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What is a similar scope to the Questar optics wise?

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31 replies to this topic

#26 Bomber Bob

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Posted 01 August 2019 - 04:20 PM

Buy used, and save $2000 to $4000.  I got my 1958 Standard from Gary Hand, and it looked mint on delivery.

 

Yes, my Vixen 80mm F8 fluorite beats my Q on every object type, and it's much more versatile (wide field to high-power planetary); but, even though I've taken steps to keep it light, it's still much heavier & clunkier to deal with than my Q on a Meade 884 tripod.  I don't know of any scope available that beats the Q 3.5 for portability, functionality, and ease-of-use.  It is a shoe-box observatory.  And yes, the mechanics & cosmetics are top-notch.

 

No, I don't think it should be your only scope.  Look at my signature inventory (yeah, I'm trying to down-size).  I have lots of options.  I bought the Q for my decrepit years, and haven't used it much -- trying to keep it preserved.  But these scopes can take regular use.  And the more you use them, the more amazing they are, as the design has held up for over 60 years.  


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#27 munirocks

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Posted 12 August 2019 - 07:16 AM

Another Maksutov Cassegrain similar to the Questar is the old ETX105.

 

I compared the two over the weekend (optics-wise only, as my ETX105 is the OTA only). It was daytime, comparing distant moss, spider webs, and insect legs from about 100 feet away. The Questar was slightly sharper but it was really very close. I'd say that resolution-wise my ETX90 is 90% of my Questar, and my ETX105 is 95% of the Q. (Not 105%, just in case you were hoping for a simple algorithm.)

 

I've also heard (unconfirmed) that because the ETX105 uses the same base as the ETX125 but weighs less, the ETX105 is the best optics-mount combination of the old ETX series. (Although I don't think the 105/125 base has any manual controls that you can use, in case the electronics give up the ghost.)

 

They say that all other things being equal (figuring, coatings, baffling, etc), aperture always wins. But the "other things" are never equal. After my experience with ETXes (which are very good indeed optically) I'll go out on a limb and say that if you want a Cassegrain (Mak or SCT) that matches the Q optically then you need to look for a well-figured well-designed system that is about 20% larger than the Q.


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#28 GQuestar

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Posted 11 October 2019 - 11:54 AM

I’m new to using a Questar... just got my first yesterday.

One figure I’ve been trying to find on the Questars to compare against my other scope is the highest useful magnification level...

I found this in the included Questar manual and just loved reading this (answering my question, I think):

 

“We ask the ultimate of this class of “perfect” instruments.  Their images must stay sharp and clear at powers so high that the limit of useful magnification is set only by external causes, such as turbulence of air or dimness of the object viewed”.

 

What a statement!

I’m I reading it correctly that there is NOT a defined highest/lowest useful magnification level, it’s just based on your seeing conditions at any given time?

 

What’s the highest power you guys are having success with?

 

Thanks, Greg



#29 Gregory Gross

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Posted 11 October 2019 - 02:28 PM

The widely cited rule of thumb is 50x per inch of aperture. But according to my own experience with any scope (Questar or not), my practical and admittedly conservative maximum under *typical* seeing conditions is around 35x per inch of aperture. (I have a feeling that statement of mine will stoke debate.)

 

I know that Questar optics are more than a notch or two above mass produced optics, but I still think that no telescope can break the laws of physics. 90mm of aperture can gather only so much light. On top of the quality of the optics, the light gathering ability of a telescope determines how well it resolves an object. To be sure, the quality dimension can't be dismissed: a 10-inch telescope with sub-par optics will simply not provide as pleasing a view as a smaller scope with superior optics especially at high power. But there is a practical limit to what a small scope can do no matter how good its optics are.

 

GQuestar, I know your 1960 scope comes with an 80-160x eyepiece, the 160x magnification being achieved by means of the internal Barlow. In your experience, how well does your Q perform at that magnification?



#30 Loren Gibson

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Posted 11 October 2019 - 03:51 PM

What a statement!

I’m I reading it correctly that there is NOT a defined highest/lowest useful magnification level, it’s just based on your seeing conditions at any given time?

 

I can give you one data point, my own experience with my Questar. Yes, when the seeing permitted, I was using my 6 mm Brandon and the barlow for 400x, about 110x per inch, and full image sharpness was amazingly preserved. The only things I looked at with magnifications like that was the terminator of the moon and the sun, using the Questar full-aperture solar filter. I also used this to examine tight double stars.

 

If the seeing isn't near perfect, these kinds of magnifications don't provide pleasing images. I think Gregory's 35x per inch rule for high magnification is probably a good one for typical seeing in many locations, although your peninsular FL location may give you typical seeing that is very good! You'll have to see for yourself what works for you.

 

Image dimming makes extra-high magnifications useless for most objects, and even on bright objects the extra magnification does not reveal more detail than the more ordinary high magnifications. It just makes the same details bigger. Also, when you push the magnification too high on (for example) Jupiter or the moon away from the terminator, you lose the ability to see the subtle changes in surface brightness, so you don't see Jupiter's belts or adjacent different tones in the moon's surface that you can at modest magnifications.

 

I'm not using those kinds of high powers any longer, as the tiny exit pupil results in enough eyeball debris being seen to be somewhat distracting (with the sun and moon especially). A typical high power for me now is with the 16 mm eyepiece and barlow, 150x. I occasionally up it to 200x with the 12 mm eyepiece and barlow.

 

Loren



#31 Gregory Gross

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Posted 11 October 2019 - 04:17 PM

Loren's thoughtful comments made me realize that I should have added in my own earlier posting to this thread that I base my 35x-per-inch-of-aperture rule on planetary observing. When observing the Moon and Sun, I rarely go larger than full-disk observing, so I never really explore the limits of magnification on those objects. Planetary observing, however, is another animal altogether. It's that area that I find myself exploring the limits on how much magnification I can throw at Jupiter and Saturn in particular. There, too, I should also add that, since these planets have been at low altitude in recent years, it's all the more challenging to get crisp high-power views. Especially as Jupiter rebounds to higher altitudes in, say, three or five years, I'll be keen to re-evaluate my 35x-per-inch-of-aperture rule.

 

One advantage a scope the size of a 3.5" Questar has over, say, my C8 is that the smaller scope has to look through a narrower column of atmosphere out into space and is thus less prone to the effects of bad seeing. Lately, I've gotten surprisingly sharp but significantly dimmer views of Saturn in my Synta-built 4" Mak and Orion Edge-On 9mm eyepiece (144x). Most often, I use either a 14.5 or 12.5mm Edge-On eyepiece with my C8 for planetary observing (140x and 163x, respectively). The view is much brighter in the C8, but I find I rarely use my 9mm eyepiece (225x) in that larger scope simply because the seeing just doesn't permit it most often.

 

I will also admit that my '62 Questar has failed coatings, so any high-powered views in that scope are compromised. This discussion is all the more fuel on the fire in terms of me wanting to restore the optics on my Q. Still, my expectations about what that little scope can do are tempered by simple virtue of its small aperture. But who knows? After I get my optics fixed up, maybe those expectations will be confounded just like my initial expectations with what my Q can do even its current state were (see this recent post of mine).


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#32 RichA

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Posted 11 October 2019 - 11:30 PM

I've heard say that the tele Vue TV-85 is very similar in optics.  Obviously, it's a refractor rather than a Maksutov, and f/7 rather than f/13 (13.5?) but I think it's very similar in optical performance.

 

Just my 2 cents worth...

 

smp

TV76 is a better comparison.  Lower resolution, but light throughput is similar and apochromatism closer to the Q3.5.


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