Which narrow band filter bandwidth?

[Quatermass]

My skywatcher 200p with its coma corrector fitted is f4.5 so which bandwidth for a Ha narrow band filter is suitable 12 or 7nm? Going to get a baader ha 2inch filter to fit on the end of the coma corrector and try some narrow band imaging just not sure what band width matches my focal length? Any one got any suggestions who does narrow band with a modded dslr I'm using a modded canon 350d.

Qm

Sent from my Nexus 7 using Tapatalk

[ollypenrice]

Without doubt the 7. It will give you better contrast and will also be slightly more moonproof. I've tried 13, 7 and the headbanging Astrodon 3! In my book narrower is better.

Olly

[Quatermass]

Thanks for that Olly its just that the 12nb is a little bit less pricey and I wanted to match my scopes focal length with the ability's of the filter as I read that the faster scopes dont need such a narrow bandwidth. However I will take your advice as you have used all of them and know what your talking about, thank you very much.

Second question, can I get away with just the Ha and OIII filters and use the Oiii filter matched to blue and green  and Ha to red for the hubble pallette as pointed out in Astrodons imaging tutorials?

http://youtu.be/_aIT_FAH_sI

[ollypenrice]

I can't help with your second question. I never do colour mapped imaging, I'm afraid.

Olly

[Quatermass]

Really that surprizes me Olly though you would have tryed that out but I guess you dont need to if you have the right gear, one day I will get a proper ccd camera when I can afford it but for now just want to try out some narrow band imaging and take advantage of the moon lit nights that I so often just use for practising my guiding with.

Thank  you for your help appreciate it.

[swag72]

Can you get away with just an Ha and OIII filter? ............. You bet!! I've never used my SII yet and just stick to bi colour. My images are rather orange and are absolutely not everyone's cup of tea, but I like it!! I'm afraid I'm another who extols the virtues of the 3nm Astrodon filters - They are superb! So the narrower the better in my book.

A couple of examples.

https://www.flickr.com/photos/swag72/9855898385/

https://www.flickr.com/photos/swag72/11835230684

https://www.flickr.com/photos/swag72/12350767044

[Sandancer10]

Sara, I've just checked your Flickr images out and they are fantastic.

I understand the kit you use is probably one of the best setups for imaging, but I was wondering which pre and processing packages you use. I'm having a go with Iris for pre-processing, but still have to do a fair amount in PS.

[Stephen]

Narrower, narrower, narrower I've seen noticeable differences (improvements) going from 12 to 7 to 5 ... 3 is calling me but my wallet is fighting it

On the subject of bi-colour, I'm not a fan - but that's just my opinion. I prefer to put the time in and get all three channels

[swag72]

.... but I was wondering which pre and processing packages you use. I'm having a go with Iris for pre-processing, but still have to do a fair amount in PS.

I use PixInsight for calibration, stacking and gradient removal if needed. Than everything else is done in PS.

[johnrt]

I would also say narrow wins the day! But would I put a 3nm or even 5nm Ha filter anywhere near a DSLR, no I don't think I would - you're fighting a difficult enough battle as it is (I had a 12nm on my modded DSLR back in the day).

Wouldn't put an OIII filter on one either, many people have proposed it but I've never seen a single image done in total narrowband by DSLR. The OIII signal is simply too diffuse and tenuous to be detected in my opinion.

[opticalpath]

Agree with the post above - just what I was thinking: ultra-narrow band filters excellent with astro cameras that have good sensitivity at Ha wavelength, but even modified DSLRs are considerably less sensitive. It would be interesting to hear from someone who's actually using a 5nm (say) Ha filter with a DSLR and see some results before you decide.

Adrian

[Tim]

What camera will you be using?

Unless you have a large format camera, I can't help think that 2" filters would be an unnecessary expense???

Narrowband with a DSLR is hard work. Only 1/4 of the pixel will accept the ha emissions. Oiii is a lot more productive, but you are limited on the nights you can use it, not great in a bright moon.

You need at least 20 minute exposures to get a decent result from a ha filter, and preferably longer.

[Tim]

Normally the wider band filters are recommended for modded dslrs IIRC.

[Tim]

Oh, Btw, the normal hst pallete maps ha to green, s2 to red, Oiii to blue. S2 with a DSLR would be a waste of time, but if you can work out the issues with getting decent ha exposures, then together with the Oiii you can get some nice results. (You can also fake the s2 if you so wish, it's easy )

It was trying narrowband with a 350d that inspired me to get a ccd. Before you spend on a filter, I would make sure the your kit is capable of at least 20 min subs, and that tracking and thermal noise don't make the pictures unusable.

Hth

Tim

[Quatermass]

Great advice everyone thank you so much  . I am using a modded canon 350d so thought the 7nm ha filter would be a good choice its that or a 12nm but looking at Hunter Wilsons website and his narrow band pics he is using the 7nm Ha filter on a modded 350d so I think that looks like a good one. His sub are 10min long and I can manage that quite well now. Just dipping my feet in the narrow band waters at the moment so dont want to dive into the deep end just yet.