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Old 04-06-2009, 11:47 PM
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citivolus (Ric)
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William Optics Flattener 4

The William Optics Flattener 4 is set to start shipping again. Apparently the first batch which triggered a redesign had an element reversed or something.

Anyway, I'm biting the bullet and ordering one to try on the Megrez 90 and FLT 98. I'll report back on my results and a comparison to the Flat III and Borg flattener as well, once I have done some testing.

The new design is no longer a reducer, just a flattener.

They have posted this image and this image on their web site, taken with a FF4 and FLT 98. As the second was taken at Coona, I am curious the person who took it is a member here

Last edited by citivolus; 15-06-2009 at 02:38 PM.
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Old 15-06-2009, 03:16 AM
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I have received this and hopefully will be able to test it in the next few nights against the Flat-III and the Borg. One thing I can say, it is huge next to them. There should be no internal vignetting problems with this one. I'll try to get some pictures up of a physical comparison later today.
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Old 15-06-2009, 02:13 PM
DeanoNZL (Adrian)
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Ric,
Would like to see your results on the Flat-4.
I own a Flat-2 & 3, the latter being not so nice at the edges of the field.
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Old 15-06-2009, 02:36 PM
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As it is cloudy today, I'm limited to physical measurements.

All are as equipped to use in a 2" focuser, and with a Canon EF mount.

William Optics x0.8 Flattener III
Weight: 302g
Length: 76.5mm
Width: 77.8mm
Clear Aperture: 38.7mm
Cost (US Dollars): $257 + lens mount

William Optics Variable Flattener 4
Weight: 643g
Length: 157.5mm
Width: 84.8mm
Clear Aperture: 38.7mm
Cost (US Dollars): $300 + lens mount

Borg Oasis Reducer 0.85x DG-L (7887):
Weight: 173g
Length: 82.0mm
Width: 65.2mm
Clear Aperture: 46.9mm
Cost (US Dollars): $349 + lens mount ($23, #5005 for Canon EF) + 2" focuser tube (39, #7425)


All specs are as measured by me and not necessarily those stated by the manufacturer.

In the attached image, the Borg is on the left, the Flattener 4 in the middle, and the Flattener 3 is on the right.
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Old 15-06-2009, 04:43 PM
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Ric

I also have a WOx0.8III, and I find the physical differences you have measured quite surprising. The WO4 is much larger than I expected. I will be especially interested in how the WO4 comes to focus.

Lets hope it clears soon for you to try the gear out and post the pics.

Darrell
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Old 28-07-2009, 04:00 PM
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I too look forward to seeing some results from the three as well...

The WO4 is MASSIVE compared to the III... I think having seen some images you sent me, and some in another thread you posted regarding the Borg DG-L, that I'll end up with the borg myself.. But I am waiting to see your results with the WO4..

I was under the impression that the WO4 was a reducer/flattener... If not, it could be very interesting.. As I dont necessarily want to reduce the focal length as much as I just want the field to be FLAT!!
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Old 31-07-2009, 02:09 PM
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Initial tests

I've just done a test in daylight to measure the reduction factor of the following reducers:

WO Flat III, manufacturer stated 0.8x
Borg DG-L, manufacturer stated 0.85x
WO Flat IV, manufacturer stated 1.1x ~ 1.2x (info recently added to WO web site)
vs native magnification, on the FLT98

I set up the scope in my garage, with a view of a fence about 250m away. This gave me a good reference point for measuring field width in each of the 4 configurations.

For the Flat IV, as it is adjustable, I measured with it in the central position. As you move towards the outer and inner stops, it increases/decreases the reduction/magnifiction factor by a few percent.

On each of the sample images, you will see two small x marks on the fence, which indicate my measurement point. The distances were measured on the original images, using Photoshop's ruler tool. Those distance were then compared with the reference distance to arrive at the following results:

WO Flat III: 80.4%
Borg DG-L: 89.2%
WO Flat IV: 120%

Borg states that the reduction factor of their flattener will vary depending on the thickness of the spacer ring that you have installed, so I knew that it wouldn't be exactly 85%. 89% was no surprise in this case.

The real surprise was the Flat IV, which had a magnification rather than reduction. This would turn my 618mm f/6.3 FLT98 into a 740mm, f/7.56 configuration. WO has recently modified their description of this item to include the magnification factor. At the time that it was shipped, the factor was undisclosed.

I have not yet measured flatness, which will require steadier seeing than I have gotten during daylight hours, but will hopefully get a chance to do that tonight if my autoguiding plays nice.

Regards,
Eric
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Old 31-07-2009, 02:26 PM
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Some additional calculations based on these factors:

Field Size, FLT98 and Canon 50D

Flat IV, mid setting, 103.5' x 69.1' (1.73 x 1.15 degrees)
Native, 124.2' x 83.0' (2.07 x 1.38 degrees)
DG-L, 139.18' x 93.0' (2.32 x 1.55 degrees)
Flat III, 154.4' x 103.2' (2.57 x 1.72 degrees)

In other words, the Flat III has almost a 50% wider field than the Flat IV.
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Old 31-07-2009, 02:44 PM
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Wow... 1.2x magnification from the flat4... Very strange indeed... I think im slowly but surely leaning towards the Borg DG-L... I like the 0.8x factor of the Flat 3, but its a bit of a waste if I'd still have to crop the field to get flat stars... 0.89x is still good....
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Old 31-07-2009, 11:37 PM
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I had smoke in the air and a very bright moon when doing these tests tonight, but they got the job done.

I took single 1 minute subs of M20, through the FLT98, with a Canon 40D.

The attachments are in the order of DG-L, Flat III, Flat IV.

The verdict:

The DG-L is just very slightly under-correcting on the FLT98, so I suspect I need to change the spacer ring that I am using to compensate. On the Megrez 90, I was unable to detect any under-correction when I last tested.

The Flattener III has, as always, lots of astigmatism. If you crop the centre 80% you probably would be fine, so if you are using a smaller chip than this it may work for you.

The Flattener IV was indeed flat to the edge when set to one end of its range. However, the magnification that it gives and the resulting loss of f/ratio has a dramatic impact on brightness.

For pixel peepers, I have these unresized images (converted to .jpg from raw)

Borg DG-L
WO Flattener III
WO Flattener IV

Edit: The fully processed image combining 10x 60 second subs from the Borg DG-L can be found here. You can tell which flattener I will be keeping

Regards,
Eric
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Last edited by citivolus; 01-08-2009 at 02:24 AM.
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Old 01-08-2009, 02:29 PM
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At the suggestion of DeanoNZL, I ran the calibrated subs through CCD Inspector.

It looks like I still have some work to do to find the sweet spot on the Flat 4

Attachment order is DG-L, Flat 3, Flat 4.

Regards,
Eric
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Old 01-08-2009, 03:26 PM
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I'd be interested to see how the 4 goes through an ED80 or a WO72 (which is the one I'm really intereted in ). You wouldn't happen to be going to Astrofest would you Eric???
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Old 01-08-2009, 04:38 PM
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Paul... I can tell you, I've seen results using the Televue TRF-2008 0.8x reducer flattener in a WO Megrez 72, and they were fantastic.. I'll see if i can dig up a link for you...
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Old 01-08-2009, 05:48 PM
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I'd much rather the flattener Alex

Cheers, thanks.
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Old 02-08-2009, 03:09 AM
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I'll pick up a Megrez 72 to test it in for you :p At least, that is what I can tell my wife. I'm missing the second refractor already

I'm still trying to convince her to let me go to Astrofest. I do really want to go.
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Old 02-08-2009, 06:29 AM
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Its a great time Eric, plus you could try your FRs out on my 72 and then write a supplement to the Refractor FR article I did. It needs a good update.
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Old 11-08-2009, 12:09 PM
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I've received my Megrez 72 so one of these nights I'll be trying the reducers on it. Wow is it a compact scope.

I'll also be at Astrofest from next Wednesday on.

Regards,
Eric
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Old 11-08-2009, 09:08 PM
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Its a nice little scope that 72 FD Ric
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Old 06-09-2009, 04:16 PM
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The current version of the FF4 is advertised as also being an 0.8 reducer.
Anyone have any experience with the current FF4?
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Old 06-09-2009, 07:12 PM
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Lol, they changed it again and added a set screw for the focal length. It looks a bit more reasonable now

With that serious a redesign, it should have been the Flattener 5.
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