Cannon IR removal - err confused

[johnb]

Hi

I want to send off my Cannon 450d to get the IR Filter removed, that much I understand but I see that whats offered is "This is done by replacing the original IR blocking and antialiasing filter with a Baader IR and UV blocking filter."

I was not aware that the filter was replaced - just wanted to check im doing the right thing before I hand over the cash.

regards

John B

[swag72]

I thought that you could just have the filter removed and nothing put in it's place - That's what I am going for.

[beamish]

Filter replacement ( as mentioned)= higher IR ( red response) and maintains Auto focus capability or

Filter removal ( full spectrum)= no replacement filter fitted, No AF capability and as it says "Full Spectrum " response

HTH

[johnb]

hmm even more confused now, well i guess i wont need Auto Focus for one but full spectum v higher IR

Help

John B

[swag72]

I take it that as long as you are not requiring any AF, then the total filter removal is the better of the two options?

[johnb]

Thats what I thought and it does say complete removal full spectrum

john b

[beamish]

Sorry , not quite sure what is confusing- if you don't need AF then go for full spectrum response "Filter REMOVAL', if you'd still need AF for daytime photography ( using Custom WB) then go for filter REPLACEMENT

????????

filter replacement does not offer FULL spectrum response.

If in doubt talk to the co who you're planning to use to do the job.

Q IS the this just for AP ? if yes then filter removal would be best !

[johnb]

Thanks, no longer confused Full removal it is then

Regards

John B

[Psychobilly]

To add to the confusion there is also the option of clear glass replacement which will give full spectrum and retain AF... but you will need to take care of UV and IR cut in external filtering... unless of course your shooting IR pass...

Billy...

[beamish]

Cheers Peter

[Merlin66]

Ken Ellis makes the point, that for the majority of "normal" day to day family imaging it is possible to remove the original filter, no replacement, and still AF.

I have the filter removed from my 1000D and it still works for normal photography. NOTE: the earlier Canons do need a filter replacement for AF.

Autofocus.

A majority of people who have their cameras modified for astronomy only use them for this purpose, so retaining the autofocus is not important as focussing is done manually either through a lens or telescope, so removing the rear filter is generally the better option for these people when modifying a dual filter camera. As it is, the filter that is removed is only 0.8mm thick so the difference in the focus point when considering the refractive index of glass vs the refractive index of air is very slight. In practice, this means that the difference is practically unnoticeable when taking everyday snaps. When using very 'fast' lenses or ones with a very short focal length, i.e., for macros and fish-eye shots, this slight mis-focus becomes more noticeable.

See his site for more info:

http://www.astronomiser.co.uk/eosfilter.htm

[themos]

Additionally, I think the second filter that is NOT removed is an IR filter as well so I don't think you get a "full spectrum" camera.

[carastro]

It's the IR filter that is removed. If you don't replace the filter with a Baader filter or a piece of glass I was told by Andy (Astronomiser) that you would not be able to use the camera for day time use.

Carole

[themos]

Blocking UV and IR light.

In a dual filter camera,the front filter blocks UV and IR light with a very sharp cut off at the edges of the visible spectrum. This is information that has come to light recently when a well known filter manufacturer tested these filters after noting that they blocked IR light. The filter blocks UV and IR very effectively and is of very high quality. This means that no second filter is required to block UV and IR and the Baader filter would not do a better job.

from Astronomiser - Automated Astronomy and AstroImaging Solutions

[Merlin66]

Hmmm

The 1000D I have was modified by Astronomiser. I can assure you it has a full spectral coverage well into the UV and IR. I use it for spectroscopy.

I can also use it for normal photography ( obviously using a Custom white balance setting)

[themos]

Maybe he removed the top "antialiasing" filter as well?

[Starblazer]

Having already removed the rear filter I'm considering removing the top filter also, what extra can you grab without it in?

[Merlin66]

I'm certainly no expert or specialist...

I understood the two "filter" design (introduced with the 450D?) had a front "dust shaker" filter and then the proper UV-IR filter.

I haven't seen any optical specs for the dust filter element...

Does this make any sense? If so what filter is what?

[Merlin66]

Astronomik Clear Glass Modification for Canon DSLRs - Astro Imaging and Infrared Photography - by Gary Honis

At the bottom of the page there's a diagram of the various filters:

lowpass #1 (vibrating cleaning element)

IR filter

Lowpass #2 ( a sandwich with thhe IR filter)

Gary infers that all these elements are removed when a clear glass replacement is done....

When the "total" filter is removed...

Canon Digital Rebel XSi 450D IR Filter Removal Modification - Imaging Chip Disassembly - Page 4 -by Gary Honis

The front low pass #1 is retained and the other(s) physically removed.

[simon hicks]

Hi Merlin66,

You say you use it for spectroscopy work. How far in each direction can you go? A silicon sensor will typically go from about 190nm (albeit in vacuum) to about 1100nm. But the optics will not be designed for that. Just wondering how far in each direction you can go. And is this limited by the spectrometer or by something else?

Cheers

Simon

[Merlin66]

The wavelength is limited by the atmosphere transmission and the type of glass used in the telescope/ objective.

I can get down to around 360-370nm (?) and well up into the NIR....

I've never actually measured in the far red as it gets contaminated by the second order blue spectrum! ( ie 700nm (red) in the 1st order spectrum has a 350nm (blue) 2nd order overlaid) Sorting filters are used to suppress the one you don't want.