Astrotech 8" RC for 1395USD

[netwolf]

Looks like AT in the US is cutting prices due to cheaper prices from GSO. If the dollar were higher this would be a incredible bargain. I wonder if local retailers of this GSO 8" RC will also drop the price.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2934812/page/0/view/collapsed/sb/5/o/all/fpart/1

[Tilt]

As you mentioned, if our dollar was better that would be a very good deal. At current rates it puts this around the $2200 AUD mark, so its still kind of exy. Andrews has them for $2800, should be interesting to see what happens to the price of the GSO RC's here.

Michael

[Kal]

If you add GST to the $2200 then it brings it up to ~2400ish

I think if you rang Lee Andrews and negotiated then you would probably have a good chance of getting a little bit off that $2800 too.

[gregbradley]

The key question is how accurate are the mirrors.

I read one post on the net that quality checking of mirrors (not sure what type of scope and not necessarily these at all) was simply a guy putting the mirrors on a wall and shining a torch at them from a distance and then checking if they passed or not!

So I would want to see some images from them. RC optics are hard to make and Star Instruments have been making 1/24th wave mirrors for a long time. I believe it takes a long time. I know the Chinese industries pay their workers practically nothing but even so it takes skills and I doubt they have these. Not that they can't learn but it may take a decade or two.

Greg.

[Kal]

If GSO has a guy with a torch doing the QC on their dobs then he must have a pretty decent eye ;)

[marki]

:rofl::rofl::rofl::rofl::rofl::rofl :

With the massive US investment into Taiwan, they have some of the most advanced production facilities on the planet. I am sure they must at least have an inferometer lying around some where :).




I agree and I think many of us are waiting to see pics from these scopes. I remember making a similar comment on another thread about the 1/24th wave optics of the star instrument mirrors. I was shot down in flames by our expert optician and it turns out that the primary and secondary combined only provide 1/4 to 1/8 wave optics which is ok for an instrument with such a large obstruction :shrug:.

Mark

[Gama]

Where do you think the computer your using, and monitor your watching, and most everything in your house, office is made. Hmmm, U.S.A, NOOOOOOOOOOOOOOOOOOOOOOOOOOO

Its 1/24 wave CHINA baby !!


Theo

[Satchmo]

There is no mystery about this. As far as I know those figures are for primary and secondary combined, as a functioning instrument. The Star Instruments web site , who make RC Optical instruments clearlys state that these wavefront figures are Root Mean Square, not P-V .

So assuming the surface figure is smooth, 1/24 RMS would equate to 1/6 wave PV wavefront. In the situation where they are measuring points all over the surface it makes sense to stick to talking in RMS as simply picking the highest and lowest point on the wavfront to define its quality simply makes no sense.

A heavily obstructed instrument like this has its Strehl ratio knocked down into 60's regardless of how good the mirrors are because of the large obstruction, so any wavefront better than 1/4 wave , 1/20 RMS is fine for the job of prime focus.

I did ray traces once that showed perfected optics with a 45% obstruction producced an EER ( Strehl taking into account the obstruction ) of 0.72 and system with 1/4 wave spherical aberration of 0.8 ended up at EER of 0.68 obstructed.

Its the guys doing planetary photography at 4X-5X their native focal length that will pick the difference between 0.95 and 0.8 Strehl wavefronts.

Clearly the lesson is to keep the obstruction to a minimum which generally visual observers, and planatary photographers have the luxury of doing.

Mark

[toryglen-boy]

i didnt understand any of that ....

but now i feel strangely aroused


;)

[Analog6]

Ditto on the not understanding, toryglen boy. It's all double dutch to me, some study ahead obviously.

[toryglen-boy]

LOL

i did understand it really .... :thumbsup:


it was more the passion that was embued by the poster in explaining it


;)

[TrevorW]

Simplified I think it means the're good mirrors for DSO and OK for planetary at high mag but not as good as some.

IMO

[Satchmo]

To calarify :

The Strehl ratio is the proportion of possible light into the the Airy disc that
optics can deliver. In broad terms an unobstructed system can theoretically deliver 1.0 and a system with 1/4 wave P-V of pure spherical aberration delivers 80% into the disc and 20 % scattered into the rings.

My example of the 45% obstructed instrument was to show that a system with `perfect' optics and a Strehl ratio indicating a full 20% more light intensity into the centre of the airy disc ( compared to the the 1/4 wave system ) only achieves a real gain of 5% when the large obstruction is taken into account. In other words it's really a case of diminishing returns seeking perfection in a heavily obstructed instrument..

Hope this is not too arousing :)

Mark

[marki]

Thanks for explaining that again Mark. I couldn't find the thread last night to link to.

Ciao Mark

[Paddy]

:rofl::rofl::rofl::rofl::rofl::rofl ::rofl::rofl::rofl::rofl::rofl::rof l::rofl::rofl::rofl::rofl::rofl::ro fl::rofl::rofl::rofl::rofl::rofl::r ofl::rofl::rofl::rofl::rofl::rofl:: rofl::rofl::rofl::rofl::rofl::rofl: :rofl::rofl::rofl::rofl:

[gregbradley]

That is a good point. Its the strehl ratio at the eyepiece that should be quoted.

Another reason a good refractor can outperform its aperture compared to compound scopes.

However at a certain size compound scopes take the lead as a 10 inch APO is too big, heavy, long and expensive compared to say a 14 inch compound scope.

Where they meet is a point of debate but I estimate from my experience a good 7 inch APO will match or even surpass a 12.5 inch compound scope even an RC. The RC will get a bit more detail but not necessarily a more pleasing image and will take longer exposure to get there.

A 14.25 inch RC though I would say has a definite advantage over a 7 inch APO but is less versatile as reducers do not work on RC scopes with big chip cameras which nearly all new modern cameras are.

So with that in mind are you better off getting an ED120 or EON120 or the APO127 which I think are a similar proce tag compared to an 8 inch RC with unproven and most lilkely poor optics.

Are these RCs made in Taiwan? If they are I would have more confidence in them. Astrotech make really nice refractors.

Greg.

[toryglen-boy]

thank you !!

try the fish, i am here all week


;)

[AlexN]

:) I think I'll be investing in one of these in the not too distant future. :)

Alex.

[KenGee]

I think Greg is right, The Chinese are not dumb. If they could make RC as good or better then say Star instruments why would you sell them for less than a 1/5 of the price? If you have ever been to china you would know, the Chinese know more about capitalism then the yanks. In the end you get what you pay for. A good example The cameras that Theo imports are good, but they are not as good as say Sbig. I’m sure that the guy who makes could learn to make cameras as good, but I bet you the price would be about the same.

[Tilt]

So you already have one in the mail heading your way Alex?

Michael

[AlexN]

Not quite Michael... Waiting on some real world reviews to come out.. I wouldnt spend that kind of money based purely on marketing... :)

[marki]

All right I think I am up for this :sadeyes:. GSO do work out of Taiwan and produce some reasonable products and these RC's look the part if nothing else. Their effectiveness is yet to be seen but I am fairly confident that the optics will perform well enough for the price.

I often read threads that bash CATS due to their central obstruction with arguments based around loss of contrast. Yes contrast is lost but to suggest that you will need roughly double the aperture to achieve comparative results..... well hmmmm. The refractors have an advantage on planets with their higher contrast but lose out with their wide fields and in any case there are only 3 planets worth looking at in my book. The best pics of DSO's are mostly but not exclusively the products of CATS and there are far more than 3 of these :). You just cant beat the brute force of a big mirror and these can be held on target when using refractors as guide scopes which in my book is their best use.:wink2::whistle::D

[Rant finished]

Ciao Mark

[AlexN]

From a fellow CAT supporter.. Here Here!

Mirrors over Lenses any day! :)

[marki]

I am just being naughty Alex although I am currently curled up in the feotal position as I await the fire and brimstone from the refractor gods.:scared3::poke: :P:lol::D.

[AlexN]

lol... what are they going to do... smite you with their sissy scopes? :)

[gregbradley]

This is a funny thread. Its nice to be in an Aussie site where we have a sense of humour and don't take things seriously.

If you want to see some childish behaviour go see the refractors Yahoo Group. Man you would think someone insulted their mother if someone dares say their particular brand of refractor is no good let alone refractors versus reflectors.

I have both types of scope and have had several models of both. I like them both and for different reasons. They both have their appeals and strengths and weaknesses.

Reflectors biggest strength in my opinion is bang for your aperture buck.
Noone really makes a 24 inch APO but they do make 24 inch RCOs's.

Greg.

[marki]

Hi Greg

Great to see you are having a good laugh as well :D. I too have veiwed a number of those forums where it is considered treason to cast doubt on ones beloved possession and some people just take it far too seriously. Different scopes have different uses and they all excell somewhere.

Like Alex I am sitting on the fence when it comes to the GSO RC's but do consider them an exciting prospect particularly if the optics are half decent. I think Marks comment about limited gain for huge amount of work makes it all the more interesting. RCOS scopes are certainly a work of art but much of the cost must come as a consequence of their pursuit of perfection and the value of the brand name. I would certainly like to see what their profit margins are. If the GSO scopes can deliver images even 70% as good as an RCOS then I am definately going to buy one. As for the quality of chinese manufacturing remember the massive investment that has been made by the US and other countries in moving all of their tooling to China and Tiawan. Just about every bit on your computer is made in one of these countries as is just about anything we buy these days. I don't know about the learning curve though as the way I see it is that they are restricting themselves to fill a market niche which will in get more money into the country. Remember who came up with the technology to shoot a satillite out of orbit first, not the yanks but it was a good wake up call for them. The Japanese also come to mind where we all thought their products were rubbish once upon a time.

Ciao Mark

[Satchmo]

The general rule of thumb for the equivelent refractor ( at least in the ability to reproduce low level contrast features is to subtract the diameter of the secondary obstruction. I verified this under good seeing conditions when a stock 10" F6 Newt with 2" secondary clearly gave better images of Jupiter than a 7" F9 Starfire Apo ( and both instruments were well aclimatised. A 14" RC would have about a 6" obstruction at the baffle so a 7" Apo would theoretically be a match for a 14" RC , not in light gathering of course.

Mark

[Satchmo]

Its important to understand that a 50% obstructed instrument reproduces high contrast objects just as well as an unobstructed one. For example high contrast objects like lunar craters, double stars, planetary Moons etc will still look the same in a large obstructed instrument. Its the loss of the ability to reproduce lower contrast detail that is the problem..a lot of planetary detail is in the low contrast area.

The obstruction causes light to be thrown from the Airy Disc into the surrounding rings in the diffraction pattern. In the presence of inclement seeing this can cause star images to appear a little more bloated than they might otherwise . Pure spherical aberration in an unobstructed system will have exactly the same effect. This can sometimes be confused with loss of contrast although it is really loss of sharpness which indirectly effects the ability to reproduce low contrast features.

Mark

[marki]

Thanks again Mark

I must admit I choked a bit when I looked at the RC being built on the ATM forum. A 6" secondary on a 12" mirror, I am suprised any light gets through at all. My LX 200 secondary is only about 3" on a ten inch mirror but I guess it wouldn't light up a full format camera any where near as well though even with the large format visualback.

Ciao Mark

[gregbradley]

I would also be interested in seeing the images from these scopes and I guess until that occurs its all speculation. The proof will be in the images.

In the meantime the US scope make Deep Sky Instruments are using Star Optics and have a much cheaper 10 inch RC than RCOS.

I would not describe an RCOS as perfect or a work of art having owned one. The Star Optics are good and RCOS machining etc is "adequate".
Certainly there are abundant super images from their larger scopes.
Planewave though have probably taken the technological lead from RCOS as corrected dall-kirkhams appear to be a more flexible and superior imaging/visual system than a straight RC. RCOS customer service also is very poor.

Takahashi, AstroPhysics, to slightly lesser degree TEC (their machining is not quite in the same league but their optics are), perhaps TMB/APM have close to perfect products.

Greg.


Great to see you are having a good laugh as well :D. I too have veiwed a number of those forums where it is considered treason to cast doubt on ones beloved possession and some people just take it far too seriously. Different scopes have different uses and they all excell somewhere.

Like Alex I am sitting on the fence when it comes to the GSO RC's but do consider them an exciting prospect particularly if the optics are half decent. I think Marks comment about limited gain for huge amount of work makes it all the more interesting. RCOS scopes are certainly a work of art but much of the cost must come as a consequence of their pursuit of perfection and the value of the brand name. I would certainly like to see what their profit margins are. If the GSO scopes can deliver images even 70% as good as an RCOS then I am definately going to buy one. As for the quality of chinese manufacturing remember the massive investment that has been made by the US and other countries in moving all of their tooling to China and Tiawan. Just about every bit on your computer is made in one of these countries as is just about anything we buy these days. I don't know about the learning curve though as the way I see it is that they are restricting themselves to fill a market niche which will in get more money into the country. Remember who came up with the technology to shoot a satillite out of orbit first, not the yanks but it was a good wake up call for them. The Japanese also come to mind where we all thought their products were rubbish once upon a time.

Ciao Mark[/quote]

[gregbradley]

Interesting.

I had a Nexstar 11 GPS and it gave slightly brighter views than a Tak FS152. But the Tak gave brighter views than an LX90 (8 inch SCT) that I had. So hence the rough conversion - a bit subjective as well.

Small central obstruction seems to be the go for visual.
Its no good for imaging though as it would give too small a corrected field to be useful with today's large chipped cameras hence the 50% obstructions a lot use for astrographs. This makes them less useful as visual instruments.

Greg.

[marki]

HI Greg

Fair comment as I have not owned an RCOS but they sure look look the part to me. There are also a mob out of Russia building RC's which appear to be cheaper then the RCOS as well but like I said whats the cost of a brand name??? The planewaves seem interesting on paper and their spot diagrams etc certainly look promising. Just waiting for Theo to post some stunning images to wow us all :D.

For me I have far too many hobbies to justify spending vast sums of money on astronomy alone and thus would not consider any of the above scopes even if I won lotto (although I wouldn't mind having a go at machining an RC as I have the gear to do that.) My interest in the GSO is two fold. If the optics are ok I can have fun making up other bits to make it better. Secondly I am trying to convince the college where I work to set up an observatory and get kids interested as well as assist in teaching physics in the final years. It is much easier to sell the admin a $3000 scope then a $20 000 scope. Likewise I am sure they would be more interested in a camera costing $2500 then one costing $10000 +.

Ciao Mark

[dpastern]

I'll add my 2.2c inc. GST worth to the debate - I have someone over in the UK who has a Astrotech RC 8" scope, and is going to test it and let me know what it's like. Pending if he ever gets clear weather ;-)

A private discussion with a prominent Australian Telescope retailer indicated that the GSO RCs (astro tech units are rebadged GSOs) that there were issues with collimation with the units, and that pending that being fixed, they would not stock the units. Reading between the lines, I felt that this particular reseller was not impressed with the quality.

I initially considered looking at an astrotech (rather than GSO) RC 8" myself, but have decided on saving up for a Deepsky instruments units 10", which uses the same optics as RCOS does I believe. I'm just a bit nervous about the GSO and derivative units optical quality.

Dave

[Gama]

Collimation is a issue with RC's. This is where it will make or break you viewing/imaging pleasure.
Although next to near impossible to get spot on collimation on a RC, at least the higher end manufacturers have taken precautions and designed measures to counter act as much error and alignment effects when using the collimation/focus system as possible.
Of course paying top dollar you would expect the development time to be quite high.
The higher end scopes are expensive for a reason, but i hope (GSO etc) they also spent many an hour looking at this exact issue with the cheap alternative.

Theo

[dpastern]

Not from the gist I got from this EMail from a particular reseller. By all accounts, collimation was MOST definitely an issue. I presume collimation is difficult because of the hyperbolical mirrors?

Dave