Upgrading Narrowband Filters - Is it worth it?

[groberts]

I'm currently using the 7nm range of Ha-OIII-SII 31mm unmounted filters that go with the ZWO x8 EFW & ZWO1600MM-Cool mono camera and my WO GT81 scope, with decent results.  However, I'm beginning to think about whether it's worth upgrading to better quality / narrower wavelength range? 

Considering Chroma Ha 3nm and perhaps OIII & SII too (wavelength?).  They are, of course, ridiculously expensive, so before proceeding would appreciate any thoughts (a) is it worth it and (b) which wavelengths are best?(c) anything else to be considered?      

Thanks, Graham

[Adam J]

35 minutes ago, groberts said:

I'm currently using the 7nm range of Ha-OIII-SII 31mm unmounted filters that go with the ZWO x8 EFW & ZWO1600MM-Cool mono camera and my WO GT81 scope, with decent results.  However, I'm beginning to think about whether it's worth upgrading to better quality / narrower wavelength range? 

Considering Chroma Ha 3nm and perhaps OIII & SII too (wavelength?).  They are, of course, ridiculously expensive, so before proceeding would appreciate any thoughts (a) is it worth it and (b) which wavelengths are best?(c) anything else to be considered?      

Thanks, Graham

I am using the 5nm Astrodon filters (Ha +  OIII), ill get a SII when I can afford it. For me it was less about narrower band pass and more about consistency and better anti-reflection coatings most so in the case of OIII.

 

[Jkulin]

I should have my 3nm NB Chroma 2" unmounted filters in the next day or so, I bought them direct from Chroma as it was so much cheaper.

Nothing wrong with my Optolong, but just wanted to try better filters.

[DaveS]

I was getting terrible halos with my Baader 7nm [OIII] filter so bit the bullet and went for a full-house of 3nm Astrodons. I can say that the 3nm bandwidth makes a huge difference under moonlight, even with the local light pollution, and even with astronomical twilight. Given the rarity of clear skies here, it can make the difference between imaging and not imaging.

[groberts]

Thanks everyone. 

I can understand the increased benefit in moonlight but in 'normal' conditions is there still a noticeable benefit?  

[DaveS]

Well, even without moonlight, if you have light pollution then 3nm will give you that much more signal to noise, and given the number of summer targets it'll enable you to image during the darker parts of astronomical twilight.

[groberts]

Thanks Dave.

So, if I'm going to get all three NB filters what wavelength?

I'm presuming 3nm Ha but what about OIII and SII also 3nm?

[DaveS]

My understanding is that [OIII] responds even more to 3nm bandwidth than HII. I don't know so much about [SII] as I've not used it for years. I think you could get away with 5nm.

Certainly [OIII] is more affected by moonlight than HII.

[don4l]

I've just got a 3nm Chroma, and it really is very good indeed.  However,  I now think that a 3nm OIII would have been better value, for reasons given above.  I can use a 6nm Ha at any time of the month, but OIII is really affected by the moon.

You ask about other thins to consider.  My Chroma filter is unmounted, and 3mm thick.  It won't fit in my filter wheel because it is too thick.   There isn't room for the O ring.  The only other thing is that it takes ages to focus unless you find a bright star.

[tomato]

I’ll probably be shot for this but here are two single 20 min stretched exposures, the first with a 3nm Astrodon Ha filter, the second with a 7nm Baader filter, but NOT shot  on the same scope or camera, so it’s definitely NOT a scientific controlled comparison. The point I’m making is the Astrodon image is superior, but is it £££s superior? My own view is I cannot justify the extra cost of the quality filters as there are lots of areas of AP I need to improve first before I would realise the benefit, plus my main area of interest is LRGB imaging.

[groberts]

42 minutes ago, don4l said:

I've just got a 3nm Chroma, and it really is very good indeed.  However,  I now think that a 3nm OIII would have been better value, for reasons given above.  I can use a 6nm Ha at any time of the month, but OIII is really affected by the moon.

You ask about other thins to consider.  My Chroma filter is unmounted, and 3mm thick.  It won't fit in my filter wheel because it is too thick.   There isn't room for the O ring.  The only other thing is that it takes ages to focus unless you find a bright star.

Hmm, now you got me worried.  Does anybody know if the 31mm unmounted 3nm Chroma filters will fit a ZWO x8EFW?  

[don4l]

15 minutes ago, groberts said:

Hmm, now you got me worried.  Does anybody know if the 31mm unmounted 3nm Chroma filters will fit a ZWO x8EFW?  

Check the depth that you have available.  Also, check the thickness of the Chroma filter.  I don't know if they are all the same thickness.

I managed to fit the filter into the SBIG internal wheel which uses little screws and washers to retain the filter.  The filter did fit into the Trutek,  but there was no way of holding it in place.

[groberts]

OK thanks, the ZWO EFW also uses small screws and washers = a devil to fit.

 

[Adam J]

1 hour ago, groberts said:

Hmm, now you got me worried.  Does anybody know if the 31mm unmounted 3nm Chroma filters will fit a ZWO x8EFW?  

If your scope is slower than F4 then the 1.25 will work fine. If its slower than F4.5 then you wont even notice the difference moving to 31mm with the ASI1600mm pro just so long as you use flats...which you need to anyway.

[groberts]

10 hours ago, Adam J said:

If your scope is slower than F4 then the 1.25 will work fine. If its slower than F4.5 then you wont even notice the difference moving to 31mm with the ASI1600mm pro just so long as you use flats...which you need to anyway.

I already have 31mm ZWO filters which fit OK but from comments was concerned about the thickness of the Chroma filters (3.00mm v 1.90mm?) and, like some others mentioned, whether there was plastic round the edge - thus increasing it's actual diameter. 

Another point made is also something I was surprised by, that focussing is slower?     

[DaveS]

I don't know about Chroma filters, but I run Astrodons in my ZWO filter wheel.

Focusing will be slower as you need longer exposures due to the loss of light through the narrow bandwidth. with a Bahtinov mask I often have to use 5 or 10 sec exposures.

[don4l]

It isn't just the focusing that is slower, but  I always plate solve as part of the "finding and framing" setup.  My platesolving exposures are typically 18s each at 3nm, whereas they were 12s at 6nm.

 

My focusing exposures are about double (maybe more) than they were with the 6nm filter.  I'm not using a mask, but 5s exposures are not uncommon.

Overall, I would say that it takes at least an extra 20 minutes to get going.

You do, however, make up the time once you start taking the images.  The individual frames are visibly cleaner.

[Jkulin]

If you plate solve and frame and focus using the Lum filter, you can then rotate to the NB once in position, that's what I do.