janek

I am considering getting a 3rd Gen NV device and stumbled upon some CloudyNights discussions how dielectric coatings are optimised for visual wavelengths whereas NV is most sensitive in near infra-red. I found that my 16 inch Dobsonian's mirrors have dielectric coatings with reflectivity decreasing dramatically outside the visible spectrum. For nebulas this is not an issue but one of the reasons I wanted the night vision was the better view of edge-on galaxies. Does anyone have experience with how much worse the dielectric coatings could be for this particular target?

Thanks for making this point, I tried that yesterday and the oval shapes "travel" along with my eye, time to have them checked by a doctor. I have read elsewhere that people have found contact lenses very helpful for observing so I might consider those as well in the future.

I tried with glasses on but unfortunately they have a lot of small deformities which became quite obvious during the observation - everything was even blurrier with them. I will get new ones soon, but the eye relief in my Nagler 31 and 22 mm is quite small and does not allow observing with glasses on anyway (I tried and could see only about half the field). I might consider getting contact lenses just for this if it bothers me too much and for now I will try to learn how to observe with my right eye. Thank you vlaiv for the great advice, helped a lot to clear this up for me

I did some more testing tonight and it turns out I have some bad astigmatism in my left eye. The right eye is a bit better. Thank you guys for helping in identifying the issue! I had no idea I had this. Now I need to fix my eyes, but at least I don't have to return my scope 🙂

If I have astigmatism that would be new to me, but can be very well possible. I will definitely try your suggestions tonight. Tightening up the focuser was indeed needed and I did that as one of the first things. The star images are elliptical when both in/out focus and they also rotate by 90 degrees. If this indeed is a fault in the scope, is it common to request a replacement in this kind of case?

I wear glasses but not during observation. I will give it a try to see if my other eye sees anything differently and/or try with glasses. I used laser to collimate the scope. The focuser on this model has two screws that enable collimation to some extent. I tried to perform a star test and interestingly when out of focus the star appears elliptical (I did not see any concentric rings though, I was too focused on the elliptical shape). The elliptical shape is more pronounced in lower powers and less in higher powers. Would this point to astigmatism in my eye? Strangely I never noticed this in my Dobsonian.

The scope was cooled properly. So far I have been able to test just from the house's rooftop. But I think I can rule out that this would have to do with the scope's temperature and atmospheric conditions. I have observed with a Dobsonian before here and could tell if it was something like that. That's why I am a bit desperate 🙂

It's a brand new scope 🙂

Hello guys, I recently bought a SKy-Watcher 120/600 achromatic refractor hoping for nice wide-field views and pinpoint stars. It turns out that even faint stars are blurry - as if there are many overlapping images of the same star, and the "overlapping" depends a lot on my eye placement at the eyepiece. Often even faint stars can look like double stars as the image gets distorted to one or the other side (again depending on the eye placement). I was expecting a little CA around brighter objects but not this blurriness with this scope. I have tried various things: I fixed collimation, used different diagonals, different eyepieces (both cheap and expensive ones like Nagler 31mm, Nagler 22mm, Delos 8mm...), used a baffle to reduce the aperture. What helps a lot is using the baffle but that reduces the aperture from 120mm to barely 55mm. Also using eyepieces with shorter focal length seems to help a little - at least the image becomes less sensitive to eye-placement. I have a theory that the problem might have something to do with the size of the exit pupil - the bigger it is the more I need to be careful where I put my eye. I will just add that in terrestrial observing I see a nicely focused image, as far as I can tell ..., so I am not sure that this could be a fault of the telescope's optics. Has anyone had a similar issue with an achromatic refractor?