Fuzzy images in PHD2

[Kaban]

Hello.

I have been using PHD2 for a while alraeady. It works pretty well, but i do not understand why the pictures on PHD2 are so fuzzy. 

If i compare a picture of the same field taken with CCDSoft and PHD2 with the same exposure, the difference is obvious.

Of course i tried to play with the sliders and histogram but the stars in CCDSoft are more clear, and some stars are too faint to be used in PHD2 while CCDSoft shows them clearly.

I tried with two different cameras, an Atik Titan and an ASI 174 mini, with the same results.

I am attaching two screen shots of the same field with the same exposure.

The guiding camera is attached to a LISA spectroscope and for that reason the stars appear to be "double", due to the slit mirror reflections, but that is normal.

Thanks.

David Cejudo.

[David Kerber]

That just means your guide scope isn't as well focused as your imaging
scope. You'll generally get better guiding if your guide scope is well
focused (though it doesn't need to be as good as your main scope).

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[Kaban]

But both images are taken with the same set up, same camera, same focus position, same exposition. Whay are they shown so different in CCDSoft and PHD2?

[David Kerber]

Ok, I didn't catch that it was the same camera and location, just a
different program. I imagine CCD soft is doing some processing on the
image, such as a stretch, maybe sharpening, etc. PHD doesn't do any of
that, and will often guide on stars that aren't even visible in the
image. Did you try adjusting the gamma slider in PHD to see if that
changes anything in what you see? It won't change what PHD uses for
guiding, it just changes the display that the user sees.

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[bw_msgboard]

Hi David.  PHD2 doesn’t worry about what the star field looks like in the image display and it’s not really useful to try to compare screen-shots.  PHD2 works on the raw, un-stretched frames obtained from the guide camera.  If you really want to see what PHD2 is working with, you should capture a typical frame (File/Save) and then examine that data in a suitable imaging app – one that can compute areal statistics, stretching according to your wishes, etc.  Obviously, the data obtained with different apps using the same camera must also be using the same camera driver with the same settings, especially things like 8-bit vs 16-bit and gain.  You should also disable dark-frame or bad-pix map corrections to make comparisons. But in such experiments, you should always be comparing raw data frames.

 

Bruce

 

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[Kaban]

Thanks.

I understand now how it works.

The problem i find here is that sometimes is very difficult to see a star that may be suitable for guiding by PHD2, but is difficult to see in the image to select.

Also, for my spectrograph, placing a faint nebula -most are faint- in the slit becomes an art of guessing where is it by looking at other stars in the field.

Anyway the software works pretty well!

David Cejudo.

Observatorio El gallinero.

El Berrueco, Madrid.

[bw_msgboard]

You should be able to solve the first problem by doing auto-select, that’s what we recommend.  It doesn’t matter what you see on the screen, the selection is based on the stellar properties that are important for guiding.  And you must do that if you decide to start using multi-star guiding.

 

Good luck,

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