I've busy making a few things OAG and remote imaging control.

[Stockton Astronomical Society]

Hi all sorry I've been away. I have been busy though working on a few projects.

I set my scope up for remote imaging a few months back and will post about that later. For now I'm going to talk about my on going project an OAG (On Axis Guider). This is a conversation (on going) on another astronomy forum. I thought it would explain thing better than rewriting it. Those who do imaging will find this more interesting than observers only. 

A very critical feature about imaging is something called Back Focus (BF) and this is a piece of equipment that helps with that subject. It refers to the distance needed to have your camera in focus when astro imaging. The most common universal BF distance is 55mm but there are some caveats. With OAG  and all other systems filters add to that distance plus there is the challenge to get TWO cameras in focus at the same time one to guide the telescope and the other to take the picture. 

OK..On to that post and some pictures:

Things are coming along on my OAG project. This is just an update from my last post. I have a dozen made up and temporally assembled two for testing with the prisms. I’ve found a few changes to be made but nothing that I can’t fix. I machined up the shims today. I’d forgotten just how long it takes to make shim fixtures but they will be completed in the morning. Next is the masking fixtures for sand blasting the part ID’s.

This OAG (On Axis Guider) is designed with specific features in mind. One of the most important was to utilize the full field of a Sony IMX174LLJ / IMX174LQJ 1/1.2″ sensor (11.3 mm x 7.1 mm) an example being the ZWOASI174 mini. This is accomplished with a custom prism and a generously large light tunnel to allow the light path to be available to the complete sensor face.

The body of the OAG with provided telescope adapters are calibrated to be 54 mm +/- .200mm and shims are provided to adjust for precise thickness of 55mm or 56mm without the need to measure or change a bunch of adapters to get the proper BF.

(The mirror reflection behind the prism is a 2" test filter so you cannot see the sensor.)

The OSC (one shot color) camera adapter is internally threaded to allow for installation of two inch threaded filters and an insert is available for use with smaller filters. There may be a filter drawer in the future as there is enough room but I’m not fond of them because they can be a light leak source. I’m using a ZWOASI2600MC and the Back Focus is set without shims at 54 mm +/- .200mm.The mono camera shown is a ZWOASI1600MM with the 20mm thick EFW at 54mm +/- .200 Back Focus. Both the front telescope adapter and the camera adapters are rotationally adjustable in 5 degree increments to allow clocking without shimming of the image frames and positions. but optionally you could also use shims it you wanted to.

 This OAG maintains Back Focus when going from Field Flattener to a Field Flattener/Reducer as long as they both have the same Back Focus. In this case it’s 56mm with the filters. It maintains BF between cameras as the distance is controlled by the camera flange adapters thickness.

The BF on the guide camera does not changed when switching between cameras or cameras and flatteners. The guide and main cameras can be removed without changing its focus relationships as the adapters are focus matched after the first setup.

That is it for now. Hopefully I will get some time to post about the remote imaging project soon.

Steve

[s.clark]

Whoops looks like I posted not as the member in the title.  Steve Clark