Superzoom compact camera crops my Schlieren!
I am playing with Schlieren photography which makes differences in air density visible. Lots of explanations on how it all works on the web so I'll just detail my issues here. This is the basic setup...
The issue is that the light coming into the camera is at some very extreme angles. With a fixed lens camera this is not an issue, but with a superzoom the lens is long and complicated and the light ends up getting cropped somewhere inside. Here is a rough idea of what is happening in the camera...
So I end up only seeing a small part of the image I am hoping for, the rest cut off. Now, this is just point source light. You can clearly see the entire mirror, but instead of the mirror being filled with light, only the center 1/3rd is.
I have done a ton of work nailing down the issue here, and it is my camera, no doubt. I borrowed a friends DSLR and it works perfectly with no cropping when I use his telephoto lens, but both my compact cameras and my camcorder all have the irising issue.
The camera is a Cannon S5 IS. I lock the fstop as wide as it can go at 2.7 using CHDK.
So the question is.... anything I can do about this? I assume some sort of corrective lens after the focal point could bend the light to a smaller angle and get it all through the problem aperture. One issue is that it will also distort anything I am filming that is in front of the mirror.
Things that sadly can not be changed. A color filter HAS to be placed at the focal point, so the camera must be behind that point. I can't move the camera closer to the focal point, it's all ready less than 1mm from the front of the lens. I can't afford to go out and buy a DSLR and matching telephoto lens.
Here is an example of the pictures I am taking... you can see more at my web site http://www.ian.org/Schlieren/ page. It really is fun, but this one last problem is pretty frustrating.
The issue is that the light coming into the camera is at some very extreme angles. With a fixed lens camera this is not an issue, but with a superzoom the lens is long and complicated and the light ends up getting cropped somewhere inside. Here is a rough idea of what is happening in the camera...
So I end up only seeing a small part of the image I am hoping for, the rest cut off. Now, this is just point source light. You can clearly see the entire mirror, but instead of the mirror being filled with light, only the center 1/3rd is.
I have done a ton of work nailing down the issue here, and it is my camera, no doubt. I borrowed a friends DSLR and it works perfectly with no cropping when I use his telephoto lens, but both my compact cameras and my camcorder all have the irising issue.
The camera is a Cannon S5 IS. I lock the fstop as wide as it can go at 2.7 using CHDK.
So the question is.... anything I can do about this? I assume some sort of corrective lens after the focal point could bend the light to a smaller angle and get it all through the problem aperture. One issue is that it will also distort anything I am filming that is in front of the mirror.
Things that sadly can not be changed. A color filter HAS to be placed at the focal point, so the camera must be behind that point. I can't move the camera closer to the focal point, it's all ready less than 1mm from the front of the lens. I can't afford to go out and buy a DSLR and matching telephoto lens.
Here is an example of the pictures I am taking... you can see more at my web site http://www.ian.org/Schlieren/ page. It really is fun, but this one last problem is pretty frustrating.
0
Comments
Do you have any other optics in the light path besides the camera lens?
Have you tried the macro mode on the camera?
Are you using a knife edge or a pinhole at the focal point of the Schlieren system?
Moderator of the Cameras and Accessories forums
It's just the mirror and the camera.
I can't use macro mode because I need to zoom in. The mirror is 12 feet away.
When taking pictures I use a slide with stripes of color in place of a knifes edge. But for testing I remove it, as the problem shows up without it from the angle of the light entering the camera.
I can move my camera forward so the focal point ends up inside the lens housing and get the full image, but now of course I can't use a knifes edge or filter.
I know one of those nice new micro four-thirds cameras with a telephoto lens and HD recording would solve my problem. :-)
Try using macro mode. You may actually have to move the camera back a bit. It may invert the image but that should be OK in that you can right the image in software.
Moderator of the Cameras and Accessories forums
The further back the camera is the worse the problem becaomes due to the light spreading out rappidly once past the point where all the light comes to a point at the knifes edge location.
I wish I could just take the lens off the camera. Somhow I doubt that would end well!
http://www.bhphotovideo.com/c/product/381969-REG/Canon_0300B001_TC_DC58B_1_5x_Teleconverter_Lens.html#accessories
http://www.bhphotovideo.com/c/product/381970-REG/Canon_0301B001_LAH_DC20_Lens_Adapter_Hood_Set.html
Moderator of the Cameras and Accessories forums