Removal of IR Highpass filter

[adhocphotographer]

Hi all,

How many of you guys have removed the IR highpass filter in your DSLR. I have an old, abused, well loved but unused 450D sitting around and i would love dearly to breath some new life into it. I have tried to sell it but to be honest the street value of it (lensless) is not worth me selling.... this was my first camera, and well, i love the little fella! As such, I'm looking into getting the IR filter removed....

How many of you guys have done this? any advice? I don't think i will replace it with another filter (e.g. Baader BCF), but am also considering removing the AA filter too (a 450DE one might say). However this would remove the dust-removal feature.... anyone done this? was sensor dust then a problem?

Thanks for any advice/experience in this area!

John

 

[Loswr]

I'm looking into getting the IR filter removed....

...but am also considering removing the AA filter too (a 450DE one might say). However this would remove the dust-removal feature.... anyone done this? was sensor dust then a problem?

From the diagrams I've seen, it appears that the IR cut filter and the horizontal part of the AA filter (along with the 1/4-wave plate) are all stacked together in the assembly that is piezoelectrically vibrated for 'sensor cleaning'.

 

[adhocphotographer]

I'm looking into getting the IR filter removed....

...but am also considering removing the AA filter too (a 450DE one might say). However this would remove the dust-removal feature.... anyone done this? was sensor dust then a problem?

From the diagrams I've seen, it appears that the IR cut filter and the horizontal part of the AA filter (along with the 1/4-wave plate) are all stacked together in the assembly that is piezoelectrically vibrated for 'sensor cleaning'.

I thought that in the 450D the AA + dust removal where a singular, separate, unit to the high-pass (it is a high-pass right?), though your wisdom being what it is i will definitely re-check. Does that mean that even removing the IR-cut would abolish the dust removal system (DRS), or only once the AA filter is removed will the DRS be abolished?

 

[arjay]

If you haven't seen this site, it gives step by step instructions, with photos
http://ghonis2.ho8.com/rebelmod450d1.html
good luck.

 

[TrabimanUK]

Hi,
I've not done it, but I'm looking at getting my 40D coverted to IR by a company. Do a google / youtube search, as I believe there are a lot of tutorials on removing the filter and then adding differnt IR/UV filters (though you won't want to add the new bits).

you could try:
http://ghonis2.ho8.com/rebelmod450d4.html

 

[Loswr]

I thought that in the 450D the AA + dust removal where a singular, separate, unit to the high-pass (it is a high-pass right?), though your wisdom being what it is i will definitely re-check. Does that mean that even removing the IR-cut would abolish the dust removal system (DRS), or only once the AA filter is removed will the DRS be abolished?

Sorry - you're right. On the 450D, the horizontal low pass filter is the only thing in the vibrating part, so you can leave that in place. However, the IR cut filter is sandwiched with the 1/4-wave plate (Canon calls that a phaser layer) and the vertical low pass filter. (It's low-pass, BTW - the AA filter is aka OLPF = optical low-pass filter.) So, you can remove the IR filter and leave the dust removal intact.

Note that since the IR cut filter is not separable from the 1/4-wave plate and vertical low-pass filtter, by removing the IR filter, you're also removing half of the AA filter, giving your camera astigmatism (the horizontal resolution will still be reduced, the vertical resolution will not).

 

[adhocphotographer]

I thought that in the 450D the AA + dust removal where a singular, separate, unit to the high-pass (it is a high-pass right?), though your wisdom being what it is i will definitely re-check. Does that mean that even removing the IR-cut would abolish the dust removal system (DRS), or only once the AA filter is removed will the DRS be abolished?

Sorry - you're right. On the 450D, the horizontal low pass filter is the only thing in the vibrating part, so you can leave that in place. However, the IR cut filter is sandwiched with the 1/4-wave plate (Canon calls that a phaser layer) and the vertical low pass filter. (It's low-pass, BTW - the AA filter is aka OLPF = optical low-pass filter.) So, you can remove the IR filter and leave the dust removal intact.

Note that since the IR cut filter is not separable from the 1/4-wave plate and vertical low-pass filtter, by removing the IR filter, you're also removing half of the AA filter, giving your camera astigmatism (the horizontal resolution will still be reduced, the vertical resolution will not).

In which case, I might as well remove the AA filter too. the street value of a 450D is sooooo low, i think i'm going to give it a go. yes indeed it is a LP not a HP, i wasn't thinking! It has been a long time since i had to make a confocal!

TrabimanUK & arjay - seen it and taken note, thanks!

 

[KyleSTL]

Really good DIY step-by-step (with excellent pictures):

http://www.lifepixel.com/tutorials/infrared-diy-tutorials
http://www.lifepixel.com/tutorials/infrared-diy-tutorials/canon-drebel-xti

I have removed the IR filter from an XSi that was damaged beyond repair (the sensor was still in good shape). The removal was not as easy as most tutorials indicate (the glass cracked multiple times as I was prying it out of the dust removal frame). Have not put it into an operable camera yet to see what the results look like, yet. I should be done fixing another XSi in the next couple of weeks and I'd like to throw it in there to see what results I get.

 

[Fleetie]

Why is the 1/4 wave plate there?


Don't know much about wave plates, except that a CPL has one following the linear polariser, to retard one of the fields by 1/4 wave, making the resultant passed light circularly polarised. That is desirable because the camera doesn't like linearly-polarised light; it can give unreliable metering etc..


Also I have noticed an effect of linearly-polarised light when looking through the viewfinder of my Olympus film SLR, right upwards at the blue evening sky. Such sky exhibits reasonably strong linear polarisation, and it showed when I looked through the viewfinder. I don't remember the detail of how it looked, but it was odd, and "wrong". I think half the image was significantly darker than the other half, and I think the border between the 2 halves ran vertically from top to bottom in the middle of the image.


So why the 1/4 wave plate in a DSLR? To circularise any linearly-polarised light? Seems unlikely right before the sensor; you'd want one before the whole flange/mirror-box if anywhere, for that.

 

[Loswr]

Why is the 1/4 wave plate there?

The AA filter blurs the image slightly by passing the light through two layers of a birefringent material (lithium niobate). That birefringent material separates incoming light into two rays, essentially polarizing it. The two layers are oriented orthogonally to one another. The light passes through the first one, but if it went straight into the second one, it would be blocked. That's analogous to a variable ND filter beyond the max setting - crossing two polarizers blocks the light. You also see this phenomenon with polarized sunglasses and some LCD displays, which 'go black' if you tilt your head (this is true for some camera rear LCDs, making them a pain to use with polarized glasses as you can't see anything with the camera in portrait orientation). So, to prevent that for the AA filter, there's a 1/4-wave plate in between the two layers to circularly polarize the light after it passes through the first layer of lithium niobate.

Side note: the D800E actually has the two layers of lithium niobate like an AA filter. However, instead the two layers being oriented orthogonally, they are both oriented to separate light vertically, but in the opposite direction, and there's no 1/4-wave plate. So, the light is split then recombined - basically, a non-functional AA filter. I presume they did that for manufacturing reasons, to keep the layers of filters over the sensor close to the same total thickness and thus maintain alignment with the AF sensor assembly, etc.