Unclear image in Powerseeker 80AZS telescope

[abstrusevaibhav]

I bought a Powerseeker 80AZS 2 days ago. While watching Saturn and Jupiter, I observed that the image is blurred when the telescope aperture cap is fully open. When I cover it with aperture cap to cover half of aperture, the blurriness is gone. Is this a defect in the telescope? Please suggest.

[lenscap]

This suggests that the focusing may have not been set perfectly. A very tiny adjustment may have been required.

When you reduced the aperture this increased the depth of field so that focusing became much less critical.

Having said that it is difficult to get good views of the planets at the moment because they are so low.

[vlaiv]

Hi and welcome to SGL.

Powerseeker 80AZS is short focal length achromat, and it will suffer from quite a bit of chromatic aberration. This is normal shortcoming and to be expected of the design. If most of the blur is in form of purple halo around bright objects, this is to blame.

However, it also might indicate poor figure of lens glass. By using aperture mask (lens cap with a hole in it) you are "restricting" light to go only thru central part of the lens, which might have satisfactory figure, while there is problem with outer edge. Using aperture mask also reduces chromatic blur, so it is hard to tell which one of these might be the problem.

Easiest way to see if your optics is sharp is to observe star at high power (and that scope is really not suited for high power observing) - if it is still pin point regardless of any violet halo or does it look kind of soft? (for this to work, you need to be able to tell if atmosphere is stable enough - requires some experience).

Another way to check this is to do defocused star test, but that is topic on its own, and depending on your observing skills might not be something that you could easily do. Technique is pretty simple, but reading of results requires experience.

 

[SIDO]

I would take the scope outside in day light making sure not to point the scope anywhere near the sun and while under some shade begin pointing the scope first at close objects then farther objects using low magnification and no aperture mask refocusing as nessesary, there is a thing called infinity when you reach this distance every point beyond it will not need focusing and preceeding it every point will, taking note that once at or beyond infinity all objects in view will be in focus and preceeding it only the objects at the same distance will be in focus. If this test shows clear imagry leading up to and beyond infinity there is likely nothing wrong with your optics and your just seeing chromatic aborations at higher magnification that when using an aperture mask the extended focal ratio is then reducing these cleaning up the observed image which is normal. To me it sounds like your optics are operating normally but this test will help to determine if this is the case ?

[abstrusevaibhav]

Really appreciate the help and all answers. The issue is not like chromatic aberration but more of a blurring of image to one side (to the right in my case). Are refractors prone to collimation errors? Is there any chance that lens is tilted to one side giving rise to a sideways blur? Please suggest.

[vlaiv]

2 minutes ago, abstrusevaibhav said:

Really appreciate the help and all answers. The issue is not like chromatic aberration but more of a blurring of image to one side (to the right in my case). Are refractors prone to collimation errors? Is there any chance that lens is tilted to one side giving rise to a sideways blur? Please suggest.

Yes it can happen, I'm not sure if that scope has lens cell that can be collimated (I believe it probably does not have such lens cell).

Your options are to send it back as faulty if retailer accepts returns, or to try to fix it your self (I'm pretty sure that fixing your self will void warranty). Short tube 80 can be fixed up to a point. You can try to properly seat the lens in cell, and there might be issue with focuser not being square with the lens.

Have look at this thread:

You might also search the internet for lens centering "by tapping" for ST80 scopes, and see how successful technique is at fixing such problem.

Have a look at this video if you decide to do it yourself:

 

[SIDO]

I agree with Vlaiv, first I would try returning or exchanging then if that's not doable you can try reseating the cell assembly if your comfortable doing that but if the issue is due to optical figuring than it's just a loss.