M48 and 48mm camera filter - compatible threads?

[michaelmorris]

I want to mount a filter in-line in my imaging train.  The current train is an Skywatcher ED80>Skywatcher ED80 focal reducer>M48 to T mount adaptor> Canon 1100D with Hutech IDAS filter (clip in type mounting).  It would be nice to be able to insert a filter between the Skywatcher ED80>Skywatcher ED80 focal reducer or the Skywatcher ED80 focal reducer>M48 to T mount adaptor parts of the train. 

Is the 48mm filter fitting for camera lens the same as M48?  (My guess is that the camera filter fitting is probably a finer thread with a shallower pitch.)

I've alreday considered adding a '2" to Skywatcher ED80 focal reducer adaptor' in the train as this has a 2" filter thread in it.  However, the current set up has very low flexure because everything is screw-threaded together and I'd prefer to keep it that way.

Thanks

[Merlin66]

The 48mm camera filters fit the 2" astro filter thread.

I use my ol' photo filters as sort filters with the spectroscope.

No issues.

[michaelmorris]

Thanks for that information, but I'm not sure it answers my question - will a 48mm camera filter fit in an M48 thread?

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[Merlin66]

Michael,

I thought you were talking about the standard m48 filter thread on the 2" astro fitting...

I see now you may have a M48 metric thread adaptor - IMHO no, I don't think it will fit. 0.5 pitch v's 0.75 pitch.

[Steve Ward]

You need one of these Michael ... http://www.firstlightoptics.com/adaptors/flo-adapter-for-skywatcher-focal-reducers.html

[IanL]

You need one of these Michael ... http://www.firstlightoptics.com/adaptors/flo-adapter-for-skywatcher-focal-reducers.html

And one of these:

http://www.firstlightoptics.com/adaptors/baader-click-lock-2956256-m56-celestron-skywatcher.html

I had my 2" IDAS filter screwed between DSLR adaptor and the 0.85x focal reducer, but this adds too much spacing and you will end up with (badly) elongated stars in the corners of the image.  I was also reluctant to mess with things for fear of adding flexure, but the combination of the clic-lock and the adaptor above has zero flexure (and also makes it easy to rotate the camera for framing, which I couldn't do before). I certainly wouldn't trust the comedy thumbscrews that come with the 80ED, that's for sure.

The 2" filter screws in to the front of the adaptor using the standard 48mm filter thread.

[michaelmorris]

And one of these:

http://www.firstlightoptics.com/adaptors/baader-click-lock-2956256-m56-celestron-skywatcher.html

I had my 2" IDAS filter screwed between DSLR adaptor and the 0.85x focal reducer, but this adds too much spacing and you will end up with (badly) elongated stars in the corners of the image.  I was also reluctant to mess with things for fear of adding flexure, but the combination of the clic-lock and the adaptor above has zero flexure (and also makes it easy to rotate the camera for framing, which I couldn't do before). I certainly wouldn't trust the comedy thumbscrews that come with the 80ED, that's for sure.

The 2" filter screws in to the front of the adaptor using the standard 48mm filter thread.

I didn't realise that Baader made a click-lock system for direct mounting on a Skywatcher 80ED focusser.  Just how good are these at holding attachments orhtogonal and reducing the risk of flexure when compared to the standard two-screw eyepiece holder that comes with the scope?

[IanL]

I didn't realise that Baader made a click-lock system for direct mounting on a Skywatcher 80ED focusser.  Just how good are these at holding attachments orhtogonal and reducing the risk of flexure when compared to the standard two-screw eyepiece holder that comes with the scope?

Worlds apart I'd say.  I don't trust the standard comedy thumbscrew holder; on the one I have the threads are not a particularly tight fit and the slightest touch will start to slacken them off leading to shifting and potential for the camera to end up on the ground.

The click-lock screws on to the M56 at the end of the focuser drawtube (and can be further locked in place using the black threaded ring that is standard on the drawtube).  It has a large metal compression ring which tightens as you rotate the locking mechanism.

It is rock solid and holds the FLO adaptor perfectly straight in the tube, no flexure and no problems with non-orthonganlity that I can detect.  Due to the extra length of the click-lock you also have to rack the draw tube in so that there is only about a cm or so of it protruding from the focuser body, which I presume will help a bit with any existing flexure in the focuser.

[michaelmorris]

Thanks. It looks as though the Baader click-lock and FLO adaptor will be going on my shopping list. I'll see if I can pick up the Baader cheap at Astrofest on Friday.

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[russellhq]

I agree with Ian on the ED80 thumbscrews. I bought the FLO adapter and just could not get the image sensor orthogonal using the thumb screws. I ended up just screwing the 2" IDAS filter into the image train and ditching the FLO adapter;

I did sketch up an adapter that could screw into the back of the ED80 reducer that would then screw onto the focus tube and let you fit a 2" filter into the train. But for speed and ease of use, I think the Baader click-lock is the way to go.

Adapter: