Light Pollution Filter in Star Diagonal - is this correct

[bdlbug]

Hi everyone,

bit of a newbie working with a second hand celestron SCT question. I ,like most everyone, have a lot of street lights around my house and so I thought I would try using a light pollution filter, so I ordered a Baader Neodymium Filter, took a sharp intake of breath at the cost but hit the add to basket anyway .

So I read somewhere on some forum somewhere, as you do when surfing around, that putting the filter in the star diagonal , especially something like a broad band pass for light pollution is a good idea as it avoids a) having to constantly screw and unscrew an expensive and delicate filter into the bottom of the eyepiece selected or having to buy multiple expensive filters for every eyepiece.

So to my question, when said expensive filter arrived I struggled to work out where it could screw into the star diagonal, I eventually found that the threads matched at the point indicated on my attached image.

I am concerned that this is not correct as the filter as I said above seems very delicate and having it at the position I do it will take full weight of my eyepieces (Axioms) and may fail.

Can someone with some knowledge and experience let me know if I have done something daft or if this is indeed where a filter can be permanently mounted in the optical path ?

many thanks

Bryan

[jonathan]

Hmm, isn't there a suitable thread on the end of the piece that fits into the visual back (back of the telescope)? That looks like the same Williams Optics 2" diagonal that I have, mine has a thread on the end.

Then again, I use a Baader Steeltrack focuser with my SCT so my diagonal doesn't attach directly to the back of the telescope, it's been a long time since I used it without the focuser (which quite frankly I wouldn't want to do because I love the dual speed thing).

Not sure how you have it right up against the diagonal body like that, I've never dismantled mine. I think I see what you're getting at though, the weight of a big eyepiece might be enough to stretch the threads or rip the filter apart, unlikely providing you don't pull hard on the eyepiece with some clothing or something, I think the telescope is likely to fall over before the filter breaks apart.

[LukeSkywatcher]

If your star diagonal accepts the LP filter then there is no problem. It will save you having to remove it and replace it on every EP that you use in your observing sessions. The EP is not worried if you have the LP filter infront of, or behind it. It does the same job either way.

[scarp15]

Hmmm this does not appear correct to me. I use an orion ultra block filter, which is designed to fit directly onto the rear draw tube thread of the OTA and then screws onto my diagonal (an SCT type). So I would have thought that the (2") filter would attach directly onto the draw tube.

Not familiar with this filter, but I think that it is used for attaching directly to eyepiece's or onto an extender with a reflector type focuser. I can though recommend the Orion Ultra Block - SCT type.

[bdlbug]

I have just looked up the Orion ultrablock for SCT and yes I can see exactly how that fits. I think I have put the filter into a load bearing position that it is not designed for. Unfortunately I just tried to remove it and its stuck fast. This may have been a very costly experiment.

Thanks for the comments and advice,

[DoctorD]

Hi BDL_BUG

Look for Baby Boa mini strap wrench on Amazon - just the thing for removing stuck filters - I have a pair as I find them invaluable!!

HTH

Paul

[DoctorD]

It also looks like you have the SCT version of the diagonal - I think the push fit one has a filter thread on the nose piece and this is where the filter should go, but not sure about the SCT fit one - I'll check when I'm back home.

Clear skies

Paul

[M4lcs67]

I have looked at this and it looks like you have used the threaded collar on your Williams Optics diagonal and removed the original nosepiece??? If that is the case then, yes it will be used in a loadbearing way and could cause it to break. I have just bought a new Willams Optics 2" Dielectric diagonal and while it does come supplied with the additional collar that screws directly into the back of the scope, I was worried about constantly re-adjusting the diagonal everytime the scope slewed to a new object as the thread could wear over time, so I bought a Baader 2" Quicklock collar so I could use the original smooth nosepiece. The nosepiece has a thread on the inside of it where you can attach the filter. This is non loadbearing and will be ideal. In fact that is what I am going to do when I get a LPF for it.

[alanjgreen]

+1 Quick lock

this will give you a more "useful" opening on the back of your SCT and as M4lcs67 writes then you just revert to using the standard nosepiece on your diagonal

The standard nosepiece accepts 2" filters

[alanjgreen]

Oops - I mean +1 "Click lock"

http://www.firstlightoptics.com/adaptors/baader-click-lock-2-for-celestron-meade-sct.html

[alanjgreen]

Oops - I mean +1 "Click lock"

http://www.firstlightoptics.com/adaptors/baader-click-lock-2-for-celestron-meade-sct.html

[alanjgreen]

Oops - I mean +1 "Click lock"

http://www.firstlightoptics.com/adaptors/baader-click-lock-2-for-celestron-meade-sct.html

[alanjgreen]

WFT! apologies for that

[DoctorD]

Hi Just checked my diagonal and you cannot fit a 2" filter at the front of the SCT adapter, you need to use the2" nose piece and a 2" visual back such as the Quicklock mentioned above.

Hope this helps.

Paul