Telescope image problems

[tellurian83]

Hello,

I recently purchased a Konus Konusky Motor 200mm and potentially made the silly decision of moving it to East Africa without checking it properly. My understanding of telescopes is quite limited so I'm not sure whether the image problems I'm encountering are solvable or inherent with the Konus Konusky. I have tried using 7.5mm to 25mm eyepieces.

Firstly, the images have no distinguishable colors - all the planets look exactly the same - e.g. Jupiter is a big whitish blob with no discernable planetary features. Even more disturbing is the image distortion for stars, etc. - all I can see is diffraction and airy discs - sort of like blurry mini-rainbows (without the rainbow shape). All objects outside the solar system seem to have the same problem.

Is there anything I can do to improve the image quality of this telescope? Any suggestions would be greatly appreciated.

Thanks.

[redshifter]

Have you collimated this scope? Under what conditions are you using it? You're not looking at objects through a window or anything like that are you?

[Bojan]

Sometimes our expectations do not match the reality... and observing through telescope certainly requires a bit of training and experience, to be able to fully enjoy the view.
I suggest you get in contact with local astronomy amateurs club, or at least someone with experience.
From your remarks my guess is you have not used a telescope before. What you are describing as what you see stars may be just a not focused image..
Planets (Jupiter) do have details, but they are not so prominent or catchy for un-trained eye as they are visible on the various photograps, which are usually enhanced with boosted color saturation and contrast. That is especially true for deep sky objects, where you have to have very dark sky (and your eyes must be adapted to dark) to be able to glimpse the shapes and colors. The local weather conditions also play a great role here. You have to leave your telescope outside for a while to let it reach the thermal equilibrium.
And, most of all: you need a lot of patience :-)

[Dave Mitsky]

I did some research on that model. Its f/ratio is a fast f/5 so proper collimation is very important. Your telescope mirror must also be at ambient temperature so some cooldown time is required.

Jupiter is now very much on the wane. When any celestial object is near the horizon, bad seeing (poor atmospheric steadiness) and atmospheric prismatic dispersion often combine to result in mediocre telescopic images.

Very few celestial objects exhibit much color to begin with when viewed through a telescope. They do not begin to look like they do in photographs and digital images. Under good conditions (when its high in the sky, the seeing is steady, and a large aperture is being used) there is some subtle color to be seen in the Jovian cloudtops.

Dave Mitsky

[Kaptain K]

The first thing I would do is take the scope outside in the daytime and look at distant objects. Aside from being upside down, you should be able to get clean, sharp images. If you can't get a clear focus, then you probably need to collimate the scope.

[tellurian83]

Thanks for your suggestions. Whereas, I do not have a lot of experience with telescopes, I have definetely used telescopes before.

With regards to viewing conditions, they are infact quite ideal. However, I take your point, Dave, with regards to Jupiter being near the horizon.

But, as earlier, what is most worrying is the image distortion with objects outside the solar system. I don't think the focusing is the problem - if you focus on a star for example, you should be able to see a bright spot with a airy disc. You can also tell if something is getting near focus because it goes from blurry to less blurry to more blurry again. Now, in the least blurry bit, what I see instead is a just blur of colors with no bright spot in the center. I suppose as you say, Bojan, I might just be being a little too optimistic but I just find it a little suspicious that my old 90mm refractor gave better images than my current telescope.

With regards to the collimation, as far I can tell, its properly collimated (the image is in the center of the secondary mirror) - but is there a low-tech way of checking? (Unfortunately there is no amateur astronomy club in these parts).

Once again, any suggestions, would be greatly appreciated.

Thanks.

[Dave Mitsky]

What you describe regarding star images shouldn't be happening but I'm not sure exactly what the problem is. If your telescope were an optically compromised Jones-Bird design using a spherical mirror, the problem might have something to do with the achromatic lens coma correcter.

Here are some sites with information on collimating Newtonian reflectors:

http://www.catseyecollimation.com/mccluney.html
http://www.fpi-protostar.com/collim.htm
http://www.atmsite.org/contrib/Carlin/collimation/
http://www.propermotion.com/jwreed/ATM/Collimate/Collimate.htm
http://www.amateurastronomy.com/collimate.html
http://web.telia.com/~u41105032/myths/myths.htm

Dave Mitsky

[Bojan]

But, as earlier, what is most worrying is the image distortion with objects outside the solar system. I don't think the focusing is the problem - if you focus on a star for example, you should be able to see a bright spot with a airy disc. You can also tell if something is getting near focus because it goes from blurry to less blurry to more blurry again. Now, in the least blurry bit, what I see instead is a just blur of colors with no bright spot in the center. I suppose as you say, Bojan, I might just be being a little too optimistic but I just find it a little suspicious that my old 90mm refractor gave better images than my current telescope.

Well... then this must be something to do with either coma corrector (does it exist in the system? it is not clear on websites selling this scope) or bad eyepieces (I had a bad experience with certain Meade eyepieces in the past)..

Collimation may definitelly be part of the problem here.... but collimation errors will not produce coloured images of stars, this is the problem created by light passing through optical media (glass), that means lenses... Are you using barlow lens?
Perhaps you should try to test the same eyepieces on your 90mm refractor and vice versa.

If the reflection of you eye (when you look down the tube without eyepiece) looks centered, this still does not mean that the scope is correctly collimated.

Also, it may be worth checking if your mirror is over-stressed in its cell... this will in general produce triangular shaped images of stars when near focus.

[tellurian83]

I unfortunately don't have the refractor or its eyepieces with me anymore. With regards to the barlow - I have the same problem whether I use the barlow or not. (The eyepieces I have are 25mm, 10mm and 7.5mm Plossl and 2X barlow).

I would like to check the collimation but I don't have any instruments to do this. Is it possible with just a normal laser pen or do you really need something more specially designed for the purpose?

With regards to the mirror being overstressed - I'll recheck tonight to be sure, but I think the image could be explained by pinched optics (perhaps an abberation with problems of pinching). I'm a little nervous about opening the scope (I've never really toyed with a reflector before) - so could you tell me how one would specifically go about checking and potentially repairing this?

Thanks.

[Dave Mitsky]

The real issue is that there should be no false color, if that's actually what you're describing, whatsoever with a simple Newtonian reflector. Improper collimation or a pinched mirror would have no bearing on this.

Dave Mitsky

[tellurian83]

I'm not entirely sure what you mean by "false color".... What I see is sort of a distorted diffraction pattern (in terms of shape and size). Is that false color?

But, the telescope is definetely a reflector and what I'm trying to describe is all I can see through it unfortunately.

Thanks.

[Bojan]

Tellurian, with reflector, you should not see any colors at the edges of an image, because the light of all wavelenghts is reflecting from mirrors in a same way (unless the reflecting surface is damaged in some very peculiar way such that it acts as a difraction grating... but this is highly unlikely.
If you see the stars as distroted shapes with coloured edges, this colouring is definitelly happening in your eyepieces. It is strange though that all of them have the similar problem (or do they?). Distortion of star images could be the consequence of pinched mirror and/or poor collimation though, but not necessarily to the extent you are describing. If eyepieces are so bad to cause the significant colur aberartion, they will also produce unsharp images in general.
To check the pinching, you should first determine if there is one.
It is not hard to open the back of the telescope, I guess there will be 3 screws at the back end of the tube that hold the mirror cell.
When you remove it, just check if mirror is tied too hard. The 3 side clamps should just prevet it from falling out of the cell, but there should be no pressure at all at any side to the glass.

To check the collimation, you do not really need a specific instrument, just follow the instructions on links Dave gave you previously.
To do the collimation properly, you will have to remove the mirror cell and clearly mark the exact centre of the mirror with waterproof marker or some sticker (do not worry, the central part of the mirror is not in the game anyway.... except for collimation :-)

[tellurian83]

In fact, I made a disturbing discovery last night as I was trying to check if the primary was pinched. What I noticed were lots and lots of hairline scratches on the mirror. (I have no idea how they got there!) As you say, Bojan this could potentially explain the peculiar diffraction pattern I see. I've never dealt with scratching like this before - there are maybe 100+ hairline scratches. Could that in addition to potentially bad collimation explain what I'm seeing?

If that could indeed be the problem, what do you think my options are? I have not heard back from the Konus people regarding where I should send back the telescope but just getting a new mirror will be cheaper than mailing the OTA back to Italy and then back again. Is this something you would recommend? Is there someway in which the mirror could be repaired? Could I just go to a glass maker here (yes, there are glass makers here) and ask them to fix the mirror or do you think that is that a little too risque?

Thanks.

[Bojan]

In fact, I made a disturbing discovery last night as I was trying to check if the primary was pinched. What I noticed were lots and lots of hairline scratches on the mirror. (I have no idea how they got there!) As you say, Bojan this could potentially explain the peculiar diffraction pattern I see. I've never dealt with scratching like this before - there are maybe 100+ hairline scratches. Could that in addition to potentially bad collimation explain what I'm seeing?

If that could indeed be the problem, what do you think my options are? I have not heard back from the Konus people regarding where I should send back the telescope but just getting a new mirror will be cheaper than mailing the OTA back to Italy and then back again. Is this something you would recommend? Is there someway in which the mirror could be repaired? Could I just go to a glass maker here (yes, there are glass makers here) and ask them to fix the mirror or do you think that is that a little too risque?

Thanks.

Yes, those hairline scatches are the cause for your problem. How this could have happened I have no idea. Maybe the mirror was stressed and partially cracked??!!

Anyway, it is possible that the new mirror may be the only option/
If the glass cracked, there is no point in trying to repair it. Also, there are probably internal stresses still present within the glass so the same thing may happen again.
If the aluminium coating peeled off, then perhaps it may be re-aluminized, but this can be done only in specialized facilities, that means at manfacturer.
So I think you should get another mirror...
Try with the Konus again, this is definitelly the manufacturing fault, it could not happen in the transport or normal use.
If you can not get them to give you another mirror, then you will have to buy a new one...200mm f5 could be ~ US$240.00 (Coulter Optical in US, as an example).
I am really sorry you have all this trouble, I have never heard of anything like this before...What a bad luck..... :-(

[glasspusher]

Are the scraches deep or just very faint, like someone wiped the dust off with a cloth? Very faint scraches that are in the coating only won't affect the image much. It isn't any worse than the dust that collects on the mirror. However, if the surface of the glass has small crack in it, then the mirror is junk. This would indicate that the glass is stressed and it has changed shape and will never give a good image. As for the rainbow effect you talked about, this could be in the EP. But if the mirror has cracks in its surface, then this would also cause the rainbow effect. Wish I could see this mirror for myself. A simple Ronchi test could tell a lot.

[tellurian83]

I also really don't know how the scratches got there - I've never opened the scope before and its always been transported in its original packing. I'm guessing they've been there since I brought it....

But the scrathes are in fact quite faint as far as I can tell. The best description is really hairline scratches (thin and long). I think the mirror is in tact apart from that - there is no "cracking".

Do hairline scratches not result in a degradation of the image? There really isn't any cracking of the mirror. Just a lot of rather long hairline scratches....

I will take try to take a picture of the mirror next week and post it but my digital camera is acting up a little bit... What is a Ronchi test?

(Still trying to contact Konus... lets hope I have some luck...)

Thanks as always...

[glasspusher]

Fine scraches don't cause a real problem. They only scatter a very small amout of light. But there are so many things that do exactly that, small errors in the surface of the mirror, dust on the mirror, the vanes that hold the secondary mirror and so on. All these things tend to rob contrast from the image.
The Ronchi test is a way to check the overall figure of the mirror, or shape of the curve of the mirror. Its a quick easy way to test for large errors in the mirror. There a number of web sites that can tell you how to do the test yourself. The Ronchi grating used can easly be made yourself as well. You only need a piece of thin clear plastic, a sharpie marker and a ruler. Just draw a series of parallel lines as close together as you can on the plastic and you've got it. I've done this myself and it works quite well. It turns out that each line you draw is a series of small lines in its self when viewed at high magnification.
But before going through all the trouble of that, you should try collimating the optics first. It may seem a daunting task at first, however, after you get used to it, its easy and quick to do. Its something you will need to learn anyway if you own a reflector and want good clear views.

[Bojan]

Well.... if you have many parallel scratches on your mirror, this will definetelly act as a difraction grating, destroying your image at higher magnifications.
It all depends what portion of mirror surface they occupy...

To illustrate drastically what paralel scratches can do to a reflected image, just have a look at the reflection from CD. If those scratches are only partly like this, your mirror is bad and has to be replaced (by manyfacturer).

Could you post us a photo of your mirror so we can see what they look like?

[tellurian83]

There are defnitely many many scratches and many of them are parallel. I will try to put up an image of the mirror next week - I will get a new camera then. (After collimating it - I will also try to get a collimating eye piece next week).

Thanks for your all your suggestions.

[tellurian83]

I'm sorry for taking quite so to post. Unfortuantely, I was unable to get a proper picture of mirror posted because my little dingy camera couldn't focus on the scratches without blocking them with its reflection. However, I did properly collimate the scope through a laser collimator but the image quality did not improve.

But I finally managed to contact the shop that sold me the telescope and I just got the mirror back to them so that it can be replaced by Konus. I will defnitely let you know if there are improvements in the image quality once I have a new mirror. (Although, with the current pace of thing, this is not likely to be before 2 months...)

Thanks for all your help.

[Bojan]

Well, astronomers must be patient people ... :-) There are things no-one can speed up :-)
I am quite sure that with the new mirror you will have a decent telescope .
good luck, Bojan