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To allow IR then not to !


Guest peepshow
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Guest peepshow

We are told that to get better Ha then a DSLR camera should be modded to have its IR filter removed.


 


Now I find that there is an Astronomic CLS CCD filter which is not only an LP filter but removes IR too. 


 


I find that all a bit confusing but would I be right in assuming that this CLS CCD filter just removes the unwanted part of IR that is not the Ha part of the spectrum ?


 


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My understanding is some dslr cameras have two internal filters; one uv/ir blocking, and the other corrects the colour (or something); hydrogen alpha mostly passes through the ir blocking one, but gets blocked partially by the other one. The modification can either just remove the colour correcting filter, allowing most of the hydrogen alpha through, or remove both filters (which probably doesn't make much more difference to hydrogen alpha but allows the user to decide if they subsequently want to block ir or uv when imaging, as they could use additional filters).

I think.

Jd

Edited by dawson
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Also, as is being discussed on another thread about "which planetary camera", some users prefer to use an expensive and potentially higher quality IR blocking filter, which may have a narrower or wider range of wavelengths it blocks than the standard factory fit ones. Just gives the user more control over what is blocked/allowed through to the sensor.

Jd

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Guest Kheldar

There's IR ... and then there's IR ...


 


IR is a very wide bandpass encompasing lots of wavelengths - Canon stock filters tend to block it all out


 


Astro IR filters block only a smaller section of this, allowing the Ha through


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Guest Kheldar

Stephen, does the bayer matrix "filter" block out much hydrogen alpha?

 

I'm not sure whether it's the bayer matrix or the inherent nature of a DSLR but yes - a DSLR is less sensitive to Ha

 

Does not mean it's not a useable tool however

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Guest peepshow

Just a follow up question...what do the initials in the Astronomik CLS CCD filter mean?


I shouldn't think that the CCD means sensor types as this filter is used on CMOS cameras.


 


It seems then that reading the replies, the best for a DSLR is to have the IR filter removed


and then add a CLS CCD filter to block the  unwanted IR.......more expense. :lol:


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Guest peepshow

It seems that although Astronomic modified their NB filters some years ago to prevent halos around brightish stars,


it still happens on some lenses....one of mine. :(   Haven't tried any others yet, so fingers crossed.


 


So be careful when getting a rear mounted filter (clip type) that you too


don't finish up with a halo, even though you maybe are a good chap. :lol:

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It's me again Richard! I bought a used, converted, Canon 450 but the seller couldn't remember what had been done. I think that the filters have been removed completely as .1. The auto focus is inaccurate. 2. My lenses didn't seem to be able to focus the full spectrum recorded by the sensor ( blue halo or red  moving through focus). 


So I use a UV / IR cut filter (Baader 2459210A) in front of my smaller lenses or inside the 300mm f4. adaptor rings to mount the 48mm threaded filter from e-bay. This does help but isn't a complete fix. Also, I have an Astronomic CLS clip filter in the camera. ( City Light ?????)


If anything I still have too much red response but it's good for Ha objects like NGC 7000.


I tried to find a combined clip filter to cut light pollution and IR / UV which would have solved my problem but couldn't. If you find one please let me know.


If I was having  a camera modded I'd have a Baader IR /UV cut filter fitted on the sensor in place of the original to save all the muckin' about I have to do. A 60Da would sort it!


This is the result of my filter combination.


 


13677586053_8e25b99b3f.jpg


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Guest peepshow

I believe that if all the filters are removed then one gets bloated stars.


 


My camera is a 450d just with the IR filter removed. 


I put in an Astonomik CLS CCD clip filter which gives me the red halos around bright stars.


 


You too use a clip filter I see, Alan,  but I don't see any halo problems on your stars.


Maybe it depends on the distance between the lens rear component and the clip filter ?


 


My rear lens is very close, but I have another with a greater distance to be tried out when the


clouds clear.........in 10 years. :D

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  • 2 weeks later...
Guest AstroOlly

Most of the newer canon cameras have two filters in front of the sensor, but usually only the front one is removed as this is the one that cuts most of the Ha, and so removing this will make the camera more sensitive. This filter does also cut the IR and cuts it too much, another reason to remove this filter.

The rear filter that is left in the camera still has IR cut and so leaving that in the camera is a good thing, and it is a very good IR cut too as it has a sharp cut off, and is enough to stop the halos and star bloating.

So as long as the rear filter is left in place then you DO NOT need the CLS CCD filter, that is for cameras with no IR cut, like a full spectrum modded DSLR (both filters removed) or CCD camera, you will only need the slightly cheaper CLS LP filter which is exactly the same but without the IR cut.

Hope that helps

Olly

Edited by AstroOlly
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Guest peepshow

As Stephen said, "There's IR ... and then there's IR ..."


 


As I understood it, Olly,  the rear canon filter, although cutting IR,


 still passes some unwanted IR so the CLS CCD filter version


is still useful in this regard.......so I have read. :)


 


BTW, I wrote to Astronomik about my red halos.  They replied very quickly and asked for a sample image.


Their opinion is that the red halo around bright stars is caused by the optics on my poor lenses.


 


I use a Canon 450d with just one filter removed. 


There were NOT any red halos with my poor lenses at all until I added the CLS CCD filter !


 


So my experience doesn't tie in with what Astronomik said.


Edited by peepshow
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Guest AstroOlly

As Stephen said, "There's IR ... and then there's IR ..."

As I understood it, Olly, the rear canon filter, although cutting IR,

still passes some unwanted IR so the CLS CCD filter version

is still useful in this regard.......so I have read. :)

BTW, I wrote to Astronomik about my red halos. They replied very quickly and asked for a sample image.

Their opinion is that the red halo around bright stars is caused by the optics on my poor lenses.

I use a Canon 450d with just one filter removed.

There were NOT any red halos with my poor lenses at all until I added the CLS CCD filter !

So my experience doesn't tie in with what Astronomik said.

I have not heard the comment about the rear filter still letting unwanted IR through, I am not saying you are wrong, but I would want more proof of that, I am lead to believe the rear filter is a very good IR filter and hence that is why it is nearly always left in, I have that mod and use the normal CLS LP clip filter and don't get any star bloating or any other unwanted artifacts in my images, not that I have done that many....lol

The halos could be due to having 2 IR block filters in place and being different strengths working against each other, at the end of the day the more glass you have in the imaging train the more problems can arise.

Regards

Olly

Edited by AstroOlly
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Guest peepshow

OK, Olly and Stephen on all that.


I too think it's the Astronomik filter and not my poor lenses. :)


 


Some years Astronomik they said they cured all halos.


 I checked my filter serial number with them and it is a new manufacture, this year.


 


So there we are.  


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I've got an Astronomic CLS clip for my 7D. I've not seen any haloes but then everything I have done with it has been at prime focus on either 150p Newt or ED80.


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Guest peepshow

Glad to hear that you have no halo problems, Leigh.  Many using clip filters have no problems I have read. Others do.


 


BTW, I tried 2 different lenses.   


One with the lens rear element near to the clip filter (a Chinnon 200mm fixed) and the other further away from it. (a Tamron 70-300mm )


 


It made no difference to the red halos at all. 


So it must be inside the filter.


QED. :)

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Guest peepshow

Just further to this.........


I have an old 500mm mirror lens. 


 


Last night I took a long 15 minute exposure on my Canon set at 1600 ISA with the


Astronomik filter in.


 


Although the focus was not spot on there was no sign of red halos at all.  :rolleyes:

Edited by peepshow
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Guest peepshow

Here's yet another effect using the CLS CCD filter, Leigh. 


 


This is a big blow up of a somewhat distorted star in the corner of an image taken with a wide angle lens.  (28mm). 


 


In each corner of the image there is this red 'echoed' image of the star further out from it.


 


In the centre there are no such red echoes nor halos. 


 


Rather pretty, eh?  :lol:


 


 


13922247691_80a7449b13.jpg

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