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8” Reflector eyepiece advice (I’m a newbie)

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#1 MacTec

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Posted 18 October 2020 - 05:17 AM

Hi guys. I’m extremely new to this stuff and picked up an 200mm (8”)dobsonian reflector 1,200mm focal length ( I’m from Australia, so, you know, metric system) which came with the stock standard 10mm and 25mm plossl eyepieces. I managed to view a bit of Jupiter but not convinced that the scope is properly collimated and the included eyepiece aren’t great to look through so first up I’ve ordered a laser collimator to check the mirrors, but I’m also thinking I should invest in a better eyepiece. 
 

So the question I need help with is, if I could only buy one size eyepiece that would give me decent deep sky viewing but also if I then also grabbed a 2x Barlow, would give me good planetary viewing ie details on Jupiter and Saturn’s rings etc. what would be the most appropriate size?

 

The other question is, to get viewing of Andromeda would I need to get a focal reducer, or just not really possible with a telescope this size?

 

Many thanks for any advice. 


Edited by MacTec, 18 October 2020 - 05:18 AM.


#2 MickTaurus

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Posted 18 October 2020 - 06:38 AM

So the question I need help with is, if I could only buy one size eyepiece that would give me decent deep sky viewing but also if I then also grabbed a 2x Barlow, would give me good planetary viewing ie details on Jupiter and Saturn’s rings etc. what would be the most appropriate size?

 

The other question is, to get viewing of Andromeda would I need to get a focal reducer, or just not really possible with a telescope this size?

 

Many thanks for any advice. 

Hi Mac, I have a NexStar 8se and find 32mm Omni Plossl one of the best for DSO's.

 

This FOV calculator might help you decide:

http://astronomy.too...field_of_view/ 



#3 MellonLake

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Posted 18 October 2020 - 07:42 AM

Open clusters, nebulae and galaxies are vest viewed in your telescope with 14mm to 32mm eyepieces (with about 25mm being where you can see most objects).  Planets, planetary nebula and globular clusters will be best viewed in 5mm to 10mm eyepieces (with about 8mm to 10mm being good for most of these objects).  This is why your telescope came with 25mm and 10mm eyepieces, these are in the best ranges for viewing different types of objects.  Most of my viewing (my telescope is the same focal length as yours is with an 8.8mm and a 24mm). 

 

I did the same as you are suggesting, tried to fill gaps where I did not have eyepieces with other eyepieces.  In hind sight, I wish I had spent the money on better eyepieces in the general area of the eyepieces I already had. 

 

I don't know what your budget is but in the mid price range the following 2 eyepieces will give your great value and performance (of the two I would by the Explore Scientific 24mm 68° first):

 

Explore Scientific 24mm 68° (this will give the widest view with a 1.25" eyepiece).  It gives great widefield views, is very well corrected and is not too expensive.  This is an ideal eyepiece for galaxies and nebulae.  With a barlow it would give 12mm which is ideal for smaller galaxies from dark skies.  This is an ideal eyepiece for open clusters, galaxies and nebulae.    

 

Meade UWA 82° 8.8mm.   This eyepieces is very good for planetary, planetary nebulae and globular clusters.  The 82° field of view allows you to keep the smaller objects in the field of view longer.  With a Barlow it will be near the maximum magnification you telescope can produce (only usable on very rare nights of exceptional seeing (stillness in the atmosphere). 

 

 

There are a lot of choices at various price points but these are two better quality eyepieces and are great value.

 

Rob 



#4 Paul Sweeney

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Posted 18 October 2020 - 07:51 AM

An easy way to check your collimation is to aim at a bright star, and slowly defocus a small amount. You should see a series of light and dark rings, with a point in the middle. If the rings are nice and round, and the point in the center, you are good to go. Be careful with a laser. They need to be collimated, too, or they can cause you to worsen the collimation. I eventually gave up on lasers and cot a cheshire with cross hairs.

At f/6, your scope can be a bit off on the collimation and still deliver good images.

Your scope will work well with good general purpose eyepieces. If you want wide field eyepieces, it is best to try them in advance. Some will be blurry over a good portion of the field, others will be sharp. If there is a club in your area, contact them. Then you can try out various eyepieces to see which work well for you.

Unless you live in an area with really steady skies, you will seldom have a chance to observe the planets at more than 250x, more often it will top out at 150 - 200x. So you might want to plan a series of magnification steps when choosing eyepieces. A zoom eyepiece is also useful, though they tend go have a narrow field of view.
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#5 epee

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Posted 18 October 2020 - 07:57 AM

A 32mm Plossl is the best bet if you're on a budget and want to Barlow the eyepiece.

Your viewing let-down could be caused by collimation, or the astronomical "seeing" at the time you were looking.

"Seeing" is a form of weather; basically the steadiness of the atmosphere. This can vary from hour to hour and due to local conditions.

It's always best to avoid looking over nearby rooftops and parking lots; they send columns of turbulent, heated air into the night sky for almost the entire night. Bodies of water are expanses of thermal stability as a general rule. Changing weather can also bring turbulence, even with clarity. Those nights are best for deep sky viewing. Hazy or foggy nights are often best for planets because those conditions require a calm atmosphere.

#6 epee

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Posted 18 October 2020 - 07:58 AM

A 32mm Plossl is the best bet if you're on a budget and want to Barlow the eyepiece.

Your viewing let-down could be caused by collimation, or the astronomical "seeing" at the time you were looking.

"Seeing" is a form of weather; basically the steadiness of the atmosphere. This can vary from hour to hour and due to local conditions.

It's always best to avoid looking over nearby rooftops and parking lots; they send columns of turbulent, heated air into the night sky for almost the entire night. Bodies of water are expanses of thermal stability as a general rule. Changing weather can also bring turbulence, even with clarity. Those nights are best for deep sky viewing. Hazy or foggy nights are often best for planets because those conditions require a calm atmosphere.

#7 MellonLake

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Posted 18 October 2020 - 09:14 AM

To see what Andromeda will look like with different eyepieces in your telescope use: https://astronomy.to.../field_of_view/

 

To see most of Andromeda in your telescope you need something like the APM 30mm UFF 70° eyepiece ($230 USD) or a Televue 35mm Panoptic or a 31mm Nagler (think $400 to $600USD). 

 

However, the Explore Scientific 24mm 68° will do a good job showing you most of the disc (and M110 in the same field of view).   ($190USD).  

 

The cheapest good option would be a 32mm Plossl which also gives you the widest field of view with a 1.25" eyepiece but it is not as well corrected at the edges of the field of view.  I much prefer the Explore Scientific 24mm 68° to my 32mm Plossl.  

 

Andromeda is a tough object for larger aperture telescopes because of the longer focal length of these telescopes.  It takes a short focal length telescope to see all of Andromeda (think 600mm or less).


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#8 druhela

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Posted 18 October 2020 - 09:51 AM

which came with the stock standard 10mm and 25mm plossl eyepieces.

Great advice above. :) But I'm curious as to why the eyepieces you own aren't working. What brand are these stock plossls? 



#9 aeajr

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Posted 18 October 2020 - 10:30 AM

Hi guys. I’m extremely new to this stuff and picked up an 200mm (8”)dobsonian reflector 1,200mm focal length ( I’m from Australia, so, you know, metric system) which came with the stock standard 10mm and 25mm plossl eyepieces. I managed to view a bit of Jupiter but not convinced that the scope is properly collimated and the included eyepiece aren’t great to look through so first up I’ve ordered a laser collimator to check the mirrors, but I’m also thinking I should invest in a better eyepiece. 
 

So the question I need help with is, if I could only buy one size eyepiece that would give me decent deep sky viewing but also if I then also grabbed a 2x Barlow, would give me good planetary viewing ie details on Jupiter and Saturn’s rings etc. what would be the most appropriate size?

 

The other question is, to get viewing of Andromeda would I need to get a focal reducer, or just not really possible with a telescope this size?

 

Many thanks for any advice. 

 

Understanding Telescope Eyepieces

https://opticsaide.c...-for-telescope/

 

 

First, it would help to know what scope you have and if it will accept 2" eyepieces.   For Andromeda you would want a low power wide view eyepiece in the 30 to 38 mm range and 65 to 82 degree AFOV range.  Here are some examples.

https://agenaastro.c...0_1mm_40mm.html

 

 

You have given us no information about budget.

 

A focal reducer is not needed for that scope and is more typically associated with SCTs and Maks.  Not even sure it would work in a Newtonian.

 

 

The included Plossl eyepieces are likely very good eyepieces, just not as wide as some of the others available today.  I would not use a Plossl less than 10 mm in FL because the eye relief gets too short.

 

 

Plossls are very good eyepieces  – Good discussion
https://www.cloudyni...s/#entry8285208

 

 

If you could get just one eyepiece and a 2X barlow I would recommend the Baader Hyperion Zoom 8-24.  That was my main eyepiece in my 8" and is now my main eyepiece in my 12" Dob.

http://www.astroanar...r_Zoom_Mk4.html

 

Your focal length is 1200 mm so the zoom will give you 50X to 150X and everything in between.   In a 2X barlow it will give you 100X to 300X and everything in between.  That is about all you need other than the 2" low power mentioned above. 

 

 

This was the eyepiece set I accumulated over 4 years for my 8" and now my 12" Dobs.  The bolded ones are the most used eyepieces.

 

Orion XT8i – 8”/203 mm manual Dob Newtonian, 1200 mm FL F5.9
Resolving power -  .6 arc Seconds

AA  70            38 mm                  31.5 and    2.2 degrees  FOV   2”
Meade 82      20 mm                  60X  and  1.37 degrees   2”
    

      
ES 82             8.8 mm                136X and    .6  degrees   FOV       
ES 82             6.7 mm                179X and    .45 degrees         
Meade 82      5.5 mm                 218X and    .37 degrees 
ES 82             8.8+2XB               272X and    .3 degrees
ES 82             6.7+2XB               358X and    .22 degrees
Meade 82      5.5+2XB                436X and    .18 degrees

 

Baader Hyperion 8-24  zoom       50X to 150X

Baader Hyperion 8-24+1.5XB  75X to 225X (My most used 1.25” eyepiece in this scope)
Baader Hyperion 8-24+2XB   100X to 300X


Edited by aeajr, 18 October 2020 - 10:36 AM.

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#10 Dave Mitsky

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Posted 18 October 2020 - 12:11 PM

So the question I need help with is, if I could only buy one size eyepiece that would give me decent deep sky viewing but also if I then also grabbed a 2x Barlow, would give me good planetary viewing ie details on Jupiter and Saturn’s rings etc. what would be the most appropriate size?

 

I like to use a minimum of 200x on the gas giants which means a 6mm eyepiece with a 1200mm focal length telescope.  

 

The 14mm Meade Series 5000 UHD eyepiece would be a fair compromise for a dual DSO/planetary eyepiece (86x and 171x), with the use of a 2x Barlow lens for the latter purpose, at relatively low cost.  A 2.5x Barlow lens would produce more magnification (214x), of course.

https://www.meade.co...piece-1-25.html
 



#11 vtornado

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Posted 18 October 2020 - 06:54 PM

Use your 10mm eyepiece and perform a star test like Paul says,  Pick a bright star near the Southern celestrial pole so it does not

move very fast.   If you get nice concentric rings there no reason to adjust the primary.

 

I suggest using a barlowed laser to test collimation as it removes laser errors.   The secondary is best adjusted by a site tube,

but usually the secondary is an adjust once and forget it.  The primary may need a small tweak each time depending upon

how roughly the scope is handled during moving and setup.


Edited by vtornado, 18 October 2020 - 06:56 PM.


#12 spaceoddity

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Posted 18 October 2020 - 07:49 PM

The 38mm SWA(from agena astro and other labels like orion Q70) would be a good low power eyepiece on a budget that will give you the max field of view for objects like andromeda, large open clusters, large nebulae, and for an all-purpose finder/scanning eyepiece. Of course it's not the best out there as far as edge correction but with your scope @ f/5.9, it's serviceable and will give you a huge immersive FOV. If you have a higher budget there's ep's that will perform better. Let us know how much you want to spend. For planets, I'd say something in the 6-9mm range would be good. At higher powers the objects cruise through the field pretty quick in a manually operated scope so having a wide field like the Meade UWA's or ES82's are a nice thing to have, makes getting the object in view easier and gives you more time to observe before nudging. The 8.8mm recommended above would be good. The 2X GSO barlow, which has a removable cell that can be threaded on the eyepiece itself to yield about 1.5X, would give you a 3 ideal power options at high magnifications. There are cheaper options with a smaller FOV(60-70 degrees) that would be OK, and of course more expensive high performance options. Again, let us know how much you are looking to spend.  



#13 MacTec

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Posted 18 October 2020 - 09:43 PM

Thanks for all the advice/guidance so far everyone, really appreciate it. 
 

My laser collimator arrived today so I’ll check alignment first and then retry the included plossl eyepieces and see if it’s any better. 
 

Being new to this there may also be a bit of eye fatigue as I get used to looking through the eyepiece and try to get focus and not strain.

 

The most I’d be looking to spend on better eyepieces at this stage is around the $200-$250 AUD range (based on what I’ve seen on some local store websites). 
 




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