William Optics Flat73A Adjustable Flattener

[TerryMcK]

I've just received the WO Flat73A Adjustable Flattener for my WO ZenithStar 73 APO. I am dismayed to find that there is no internal M48 thread for filters within the body of the flattener  .

I think the non adjustable version has an internal M48 thread but I needed this particular adjustable version. I'm using the IDAS LPS-D2 which successfully filters out the LED/sodium lights but now have to hang a camera off the filter itself!

The adjustable flattener needs to be 11.3 mm and I am assuming this is when a filter is not attached. Do I need to take into account the extra distance that the filter glass effectively moves the camera sensor away from the flattener. It is 1mm thick glass and therefore the flattener shoul;d be set at 10.3mm to maintain that correct distance to the sensor (I think it is 55mm for a Canon DSLR)

[Adam J]

46 minutes ago, TerryMcK said:

I've just received the WO Flat73A Adjustable Flattener for my WO ZenithStar 73 APO. I am dismayed to find that there is no internal M48 thread for filters within the body of the flattener  .

I think the non adjustable version has an internal M48 thread but I needed this particular adjustable version. I'm using the IDAS LPS-D2 which successfully filters out the LED/sodium lights but now have to hang a camera off the filter itself!

The adjustable flattener needs to be 11.3 mm and I am assuming this is when a filter is not attached. Do I need to take into account the extra distance that the filter glass effectively moves the camera sensor away from the flattener. It is 1mm thick glass and therefore the flattener shoul;d be set at 10.3mm to maintain that correct distance to the sensor (I think it is 55mm for a Canon DSLR)

I have half a memory of someone selling an filter adaptor to accomplish this. Filter rings are not really structural and I would not recommend using the as a spacer. 

Edited September 25, 2019 by Adam J

[fwm891]

1 hour ago, TerryMcK said:

I've just received the WO Flat73A Adjustable Flattener for my WO ZenithStar 73 APO. I am dismayed to find that there is no internal M48 thread for filters within the body of the flattener  .

I think the non adjustable version has an internal M48 thread but I needed this particular adjustable version. I'm using the IDAS LPS-D2 which successfully filters out the LED/sodium lights but now have to hang a camera off the filter itself!

The adjustable flattener needs to be 11.3 mm and I am assuming this is when a filter is not attached. Do I need to take into account the extra distance that the filter glass effectively moves the camera sensor away from the flattener. It is 1mm thick glass and therefore the flattener shoul;d be set at 10.3mm to maintain that correct distance to the sensor (I think it is 55mm for a Canon DSLR)

There is. You remove the rear collar you attach your camera T mount to. Photo shows a 2" (48mm) Baader 7nm Ha filter in place

Edited September 25, 2019 by fwm891
text added

[TerryMcK]

8 minutes ago, fwm891 said:

There is. You remove the rear collar you attach your camera T mount to. 

Fantastic. That's the solution. Thanks Francis.

[fwm891]

Ideally it needs a short male to male adapter so the filter can be inserted the correct way round as the female side of the filter should face the sky...

[alan potts]

Terry,

That LED pollution filter sounds good, I have one small area of LP to the South East where of course many things rise, this is from a town 4 miles away. Above say 45 degrees and a bit either side there is no problem. I normally just wait for things to clear. However even at 175 quid if it works it makes working lower down much easier and I feel would benefit even me.  In all other directions I am without any light at all, the town sort of spoils the show, it is only the 3 years since they changed all the lights I have had something to moan about.

Alan

[TerryMcK]

6 hours ago, fwm891 said:

Ideally it needs a short male to male adapter so the filter can be inserted the correct way round as the female side of the filter should face the sky...

Yes I did have a thought about that (having read most filters are one way only) and Hutech show in detail here https://www.sciencecenter.net/hutech/idas/lps2.htm the anti reflectance coating is on the sky side. It’s important that they are the correct way around in the imaging chain. So I’ve ordered a TS-Optics M48a-M48a gender changer. Essentially it is a M48 threaded tube 7.5mm long that converts the female thread inside the back end of the flattener to a male thread. Hence filters will then be facing the correct way around.

I could only find the adapter from Teleskope-express.de or their shop on eBay. Here is the item https://www.teleskop-express.de/shop/product_info.php/info/p4516_TS-Optics-Adapter---continuous-male-M48-thread--as-with-2--filters-.html

William Optics gear is fantastic but this particular oversight in the design of the flattener seems to be a schoolboy error. Fortunately WO are in continuous development and the next version of the flattener may allow the filters to be orientated the correct way around.

Astrophotography is an expensive hobby due, in small part, to all the little bits and bobs you need to screw everything together!

 

[david_taurus83]

8 hours ago, fwm891 said:

Ideally it needs a short male to male adapter so the filter can be inserted the correct way round as the female side of the filter should face the sky...

 

 

You could always try and unscrew the retaining ring that holds the glass in place and flip it round? The 1.25" Baaders all look to have a ring with notches. Would just need to use some careful persuasion.

 

@Skipper Billy just a thought, maybe your 2" OIII can be flipped around?

 

[fwm891]

5 hours ago, david_taurus83 said:

 

You could always try and unscrew the retaining ring that holds the glass in place and flip it round? The 1.25" Baaders all look to have a ring with notches. Would just need to use some careful persuasion.

 

@Skipper Billy just a thought, maybe your 2" OIII can be flipped around?

 

Then keep swapping it back to use on something else - easier to use a male/male adapter.

[david_taurus83]

2 hours ago, fwm891 said:

Then keep swapping it back to use on something else - easier to use a male/male adapter.

Agreed, but if used in a filterwheel the spacing might not always work.

[Adam J]

6 hours ago, david_taurus83 said:

Agreed, but if used in a filterwheel the spacing might not always work.

Actually as its so close to the optical element and further spaced from the sensor then it would be in a wheel you might actially want to use it that way around anyhow as that way the AR coating is pointing towards the optics. Usually the other way but here I think the normal rule may be reversed. 

Adam 

[david_taurus83]

2 hours ago, Adam J said:

Actually as its so close to the optical element and further spaced from the sensor then it would be in a wheel you might actially want to use it that way around anyhow as that way the AR coating is pointing towards the optics. Usually the other way but here I think the normal rule may be reversed. 

Adam 

I have always understood that Baader mounted filters have the AR coated side facing the optics, on the female threaded side of the filter cell.

 

[Adam J]

14 minutes ago, david_taurus83 said:

I have always understood that Baader mounted filters have the AR coated side facing the optics, on the female threaded side of the filter cell.

 

No its the other way around the shiny side on the female side of the filter cell is not AR coated the other side with the male thread is AR coated. The main issue AR coatings are trying to prevent is reflections back towards the filter from the sensor itself. 

Edited September 26, 2019 by Adam J