0

I am buying a JVC camcorder for my dad for Christmas who does ghost hunting. I want to convert this to IR which many people do with this particular model.

I know I need to remove the IR filter from the sensor which is around 8x8x0.5mm in size. But I can't find a 850nm filter that size to put in its place.

Could I remove this filter altogether, and instead attach a 30.5mm 850nm bypass filter instead? Will this achieve the same effect?

  • 1
    Hunting ghosts at the single wavelength is impractical TBH. – Euri Pinhollow Dec 8 '16 at 16:02
  • I found this guy who converts the camera's, but he's revealed in one of his YouTube videos that all of his camers can see in the visible spectrum too. I think I'll try without any filter and see what the results are. – user2924019 Dec 8 '16 at 22:30
3

The on-sensor optical filter has an effect on the optical distance between the sensor and the objective.

Whenever you remove glass from the space between the sensor and the objective, you are very slightly enlarging the FoV and, what is more important, shifting the range of distances the camera can focus at towards infinity+ - that is, if the camera focuses at distances between 1m and infinity now it will focus at distances from 2m to infinity after you remove the glass (and it will focus the converging light if focused beyond infinity).

Other than that little downside - yes, you will have same effect with the filter placed in front of objective instead of filter placed on the sensor.

  • Many thanks, I have confirmed this by removing the filter, reassembling the camera, and the image is blury unless zoomed right in (X6). I am now looking for a filter. The filter I removed was 1.1mm thick, however I can only find 1mm thick filters. Do you think this will make much difference? – user2924019 Dec 16 '16 at 12:41
  • @user2924019: 1mm filter adds approximately 0,5mm of optical distance, 1,1mm filter will add 0,55mm of optical distance. 1mm filter will definitely make difference. You may check whether if it will be enough by using almost any 1mm thick glass, the refractive index is roughly 1,5 for most glass. – Euri Pinhollow Dec 16 '16 at 17:43
  • Hi, I have bought some microscope slides of various thicknesses to do some testing. I could always use thicker glass and add a shim around the sensor for some spacing. I did actually try using a 1mm filter from another camera and it looks pretty clear. I will have to record and display on a larger screen to be sure. – user2924019 Dec 19 '16 at 15:25
2

By adding a filter to the front of the lens, you are adding an air-glass interface (between the back of the filter and the front of the lens) that wasn't designed into the camera.

This additional air-glass interface can create reflections that are transmitted through the lens and picked up by the sensor as flare, or as a type of flare coincidentally called "ghosts". This can happen any time you use filters, and is problematic when a strong light source is in the field of view of the camera (also just outside the field of view).

Better filters are multi-coated to strongly attenuate the flare and ghosts, but the problem can still appear, so it is something to be aware of.

  • I've just found out that some people just remove the filter altogether and still get great IR results with it. Not so great in the daylight obviously. I will try it without first of all. I am worried about what you say with the glare, as this can be misleading. – user2924019 Dec 8 '16 at 22:28
  • True enough. However, I cannot remeber a single time when a non-coated protector has caused any significant problems for me except when exceptionally bright sources were withing the frame (they would cause problems without filter too). – Euri Pinhollow Dec 9 '16 at 18:23
  • @EuriPinhollow happens to me all the time with NDs and ND grads while taking sunset pictures. I get green flare because of the parallel filter planes. Without the filters, I don't get the same flare, nor do I get it when using a high quality coated polarizer (at least to the degree that I do with my NDs) – scottbb Dec 9 '16 at 18:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.