BF10 blocking filter straight through adapter

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DJD
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BF10 blocking filter straight through adapter

Post by DJD » Mon Jul 24, 2017 10:42 am

Dear modding experts,
I have an assembly that I carry out to my Tal 100 that incorporates my old PST etalon and a BF10 blocking filter unit only.
The assembly maintains the magic spacings so that when I focus the Tal, everything is set correctly, hence no need for a secondary
focuser in the assembly.
The blocking filter unit currently screws into a standard 1.25" diagonal in place of the original 1.25" push-fit, but I need to rescue
a bit of space in the whole assembly by taking out the diagonal. Is there an off the shelf adapter that goes from the BF bottom thread ( whatever it's size) to standard T thread or similar ? I need the extra space for a tilt adjuster and/or secondary fine focuser.
Best wishes,
David
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Re: BF10 blocking filter straight through adapter

Post by marktownley » Mon Jul 24, 2017 8:09 pm

post a pic of it david so can see where the savings could be made
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Re: BF10 blocking filter straight through adapter

Post by DJD » Tue Jul 25, 2017 5:53 am

Will do Mark.
I should have mentioned that the whole assembly ( from etalon back)will screw back into the PST bronze tube and be in focus.
Also the part assembly from BF back is interchangeable with my camera and is parfocal with it. Makes focusing and centering
then swapping in the camera straight forward ( bar the finest of focussing touches ).
I did a search of past threads and someone measured the BF unit threads as 33mm x 0.75mm. I have done a trawl of the usual
places on the internet and can't find any simple adapters that will do. I have found a couple of suggested solutions of embedding
the BF inside a 2" extension, but again that would need some machining.
Thanks,
David
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Re: BF10 blocking filter straight through adapter

Post by Merlin66 » Tue Jul 25, 2017 7:13 am

There's 200mm behind the etalon to final focus....
Which camera are you using?
I can fit a Borg focuser, the BF10 diagonal and any fast camera (ASI 174mm) with a T2 tilter in the available space......
Need to see your current spacer arrangement.
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Re: BF10 blocking filter straight through adapter

Post by DJD » Tue Jul 25, 2017 7:27 am

Merlin,
I am a cheapskate ! I can probably fit everything I need in the space I can make by replacing just the BF in diagonal with a minimal
BF thread adapter ( if it existed, which was my starting point ). I want to save the expense of buying another focuser and tilt adapter
if I can. The tilt adapter can be accomodated in just the camera part as it has extenders to make it parfocal with the eyepiece module.
Hopefully all be clear when I can get some pictures up.
Best wishes and thanks ,
David
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Re: BF10 blocking filter straight through adapter

Post by DJD » Tue Jul 25, 2017 8:14 am

OK, a couple of images....
the unit as I use it on the Tal visually, the BF is screwed into the diagonal. If I remove the 2" etalon adapter and screw in the bronze tube
then it will be in focus.
Adapters1small.jpg
Adapters1small.jpg (741.56 KiB) Viewed 1064 times
And if I remove the eyepiece unit from the BF and replace with the camera unit, it is parfocal. Hope that makes sense.
Adapters2small.jpg
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Re: BF10 blocking filter straight through adapter

Post by marktownley » Tue Jul 25, 2017 8:12 pm

Simples. Don't use the 1.25" diagonal and just space everything out to get to where you need.
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Re: BF10 blocking filter straight through adapter

Post by DJD » Wed Jul 26, 2017 6:29 am

But there is a hole in my bucket dear Lisa ....
As per top of the thread Mark, where do I get a BF 33mm x 0.75mm thread adapter to move it off the diagonal and into
the straight-through image train ?
Late night Mark ? :-)
Best wishes,
David
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Re: BF10 blocking filter straight through adapter

Post by Merlin66 » Wed Jul 26, 2017 8:30 am

David,
Where's the usual up front ITF located? This is usually mounted at the front of the BF diagonal....
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Re: BF10 blocking filter straight through adapter

Post by DJD » Wed Jul 26, 2017 10:13 am

Merlin,
good spot.
I have replaced the ITF with 35nm Ha and baader UV/IR-cut at various places at various times, I currently have a 2" 35nm filter
attached to the nosepiece pre etalon and a 1.25" UV/IR-cut pre eyepiece/camera. I did have them attached to the nosepiece of the
diagonal, but then bought a 2" 35nm.
Best wishes,
David
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Re: BF10 blocking filter straight through adapter

Post by Carbon60 » Thu Jul 27, 2017 5:52 am

David, maybe draw up the adapter and have one made at a local machine shop. This is what I tend to do to make 'specials'.

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Re: BF10 blocking filter straight through adapter

Post by marktownley » Thu Jul 27, 2017 7:14 am

DJD wrote:
Wed Jul 26, 2017 6:29 am
But there is a hole in my bucket dear Lisa ....
As per top of the thread Mark, where do I get a BF 33mm x 0.75mm thread adapter to move it off the diagonal and into
the straight-through image train ?
Late night Mark ? :-)
Best wishes,
David
You don't need too. The whole of the base cell in the BF10 (which houses the filter) pushes out. Look underneath you will see a couple of dabs of loctite which if you pick off you will be able to push the base of the cell off. This can then be mounted in the cell from an old 1.25 barlow or reducer etc.

Depending on how much space you are trying to gain: replace the 2" to 1.25" reducer with a zero length one, that one seems to add 10mm. Or, take a hack saw / chop saw to the 2" adapter (AOK Swiss?) at the back of the etalon and remove a set length, drill and tap new hole for tightening bolt.

Seems to be a lot happening on the nose of the camera? what adapters etc are there?
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Re: BF10 blocking filter straight through adapter

Post by DJD » Thu Jul 27, 2017 8:21 am

Mark,Stu, thanks for the replies.
Mark, the first objective was to get rid of the diagonal. I will explore your suggestion of remounting the base cell component.
Once I have a straight though train, then I can clean up the spacers. It was a hodge-podge of bits I had available to make the
camera and eyepiece par-focal, no design just a cobble together. I will start the process of getting a tilt adapter and fine focuser
once I have a more definitive limit of space to work within.
Thanks again,
David
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Re: BF10 blocking filter straight through adapter

Post by DJD » Tue Aug 01, 2017 2:30 pm

Dear All,
I have managed to push out the BF optical unit out of its housing.
It is an awkward size and is too big for a filter holder cell and too small for most other adapters I have.
I finally managed to hold it firm utilising a couple of flat rings inside an extension tube
and a M42 to T adapter. This is the shortest I could make it outside of having a custom adapter made.
I did find a chap in Portugal that sells ready made 33mmx0.75mm to T adapters if you want to utilise the whole
BF screw in unit.
I am not sure if it is better to get the BF unit closer to the camera than it is in my arrangement ( see following photo ).
Perhaps someone can advise ?
I could replace my T to C unit with a low profile one and/or put the BF unit on the other side of the tilt unit .
Or do I want to get the tilt unit closer to the camera ?
Either way I now have a straight through arrangement with plenty of space to put in a secondary fine focuser if I need it.

Best wishes,
David
Right click and view image for larger size
StraightTrainAno_filtered.jpg
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Re: BF10 blocking filter straight through adapter

Post by marktownley » Sat Aug 05, 2017 2:43 pm

looks good!
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