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  #1  
Old 16-05-2012, 08:20 PM
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Nico13 (Ken)
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HA or OIII filters with unmoded SLR?????

Can anyone tell me if you can use HA or OIII filters with an unmoded SLR or are they only suited to mono astro camera's.
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  #2  
Old 16-05-2012, 08:36 PM
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dugnsuz (Doug)
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Hi Ken,
From the Astronomik website it seems that a modded dslr is 'desirable' but not a prerequisite for their use.
http://www.astronomik.com/en/clip-filter-system.html

Here's a link to a recent image I did with my modded dslr and Ha/OIII filters...
http://s327.photobucket.com/albums/k...filter=noflash

Your Ha response would be hobbled in an unmodded camera -as to how much, others may have examples.
Cheers
Doug
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  #3  
Old 16-05-2012, 09:02 PM
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Nico13 (Ken)
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Quote:
Originally Posted by dugnsuz View Post
Hi Ken,
From the Astronomik website it seems that a modded dslr is 'desirable' but not a prerequisite for their use.
http://www.astronomik.com/en/clip-filter-system.html

Here's a link to a recent image I did with my modded dslr and Ha/OIII filters...
http://s327.photobucket.com/albums/k...filter=noflash

Your Ha response would be hobbled in an unmodded camera -as to how much, others may have examples.
Cheers
Doug
Thanks Doug,
Great image, I can see it will be worth looking at getting some filters.
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  #4  
Old 17-05-2012, 11:58 AM
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Ryderscope (Rodney)
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Ken,

I have been playing with the Astronomik CLS-CCD filter for a while now and whilst I am still experimenting with the camera settings and processing techniques I am encouraged by the results so far. I have attached an example image of the Crux/Carina area. Details of the image are:

- Canon 550D unmodified
- Astronomik CLS-CCD clip in filter
- 50mm F1.4 USM lens @ f4.0
- Taken from the ASNSW dark sky site at Wiruna NSW
- ISO800, 120 seconds
- Losmandy GM8 mount
- Manual guiding
- Quick processing in PS CS4 to adjust curves, colour balance, black point

I shoot both raw and large JPEG and the attached image is one JPEG so no stacking at this point. I have set the white balance to custom in the camera using an image taken of a grey card in on a clear sunny day. This is necessary to rectify the colour shift introduced by the filter. I am yet to master the stacking and processing and am experimenting with Image Plus.

Some of the stars in the image have orange halos which I believe to be caused by chromatic aberration which I have rectified somewhat by stopping the lens down but I think I may have to go down one more stop to eliminate it (unless there is a way to remove this in post processing which I am unaware of).

To me the results so far with the clip in CLS-CCD filter with an unmodified camera and encouraging as it helps in bringing out the Ha nebulosity.

Hope this helps,
Rodney
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Click for full-size image (crux carina iso800 120s 50mm f4 800px.jpg)
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  #5  
Old 17-05-2012, 12:31 PM
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bmitchell82 (Brendan)
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I guess what you guys actually need to start thinking about is not that a certain type of filter magically makes certain emission lines appear. Im sorry they don't.

Light as we know is electromagnetic, but we generally represent it as a sinusoidal wave. depending on the frequency of that wave is depending on what colour our eyes are stimulated to see.

So when you put a UV/IR block filter pretty much anything that lands outside the specified "band range" is stopped.

In an unmodified DSLR the IR block range is letting a TINY amount of hydrogen alpha range which is on the ass end of red but right on the start of Infra red hence half of it is moot.

Sometimes various nebula enhancing filters all they are doing is blocking out big streams of wavelengths which gives the impression that you are capturing more for instance Hydrogen alpha. Truth is your not, its just killed everything else!

This is why narrow band images appear to have so much detail, is the other bands of light aren't filling in the spots where there is no (for instance) Hydrogen alpha.

My advice for you on the Ha, OIII and SII filters for unmodified DSLRs is this.

Your running a RGGB bayer filter. Halpa is in the red neck of the woods hence your really only getting 1 pixel in 4 capturing usable data.

SII i believe is just under Ha and is in the red neck of the woods hence your using 1 piexel in 4 to capture useable data

OIII is in the bluey section of the wave lengths once again your only using 1 pixel in 4 to capture data, with a added smash in the face that OIII is actually hard to get as there isn't that much around!

So you have to start pushing your dslr in the OIII for huge hours of data, with 20+min exposures, your Ha well its like using a 16" telescope but stopping it down to 8". I would either modify your camera to allow the maximum amount of Ha in or just wait and save your dollars for a proper cooled astro CCD.

In saying this the filters will not be 100% useless its just they don't give much return back for time spent as apposed to other cameras. Of course if your handy with Photoshop you can magically make colours appear For reference Ha is not a deep red its more of a salmon red
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