Can I use my 2" filters with my 1.25" EPs?

[quesne]

I have an Orion XT8i (8" Dobsonian) for which I have five 1.25" EPs (25mm, 18mm, 10mm, 9mm and 4mm) plus a 1.25" 2x shorty Barlow lens.  I also have a 1.25" Orion 13% moon filter.

I recently bought the Celestron 2" EP and filter kit -- which comes with 5 lunar and planetary filters -- as well as this 2" GSO coma corrector.  I am wondering whether there is a way of using the 2" filters with my 1.25" EPs, using the fittings that I already possess.

It does appear that the 2" Barlow lens accepts a filter, and thus (using the included adapter) I suppose I can use the 1.25" EPs at 2x mag.  I am wondering, however, if I can benefit from the filters at the 1.25" EPs' native magnifications.  BTW - The coma corrector has no 1.25" adapter, so I presume it is compatible only with 2" EPs.  I am mentioning it here simply for completeness.

Thanks in advance for any assistance :-)

[Moonshane]

http://stargazerslounge.com/topic/84086-novel-use-for-baader-fine-tuning-rings/

[John]

The link that Moonshane gives will help with using the 2" filters with 1.25" eyepieces. It looks to me as if the Coma Corrector will accept a standard 2" to 1.25" eyepiece adapter which will let you use 1.25" eyepieces with it - you just need to get the adapter.

[Merlin66]

If the focuser you have is a 2", you normally find the 2" to 1.25" adaptor used for your eyepieces has a 48mm filter thread at the front. Just be careful the eyepiece doesn't impact on the filter when you fit them.

[quesne]

Thanks very much Moonshane, John and Merlin66 for the help and valuable information.  I took a good look at all of the equipment, and the most important questions are cleared up, but it brings up one or two smaller ones.

FYI - The Orion does have a 2" focuser but, interestingly, the stock adapter does not have the threading for a filter.  On the other hand, the Celestron EP kit comes with a 2" mirror diagonal which DOES include a 1.25" filter-threaded adapter.  I can, therefore, put the 2" filter on that adapter and then use 1.25" EPs (so far so good).

As your above comments and linked article point out, however, there may be a danger that the 1.25" EP tube will slide too far into the adapter and potentially damage the 2" filter.  The adapter is pretty shallow, so I think this could be a problem.

Considering this, I have two questions:

1.If I 

[Merlin66]

Hmmm

It's unusual to have enough back focus to be able to use a diagonal on a Newtonian....

[John]

Hmmm

It's unusual to have enough back focus to be able to use a diagonal on a Newtonian....

Agreed. I don't think it's possible in fact.

Can the stock 2" - 1.25" adapter be replaced by one that is threaded for 2" filters ?.  If so, you can add a 14mm Baader Fine Tuning Ring to that to ensure that no 1.25" eyepiece barrels contact a filter.

[quesne]

Sorry for the disconnect.  It is incredibly annoying that my web browser decides to post my comments before I've completed them!

Anyway, as I was saying.....2 questions:

1.  The coma corrector does have threads for the 2" filters.  If I use the coma corrector with a 1.25" adapter as my filter "housing", will the optical quality of the 1.25" EPs be adversely affected?

2.  Are the Baader fine tuning rings simply extension tubes for any standard 2" EP body to allow an extended FL, or is there something more subtle to understand?  I have read the detailed description on Amazon, and it appears they are very specific to Hyperion EPs (which I do not have).  I'm just trying to understand if this is a simple solution for me, or whether I would need something else (like a thread adapter).

Thanks :-)

[quesne]

Answering the questions about the diagonal.....

Yes, I agree.  I am not suggesting that I use the whole diagonal on my scope.  The threaded 2" to 1.25" adapter is removable, however, and could serve pretty much as John suggests (i.e. it can replace the stock adapter).  The depth of "play" for the 1.25" EP tube then remains the only issue.

[Moonshane]

Yes re the adapter. I use my paracorr like this. Theoretically there is a possibility it may affect the effectiveness of the cc due to spacings but I don't see any.

The baader rings ar e just an extension tube but the hyperiobs have a built in barlow in the nose. Changing the spacing affects the eyepiece focal length. This does not apply to you.

[quesne]

Thanks Moonshane.  I appreciate that input.  Based on your experience with the Paracorr, it sounds as though I can probably use the GSO coma corrector as my filter housing.  

I expect (hope) to have some nice seeing from the garden on Thursday evening.  I will run my 1.25" EPs and filters through a few paces and post my observations here.

Thanks again to everyone for the helpful comments :-)

[Owmuchonomy]

Yep I can vouch for the Baader FTRs as multi purpose extension rings. They also do adjustable stop rings to prevent over insertion of EPs.

[quesne]

As promised, I offer a short report on using the GSO coma corrector as a filter housing.

Skies were bright and clear this evening at Valley Forge NP. My son and I hunted down the usual suspects: M31, M42, Jupiter, the Pleiades.

Suggestions on the cc were spot on. It worked like a charm. I left it in the scope all evening, save for swapping out a filter from time to time. Light transmission was excellent. I could not tell it was there. Pleiades with a blue filter and the cc was stunning.

The only hitch came when we wanted to zoom in a bit more on Jupiter the see the fourth moon emerging from behind her. When I slid in my 2" Barlow, I got quite a shock when the tube bottomed out on what sounded an aweful lot like glass! My heart skipped a beat and I peered in there fully expecting to see a chip or some abrasive marks on the corrector lens. Thankfully, it was an interior alum or steel rim, machined (I presume) for the very purpose of limiting the depth of the EP.

BTW - It was also a bit of a challenge getting the whole 3 piece ensemble to focus (cc + Barlow + EP). I had to back out both the cc and Barlow from their seating depths quite a bit to find the FP (I have the feeling it also mucked with the Barlow magnification). Once I did, though, it was a beautiful view, with the exception of the loss of a considerable amount of eye relief (I suspect this is no surprise).

Anyway, thanks again for the great suggestions. Merry Christmas and Happy New Year to all