Wide angle eyepiece question

[Danny83uk]

Hi all. I'm interested in viewing deep space objects and have a skywatcher 900x130 dobsonian. With it came a 10mm, 25mm wide angle EP and a 2x barlow(since invested in a new Barlow with the screw thread for camera mounting). What I'm not sure on is if my low power eyepiece having the wide angle is going to mean I won't see nebula or other dso as well as a non wide angle.

Really appreciate any help on clarifying this.

Thanks.

[brantuk]

Hi Danny and welcome to SGL

Your high power eyepieces (10mm and barlow) will enable you to see planet and moon details more closely. The low power wide angle eyepiece can be used to view larger objects like galaxies, nebulae, and open star clusters. As you build a range of 4 or 5  eyepieces you'll get to know which size suits which object.

But the eyepiece types/sizes aren't the only thing that determines what you can see. A clear sky with good transparency and a very dark observing site make a huge difference. Choose a moonless night where possible and get your eyes dark adapted for 20mins. Observe objects high in the sky so they are well risen away from horizontal atmosphere. And where appropriate a filter can help (eg LPR, UHC, Oiii, etc). You can also "train your eye" to look at objects - eg using methods like averted vision.

Hope that helps

[rwilkey]

Hi Danny, the 25mm 'wide-angle' ep is not a true wide-angle unfortunately.  You will need to look elsewhere for a decent wide-angle.  A 30mm wide-angle would go a long way in this direction but they often only available in the 2" barrel, which may not fit your scope, otherwise the 32mm Plossl would be a good choice, though not a wide-angle.

[Danny83uk]

Thank you for your replies. I am looking at a few more EP's using wharthogs guide on this forum. I've been gazing for over a year now and getting the itch to upgrade my scope. But I know that a good eyepiece upgrade from the manufacturer box set ones can boost the quality. My difficulty is a)deciding on which brand is good and value for money and understanding the wide angle vs non wide angle EP's. My viewings of Orions nebula and andromeda where limited to small grey smudges ineffect. Is this the best I can hope with my current setup of scope/EP.

[Danny83uk]

That is a b ) to clarify.

[Mak the Night]

A 32mm Plossl with a 27mm field stop might be good with your scope. It will give you a 4.6mm exit pupil for a 28x magnification. Good for faint DSO's.

[Chipela]

Thank you for your replies. I am looking at a few more EP's using wharthogs guide on this forum. I've been gazing for over a year now and getting the itch to upgrade my scope. But I know that a good eyepiece upgrade from the manufacturer box set ones can boost the quality. My difficulty is a)deciding on which brand is good and value for money and understanding the wide angle vs non wide angle EP's. My viewings of Orions nebula and andromeda where limited to small grey smudges ineffect. Is this the best I can hope with my current setup of scope/EP.

My experience of Orion nebula vs Andromeda is that Andromeda is just a grey smudge but Orion nebula shows a beautiful nebula (and most probably I still miss most of it). So there should be a difference between these targets. By the way, my observations are from a moderately light polluted backyard.

[Charic]

Danny83uk......Ive got a 1200/200/f6 telescope and Andromeda is just a faint smudge for me too, and thats the main core of the galaxy!

Go to a proper dark site and look again, for me, its like having a new telescope? The view is just stunning. You need the darkest conditions, good seeing and your longest focal length eyepiece.

[Stu]

Danny, what are your skies like? As Brantuk says, getting yourself to a dark site can have a dramatic impact on what you see, more than a different eyepiece!

A scope upgrade, say to a 200p will also give you a big boost if you can afford it.

Don't be misled by the wide angle label on the 25mm, this just means that it is lower power than the 10mm and shows more sky. I'm sure it is still a 50 degree apparent field of view. This concept is worth understanding. The larger the afov, the more sky you will see at the same magnification. This is of benefit because often observing at higher powers can darken the sky background and give the effect of better contrast. Having a wide afov helps you maintain a good field of view whilst doing this.

An example of this might be a Televue 19mm Panoptic vs your 25mm standard eyepiece. It gives a higher power, darker sky background whilst also giving a slightly wider field of view.

The outside ring here is the Televue giving x47 mag vs x36 for the standard eyepiece.

Note that I'm not suggesting you buy a Panoptic, this was just to illustrate the point.

I am suggesting getting yourself somewhere darker to try you scope there and given it a better chance. Is that practical for you?

[John]

I've observed a couple of times recently with someone who has the same scope as you do.

We tried a Maxvision 24mm 68 degree eyepiece that I had with me in his scope and the difference between that and the stock "wide angle 25" was really very noticable. He spent the next couple of hours using it !

Within the constraints of the 1.25" focuser on the scope, the Maxvision 24mm 68 shows as much sky as you can see. The eyepiece is still available from some UK suppliers I think at between £60 and £70 new.

My usual eyepieces are Tele Vue and Pentax but I've been very impressed with the Maxvision 24mmm 68 - one of the best lower cost wide angle eyepieces I've used

[Ruud]

A 24mm 68° or 32mm 52° will show you the biggest patch of sky that you can see in a 1.25" focuser. Big views are nice, for instance on the Milky Way's star fields and also for star clusters.

If you can still find one: a Maxvision 24mm 68° is good and doesn't cost much at all for its quality. 68° is a generous, wide view.

A 24 mm will give you a darker background than a 32 mm. Darker backgrounds make nebulae stand out a bit better.

Your telescope is an f/6.9 because 900/130 is about 6.9.. This number is important for calculating the exit pupil that any given eyepiece will have on your telescope.

To know the exit pupil of an eyepiece divide its focal length by the f/ratio of the telescope. For instance: a 24 mm eyepiece will give you an exit pupil of 24/6.9 = 3.5 mm.

An exit pupil of 0.5 to 1 mm is good for the Moon and planets (very high to high magnification - for the telescope),

an exit pupil between 2 and 3.5 mm is good for nebulae and galaxies (faint fuzzies), and

an exit pupil up to 5 mm is ideal for rich field viewing (Milky Way star fields).

These are rules of thumb and some have slightly different preferences.

When the exit pupil gets above 5 mm the sky background may get too bright. Unless you are observing in a dark place; there you can use an exit pupil up to the size of your dark adapted pupil.

[Mak the Night]

My Explorer 130 has the same focal ratio as your scope.

According to Stellarium this is what M42 would look like with a TeleVue 25mm Plossl ~

And with a 19mm TeleVue Panoptic ~

[Danny83uk]

Thanks to all who have offered me answers to try to understand the next step. Up untill now ive been pointing and looking without really understanding the equipment.

Danny, what are your skies like? As Brantuk says, getting yourself to a dark site can have a dramatic impact on what you see, more than a different eyepiece!

A scope upgrade, say to a 200p will also give you a big boost if you can afford it.

Don't be misled by the wide angle label on the 25mm, this just means that it is lower power than the 10mm and shows more sky. I'm sure it is still a 50 degree apparent field of view. This concept is worth understanding. The larger the afov, the more sky you will see at the same magnification. This is of benefit because often observing at higher powers can darken the sky background and give the effect of better contrast. Having a wide afov helps you maintain a good field of view whilst doing this.

An example of this might be a Televue 19mm Panoptic vs your 25mm standard eyepiece. It gives a higher power, darker sky background whilst also giving a slightly wider field of view.

The outside ring here is the Televue giving x47 mag vs x36 for the standard eyepiece.



Note that I'm not suggesting you buy a Panoptic, this was just to illustrate the point.

I am suggesting getting yourself somewhere darker to try you scope there and given it a better chance. Is that practical for you?

Hi Stu, Im limited to traveling really as i recently suffered a brain hemmoridge leaving me Partially blind and the DVLA deem this a reason to revoke my licence. Having said that my views from my garden can be quite good on a clear night if i position myself so the house blocks the street light some 100 yards away. Im grateful for your explaination of aFOV, I wasnt sure if because you had a wider angle and thus more on display it reduced to quality of the image you see. But now i see that because its wider you gather more light to view by. One thing i do notice where i live, is if i fail to find my target in the first 30 minutes of looking it can become impossible as there is just too many stars and i lose the signposts among them. So in that respect the skies are rather good.

I've observed a couple of times recently with someone who has the same scope as you do.

We tried a Maxvision 24mm 68 degree eyepiece that I had with me in his scope and the difference between that and the stock "wide angle 25" was really very noticable. He spent the next couple of hours using it !

Within the constraints of the 1.25" focuser on the scope, the Maxvision 24mm 68 shows as much sky as you can see. The eyepiece is still available from some UK suppliers I think at between £60 and £70 new.

My usual eyepieces are Tele Vue and Pentax but I've been very impressed with the Maxvision 24mmm 68 - one of the best lower cost wide angle eyepieces I've used

Hi John, Im looking to form a collection along the lines of 5mm,8-9mm,14mm,21mm. Ive been speaking to a few people at work who have a shown interest after i posted an image take on social media (Its amazing how many closet astronomers there are) All have similiar quality Ep's to me but i think if we can trade about the different sizes i can narrow down what i need.

The Image that got the interest was

https://www.dropbox.com/s/w3qy0ennh6yw0y6/7-01-13%20%233%20Stack2.jpg?dl=0

A 24mm 68° or 32mm 52° will show you the biggest patch of sky that you can see in a 1.25" focuser. Big views are nice, for instance on the Milky Way's star fields and also for star clusters.

If you can still find one: a Maxvision 24mm 68° is good and doesn't cost much at all for its quality. 68° is a generous, wide view.

A 24 mm will give you a darker background than a 32 mm. Darker backgrounds make nebulae stand out a bit better.

Your telescope is an f/6.9 because 900/130 is about 6.9.. This number is important for calculating the exit pupil that any given eyepiece will have on your telescope.

To know the exit pupil of an eyepiece divide its focal length by the f/ratio of the telescope. For instance: a 24 mm eyepiece will give you an exit pupil of 24/6.9 = 3.5 mm.

An exit pupil of 0.5 to 1 mm is good for the Moon and planets (very high to high magnification - for the telescope),

an exit pupil between 2 and 3.5 mm is good for nebulae and galaxies (faint fuzzies), and

an exit pupil up to 5 mm is ideal for rich field viewing (Milky Way star fields).

These are rules of thumb and some have slightly different preferences.

When the exit pupil gets above 5 mm the sky background may get too bright. Unless you are observing in a dark place; there you can use an exit pupil up to the size of your dark adapted pupil.

Is exit pupil here a figure used as a measurement of light rather then its physical size as ive read that having the EP too small for your age makes viewing hard/Impossible.

[Mak the Night]

24mm Panoptic

[Mak the Night]

Exit pupil: https://www.astronomics.com/exitpupil_t.aspx

'The circular image or beam of light formed by the eyepiece of a telescope. To take full advantage of a scope's light-gathering capacity, the diameter of an eyepiece exit pupil should be no larger than the 7mm diameter of your eye's dark-adapted pupil, so that all of the light collected by the telescope enters your eye. (The eyepiece exit pupil diameter is found by dividing the eyepiece focal length by the telescope focal ratio.) Your eye's ability to dilate declines with increasing age (to a dark-adapted pupil of about 5mm by age 50 or so). For those in this age group, eyepieces with exit pupils larger than their eyes can dilate to simply waste their telescope's light-gathering capacity, as some of the scope's light will fall on their iris instead of entering their eye.' ~ op cit

I find on my small Mak (102mm) an exit pupil of around 3mm will allow me to utilise a nebula filter. I need to use a 40mm eyepiece to achieve this. I tend to use my small Mak (f/12.7) a lot as bleeding on the brain paralysed me on my right side a couple of years ago. So a small compact scope like an SCT or Mak is easier for me to use. Unfortunately Mak/SCT's can be difficult to get low power views with. The upside is that high magnifications (lunar/planetary) are easy lol.

[Ruud]

Yes, Mark is right. It is a physical thing. 

Starlight enters the objective as a wide beam, and leaves the eyepiece as a narrow beam. The width of the latter is the exit pupil.

To see all the beams that leave the eyepiece, you must place your pupil at the right distance from the eye lens of the eyepiece. This is called the eye relief.

Here is an animation to clarify the concepts:

[Danny83uk]

Exit pupil: https://www.astronomics.com/exitpupil_t.aspx

'The circular image or beam of light formed by the eyepiece of a telescope. To take full advantage of a scope's light-gathering capacity, the diameter of an eyepiece exit pupil should be no larger than the 7mm diameter of your eye's dark-adapted pupil, so that all of the light collected by the telescope enters your eye. (The eyepiece exit pupil diameter is found by dividing the eyepiece focal length by the telescope focal ratio.) Your eye's ability to dilate declines with increasing age (to a dark-adapted pupil of about 5mm by age 50 or so). For those in this age group, eyepieces with exit pupils larger than their eyes can dilate to simply waste their telescope's light-gathering capacity, as some of the scope's light will fall on their iris instead of entering their eye.' ~ op cit

I find on my small Mak (102mm) an exit pupil of around 3mm will allow me to utilise a nebula filter. I need to use a 40mm eyepiece to achieve this. I tend to use my small Mak (f/12.7) a lot as bleeding on the brain paralysed me on my right side a couple of years ago. So a small compact scope like an SCT or Mak is easier for me to use. Unfortunately Mak/SCT's can be difficult to get low power views with. The upside is that high magnifications (lunar/planetary) are easy lol.

So with my 25mm ill be seeing an exit pupil of  3.5. That puts it at the upper end of the Nebula viewing based on Ruud's earlier clarification. So if i am to invest in something around the 21mm range (once again based on wharthogs guide to a set) ill have a staggered EP and not duplicating prehaps? Or do i look at the 24mm tested in Johns comment. Also what program are you using to show these images? On a personal note i understand your suffering, I suffered a bleed on the brain from a ruptured AVM which has left me with short term memory lssues and a loss of vision down my left side. One reason ive turned to astronomy as i can no longer confidently through myself down mountains on a bike like i used too.

Yes, Mark is right. It is a physical thing. 

Starlight enters the objective as a wide beam, and leaves the eyepiece as a narrow beam. The width of the latter is the exit pupil.

To see all the beams that leave the eyepiece, you must place your pupil at the right distance from the eye lens of the eyepiece. This is called the eye relief.

Here is an animation to clarify the concepts:

ep6a.gif

It is true what they say about a picture saying a thousand words. Thanks for that.

[Mak the Night]

So with my 25mm ill be seeing an exit pupil of  3.5. That puts it at the upper end of the Nebula viewing based on Ruud's earlier clarification. So if i am to invest in something around the 21mm range (once again based on wharthogs guide to a set) ill have a staggered EP and not duplicating prehaps? Or do i look at the 24mm tested in Johns comment. Also what program are you using to show these images? On a personal note i understand your suffering, I suffered a bleed on the brain from a ruptured AVM which has left me with short term memory lssues and a loss of vision down my left side. One reason ive turned to astronomy as i can no longer confidently through myself down mountains on a bike like i used too.

I make it 3.6mm with a 25mm eyepiece (25/6.9). Depending on the target and filter employed when using a filter the best exit pupil diameter can vary considerably I believe, although most people agree that usually an exit pupil range of between 2 & 4mm is the average for a UHC filter. 

Take a look at this:

http://www.lumicon.com/pdf/3filterspec_prnt.pdf

I'm planning on getting a 235mm f/10 SCT soon so I will have much more range with exit pupils as I should be able to use a 55mm Plossl with it. On my 4" Mak I can successfully use stacked Neodymium and UHC filters viewing the Orion Nebulae with a 40mm Plossl (3.1mm exit pupil). I can get a 2.51mm exit pupil with a 32mm Plossl. Which is about the limit with a filter. Anything smaller tends to darken the image too much. I have a 25mm TeleVue Plossl which is a bit brighter than my 24mm Panoptic, but not by much. I personally think the Plossl gives slightly brighter views because it is a simpler design than the Panoptic. If you can get a 24mm TeleVue Panoptic though you won't regret it. I believe it would work well on your scope with a filter. Panoptics aren't cheap though, mine cost more than my Mak!

The program in the jpegs is Stellarium http://www.stellarium.org/en_GB/

You can get a Chrome plug-in and run Stellarium online https://chrome.google.com/webstore/detail/stellarium-on-rollapp/koecfllbdgblbpiicoekgjbhdnmgdcnm?utm_source=chrome-ntp-icon

The Ocular feature is a Stellarium plug-in and I think runs at start up by default. I only run Stellarium on Ubuntu as it's in the Ubuntu repo. The ocular plug-in is fairly intuitive to use but it helps if you know the field stop size of the eyepiece in question as well as its f/l and AFOV when you type the details into the plug-in input box.

Yeah, brain bleeds aren't for wimps. When people ask me how I can justify the cost of some of my TV eyepieces I just blame the brain damage lol. I'm making a lot of progress in physiotherapy. I can do things now I couldn't do a year ago. I don't think I'll be practising ju jutsu again for a while just yet though. 

M42 with a 40mm Plossl on a 102mm Mak:

Although it looked much more like this in actuality (Baader UHC-S filter):

[Danny83uk]

Yeah, brain bleeds aren't for wimps. When people ask me how I can justify the cost of some of my TV eyepieces I just blame the brain damage lol. I'm making a lot of progress in physiotherapy. I can do things now I couldn't do a year ago. I don't think I'll be practising ju jutsu again for a while just yet though. 

You've got to have comedy. my partner now is at a stage she can laugh when i walk into stuff or headbutt things i cant see. And we end up laughing when i have to ask why we arnt talking because ive forgotten what we argued about.

[Mak the Night]

You've got to have comedy. my partner now is at a stage she can laugh when i walk into stuff or headbutt things i cant see. And we end up laughing when i have to ask why we arnt talking because ive forgotten what we argued about.

Luckily my cognitive functions weren't affected. I know all about comedy. At 4 am this morning I could see both Mars and Jupiter high in the plane of the ecliptic in the south. Mars was visibly red. I'd just got the binoviewer case outside and the tripod set up and only had two more trips (for the OTA & mount) when the clouds covered the sky. Laugh? I could have cried lol!

[Danny83uk]

Yup, Ive got in from work and looked up. Thought perfect ill go gaze tonight. Then i open the door and remember i have two children who insist that tonight not any other night is the night that a Lego farm needs to be made. But its lego so you cant not want to do that.

[Danny83uk]

Has anyone had any experience with explore scientific as a manufacturer?

http://www.explorescientific.co.uk/en/Eyepieces/Explore-Scientific-Maxvision-68-Okular-24mm.html

This is correct as suggested is it not?

[John]

Has anyone had any experience with explore scientific as a manufacturer?

http://www.explorescientific.co.uk/en/Eyepieces/Explore-Scientific-Maxvision-68-Okular-24mm.html

This is correct as suggested is it not?

I've got one of those as I mentioned earlier in the thread. For the money they are really very good.

[Danny83uk]

Sorry I'm not able to edit posts? That item is sold out/discontinued.

[John]

Try this instead - it's slightly better again and this one is on sale at the moment so less than the one above:

http://www.bresser.de/en/Sale/Display-Items/Explore-Scientific-68-Ar-Eyepiece-24mm-1-25.html