QSI 683 wsg with Imaging Source Guide Cam

[OzDave]

I have a QSI 683 wsg camera for imaging. This is the model with the built-in OAG and filter wheel.

Tonight I decided to try out the OAG for the first time, which of course required me to get the guide cam focused.

I connected my imaging source canera to the guide cam adapter on the QSI and adter some time managed to locate myself a donut shaped star on the guide cam sensor.

Trying to get this focused I realised that even with the guide cam "stalk" fully screwed in so the loght path is as short as possible, I still could not get the image focused. It needed less distance still.

So I removed the C-thread to T-thread adapter and the QSI oag ring that the guide can attaches to and played around a bit with the distance. It needs to be something like 2-3mm closer than what the adapter rings allow me.

Do I need a different OAG ring with a C thread or something? Has anyone used an imaging source camera for guiding with the OAG?

David

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[ollypenrice]

I really don't know, but did you try guiding with the out of focus star? It is not necessary, or even necessarily a good thing, to have a perfect focus for guiding.

Olly

[NickK]

My last image (M57) had a out of focus star in the OAG:

[OzDave]

I really don't know, but did you try guiding with the out of focus star? It is not necessary, or even necessarily a good thing, to have a perfect focus for guiding.

Olly

No I didn't try guiding. The star was well out of focus, like filling most of the guide chip with the donut. It may have worked, but I doubt the centroiding would have worked properly.

I have since discovered that there is a special adapter ring for C thread cameras that you can purchase for the bargain basement price of just $99. I'm not sure, but I suspect there is a fair amount of margin in that price

[OzDave]

So when you say that it is sometimesx beneficial to have the guide star slightly out of focus, how does that help matters?

Does it lessen the effects of seeing?

How far out of focus should one aim for? Assuming the focused star had a half flux radius of say 3 pixels, what would a good HFR be for guiding?

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[NickK]

The out of focus OAG guide star has it's pros and cons:

+ change in seeing movement didn't affect the bright point.

+ change in focus is not a problem

- as it's unfocused, changes in brightness can quickly reduce the brightness of the guide star.

- no post analysis for PSF

I've done guiding on donuts and the same is true.

[OzDave]

The out of focus OAG guide star has it's pros and cons:

+ change in seeing movement didn't affect the bright point.

+ change in focus is not a problem

- as it's unfocused, changes in brightness can quickly reduce the brightness of the guide star.

- no post analysis for PSF

I've done guiding on donuts and the same is true.

I think the pros are much more important than the cons, at least for me. I have no interest in doing PSF analysis, and if I choose a bright enough star, then the brightness issue probably isn't a big deal. I'll give this a go next time I head out.

I'll also have to get one of those C-thread adapter rings...although I do fancy a Lodestar also (which would just attach to the QSI as is)...arrgh!

David