QHY8L scratched IR window glass

[emyliano2000]

Hi guys.

I got my hands on a used QHY8L and on closer inspection I noticed the IR glass window is quite badly scratched.

Would this affect my images?

Searched on the QHYCCD website and they say it doesn't.

Thanks.

Emil

[Oddsocks]

With the flash-flare and slightly poor focus on the window It’s impossible to make a diagnosis ftom the image Emil.

When inspecting the window did you use a magnifying glass or loupe to determine if they really are scratches or just smeared dirt and grease that will wipe away with isopropyl alcohol and lens tissue?

Any scratches around the periphery and not within a few mm of the edges of the sensor will not be in the focal path so can be ignored. Any scratches that are above the sensor and in the focal path may cause a localised brightening of a few pixels if the IR coating is damaged but otherwise would be very hard to detect. Any density variations would be removed by flats. There would be very little in the way of refraction effects unless the scratches are really deep and wide.

The standard test for sensor optical path artefacts is to clean the optical window with appropriate approved materials then attach a lens/telescope and stop down the aperture with a mask, you can make your own mask from thick card. For a refractor the mask should have a central hole around 5mm diameter, for a reflector the mask should have a 5mm hole offset from the centre to clear the secondary mirror.

Focus on infinity and take an outdoor twilight sky flat image with the mask in place to ensure a broad spectrum of wavelengths including IR is captured and inspect the result for shadows or bright patches, then rotate the camera 45 degrees with respect to the OTA and take another image, any non circular optical artefacts that are present and remain in the same location after rotation are on the sensor or the window, dark circular artefacts will most likely be simple dust particles, bright patches may indicate damage to the IR coating.

Resolution testing is more difficult using a telescope due to the focal length and you would need to attach a short focal length high quality reference lens to the camera for that and take images of standard photographic test cards, then carefully analyse the results to pick out any areas that show loss of contrast or diffraction effects, really resolution testing is a job for an experienced professional. 

TBH I doubt you will see any problems, give the window a good clean, blowing away any dust or grit first then a wipe over with a lens tissue moistened with isopropyl alchohol and dry with lens tisues. Use a tissue for one wipe only then bin and use a fresh one for the next wipe. Wipe from the centre of the window out towards the edge in one direction and never in circles around the edge or from the edge towards the centre because you will just pick up oil and grease from the window retainer threads and drag it across the window. Expect to use at least twenty or thirty lens tissues. Dont overdo the isopropyl, the tissue should be damp, not wet.

Then get outside and take some astro images, it is unlikely you will see any problem, excessive testing just makes one paranoid!

HTH

William.

[emyliano2000]

I have a lens cleaning kit that I use with all my gear and I gave it a try but nothing. It's scratched all over the place. 

Here are 2 more photos.

I might be paranoid but to be honest I'm not ready to pay a large amount of money for something that is scratched as bad as this. I spoke to the guy and he's gonna take it back.

Better luck next time, I guess.

Thanks for your comments.

Emil

[drjolo]

It does not look good. Artifacts from this kind of scratches can be removed with flat, but quality will suffer due to contrast loss and scattered light. I would return this camera. Or have this window replaced. At least basing on the images you pasted. I agree that this loss may not be huge, but this is not 10$ toy. 

[Oddsocks]

1 hour ago, emyliano2000 said:

I spoke to the guy and he's gonna take it back

Thats a shame Emil, maybe a lucky escape though given the number of open tickets on several software vendors sites at the moment for problems with this camera's ASCOM driver.

If I recall, though not certain, the QHY8L camera has a bonded heated window? so not likely to be a cheap job to have the camera shipped back to China and have the window replaced.

A good example I think of how to destroy second hand value by lack of care.

[emyliano2000]

5 hours ago, Oddsocks said:

Thats a shame Emil, maybe a lucky escape though given the number of open tickets on several software vendors sites at the moment for problems with this camera's ASCOM driver.

If I recall, though not certain, the QHY8L camera has a bonded heated window? so not likely to be a cheap job to have the camera shipped back to China and have the window replaced.

A good example I think of how to destroy second hand value by lack of care.

I spoke to Bernard at Modern astronomy and he told me that he can supply the filter but he can't replace it because it's not an easy job and it's time consuming.