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Old 15-09-2016, 07:01 PM
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Crushellon (Tim)
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55mm spacing for flattener reducer

I've got my new starlight xpress filter wheel arriving tomorrow and I'll probably have to make some spacers to attach it to the 0.85x on the ed80. Just wondering with the 55mm that is required to the chip on the ccd, is that from the base of the thread on the reducer or from the top of the thread. I assume it is from the base of the thread but I'm just checking before I go turning down one of my spacers.

Tim
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Old 15-09-2016, 08:06 PM
glend (Glen)
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It is usually measured from the shoulder (ie base) of the reducer or flattener. Do not forget that every glass element between the sensor surface and the reducer will need to be compensated for in your spacer length. For example, if you have a 2mm filter, and the sensor has a 1mm cover glass, which is a total of 3mm of glass, you need to use the rule of 1/3s and add an extra 1mm to the spacer to compensate for the glass effect.
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Old 15-09-2016, 08:50 PM
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Crushellon (Tim)
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I figured it would be from the base.

I didn't know you had to allow for glass thicknesses. I also wasn't aware of a glass cover on the sensor and can't find any details regarding its thickness in the manuals.

In the manual for the stf-8300m it says the mechanical distance to the focal plane is .7" and the optical distance to the focal plane is .69" do I go from mechanical or optical?

so I'll assume it's the optical distance for now. And I'll assume the glass cover is 1mm, the filters I will be using are 2mm.

So, 55mm for the reducer add 1mm to allow for 3mm of glass = 56mm

56mm minus the optical distance to the focal plane on the 8300 which is .69" (17.526mm) = 38.474mm

So the distance from the face of the camera to the base of the frot off the flattener needs to be 38.474mm is that right?

Last edited by Crushellon; 15-09-2016 at 10:12 PM.
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Old 15-09-2016, 09:36 PM
glend (Glen)
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Have you taken into account the thickness of the filter wheel and any adaptors required. I do not know your camera but some require an adaptor to connect to the camera, then there is the thickness of the wheel housing, then the spacer then the reducer.
You need to reduce the spacer to allow for the wheel thickness.
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Old 15-09-2016, 09:41 PM
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Crushellon (Tim)
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Yeh I get the wheel tomorrow and I'll be machining down a spacer for between the wheel and the flattener. I just need to work out the total distance needed between the camera and the flattener.
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Old 16-09-2016, 04:23 PM
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Crushellon (Tim)
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How much of a difference will +1mm make. I could only get it down to 39.5mm when I needed 38.474.

Also do I really need the flattener for a 22.5mm diag sensor on a Skywatcher ed80?
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Old 16-09-2016, 06:05 PM
glend (Glen)
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Try it and see. You can always crop it.
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