OAG field of view too narrow for guide stars.: Page 3

OAG field of view too narrow for guide stars.

c131frdave

Thanks Chen. I'm using a 10" F4 newtonian. Pretty fast.

JeffMorgan

c131frdave I tried 1.5mm, 1.2mm, and .0050" hex keys with no luck.

What I did was take a precision screwdriver and filed it down until it a good fit was achieved.

rjl

I'm glad I have the new model ZWO OAG (with the larger prism port). The old model (with small circle port) doesn't look very fun. I use the ASI120-Mini camera and can find guide stars. I just rotate the entire OAG assembly (with main camera attached) until I find a star on the PHD screen. Stars may be appear dimmer (or somewhat obscure) off the prism, but a 2s exposure time (not always 1s) can be used in PHD to prevent losing the star. (By the way, the PHD program defaults to 2.0 seconds when installed). When the mount continues to track towards the horizon, exposure can be increased to 2.5s because the star will begin to dim due the thicker atmosphere near the horizon. (You don't want to lose the star).

Some other "passed-on-hearsay" must be that the RMS error on the PHD graph should always be less than 1. However, in OAG guiding, I'm getting RMS values of 2 to 3 and higher - but yielding satisfactory results:

https://bbs.astronomy-imaging-camera.com/d/14352-long-exposure-checking-the-cameras-supposed-upper-limit-asi183mc-cooled

rjl

For the record, the PHD User Manual recommends 1 to 3 second exposure time and PHD2 Best Practices (supplementary guide to PHD) recommends 2 to 4 seconds.

RMS values on the graph are the standard deviation of all the star movements. OAG guiding may pick up more star movement because in the case of the Newtonian Reflector, the OAG is seeing the image-shift inherent in the Reflector's optics along with anything else (atmospheric refraction, polar misalignment, etc.). Therefore, RMS with a Reflector telescope will show higher.

Also, if you rotate the OAG to better locate a guide star, you should consider recalibrating PHD (shift-click the guide icon to force a new calibration, or choose through the menu).

jaspetropoulos

Hello everyone

what is the hex screw size please? does anyone know?

thanks

Tech@ZWO

jaspetropoulos Which screw do you mean?

jaspetropoulos

@Tech@ZWO#59667 that holds the prism

Tech@ZWO

jaspetropoulos It's M4

jaspetropoulos

@Tech@ZWO#59790 are you sure? M4 does not fit
seems to be less than 1.5mm

Tech@ZWO

jaspetropoulos
Do you mean this one?
It's an M4 jackscrew.

jaspetropoulos

@Tech@ZWO#59903

thanks for your reply, i'm talking about the tiny screw that holds the prism, please look the red arrow in the attached pic 🙂

Tech@ZWO

jaspetropoulos Got it, it is M2

jaspetropoulos

WalterT

Hey Walter.. 😊
How much pressure did you have to apply in order for the prism to pop out?

Your water was at boiling temperature?

Thanks

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