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Old 28-05-2013, 04:12 PM
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New Rings for the RH200

To eliminate the last bits of flexure I ordered these rings from Officina Stellare.

I will test the result tonight.


The whole image train you see in the image weighs over twenty kg.


Bert
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Old 28-05-2013, 04:16 PM
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multiweb (Marc)
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Quote:
Originally Posted by avandonk View Post
To eliminate the last bits of flexure I ordered these rings from Officina Stellare.

I will test the result tonight.


The whole image train you see in the image weighs over twenty kg.


Bert
Wow! Even the camera has its own dovetail. Hard yakka to lift that onto the mount. I topped my C11/hyperstar/guider at 25kg once. Did my back putting it on the pier over my head. Silly man...
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Old 28-05-2013, 04:32 PM
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Being a 'smart' old fart I carried the lot out and put it on a high chair near the mount. Had a smoke and paused. Lifted the lot with the mount oriented at an accepting angle. It did slide on, once I strained ligaments I did not know I had. It is bit like RSI all over.

I am recuperating with a few beers. The pain will go away when I see the images.

Bert
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Old 29-05-2013, 11:54 AM
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looks great - all you need now is a screen printed logo on the shower cap - donking great photon collector
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Old 30-05-2013, 06:30 AM
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Wow! Even the camera has its own dovetail. Hard yakka to lift that onto the mount. I topped my C11/hyperstar/guider at 25kg once. Did my back putting it on the pier over my head. Silly man...
The frame that holds the camera has longitudinal and lateral dovetails. I can adjust the camera position laterally to get perfect alignment with the optic axis. The frame has adjustment for height to do the same thing. As the RH200 is factory set for collimation and alignment there is no need to fiddle with the camera adjustments.

I simply take a 30s exposure while jogging the mount by 30' every couple of seconds with a Bahtinov mask. The image below is the result. I can then tell which way to move by the diffraction patterns.

The top diffraction pattern tells me it is further back than the bottom diffraction patten. This means the bottom of the camera is further back than than the top so the camera needs to be adjusted down. These movements are typically fractions of a mm. I have a dial indicator for the lateral movement. For vertical a 1mm pitch bolt with a nut that holds the bottom plate of the camera holder.

If these clouds would go away I could get it all done and get some data.

Bert
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Old 30-05-2013, 06:34 AM
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I simply take a 30s exposure while jogging the mount by 30' every couple of seconds with a Bahtinov mask. The image below is the result. I can then tell which way to move by the diffraction patterns.

The top diffraction pattern tells me it is further back than the bottom diffraction patten. This means the bottom of the camera is further back than than the top so the camera needs to be adjusted down. These movements are typically fractions of a mm. I have a dial indicator for the lateral movement.
Ha! That's clever. Never thought about using a bathinov this way. I assume your field curvature across the sensor is nill then.
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Old 30-05-2013, 06:51 AM
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Ha! That's clever. Never thought about using a bathinov this way. I assume your field curvature across the sensor is nill then.
The field curvature of the RH200 is near enough to nil. The critical focus zone at F3 is about 10 to 20 micron. That is why the orthogonality of the sensor is critical for stars good to the corners. This is why any flexure is a major problem that does not matter at F5 to F10. Having a 3.5 X 3.5 degree field adds to these constraints.

I already had the lateral camera position adjusted and as usual clouds spoiled the party.

Using a Bahtinov mask for sensor alignment gives a visual image of what is going on. The trick is to remember the image is inverted in the camera.

Bert
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Old 30-05-2013, 03:12 PM
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Hi Bert,

thanks for this.
How did you know it was tube flexure and not ccd non-orthogonality?

could this method be used to find where the ccd is tilted so i can use some shims?

Josh
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Old 30-05-2013, 04:01 PM
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Hi Bert,

thanks for this.
How did you know it was tube flexure and not ccd non-orthogonality?

could this method be used to find where the ccd is tilted so i can use some shims?

Josh
The FLI camera is almost perfect as far as orthogonality. It was all flexure.

I took a one hour exposure at the zenith and it was perfect. The whole image train was vertical so there was no gravitational forces acting on it.Bert

Point your system vertical and take an image. Then take an image at about 30 degrees fom the horizon. This will tell you whether you have flexure or misalignment.
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Old 31-05-2013, 12:04 AM
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Thanks Bert. I will do that.

Josh
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