Help with filters

[TracyH]

I am thinking of buying some filters for my skywatcher 150PL and just wondered what ones I 'must' have!! Lol

Also, I wondered about a H-Alpha filter, but they say suitable for CCD photography only. This is probably a stupid question, but does that mean that you can only use if you're using a ccd imager? I wanted something to enhance my solar viewing with my telescope and wondered if that would help.

Many thanks

Tracy

[Floater]

The general filters query I'll leave to others with more expertise, but the H-alpha question sets off an alarm bell.

What does your 'solar viewing' involve at present? It's extremely important - blindness important! - that you don't look through your scope at the sun unless it is PROPERLY filtered and your eyesight is fully protected. There are different grades of filter material for visual and imaging. Please, please, be very careful.

I repeat: what are you doing solar-wise with your scope?

[TracyH]

The general filters query I'll leave to others with more expertise, but the H-alpha question sets off an alarm bell.

What does your 'solar viewing' involve at present? It's extremely important - blindness important! - that you don't look through your scope at the sun unless it is PROPERLY filtered and your eyesight is fully protected. There are different grades of filter material for visual and imaging. Please, please, be very careful.

I repeat: what are you doing solar-wise with your scope?

Thanks for replying.

I have a proper solar filter fitted, and it was fitted by a member of my astronomy group so was done properly.

It was drilled into me when I first started going to the group about solar viewing safety!!

When I view the sun at present it's just a white disk with - if I'm lucky that day! - sunspots. I just wondered if the H-Alpha filter would show more detail.

[ronin]

The Ha filter is really for imaging, it is (should) be a narrow band filter that passes 656nm and not much else either side, so not really a visual item.

I do not think that adding a Ha to a white filter will do very much at least visually.

Not very much light will actually be transmitted and even then at 656nm it is getting to the region where the eye is less responsive, it is or can be classed as NIR (Near Infra Red).

Usually people go searching out either OIII filters or UHC filters for nebula and other deep sky objects.

Now which is best and suitable is a good start of an arguement/discussion.

I think they are applicable to different forms of emission so it depends on what you are specifically looking at.

Do remember that all filters remove something, the idea is that the chosen filter removes more of the crud you do not want thus leaving a slightly better contrast between that and what you do want.

[Floater]

Good stuff, Tracy. You're obviously well sorted. I just had a horrible fear that - well, you know.

White light and Ha viewing are very different aspects of solar viewing. I've never heard of a Ha filter gong onto an eyepiece for visual use and I'm fairly sure - no, absolutely sure - that it shouldn't be done. I'm almost certain that your 150, like mine, can only be used for white light viewing. For Ha you need a dedicated solar scope or something like a Quark filter/etalon fitted to a refractor. Again, others more experienced in these things may well come in here.

Stay safe. And the white light can be very interesting in its own right, can't it?

[MarsG76]

Hello Tracey,

I agree with Floater, unless you're using the Baader solar film or equivalent ND5 kind of solar filter at the front of your scope or a dedicated Hydrogen alpha SOLAR scope you're risking permanent eye damage.

Best solution of filtering is at the front of your scope before the main objective lens/mirror, not the ones you insert just before the eyepiece, especially in compound telescopes, the potential heat build up can damage mirrors AND the can CRACK the filter resulting in instant eye damage!!!

To enhance your solar viewing noting beats a Solar scope like the Colorado Solarmax/PST or the Lunt solar scopes, but for white light a combination of the Baader Solar Continuum filter with solar film revealed more detail in sun spots and granulation in the solar surface.

Where as filters for night time viewing I tried a few different filters and my personal favorites are are the Celestron OIII and Lumicon UHC filters for nebulae... it's amazing how much difference they made... once my eyes are night adapted the nebulosity the UHC revealed on the Carina nebula and OIII on Orion nebula, for example, are amazing.

Hydrogen alpha is useless for viewing since our eyes are not sensitive to such a deep red spectrum, only useful for imaging and didn't show any more detail in the sun either, actually it was less I thought. 

[TracyH]

Hello Tracey,

I agree with Floater, unless you're using the Baader solar film or equivalent ND5 kind of solar filter at the front of your scope or a dedicated Hydrogen alpha SOLAR scope you're risking permanent eye damage.

Best solution of filtering is at the front of your scope before the main objective lens/mirror, not the ones you insert just before the eyepiece, especially in compound telescopes, the potential heat build up can damage mirrors AND the can CRACK the filter resulting in instant eye damage!!!

To enhance your solar viewing noting beats a Solar scope like the Colorado Solarmax/PST or the Lunt solar scopes, but for white light a combination of the Baader Solar Continuum filter with solar film revealed more detail in sun spots and granulation in the solar surface.

Where as filters for night time viewing I tried a few different filters and my personal favorites are are the Celestron OIII and Lumicon UHC filters for nebulae... it's amazing how much difference they made... once my eyes are night adapted the nebulosity the UHC revealed on the Carina nebula and OIII on Orion nebula, for example, are amazing.

Hydrogen alpha is useless for viewing since our eyes are not sensitive to such a deep red spectrum, only useful for imaging and didn't show any more detail in the sun either, actually it was less I thought.

Thanks.

I have a filter fitted at the front of the scope so I'll check out the continuum filter. I would love to have a solar scope but unfortunately I don't have the money

Thanks again ☺

[TracyH]

Good stuff, Tracy. You're obviously well sorted. I just had a horrible fear that - well, you know.

White light and Ha viewing are very different aspects of solar viewing. I've never heard of a Ha filter gong onto an eyepiece for visual use and I'm fairly sure - no, absolutely sure - that it shouldn't be done. I'm almost certain that your 150, like mine, can only be used for white light viewing. For Ha you need a dedicated solar scope or something like a Quark filter/etalon fitted to a refractor. Again, others more experienced in these things may well come in here.

Stay safe. And the white light can be very interesting in its own right, can't it?

Yes white light can be very interesting, I've been taking photos with my phone and can see the sunspots and have been able to zoom in. I'm going to try modifying a webcam to take images and then process in registax to see if I can get clearer images.

I would love to be able to see more detail, so maybe I really do need a solar scope...... That'll take a bit of saving up! Lol

[ghostdance]

If you can, try and borrow a Solar Continuum filter before you decide to buy, or look for a used one in good condition. I did the latter, but with my 6" reflector (and solarfilm filter) did not find it added a notable amount of detail if any - beyond a fetching bright green cast! I rehomed mine easily, so it can be worth the experiment with a used one...good luck!

Steve

ps check out a UHC filter for bringing some pop and detail to some nebulae. My most used and useful filter ( the 0III is next in line, but can be tricky with my small aperture scopes - darkens the background stars sometimes a bit too much). HTH

[ronin]

Not sure I can attach very well.

4365289-knisely3.xls

Just "stole" it from CN where someone asked about an "old" excel file for filters and objects. :eek:

You have Constellation, Object, Scope used and then what I assume are the recommended filters, or not as may be.

[Lodds]

Just to add my to this thread as I am looking also to make a solar filter for my 8" scope.

I mistakenly thought that I could view the sun without filter but reflect the image onto a white background.  I remember doing this years ago but the scope was a refractor, more or less a toy. 

I tried this on my new Skywatcher 200mm reflector and was surprised to see smoke coming out of the tube.  My eyepiece had melted.  Fortunately the eyepiece was the original one that came with the scope and not some expensive upgrade. But Lesson learned.   :Envy:    

[Stu]

Just to add my to this thread as I am looking also to make a solar filter for my 8" scope.

I mistakenly thought that I could view the sun without filter but reflect the image onto a white background. I remember doing this years ago but the scope was a refractor, more or less a toy.

I tried this on my new Skywatcher 200mm reflector and was surprised to see smoke coming out of the tube. My eyepiece had melted. Fortunately the eyepiece was the original one that came with the scope and not some expensive upgrade. But Lesson learned. :Envy:

You are very lucky it was just the eyepiece which melted. It's quite likely that the secondary might either come off its mounting due to the glue melting, or worse, crack due to the heat build up.

Using a reflector like this is also dangerous incase anyone inadvertently looks down the tube and gets an eyeful of sun at its focal point.

Please be careful.

[Adrian Condon]

Hi,

I agree wholeheartedly with Stu, the best advice is not to use a reflector.

If you are  interested in solar observing, there is a very good book called

How to Observe the Sun Safely by Lee Macdonald. It is on the expensive side at £31.99 for 214 pages of extremely useful information.

The problem with some Newtonians is that they become a solar furnace, the heat causes tube currents that give further problems with the seeing.

If using a Reflector, it is important that front cap is taped to the scope to prevent it coming off accidentally and has a hole of approx 60mm off centre and away from the vanes. Make sure that the secondary mirror is protected from direct sunlight.  If you have a Telrad make sure that it is not on the scope, they have a way of melting away!

Melting glue and the sonic boom of the secondary mirror colliding with the primary mirror gives a painful feel in the pocket.

I have used solar film on my refractor with good results.... I have bought a Baader Herschel wedge.

I plan to purchase a Lunt solar scope next year when I have more funds available.

Safe Viewing !!!

Adrian

[Lodds]

If using a Reflector, it is important that front cap is taped to the scope to prevent it coming off accidentally and has a hole of approx 60mm off centre and away from the vanes.

Thanks for the info.. It appears I was very lucky but better check the collimation tonight.

I wondered what the offset hole in my dustcap was for. I have some solar film now, I think I will make a filter for the hole. Would that be okay do you think?

I'll also check out the book you recommended.

Tony

[Adrian Condon]

Hi Tony,

Yes,  it should be ok.

Make sure that there are no pinholes in the solar film and follow the instructions.

Lining the scope up with the sun can be great fun, remember do not look at the sun directly.

I try following the shadow of the scope. There is a little finder, and I mean little from Televue. 

http://www.televue.com/engine/TV3b_page.asp?id=66#.VaVKsHg-DBI

I use a Televise Sol-Searcher, it has the advantage that you don't have your eyes following the Sun. It does take some time to line it up properly.

If you have a finder on the scope, I would recommend removing it or tapping the little caps so that no children can look through there finder.

Stay Safe......

Cheers

Adrian