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  #1  
Old 19-10-2008, 02:34 AM
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Tandum (Robin)
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Narrowband Imaging with a DSLR

Is there any point to narrowband imaging with a modified DSLR?

The filters for Ha, O3 and S2 and very expensive to start with, over $1K worth and as far as I know, a modified DSLR will only see the light in the red pixels.

So, is it really worth the money or should these filters be included in the cost of a mono camera purchase? Is anyone imaging this way and producing decent results?

I figure narrow band is my only way around light pollution in this city.
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  #2  
Old 19-10-2008, 06:58 AM
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Merlin66 (Ken)
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A set of 2" filters will cost you about $500-600
The modified DSLR not only sees further into the red but does give good response across the spectrum.
So, these filters can be used to give narrowband images which, when combined will be impressive.
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Old 19-10-2008, 11:20 AM
Ian Robinson
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Why not ?

the sensors can detect light from UV to IR, the point of modifying them is to "enhance" the red end of their response.

I still see no real need to mod my 40D BTW, it's used more for happy snaps and general photography than astro stuff and I am not impressed with the results people get with the "fix" they apply to their modded DSLRs to use them in general photography .... modding is more bother than it's worth in my opinion.

There is no reason why narrow band Ha ,OIII and SII photography wont be successful with a DSLR , and it need not be a modded DSLR either. It's just a matter of using appropriate exposures for the camera's sensitivity in that band.

Last edited by Ian Robinson; 19-10-2008 at 11:31 AM.
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Old 19-10-2008, 03:59 PM
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Quote:
Originally Posted by Merlin66 View Post
A set of 2" filters will cost you about $500-600
Where do you see them at that price Merlin?

Quote:
Originally Posted by Ian Robinson View Post
There is no reason why narrow band Ha ,OIII and SII photography wont be successful with a DSLR , and it need not be a modded DSLR either. It's just a matter of using appropriate exposures for the camera's sensitivity in that band.
Have you tried this Ian? Looking at response curves for the default canon IR Filter, it blocks 70% of Ha at 656 and 80% of SII at 673, so your exposure time would need to be two to three times longer than with a Baader IR Filter installed plus only the red pixels will be detecting anything. I'd never get decent images if I had to do 30minute exposures.
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Old 19-10-2008, 04:15 PM
Sylvain (Jon)
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Ian, i'd be interested in comparing pics taken by both modded and normal 40D, would you have a link for that ?

Tandum, i'm not an expert at all, but i think when imaging in narrowband, you'll always end up multiplying the exposure time quite a lot (i heard between 2 to 3 times depending on the filter used)

--> Correct me if i'm wrong
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Old 19-10-2008, 04:59 PM
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Quote:
Originally Posted by Tandum View Post
Where do you see them at that price Merlin?


Have you tried this Ian? Looking at response curves for the default canon IR Filter, it blocks 70% of Ha at 656 and 80% of SII at 673, so your exposure time would need to be two to three times longer than with a Baader IR Filter installed plus only the red pixels will be detecting anything. I'd never get decent images if I had to do 30minute exposures.
Yes - I've seen the sensitivity curve for the 40D modded and standard chip. I've also seen how modded 400D and 40D DSLRs perform for normal photography even after images have been post processed to compensate for the horrible white balance - way not impressed !! Thoroughly investigated this back in June before I bit the bullet and bought the 40D and made my decision that modding was not necessary and has more cons than advantages (for me).

Not a big deal that the sensitivity is less than 10% at the IR end, it is still capable of recording photons , all you need to do is compensate for the lower relative sensitivity by using longer exposures (or more subs) if you need to record that data.

The stock fllter blocks 70% of Ha at 656nm
==> 30% of the Ha still gets through (so use a Ha narrow band filter and 2-3x the exposure)
and 80% of SII at 673nm
==> 20% of SII still gets through (so use a SII narrow band filter and 4x the exposure).

Last edited by Ian Robinson; 19-10-2008 at 05:26 PM.
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Old 19-10-2008, 05:07 PM
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Quote:
Originally Posted by Tandum View Post
Where do you see them at that price Merlin?


Have you tried this Ian? Looking at response curves for the default canon IR Filter, it blocks 70% of Ha at 656 and 80% of SII at 673, so your exposure time would need to be two to three times longer than with a Baader IR Filter installed plus only the red pixels will be detecting anything. I'd never get decent images if I had to do 30minute exposures.
You have to take the response of the CCD into consideration as well. Modding the camera doesn't increase the responsiveness of the CCD at that frequency just gets rid of the filter. If you run this document through babelfish it explains the spectral response well. There is a good argument for modding but there is more objects to imaging than just Ha regions.
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Old 19-10-2008, 05:09 PM
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http://www.telescopes.com/telescope-...dfilter7nm.cfm
http://www.opticsplanet.net/celestro...3-filters.html
http://www.optcorp.com/ProductList.a...05-156-840-852

Christian Buil has done a lot of investigation on the subject.
http://astrosurf.com/buil/filters/curves.htm
http://astrosurf.com/buil/350d/350d.htm
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Old 19-10-2008, 05:19 PM
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Quote:
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Ian, i'd be interested in comparing pics taken by both modded and normal 40D, would you have a link for that ?

Tandum, i'm not an expert at all, but i think when imaging in narrowband, you'll always end up multiplying the exposure time quite a lot (i heard between 2 to 3 times depending on the filter used)

--> Correct me if i'm wrong
That will be because you are dealing with very small numbers of photons when using narrow band filters compared with broadband or bandpass or band stop filters , and assuming the transmission of light in the permitted band is near 100%.

The sensitivity of the detector in the pass band is also important and needs to be compensated for , is 1/2 the light ==> 2x the exposure or one less lens stop (ie f/2.8 becomes f/2 etc)
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Old 19-10-2008, 05:42 PM
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Quote:
Originally Posted by Ian Robinson View Post
Yes - I've seen the sensitivity curve for the 40D modded and standard chip. I've also seen how modded 400D and 40D DSLRs perform for normal photography even after images have been post processed to compensate for the horrible white balance - way not impressed !! Thoroughly investigated this back in June before I bit the bullet and bought the 40D and made my decision that modding was not necessary and has more cons than advantages (for me).
These images are from my modded 40d set to full auto with auto white balance and no post processing. They where shot through a Hutech VLC filter. Looks ok to me.
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  #11  
Old 21-10-2008, 06:43 PM
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Quote:
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These images are from my modded 40d set to full auto with auto white balance and no post processing. They where shot through a Hutech VLC filter. Looks ok to me.
Hard to tell from just two photos.

Comes down to how the camera will be predominantly used most the time.

If you are mostly using the camera for astronomy , and rarely use it for daylight "happy" snaps and don't mind stuffing up your warantee , and are prepared to risk disassembling your camera (which may have cost over $1800 or more if a full frame if bought locally , which is not an insignificant amount of money for most of us , and a significant outlay ) , don't mind limiting yourself to only EF lenses to "undo" the mod with a dropin filter (also from Hutech ) , and the expense involved in all this.
Or have more than one camera. Go for it.

But - some of us only have the one good DSLR and it is used predominantly for "happy" snaps then the expense involved , jepodising the warantee , and deterioration in colour response for daylight photography ("fix" dropin and custom white balancing aside) is simply not worth the bother.
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Old 22-10-2008, 11:22 PM
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Quote:
Originally Posted by Ian Robinson View Post
If you are mostly using the camera for astronomy , and rarely use it for daylight "happy" snaps and don't mind stuffing up your warantee , and are prepared to risk disassembling your camera (which may have cost over $1800 or more if a full frame if bought locally , which is not an insignificant amount of money for most of us , and a significant outlay ) , don't mind limiting yourself to only EF lenses to "undo" the mod with a dropin filter (also from Hutech ) , and the expense involved in all this.
Or have more than one camera. Go for it.

But - some of us only have the one good DSLR and it is used predominantly for "happy" snaps then the expense involved , jepodising the warantee , and deterioration in colour response for daylight photography ("fix" dropin and custom white balancing aside) is simply not worth the bother.
Oh Come on Ian...Live a little!!

I have grown to love the HA response from my modded 40D - the mod was a risk - granted, but done by a reputable dealer (overseas).
As for happy snaps - unless you're after studio quality on every pic, a simple CWB of a white sheet in ambient light seems to work reasonably well. I thought I would need some sort of filter to achieve decent results, but this hasn't been the case for me.
All up, modding my 40D cost me $238AU - postage/insurance both ways + the Baader replacement filter.
I'm very happy I did it.
If the same dealer offers a cheap cooling mod I'll be there!!


ps...back to topic, there is a cheap narrowband option for DSLR users on the Hutech site...
http://www.sciencecenter.net/hutech/haimage.htm
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Old 23-10-2008, 12:11 AM
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That's a cheap mod Doug, Who did that? The filters must cost AU$150+ these days.

Allan has been messing about with narrowband DSLR here:-
http://www.iceinspace.com.au/forum/s...ad.php?t=37106
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Old 23-10-2008, 12:16 AM
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That's a cheap mod Doug, Who did that? The filters must cost AU$150+ these days.

Allan has been messing about with narrowband DSLR here:-
http://www.iceinspace.com.au/forum/s...ad.php?t=37106
Peter Tan in Hong Kong Robin...
http://www.tan14.com/gears.htm

Unfortunately the stock market crash has stuffed the AU - HK $ Exchange, so things aren't as favourable now.

I can recommend his service though.

Doug
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Old 23-10-2008, 12:17 AM
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Ahh, old Hong Kong Pete .... He gets around

No GST problems getting it back into oz I take it
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Old 23-10-2008, 12:28 AM
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No GST problems getting it back into oz I take it
None at all really, I took a punt and insured it for just under $1000AU for the return journey. But, that was probably an unnecessarily frugal move as I had all the receipts of purchase in AUS. Just did it to avoid delay of the camera.
Doug
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Old 23-10-2008, 02:27 AM
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Oh Come on Ian...Live a little!!

I have grown to love the HA response from my modded 40D - the mod was a risk - granted, but done by a reputable dealer (overseas).
As for happy snaps - unless you're after studio quality on every pic, a simple CWB of a white sheet in ambient light seems to work reasonably well. I thought I would need some sort of filter to achieve decent results, but this hasn't been the case for me.
All up, modding my 40D cost me $238AU - postage/insurance both ways + the Baader replacement filter.
I'm very happy I did it.
If the same dealer offers a cheap cooling mod I'll be there!!


ps...back to topic, there is a cheap narrowband option for DSLR users on the Hutech site...
http://www.sciencecenter.net/hutech/haimage.htm
Yes - I expect near perfect photos everytime , I didn't spend so much money to get otherwize.

The 40D is afterall a step above to a professional entry level camera , it is not a toy like the 400D , 450D and 1000D or those point and shoots.
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Old 23-10-2008, 07:35 AM
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Could we bring the thread back on topic. The original thread about narrowband imaging with a DSLR is getting lost in OT conversation. If a discussion about the pros and cons of modded DSLRs is wanted please start a new thread and I will join the relevant posts from this thread to that one.

Thank you.
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  #19  
Old 25-10-2008, 07:35 PM
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Here some pics before/after mod. my 40D

Hi everyone,

I'm from portugal and I have a modified 40D. All pics taken with a Tak FS102NSV (at f6.2). Sorry for the low quality (resulted from the jpeg compression).

Cheers,

paulo
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Old 25-10-2008, 09:13 PM
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Even with a modded camera only a quarter of the pixels on the sensor will usefully pick up HA. As for O3 as this wavelength lies on the overlap of the Bayer filters of the green and blue pixels on your sensor you are using three quarters of your useful pixels as green pixels are half of the total and blue like red a quarter. The real advantage is increased signal to noise. Exposures can be far longer as the total number of photons over a given exposure is far less. Any light pollution is also minimised to only be recorded for the bandpass of the filter being used. Do not think that the Moon is no problem as it can give very nasty gradients depending on where it is to your target and how bright it is.

If you live in a light polluted area it is the only way to get faint nebula data. Patience is a useful attribute as it can take several nights to get a decent image.

Is it worth it ? Definitely as it can be quicker than going to a dark sky site and be beaten by the weather.

Bert
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