QHY5Lii - guidecam image problem

[Demonperformer]

I originally put this query on a different board (with hindsight, I think the wrong one), but got no response, so am trying again here.

My aim is to attach my qhy5lii camera to my oag as a guide camera. Before trying it at night under the stars, I set it up during the day (to make sure phd2 would talk and it would get along) and it produced the attached screenshot (overexposed view of one of the local trees).

The pattern of light and dark lines across the image is surely not normal? My guess (and that is all it is) is that is might be something to do with the pattern of pixels on the camera.

This camera has been touted as a suitable guidecam and I'm sure I have read posts of people who actually do use it as such.

What can I do to get rid of this pattern, which will surely be a distraction for guiding?

Thanks.

[Merlin66]

Well the good news is that I use the same camera “on axis guided” in the spectroscope - I don’t have those artifacts.

Are there different options available in PHD2 for the camera?

Try similar exposure under FireCapture/ SharpCap.

 

[ChrisEll]

I'm guessing you're seeing those check patterns cos your gamma slider is all the way to the right. That slider does not affect what PHD2 sees when guiding, it's for the user's benefit to see faint stars.

[Demonperformer]

Thanks for the suggestions. I will set up and try them and see if they make any difference later.

[MarsG76]

It looks like moire pattern scaled down without any smoothing. If the pattern disappears when your frame is full frame than that is what it is.

Try setting the video output as 640x480 (not scaling the full res down to 640x480), even if you need to choose a region of interest so that PHD doesn't scale down the incoming frames.

[Oddsocks]

Are you sure you have the mono version of the QHY5l-ii, your images look typical for a colour camera, the checkerboard pattern simply being the bayer colour matrix.

When you guide with a colour camera you don't debayer the incoming image as it takes too long and would reduce your guiding rate (images per minute) considerably, the guide software should still be able to find the centroid for any suitable guide star in the non-debayered image. If your guiding software supports the use of calibration frames for the guide camera then use a flat at least as this will help reduce any density differences between adjacent colour pixels of a colour camera. Using calibration frames will slow down the frame rate a little but nothing like as much as debayering would.

While a colour camera can be used for guiding you do pay a price in reduced sensitivity overall plus some bright guide stars become unsuitable if they have a strong red or blue colour since only a single pixel in each group of four will actually record them.  Mono camera is always a better choice for a guide camera in that respect.

For your relative alignment question in your other thread, so far as matching the alignment of the guide camera to the axis of the mount and the main imaging camera, most guiding software won’t care. When it calibrates the mount it simply compares where the star moves to in the guide image for a given direction input to the mount motors, once it has calculated that then it will guide just as well if the mount to camera axis are coincident or at any other angle.

The main reason to have the guide camera axis parallel to the mount axis is simply to help determine guiding problems, being a lot easier to match guide images to mount movements if the two have an apparent logical connection. But that is just for us humans, the software won’t care.

If you really must have both main and guide cameras aligned then it is ok to add a shim spacer under the guide camera connection, a little defocusing wont hurt, in some circumstances defocusing the guide camera is a good thing as it spreads the stars disk over a greater number of pixels and makes it easier for the guide software to determine the guide star centroid.

HTH

[Demonperformer]

Thanks for the input.

My camera is the colour version, used because I have it rather than because I purchased it for guiding. I'm not sure if PHD2 will use a flat frame (it will use a dark frame or a BPM, but haven't seen mention of a flat frame) - will have to do a little bit of investigative work. Would really prefer not to have to fork out for another camera just at the moment!

I will try to work with the main camera 'flat' and the guider at an angle, then, initially. The worst that can happen is that it totally fails [been there, done that, and the universe did not collapse in on itself ]

Thanks.

[michael8554]

4 hours ago, Oddsocks said:

defocusing the guide camera is a good thing

The PHD2 Forum frequently reports that guidecam focus needs to be spot on, defocusing appears to be a myth.

Michael 

[Demonperformer]

Thanks, Michael.