1.25 or 2" filter?

[-Aldebaran-]

I'm looking at getting the astronomik uhc filter and I use both 2" and 1.25 eyepieces, I've heard that you can thread a 2" filter to an adapter and use it for both fittings, but the eyepiece tube I have has no thread, so I was wondering how it worked, what adapter would I need to purchase for this??

[RikM]

I use an Orion self centring adapter for my 1.25" eyepieces. This is threaded for 2" filters and I screw them on there. You have to be careful that the eyepiece barrel don't poke out too far as they will then damage the filter. All of mine are fine though there is only a couple of mm clearance. If you find your eyepiece barrels are too long, you can just add a Baader fine tuning ring to extend the adaptor thread a bit.

[rwilkey]

Hi Rik, that's exactly the arrangement I use, and it works very well.  Telescope House sell them but currently showing as 'sold out' here: http://www.telescopehouse.com/acatalog/Orion_Precision_Eyepiece_Centering_Adaptor__2513.html  However, there are other suppliers of this type of adaptor, just re-badged.  I bought mine cheaper off Ebay.

[-Aldebaran-]

Ok, so if it's a 1.25 to 2" converter where does the 2" ep fit? Or would it be a case of just removing the adapter and filter and fit filter on 2" as normal, is that how it's done?

[RikM]

Ok, so if it's a 1.25 to 2" converter where does the 2" ep fit? Or would it be a case of just removing the adapter and filter and fit filter on 2" as normal, is that how it's done?

Yes, that's right.

[-Aldebaran-]

A bit of a fiddle but I guess it saves some cash, unless I don't really need a 2" filter of cours, I think I remember John (mod) mentioning elswhere that most DSO's fit in the fov in a long fl eyepiece?? Would a filtered 24mm X50 mag suffice??

[Pig]

You could screw the filter into the front of a 2" diagonal and use a 1.25" eyepiece adapter  would this be as effective ?

[-Aldebaran-]

Sorry, not clued up on what a diagonal is or what it's purpose serves.

[Dave In Vermont]

You could screw the filter into the front of a 2" diagonal and use a 1.25" eyepiece adapter  would this be as effective ?

From the signature, Aldebaran is using a Dob. Hence a diagonal is an unknown entity. That was my first thought too actually.

Clear Skies,

Dave

[Pig]

The diagonal (prism) is the right angled unit that slides into your focuser and where your eyepiece barrel sits.

[Pig]

That will teach him not to buy a refractor  the thought didn't enter my head at all.....silly Dob's

[Piero]

if you haven't an OIII filter already, I would possibly consider the OIII filter first and then a UHC, if you plan to use it on your Dob 200.

A 200mm collects enough light to enable you to successfully use the filter with high magnifications (you have a sufficiently long exit pupil at high magnification). 

Therefore, I think you can better take full advantage of an OIII filter without compromising loss of light (e.g. for planetary nebulae).

Plus, it will also improve all already visible nebula targets (e.g. orion nebula) and allow you to see 'invisible' targets (invisible without filter) like the vela.

24mm using an F6 corresponds to an exit pupil of 4.0mm which is okay for many low power targets. 

For planetary nebulae, you can go down till 2.0-1.0mm exit pupil (~12mm, 6mm ep focal lengths). 

These filters (OIII, UHC) can improve the view, but unfortunately, the real bad filters are light pollution and bad transparency. 

=> a dark place gives you more than a good filter. 

Good luck, and look forward to reading your findings! 

[-Aldebaran-]

I have been looking into Oiii also, but I thought the Oiii was more selective to (hence fewer) objects, is this true?

[RikM]

I have been looking into Oiii also, but I thought the Oiii was more selective to (hence fewer) objects, is this true?

Somewhat correct, yes, but an OIII gives more contrast than a UHC. A UHC will make objects you can already see look better. And OIII can make objects visible that you almost can't see at all without a filter.

[-Aldebaran-]

Hmm decisions,thanks for all the advice guys!!

[Dave In Vermont]

For an excellent article on which filters do the best for different objects, you can't go wrong by reading this:

http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performance-comparisons-for-some-common-nebulae/

I have a copy on my wall.

Clear & Filtered Skies,

Dave

[Piero]

filters are a *tough* (and interesting) argument.. Decisions are difficult and very personal too.   

It also matters how dark the location you observe is. 

I like them both to be honest and on my telescope, so far, I don't have a specific preference. However, this is because I am limited with magnification, meaning that with few magnification steps, the image becomes noticeably darker. This is because my scope has a focal length of only 360mm. 

If I were using something bigger (e.g. focal length > 1000mm), I would probably go for an OIII only as this gives you more control on magnification without reducing too much the exit pupil. I don't really see targets that an UHC can do and an OIII cannot. 

[SpaceWalker]

I have been looking into Oiii also, but I thought the Oiii was more selective to (hence fewer) objects, is this true?

Yes, you're right, the OIII is a line filter and more selective. The UHC is a narrowband filter and works on larger amount of objects, so if you can have only one than get the UHC, IMO. You may want to read Dave Knisely's filter guide, Filter Performance Comparisons For Some Common Nebulae.