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Old 16-07-2018, 08:54 AM
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rcheshire (Rowland)
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FS60CB flattener - eggy stars

Referring to the FS60CB system chart and use of the flattener.

Having followed the diagram and all combinations of adapters / elements shown, stars in all corners are eggy. More like long grain rice?

Thinking this through. Given that there is no way of attaching the flattener backwards, it seems that the distance between the flattener and camera rotator / focus tube and / or flattener and camera is important - though, the SD ring is optional, which leaves distance to the camera.

Worse, could the flattener elements have moved? Is that likely? I do not recall dropping the flattener and there are no rattles.
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Old 16-07-2018, 09:06 AM
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Lognic04 (Logan)
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I have the same issue with my MT - no matter the spacing there are always edge problems
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Old 16-07-2018, 01:44 PM
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Looking around, this question has been asked before, one way or another. And, I'm not sure why the documented setup doesn't work for me. Takahashi specs cite 56mm back focus. Now back focus appears to be as indicated in the diagram. However, another source suggests BF is measured from the back of the flattener. I'll measure it all up and see what gives.

Edit: 'Metal back focus' is the distance from the union of the flattener and camera adapter to the photographic plane.
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Last edited by rcheshire; 16-07-2018 at 02:12 PM.
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Old 16-07-2018, 02:04 PM
glend (Glen)
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Where are all the TAK experts on this? Certainly sounds like spacing, at least on any other scope it might be. You could try increasing the spacing a bit at a time. Most reducer correctors seem to have a tolerance range of at least +-2mm. A variable spacing ring is a nice tool for this sort of fiddling.
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Old 16-07-2018, 02:17 PM
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rcheshire (Rowland)
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I may have asked too soon. Added metal back focus table which includes a definition. It's just the way the information is presented. It doesn't matter whether a spacer is used ahead of the flattener. Providing there is sufficient focus travel, which gives me an idea to minimize camera tilt.
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Old 16-07-2018, 05:13 PM
LewisM
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Metal back is ALWAYS from the very rear of the flattener (or reducer) - NOT accounting the threads - to the sensor plane.

Last edited by LewisM; 16-07-2018 at 07:18 PM.
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Old 16-07-2018, 06:22 PM
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Thanks for the absolutes... Logan, if I find a way to tweak this, I'll report back.
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