Adding filters to flatteners?

[fwm891]

I've just purchased a William Optics 73 APO and Flat 73A flattener. 

My question is: the blurb says that I can fit 2 inch (48mm threaded) filters inside the flattener. For normal use W.O. give the spacing distance on the flattener as 11.4mm but adding the filter will a) shift the focus b)require the flattener's spacing to change ?

Has anyone tried inserting a filter inside a flattener (any not just W.O.) I have emailed W.O. support and awaiting their reply.

Thanks

Francis

[Laurin Dave]

Which side of the flattener does the filter screw into?  If its the objective side then I wouldn't have though it would make a difference to the backfocus.  Could be wrong of course..

Dave

[fwm891]

1 minute ago, Laurin Dave said:

Which side of the flattener does the filter screw into?  If its the objective side then I wouldn't have though it would make a difference to the backfocus.  Could be wrong of course..

Dave

Dave - It's on the camera side of the flat and requires the flattener's rear barrel to be removed and the filter inserted, then return the rear barrel with camera adapter. I'll try and get some photos. The other thing is that the filter has to be inserted with the coatings side towards the camera but Baader say the coatings should face the sky... Need a straight 48mm male adapter to reverse the filter.

[Anthonyexmouth]

4 minutes ago, fwm891 said:

Dave - It's on the camera side of the flat and requires the flattener's rear barrel to be removed and the filter inserted, then return the rear barrel with camera adapter. I'll try and get some photos. The other thing is that the filter has to be inserted with the coatings side towards the camera but Baader say the coatings should face the sky... Need a straight 48mm male adapter to reverse the filter.

Are you 100% sure? i thought they screwed onto the front of the flattener on the nose. 

[Laurin Dave]

Hi Francis if it's the camera side then you'll need to add the usual 1/3rd the thickness of the filter to the spacing..  I have Skywatcher FF and with that you screw them in on the objective side

Dave

[fwm891]

Quote

 

@Anthonyexmouth The front of the flattener is to big to take 2 inch filters. The only place they will go is internally -Photos...

First photo shows the filter thread inside the flattner

Second with filter in place

Third with the rear barrel and camera mount replaced.

 

[Anthonyexmouth]

cant it screw inside the front, recessed? sure thats how i've seen it in review videos. i could be wrong though. 

[fwm891]

10 minutes ago, Anthonyexmouth said:

cant it screw inside the front, recessed? sure thats how i've seen it in review videos. i could be wrong though. 

No. Not 2 inch filters. - I tried that first but that glass element is bigger than the filter thread. Just measured that thread it's circa 51mm OD and a 2 inch filter just floats inside that aperture without engaging - bluetack might work!

[Anthonyexmouth]

3 minutes ago, fwm891 said:

No. Not 2 inch filters. 55mm perhaps - I tried that first but that glass element is bigger than the filter thread.

Is this not the same flattener? this shows it in front of the glass doesnt it?, thats the t ring in the palm of his hand. 

[fwm891]

Not the same flattener. That's the flat 73 not the flat 73A which I have

The thread inside diameter on the flattener body is 49.5mm the outside diameter of the 2 inch filters is 48mm - just measured with a Vernier calliper.

[symmetal]

On the WO site the  flat73A info shows the way to insert a filter near the bottom of the page. As it's after the flattener you'll need to add 1/3 filter thickness to the spacing required as mentioned above. 

Alan

[fwm891]

• Thanks Alan. That's where I thought. Just need some spacing test now...