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Refractor telescope for long-distance views of waterfowl (1 Viewer)

PedroP

Member
Czech Republic
I am searching for a scope that covers longer distances (ca 0,3-1,0 km) to observe waterfowl in the lakes. Now I own Canon 12x32 IS III + Celestron Regal M2 with Astro eyepiece Bader Morpheus 9mm, which gives me 42x magnification. I want to upgrade for a longer distance. Initially, I thought to use my Celestron C5, but it is bulky, needs temperation, and the image is not very clear and contrasting. I am considering TS Optics Photoline dublet with 80 mm f/7 - FPL-53 / Lanthanum glass (optical length 560mm, weight 3 kg) for 600 EUR. I am expecting a more crisp, clear, and contrasting view (if no remarkable seeing occurs). I will observe from a fixed position on a firm tripod and want to double my current magnification up to 70-80x. Occasionally, I want to employ a bino viewer attached to the refractor. What are your thoughts?

Thanks, Petr
 
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The human iris cannot constrict to much less than 2 mm, so at smaller exit pupils there is a significant loss of brightness.
The general concensus is that for terrestrial obsevation (e.g König/Köhler) exit pupils under 1 mm don't make much sense.
Direct sunlight and still air is an unusual combination but I once set up my 65 mm and 88 mm birding scopes side by side and viewed 3mm lettering from an elevated position at 66 m.
Both were set to 60x, the 88 mm at maximum zoom and the 65 mm with a 7,5 mm astro eyepiece and in direct sunlight I could read the lettering in both.
However, when the target fell into shadow I could still read it in the 88 mm scope but no longer in the 65 mm scope.
YMMV but for me an exit pupil of 1,5 mm is the lower practical limit and this corresponds roughly to the maximum magnification available on birding scopes with OEM eyepieces.
A magnification of 42x on your Celestron scope also gives you a 1,5 mm exit pupil, so if it is a good example I suggest that before you take the plunge you determine the maximum range at which you can read newsprint at 42x and see if that range can be extended with a 6 mm or 7 mm eyepiece.

John

PS:- The astro scope will, of course, not offer you a correct image and AFAIK ther is only one good (and expensive) 90° correct image erecting prism.
You can expect the astro scope to be diffraction limited, which the Regal M2 may not be, but a good 80 mm is only going offer you 23% more range than a good 65 mm scope and comes with a big penalty in weight and bulk.
 
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Dear Jonh,
Thanks for all your suggestions. So, do you have in mind any solution that will help me extend the reach up to double magnification? I.e., a larger diameter of about 90 or 95 mm. Yes, I understood that it is a more expensive and bulkier solution, but when I have double use for it (astronomy and birds) and get it in less than 1,000 eur (still cheap comparing to high quality spective as Kowa or Swaro over 3,000), then it could be still attractive to me.

Petr
 
Hi Petr,
If your 65 mm scope were really good, you would need a 130 mm scope to double its range and even then seeing conditions would have to be perfect, which is seldom the case.
It's all a question of diminishing returns. The Takahashi FOA-60 is allegedly the best telescope relative to its size ever made and costs €1500.
The TOA-130 costs €6500! I'm not sure though if you would notice optical differences to an instrument from TS Optics of equivalent size.
Opinions here on the forum differ. Some are willing to pay a lot for a 100 mm scope offering 70x magnification in good conditions and sacrifice portability. Others consider a 65 mm scope as an ideal compromise, where 45-50x is more like the upper limit.

John
 
Dear John,
I will consider your experience. Thanks you for your informed opinion. I have a chance to test some small Takahashi of my friends with binoviewer and compare them with another 1-2 refractor types. I am now also considering if faster (i.e. F4-6) or slower (F=7-10) will be better for my purposes including astro viewing (no photo planned) and birding.
What I heard from the reviews is that the faster ones suffer more from various optical problems (colour), but a higher diameter brings more light, which is advantageous for binoviewer use (larger exit pupil). But lower F is compromised by shorter focal length, thus lower magnification. I know everything is about compromises. I am planning to do some research and testing and then decide if a new refractor is worth for my purposes.

Many thanks, Petr
 
I'm using a pair of 102mm, FPL-53 triplet, f/7s in binoscope configuration with erect image mirrors. I'm getting great views at 24X that rival higher magnification in my other binos. High magnification is good too, but some target context/perspective is lost. It's great being able to see a bird blink, or look through the nostrils of a vulture's beak at 300m, but it's also pleasant to see them move about in their surroundings.

I don't see CA & color fringing, and overall color tone is neutral. As I understand it, good color correction is a feature of a triplet design, which is something to consider. There is a little weight penalty in the triplet design though. I have the luxury of a tripod dolly and smooth surfaces to roll across most of the time. In the field extra schlepping is required to set up a viewing spot.

My advice is to purchase the best high payload tripod (or pier), and an ultra smooth high capacity mount. Visual stability is paramount at high magnification. When in the field a brisk wind can be disruptive. If a mount has stiction, starts & stops and scans & pans literally become a drag. Also evaluate your refractor choices for build robustness. If you plan to move it much be sure the coupling mechanisms/rings for the focuser have secure connections and they don't rely on a few tiny set-screws to hold things together. And, think about a quality shroud to protect the refractor from the elements, and dry storage area when not in use.

I say go for it and enjoy.
 
Thanks K-day for sharing your practical experience. I agree with your suggestions - I own a sturdy Manfrotto tripod with a central column which could hold more than 10 kg (I am planning to buy a woody Berlebach to reduce vibrations) with a good videohead Berlebach 553. I am just thinking about a doublet refractor (TS or Skywatcher) up to 3 kg (to reduce weight) with an aperture of about 72-95mm and a focal length of 450-600 with a robust attachment to hold my Maxbright binoviewer with a pair of Panoptics 24mm or Explore Scientific 16mm. I use also Baader correctors/extenders 1.7x and 2.6x. Why are you not using higher magnifications than 24x as I am planning to use the highest magnification about 40x-60 if the exit pupil over 1.5 allows it.
 
I use higher magnifications up to 70X for terrestrial viewing in my refractor binoscope. I often use an exceptionally sharp eyepiece of 57X. I was highlighting a point about large aperture and long FL improving performance at a given magnification in a refractor. Large aperture with conversely short FL has it strengths like brightness and wider FOV at the lower end of magnification. For the higher magnifications you want, you'll need the upper range of your aperture and FL goals.

The 24X eyepiece I mentioned is a 30mm 2" (not compatible with your binoviewer). Its most prominent feature is a wide field stop & useable (good edge correction) FOV. I don't always need to peer through a finder to locate the target when using that eyepiece.

I'm not trying to be a snob, so please don't take offense at my comments about equipment selection. Consider a Manfrotto 161MK2b tripod for getting the vibration reduction you're looking for, and the versatility you don't yet know you need. Think about a Manfrotto NT608 fluid head over a friction-only head.
 
Thanks for the equipment suggestion, the Manfrotto tripod is exactly the type I have, suggested fluid head looks robust and I have a lower model of the Manfrotto head but plan to use a lower load capacity (but understand that for your set with more than 6 kilos fluid head is necessary).
I am doing some research now and testing in the field and then make a decision. Thanks for help!
 
I have a 3.7 kilo BT (without eyepieces) on a DT608. The main benefits of this fluid head are low effort to nudge, little to no backlash, and it isn't disturbed easily. Those subtle luxuries are nice to have.
 
Hi,

if size and weight are not an issue, an ED120 f7,5 doublet with FPL53 glass (various brands, Skywatcher is most prominent) comes to mind. These can be had used for 1000€ or slightly above with a bit of patience. You will probably have to add a few hundred euros for gas as these usually are not usually sent via mail - and you certainly want a quick star test with a diy artificial star before buying...
There is also a 100mm f9 version of this which is usually available new for 900 and used for 550 or so. But the exit pupil at 80x would be 1,25mm which is a bit on the small side.

In general you want a bit more relaxed focal ratio of around f7,5 or slower and ED glass. Very fast refractors (f6 and below) are built either for astro imaging or for birders and come with certain challenges for the designer and in manufacturing.

Joachim
 
Thanks both for the comments, 3.7 kg looks pretty lightweight which is nearly my 4 kg maximum for the whole combo to keep mobility of the set (will see if the better fluid head will be necessary). I tend to something about F7, but the aperture not above 95 mm, ideally doublet with FPL53 to reach a maximum something between 60-70x magnification (to reduce weight, I pick maybe the carbon version even at a higher price). Thanks for the advice.

Petr
 

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