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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Scopes v bins at night (1 Viewer)

CharleyBird

Well-known member
England
I've been watching a blackbird family under a very thick laurel shrub, a fixed view through a gap in the foliage, and comparing various bins with my Swaro 30x85.

(Disregarding the practicality bins bring to birding) I've been wondering about the optical ability of a large scope, say the Swaro 115 at 20x, to 'see more' than say, a quality 8x56 bin?
In near darkness.

Curious to know of any research comparing bins & scopes.
What scope is a 7x42 bin equal to.
An 8x50 bin equal to..., an 8x56...

Regards
Andy
 
Divide the big number by the small number to get the exit pupil, which will give you an indication if relative brightness in dark conditions (where your eyes pupil will open fully). Spotting scopes do not tend to give especially large exit pupils, most binoculars are 5mm or below.
I’ve just picked up an 8x56 and it does a very good job in the dark. Was out watching barn owls hunt and the binos I had let me stay out after the camera wielding people had all packed up and gone home.

Peter
 
The 115 swaro you mention at 20x will give you a 5.75mm exit pupil, the 8x56 bins will give you a 7mm exit pupil so will be brighter providing your own pupils dilation is more than 5.75mm.

That's only part of the story though as you will be much closer to the subject at 20x than 8 so able to discern much greater detail - even without using all of the available exit pupil.

I tend to adjust the zoom on my scope when it gets darker as well as when weather conditions don't allow a high amount of zoom, less zoom often gives a more useful image as it's brighter when discussing the really small exit pupils even large scopes provide at hight magnification.

Will
I've been watching a blackbird family under a very thick laurel shrub, a fixed view through a gap in the foliage, and comparing various bins with my Swaro 30x85.

(Disregarding the practicality bins bring to birding) I've been wondering about the optical ability of a large scope, say the Swaro 115 at 20x, to 'see more' than say, a quality 8x56 bin?
In near darkness.

Curious to know of any research comparing bins & scopes.
What scope is a 7x42 bin equal to.
An 8x50 bin equal to..., an 8x56...

Regards
Andy
 
When comet Neowise was visible a couple of years back I made the mistake of directing my 30x65 scope at it. It was only visible as a faint blob, whereas my 7x42 binocular at least showed a tail.
Earlier this year looking for Short-eared owls in twilight, my 8x56 SLC was distinctly brighter than a fellow birder's 10x42 Canon IS, but not noticeably better than a 10x50 EL. I'm in my late 70s though, so my pupils probably only dilate to around 5 mm.
That 115 mm ATX btw has a minimum magnification of 30x and an exit pupil under 4 mm. I can get about 4,75 mm on my Kowa 883 with a 27 mm astro eyepiece but at the expense of 45° AFoV. Anything with a larger field stop would get vignetted by the sealing window in the scope body.
If your 30x85 Swaro is the draw-tube scope with removable eyepiece, it may lack the sealing window and with an astro adapter you could use a 32 mm Plössl for an exit pupil of nearly 6 mm.

John
 
Interesting, thanks.

Yes I have the 85mm drawtube scope and shall investigate the sealing window & Plossl eyepiece.

Would a 30x115 ATX have outperformed your 7x42 looking at that comet in the night sky I wonder? Astronomy brings in a further variable of light pollution.
 
Would a 30x115 ATX have outperformed your 7x42 looking at that comet in the night sky I wonder? Astronomy brings in a further variable of light pollution.
I really couldn't judge that trade-off of exit pupil for magnification, but it's certainly true that the visibility of faint diffuse objects like comets or galaxies is strongly affected by light polution.
So far I've only seen Andromeda in my 8x56 but was surprised to read recently on Cloudy Nights that a member had good views of M51 and M101 in his 8x54 HT just before moonrise.
The "white nights" should soon be over, so this has spurred my ambition to get down to a dark site in the Eifel around new moon and try to see some other galaxies.

John

PS:- I'm not sure if astro adapters for Swarovski scopes are still available but am fairly certain that the bayonet of the Kamakura-made Zeiss Gavia, for which an astro adapter is available, is a Swarovski clone: Teleskop-Express: ZEISS Astro Adapter for ZEISS Conquest Gavia 85
 
It depends on the comet, the degree of condensation, the size and the brightness of the comet.

Comet Halley was best seen on La Palma near 8,000 ft altitude in my 20x80 Japanese Celestron compared to 6 inch Newtonians and 5 inch SCTs, and smaller binoculars.

Many deep sky objects are just too faint for hand held binoculars.

There are numerous comets available at any one time.
The instruments used are from naked eye, various size binoculars, refractors up to 12 inch aperture and mirror scopes of all sorts and all sizes.

I could see M33 clearly with direct vision without optical aid although others couldn't.

There is no one answer to the question.

Regards,
B.
 

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