Let's talk filters

[John]

8 minutes ago, RobertI said:

Informative thread. 🙂 I have a question and hope it’s ok to put it here rather than starting a new thread. 

I am looking to get an OIII filter, primarily for the Veil, but also any other nebs which may benefit from OIII. I had settled on the Astronomik OIII. I’m now wondering if the Astronomik UHC might be a better bet, not quite so good on Veil but possibly a better all rounder. I’d be using it with a C8 (+0.63 reducer), 150PL and possibly 130P. The lowest power eyepiece I have a present is the Hyperion 21mm. 

What do folks think - Astronomik OIII or Astronomik UHC? 

Thanks. 👍

In due course you will want to have both but a UHC is useful on a wider range of targets. The "kick" that the O-III gives to the Veil, Owl and others is highly addictive as well though !

Maybe get the UHC now and start saving for an O-III ?

 

[Stardaze]

I've managed to pick up an Astronomik O-III this last week and plan to get a UHC towards the end of the year. Desperately want to see the Veil in all of it's glory first. I'd like the UHC for Orion ideally. 

[John]

5 minutes ago, Stardaze said:

I've managed to pick up an Astronomik O-III this last week and plan to get a UHC towards the end of the year. Desperately want to see the Veil in all of it's glory first. I'd like the UHC for Orion ideally. 

I was observing the Veil last night with my 100mm refractor. Both the UHC (an older Meade 4000) and O-III (Astronomik) filters showed the east and west segments quite nicely. In the field of view that I had last night, I could only fit one segment in at a time !

Without a filter = no nebulosity to be seen at all !

The O-III nicely bought out the halo surround the "apple core" of the Dumbell nebula as well.

You need dark skies though - these filters are not "magic bullets" if there is much light pollution about.

 

[Stardaze]

15 minutes ago, John said:

I was observing the Veil last night with my 100mm refractor. Both the UHC (an older Meade 4000) and O-III (Astronomik) filters showed the east and west segments quite nicely. In the field of view that I had last night, I could only fit one segment in at a time !

Without a filter = no nebulosity to be seen at all !

The O-III nicely bought out the halo surround the "apple core" of the Dumbell nebula as well.

You need dark skies though - these filters are not "magic bullets" if there is much light pollution about.

 

I couldn't see anything Friday night without a filter (turned up Sat morning) I did however see the Dumbell without one, so at least I have a reference there to see how it differs. 

It looks to be forecast for a clear evening tonight, but I've got too much on with work this week to afford such a late night, maybe towards the end of the week, fingers crossed. 

[John]

Yes - the Dumbbell is great with and without filters.

 

[Stardaze]

30 minutes ago, John said:

Yes - the Dumbbell is great with and without filters.

 

There isn't a thread I've noted for screwing the 2" filter below a 2" eyepiece on my Bresser, only at the bottom of the 2"-1.25" reducer, which is annoying. Going to change it to a Baader click-lock soon anyway as it quite poor securing a heavy EP. I'll have to screw the filter onto the EP for now. 

[jetstream]

2 hours ago, RobertI said:

I’m now wondering if the Astronomik UHC might be a better bet, not quite so good on Veil but possibly a better all rounder

How dark are your skies?

The old exit pupil deal applies- both OIII and UHC like a bit more than the 21mm Hyperion gives at f6.3. For the Veil itself the OIII is what you want and it will also excel on many other targets. The extra detail you might have heard about with a UHC typically comes from using one under dark skies IMHO.

The newest Astronomik OIIIs have a vg tight passband, the older ones are a bit wider.

[RobertI]

1 minute ago, jetstream said:

How dark are your skies?

The old exit pupil deal applies- both OIII and UHC like a bit more than the 21mm Hyperion gives at f6.3. For the Veil itself the OIII is what you want and it will also excel on many other targets. The extra detail you might have heard about with a UHC typically comes from using one under dark skies IMHO.

The newest Astronomik OIIIs have a vg tight passband, the older ones are a bit wider.

My skies are Bortle 4 on a good night. Overhead can be really dark on a nice transparent night, which are not that frequent. Darkness also depends on which neighbour happens to be going to the lavatory.  

[bomberbaz]

I used to have a link to a website which had a lot of useful information regarding filter exit pupils, seems it has now been taken down. 

However I seem to remember that as a rule of thumb and by no means written in stone it was 4-6 mm for HB with 5mm being optimum.

3-5mm for the O=III and UHC having the broadest spectrum of anything down to 1mm exit pupil depending on the object being viewed for a UHC.

Of course in some OTA's you naturally have a smaller exit pupil, maks being an obvious example although this applies any slower OTA.

I think though it was aimed more at newtonian DOB users where the gradiant in exit pupil is far higher due to most of them being quite fast scopes in the first place. 

[Stardaze]

14 minutes ago, bomberbaz said:

I used to have a link to a website which had a lot of useful information regarding filter exit pupils, seems it has now been taken down. 

However I seem to remember that as a rule of thumb and by no means written in stone it was 4-6 mm for HB with 5mm being optimum.

3-5mm for the O=III and UHC having the broadest spectrum of anything down to 1mm exit pupil depending on the object being viewed for a UHC.

Of course in some OTA's you naturally have a smaller exit pupil, maks being an obvious example although this applies any slower OTA.

I think though it was aimed more at newtonian DOB users where the gradiant in exit pupil is far higher due to most of them being quite fast scopes in the first place. 

@John how does this stack up with you? Just working out that my new APM 13 would give me an exit pupil of 2.67mm, so the O-III might not be ideal? What do you use mostly with the O-III filter in terms of EP's? 

[John]

49 minutes ago, Stardaze said:

@John how does this stack up with you? Just working out that my new APM 13 would give me an exit pupil of 2.67mm, so the O-III might not be ideal? What do you use mostly with the O-III filter in terms of EP's? 

This post on another forum by the filter expert David Knisely is worth a read:

https://www.cloudynights.com/topic/549184-narrow-and-broad-band-contrast-filters-and-exit-pupil/?p=7417928

[Stardaze]

2 minutes ago, John said:

This post on another forum by the filter expert David Knisely is worth a read:

https://www.cloudynights.com/topic/549184-narrow-and-broad-band-contrast-filters-and-exit-pupil/?p=7417928

Thanks - I'll have a read later 👍

I'll have to see how the APM 13 performs. I shall no doubt add the 20 in the coming months if I really like it but looking at that compared to the ES 24 I have, the FOV is very similar. Noted that you said you normally step down from 21 to 13 so I'll see whether the 16 gets much use too. The 9mm might be the dilemma, as I'm not sure the 100 degree is going to be that necessary in that mag? The ES 8.8 would also Barlow easier an offer some flexibility?. Anyway, this was/is about filters, though one subject leads onto another. 

[Pixies]

Hi,

Is this thread worth being made into a 'sticky'? It' got sooo much useful information, I'm using a shortcut to it for future reference.

[bomberbaz]

2 hours ago, John said:

This post on another forum by the filter expert David Knisely is worth a read:

https://www.cloudynights.com/topic/549184-narrow-and-broad-band-contrast-filters-and-exit-pupil/?p=7417928

Perhaps I am miss-reading this John but on one hand David appears to state that narrower bands work at lower pupillary size which mean higher power and on the other that when he goes to higher power he often switches from O-III to UHC. 

Actually I just re-read David's opening statement in bold. I will leave the comment above in case anybody else thinks similar but what I think he is saying is the  narrower bands benefit from less magnification per inch of aperture (lower half of the range). Glad I cleared that up 🤦‍♂️😬

Totally agree with what he says though. There are rules to using filters which are frequently broken. I often use an O-III on x150 (x15 per inch) on the ring nebula.

That's why i am a big fan of filters, allows you to play around and experiment. 👍

[John]

That's what I do - play around and see what works best

 

[Littleguy80]

2 hours ago, John said:

That's what I do - play around and see what works best

 

Best way. As observers we form part of the system and there’s a great variety in our own optics and observing skills. That’s why there are no rules, only broad guides as to what to use. 

I use my filters across a wide range of exit pupils, even over 8mm (40mm eyepiece in my 10” dob). When you experiment you can find some quite unexpectedly successful combinations. I observed Barnard’s Loop in my 10” dob, 40mm Aero eyepiece and Astronomik HB filter. 

With regards to light pollution, for fine detail you need dark skies but brighter objects can certainly be noticeably improved under moderately light polluted with an OIII or UHC in my experience. 

[bomberbaz]

33 minutes ago, Littleguy80 said:

Best way. As observers we form part of the system and there’s a great variety in our own optics and observing skills. That’s why there are no rules, only broad guides as to what to use. 

I use my filters across a wide range of exit pupils, even over 8mm (40mm eyepiece in my 10” dob). When you experiment you can find some quite unexpectedly successful combinations. I observed Barnard’s Loop in my 10” dob, 40mm Aero eyepiece and Astronomik HB filter. 

With regards to light pollution, for fine detail you need dark skies but brighter objects can certainly be noticeably improved under moderately light polluted with an OIII or UHC in my experience. 

Worth knowing that is Neil, I will put that on my ever growin winter list

[Stardaze]

And that ultimately means I’ll need an HB filter after all 😂 Better write to Santa..

Edited June 22, 2020 by Stardaze

[John]

3 minutes ago, Stardaze said:

And that ultimately means I’ll need an HB filter after all 😂 Better write to Santa..

I have an Astronomik HB. I use it very rarely. It did help me to (eventually) see the Horsehead Nebula but I have to be honest and say that is the only object that I have actually managed to see with it. I'm pleased that I have the filter if that was it's only achievement after a few years of trying.

I know there are some other HB targets out there. I probably need to put more time into those.

 

 

[Littleguy80]

Here’s my SkySafari list of HB targets. Some well known targets can reveal some extra detail when viewed through an HB filter. I’m sure you wrote an excellent report on doing just that with M42, John. 

H-Beta Targets.skylist

[bomberbaz]

14 minutes ago, Littleguy80 said:

Here’s my SkySafari list of HB targets. Some well known targets can reveal some extra detail when viewed through an HB filter. I’m sure you wrote an excellent report on doing just that with M42, John. 

H-Beta Targets.skylist 2.98 kB · 1 download

what file extention Neil, my laptop won't open it! EDIT- wordpad works

Edited June 22, 2020 by bomberbaz

[John]

9 minutes ago, Littleguy80 said:

Here’s my SkySafari list of HB targets. Some well known targets can reveal some extra detail when viewed through an HB filter. I’m sure you wrote an excellent report on doing just that with M42, John. 

H-Beta Targets.skylist 2.98 kB · 0 downloads

I did actually use the HB filter last night - by accident !

I was observing the Dumbbell with my 100mm refractor and wanted to see what impact the Astronomik O-III would have. In dim light I selected the Astronomik HB instead, installed it and spent a frustrating 10 minutes wondering why I could not see M27 at all with the filter when it had been quite nice without a filter. And then the penny dropped .....

I did actually manage to see a trace of the Dumbbell eventually with the HB but it was virtually invisible compared with the filterless view. The O-III bought out the halo surrounding the core very nicely - when I managed to find the right filter.

Obviously M27 is not a good HB filter target !

[bomberbaz]

I have found a reference to exit pupil sizes I alluded to earlier in this thread. It isn;t the one I used to have a link to but it does appear to have identical information as I remember. (Caveat my memory can be a little shaky these days)

It is agenaastro on this page, article 4. Filter guide The whole article is well worth a read but 4 is where the info is I remember.  Worth bookmarking.

Anyway, I wasn't a million miles off what I said and again, as mentioned already in this thread the rules/guidelines whatever regarding filters seem to be more relaxed and personal than most other areas of this hobby.

 

[bomberbaz]

Nearly forgot about this link.  It's the same David Knisely from your earlier link @John

It is a list of many popular Northern hemisphere nebula and gives "his" opinion on what filter works best for them.  

I have used this list a lot when considering my viewing options for a given night where nebula are a consideration.

Hope this helps 

https://www.cloudynights.com/articles/cat/user-reviews/accessories/astronomical-filters/filter-performance-comparisons-r1471#top

Steve

[jetstream]

Ok, I'll use a filter at 1.7mm exit pupil for small planetary nebula. Some of this stuff is object specific but in general a tight OIII likes 4mm-6mm with 5mm being preferred by many in dark skies and 4ishmm in lighter skies.

The only real way to find out is to try different fl eyepieces but it is a mistake to use a higher power eyepiece right off the bat IMHO. Many have done this only to think filter performance is marginal.

Our H130 with a vg copy of the DGM NPB and a 5mm exit pupil shows: Veil-both plus Pickerings Wisp, Flaming Star, Pacman. Monkeyhead,Rosette, Merope, IC 1318, Nort American neb, Pelican ....

Edited June 22, 2020 by jetstream