Can this be done ?

[BRUN]

From my garden I have a fair bit of light pollution, im wondering if its possible for me to buy a 2" CLS filter and have it in place all the time. Ill only ever be using 1.25" EP's as I cant afford to splash out on 2" versions good enough for my scope, which is a Flextube 250px. My thinking is that I wouldnt have to keep swapping a filter in and out of different EP's, if I can put it further in somewhere.

Is this possible, and if so what would I need to buy.

Thanks !

[MrsGnomus]

Our star diagonals all have a 2" thread for exactly this purpose. We use a 2" ND filter in our star diagonal when viewing the moon and then just swap over the eyepieces as you suggest. Not sure which star diagonal you are using but I would be surprised if it doesn't have an internal thread.

[alanjgreen]

As said above, your existing star diagonal should have an internal thread on the scope end, filters screw onto this thread. 

If not, then any you could buy will have a thread, so you could just get a new diagonal if you have to . This picture shows the internal thread quite clearly...

https://www.firstlightoptics.com/diagonals/skywatcher-di-electric-star-diagonal.html

 

it you want to cut out pollution then also read up on these...

https://www.firstlightoptics.com/light-pollution-reduction/baader-neodymium-filter.html

they are great for cutting out moon glow and street light glow. I also found it to work well on jupiter and mars for picking out more detail. Can be used on the moon too as a fairly light moon filter.

[BRUN]

I dont think I have a diagonal on my scope ? Sorry im totally new to all this, ive never seen anything like that on my scope

[alanjgreen]

What scope is it?

put your scope details in your "signature" then all can see

[mikeyj1]

if you don't have a diagonal, (on a 250px i dont think you do?), you can also use a barlow type adapter, and replace the barlow lens with the filter 

[alanjgreen]

If you have a reflector/dob then a parallizer will do the job you want.

https://www.firstlightoptics.com/adapters/howie-glatter-parallizer.html

it has a filter thread on the other side

 

or a nice clicklock

https://www.firstlightoptics.com/adapters/baader-clicklock-2-125-adapter-2956214.html

this is threaded for filters and nice for changing eyepieces! You just give the top a quarter turn to release your eyepiece. No more thumb screws!!

[BRUN]

thanks, ive just updated my signature

[BRUN]

this is what I have on mine

[alanjgreen]

If you release the 2" screws and slide out the 1.25 adapter, is the 1.25 threaded on the inside edge of the end the disappears into the focuser?

 

[Cosmic Geoff]

What kind of light pollution? If it comes mainly from the new white LED streetlights, nothing will filter it out because they emit a continuous spectrum, unlike the older sodium or mercury lights.  I checked the streetlights around my house with a diffraction grating a few months ago.

St Helens has a LED street lighting programme and the council has installed 2900 of them.

[rockystar]

I've replaced my extension tube with one of these https://www.altairastro.com/altair-2-precision-self-centring-tube-with-35mm-barrel-twist-lock.html

it has a thread at the bottom, so you can screw in your 2" filter.

I've also got an adapter for my 1 25" eyepieces:

https://www.altairastro.com/altair-2-1.25-self-centering-eyepiece-adapter.html

 

[BRUN]

the street lights around my house are all currently the old type

[alanjgreen]

Rockystar is right, looking at the LENGTH of your 1.25 adapter, it suggests you would need to replace it with something of equal length for you to be able to reach focus with 1.25 eyepieces.

As he has a dob and has an alternative that works then I would copy his advice rather than mine  

[BRUN]

Thanks guys, helpful as always !

[Dave In Vermont]

That the scope in question was a Dob, that's the first thing that came to my mind: A rare case where a refractor would have a distinct advantage due to it's having a diagonal - or most likely would.

Unless, maybe, the focuser itself is threaded for filters on the SW 250mm Flextube?

Hmmm...

Dave

[BRUN]

Ive just seen this

http://www.rothervalleyoptics.co.uk/skywatcher-twist-lock-adaptor-2-125.html

Would this be deep enough ?

Or this ?

http://www.rothervalleyoptics.co.uk/antares-2-125-twist-lock-adaptor-.html

Or would I need the depth given by using the 2 adapters previously mentioned ?

[alanjgreen]

Brun,

No, I dont think either of those will do. They are too short.

I would go with Rockystar's recommendations above (you really need an extension tube rather than just an adapter)

Alan

 

[rockystar]

Agreed, this is just an adapter to allow you to put 1.25" eyepieces in a 2" focuser, you would need the extension tube also, otherwise you won't have enough outward travel to achieve focus.

[Marci]

Sounds like a (somewhat typical) case of missing 2” extension tube, into which you’d insert the twist locks you linked to. (My 200P is also lacking one)

Middle item in this picture: IMG_7640.JPG.ffcb07a58512db907d85f190777b71f0.JPG

Which is in the forsale section with the other 2 accompanied bits for £15 + p&p!

Into that centre item, you’d then drop: http://www.rothervalleyoptics.co.uk/skywatcher-twist-lock-adaptor-2-125.html with the filter in the bottom... and then, finally, your eyepiece.

[BRUN]

Cheers guys, seems mad to produce a product which then needs another product added to it, I presume some other scopes must be able to just the the adapter on its own

[brantuk]

The thing is - its main purpose is not just a filter holder. It's a self centering T-adaptor with an easy to use twist lock action and non marring compression ring. It just happens to have a thread for a filter inside it too. So that's four features in addition to your single feature requirement.

Filter holders tend to be circular and hold multiple filters typically five or seven, and they allow you to change filters for any eyepiece or camera attached and usually used for imaging. Some are mechanical, other electronic. The filter holders for newts are are typically on a sliding tray that fits inside the tube and holds three or four interchangeable filters. There are other designs too that are included in some specialised focusers like e.g. Moonlite.

What I'd advise is to surf around the different astro websites to find a more simple eyepiece adaptor. You want a low profile one (so you don't push the eyepiece out of the field of focus) which is threaded for 1.25" filters. Or a 2" to 1.25" one where the 1.25" piece is threaded for filters as well as the 2" part - then you have the choice of both sizes. FLO have a good selection and so too do 365-Astronomy. Hth

 

[alanjgreen]

2 hours ago, BRUN said:

Cheers guys, seems mad to produce a product which then needs another product added to it, I presume some other scopes must be able to just the the adapter on its own

(cynical view) By pushing the focus point out, manufacturer can make the main tube shorter as more of the light path is consumed in the horizontal rather than the vertical, saving them money.

(marketing view) product allows more flexibility to reach focus with a camera or binoviewer as you can remove the extension tube to gain the extra in-focus needed

 

take your pick