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What can I see with an 80mm f/5 refractor?

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#1 Leon't

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Posted 06 April 2020 - 03:05 AM

What can I expect to see in emission nebula and the messier objects with an 80mm f/5 refractor and a default 25mm lens from a b4 site and good dark adaptation? Will I be able to make out things like the Eagle nebula? If I throw in the Orion SkyGlow broadband filter, will I be able to see nebulas in at least slightly improved contrast? If I were to buy a UHC filter for the eyepiece, how much of a difference in contrast will it make for the emission nebulae?

 

CS,

Leon't


Edited by Leon't, 06 April 2020 - 03:05 AM.

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#2 Astrojensen

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Posted 06 April 2020 - 03:40 AM

Why do you ask? We know nothing about your eyesight or how experienced you are, which are OVERWHELMINGLY more important than aperture. The best way to find out is to go out and look for yourself. 

 

 

Clear skies!
Thomas, Denmark


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#3 DLuders

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Posted 06 April 2020 - 04:08 AM

Welcome to Cloudy Nights!  smile.gif   You may know that Magnification = (Focal Length of Telescope) / (Focal Length of Eyepiece).  The f/5 Refractor means that its Focal Ratio is 5 --> 5 x 80mm = about a 400mm Focal Length.  So, the magnificaiton with your default 25mm eyepiece is (400mm) / (25mm) = 16x, which isn't very much.

 

You can use the Stelvision Telescope Simulator to see what various astronomical objects will look like with your telescope+eyepiece combination.  Enter your telescope's diameter (80mm) and click on the "Detailed Simulation -- Choose Your Eyepieces" wording to see the images. 

 

You may enjoy the Prairie Astronomy Club's "Useful Filters For Viewing Deep Sky Objects" (DSOs) article.  


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#4 Leon't

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Posted 06 April 2020 - 06:02 AM

Thanks for the quick replies! smile.gif

 

Anyway, does eyesight change how I'll view deep sky objects? I've done a lot of searching around on the internet and I know experience is extremely important for observing DSOs but I've never heard stuff about eyesight changing how well I'll be able to observe the faint fuzzies. 

 

CS,

Leon't



#5 vdog

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Posted 06 April 2020 - 10:15 AM

Welcome to CN, Leon't.

 

How dark your skies are will make a big difference, in addition to the other factors. My skies are challenging (Bortle 6, according to web sources) but I can see quite a few Messier objects with a 25mm eyepiece and my 80mm f/5 refractor.  Of course, I know what I'm looking for, where it is, and what it looks like, so that's where the experience factor comes in.

 

I would start with bright open clusters on the list (M41 in Canis Major is a easy one, maybe M35, 36, 37, 38 in Gemini and Auriga as well).  You should also be able to see globular clusters like M3, M5, and M13.

 

At 16x, these objects will be small and some will appear nebulous.  If you want to zoom in, you'll need a Barlow or shorter focal length eyepiece.  I've considered getting an inexpensive zoom eyepiece (like a Celestron) for use with my refractor, but I have other scopes so it hasn't been a priority.

 

I wouldn't expect a broadband filter to make a huge difference for emission and planetary nebulae. I would recommend a good UHC filter (Lumicon, Televue, Astronomik).  If your skies are decent and you don't mind getting up in the a.m. hours, you should be able to see all kinds of targets in Scorpius and Sagittarius, including the nebulae M8 and M17. The Eagle Nebula needs either dark skies, big aperture, or both. With an 80mm, you might see the star cluster, but not the nebula unless you're under some really dark skies.

 

Here's a good resource for observing Messier objects:

 

https://tonyflanders...essier-project/

 

Good hunting.


Edited by vdog, 06 April 2020 - 11:15 AM.

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#6 Tony Flanders

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Posted 06 April 2020 - 11:26 AM

Does eyesight change how I'll view deep sky objects? I've done a lot of searching around on the internet and I know experience is extremely important for observing DSOs but I've never heard stuff about eyesight changing how well I'll be able to observe the faint fuzzies.


I'm not sure that the it's possible to make a hard-and-fast distinction between eyesight and experience. Human senses are complex things; you can't really untangle the cognitive aspect from the physiological aspect.

 

Having said that, physiological differences certainly do affect what you can see through a telescope. My ability to see deep-sky objects has deteriorated as I get older, presumably because of cataracts and floaters. My wife needs averted visions to see things that seem not merely obvious to me with direct vision, but quite bright.

 

Myopia as such is not an issue, because you can compensate for it fully by refocusing the eyepiece.



#7 quazy4quasars

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Posted 06 April 2020 - 12:20 PM

I use an 80 mm as a finder on my big scopes;  I am often surprised that moderately bright galaxies are readily visible (though much smaller at the lower magnifications required to preserve surface brightness, of course) -such as the core of the Coma Cluster and many other "big scope" targets like NGC 4565 etc. There are hundreds within reach, if you can find them - in your Bortle 4 zone.  But beware;  You will want for a better sky and a closer look:  You may acquire "Aperture Fever", my friend.



#8 cookjaiii

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Posted 06 April 2020 - 06:10 PM

I wouldn't hesitate to buy an 80mm f/5 refractor.  Obviously it won't match the performance of an 8" f/6 Dob (often recommended as a starting telescope), but an 80mm will show you a lot, especially under dark skies.   And you will probably want to keep it as a grab-and-go telescope once you graduate to something bigger and better.  Don't expect great views of most nebulae and galaxies, but globular and open clusters are well within reach.  Try working you way through the Messier album, and when you are through, you will have a much better idea of what your next step should be.

 

Welcome to cloudy nights!



#9 Migwan

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Posted 06 April 2020 - 07:31 PM

My best overall view of the Andromeda Galaxy to date, was thru my ST80 and there are plenty of other targets.  One thing the 80 F5 is not so good at is trying to view faint nebula.   Many filters really only work with larger scopes, so I wouldn't recommend that you start there.   One exception to that might be for a moon (polarizing) filter.  

 

Here's another useful means to find targets visible in the 80mm.  Just check Naked Eye, Binocular and Small Scope and all sorts of targets will come up. 

 

jd


Edited by Migwan, 06 April 2020 - 07:31 PM.


#10 Dave Mitsky

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Posted 09 April 2020 - 12:05 AM

A narrowband or OIII filter will certainly work quite well with an 80mm f/5 achromatic refractor on large nebulae such as NGC 7000 (the North America Nebula) from a good dark site.  This type of telescope is really intended for low-power, rich-field observing.  Don't expect too much in the way of planetary performance.

With such a fast focal ratio, chromatic aberration (false color) is going to be evident on bright objects like the Moon at higher magnifications.  

I've attached two photos of my 80mm f/5 Orion ShortTube refractor, which I purchased to view the 1998 total solar eclipse from the Caribbean.  I was using it the other night to observe Venus and M45. 
 

Attached Thumbnails

  • ST80 April 4 IMG_7914 Processed Resized CN.jpg
  • ST80 April 4 IMG_7925 Resized CN.jpg
  • Venus and M45 ST80 April 4 Correct Image.jpg

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#11 jcj380

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Posted 09 April 2020 - 10:27 AM

My 80mm does ok from my rather badly light-polluted backyard.  Most galaxies are a no-go, but open clusters really pop.  Nebulae vary - big, bright things are pretty good (as you'd expect), but don't expect to see the Pillars of Creation.  25mm doesn't darken the sky much for me, so I usually start at 15mm and go from there.

 

A dark site turns it into an animal - huge difference.  

 

The usual variables apply - eyesight, optics, transparency, LP, seeing, experience.


Edited by jcj380, 09 April 2020 - 10:31 AM.

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#12 Sketcher

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Posted 09 April 2020 - 06:10 PM

What can YOU see?  My first thoughts were the same as Thomas's (post #2).

 

In all seriousness, there's a huge range of possibilities; but in the end, the only way to find out is to go out and look -- on a regular basis, at a large number of objects, over a lengthy period of time.

 

Some can see an entire universe full of wondrous views when using an 80mm f/5 refractor.  Others will see only a handful of disappointing objects.  Where you'll fit in?  There's no good way of predicting.  You might even start out in the disappointed niche, only to later (perhaps after a few years of experience) discover that there's so much more that the eye had failed to previously notice.

 

In my opinion, you're shooting yourself in the foot by sticking with a single, 25mm (16x) eyepiece.  Almost everything will look better at higher magnifications.  Furthermore, more objects will be noticed when higher magnifications are used.  If I were to stick with only one eyepiece for DSO observing with an 80mm f/5 I would choose a magnification around 25x.  But the reallity -- what I actually use -- is a variety of eyepieces that provide various magnifications from 20x up through 67x or more.

 

Here's my re-painted and somewhat customized 80mm f/5 refractor:

 

Little Red Riding Scope    Sketcher Sept 4 2019
 
This telescope has provided me with countless impressive views of deep-sky (and other) objects over many years of use.

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#13 Tony Flanders

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Posted 10 April 2020 - 06:56 AM

In my opinion, you're shooting yourself in the foot by sticking with a single, 25mm (16x) eyepiece.  Almost everything will look better at higher magnifications.


I agree 100%. It's crazy to talk about buying filters until you have enough eyepieces to achieve a reasonable range of magnifications. Yes, a nebula filter makes a big difference on certain nebulae. But not nearly as much difference as switching from a 25-mm eyepiece to a 10-mm eyepiece! And the 10-mm eyepiece will help with 99% of the objects in the sky, not just the 5% that happen to be emission nebulae or planetary nebulae.


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#14 Dave Mitsky

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Posted 10 April 2020 - 06:07 PM

A 5mm eyepiece or a 10mm eyepiece coupled with a 2x Barlow lens is only going to produce 80x (at a rather small 1.0mm exit pupil) with an 80mm f/5 to underscore what I said about such telescopes not being great on the planets.  I don't usually use more than 57x (7mm Tele Vue Nagler type 6) with mine.

I'll second what vdog said about M16's nebulosity.  Seeing the so-called Pillars of Creation requires a fairly large aperture, a nebula filter, and dark skies.



#15 Tony Flanders

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Posted 10 April 2020 - 08:51 PM

I'll second what vdog said about M16's nebulosity.  Seeing the so-called Pillars of Creation requires a fairly large aperture, a nebula filter, and dark skies.


That's certainly true about the Pillars of Creation, or Dark Queen, or whatever you want to call the dark nebula that protrudes into M16. But simply detecting the nebulosity surrounding the star cluster is quite easy with an 80-mm scope under dark skies with no filter, or with an 80-mm scope equipped with a nebula filter under skies where the summer Milky Way is readily visible but washed out and lacking much in the way of detail.


Edited by Tony Flanders, 11 April 2020 - 04:32 AM.


#16 Dave Mitsky

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Posted 11 April 2020 - 12:37 AM

That's certainly true about the Pillars of Creation, or Dark Queen, or whatever you want to call the dark nebula that protrudes into M16. But simply detecting the nebulosity surrounding the star cluster is quite easy with an 80-mm scope under dark skies with no filter, or with an 80-mm scope under skies where the summer Milky Way is readily visible but washed out and lacking much in the way of detail.

Didn't you mean to say with a nebula filter at the end of the second sentence?



#17 Sketcher

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Posted 11 April 2020 - 01:34 PM

A 5mm eyepiece or a 10mm eyepiece coupled with a 2x Barlow lens is only going to produce 80x (at a rather small 1.0mm exit pupil) with an 80mm f/5 to underscore what I said about such telescopes not being great on the planets.  I don't usually use more than 57x (7mm Tele Vue Nagler type 6) with mine.

Nevertheless, an 80mm f/5 is still usable on planets and is capable of showing far more than anyone could possibly see with the naked eye.  A 3.8mm Ultrascopic eyepiece was used with an old Orion ST-80 achromat (Little Red Riding Scope -- pictured in post #12 above) for the following two sketches:

 

ST 80 Jupiter   Sketcher
 
ST 80 Saturn   Sketcher
 
As for deep-sky, even stopped down to a 1-inch aperture an 80mm f/5 can show "stuff" -- depending, of course, on sky darkness, transparency, and observer experience.  A 20mm Orion Expanse eyepiece was used for the following view:
 
M31 32 110  1 inch aperture 5 Dec 2018 20x Sketcher   text 1

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#18 Dave Mitsky

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Posted 11 April 2020 - 03:43 PM

 

Nevertheless, an 80mm f/5 is still usable on planets and is capable of showing far more than anyone could possibly see with the naked eye.  A 3.8mm Ultrascopic eyepiece was used with an old Orion ST-80 achromat (Little Red Riding Scope -- pictured in post #12 above) for the following two sketches:

 

 
 
 
 
As for deep-sky, even stopped down to a 1-inch aperture an 80mm f/5 can show "stuff" -- depending, of course, on sky darkness, transparency, and observer experience.  A 20mm Orion Expanse eyepiece was used for the following view:

 

Be that as it may, if someone is interested in pleasing planetary views, an 80mm f/5 achromat is not the telescope to choose.



#19 Tony Flanders

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Posted 12 April 2020 - 05:31 AM

Be that as it may, if someone is interested in pleasing planetary views, an 80mm f/5 achromat is not the telescope to choose.


Agreed -- unless other constraints force you in that direction. In particular, there is a little niche at the intersection of low price and portability where an 80-mm f/5 might be the best choice for viewing the planets. If portability is no concern, a small Dob would do much better at a comparable price. If price is no concern, an 80-mm APO would do much better with little loss in portability. But taking both constraints together, an 80-mm f/5 achromat is at least a serious contender.


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#20 Pcbessa

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Posted 13 April 2020 - 10:39 AM

Hi, go instead for a 6inch Dob for a good starting scope, and drive to dark skies if you dont have them at home. Thats the minimum.

Dark skies are a must for nebula. Take Rosette for example. Beautiful from very dark skies, almost invisible from slightly dark skies (transition suburban to rural). M16 needs also dark skies.

#21 Astrojedi

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Posted 13 April 2020 - 07:07 PM

What can I expect to see in emission nebula and the messier objects with an 80mm f/5 refractor and a default 25mm lens from a b4 site and good dark adaptation? Will I be able to make out things like the Eagle nebula? If I throw in the Orion SkyGlow broadband filter, will I be able to see nebulas in at least slightly improved contrast? If I were to buy a UHC filter for the eyepiece, how much of a difference in contrast will it make for the emission nebulae?

 

CS,

Leon't

Welcome to CN. You can see a lot. This is a good article: http://www.deepskywa...-telescope.html



#22 bjkaras

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Posted 23 May 2020 - 01:58 PM

I use 80mm refractors as finders on both of my scopes. From reasonably dark sites you can see DSOs directly through the finder. If you live near any dark sites you should make a trip. Through an 80mm scope you should be able to see lots of DSOs without too much trouble. Get a couple higher power eyepieces too, so you can see a little detail.




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