to take a CCD/CMOS sensor and a wide angle, very short focal length lens.
But I'm not sure if it is possible to manage with only one lens.

[Dave Humphries]

Welcome to the CiC forums "tig",

~ an object with the size L=100 mm, W=40 mm.
The distance of the object from the camera lens should be ~10-30 mm.

The simplest way is to take a CCD/CMOS sensor and a wide angle, very short focal length lens.
But I'm not sure if it is possible to manage with only one lens.

I am wondering, even with this approach, whether you'll be able to produce a 'photographic' image with sufficient Depth of Field (allied with flatness of plane of focus) to maintain sharp focus. Perhaps you don't need a 'photographic' quality of image (as we would know it) though - depends upon what you need the image for.

Perhaps some version of 'scanning' technology might provide the solution???

Could you do me a favour please?
Could you click Settings (right at the top),
then Edit Profile (on left)
and put your first name in the Real Name field
and where you are (roughly) in the Location field?
this helps everyone give you more personal and relevant answers - thanks.


Anyway, good luck, Dave

[rpcrowe]

I read this post several times and am still not sure if I understand it... It seems as if the operational part of the post reads as follows:

"The device which I design should be able to take an image of the object with the size L=100 mm, W=40 mm.
The distance of the object from the camera lens should be ~10-30 mm. Actually the device size is ~50 mm that's why I choose that object distance."

Let's see if I do understand your needs...

You want to shoot an image of a subject that is 100mm x 40mm... This would equate to a image to subject ratio of far less than 1:1.

If you were shooting at a 1:1 ratio, the largest area you could capture using a full frame camera would be 36 x 24 mm. With a Nikon APS-C crop camera the largest area captured at 1:1 would be 23.6 x 15.7 mm while the largest area captured at 1:1 shooting with a Canon APS-H would be 28.7 x 19 mm,

In order to cover your 100 x 40 mm subject with a full frame camera, your ratio would need to be around 1:2.77 which would allow you to cover an area of approximately 100 x 66 mm.

The focal length of your lens would control the lens to subject distance needed to achieve a 1:2.77 ratio with a shorter focal length allowing/requiring a closer distance and longer focal lengths allowing/requiring a longer distance between lens and subject.

The image achieved at 1:1 using a 50mm macro lens would be virtually the same as if you used a 60mm, a 90mm, a 100mm or a 180mm lens. The only difference would be the distance between lens and subject required.

So, if I were presented with your problem, I would ascertain these parameters in order:

1. The size of the area you need to cover

2. The size of your sensor (the ratio between 1 and 2 is the image ratio you would need)

3. Once you decide what image ratio you need, decide the maximum distance from the subject that your camera/lens will physically fit.

4. The image ratio needed along with the maximum lens to subject distance would determine the focal length that you need to use. If there is no physical limitation of lens to subject distance, any macro lens of any focal length would work. In fact, some non-macro lenses can achieve a 1:2.77 ratio.

BTW: the lens to subject distance would be the same for a non-macro lens as it would be for a macro lens, given that the non-macro lens can focus close enough to achieve the same image ratio...

I may be totally in left field regarding your needs. If so, please accept my apologies...

[Inkanyezi]

Essentially, my suggestion of a camera module of the type that is used for cellphones, was the suggested close distance, which in a way indicates that we are in somewhat crammed quarters. The dentist's camera, that is used for imaging within the oral cavity does exactly what you are asking for, and its imaging device is the same as in many cellphones. Those imaging devices come with various pixel densities, from low resolution ones to extremely high resolution. Often they have a lens that is in the region of about 2 mm focal length and an aperture of about f/2. Most of them are a single unit with serial output.

An ordinary camera lens of more than about 25 mm focal length cannot be brought so close to the subject, and the camera itself adds substantial bulk. It is feasible, but I would prefer a simple module, as those that sit in cellphones.

Could you elaborate a bit upon the idea, as to why it has to be so close to the subject, and what kind of resolution that might be needed, and also what imaging errors that could be accepted. At a wide angle, you should expect both optical errors and vignetting. Both can be corrected.

The device in thie link is connected to USB of the computer and has its own light source. The lens is in the middle of the light source.
http://www.ildentistaveneto.com/lang...eo-camera.html

[jcuknz]

I had an absess in my mouth a few months ago and while I waited for the dentist to see me I saw my doctor and he took a picture of it using his cute little Panasonic P&S camera ... obviously as a Pany man myself the past decade I approved his choice of camera but it simply proved to me just what the modern P&S is capable of. All this mucking around with bellows extension tubes macro lenses is strictly old hat Just get a good P&S. I gave the print to the dentist who was standing in for the owner of the business so i cannot show it here.... but "Open wIde", camera almost in mouth, CLICK! and bob's your uncle great record shot using built in flash for illumination

[tig]

Thank you very much guys.
You spent a lot of time to answer me and it is very appreciated.

The device which I'm designing, is color recognition device. It should scan the paper and detect the colors on it.
The smallest part which should be recognized, has a size 0.1 mm.

Let me try to answer the question "why it has to be so close to the subject?"

The paper should be placed into the device and then scanned. It is completely closed environment. The external size of device has a limitation L = 110 mm, W = 60 mm. That's why the object should be so close to the camera.

Concerning the resolution, I can guess that VGA should be enough.
I'm going to use the sensors with the following formats: 1/3", 1/4" or 1/9".

May be scanning technology might provide the solution as suggested Dave. I don't know yet and going to investigate that.

Best Regards,
Tig

[tig]

Essentially, my suggestion of a camera module of the type that is used for cellphones, was the suggested close distance, which in a way indicates that we are in somewhat crammed quarters. The dentist's camera, that is used for imaging within the oral cavity does exactly what you are asking for, and its imaging device is the same as in many cellphones. Those imaging devices come with various pixel densities, from low resolution ones to extremely high resolution. Often they have a lens that is in the region of about 2 mm focal length and an aperture of about f/2. Most of them are a single unit with serial output.

An ordinary camera lens of more than about 25 mm focal length cannot be brought so close to the subject, and the camera itself adds substantial bulk. It is feasible, but I would prefer a simple module, as those that sit in cellphones.

Could you elaborate a bit upon the idea, as to why it has to be so close to the subject, and what kind of resolution that might be needed, and also what imaging errors that could be accepted. At a wide angle, you should expect both optical errors and vignetting. Both can be corrected.

The device in thie link is connected to USB of the computer and has its own light source. The lens is in the middle of the light source.
http://www.ildentistaveneto.com/lang...eo-camera.html

Hi Inkanyezi,

What type of optical errors do you mean?
Distortion, Aberrations, ... ?

Bests,
Tig