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  #81  
Old 14-07-2013, 11:34 AM
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Agreed 110% Matt. Last night's viewing, for all but the briefest of time, was breath-taking, even in my light polluted suburbia. Absolute pinprick's of stars, with a dearth of colours.

From plonking the mount down to full 3 star alignment then off to perfect GOTOS - 8 minutes. Break down at the end of the night - 2 minutes maximum, including carrying it back into the storage room. And that's just with my own hands.

I personally find telescopes with ANY central obstruction annoying. I have VERY light sensitive eyes, and I can easily detect the shadow of the central obstruction and it really bugs me.

There is something intangible about a GOOD quality refractor that is hard to beat or ignore. If I want to see the whispy details, I'll attach the CCD and do images of it - sure, it'll take MORE subs than a light bucket, but I will get there in the end and without artificial design induced artifacts.
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  #82  
Old 14-07-2013, 11:37 AM
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My point is that the price point of refractors can lead to a stunting of growth in your horizons as an amateur astronomer. My 120ED is about 13kg in its case - similar to a 10" F5 Newt and a 10" is a far far more useful machine for astronomy than a 5" scope ( I hang on to mine with the idea of imaging one day ) . Theres definately a grab n'go zone for refractors and I can understand some people wanting to stay there !

I have no problem with those that stay in small aperture land all their lives- I do have a problem with people who claim their scopes defy the laws of physics.
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  #83  
Old 14-07-2013, 11:43 AM
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Originally Posted by LewisM View Post
I have VERY light sensitive eyes, and I can easily detect the shadow of the central obstruction and it really bugs me.
Lewis - central obstruction shadow or vignetting occurs when the image of the central obstruction in the exit pupil is actually hardly smaller than your eye pupil. If you have noticed this then you must have used low magnifications giving an exit pupil much larger than your eyes' opening and your eye is just not opening up nearly as much as you think either due to ambient light levels and or age. This is not a fault of the telescope - you need to calculate the exit pupil and judge whether you are likely to lose light - is my eye going to be 8mm pupil in this lit urban enviroment or more likely 3mm ? Perhaps I should use a higher magnification.....
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  #84  
Old 14-07-2013, 11:44 AM
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Hi prof, kunama, all.Yes i did exactly that last night on saturn,and enjoyed the view more in the smaller mak than10 sct.Sure there was more resolution in ths sct but the lovely steady crisper image in the mak was visually more pleasing.So go figure!I think we can also confuse resolution with actual sharpness and clarity of image.More bands were seen in the sct BUT the mak served up the more pleasing image hmmm v interesting.Even tuc47 looked good in a nagler with only partial resolution.So there you are then.Or is some of it also the thrill of hunting down faint stuff in smaller apertures also?
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  #85  
Old 14-07-2013, 12:01 PM
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Originally Posted by Satchmo View Post
My point is that the price point of refractors can lead to a stunting of growth in your horizons as an amateur astronomer. My 120ED is about 13kg in its case - similar to a 10" F5 Newt and a 10" is a far far more useful machine for astronomy than a 5" scope ( I hang on to mine with the idea of imaging one day ) . Theres definately a grab n'go zone for refractors and I can understand some people wanting to stay there !

I have no problem with those that stay in small aperture land all their lives- I do have a problem with people who claim their scopes defy the laws of physics.
Mark I agree with what you're saying and I think anyone planning on owning only a single scope with a view to it giving them a satisfying visual experience should look at the 8"-10" reflector as an allrounder. Personally, as I previously discussed with you, my future plans (after I finish the 2 80mm F15 refractors currently being built) include the building of a "Photon Hog" to complement my current 120mm scope, something from 12.5" to 18" range.

Yes there are always going to be claims of small scopes bending the laws of physics, personally I have had enough time with 80mm to 150mm refractors to know where their limits are for VISUAL. Within those limits and expectations these scopes are very enjoyable.

I agree it would be a shame for someone to never venture into the territory of the 12" and larger scopes, even if only borrowed views at starparties.

BUT we digress, the OP asked whether the difference between an ED120 and a top shelf APO 120 was sufficient to warrant the extra $$$$. For me, yes but is it necessary to spend that amount for visual, NO.
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  #86  
Old 14-07-2013, 06:03 PM
issdaol (Phil)
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Originally Posted by Satchmo View Post
My point is that the price point of refractors can lead to a stunting of growth in your horizons as an amateur astronomer.



Not sure what you mean or validity of this statement. I don't see how the price point of refractors can stunt anyone's growth as an astronomer provided they can afford it and use it to best advantage.

Quote:
Originally Posted by Satchmo View Post
I have no problem with those that stay in small aperture land all their lives- I do have a problem with people who claim their scopes defy the laws of physics.
I don't think anyone is claiming that their scopes defy the laws of physics. But there is more to scopes and image quality than just how Big the Aperture/Mirror is. A crappy 20 inch mirror will most probably be worse than a 5 inch APO. Similarly a excellent 20 inch mirror scope that is poorly mounted and aligned in a poorly designed tube/truss will require a lot of effort and maintenance to use.

Also not everyone has small trucks, trailers or wagons to cart around some of the massive "so called cheap" dobsonians

The other thing that I find interesting is the armchair critics that provide seemingly expert comments/advice on scopes that they have never owned or used. ( Not to mention the scope owners that love to try and say that Tak, TV, TEC or AP owners were ripped off or stupid for having paid more than their cheaper Chinese scopes ).

The point is many people have different uses, preferences, budgets etc so their choices may be different for different reasons.
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  #87  
Old 14-07-2013, 06:46 PM
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My experience at Katoomba last week may be what Mark's getting at.

I spent most of the evening happily fiddling with my new mount and the two scopes I had on it - a 110mm ED refractor and a 6" Mak (also new). About 10 metres away were a couple of guys with a decent-sized Dob, I'm guessing around 14"-16". While I was content to find stuff I hadn't seen before, thanks to the Sky Commander on the mount, I was aware that while I was looking at grey "smudges", the other guys were describing glorious spiral arms and other sights that are beyond the reach of small scopes.

I don't feel stunted because I still have a lot to see with my current scopes, but I am certainly aware of their limitations in the detail they can show. And so the next time I get the chance I plan to spend a bit of time away from my own scopes and pester the owners of the big Dobs for a proper look through them.

And as for price point, it is interesting to think what kind of medium-large Dob I could get for the money I've spent on all my "small" gear...
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  #88  
Old 14-07-2013, 06:48 PM
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Originally Posted by issdaol View Post


Not sure what you mean or validity of this statement. I don't see how the price point of refractors can stunt anyone's growth as an astronomer provided they can afford it and use it to best advantage.
Thats simple Phil - if you believe that you must own just high -end refractors you are probably never going to own anything bigger than a 6" refractor and that is going to really narrow the horizons of what you can see. ( And I have indeed been looking through all kinds of telescopes including Tak refractors for 40 years. )

I am not arguing retractors against massive reflectors in this thread - I'm saying that a good 8" to 10" scope is where the field of what you can see and how many objects blows right open and your 4" APO regardless of how much you pay for it is not going to come close in overall usefullness . Phil , I notice you have a 12" Tak Mewlon as one of your two telescopes so you are not limited to 120mm aperture ...

And other designs can do very well, in low contrast resolution of planetary detail . We once had a shoot out betwen a 10" Newtonian and an Astrophysics 7" F9 Starfire refractor under very steady skies and everyone agreed even on Jupiter the view in the 10" won hand down. W must remember that smaller scopes just cannot resolve the seeing which is usally diffraction limited at 4 to 6" aperture - any larger scope unless the seeing is really good will give the perception of a loss of sharpness earlier than one that breaks down a view into airy discs at a similar magnification in X per inch. So the smaller aperture scope has the `sales' advantage of superficially sharper images , becasue it is not capable of resolving the turbulence in the atmosphere.

Anyway I'm not sure what conclusions about improvment of a Tak vs cheaper 120ED which was the subject of the thread. My comment is that if your refractor returns a good star test and is colour free then it is going to be near perfect at the focal plane no matter how much or how little you pay for it . I would maintain as an experienced optician that a lot of the fervent chatter about Taks is due to good quality control which you pay for . Any telescope with freedom from spherical aberration and astigmatism with well polished smooth surfaces will perform brilliantly at the eyepeice- its a zing you can get with any good scope - that feeling that there is nothing in between your eye and the object you are looking at .

Last edited by Satchmo; 14-07-2013 at 07:18 PM.
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  #89  
Old 14-07-2013, 07:09 PM
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Refractors , gotta love them .
87 posts and still going strong .
. Reflecting on this ...

Brian.
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  #90  
Old 14-07-2013, 07:23 PM
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against physics , my Tak sky90 f5.5 and SW 102 f5 , both 500mm f/l's , the Tak shows more on luna, planetary and deep space than the sky watcher? .
Don't give me the "Coatings" thingy , ok , the SW coatings are new generation . The SKY90's are 10 years old , technology wise ? don't think so ..
Please explain ..
( See my post in Celestial events chapter titled this , spotted something this morning ....) ..

In my opinion a 120mm SW using an fl53 doublet APO is the bees knees , grab one and enjoy . Gonna be a classic like the ED80 .

Brian
Quote:
Originally Posted by Profiler View Post
They are generally regarded to be excellent bang for your buck however there are, naturally, some differences with premium brand refractors. For VA it is fantastic however it might be worth also looking at the latest 100mm Tak doublet FC-100DC which is roughly the same price

http://www.astronomy-electronics-centre.com.au/
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  #91  
Old 14-07-2013, 07:31 PM
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If there's such a thing as a usable, cheap massive Dobsonian I've never come across it. And for what it's worth I also own a Tak, as well as a pretty respectable stable of Unitrons, Meades, Celestrons and a few quality home brew optics. Despite this, I have friends; so add in Astrophysics, TMB, Zeiss, Questar, Zambuto and even the obscure Suching to the list of products I've been able to assess objectively over time. Resolution and visual limiting magnitude are a function of aperture. End of story. Get over it. Contrast is pretty much a function of good instrument design and maintenence.

I spent the money on the Tak to get the flat field and good aberration control for photography with a full-frame DSLR. In the world of astrophotography there are plenty of great images online taken with 'lesser' scopes, although once you've stumped up for the upgraded focuser and field flattener you may have been better off with the Tak...
For visual use, which is what this thread is all about, the eye is far more tolerant of field curvature and chromatic aberration than a sensor, and I would imagine that there are few people more qualified than a master optician who owns an ED120 to comment on whether it's as good visually as a reflector of equivalent cost.
I've heard plenty of Tak and AP owners claim that their scope regularly outperforms a scope of twice the aperture, but have yet to see it for myself. And to returen to the topic of this thread, my APO Tak is no better than either of my 30 year old achromatic Unitrons visually, but I love the digital images it produces, and there is no way I could take them through an f15 Unitron.
Cheers!
Andrew.

Quote:
Originally Posted by issdaol View Post


I don't think anyone is claiming that their scopes defy the laws of physics. But there is more to scopes and image quality than just how Big the Aperture/Mirror is. A crappy 20 inch mirror will most probably be worse than a 5 inch APO. Similarly a excellent 20 inch mirror scope that is poorly mounted and aligned in a poorly designed tube/truss will require a lot of effort and maintenance to use.

Also not everyone has small trucks, trailers or wagons to cart around some of the massive "so called cheap" dobsonians

The other thing that I find interesting is the armchair critics that provide seemingly expert comments/advice on scopes that they have never owned or used. ( Not to mention the scope owners that love to try and say that Tak, TV, TEC or AP owners were ripped off or stupid for having paid more than their cheaper Chinese scopes ).
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  #92  
Old 14-07-2013, 07:43 PM
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Hear you Brother , the flat field problem in both my fraks , is not there , The 120 SW's good reviews impresses me every time , its gotta be very good .
as good as my now sold ED80 that had none as well . Nice optics .
So it aint flat field ? . Buy a Panopotic,by TelVue .
Its Refractors , like a Synta 120mm f/8 APO doublet .
That allow us hard working astronomers the chance to own , use and enjoy a top notch Refractor .
Brian.
Quote:
Originally Posted by alocky View Post
If there's such a thing as a usable, cheap massive Dobsonian I've never come across it. And for what it's worth I also own a Tak, as well as a pretty respectable stable of Unitrons, Meades, Celestrons and a few quality home brew optics. Despite this, I have friends; so add in Astrophysics, TMB, Zeiss, Questar, Zambuto and even the obscure Suching to the list of products I've been able to assess objectively over time. Resolution and visual limiting magnitude are a function of aperture. End of story. Get over it. Contrast is pretty much a function of good instrument design and maintenence.

I spent the money on the Tak to get the flat field and good aberration control for photography with a full-frame DSLR. In the world of astrophotography there are plenty of great images online taken with 'lesser' scopes, although once you've stumped up for the upgraded focuser and field flattener you may have been better off with the Tak...
For visual use, which is what this thread is all about, the eye is far more tolerant of field curvature and chromatic aberration than a sensor, and I would imagine that there are few people more qualified than a master optician who owns an ED120 to comment on whether it's as good visually as a reflector of equivalent cost.
I've heard plenty of Tak and AP owners claim that their scope regularly outperforms a scope of twice the aperture, but have yet to see it for myself. And to returen to the topic of this thread, my APO Tak is no better than either of my 30 year old achromatic Unitrons visually, but I love the digital images it produces, and there is no way I could take them through an f15 Unitron.
Cheers!
Andrew.
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  #93  
Old 14-07-2013, 08:15 PM
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Originally Posted by brian nordstrom View Post
against physics , my Tak sky90 f5.5 and SW 102 f5 , both 500mm f/l's , the Tak shows more on luna, planetary and deep space than the sky watcher? .
Don't give me the "Coatings" thingy , ok , the SW coatings are new generation
Brian , the Tak Sky90 is a Flourite Doublet and the SW 102mm F5 is just an achromat ... I would call that a significant `physical' advantage
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  #94  
Old 14-07-2013, 08:35 PM
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Photon thru fare , sthell ratio ? 50 year old eyes , 20 year old eyes ?? , my Takahashi SKY90 shows more than my 102mm f5 Sky watcher , Physics ? man ..
Brian.
Brian ,
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Originally Posted by Satchmo View Post
Brian , the Tak Sky90 is a Flourite Doublet and the SW 102mm F5 is just an achromat ... I would call that a significant `physical' advantage
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  #95  
Old 14-07-2013, 09:42 PM
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As an aside I don't think referencing the Sky90 is probably the best case example. Although it certainly has some avid fans it is probably one of the few Taks ever made that has attracted criticisms as a poor design. The market concept by Tak was to make something to compete and capitalise on the legendary market niche of the AP Traveller. Some think Tak acheived this but others have criticised its degree of colour in pushing the envelope with short fl to be off-set by the genuine fluorite crystal.

However, once again I want to reiterate that it does have some strong supporters/advocates but I wouldn't regarded it as the best design from the Takahashi corporation.
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  #96  
Old 15-07-2013, 08:43 AM
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With respect to objective coatings there are clear differences in the brands epecially with respect to their durability to such things as sky gunk requiring cleaning, moisture damage/erosion and general longevity.

Ironically, the best example I have personally been able to observe of this point in the short term was with two diagonals (a GSO and TV Everbrite) I purchased at roughly the same time.

Initially, I was immensely, immensely impressed with the GSO providing great performance for an absolutely magic price and disappointed with the Everbrite being super expensive and not really any different to the GSO.

To-day, now roughly three years later however I can see deterioration of the coatings creeping in all around the edges of the GSO mirror - the Everbrite is exactly the same so rather than puffs of smoke and bravado I can accept the TV marketing as not merely hyperbole and their products in the context of life time investment etc.

Last edited by Profiler; 15-07-2013 at 03:27 PM.
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  #97  
Old 15-07-2013, 03:57 PM
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I hate to say it, but the only Tak I ever owned - an FS60 - I disliked immensely. The CA on even medium mag stars was REALLY noticeable, let alone on planets. I was very disappointed, though Tak never claimed it to be super corrected (I found it WORSE than a SW achromat I once had). Beautifully made, superb focus (once I got enough damned doodads and adapters to get it to focus!), but the CA spooked me big time. I found the finder better corrected

I note NO CA in my FL102S. Nada, zilch, zip. And that's just a high performance fluorite doublet! And it performs beautifully photographically, no doubt because of it's remarkable Strehl ratio.

I have plans for a WO Megrez... be interesting comparisons...
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  #98  
Old 15-07-2013, 04:21 PM
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Quote:
Originally Posted by Profiler View Post
With respect to objective coatings there are clear differences in the brands epecially with respect to their durability to such things as sky gunk requiring cleaning, moisture damage/erosion and general longevity.

Ironically, the best example I have personally been able to observe of this point in the short term was with two diagonals (a GSO and TV Everbrite) I purchased at roughly the same time.

Initially, I was immensely, immensely impressed with the GSO providing great performance for an absolutely magic price and disappointed with the Everbrite being super expensive and not really any different to the GSO.

To-day, now roughly three years later however I can see deterioration of the coatings creeping in all around the edges of the GSO mirror - the Everbrite is exactly the same so rather than puffs of smoke and bravado I can accept the TV marketing as not merely hyperbole and their products in the context of life timeii investment etc.
Prof hi.If thats true then it could apply to all clones etc when ot comes to longevity o f coatings.Could it be just possible that the Gso which I also have coulld have been used more often and thus exposed to the elements more often and thus cleaned more often etc.leading to loss of coatings.Otherwise Im keeping my fingers crossed with mine
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  #99  
Old 15-07-2013, 04:55 PM
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Actually Lewis, it performs well because of its relatively slow f-ratio. Strehl is usually an on-axis measure, and the faster the scope the harder it is to keep under control as you move off axis. That's why the FSQ has 4 elements, and most of the 3 element APOs are a lot faster. Before fluorite glass was available, a flint and crown doublet around 100mm had to be f15 or thereabouts to produce an acceptable fov. That's how vixen killed Unitron!
Cheers,
Andrew.

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I hate to say it, but the only Tak I ever owned - an FS60 - I disliked immensely. The CA on even medium mag stars was REALLY noticeable, let alone on planets. I was very disappointed, though Tak never claimed it to be super corrected (I found it WORSE than a SW achromat I once had). Beautifully made, superb focus (once I got enough damned doodads and adapters to get it to focus!), but the CA spooked me big time. I found the finder better corrected

I note NO CA in my FL102S. Nada, zilch, zip. And that's just a high performance fluorite doublet! And it performs beautifully photographically, no doubt because of it's remarkable Strehl ratio.

I have plans for a WO Megrez... be interesting comparisons...
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Old 15-07-2013, 05:08 PM
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Prof hi.If thats true then it could apply to all clones etc when ot comes to longevity o f coatings.Could it be just possible that the Gso which I also have coulld have been used more often and thus exposed to the elements more often and thus cleaned more often etc.leading to loss of coatings.Otherwise Im keeping my fingers crossed with mine

I thought about that as a possibility - also - I may have simply been unlucky and got a bad one off the line but usage would be reasonably even overall or if anything more towards the Everbrite. Initially, I used the GSO until I purchased the Everbrite and then I used it instead of the GSO. Either way a bad diagonal isn't a big issue but I think it does highlight issues with coatings and I certainly wouldn't be so blase' with similar problems in objective coatings
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