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  #61  
Old 01-04-2009, 02:46 AM
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Tandum (Robin)
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OK Darth ... how much for a real 8" RC scope from you're company ?

I think what you don't understand is that we are not professionals and do not buy professional equipment.
  #62  
Old 01-04-2009, 02:47 AM
Vader (Valery)
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Quote:
Originally Posted by Tandum View Post
Vader,
Do you have any results from other domestic scopes as a comparison? I notice this 8" RC is mechanically a Vixen VC200L copy. There is no point comparing it to a 16" anything. No one here can lift a 16" scope.
The best comparition is interferometric test. I am not interested in
any these subjective comparitions at a backyard. Interferometer and
star image in collimator tell me all I need. You can surf that test scopes
site and you will not see such a crap telescope like this 8" RC by GSO.
Not even close.

However, if you all think, that I trying to foolish you all telling false
info, no problem, buy these craps and be happy.

Last edited by iceman; 01-04-2009 at 06:05 AM.
  #63  
Old 01-04-2009, 02:50 AM
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Octane (Humayun)
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Robin,

There's no need to be like that.

Part of communicating effectively is dealing with cultural differences.

I, for one, am swayed by Valery's arguments. I was initially going to spend my money and buy one of these things, but, my mind's changed now.

Regards,
Humayun
  #64  
Old 01-04-2009, 03:03 AM
celstark (Craig)
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Guys,

I think it's time we give Valery here a bit of slack. Is he a bit ... forceful ... in his delivery? Sure. He is and as long as I've "known" him on the net, he always has been (and there certainly have been times I've not agreed with his views). But, he knows a lot about optics and about telescope making and the advice he's giving here sure seems devoid of personal, financial interest. He's not telling anyone here to skip the GSO and get something he sells. (FWIW, I believe he's including the f/10 ACF scopes in with the f/8 RCX, so yes, those are available and at least in the US, an 8" f/10 ACF is the same price as the GSO f/8 RC).

I've looked long and hard at those results and they really are just plain ugly. FWIW, the fact that they are ugly has been discussed over on CN and that thread wasn't pulling any punches either. There's been another test of the scope that had it fare a bit better, but still not great:

http://74.125.91.132/translate_c?hl=...ONh17AmH_sT6Yw

There, the P-V ended up at 1/3 wave and the Strehl at 0.89. To my untrained eye, it looked worse than a Strehl of 0.89 would indicate.

There is one thing that's not been considered much in the discussions of these results and that is that as these are meant as amateur astrographs for long-exposure work, we'll all have an inherent blur imposed on our images. How much better would something with a cleaner PSF look after 5-10 minutes of a 3" FWHM atmospheric blur when sampled at 1-1.5"/pixel? If scopes off the line end up more like the telescope-service site's test and we impose our typical smear over the images, I'd not be surprised if the results weren't too far off when stacked up against the competition.

Craig
  #65  
Old 01-04-2009, 03:42 AM
Vader (Valery)
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Quote:
Originally Posted by celstark View Post

I've looked long and hard at those results and they really are just plain ugly. FWIW, the fact that they are ugly has been discussed over on CN and that thread wasn't pulling any punches either. There's been another test of the scope that had it fare a bit better, but still not great:

http://74.125.91.132/translate_c?hl=en&sl=de&u=http://www.teleskop-service.de/Testberichte/cassegrains.gso.rc.200mm.php&prev=/search%3Fq%3Dgso%2B8%2522%2BRC%26hl %3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-USfficial%26hs%3DIA0&usg=ALkJrhhd fFj20i2M200RONh17AmH_sT6Yw

There, the P-V ended up at 1/3 wave and the Strehl at 0.89. To my untrained eye, it looked worse than a Strehl of 0.89 would indicate.

Craig
It is quite obvious, that reference points at this interferogram were not
correctly placed. They were manually placed with intention to smooth down interferometric fringes - this makes final figures better.
I can bet for a lot of money, that if I will process this interferogram with
our professional software with 5-8K reference points placed automatically,
the results will be not better than Strehl 0.6 - 0.7.
This is not totally crap, but very poor. If we consider a large central
obstruction, then a real Strehl will be 0.5 at best.


As for star images during long exposures. This effect is even more
visible in large professional telescopes. However, I don't remember
even one order for professional optics with technical requirements
lower than about 0.9 Strehl.
As better your scope optics, as better star images you will obtain under
similar conditions.

As for the picture of galaxy given at that page. Too small scale for
such a long focus.
  #66  
Old 01-04-2009, 03:58 AM
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avandonk
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Robin the Vixen VC200L is a Klevtsov design. All surfaces are spherical hence 'easy' to manufacture very accurately. It is a very nice scope.

I am a bit older than most of you blokes and sheilas and I remember when a naked eight inch 1/8 wave parabolic mirror cost close to a thousand dollars in the early seventies. A large aperture APO was 70mm (with green writing on it) and cost several thousand dollars. All these prices are in seventies dollars.

They said it about the 80ED
They said it about the big Dobs

and now They are saying it about RC's

We shall all see very soon.

Bert
  #67  
Old 01-04-2009, 04:03 AM
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Tandum (Robin)
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Quote:
Originally Posted by Vader View Post
OK, buy these RC. Your money - your choice.

BTW. If you are so smart, why you are not rich? I think you are not
smart. Not even close.

Farewell.
Being rich is a state of being, but it appears you see it differently..

Why am I defending the fort ??

I'm outta here ....

Last edited by Tandum; 01-04-2009 at 04:27 AM.
  #68  
Old 01-04-2009, 04:28 AM
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avandonk
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Vader if you are still here don't take this personally but you could have been a bit more diplomatic. The last person that asked me why I was not rich if I was so smart I showed him the door. He too has done really well in the GFC meltdown NOT!. I felt like slamming his puerile mind inside of what he called a head in the door. I fortunately stopped myself as I did not want to damage my door on a twit.

Bert
  #69  
Old 01-04-2009, 04:34 AM
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Tandum (Robin)
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Didn't this start with a piece of glass in a tube ? How do you get obsessive about that?
  #70  
Old 01-04-2009, 05:56 AM
celstark (Craig)
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Quote:
Originally Posted by Vader View Post
It is quite obvious, that reference points at this interferogram were not
correctly placed. They were manually placed with intention to smooth down interferometric fringes - this makes final figures better.
I can bet for a lot of money, that if I will process this interferogram with
our professional software with 5-8K reference points placed automatically,
the results will be not better than Strehl 0.6 - 0.7.
This is not totally crap, but very poor. If we consider a large central
obstruction, then a real Strehl will be 0.5 at best.
I see this now and this makes sense. The points don't follow the midline of the bands there but are a lot smoother than that. There are clear ripples that the points don't follow at all. At least my take as to what a ~0.9 Strehl should look like here wasn't off then.

Thanks,

Craig
  #71  
Old 01-04-2009, 05:58 AM
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netwolf
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Vader, while i might agree that you seem to have some knowledge of optics and may infact be an expert on the matter. Your way of making your point shows a lack of tact. Perhaps this is lost in translation as english is not your first language. But your tone of crap crap crap is so strongly biased that any Wise person would always have to suspect something is not right. Was the sample that was tested not good yes looks like it. But to say all is crap is to say you are all knowing and I am sorry even the smartest person is not all knowing.

Before you just attacked GSO quality, ok I dont care I am not GSO. Now you attack/insult a fellow forum member and you are starting to get on my nerves. I dont care if you are the most knowledgble expert or even Roland Christensen himself. You got no right talking to anyone like that.

So STOP THAT RIGHT NOW.

Especially someone who has contributed more here than yourself.

Again i give you chance to apologise and tone your coments down. Be wise and tactful if you are indeed knowledgeble and smart. Otherwise all you will ever find is the exit. And what good is your welth and smart knowledge if you have no where to share it. Who is richer?

Regards
Fahim
  #72  
Old 01-04-2009, 06:11 AM
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iceman (Mike)
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Well we left this thread go with the hope it would get back on track, but unfortunately it spiralled the other way with personal insults and attacks.

The offending posts have been removed.

This thread will be locked now.
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