Junk scope? Please advise.

Soldant · #1 07-08-2005, 01:24 AM

(I feel really, really stupid about this.)

Hi guys,

Recently my 6" Newtonian Reflector I received as a Christmas gift last year has been playing up lately. It refuses to focus properly, and when it does, the colour is terrible and it's impossible to resolve any detail in anything at all. When I first got the scope it wasn't like this. I've checked that everything is aligned and as far as I can see, it should be working. I've tried a number of different eyepieces (very little change), swearing at it (helped me feel better but didn't do anything else) and finally researching it online.

I'm now deeply disturbed and worried that it is a junk scope. I'm a binocular observer myself, I love wide views with a bright nebula and milky way, however I got the scope for a bit of planetary viewing and for increased apeture for other DSOs. Lately it's been impossible to use.

(I'm not great with astronomy terminology, I'm a IT hardware services technician so please bare with my basic terms)

The scope is an Optisan (alarm bells already ringing!) 150mm Newtonian Reflector, with Focal Length: 1400mm. I've done some research online (there isn't much, the Optisan site is Polish, I'm entering panic mode...) and from what I've gathered, the scope has some serious problems. Most notably, apparently the scope has a spherical mirror, and the tube is too short?

I don't know how to test this so any information on what to look for would really assist me. My parents (who gave me the scope) took me to the store to talk to the guy about it, who went on with a lot of rubbish and threw Tasco into the conversation claiming that it was a good brand for astronomy (I'm really, REALLY in panic mode here) and also saying all the mirrors for every scope (he even mentioned Meade) are produced by the same people, and they're all the same quality (I almost walked out of the store).

Making matters worse, the equitorial mount doesn't seem to be of good quality either, it has a lot of slack in the controls and even when secured can move around a lot. The finderscope is definately rubbish (plastic! I can see better without it!) but I didn't expect much from it anyway.

What else can I look for to determine if the scope is junk? If it is... ouch, I'll go back to my good ol' trusty 10x50 binoculars (still the best bit of optics I've ever owned). The guy has offered to take a look at it and try to fix it, and then call Optisan (they speak English?) to find out how to fix it. My confidence isn't high after all the things he said in the shop.

Please advise me on this. If it is junk I'm going to be on 10x50's for a while until I can afford another scope, at which point I'm going to buy it myself instead of asking for one as a gift. I don't blame my parents for the gift (the guy seemed to be versed in social engineering when it comes to people who know little about scopes, probably used the ol' magnification line) since they're not well versed on telescopes. Either way, I need to know if it's rubbish and I can turn it into a pointless fishtank (don't laugh, I might actually do this) or do something else with it.

ballaratdragons (Ken) · #2 07-08-2005, 01:56 AM

Soldant,

I can take a very good guess and say it wasn't a telescope shop.

There are a thousand brands of junk telescopes out there and they may all be made in the same factory, but good ones aren't. Even Tasco aren't as bad as what you are explaining.

I would certainly try for a refund. If not, make a jolly good fish-tank.

Just another question before you destroy it though. The little arms that hold the small mirror up at the Eyepeice end, are they thin flat strips of metal only about half a millimetre thick or are they a few millimetres thick?

If they are thick it is certainly one of those $2 scopes.

If they are nice thin flat ones the scope may be salvagable and made to work better.

Some cheapies can actually be improved, but not the $2 ones.

asimov (John) · #3 07-08-2005, 02:12 AM

Hmmm. Interesting. I'm at a loss on how a telescope can give reasonable views & then deteriorate over a period of time to a point that you can see.....as you explain. Or did this suddenly happen? Did you give it a hard knock at any stage?

Sounds like collimation to me. Never actually heard of that brand. I would hesitate to say it's a piece of you know what. Gonna do a bit of googling & see what I can come up with.

Kieken · #4 07-08-2005, 05:07 AM

My first thought was collimation to. Soldant, are you sure that you alligned the mirrors correctly? Have you used some sort of tool?

I've also looked on the site and noticed that the only 6" scope they is a 150mm with focal length 750mm making it an f5. And the mirror is said to be a parabolic one.

One more thing, this scope is not as bad as you think. I own the 4.5" version (mine is from Spectron) but trust me, Optisan scope = Spectron scope

. I've had a lot of great times with it. Nice views of the planets, couple of DSOs. One thing I've should have done in the beginning was buying new EPs. Mine were made out of plastic optics (same for the 2x barlow and 1.5x Image corrector). So try to get your collimation good, and if that works, by yourself 2 new EP's (made out of glass and with coatings) and a decent barlow.

asimov (John) · #5 07-08-2005, 05:51 AM

Yes Kieken I saw that website as well. If it's F/5 it's going to be sensitive to 'ordinary' collimation. It needs to be fairly spot-on for good views. Perhaps a combo cheshire/sight-tube would be a good idea to purchase Soldant

Sounds like the mount could be a problem. In the pics on that polish site, it looks to be way under-mounted!

Kieken · #6 07-08-2005, 06:00 AM

If you would compare it with other chinese mounts I would say this would be an EQ-2. Not the best mount for the scope indeed. Tripod is rather crappy to. Still, the tube should be good enough for beginners, giving nice views of the moon, planets and bright DSOs.

asimov (John) · #7 07-08-2005, 07:32 AM

Yep. Once it's collimated, All the back-lash eliminated on the mount. (If it's possible) A decent finder scope & perhaps a couple of good plossl eyepieces, You'll have yourself a nice scope to last you for a while.

BTW try Andrews communications for the cheshire collimating eyepiece. Get the one with the cross hairs in it. You may have to take the primary mirror out & centre spot it, although you can star-test to get the primary within reason too.

You could hunt for a second hand EQ5 mount? That would hold that tube nicely.

janoskiss (Steve H) · #8 07-08-2005, 08:47 AM

Kieken & John: Short tube reflector, with focal length = 1400mm; not an f5.

Soldant, short tube + long focal length can only mean one thing: short focal length mirror with cheap barlow built into the scope (unless it cost thousands). These are meant to be the worst kind of cheap scopes. (Sorry)

Does this look familiar: link to optrons 6"? If it does, then it's probably fishtank time.

My guess is that if initially the views were OK and now suddenly you are getting a lot of false colour, the built in barlow lens may gotten misaligned. Maybe you can rip it out and try using a real barlow, but it's a long shot.

asimov (John) · #9 07-08-2005, 09:17 AM

Re-position the lens then. If it has one. According to the site (the original site) It's a parabolic mirror. But who know's. I guess Soldant will let us know if it's got the xtra lens in the focuser.

elusiver · #10 07-08-2005, 09:22 AM

could u salvage the mirrors outta those? Be a shame to junk everything.

el

asimov (John) · #11 07-08-2005, 09:26 AM

I wouldn't really know EL...Never had much to do with junky scopes. I've got a little 4.5" reflector, but it aint' junk judging by the views it gives.

asimov (John) · #12 07-08-2005, 09:29 AM

Just scrap it Soldant! Save up & score the 16" dob from Andrews!!

Soldant · #13 07-08-2005, 10:03 AM

Whoa, thanks for the reply guys!

janoskiss hit the nail on the head: except for the color of the tube, that is EXACTLY the same as my soon to be fishtank scope. So exact I'm actually laughing about it.

I've had a friend come over and try to collimate it, and after playing with it for three days we couldn't get it at all. The guy at the shop is offering to do the exact same thing, if the scope is indeed junk, hopefully he'll either break it or won't fix it and refund, though I highly doubt that he's going to do anything of the sort.

About the lense in the focuser: would it, by any chance, happen to look like this?
http://img.photobucket.com/albums/v2...t/isthisit.jpg
That's the only lense in there.

Thanks again for the feedback guys.

elusiver · #14 07-08-2005, 04:45 PM

so there is a piece of glass in the focuser? Your focuser shoudl have nothing in it.. i.e you should be able to stick your finger through the focuser and touch the secondary sort of thing.. but don't touch the secondary.

I really don't know how it all works.. but i woulda thought u coulda used the existing mirrors in a proper 1400mm tube.. and end up with a decent(as long as the mirrors were ok) f9 reflector.

But yeah.. if u can get a refund, get it. Then.. GO FOR A DOB! cause then u can be part of the dob brigade™.

el

asimov (John) · #15 07-08-2005, 05:14 PM

Not all that cluey on it myself. But I think it go's something like this: The lens is there to correct a sperical mirror. In order for a mirror to work sucessfully, it most be parabolic. The lens corrects for this, turning it into a parobolic? Hey janoskiss, is this right mate?
I'm only guessing here, lol.

asimov (John) · #16 07-08-2005, 05:19 PM

Parabolic shape eliminates spherical aberration in telescope mirrors

http://amazing-space.stsci.edu/resou...erabmirror.gif
Spherically shaped lenses and mirrors share a problem: their shape. Parallel light rays that bounce off the central region of a spherical mirror focus farther away than light rays that bounce off the edges. This results in many focal points, which produce a blurry image. To get a clear image, all rays need to focus at the same point.

Changing the shape of a mirror from spherical to parabolic solves the problem. All light rays focus at the same point and the resulting image is sharp and clear.

Soldant · #17 07-08-2005, 05:26 PM

Hmm, looks like it's junk then.
Might have to do a bit of social engineering myself to try to get a a refund out of the guy, but I don't think I have any legal legs to stand on? The guy (interestingly) doesn't advertise them anymore, I was hoping he might have advertised them as parabolic so I could catch him out. Damn.

Oh well. Guess I'll have to wait to win lotto then

thanks for the info.

asimov (John) · #18 07-08-2005, 05:33 PM

re-position the lens, then flog it off to someone you don't like!

Soldant · #19 07-08-2005, 05:39 PM

How would I go about that? It just screws into the end of the focuser, and the glass piece doesn't move inside that black ring thing?

janoskiss (Steve H) · #20 07-08-2005, 05:56 PM

The lens is not meant to correct for spherical aberration. That would be too sophisticated for a cheap scope. It is merely there to act as a barlow, i.e., increase the effective focal length (FL). Notice that the length of the tube is about half the FL = 1400mm. The mirror FL is probably 700mm. This is done to save on construction & shipping cost. Shorter & lighter tube means they can get away with a flimsier mount.

Here is a ray diagram illustrating how the barlow works:

http://members.optusnet.com.au/~janosk/misc/barlow.png

Soldant, if the scope is not fit for its intended purpose, then you have every right to demand a refund. Squeaky wheel gets the grease. So go in there and squeak!