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Old 15-04-2011, 01:03 PM
Carl
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DSLR modding and filters

I suppose this has been asked before but cant find the thread.
I want to remove IR filter in my canon 500d and replace it with a selected filter or clear filter and use Astronomiks clip in filters.
Is there a site that will give me an easy to understand visual comparison of the filters. ie the same image photographed with different filters?

Regards
Carl
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Old 16-04-2011, 07:59 AM
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philiphart (Phil Hart)
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hi Carl

I don't have image comparisons, but if you go with the clear filter option and are shooting through lenses or refractors then you will need a UV/IR cut filter either on front of the lens or the front filter in the camera (which won't fit with EF-S lenses, but will with all normal EF lenses). Otherwise you get UV blooming around all the stars.. pretty ugly. With reflectors you should be ok without them.

The clear filter gives you great IR photography potential, but if you're not interested in that you're probably better off with the extended UV/IR option.

I also have some X-Nite CC1 lens filters of various sizes I'd be happy to sell if you want to restore close to the original colour balance for daytime photography after the mod.

Phil
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Old 17-04-2011, 03:25 PM
Carl
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Modded camera

Hi Phil
Havent spoken scince you came up to Border Stargaze.
I'm just starting out on the filters thing so you'll have to forgive my lack of knowledge.
Gary Honis in the US also states that by just removing the IR filter and replacing it with clear glass you cannot get sharp focus. You need a UV/IR filter.
Now I'm confused. If i remove the factory IR filter and replace it with a UV/IR filter havent i just defeated the purpose of modifying my camera?
Any advise appreciated
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Old 17-04-2011, 03:54 PM
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Merlin66 (Ken)
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Don't know about the 500D
but my modded 1000D (filter removed for total spectrum) still works and focuses with the normal lenses.
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Old 17-04-2011, 04:29 PM
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Merlin66 (Ken)
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Carl,
I think you need to consider what is happening when you change these filters....
1. The original filter in the camera is designed to suppress the UV and IR to give a "realistic" natural colouring with minimal chromatic focus issues. Unfortunately for astro imaging the cut-off wavelength in the IR is close to the Ha emission and the efficiency in this area is pretty low (around 25%)
2. If the filter is replaced with a Baader filter (or similar) then the cut-off wavelengths are much more defined (400nm and 700nm) - this allows a much higher efficiency at Ha (up to 50-60%). Yoy still have the benefit of the UV-IR suppression to reduce star image "bloating".
3. If you remove the filter completely...then all the UV and IR light is allowed through. Great for spectroscopy
but it does mean in refractors that the star images will look bloated due to the excess UV (blue ) or the NIR (red). You also need to use the inbuilt Custom colour balance to use the camera for "normal family shots"
4. For option 4 you can "compensate" by adding a clip in filter which effective operates like option#3 Some filters, besides providing UV-IR cut-off can also act as a light pollution filter (ie CLS etc)

In all the modern Canon cameras (400D onwards) there are two filters - one is a "mild" UV-IR which has the shake rattle an' roll for sensor cleaning and a second filter (much thinner than the original back in the 300/ 350D series) which is the actual "heavy" UV-IR filter - this is the one that is normally replaced/ removed. As it's so thin, it can still be removed and the camera still focus normally with standard lenses ( which was NOT the case with the 300/ 350D)
HTH
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