Help confused again with Ha, Baader, modded and OIII

[Catanonia]

Bare with me guys as I am getting confused.

Ok I have a Canon EOS 350D modded with a Baader lens. I believe this is to remove the IR filter and replace with baader clear lens to keep focus. Correct ?

Now for the following questions..

Is my 350D modded collecting Ha as everyone talks about or is Ha different?

If Ha is different, is it possible to get a filter to collect Ha with the 350D ?

Can the same be done with OIII ?

Just need to get it sorted out in my head, I think that Ha is different to the 350D mod as the mode is for IR and that is different to Ha.

[steve51450]

Hi Cat

the mod to your camera means it is still ir blocking as it has the baader replacement filter but it improved its response to ha (hydrogen Alpha wave lengths) which you will see as red in ngc 7000 for instance

You can then put a ha filter on the front of your camera which only let through hydrogen alpha or you can put an OIII lens on the front that only lets through OIII

the reason for the mod is to make the camera more receptive to hydrogen alpha it is not a hydrogen alpha filter

so you can use filters this way

OIII filter which is green

SII filter which is blue

HA filter which is red

this will enable you to do rgb imaging with narrowband filters by assigning them to the correct colour channels

i am sure someone on here can explain it better than me

steve

[Catanonia]

ah, many thanks Steve for clearing that up. I was getting very confused as to what it actually did the Baader mod on the 350D.

Now for the obvious question.

What Ha and OIII filters should I use for my 350D considering I am imaging via a 2inch focuser on 80 and 120 ED's.

I already have and use all the time the Astronomic CSL clip LP filter on the 350D

I have decided for the meantime to keep the scopes I have and learn to image regions of the sky to build up my understanding.

Some of my pictures are missing some 'pop' and i think the addition of some Ha subs might help that and bring out some nebula structure.

I am getting quite hooked on nebulas btw.

Cat

[steve51450]

to be honest Cat You are getting into a more difficult world with narrowband filters as everything from focusing to data collection just takes a whole heap longer. I do not mean don't have a go but i think there is more than enough out that their for you to play with at the moment before you go out spending £500-600 on 2" mid-band filters

It was 18months of trial and error before i ventured into hubble palette and rgb narrowband and i found it a whole heap easier with a dedicated ccd because of the sesitivity of them

If you do want to get one, get the 35nm HA filter in either clip or 2" as i think that will suit your 350d much better and will give you some pleasing mono results

you will find collection of some of the other emission lines like SII & OII much much harder!!

i hope this rambling helps

steve

[Whippy]

I think that's pretty much it Steve .

Cat, what people talk about when they mean Ha is the Hydrogen Alpha light wavelength that's emitted by emission and planetary nebulae such as NGC 7000. As Steve has mentioned, replacing the filter on your Canon has improved the response to the Ha wavelength (IIRC, the original Canon filters block IR but also cut a lot of the Ha wavelength becuase it's close to Infra Red). When you see people imaging in Ha means that a narrowband filter is being used which only lets through Ha light which is why most of those images are mono. You can also buy filters for different wavelengths such as OIII, SII & Hb when you can then assign to different colours like you would in RGB processing such as assigning Ha to Red, OIII to Blue and SII to Green. this is what's known as 'false' colour imaging.

The big attraction to narrowband imaging is that you can image when the Moon is big and bright and/or imaging in an urban location that has terrible LP, imaging would prove very difficult otherwise.

Tony..

[Catanonia]

Steve,

Thanks for your honesty, it is what has keep me on the 'somewhat' straight and level these last few weeks

Yes you are correct about learning what I have and I intend to do so with the scopes I have (unless I win big again).

I know if I start serious about these filters, then I start into the whole dedicated CCD's with filter wheels etc etc and loads of money.

That 35nm Ha clip sounds just perfect for the results I am after. A bit of structure in the Ha to the images to combine into the RGB I already have to give that 'pop'.

Will keep my eyes out for one and try to forget about all the other stuff I could buy.

So if I find one of these 35nm Ha's I can remove the CLS clip and use that for some subs to give structure. Sounds perfect.

Many thanks again Steve, very useful and clear to the point as always Your heads up on the CLS LP clip filter was perfect.

Cat

to be honest Cat You are getting into a more difficult world with narrowband filters as everything from focusing to data collection just takes a whole heap longer. I do not mean don't have a go but i think there is more than enough out that their for you to play with at the moment before you go out spending £500-600 on 2" mid-band filters

It was 18months of trial and error before i ventured into hubble palette and rgb narrowband and i found it a whole heap easier with a dedicated ccd because of the sesitivity of them

If you do want to get one, get the 35nm HA filter in either clip or 2" as i think that will suit your 350d much better and will give you some pleasing mono results

you will find collection of some of the other emission lines like SII & OII much much harder!!

i hope this rambling helps

steve

[Catanonia]

Now this is what I love about this forum.

Two sets of brilliant answers explaining everything I needed to know.

Many thanks Whippy, you filled in a couple of the missing links for me.

Cat

I think that's pretty much it Steve .

Cat, what people talk about when they mean Ha is the Hydrogen Alpha light wavelength that's emitted by emission and planetary nebulae such as NGC 7000. As Steve has mentioned, replacing the filter on your Canon has improved the response to the Ha wavelength (IIRC, the original Canon filters block IR but also cut a lot of the Ha wavelength becuase it's close to Infra Red). When you see people imaging in Ha means that a narrowband filter is being used which only lets through Ha light which is why most of those images are mono. You can also buy filters for different wavelengths such as OIII, SII & Hb when you can then assign to different colours like you would in RGB processing such as assigning Ha to Red, OIII to Blue and SII to Green. this is what's known as 'false' colour imaging.

The big attraction to narrowband imaging is that you can image when the Moon is big and bright and/or imaging in an urban location that has terrible LP, imaging would prove very difficult otherwise.

Tony..

[Psychobilly]

I'm still not convinced about the usefulness of the nm filter.... hopefully will get some decent nights so that I can give it a more thorough test... Even the 35nm filter made focusing a much slower process... and couldnt even see deneb through the viewfinder...

Peter...

[Catanonia]

I'm still not convinced about the usefulness of the nm filter.... hopefully will get some decent nights so that I can give it a more thorough test... Even the 35nm filter made focusing a much slower process... and couldnt even see deneb through the viewfinder...

Peter...

Peter,

Saw your NGC7000 with the Ha filter and that looked great. I imagine using that as contrast ontop of my RGB to give more structure and pop.

What filter did you get ? do you have a link ?

Do you use it with a DSLR ?

I assume if I got a clip version, i could focus with normal filter, remove it and replace with the Ha one.

Either that or put in bigger ISO for focusing only.

[Whippy]

I assume if I got a clip version, i could focus with normal filter, remove it and replace with the Ha one.

Unless the filters are parfocal, than that won't work.

Tony..

[Psychobilly]

Its not a clip in its the Baader 2" one came as a pressie from SAN

I was having to take 10s exposures at ISO1600 to get a usable pattern with the Bahtinov on the Megrez 72 FF III ... normally a 2s provides a much better image..

I dont know what I was really expecting from the filter...... the sky wasnt brilliant onthe night of the test the stars weren't leaping out at you and there was high cloud scooting around which quickly became mid level and brought the premature end to the test...

Peter...

[Catanonia]

mmm, they do a 12nm EOS clip Ha filter at retail of 150 Euros.

Got ya Whippy on the focusing.

Peter : 10 Seconds at 1600 isn't too bad and shouldn't take to long. About what I am used to with Bahtinov when in twilight as I set up.

By the time I go for the Ha subs, will be nice and dark.

[Aza]

If you get one, go for the EOS clip in filter.

I think the 12nm is ideal in my experience.

I never had any trouble focussing with it. I always focus on Vega or Capella, depending on the time of the year.

But be prepared to go for 15 minute subs.

Forget about SII and OIII for now, and even in the future, I dont think they are usefull with a DSLR...even a CCD has trouble picking those up in most cases!

[Aza]

Here is an example of what I did using mine:

http://stargazerslounge.com/imaging-deep-sky/71608-dslr-pacman-hargb.html

[narrowbandpaul]

i will throw in my two centines also.

your 350D has been modified. This removed the standard canon IR filter, which they put in to achieve a proper white balance. It is also important because camera lens, and indeed most telescopes will not focus IR and visible light at the same time, similar in the way that an achromatic refractor will not focus blue and red at the same time.

however the standard canon filter blocks out not just the IR but some red light too. Even worse it cuts out the red light associated with most nebulae....the Hydrogen Alpha Wavelength, at 656nm. The reason nebulae are red is because of this wavelength. It is the most important wavelength in optical astronomy, because there is so much of it.

The modification removes the bad canon IR filter and can either replace the filter with a baader one, which has much higher transmission at Halpha, or the filter can be left out, and the IR can now be detected.

The mod only makes your camera more efficient, it doesnt preferrentially let through Ha and block others, the mod allows Ha, and other red wavelengths through.

Now for narrowband imaging, or emission line imaging, which is perhaps more descriptive.

Emission nebulae, which are objects that emit light, not reflect it like reflection nebulae..M45 is a reflection nebula. Emission nebulae emit light because there is some object, usually a hot star or cluster of stars, that gives energy to the gas that compose these nebulae. Most red looking objects are good emission nebulae, although some only emit Ha. Great examples are NGC7000, Orion Nebula, M27, M57, IC1396, Veil Nebula.

because of the physics involved, each element present in the gas mixture emits very distinct wavelengths....emission lines. If one was able to split the light from these nebulae in to the component colours we would see a series of lines. For example, most emission nebulae (include supernova remnants and planetary nebs) will show:

1)Hydrogen alpha, red light at 656nm

2)Oxygen3 O[iII] at 495 and 500.7nm...greenish

3)Hydrogen Beta, blue at 486nm

4) Helium2 HeII at 468nm, blue

5) Sulphur2 S[iI] red at 671/673nm

there are others.

The most prominent 'species' are Ha O[iII] and Hbeta. From a personal view, I dont use Hbeta, basically because there is no point. Let me explain.

Both Ha and Hbeta come from Hydrogen gas. Now it doesnt matter that the emission wavelengths are different, the fact it came from Hydrogen, means the distribution of gas seen in these two wavelengths will be exactly the same. The nebula will have the same shape and structure in both Ha and Hbeta light. The only difference is again governed by that cruel mistress, physics. According to quantum mechanics, because the Hbeta is a higher energy photon, it is less likely to be emitted. The maths says it is 0.292x as likely to be emitted as Ha.

so, the Hbeta is only 0.292x the strength of the Ha signal. Therefore, if you take an image in Ha, then multiply by 0.292, the result is exactly equivalent to Hbeta. You get Hbeta free......when you shoot Ha images.

0.292 is wrong however. Its correct at the nebula end, but once it travels through dark and dusty space blue light is impeded more than red. So the observed ratio is near 0.15-0.2.

the result of using say Ha, Hb and O[iII] for an image using the normal pallette of Ha=R O[iII]=G and Hb=B, results in a red looking image. Which is the same as RGB. For this reason I dont use Hbeta. But the choice is of course up to the imager.

the hubble team use a colour scheme containing Ha O[iII] and S[iI]. The O[iII] and S[iI] are typically much weaker than the Ha, so more time must be spent collecting this data. The reason that these wavelengths are chosen is that they are all uncorrelated. That is the amount of one emission does not affect the amount seen of any of the others. The same cannot be said for Ha and Hbeta. Here Hb is 0.292xHa.

The normal method for combining the 3 filtered images in to a colour version uses the now called, Hubble Pallette, where S[iI]=R Ha=G O[iII]=B, ie a wavelength ordered pallete. The longest wavelength filter, S[iI] goes to red, and the shortest goes to blue, O[iII].

You can but all these filters separately, and attach them to the end of a nosepiece. Even with a cooled sensitive CCD, it is quite common to use between 10-30minute subframes. I typically use 20minutes, even imaging with a fast focal ratio of f/4.

The result of using these filters creates a very striking result. In RGB imaging, nebulae turn out mostly red. With narrowband, suddenly there are reds, greens and blue. And these filters show some interesting effects going on. The O[iII], which is doubly ionised, requires a temperature of around 650,000K to knock off two electrons. Thus images taken with this filter show very hot energetic regions. The S[iI] shows up well in compression areas, like the cygnus wall, the neck of the pelican, and the edges of some 'round' nebula like the Heart and Soul, M8. This filter gives an impression of a 3d object.

you can buy all the neccessary filters and screw them in, but with the colour filter array, and the weak species, Ha may be the best bet. Wth a mono CCD, the universe is the limit.

hope that helps.

paul

[narrowbandpaul]

for focussing Ha filter, it is best to use stars that arent white....the light output falls off exponentially after the peak. A bright red star, like Sadr or betelgeuse eventually will work better with an Ha in place. spectral class G K M will work nicely.....most planetarium software should show the spectral class of most bright stars

hope that helps

[Catanonia]

Here is an example of what I did using mine:

http://stargazerslounge.com/imaging-deep-sky/71608-dslr-pacman-hargb.html

Aaron,

That was the thread I looked at and gave me the idea from the discussions, but wasn't sure of the physics / filters possible / needed.

Perfect example of what I want to achieve. Some Ha to give it structure and 'pop'

Many thanks mate, keeping my eye out for a 12nm Ha EOS clip

[Catanonia]

Paul,

WOW...... OK this deserves about 3 re-reads

And I did chemisty at A level

Many thanks

Cat

[narrowbandpaul]

just doing my duty....

someone mentioned narrowband and my ears pricked up.

paul

I just found smileys.

[narrowbandpaul]

here is an article from richard crisp, amateur popularizer of narrowband. He developed the technique

http://www.narrowbandimaging.com/images/Crisp_emission_submit_final_release.pdf

[Catanonia]

LOL, this thread should be made sticky and titled

DSLR Cameras and Filter Options.

Any mods want to take it up ?

just doing my duty....

someone mentioned narrowband and my ears pricked up.

paul

I just found smileys.