An Alternative way to Mod your DSLR (no glass removed)

[nebulosity. (Jo)]

G'day everyone,

I did some experimenting yesterday to see if I could remove the offending IR cut coating from the filter assembly on my sensor, without having to remove the glass and muck up focus etc.

It seems that it IR cut coating is on the front surface of the filter assembly and can easily be polished off with a dremel and some metal polish, without harming the glass in any way (no clouding, scratches, etc)

I thought is might be of interest to anyone who wants to mod their camera but doesn't want to lose lens focussing ability (and who doesn't what to fork out money on a replacement filter)

Cheers
Jo

[nebulosity. (Jo)]

And here are a few images I took with the camera (350D) this morning, seems to be functioning great. Will try it out on the sky as soon a possible.

No adjustments have been made to the images.

[nebulosity. (Jo)]

Here is a before and after shot, as expected the red response is much improved.

[alistairsam]

Nice one Jo. But are you sure its just the coating on most dslr IR glasses and not the glass itself?
The DSO test would be proof. with the coating removed glass and without the glass.

Cheers
Alistair

[nebulosity. (Jo)]

Originally Posted by alistairsam

Nice one Jo. But are you sure its just the coating on most dslr IR glasses and not the glass itself?
The DSO test would be proof. with the coating removed glass and without the glass.

Cheers
Alistair

Yeah that's a good idea, I'll do a with and without the glass test tomorrow night, it's raining at the moment. I'm pretty sure it is only the coating that kills the Ha though, without it the glass just has a blue tint.

Jo

[Merlin66 (Ken)]

Jo,
I believe the "coating" is just an AR coating with some IR rejection.
There's only one (thick) filter in the older Canon's and as far as I know (based on the filter glass specs) the glass is providing the "colour balance" correction which has the dramatic effect on the red sensitivity.
If you can obtain measurable Ha intensities and compare this may be easily resolved.
A slit spectroscope and the solar spectrum is one of the easiest ways of verification.

[nebulosity. (Jo)]

Originally Posted by Merlin66

Jo,
I believe the "coating" is just an AR coating with some IR rejection.
There's only one (thick) filter in the older Canon's and as far as I know (based on the filter glass specs) the glass is providing the "colour balance" correction which has the dramatic effect on the red sensitivity.
If you can obtain measurable Ha intensities and compare this may be easily resolved.
A slit spectroscope and the solar spectrum is one of the easiest ways of verification.

I think you might be right Ken, did some tests last night taking images of an IR led though the various filters and and my results were roughly:

With original filter; almost no light visible.

With modified filter; light about 50% as bright as with no filter.

So it seems the bare glass does still cut down on the IR. But is still letting though about 50% more than the original filter. Also Ha transmission might be different than IR.

Will do proper tests to night on some nebulae. Skies are looking nice and clear

Cheers
Jo

PS, yeah the filter is one piece, looks like two bits of glass glued together. I wonder if it's the glue that makes the blue colour? The glass itself looks clear.

[gbeal]

While I am the first to agree a stint of DIY is a great way to while the time away, the non-techie type in me wonders why not just biff the glass and be done with it?

So the focus point shifts slightly due to an optical surface not being there, why not just move the sensor the appropriate amount, if auto-focus etc is still required?
Gary

[nebulosity. (Jo)]

Originally Posted by gbeal

While I am the first to agree a stint of DIY is a great way to while the time away, the non-techie type in me wonders why not just biff the glass and be done with it?

So the focus point shifts slightly due to an optical surface not being there, why not just move the sensor the appropriate amount, if auto-focus etc is still required?
Gary

It isn't really possible to move the sensor any more than maybe 0.5mm and that isn't enough (need at least 2.5 to 3 mm shift)

I have been able to cut the camera frame (on one of my 350D's) an move the eos mount in 3mm but that isn't a very practical way of over coming the problem.

Auto focus isn't a concern for me, I don't ever use it, the problem it that with the glass removed most of my lenses can't focus at infinity, and I like doing wide fields so that is unacceptable.

Cheers
Jo

[Merlin66 (Ken)]

Removing the filter element completely on the older Canons, removes 3mm thickness of glass which affects the focus point by 1mm

[Garbz (Chris)]

Just a note to anyone thinking of doing this with a Nikon, don't, or at least do some research. Many Nikons have a sandwich type glass arrangement with the IR cutting component being ... the middle element. There's nothing to polish.

[nebulosity. (Jo)]

Originally Posted by Garbz

Just a note to anyone thinking of doing this with a Nikon, don't, or at least do some research. Many Nikons have a sandwich type glass arrangement with the IR cutting component being ... the middle element. There's nothing to polish.

Thanks for the info, I didn't know that

Jo

[Joss (Jonathan)]

Interesting. I have a Nikon D70 which I only use on my telescope, meaning I don't care about a focus shift. What are my options for improving Ha/IR?

<edit> Its OK...I found an answer...
http://www.astrosurf.com/buil/d70/ircut.htm