Hi group,

I have an Argo Navis + servocat on an 18" Dob. I need to do lucky cam imaging at high resolution. I center a bright start visually using medium magnification, then remove the eyepiece and replace it with my 4x barlow, filterwheel, camera. Doing this adds some weight that wasn't there with the eyepiece => dob sags a bit and star is gone from FOV. Is it possible to 'mark' a reference position when the star is centered visually, then get back to it when the imaging setup has been mounted? cheers, Mikael

Hi Mikael,

Thanks for the post and the interesting question.

When the eyepiece is replaced by the much heavier camera, one of three things can happen.

1) The OTA drops in altitude but this drop is reflected by a corresponding change in the altitude encoder values.

2) The top end of the OTA "droops" in altitude as either the truss poles flex, the secondary cage shifts with respect the truss poles or the truss poles shift with respect the split blocks.

3) The camera itself shifts within the eyepiece holder.

I gather from your description you suspect the truss poles flex?

To eliminate 1) as the cause, dial up MODE ENCODER and whilst trying to accidentally nudge the OTA, note whether the altitude encoder values change when replacing the eyepiece with the camera.

Flexure of the truss poles as in 2) is a function of altitude with the maximum flexure occurring when the scope is pointed toward the horizon.
If the flexure is only small, that is within arc minutes, you might get away with a simple linear model.

One approach might be to create a simple TPAS model when the eyepiece is attached. Do a two-star alignment then sample say 6 stars using the SETUP MNT ERRORS functionality.
COMPUTE the model say using only the IE term and apply the model by selecting USE NOW.

When you replace the eyepiece with the camera, using the SET ERROR VALUES, IN USE NOW submenu, you could try changing the INDEX ERROR EL (ID) value to shift the apparent
pointing position in altitude. Perhaps with some trial and error you could ascertain a typical offset.

This approach might also work for 3).

One could also create a more dynamic offset, that is one that is a function of altitude, by creating a model that uses IE, ECEC and ECES, but finding suitable values would be more challenging.

I've never tried this, but the TPAS model and tweaking IE would be my first experiment if it were me. One assumes the shift is systematic rather than a sudden random shift.
I would be interested to hear how you get on.

My name is Allen Grundmeier.

I just received my Argo Navis yesterday.
I'm taking it slow to make sure I don't assume that I know where I'm at in the set up process.

This is my question:

I've got a Win 10 computer. I'm trying to find the correct COM port as descriibed on pg (Com & LPT) ports as described on pg 169.

Allen Grundmeier
Robbinsdale, Minnesota

Allen Grundmeier wrote:My name is Allen Grundmeier.

I just received my Argo Navis yesterday.
I'm taking it slow to make sure I don't assume that I know where I'm at in the set up process.

This is my question:

I've got a Win 10 computer. I'm trying to find the correct COM port as descriibed on pg (Com & LPT) ports as described on pg 169.

Allen Grundmeier
Robbinsdale, Minnesota

Hi Allen,

Welcome to the forum.

The Keypan USA-19HS comes with a CDROM with software on it. Be sure to install it first before plugging in the USB Serial Adapter for the first time.

The software on the CDROM includes the Window's device driver and a convenient utility called the Keyspan Serial Assistant.

On Windows 10, locate the "This PC" icon on the Deskop, right click on it and select Properties.

A dialog will open. On the left hand side of that dialog select "Device Manager".

Once the Device Manager dialog opens, follow the instructions in the Argo Navis Users Manual and drill down through the Ports (COM & LPT) hierarchy to determine the COM port
number Windows has assigned the Keypsan USB Serial Adapter and to change it to an unused port in the range 1 thru 4 if need be.

Alternatively, click on the Window's Start button on the lower left of the Desktop, left click on it and look for the Keyspan USB Serial Adapter folder.
Within it, select the Keyspan Serial Assistant. When the approval dialog open,s allow it to make changes to your computer. Select the Port Mappings tab and change the COM port that way.

Once you have assigned the USB Serial Adapter an port number of 1 thru 4, when you open the Argonaut software utility, select the corresponding number 1 thru 4 in the Port pulldown.
Then select Connection->Connect.

Hi Gary, thanks for the three explanations. I tried to see if the encoder reading changed - it clearly did NOT. Hence, we are looking at slight sagging or camera shift. I actually got around this problem by using the great spiral search feature. Important to do this at the low speed, high magnification setting. The latter requires the speed switch on the front panel to be changed. In this way I can easily reacquire the star if it slips outside the field. -Mikael