Is it worth buying better eyepieces if I am in a light polluted area?

[lostpleiad]

I'm starting to wonder if I should invest in some better eyepieces, but is it worth it, when I have light polluted skies?

I have a an 8inch Orion XT8 dobsonian. My eyepieces are what I could afford after shelling out on the scope.

• Seben 8-24mm zoom 
• 6mm 58 Degree BST Wide Angle Eyepiece
• Series 500 1.25" 40mm Plossl Eyepiece
• 28mm Orion 2inch eyepiece (came with scope)

These days I use the Seben or the 28mm exclusively. The 6mm and 40mm stay in their case all of the time (the first is too dim on anything except the moon, and the 40mm doesn't seem to do anything useful (I bought it hoping for nice wide views, but the 28mm is better for that).

I live in Banbury, near to the town centre with a reasonable amount of sky glow and neighbour's security lights. However, with the Seben I have seen plenty of nice objects - globular clusters, a few planetary nebulae, including some of the smaller ones like the blue snowball,  several galaxies like Bode's nebula, the Leo triplet, what I think was the Whirlpool once. I've never managed to see M1, or the Triangulum galaxy - pretty sure the computer on my scope has me looking right at it!

Hopefully that gives an idea of what I can 'get at' from my location and conditions.

So my question is - would I benefit from investing in, say, a Baader Hyperion zoom, or some Hyperion 68deg eyepieces, or the Celestron Xcel LXs? I mean - would I see more? Or better? Or would my location limit me from seeing anything more than I already can? 

Many thanks..

[ronin]

I would stick with them for a time, looks a fair enough selection, although I would likely add a 12mm or a 15mm for the medium. This is ignoring the zoom, which I will consider as somewhat seperate.

Better eyepieces will improve the quality of the image formed but LP they do not remove.

So unless the image you see is poor then no reason to run off and buy more.

[Moonshane]

The problem with even top quality eyepieces (I use Televue almost exclusively) is that whilst they do improve the views, especially in fast scopes, the difference is often subtle at best. What the better brands do is offer wider fields of better quality.

I dont believe that light pollution should agfect your decision.

The seben zoom is a decent unit (I have one for solar use) and I think any improvement will be small but nonetheless real.

[rory]

The biggest improvement possible is bunging the gear in a car and getting out of town . I only did so once so far and the difference is quite dramatic on dso's . Better than any top end eyepiece i recon . of course I realise this isn't always possible .

[Lowjiber]

First off, I feel your pain.  I live in the middle of a super nova named Las Vegas, Nv USA.

Secondly, I recommend Rod Mollise's great book entitled, "The Urban Astronomer's Guide".  Amazon carries it.

The interesting thing about light polluted skies is that you can actually find "fuzzies" better by increasing the contrast... making the background darker.  Adding something like a 17mm Hyperion or an 18mm ES 82^o eyepiece to your collection can really help.

Getting close (or even finding) the target with your 28mm and then increasing the power slightly with a mid-range EP can often enhance the contrast and allow a better overall view.  Yes, the target gets dimmer as you increase power, but the difference in contrast more than makes up for that slight loss.

Clear, Dark Skies

[nightfisher]

Have a think about the BST starguider 18mm, very good ep that may suit your needs

[MattJenko]

For wider low power views, you could go for a wider FoV EP than your 28mm stock Orion one. I am not sure which Orion EP it is, but if it is the DeepView, that is a 56 degree view. A MaxVision at 68 or an even wider 82/100 would help you get a larger star field at this magnification, which I found a great help with my manual Dob, as you are doing less moving of the Dob when viewing with the EP and you can let the stars/dsos gently glide across the field of view. This is not that affected by light pollution from my understanding and was certainly not the case for me, although I am a rural dweller.

[John]

I agree with Lowjiber. While the light pollution can't be overcome without observing from somewhere else, you can use a little more magnification to darken the background "glow" which will help with deep sky viewing. I have some light pollution where I observe and consequently don't find my 31mm eyepiece as good as my 21mm or 13mm for viewing the deep sky. To complement the additional magnification, wide or ultra wide eyepieces can still show a generous field of view.

So there may be a role that wider angle eyepieces could play in helping you make the best of your observing circumstances.

[lostpleiad]

Thanks for all the replies.

I don't understand about increasing the contrast - does increasing magnification increase contrast? Sorry for the stupid question..

I'm confused about whether to stick with what I've got, or invest in an 18mm EP - I was veering towards the X-Cel after reading a comparison with BST on here. I also had my eye on a 31mm Baader Aspheric - would that be worth getting? It's 82degs I think...

[Special K]

Hi, I'm in the process of learning about this myself, but the contrast is the difference between the objects you are observing. In this case it will be the contrast between the stellar objects and the background of sky. Increasing magnification results in less surface brightness which can effectively reduce the ambient glow of a background sky. As stars are pins of light they have a low surface area and high surface brightness and consequently do not dim as much as an object that is larger like the sky or a huge nebula.

As I understand it, it's getting the balance if magnification right for a particular object to give good contrast but not reduce it's brightness too much.

Regarding the original question, I'd say good EPs will be worth it in any case but understanding the science and math involved can help you make informed decisions about what EPs to buy. I found this site super useful:

http://www.rocketmime.com/astronomy/Telescope/telescope_eqn.html

[Lowjiber]

Thanks for all the replies.

I don't understand about increasing the contrast - does increasing magnification increase contrast? Sorry for the stupid question..

I'm confused about whether to stick with what I've got, or invest in an 18mm EP - I was veering towards the X-Cel after reading a comparison with BST on here. I also had my eye on a 31mm Baader Aspheric - would that be worth getting? It's 82degs I think...

When magnification increases (shorter focal length eyepieces), surface brightness decreases.  I know it sounds strange, but increasing the power makes the target dimmer, but (big "but" there) the background sky gets much darker as well.  Hence the increase in contrast.

I have a 31mm Baader Aspheric.  It's AFOV is 72^o.

My DSO "hunting" eyepieces are: 31mm Hyperion, 2" ES 82^o eyepieces in 24mm & 18mm.  Once I find a target, I drop down in focal length, usually one step at a time, until the contrast is better.  Obviously, there is a stopping point, but it will amaze you.  As we used to say..."Try it, you'll like it."

[Qualia]

Lostpleiad, for a good couple of years I viewed from the middle of a city and found the following tools to be quite useful.

First, if you don't have Stellarium, download it. I also found it essential to have a good star atlas, a 9x50 correct image viewfinder and something like a Telrad. That's was my basic 'getting about' gear. 

From here, I found that you do have to compromise on longer focal length eyepieces. As mentioned the background sky in light polluted areas becomes too pale, making it that much harder to tweak out faint fuzzies from the background glow. In consequence, you'll need to up the magnification a little.

By way of example, a 24mm 68º eyepiece in my f5 wasn't suitable as my sky-browsing eyepiece in the city; the background sky was just too bright for my liking. Instead, I found a 19mm 68º eyepiece a lot more suitable as my low power browser. After identifying the given deep space object, I found my 10mm or 14mm 72º eyepieces the ideal companion to tweak out detail. Essentially, these three eyepieces became my most used.

So, my advice would be to try something similar, namely, a 3 eyepiece set up and you've got an excellent short cut to see what may work. Use your zoom as a rough guide to obtaining optimum contrast on low power. Give yourself a good few sessions, with a good number of different deep space objects (nebula, perhaps a galaxy or two, a number of open clusters etc) and note down your findings. You'll probably find that around 60x in the city is about the lowest you can go before losing too much. This will be your low power browsing eyepiece.

From this, up the magnification to about 120x or 2mm exit pupil. The exit pupil is just the focal length of your scope (f5) divided by the focal length of the eyepiece. So, if you're using your zoom, click it up to around 10mm (f5 / 10mm = 2mm exit pupil) and see how this works as your middle, high-power. Again, try it on a good number of objects and note down your observations. Once you have found a suitable focal length around 120x, drop down to about 90x and see how this works for you as your middle, lower-power.

From playing around with your zoom and taking good note of the numbers used, you'll be able to make a more informed decision when it comes to purchasing a new eyepiece.

Final note, I truely believe it is a very good idea to upgrade on eyepieces when living in the city etc. Not only do you gain more aesthetically pleasing perspectives of the night sky, and may even be able to tweak out more detail, but they will help add to the incentive of actually getting out of the light polluted area and viewing the night sky in a more peaceful and forthcoming setting   

[Charic]

lostpleiad.........I find that if my eyes are averted from the light pollution, then the image from the telescope appears to look better, this is just by having the eyes dark adapted. I have a snood made from camping  underlay foam, but often just forget to apply it to the scope.  My telescope is looking through the light pollution, rather than directly at it, but my eyes are  getting the full glow when looking around the garden, but there are dark areas where I can sit, and my eyes are shielded to some degree, from direct light sources. The best results from my garden is when in/using my my Dob-Tent?

A dark bath towel over my head also helped to keep  some of the light at bay, and reduces the cold around the face, before the tent arrived.

Seriously expensive eyepieces are better corrected off-axis(no edge distortion of the image) and suitable/better for faster focal ratio telescopes and may have wider views, but they wont rid your light pollution. As Moonshane points out, could you tell if there was much difference?

I used to visit nearby Clanfield? I thought it had dark skies, but with so many new dwellings there now (since my Days) that I would assume it has more skyglow now?

[Moonshane]

Do consider though that faint dsos are never brighter than naked eye. They have a fixed brightness. Aperture increases the ability to see the object larger at the same brightness.

If you have light polluted skies then aperture, dark adaptation (or as dark adapted as pissible), increased magnification to a point (ie will the object still sit in the field) and possibly filters will help maximise the views.

Just use what you have and extract whatever you can. Observing is good if you plan properly and choose appropriate targets even from light polluted sites.

[RikM]

I'll just add my agreement with the points made already. I use my 20mm and 14mm eyepieces much more than my 28mm from home in Glos. I used to use a 30mm and the LP washed the view out. Using a higher magnification, wider angle eyepiece improves the view.

[swamp thing]

So there may be a role that wider angle eyepieces could play in helping you make the best of your observing circumstances.

Indeed

Its important to note that seeing the edge of low surface brightness objects can mean the difference between seeing them and missing them altogether.

Wide fields can really help here specially when increasing power to gain contrast.

With narrow fields its very easy to "Look through" objects rather than at them. Wide fields may help you pick out the edges better and increase your chances of success.

[Stu]

This may illustrate the point a little too.

Assuming a 10", f4.8 newtonian, a basic 25mm Plossl would give 1 degree of sky at x48 with a 5.2mm exit pupil. Under light polluted skies this is likely to give a fairly washed out sky background lacking in contrast.

You could gain a wider field of view by moving to a 24mm Panoptic with 68 degree afov or even a 2" Maxvision with 82 degree AFOV but you would still have a 5mm exit pupil.

Sticking with Plossls, to reduce the exit pupil you could come down to a 15mm or even 11mm and get down to 2.3mm exit pupil for a nice dark sky background, but your field of view would be under 0.5 degrees.

Moving from this to the king of eyepieces, the 13mm Ethos (just to illustrate the point), you would get a slightly larger FOV than the original 25mm Plossl, at x92 and a 2.7mm exit pupil.

This shows the benefit of widefield eyepieces, the same or similar amount of sky but with a darker sky background for better contrast.

This table shows the figures.....

....and these show the varying fields of view. From inside to out, they are 11mm Plossl, 25mm Plossl, 13mm Ethos and 24mm 82 degree Maxvision.

You can see that the Ethos frames the target nicely still but would give that darker sky for a better result.

Stu

Sent from my iPhone using Tapatalk

[bomberbaz]

I would love to have a bash at an ethos but I reckon i might struggle with the eye relief which is why I love the delos so much 

[lostpleiad]

Thank you to everyone who has replied on this thread. There's more information here than in most books on astronomy! Particularly thanks for the useful links and explanations - I'm still working my way through them. Unfortunately, it looks like I might be spending some money after all but at least I know what I am looking for....

[lostpleiad]

@BigMakStutov - thanks for your explanation. What I didn't understand is the effect of exit pupil. I thought that the difference between a 5mm exit pupil and a 2mm exit pupil would just be that for a dark adapted pupil, a lot of the 5mm exit pupil would be wasted. But you are talking about it as if it increases the contrast to have less exit pupil - why is that?

[lostpleiad]

Hi, I'm in the process of learning about this myself, but the contrast is the difference between the objects you are observing. In this case it will be the contrast between the stellar objects and the background of sky. Increasing magnification results in less surface brightness which can effectively reduce the ambient glow of a background sky. As stars are pins of light they have a low surface area and high surface brightness and consequently do not dim as much as an object that is larger like the sky or a huge nebula.

As I understand it, it's getting the balance if magnification right for a particular object to give good contrast but not reduce it's brightness too much.

Regarding the original question, I'd say good EPs will be worth it in any case but understanding the science and math involved can help you make informed decisions about what EPs to buy. I found this site super useful:

http://www.rocketmime.com/astronomy/Telescope/telescope_eqn.html

Great link - thanks!

[lostpleiad]

lostpleiad.........I find that if my eyes are averted from the light pollution, then the image from the telescope appears to look better, this is just by having the eyes dark adapted. I have a snood made from camping  underlay foam, but often just forget to apply it to the scope.  My telescope is looking through the light pollution, rather than directly at it, but my eyes are  getting the full glow when looking around the garden, but there are dark areas where I can sit, and my eyes are shielded to some degree, from direct light sources. The best results from my garden is when in/using my my Dob-Tent?

A dark bath towel over my head also helped to keep  some of the light at bay, and reduces the cold around the face, before the tent arrived.

Seriously expensive eyepieces are better corrected off-axis(no edge distortion of the image) and suitable/better for faster focal ratio telescopes and may have wider views, but they wont rid your light pollution. As Moonshane points out, could you tell if there was much difference?

I used to visit nearby Clanfield? I thought it had dark skies, but with so many new dwellings there now (since my Days) that I would assume it has more skyglow now?

I have a big piece of material I wrap around my neck like  a Bedouin, and pull over my head when viewing. I find it helps to cut out light distraction and prevent me straining one eye closed! But I like the idea of a dob-tent. I couldn't find anyone selling them anymore....I' wondering if I should make my own, because there a re a lot of insecurity lights around me where I am

[Charic]

I simple windbreak, the type you take to the seaside will suffice, as long as its high enough. The bedouin wrap sounds good too, just mind you don't cover the aperture?The Dob tent is a toilet/utility tent from Go Outdoors 

Edited December 14, 2014 by Charic

[Macavity]

Indeed, shielding from any direct light can certainly make a big difference.

Beyond that, a dark site? The main way I significantly increased my "tally"

of DSO targets was by switching to a GoTo mount and Video Astronomy. 

Such a direction change may (or may not) be what you envisage...

You can relate naked eye limit to sky background. Without much effort, I see

to Mag +5 on a good night? Equivalent to sky background of mag +18 (istr)?  

Even with Mag +3 skies, you should be able to see e.g. Surface Brightness

+12-14 galaxies, given sufficient aperture? Some (much) is down to skill and

patience. No comment on the former, but the latter is not always my forte!

[SpaceWalker]

Well, you've got a lot of excellent advises here. And with more practice you'll be able to see much more DSOs.
 
About eyepieces. Under light polluted skies for best contrast you shouldn't exceed an exit pupil of 3.5-4mm, better if it'll be closer to 3mm. So the best reasonably priced long focal length wide angle eyepieces for your scope (and mine too) should be ~18-22mm. For example, the 18mm ES82 or 20mm Maxvision. They'll give you an exit pupil of 3mm and 3.4mm and magnification of 67x and 60x, respectively. 
 
As for galaxies and nebulae, everything  as others said, you need a reasonable bump in magnification for better contrast under LP skies. Many smaller galaxies require exit pupil ~1.5-2mm that converts in your Dob into 8-12mm focal length or 150x-100x. If I were you I would invest into a 12mm wide angle eyepiece that'll give you 100x magnification and 2mm exit pupil as you've been advised already. For example, something like the 11mm ES82 or 12mm Celestron X-Cel LX.
 
Of course, no one eyepiece will substitute  a trip to a dark sky spot, but...there are some things that you can do relatively easy to improve the contrast like
1) Adding at least  a minimal hood  or better full size tube-like hood , you can make it yourself from any sheet of a dark plastic or tourist mat.
2) Flocking the OTA using professional dark liner like Protostar  or any other dark material. Not necessary disassembling the OTA, just read advise #5 here and flock most important area against the focuser . If you are interested read more on flocking: link 1 , link2  , link 3 .
 
I used to observe in LP skies and the improvement in contrast after I've just added the hood (even without flocking) was noticeable, I started seeing fainter objects.
 
To preserve dark adaptation people use Observer Vests and red goggles . If you have basic DIYer skills and some tools, you can fabricate light blocking screens like this or this.
 
There are much more ways you can improve your scope and make your observing experience more exciting. I can recommend you to check out this Mega-mod thread for Zhumell dobs .
 
And don't forget about a good Observing Chair like  this or this. No one premium eyepiece can improve the resolution of your scope more than a good comfortable chair  .
 
Good luck.