determining what NB filter i have

[Somnium]

so a while back i purchased a camera and filter from an IISer, the filter wheel was loaded with LRGBHa and SII filters but for whatever reason one of the NB filters was not there, the guy was god about it and returned some money for it but now i am in the position where i either have an Ha or SII filter in my filter wheel and i want to buy the other one. i think it is the Ha, but to be honest i have no good reason for thinking that, other than Ha is generally the most used filter and it was in the slot after the visual filters were in, in the standard order. but before i drop some decent money on a filter i already potentially have, is there an easy way to determine which one it is? preferably i would like to do this remotely and not have to drive to the observatory and open up the FW. i am assuming there are some targets out there that have very distinct NB regions.

any thoughts are very much appreciated.

[glend]

For doing this remotely just shoot something like Eta Carina, which has lots of Ha but much less Sii. If you see it well defined its the Ha filter, if its spotty with gaps its Sii. Works on the Lagoon as well.

[Atmos]

Another one is M16, has LOTS of Ha but it is very difficult to define SII.

[Somnium]

i just dont know if the distinction between the two is something i can trust myself to pick up in a couple of subs and without having both filters to compare side by side. maybe a planetary neb would be more distinct. Helix would be pretty good but it is not up at this time of the year

[Somnium]

hmm i get the feeling that this is still going to be a roll of the dice

[Atmos]

M16 is pretty obvious :)

[Somnium]

Thanks Colin, i was struggling to find an example of the Sii alone

[strongmanmike]

Totally agree with the two suggestions, Eta carina will be a dead give away, looks dense and bold in Ha but far more tenuous and patchy in SII - easy! :-)

Take a 5min sub, it should be obvious to us all from that :thumbsup:

Mike

[Somnium]

thanks Mike, if the clouds clear i will post something tonight

[Somnium]

it appears that my observatory is under permanent cloud cover ... i couldn't take the image. i have a friend with some land out in Bathurst who offered me some space for the observatory and i am seriously considering taking him up on the offer, should get much better weather conditions and seeing ...

[lazjen]

The clouds will follow:

:cloudy:

;)

[Somnium]

yeah true ...

[Somnium]

so this is a 60 second image of Eta carinae that i took last night. i have my thoughts on what it is but i want to see if that is consistent with other people. no stretching was done to the image, i saved as it appeared in FITS liberator which defaulted the white slider up the curve.

[glend]

Looks like SII to me.

[Atmos]

I'd be inclined towards SII also.

[rustigsmed]

I would be leaning toward SII too. it shows stars more prominent than Ha. however I probably would have gone for a target with next to no Sii to be sure to be sure. eg running chicken neb near the boks.

[Somnium]

should i do a Red and NB image side by side to compare, would that make it easier to distinguish? i really don't want to buy the same filter again so i want to be pretty damn sure

[Peter.M]

In the end there is only going to be 2 different ways to know for sure. The first one is to go down there and read what is on the side of the filter. The second if the guy who sold it to you had a full set, which seems likely. Why not contact him and see which one he still has. If he only bought 2 then it would most likely be HA, because I cant think of a reason to get SII and OIII.

[Somnium]

Believe me I have contacted him and he doesn't know, he bought both ha and SII and both were supposed to be in the fw but only 1 was. Also the filters are unmounted, just glass edges like this https://www.optcorp.com/ba-fsiin-rd50-8nm-sii-ccd-filter-50-8mm-unmounted.html

So I will need to deduce it. I also took an image of m83 last night thinking that ha regions would show up clearly and almost no detail was showing which makes me agree that it is an SII filter, I will post that pic tonight along with an image of the running chicken neb

[RobF]

NGC6188 might be a better one for demonstrating SII versus OIII/Ha?

[Somnium]

it looks like i am having issues with the filter wheel, i think that image was actually a Lum, i dont think it is actually turning. so no chance of working this one out just yet. will post when i have progress

[strongmanmike]

Having not stretched it at all makes it a little more difficult but that is definitely not SII, the fickle finger looks very different in SII compared to Red and Ha, its edges glow more with a darker immediate surrounds, it should almost look like a negative, so, that looks like Red to me as the nebulosity is not quite dense enough to be Ha, buuut possibly Lum like you say though...:question:

That didn't help much huh :question: sorry

Mike

[Somnium]

thanks mike, a reboot of the computer got the filter wheel working, i will post some examples, I am fairly confident on what it is but i will see what everyone else says

[Somnium]

okay, this is looking much more like it. the images are labelled either NB for narrow band or Red for ... red, so what do you think

on second inspection you cant see the labels, so the images with fewer stars are the NB images

[rustigsmed]

going from the running chicken shot I'm going with it not being a Sii filter.

here are a couple of reference shots Ha / Sii for people to eyeball if they like. not much stretching at all but you get the idea S2 is very very very thin near the boks even after a severe stretch (which I probably should have posted).


Rusty

[Merlin66]

Aidan,
There's a quick and accurate way of checking and confirming the bandwidth......
Is there anyone in the area with a slit spectroscope?? Two minutes with a spectroscope and some sunlight will definitely give you the answer.

[Somnium]

You know I did think of that and I actually thought you might make that suggestion. I don't know anyone in the area who has one I could borrow. If there is someone in Sydney that I can borrow one off then I wouldn't turn it down. Alternatively I will work off a consensus based on the pictures. It is not a cheap decision to make though

[loc46south]

Hi Somnium - I actually took my Sulpher Filter out of my filter wheel and replaced it with a 3nm NII and Replaced the Ha with a 3nm filter as well - couple of test images I took. Could be an idea.

Geof

[Somnium]

i might stick the the standard filters. i dont plan on doing too much NB imaging, my main focus is on galaxy imaging. however, it is good to have a target to shoot during the full moon. we get precious limited time to image that we need to utilise it all.

anyone else with ideas as to what filter it is ???

[ericwbenson]

Hi Aidan,
I am not familiar with the other objects you have posted but I do have a side by side comparison of an easy target at the moment: NGC2437 (M46).
The star cluster includes a planetary nebula that is strong in Ha and weak in S2. See the attached screen cap for a two uncalibrated frames linearly stretched the same from the bgd, both about 1297 adu, to 2000 adu, which is just above the brightest part of the ring. The very brightest part of the ring is about 100 adu for S2 vs ~700 adu for Ha above the bgd.

This is from a Apogee U16M (16803 CCD), what CCD do you have?

HTH,
EB

[codemonkey]

Pretty confident that's a Ha, mate.

Attached is two recent single exposures of mine of the same region. Noisy one is SII, smoother one is Ha.

[Somnium]

Thanks for that and to everyone that helped, I did a direct comparison to Colin's m16 and I am 99.9% sure it is Ha.