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Light pollution Clip-Filter confusion


hobsey

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While I am sitting very impatiently waiting for my Star Adventurer to land in the UK, I keep thinking of other things to buy to help me with AP.

I'm currently looking at the light pollution clip-filter but confused with the options.

My camera is a 1100D, isn't modified and won't be for some time as its practically brand new and can't decide which filter I need, I think its this one

http://www.365astronomy.com/astronomik-cls-ccd-deepsky-lightpollution-clipfilter-canoneos-p-2201.html

But it does say in the description, The Astronomik CLS CCD is suitable under light-polluted skies for DSLR Cameras, which have been remodeled for astronomical use.

Remodeled? Does that mean modified? If it does then which filter will I need?

Looking at this lot

http://www.365astronomy.com/index.php?main_page=advanced_search_result&search_in_description=1&keyword=clip-filter&x=58&y=21

I'm even more confused.

Many thanks

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The description on that site is a little unclear, I've also been looking into LP filters so I think I understand.

There are two versions of the Astronomik clip-in LP filter. The slightly cheaper one is designed for unmodded cameras, the more expensive one for modded ones. The difference is that the latter also has an IR block filter in it, as this is (usually) removed when the camera is modded. The IR filter reduces thermal noise and the number of hot pixels. An unmodded camera has an IR filter in it anyway, but being wider band it attenuates the Ha line.

(Why do they call it a CCD filter? It's misleading, but the material it was designed for a full-spectrum CCD and then adapted for DSLR use.)

If you're going to mod your camera sometime in the future you are probably better off with the CCD version. one thing to watch out for, you won't be able to use EF-S lenses with the clip in filter as they protrude further into the camera body.

One final word of caution - if you do mod your camera you won't be able to reach infinity focus with camera lenses unless the sensor is re-shimmed to preserve the distance to the lens. This is a step that the Cheap Astrophotography service carries out, but modded cameras that don't have this done are only suitable for using in a telescope (to the best of my knowledge).

Hope that is some help and that I've got everything straight there.

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Cheers, KCS

I won't be modding anytime soon if not never.

Most of my lenses are EF fit anyways.

See, this is the confusing thing. The cheaper filter is listed for visual observations, if its in a camera why would it be for visual?

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It is confusing. I think it's because the filter material comes in different sizes (1.25", 2" etc.). in that context that particular filter is optimised for visual as the eye isn't sensitive to IR, so doesn't require an IR block. They should change the description when putting it in a clip-in filter really.

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Hi

From what I understand (am no expert) the 'cheaper' one does not filter IR, but if you mod a Canon 1000D you have 2 IR filter inside. You remove IR2 and keep IR1 in place so you do not need a CLS-CCD (the expensive one with IR filter) because you already have an IR filter inside you camera.

Here is an excerpt of an explanation I read:

" If you have ANY type of filter remaining in your camera following modification, then at least 97% of all IR will be filtered anyway.  This can be either because when modded, you camera had a Baader filter installed, or be due to the fact that your model of camera has two filters, of only one is removed during modifications (for example, 1000D, 1100D, and a few other models). Therefore, save yourself some money and buy the standard version of the CLS filter."

Now the best person to ask is Gary Honis (http://dslrmodifications.com) there is a yahoo group where he posts and answers questions like that.

I also have a Canon 1000D that I will mod (remove IR2) and add a CLS clip-in astronomik filter.

IR Filter

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Note that Gary Honis made this test: "Canon DSLR Front Filter Versus Baader Filter Modification Test" to compare the infrared blocking effectiveness of a Baader modified camera for astro imaging versus relying on the original Canon front filter only to block infrared.

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I will watch when I get home but I'm not modifying or intend to modify, all I want it a clip on filter LP filter with standard IR filter.

I'm even more confused now then when I first asked because modifying and modded cameras with different filters keep getting mentioned.

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There are 2 filters in your camera: Low-pass filter 1 (LP1) and low-pass filter 2 (LP2)

(1) If you only use the camera for astro imaging you can remove LP2 and leave LP1 intact. You will then have IR filtering inside the camera so you do not need to buy a CCD filter (wich has IR filtering) you can buy the cheaper one. You will lose focus to infinity but we do not use the camera focus so ...

(2) if you use your camera for daylight photography then you might want to add a Baader filter or clear glass to reach focus to infinity (and adjust the white balance manually)

Gary shows in this video that if you only remove the LP2 filter and rely on the LP1 filter you still get some IR going through but I am not sure that it is a big issue... Now either way, the removal of the original LP2 filter is to allow the important h-alpha wavelength to pass for astro imaging.

Now, if someone wants to correct that, I'd be glad to hear from experts on this matter.

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Ok I understand...

Then if you do not mod, you do not need to filter IR ... It's already filtered inside. So you can buy a 'basic' City Light Suppression (CLS) filter :)

The CLS-CCD would be for CCD camera OR modded (IR Filter remove) DSLR.

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I have not modded either of my cameras, and use the "visual" clip filter. As both bodies have a factory fit IR filter, I do not need the CCD version. I also do not plan to mod... and in fact, using my 450d, I'm actually picking up a fair amount of Ha emissions anyway.

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one more thing from Astronomik website

" The filter blocks completely emission lines of artificial light sources like streetlights (e.g. sodium- and mercury-vapor) as well as the airglow. All 'important' emission lines as well as the spectral range of the night-adapted eye are beeing passed. The supplementary IR-blocking layer allows the use for DSLR- and Webcams without an integrated IR-block filter."

So what we really want is to block streetlights (e.g. sodium- and mercury-vapor) wavelenght ... not IR, it is already blocked inside the camera and has nothing to do with LP.

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I have not modded either of my cameras, and use the "visual" clip filter. As both bodies have a factory fit IR filter, I do not need the CCD version. I also do not plan to mod... and in fact, using my 450d, I'm actually picking up a fair amount of Ha emissions anyway.

From what I understand it is only good for emission nebula where you can divide exposure time by 2 (?)

Carole Pope's website shows a before/after modding

https://sites.google.com/site/caroleastroimaging/home/how-to-image-with-a-dslr

see section: 17. Modifying your DSLR for Astro-Imaging

Impressive ;)

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Ok I understand...

Then if you do not mod, you do not need to filter IR ... It's already filtered inside. So you can buy a 'basic' City Light Suppression (CLS) filter :)

The CLS-CCD would be for CCD camera OR modded (IR Filter remove) DSLR.

I have not modded either of my cameras, and use the "visual" clip filter. As both bodies have a factory fit IR filter, I do not need the CCD version. I also do not plan to mod... and in fact, using my 450d, I'm actually picking up a fair amount of Ha emissions anyway.

Thats more like it, these I can understand.

Thanks everyone for your help.

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The description on that site is a little unclear, I've also been looking into LP filters so I think I understand.

There are two versions of the Astronomik clip-in LP filter. The slightly cheaper one is designed for unmodded cameras, the more expensive one for modded ones. The difference is that the latter also has an IR block filter in it, as this is (usually) removed when the camera is modded. The IR filter reduces thermal noise and the number of hot pixels. An unmodded camera has an IR filter in it anyway, but being wider band it attenuates the Ha line.

(Why do they call it a CCD filter? It's misleading, but the material it was designed for a full-spectrum CCD and then adapted for DSLR use.)

If you're going to mod your camera sometime in the future you are probably better off with the CCD version. one thing to watch out for, you won't be able to use EF-S lenses with the clip in filter as they protrude further into the camera body.

One final word of caution - if you do mod your camera you won't be able to reach infinity focus with camera lenses unless the sensor is re-shimmed to preserve the distance to the lens. This is a step that the Cheap Astrophotography service carries out, but modded cameras that don't have this done are only suitable for using in a telescope (to the best of my knowledge).

Hope that is some help and that I've got everything straight there.

You are almost correct, for an un modded camera you are correct you only need the cheaper filter, but for a modded camer you still only need the cheaper filter as long as you don't have a full spectrum mod, (which most people don't) when a camera is modded there are two filters in front of the sensor, but only 1 is removed, the other is left as it gives very very good IR cut, which is needed in Digital imaging, the difference between the two mentioned filters is that one has IR cut, and the cheaper one does not, so that is the one you need for both modded or un modded, like I say unless you have a full spectrum mod and both are removed.

They advertise the more expensive filter as a CCD filter because you would need with that type of camera, as they have no filters in front of there sensors, they are in effect a full spectrum camera, so you need IR cut for them

Hope that helps

Olly

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