# Thread: Help with a Camera Obscura

1. ## Help with a Camera Obscura

So I am making a Camera Obscura in my bedroom. The window I will be using faces a wall about 10 feet away (I can take a precise measurement if needed).

So my question is this....I found the formula for the diopter strength I need....but how big should the lens be to create a good sized image on the walls....I want it to take up most of the wall....at least a 5x5 foot type of image. I have seen people use lenses as small as an inch or 2 but I feel like the projection with a lens that small would not be large enough.

Any help on this would be greatly appreciated from all you lens experts!!!

2. I'm sure you've seen the informative wiki?
http://en.wikipedia.org/wiki/Camera_obscura

3. yes i have looked thru the wiki site...it does not give me the info i need.

any help?? anyone?

4. Years ago, like maybe 20+, Scientific American had a series of articles about the camera obscura. If you dig through the archives you may find what you need. Ther only practical experience that I have came in a physics course that I took in college more years ago than I want to think about. Maybe digging through some of the online physics text books could help you.

5. Play with the image distance and focal length (diopters) to increase the image size.

The diameter of the lens will only increase the aperature which will in turn give you a shallower depth of field. A shallow depth of field will require more precise measurements for the focal length to keep the image focused.

A larger diameter lens will also require an aspheric design intergrated to keep the complete image focused otherwise you will have soft edges.

Good luck :cheers:

6. To the best of my knowledge (and I have been known to occasionally be wrong) the original camera obscura did not utilize a lens, just a pin hole. Therefore, if you use a lens you will not have a camera obscura but a camera grandus motherus.

7. Originally Posted by braheem24
Play with the image distance and focal length (diopters) to increase the image size.

The diameter of the lens will only increase the aperature which will in turn give you a shallower depth of field. A shallow depth of field will require more precise measurements for the focal length to keep the image focused.

A larger diameter lens will also require an aspheric design intergrated to keep the complete image focused otherwise you will have soft edges.

Good luck :cheers:
It's quite useful. Thanks!

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