Re: 127mm Mak-Cas or Orion 80ED?
From: David Nakamoto (res07oeg_at_verizon.net)
Date: 01/30/05
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Date: Sun, 30 Jan 2005 01:33:10 GMT
"Szaki" <szaki10@comcast.net> wrote in message
news:Dr6dneujJY1RvGHcRVn-vQ@comcast.com...
> I'm a user not a builder of telescopes. Good quality APO refractor, one can
> push over 100x per inch on a good seeing night, compound telescopes like the
> Mak, lucky if you can do 50X.
> I'm getting tired of arguing with Newt,Mak, SCT guys about this, cause I know
> they put down refractors for the price/aperture.. What I'm telling you is from
> experience, not from theory.
Same here. Obviously you're not reading my message carefully enough. I pointed
out legitimate and KNOWN deficiencies in relatively short focal ratio
inexpensive two-element refractors, while acknowledging the benefits that others
have pointed out.
And what you call theory is the collective wisdom of many decades of visual
amateur astronomer experience from a lot of people on this newsgroup. You
obviously have a strong and I must say skewed bias toward refractors, without
taking into account the differences in performance brought about by such things
as focal ratio, two vs. three-element design, et al.
And I own a short focal ratio refractor, so I know something from personal
experience, if you're going to tout that out as your badge of authority. And
one thing I would not do, which you do, is to think that a refractor is a
refractor is a refractor. Focal ratio and objective design DOES MATTER, but I
doubt you understand this, given your responses to my messages.
Whatever experience you think you have, it's clear to me you need a lot more
before you can make cogent and fact-backed statements. That, and read the
messages your responding to more carefully.
> I owned all those scopes, but I don't give up my refractor. After owning many
> telescopes, I settled to C102F APO refractor (most used), 4" Mak( MTO-11CA
> 10/1000 Telephoto Lens) for portability and a Ultima C-11 OTA for DSO's. They
> all fit on my EQ mount or the GiroII for alt/az movement.
> All these telescopes are very portable and easy to store, I know the pros and
> cons of these scopes also.
> My 4" Mak don't even come close to my TV Pronto I use to own. I heard good
> things about the Orion80ED.
So have I, but the fact remains that those reports I've gotten from observers
who I know to have lots of experience evaluating telescopes of various designs
and makes have said it was good for a two-element short focal length refractor,
meaning it will perform within the expectations of such a telescope, and NOT
like a longer focal ratio one, or a three-element one, or an expensive one, et
al.
> One has to use barlows for short focus length refractors, to get higher
> magnification, that's all. I hate to use a Mak for terrestrially, long focus
> length, narrow field. Yak!!!!
But the Mak will deliver 2.4 times the magnification for the same eyepiece, so
it is also capable of delivering higher magnification, important for planetary
viewing. And in any case, I don't think that, given what I've heard and seen of
the Orion 80ED at star parties, that you can push it much past 30x per inch of
aperture, so your objection that this is the "limit" on the Mak (something I
also disagree on, from collective experience) is moot.
And the original poster asked specifically for planets and the Moon. Why drag
terrestrial viewing when it was not specified? In this case, the Mak is an
instrument he should consider, given that for a given eyepiece it will deliver
more magnification, less color dispersion, and potentially sharper views, if the
contrast isn't too bad.
--
Sincerely,
--- Dave
----------------------------------------------------------------------
It don't mean a thing
unless it has that certain "je ne sais quoi"
Duke Ellington
----------------------------------------------------------------------
> "David Nakamoto" <res07oeg@verizon.net> wrote in message
> news:i6UKd.1078$UB6.973@trnddc01...
>> Szaki, you're thoughtless in your answers, as simple math will show.
>>
>> We're talking about an f/7.5 system in the 80ED, which you would have known
>> if you took the time to visit the Orion website, and thought anything about
>> giving correct answers instead of "showing off", and doing research before
>> writing anything down. This means the focal length is 600mm. Since "focal
>> length of telescope" / "magnification" = "focal length eyepiece", 600 / 250 =
>> 2.4 mm. Even if such an eyepiece exists, it also means you're pushing 80x per
>> inch aperture in a two element 80 mm telescope, only possible with the best
>> optics (which the Orion is not), long telescope focal ratios, and under
>> absolutely steady nights.
>>
>> And your comparison is not correct either. You're comparing a 3-inch f/15
>> refractor to a 3-inch f/7.5 refractor (the Orion ED). No matter what you do,
>> you cannot achieve as much magnification through the same eyepieces from the
>> latter as through the former. As anyone who knows optics knows, figuring and
>> testing long focal ratio systems is easier than short focal ratio systems
>> (steepness of curves as well as tighter requirements on the figure of the
>> curves for the short focal ratio systems are two reasons). I have no doubt
>> that a 3-inch f/15 refractor, if properly made would outperform a similarly
>> sized Mak (127 mm aperture and f/12 focal ratio) but we're not comparing such
>> a Mak to an f/15 instrument, but a much shorter focal ratio instrument.
>> Color dispersion is greater in such systems and affects performance, while
>> the Mak is more immune to such effects.
>> --
>> Sincerely,
>> --- Dave
>> ----------------------------------------------------------------------
>> It don't mean a thing
>> unless it has that certain "je ne sais quoi"
>> Duke Ellington
>> ----------------------------------------------------------------------
>>
>> "Szaki" <szaki10@comcast.net> wrote in message
>> news:Cf6dnVEC9em8mmHcRVn-3Q@comcast.com...
>>>
>>> "David Nakamoto" <res07oeg@verizon.net> wrote in message
>>> news:wqQKd.403$zb.85@trnddc07...
>>>> While I agree with other posters about the optical properties of the
>>>> refractor, there are two things that you should also keep in mind. First,
>>>> the Mak you mentioned is capable of over 2.5x the magnification of the
>>>> refractor you mentioned due to its focal length,
>>>
>>> That's a bull! Orion 80ED should do 250x or more any day, so 2.5x the Mak127
>>> magnificatain, as you suggesting, would put it over 600x. Never
>>> happened!Hahahaha!
>>> I owned 6" Intes-Mak-Cass, much finer and more expensive OTA than the Orion
>>> 127 Mak, but it had to have excelent seeing to perform. My 3" f/15 Edscorp
>>> refractor regularly out perfomed the 6" Mak when the seeing was not there.
>>> Mak has a larger central obstruction (<37%) than an SCT has, so one has to
>>> deal with large, multable diffrection rings around stars or the moons of
>>> Jupiter.
>>> Person who used to refractor images, would puke.
>>> Julius
>>>
>>>
>>>
>>>
>>
>>
>
>
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