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ONAG at work:

Guiding with a long focal

The images below are 1 minute (bin 1x1) unprocessed luminance frames taken with an Apogee U8300 (5.4x5.4 microns) at prime focus of a Hyperion (f =2.54m @ f/8).
Both have been cropped the same way.
Field of view: 224x224 arcsec near NGC 2683.

There are 38 minutes apart.
credit: Frank Colosimo
Blue Mtn Vista Observatory

Mount: Paramount ME
Guider: ONAG+SBIG ST402
Seeing: Average

The reference star is marked with a cross (not the guide star).

Initial image (t=0'), reference star:
FWHM=2.44 arcsec
Centroid X=80.71 Y=171.83 pixel

Star 3D profile (Maxim DL) 

2nd image (t=38'), reference star:
FWHM=2.36 arcsec
Centroid X=81.38 Y=171.40 pixel

The reference star is offset by 0.79 pixels.
With the U8300 pixels (0.43x0.43 arcsec) this translates to 0.34 arcsec.
This is a total offset including all sources of error.

Below both images have been combined, without any registration and alignment, to provide an easy estimation and visualization of the total tracking performance.



Average image, reference star:
FWHM=2.43 arcsec
Centroid X=81.08 Y=171.54 pixel


Star 3D profile (Maxim DL) 

The result shows no visible guiding effect.

To know more about guiding error
and near infrared (NIR) visit:

How much guiding error is too much?

Guiding with NIR

   

Heavy duty focuser:

Full body compressing ring

The ONAG features a low profile 1.25" guider focuser (GF) associated with a T-thread (M42 x0.75mm) and integrated with the ONAG's X/Y stage.

It has been designed to remove any possible flexure even with a heavy camera. The focuser uses a full length compressing ring mechanism made of high grade 6061 aluminum alloy. It applies a considerable pressure (on 360 degrees) all the long the focuser drawtube insuring a constant and efficient grip.

As a matter of fact when the focuser screw is hand tighten the all system is as rigid as an unique solid piece of aluminum.

The next image shows the full body compression ring element and its screw.



Unlike thumb screws used with low cost systems, the stain less steel focuser screw compresses the all focuser body against the drawtube. The mechanism is lubricated with an extended temperature range anti-seize grease. It is designed with 2 groves and set screws to insure the drawtube will not leave the focuser by accident.

Should you want, or need, to use any 1.25" nosepiece just remove the set screws and replace the focuser drawtube by your  piece of equipment. A very handy solution if your guider camera nosepiece does not come off.

Below the compressing ring with the focuser drawtube in place.