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New to CN - looking for advice... small fast refractor

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#1 felicity

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Posted 03 April 2020 - 02:38 PM

Hi there

 

New to CN. And returning to astronomy after a long hiatus. In the mid-90's had a celestron cg11 which didn't get used much after purchasing an AP Traveler from Roland.  Got out of astronomy to pursue wildlife photography - and those canon big whites and pro-bodies cost a fortune so sold everything.

 

Now retired, I'm looking to get back into astronomy - visual observing only for now... imaging will come later.

 

Need some advice. Thinking of buying an APM 120mm apo and a small refractor to mount side by side on a Losmandy AZ8 and a Planet tripod.

 

But I'm torn on the small refractor. I've looked at the Tak 106fsq (there is at least one for sale used on CN) - but there's also an "original" TMB 105mm f/6.2 LZOS CNC triplet for $2200.

Stick with the Tak or save a couple of thousand and get the TMB? I assume it will remind me of my old AP Traveler??

 

All advice appreciated. By the way, I have looked at the CN forums for a month or so now, and appreciate all the reviews and thoughtful commentary. Glad to be returning to astronomy and glad to join a great community.

 

Thanks, Felicity


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#2 Codbear

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Posted 03 April 2020 - 03:33 PM

Felicity,

 

Welcome back to astronomy! I too took a 25 or so year hiatus with raising kids, swim meets, softball games, etc. I never fully exited, keeping my trusty TeleVue Genesis sdf all those years, and always kept my Astronomy/S&T subscriptions going.

 

I'm enjoying the hobby as much as I did as a teenager, but with just slightly better equipment than my Edmund 4 1/4" f/10 reflector! lol.gif

 

I can only speak from a visual standpoint, but what I like to do is pair off telescopes that excel at different specialties. For example, having my TeleVue NP101is and Questar 7 out at the same time covers all my bases. The 4 degree FOV and f5.4 of the 101is is fantastic with its pinpoint stars and wide field for framing globs or looking at open clusters.

 

But when it comes to stepping up the magnification, the Q7 does magnificently with its f14 on planets, lunar, and DSOs, where the contrast really comes out. You will surely figure out what works best for you and what you enjoy the most.

 

Btw, I lurked for a couple of months before signing on to CN and you can't find a better and more helpful group of people here!

 

Sam


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#3 kmparsons

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Posted 03 April 2020 - 04:28 PM

As for small, fast refractors, one of the fastest and best is the AT92mm. It is fast at f/5.5 and the triplet lens gives beautiful views. I have had mine for about nine months now and it delivers every time. I had it out a few nights ago on the first clear night we have had in weeks in SE Texas. There were a number of lovely sights. Venus was a searchlight, so bright that it was almost painful, and just above it were the Pleiades. Orion, now sadly sinking towards the west, was big and beautiful, and the moon--one day before first quarter--was striking. 



#4 felicity

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Posted 03 April 2020 - 04:53 PM

Thanks Sam and Keith for your replies. For the moment, I guess I'll just buy the 120mm ed apo bins from Markus, and wait on the refractor till I hear more about that original TMB or a Tak 106fsq.

 

cheers Felicity


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#5 samovu

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Posted 03 April 2020 - 06:08 PM

Just my dos centavos (two cents), Felicity, but I’d get the LZOS. And that’s coming from a true Takahashi addict. I’ve only had experience with the TMB/LZOS 130/780 and it is truly a stunning performer. I kept it and sold my heavy TOA130F. And others seem to rave about LZOS ota’s also. 

 

If you’re going to do AP, then the FSQ would be better IMHO. I have the old FSQ106 although I don’t do AP. With the dedicated extender-q, it’s a great performer for planets, my main targets when viewing from my light polluted backyard. 

 

Cheers,

John



#6 samovu

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Posted 03 April 2020 - 06:09 PM

And welcome to CN!

 

Cheers,

John



#7 felicity

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Posted 03 April 2020 - 07:54 PM

Thanks John - not sure about astro imaging ... looks time consuming, and I already spend way too much time photographing wildlife - just recently deleted 90,000 images to free up space on the drive. BTW - I am interested in the tak fsq simply for the fast glass - kind of irrational I know...



#8 Jared

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Posted 03 April 2020 - 08:26 PM

I know you are used to faster glass in photography being synonymous with better glass. That is not the case with telescopes, though. With a camera, since your “eyepiece” is fixed, faster glass gives you a brighter view. But with astronomy, you get the extra degree of freedom of adding an appropriate focal length eyepiece for the framing that you want. End result? Faster telescopes do not yield brighter views visually. They also usually yield slight lower quality views for a given aperture, though with a well made and well corrected refractor the differences are often slight. Basically, the only advantages for visual use to a faster telescope are a shorter, lighter tube and the possibility of getting wider fields of view. The trade offs are higher levels of chromatic aberration, more spherochromatism, the need for better figured glass for a given level of correction, and the need for very short focal length eyepieces that may have uncomfortable eye relief for planetary and double star viewing.

You may know all this already given your history in astronomy, but I thought I would mention it just in case. It can be hard to get over the photographer’s bias towards fast glass.

Neither of the two scopes you are looking at will remind you of your Traveler in terms of size and weight. For their aperture, they are both relatively bulky and heavy. Both are optically superb. The 92mm that was recommended earlier is the closest current equivalent to your Traveler, though it does give up a few millimeters of aperture—enough to be noticeable.

If you don’t think you will get into astrophotography, the TMB is a great choice. It’s heavy, but the optics are really good. If you think you might get into astrophotography, the FSQ is the obvious choice. It’s perhaps the best 4” class astrograph ever made. If you just want something small, light, optically excellent, easy to transport, and reminiscent of your Traveler for not too much money, the AT92 is probably the best choice. It’s an updated version of a TMB design.
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#9 samovu

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Posted 03 April 2020 - 09:41 PM

Thanks John - not sure about astro imaging ... looks time consuming, and I already spend way too much time photographing wildlife - just recently deleted 90,000 images to free up space on the drive. BTW - I am interested in the tak fsq simply for the fast glass - kind of irrational I know...

What’s being rational got to do with getting what you want? Lol! Me, I rationalize. I figure that if I get a used Tak or LZOS glass in an OTA (or any one of the several more expensive and more desirable manufacturers), I can always sell later and get most, if not all, of my “investment” back. Sort of like paying rent as I mentioned in another thread recently. 

 

Others feel that getting a premium brand is not worth the extra expense and can find excellent examples of good scopes at reasonable prices. And that’s fine. And they, too, can sell and lose little as long as the bought used. But I digress. 

 

If you think that you might get into AP later, then go with the FSQ. If not, I agree with Jared, the TMB is a great choice. And a consideration for a light, small, and easily portable (and fast) unit is the Sky 90 II. Did I say that I was addicted to Takahashi? 

 

Cheers,

John



#10 213Cobra  Happy Birthday!

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Posted 03 April 2020 - 10:57 PM

Tak FSQ106ED any version is a an excellent visual telescope. Unlike a triplet, you get a fully optimized flat field built in instead of having to buy an aftermarket field flattener. If the financial difference isn't significant, I recommend the FSQ106. It's compact and easy to balance, as the glass is distributed well. If spending less is important, the TMB and even more affordable AT92 will be excellent triplet alternatives for you. The Tak is for the rest of your life. I have two FSQs I use for visual, and I have a couple of triplets. All are interesting and useful. But my FSQs see the most time under the sky.

 

Phil


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#11 felicity

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Posted 04 April 2020 - 11:39 AM

Thanks to everyone. John and Jared good points on fast glass in photography vs astronomy. And thank you Phil for your comments on the Tak. Even though I doubt I will get into imaging I think I'll hold out for a Tak 106fsq - they sure seem to sell quickly here and that says a lot. 

 

Cheers Felicity



#12 samovu

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Posted 05 April 2020 - 02:49 AM

Good choice, Felicity.

 

Again, welcome to CN and welcome back to astronomy. Would love to hear about your journey and thoughts once you have your APM 120ED.

 

BTW, I could never afford a white Canon lens. But my first SLR was the original F1. And what a tank it was/is. The FSQ’s are also tanks (in addition to having well figured glass or Fluorite). You will not be disappointed.

 

Cheers,

John



#13 felicity

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Posted 05 April 2020 - 12:01 PM

Thanks again John. BTW - great quote from Heisenberg. 

 

Best, Felicity



#14 samovu

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Posted 05 April 2020 - 03:38 PM

delta p times delta x is greater than or equal to h bar

Or is it h bar over 2?   OMG, I remember the nightmares 😀

 

Edit:  above equation is the Heisenberg uncertainty principle 


Edited by samovu, 05 April 2020 - 08:37 PM.


#15 213Cobra  Happy Birthday!

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Posted 05 April 2020 - 08:55 PM

Thanks to everyone. John and Jared good points on fast glass in photography vs astronomy. And thank you Phil for your comments on the Tak. Even though I doubt I will get into imaging I think I'll hold out for a Tak 106fsq - they sure seem to sell quickly here and that says a lot. 

 

Cheers Felicity

Very good. You don't have to be interested in imaging at all for a Tak FSQ to be both satisfying and the right refractor for you. I'm strictly visual. Haven't done imaging since using film occasionally over 30 years ago. After I decided to venture back into a refractor after several decades without one, I indulged the triplet worship with a LOMO, then bought a field flattener for it for visual, and then figured why not just do what I should have done in the first place and get a native flat field Tak FSQ. Zero regret; nothing missing.

 

Phil



#16 YAOG

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Posted 11 April 2020 - 02:06 PM

I know you are used to faster glass in photography being synonymous with better glass. That is not the case with telescopes, though. With a camera, since your “eyepiece” is fixed, faster glass gives you a brighter view. But with astronomy, you get the extra degree of freedom of adding an appropriate focal length eyepiece for the framing that you want. End result? Faster telescopes do not yield brighter views visually. They also usually yield slight lower quality views for a given aperture, though with a well made and well corrected refractor the differences are often slight. Basically, the only advantages for visual use to a faster telescope are a shorter, lighter tube and the possibility of getting wider fields of view. The trade offs are higher levels of chromatic aberration, more spherochromatism, the need for better figured glass for a given level of correction, and the need for very short focal length eyepieces that may have uncomfortable eye relief for planetary and double star viewing.

You may know all this already given your history in astronomy, but I thought I would mention it just in case. It can be hard to get over the photographer’s bias towards fast glass.

Neither of the two scopes you are looking at will remind you of your Traveler in terms of size and weight. For their aperture, they are both relatively bulky and heavy. Both are optically superb. The 92mm that was recommended earlier is the closest current equivalent to your Traveler, though it does give up a few millimeters of aperture—enough to be noticeable.

If you don’t think you will get into astrophotography, the TMB is a great choice. It’s heavy, but the optics are really good. If you think you might get into astrophotography, the FSQ is the obvious choice. It’s perhaps the best 4” class astrograph ever made. If you just want something small, light, optically excellent, easy to transport, and reminiscent of your Traveler for not too much money, the AT92 is probably the best choice. It’s an updated version of a TMB design.

First off faster photo lenses do not automatically give you better images, the opposite really. Also faster telescopes up to a point, do not automatically doom the user to less than perfect views, that is dependent on the execution of the lenses and mirrors not a limitation of instrument speed or focal ratio. 

 

The only reason we associate faster camera lenses with better quality is the proliferation of the pro-class Canon and Nikon lenses. The same rules for optics apply to camera lenses just as they do for astronomy lenses. There is no magic in a fast camera lens, just more complex design and a lot more use of Fluorite and ED lenses. 

 

Faster focal ratio lenses are much more demanding of than slower focal ratio lenses if you want to maintain the highest image quality. Telescopes even the highest quality apos typically use very simple lens designs with 2-3 lens elements. A fast camera lens like a Canon EF300 2.8L IS or larger EF400 2.8L IS depending on model version can have 2-3 ED and Fluorite lenses in an 8-16 element lens. These pro class Canon lenses are where the optical design knowledge for the Takahashi TOA series telescopes came from.

 

One of the common misunderstandings about camera lenses vs telescope lenses is the nomenclature used to describe a camera lens vs a telescope. Camera lenses use focal length and maximum aperture to notate a lens. For example 300mm f/2.8 tells us the two most important things needed for photography about a lens. 

 

In this example a 300mm focal length lens with a fastest aperture of f/2.8. A photographer wants to know the field of view of the lens which is based of the 300mm focal length and the size of the media or sensor. The speed of the lens is useful so the photographer knows how much light he has to work with to set exposure time for a given media sensitivity and for creative use apparent depth of field. As a photographer I have no real use for how large the objective lens is. As a photographer all I care about is the FOV and exposure, I have no use for how large the object lens is. 

 

For telescopes the commonly used nomenclature is objective size and focal ratio though on many European websites you are seeing the very useful - objective size/focal length f/ratio - specified. To a telescope user light gathering power is key for nighttime observing and the focal ratios is used to calculate focal length. As astronomers it's all about light gathering power, how deep we can see and what a useful maximum magnification we can expect with a given telescope. Also objective size gives the user one of the numbers needed to calculate telescope resolution and for visual users the very important exit pupil of an eyepiece. 

 

So the way we specify these different use lenses is different because of the way different users apply the information. The reason people are mixed up about telescope speed, visual and photographic has to do with not understanding the meaning of the basics. Namely that a bigger objective lens or mirror can collect and focus more light energy than a smaller objective and that f/ratio just tells you the relationship between the size of the objective and how long the light cone is to the point of focus. Simple. 




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