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Canon IR Filter Removal - Naked or Aftermarket

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#1 KC9EDN

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Posted 02 February 2016 - 03:49 PM

Hi all,

I'm playing around with an old Canon 20d and want to remove the internal IR filter. Since it looks like a replacement Ha sensitive filter will run me at least $100 and I am going to be using this exclusively for astrophotography, is there any real need to upgrade the internal filter or can I just use a Nebula or Deep sky filter on the OTA side of the T-mount to filter unwanted wavelengths? Thanks for your input.



#2 Jim Davis

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Posted 02 February 2016 - 03:59 PM

Read up on it on Gary Honis' web site: http://dslrmodifications.com/

 

He performs the modifications, as well as supplies how to guides. He gives the pros and cons to different options.



#3 glend

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Posted 02 February 2016 - 04:02 PM

Canons have two internal filters (LP1 and LP2). LP2 is the usual one removed for improved Ha performance. LP2 is the darker blue cast filter closest to the sensor. The front LP1 is more of a UV/IR Cut type filter and actually has a spectrum pass characteristic very close to the Baader UV/IR Cut filter. LP1 is also the anti-alysing fitler so some people prefer to keep it, and it keeps some sort of chamber ahead of the sensor cover glass. If your just starting out with mods I'd suggest just doing LP2 for now.

As per the above post, read through Gary Honis' very good instructions for the mods.


Edited by glend, 02 February 2016 - 04:03 PM.


#4 KC9EDN

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Posted 02 February 2016 - 06:38 PM

Thanks Guys. I'll read Gary's page. The 20d is old enough that I believe it only has the ir/uv filter in it rather than the 2 stage filters. In summary, I am trying to determine if I can just remove it without replacing it with a wider band filter. Filtering will then be done before light gets to the camera. All the sites I have checked seem to just want To sell a filter or conversion. Will the naked sensor work for AP? Guess I can just try and see, but who wants to take apart the camera twice. ;)



#5 mmalik

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Posted 02 February 2016 - 07:06 PM

Read mod choices here... and filter options here.... Regards


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#6 t_image

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Posted 02 February 2016 - 07:10 PM

As you muck around Gary's confusing site,

search for some other threads about mods on CN.

Short answer is yes.

I have a "naked" sensor Sony a5000 and have no problems because I filter prior to the camera.

The clear glass that remains over the sensor is more hardy than the glass above it, so cleaning it won't be too much more difficult as it your sensor will not be "naked"--consult the mono mod forums over on stargazerslounge to see what I mean.

Note that you will need some type of UV/IR filtering to find the same backfocus[without any replacement glass with the same refractive index],

but a "naked" sensor also gives you the leeway of IR pass photography and more flexibility for choosing your desired filters...

 

If you search around there are disadvantages to LP1 with the anti-aliasing filter as there are resolution drawbacks versus any moire reducing benefit. LP1 is a free IR/UV block,

but there is a reason some of the newer Nikons are leaving anti-aliasing filters out now (D3300, D5300, D5500)

 

Cheers!


Edited by t_image, 02 February 2016 - 07:12 PM.

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#7 upfyrman

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Posted 03 February 2016 - 08:13 AM

I did my own mod just recently of a canon 450d using instructions by Gary Honis, which I though were thorough fairly easy to follow. I replaced the LP2 filter with the Baader BCF1. I was a little nervous doing it, but I had great results! It was a great rainy day(s) project!

 

Steve


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#8 ZeroID

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Posted 03 February 2016 - 10:02 PM

Thanks Guys. I'll read Gary's page. The 20d is old enough that I believe it only has the ir/uv filter in it rather than the 2 stage filters. In summary, I am trying to determine if I can just remove it without replacing it with a wider band filter. Filtering will then be done before light gets to the camera. All the sites I have checked seem to just want To sell a filter or conversion. Will the naked sensor work for AP? Guess I can just try and see, but who wants to take apart the camera twice. ;)

That's called a full spectrum mod, no internal filters. You will need an external IR/UV filter on the nosepiece to control blooming replacing LP1. Not sure about the 20D but I think it will have both filters in place. The best one to mod is the 450D because with Live View yo can monitor the results a lot easier.

But if you have an old 20D then go for it. It's worth the exercise. I'd leave LP1 in place, just do the IR cut mod.

 

When I was experimenting I started on an old KM 7D I had, no value hardly then moved on to the 450D. As I was also doing a cold finger mod there was a LOT of strip and rebuild stages. I reduced the number of bits required, hacked the case somewhat and simplified the internals, it now takes about 5 mins to have the sensor out on the bench.

 

Cleanliness is all important and hard to acheive. I have removed just the LP2 filter. The cold finger mod gets me a delta of 20* C, theoretically noise is about 6% of the ambient level. Biggest issue is keeping the sensor dew free in humid environments.

 

I used Gary Honis instructions first few times. They are confusing because he inserts the variations on different models in the picture flow. You have to learn to ignore the ones hat are not yours. I drew a diag line through the 500D etc pix with a marker pen.


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#9 KC9EDN

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Posted 03 February 2016 - 10:45 PM

So I did the full spectrum mod this evening. It was very surprisingly easy. I did have to dig back in to snug a ribbon cable as it wasn't reading the CF card initially. Quick fix. I actually added some .8mm shims under the sensor to attempt to bring the autofocus closer to accurate as I read appropriate sensor offset is 1/3 of the filter thickness. AF isn't perfect, but a quick manual tweak sharpens it up. I have a 40mm peltier on order and will likely do some external cooling with heatsink and brushless fan. I'm not going to get a delta T like ZeroID, but was thinking might be fun to set up and use an arduino with heat sensor attached to body to keep tabs on temps.

 

For a camera that cost almost nothing, I'm having fun digging in and learning more. We are relocating to Maine in a few months and I'm looking forward to getting the cpc wedge mounted on a pillar in my new dark yard :)  Right now it is just baby steps toward getting in some deep sky AP and playing around with EAA. I'm just rambling now, but thanks all for your input and encouragement.


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#10 t_image

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Posted 04 February 2016 - 05:40 PM

Congrats on the DIY!

Clear Skies:)


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#11 Vickmann

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Posted 02 March 2019 - 05:48 AM

I actually added some .8mm shims under the sensor to attempt to bring the autofocus closer to accurate as I read appropriate sensor offset is 1/3 of the filter thickness. AF isn't perfect, but a quick manual tweak sharpens it up. 

Please explain a little more about how to maintain the autofocus feature with the LP2 astrophotography mod with a shims?, do you please post a pic of that shims?



#12 whooshbang

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Posted 29 October 2022 - 05:04 PM

Please explain a little more about how to maintain the autofocus feature with the LP2 astrophotography mod with a shims?, do you please post a pic of that shims?

Shame you didn't receive a reply to you question as i am also wondering about how to shim the sensor. I have plenty of adjustment on mine so i shouldn't need to shim but i wouldn't mind knowing weather the sensor need to be moved toward the front of the camera body (where lens attatches) or toward the rear of the camera?



#13 bbasiaga

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Posted 31 October 2022 - 12:30 PM

Shame you didn't receive a reply to you question as i am also wondering about how to shim the sensor. I have plenty of adjustment on mine so i shouldn't need to shim but i wouldn't mind knowing weather the sensor need to be moved toward the front of the camera body (where lens attatches) or toward the rear of the camera?

You should look up a tutorial on setting up back focus for astrophotography to double check me, but look at the filter section here....

 

https://optcorp.com/... divide it by 3.

 

Glass between the last lens in the optical system (telescope or camera lens) and the sensor, effectively reduces the back focus distance of the system because it alters how fast the light is bending.    It gets a little confusing, because when you add that glass you have to add a corresponding spacer, which makes it sounds like it is increasing the back focus, but what's its really doing is making the sensor act as if it were mechanically closer...its a semantics thing.   

 

But to summarize it - the back focus of an EF mount camera is about 44mm assuming all the glass is in place over the sensor.  If you remove glass there, the light will bend faster and hit its focus point sooner, meaning you need to move the sensor FORWARD toward the flange mount.  In the linked example, we added glass to the system and had to move the sensor farther back by adding a spacer.  In the example of removing the IR filter on a DSLR, we are taking glass away and therefore need to 'remove a spacer' or in reality shim the sensor closer to the flange.  

 

How much?  The math works out to be about 1/3 of the thickness of the glass.  This will depend on the exact refractive index of the glass, but its a starting point.  For DSLR mods, ideally you'd find a clear glass made of the same material as the original filter, that is the same thickness, and replace the removed filter with that.  That, of course, is quite hard to do which is why the sensor gets moved some to make sure the effective back focus is the same and the camera can reach its normal focus range. 

 

I hope that makes sense.  There are some good youtube videos on it too if you find a visual explanation better.  

 

-Brian


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#14 whooshbang

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Posted 31 October 2022 - 01:09 PM

This is wonderful Brian!

 

Thank you very much for sharing!

 

Dave




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