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Olli

Need help understanding Filters

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After deciding what eyepieces I’m going to get I’ve decided that I would like a filter for Nebulae to use with my 130p. However I’m a bit confused on what the difference is between the types of filters. For example when looking on FLO I see a UHC,UHC-E, UHC-S and a OIII filter. They also have a similar description apart from some saying that this is best using with a larger scope or smaller scope and it also states forbest using in light polluted areas. I have attached a screen shot from the clear outside app so you can see what my sky is like. Any help on this will be much appreciated 

Many Thanks 

5C5E87DA-1005-4EB0-BE52-3C63AFA87D97.jpeg

Edited by Dinoco

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Have a look here:

http://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/

OIII is specialized for some types of nebulae (those that emit in OIII), same goes for H beta.

Probably most useful filter will be UHC for visual, something like this:

https://www.teleskop-express.de/shop/product_info.php/info/p943_TS-Optics-Optics-1-25--Premium-UHC-Filter---more-Contrast.html

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With regards to the Astronomik and Baader filters: 

OIII is the narrowest, only passing the two (or one) OIII emission lines. The optimal width is around 12nm. 

UHC passes the two OIII emission lines and also the H beta line. Optimum width is about 25nm.

UHC-S and UHC-E look like different marketing terms for roughly the same thing. The OIII-Hbeta passband is widened to 45nm (perhaps more for UHC-S?) and there is also an additional passband in the red part of the spectrum although I don't know how this works visually as the dark adapted eye loses sensitivity to these wavelengths. 

In addition you have the Explore Scientific and Skywatcher UHC filters which have wider pass bands equivalent to the UHC-E/UHC-S filters. 

The short answer is that your first filter should be a UHC, but finances will determine which one. The link given in the post above is well worth reading. 

With regards to the passband widths, the smaller the width the higher the contrast but also the dimmer the image. To counter the dimmness you will have to increase the exit pupil which means viewing at a lower magnification. Even with a small telescope you can use the tightest filter if you pair it with the right eyepiece so I wouldn't worry too much about suggested telescope sizes for a particular filter. 

Edited by Ricochet
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The UHC filter is more suitable for a 130P 

OIII ( pronounced oh three ) are more suitable for 8" or larger apertures 

I have both but always seem to forget to use them - they turn the stars green but really give the Crab nebula and others better contrast 

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20 minutes ago, vlaiv said:

Have a look here:

http://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/

OIII is specialized for some types of nebulae (those that emit in OIII), same goes for H beta.

Probably most useful filter will be UHC for visual, something like this:

https://www.teleskop-express.de/shop/product_info.php/info/p943_TS-Optics-Optics-1-25--Premium-UHC-Filter---more-Contrast.html

Thanks for the first link was extremely helpful.

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23 minutes ago, Ricochet said:

With regards to the Astronomik and Baader filters: 

OIII is the narrowest, only passing the two (or one) OIII emission lines. The optimal width is around 12nm. 

UHC passes the two OIII emission lines and also the H beta line. Optimum width is about 25nm.

UHC-S and UHC-E look like different marketing terms for roughly the same thing. The OIII-Hbeta passband is widened to 45nm (perhaps more for UHC-S?) and there is also an additional passband in the red part of the spectrum although I don't know how this works visually as the dark adapted eye loses sensitivity to these wavelengths. 

In addition you have the Explore Scientific and Skywatcher UHC filters which have wider pass bands equivalent to the UHC-E/UHC-S filters. 

The short answer is that your first filter should be a UHC, but finances will determine which one. The link given in the post above is well worth reading. 

With regards to the passband widths, the smaller the width the higher the contrast but also the dimmer the image. To counter the dimmness you will have to increase the exit pupil which means viewing at a lower magnification. Even with a small telescope you can use the tightest filter if you pair it with the right eyepiece so I wouldn't worry too much about suggested telescope sizes for a particular filter. 

Thanks for that useful info. Has cleared things up a bit more seems like the UHC is the best bet. Is it worth it to save up for this https://www.firstlightoptics.com/uhc-oiii-visual-filters/astronomik-uhc-filter ? Or are there better ones around that price point or cheaper? FLO says it’s “the best one”

Edited by Dinoco

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13 minutes ago, Red Dwarfer said:

The UHC filter is more suitable for a 130P 

OIII ( pronounced oh three ) are more suitable for 8" or larger apertures 

I have both but always seem to forget to use them - they turn the stars green but really give the Crab nebula and others better contrast 

Thank you. And I didn’t realise that’s how you pronounce it.

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I’m going to ask stupid question here but they go on the bottom of the eyepice right ? Do I have to un screw the barrel and then put it on?

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12 minutes ago, Dinoco said:

I’m going to ask stupid question here but they go on the bottom of the eyepice right ? Do I have to un screw the barrel and then put it on?

No, most (if not all) eyepieces come with barrel that has 1.25" filter thread on them, so filters screw into that thread. There is also similar thread for 2" eyepieces, but you need larger filters for those (2" filters)

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Hi Dinoco,

As you have a 130mm scope then I would start with a UHC filter. An O3 will be a bit of a challenge with small aperture. A good brand of reasonable price is Castell. I use one of these with my 70mm binoculars.

Here is a link

https://www.365astronomy.com/castell-uhc-ultra-high-contrast-filter-1.25.html

From my experience, these are "better than skywatcher" (the same one as the "optics uhc filter" branded one that FLO sell) but not "up there with Astronomik" but for the price they are great!

Alan

Edited by alanjgreen

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1 hour ago, Dinoco said:

I’m going to ask stupid question here but they go on the bottom of the eyepice right ? Do I have to un screw the barrel and then put it on?

Here is a pic of a 1.25" filter screwed onto the bottom of a 1.25" EP

image.png.d892e980b00bc6e40e894b1679d03f5c.png

check the bottom of your EPs you will see a thread "for filters"

image.png.bc35eec06d14f33a64b6ee4a2392f533.png

Edited by alanjgreen
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39 minutes ago, alanjgreen said:

Here is a pic of a 1.25" filter screwed onto the bottom of a 1.25" EP

image.png.d892e980b00bc6e40e894b1679d03f5c.png

check the bottom of your EPs you will see a thread "for filters"

image.png.bc35eec06d14f33a64b6ee4a2392f533.png

Thanks that’s cleared it up for me :) 

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3 minutes ago, Dinoco said:

I was looking at that one as well I guess it would be a bit stupid to spend that much first.

Dinoco,

The Castell will out perform the one that FLO sell and its the same price too.

https://www.365astronomy.com/castell-uhc-ultra-high-contrast-filter-1.25.html

Alan

Edited by alanjgreen
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Some great advice given on this thread.

Personally I find an OIII filter useful even in a 4” refractor. The key is to understand how to get the best out of them.

Yes, the image is dimmer because you are filtering out much of the unneeded light; a filter increases contrast NOT brightness. Good dark adaptation is necessary to get the best out of them, this can be tricky at light polluted sites so a hood of some sort can really help.

A good sized exit pupil, 5mm or even more also really helps keep the image brightness up. I use a 40mm TMB to good effect giving 5.4mm, these lower powers are very useful on larger objects such as the Veil.

Your site looks to be quite good, so you should be able to get the best out of either a UHC or an OIII by being well dark adapted. As is mentioned in the Prairie Astronomy link, the UHC is useful on a wider range of objects, but the OIII has a more dramatic effect on the ones it works well on. I wouldn’t bother with an Hb, too limited and the objects it works on are pretty tough in general.

The ES filters are good quality and value so would be worth a shout. Astronomik are probably best of the currently available new product, but pricey.

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11 minutes ago, Stu said:

Some great advice given on this thread.

Personally I find an OIII filter useful even in a 4” refractor. The key is to understand how to get the best out of them.

Yes, the image is dimmer because you are filtering out much of the unneeded light; a filter increases contrast NOT brightness. Good dark adaptation is necessary to get the best out of them, this can be tricky at light polluted sites so a hood of some sort can really help.

A good sized exit pupil, 5mm or even more also really helps keep the image brightness up. I use a 40mm TMB to good effect giving 5.4mm, these lower powers are very useful on larger objects such as the Veil.

Your site looks to be quite good, so you should be able to get the best out of either a UHC or an OIII by being well dark adapted. As is mentioned in the Prairie Astronomy link, the UHC is useful on a wider range of objects, but the OIII has a more dramatic effect on the ones it works well on. I wouldn’t bother with an Hb, too limited and the objects it works on are pretty tough in general.

The ES filters are good quality and value so would be worth a shout. Astronomik are probably best of the currently available new product, but pricey.

Thanks Stu, I really do need to buy an Observing hood I am behind a hedge which shelters much of my own house light but the neighbors light creeps in and didn’t help yesterday when they came home and the car lights blinded me ! I’ll have another read up to see what I should get a OIII or UHC people seem to have told latter but will have another look.

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It’s easy to forget sometimes, it can take 45 mins or more to get fully dark adapted, but it is gone in an instant if you look at a bright light. It really does make a big difference to what you can see.

The annoying thing is that we seem naturally drawn to looking at any lights there happen to be around!

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I found this a very interesting thread especially the link to Prairie Astonomy Club filter performance comparison provided by vlaiv. I've been thinking about purchasing the ES 2" UHC filter to pair with my recently purchased ES 68/40mm eyepiece, so is there anyone here that has used it and would recommend it (or not), or recommend a not too expensive alternative? TIA Geof

Edited by geoflewis
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12 minutes ago, geoflewis said:

I found this a very interesting thread especially the link to Prairie Astonomy Club filter performance comparison provided by vlaiv. I've been thinking about purchasing the ES 2" UHC filter to pair with my recently purchased ES 68/40mm eyepiece, so is there anyone here that has used it and would recommend it (or not), or recommend a not to expensive alternative? TIA Geof

I’ve used the ES UHC and OIII 1.25” versions and found them very good quality as well as good value.

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1 minute ago, Stu said:

I’ve used the ES UHC and OIII 1.25” versions and found them very good quality as well as good value.

Thanks Stu, that's just the encouragement to spend that I need :smile: Cheers, Geof

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3 hours ago, Dinoco said:

Thanks for that useful info. Has cleared things up a bit more seems like the UHC is the best bet. Is it worth it to save up for this https://www.firstlightoptics.com/uhc-oiii-visual-filters/astronomik-uhc-filter ? Or are there better ones around that price point or cheaper? FLO says it’s “the best one”

That or the DGM NBP are probably the best UHC style filters. If you bought one it could be the only one you would ever need to buy (until a new scope opens up 2" eyepieces and filters) but they are expensive and the cheaper ones will still give decent results. It is similar to buying eyepieces where you can buy ever more expensive options for diminishing returns. 

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19 minutes ago, Ricochet said:

If you bought one it could be the only one you would ever need to buy (until a new scope opens up 2" eyepieces and filters) 

This exactly why I was looking at the astronomik one as it would be then “ future proof” and then wouldn’t have to waste more money on getting a better one. Not sure though yet. 

Edited by Dinoco

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