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William Optics Flat 6A II or III with ASI 1600

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#1 Tim Kimbler

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Posted 15 August 2020 - 01:58 PM

Anyone used a William Optics Flat 6A and ASI1600 with an older Meade 127 F7.5 APO? Reviewing the description it states it will work with any F6-F7.5 refractors. I also have an Astrotech 72 F6 ED I would like to use it with. I would love to hear from anyone using this reducer. Thanks

#2 nimitz69

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Posted 15 August 2020 - 06:25 PM

I have the 6A II but its on a scope that it was designed for — WO GT81 and its wonderful. Have no idea how it will perform on another scope ...

Edited by nimitz69, 15 August 2020 - 06:25 PM.


#3 Tim Kimbler

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Posted 15 August 2020 - 06:36 PM

Thanks

#4 Tim Kimbler

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Posted 17 August 2020 - 12:36 PM

Can you tell me what the adjustment is used for? I thought you used spacers to get the 55mm required for the camera. Thanks

#5 larryjh

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Posted 17 August 2020 - 08:41 PM

Hi Tim, I recently got the pflat 6AIII to use with my Skywatcher ED80.  I think the 6AII and 6AIII are similar, but with slightly different spacing requirements.  The idea of the adjustment is that it is assumed that you have a 55mm spacing already from your camera sensor to the corrector.  If you needed a 60mm spacing, you would then set the adjustment at 5mm for a total of 60mm.  I think the spacing is roughly linear with focal length.  I made a spreadsheet plot of the spacing vs. the 4 WO scopes' focal lengths in order to estimate the setting for mine:

 

 flat6Aiii.jpg

 

I used the plot to estimate the spacing at about 59mm (setting of 4mm) for my ED80 which has a focal length of 600mm.  You could do the same for your scope using the spacing numbers for the 6AII.  The estimate for the plot worked well for me, though I am still experimenting.  For fun, I put in your 952mm focal length and 55mm spacing (setting of 0) and it looks like it would need a shorter spacing than that.  So, you would have to use something shorter than 55mm for your spacers.  If you use a DSLR you'd be out of luck I think.  One other thing to note is that the flattener is designed to screw into the focuser tube.  If your tube doesn't have the same threads as the WO scopes, you may want to get their adapter so that it simply inserts into a 2 inch focuser tube.  That's what I did.  Unfortunately I then found that I didn't quite have enough in-focus and I had to remove the ring lock so that I could rack in the focuser more.  I've also ordered a lower profile 2 inch visual back from First Light Optics that fits my scope.  One last thing is that this thing is a tank.  I think it weighs close to 2 lbs.

 

Bottom line is that it worked well and gave me a very flat field compared to having no corrector (I use an ASI294MC camera).

 

Hopefully some of this is helpful for you.

   -Larry



#6 Tim Kimbler

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Posted 18 August 2020 - 04:12 PM

I have an ASI1600mc pro. Not sure I understand the graph. ASI recommends 55mm back focus. I’m trying to make sure the reducer/flattener works with my scope. I’ve read they have to match the design of the scope. Meade never made one for my scope. Tough figuring this stuff out. Thanks

#7 larryjh

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Posted 18 August 2020 - 06:06 PM

The backfocus depends on the design of the reducer/flattener and the scope.  WO has made their adjustable reducer so that it works well with many of their scopes without having to change out fixed spacers.  The graph is just showing the recommended (by WO) backfocus for each of their scopes, as a function of the scope's focal length.  The table on the left is what is plotted, and the numbers (other than "test") were gotten directly from the WO website.  Since it's roughly linear, that gives a good first guess as to the backfocus needed if you're going to try to use it on a scope from a different manufacturer.  My point was that if you used the 6AIII on your Meade 127 scope, it looks like the backfocus should likely be less than 55mm, maybe more like 52 or 53mm.  You would have to reduce your total fixed spacing to less than 55mm because there's no setting less than 0 on the variable adjustment of the reducer.  So, for example, you could try putting in 45mm of fixed spacing and setting the variable adjustment to 7 or 8 and see how that looks in an image at the corners.  You could then adjust from there in small increments if needed because it probably won't be too far off.  You'll have to also look at the ZWO mechanical drawing for your camera to see how much space there is from the sensor to the front of the camera, and then add spacers to reach the desired fixed spacing (45mm in my example).  You could probably pick a fixed spacing such that it would work with both of your scopes just by adjusting the flattener itself.  It's a matter of degree as to whether the flattener "works" with your telescope.  It probably won't work as well as one that was specifically designed for your scope (sounds like there isn't one anyway), but it will probably be a major improvement over no flattener at all.



#8 Tim Kimbler

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Posted 18 August 2020 - 06:44 PM

Very helpful thanks for the info. Currently they are on back order on all the vendor websites. I’ll just monitor availability. Thanks


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