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WO Field Flattener II versu III

Started by Joe G , Sep 07 2007 02:37 PM
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12 replies to this topic

#1 Joe G

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Posted 07 September 2007 - 02:37 PM

I bought the new Williams Optics Field Flattener III to see if it has reduced vignetting (compared to the FF II) with my WO FD80 Apograde scope. Haven't had a chance to image with it but took a couple of flats to compare. The flats were taken with a Canon 20Da, 1/2500 seconds at ISO 100. It does seem that there is less vignetting with this setup.

Attached Thumbnails

  • 1826449-WO FF Test.jpg

#2 Joe G

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Posted 07 September 2007 - 02:39 PM

If it is not obvious the WO FF II is the top and the WO FF III is the bottom. Here's a side by side comparison of the two:

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  • 1826453-WO FF.jpg

#3 Mike D

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Posted 07 September 2007 - 02:40 PM

Yes much improved.

#4 LLEEGE

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Posted 07 September 2007 - 03:26 PM

Did the old one flatten the field by vignetting out the curvature? :grin:

#5 PGW Steve

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Posted 07 September 2007 - 04:36 PM

Thanks for posting this. I ordered one of these with no prior information, just under the premise that it has to be better, it costs more.

#6 Moggi1964

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Posted 07 September 2007 - 05:18 PM

:shameonyou: :lol:

#7 Mike B.

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Posted 07 September 2007 - 06:11 PM

Joe, that's great! Thanks for testing the vignetting aspect. I can't wait to see a star test.

I was thinking really hard about getting the Mk III unit, but I want to see how it performs before I do.

#8 Joe G

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Posted 08 September 2007 - 02:10 PM

Took a shot at the Helix Nebula last night to see how it actually flattened the field. The image consists of 19x210 seconds ISO 1600 with Canon 20Da, WO FD80mm Apograde, IDAS LPS guided on Atlas mount with PHD and EQMOD. Processed with flats and darks in IP and further processing in PSP and Neat Image.

This was with the William Optics field flattener III pictured above.

The stars in the center are fairly round. Still see considerable distortion around the edges. Does it seem likely that this is the FF III? Could any of this be polar alignment error?

Link to a larger version:

http://www.flickr.co...47931258&size=l

#9 RStar

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Posted 08 September 2007 - 04:57 PM

Hmmm...I don't think it's field rotation. I got similar shaped stars using the StageII ff/fr on my ED80 but it looks like the StageIII ff/fr has more distortion. Here's a comparison with the ED80

http://www.pbase.com...o_focal_reducer

Bob

#10 Joe G

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Posted 08 September 2007 - 05:08 PM

Bob,

Well I didn't think it was field rotation but wasn't positive. I have the FF II and it seems that there is more distortion from this one (the III) than the FF II.

I believe that the FFII was optimized for the 66mm aperture scopes and William Optics indicated they could be used with the 80mm scopes but you might get vignetting which I did. This one (the III) is supposed to work with 80-110mm scopes so I thought it would work better. It seems to have less vignetting but the edge stars are more distorted. I am using it with an 80mm scope. Maybe it works better with the larger aperture scopes? It would be nice to see someone else's experience.

Thanks for the reply.

Joe G.

#11 Mike B.

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Posted 08 September 2007 - 06:24 PM

Joe, nice image, but like you said, it looks like there is more distortion with the III than version II. That's disappointing. :(

I was under the impression that W.O. designed it for their triplet refractors. Maybe it flattens them correctly but over-corrects the doublets?

You might try experimenting with the increasing the distance of the FR/FF from the sensor and see if it gets better or worse. Probably no way to get it any closer, from what I can tell.

#12 williamoptics

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Posted 10 September 2007 - 01:07 PM

On the William Optics Yahoo group, there are many tests of the v.III and v. II. You may want to check them out. There is a whole gamut of opinions and results.

#13 lineman_16735

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Posted 10 September 2007 - 10:13 PM

To me it looks like it most certainly is field rotation. Notice how the shape of the stars seem to "rotate" around the center?
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