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A question about exit-pupil and eyepieces

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#1 nyx

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Posted 19 November 2019 - 02:12 PM

When I started with visual astronomy, I read that when using an eyepiece that provides you an exit pupil greater than your pupil actually is, you lose "visual" information. Now, I understand the basic concept of exit pupil and how it relates to telescopes and eyepieces, but I have no idea how it looks like in practice.

 

So my question is: if your pupil is 5mm big and the eyepiece gives an exit pupil of 7mm, does it mean than what you see through the eyepiece is similar to an eyepiece that gives you an exit pupil of 5mm? For the sake of the example, let's assume that both views have the same FoV at the end.

 

Clear skies!


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#2 Taosmath

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Posted 19 November 2019 - 02:22 PM

I believe your understanding is correct.  You would only be collecting about 1/2 (actually 25/49) of the the light coming out of the eyepiece.  Hence you gain nothing by having the 7mm exit pupil compared to the 5mm exit pupil.  

 

In fact you probably lose, since the 5mm exit pupil eyepiece will have a higher magnification than the 7mm exit pupil eyepiece, and if there is enough light coming from the target, you might see more detail in the higher magnification image than in the lower magnification image.



#3 sg6

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Posted 19 November 2019 - 02:24 PM

Difference will be the brightness. The 7mm dia means 2 mm falls outside the pupil, whereas a 5mm means it all squeezes in.

 

However if the same scope then the magnification of the 5mm is more then the 7mm so the image on the eye is bigger and so dimmer. confused1.gif

 

I would just accept that some falls outside the pupil. Now if that is disaaterous to you go for the smaller exit pupil. Otherwise just accept that some is lost and look at the view.


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#4 havasman

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Posted 19 November 2019 - 02:35 PM

Very good question.

 

Your scope aperture captures a fixed quantity of photons and delivers them to the focal plane in as coherent a wavefront as possible. Your eyepiece takes that wavefront, magnifies it and delivers it to the entrance pupil of your eye in a collimated pencil of light the diameter of which is the exit pupil. If that exit pupil is larger than your eye's dark adapted dilated pupil, some of that collimated pencil of light carrying those precious photons will be delivered to the area outside your open pupil and will not reach your retina. So the image you perceive will be dimmer than what you will see with an eyepiece delivering a pencil of light matched to your dilated pupil.

 

But the tables declaring age-related exit pupils are unreliable. Several of us here have larger exit pupils than they indicate. Yours can easily be measured at home.

 

And there are sometimes reasons to use that larger exit pupil anyway, the predominant one is with very narrowband filters to see large faint objects from a good dark site. Quite large aperture scopes can also allow larger than optimum exit pupils as the fixed quantity of captured photons gets so that some loss can easily be ignored in favor of the wider field of a longer focal length eyepiece. (We cannot make the requested assumption as it is incorrect but it is also not a relevant factor.)


Edited by havasman, 19 November 2019 - 02:41 PM.

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#5 photoracer18

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Posted 19 November 2019 - 02:38 PM

Yeah don't rely on those tables for much. Just enjoy the view. I am 72 and it does not bother me.


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#6 nyx

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Posted 19 November 2019 - 02:46 PM

So, when shopping for eyepieces, should one take the theoretical exit pupil limits into account or just shop for the "best" eyepiece, even if it means that you may be losing some of the projected image?



#7 WarmWeatherGuy

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Posted 19 November 2019 - 02:49 PM

If you point your telescope at the moon such that all you see is bright moon then the light beam coming out of the eyepiece will have a certain diameter (exit-pupil) that you can see with a piece of tissue paper placed over the eyepiece.

 

The exit-pupil is the diameter of your scope divided by the scope's power. The power is the scope's focal length divided by the eyepiece focal length. Doing some math and knowing that the f-number of your scope is the focal length divided by the diameter we get

 

exit pupil = eyepiece focal length divided by scope fnumber. I have an f/10 scope so it is easy to calculate the exit pupil for all my eyepieces. 25mm has 2.5mm exit pupil, 12mm has 1.2mm exit pupil etc. I never have to worry about the exit pupil being too large.



#8 kathyastro

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Posted 19 November 2019 - 02:53 PM

It is true that you just lose some light if the exit pupil is larger than the pupil of your eye.  But the light is not lost evenly across the field of view. 

 

The light that is lost is the light that would have filled in the shadow of the secondary mirror.  Not a big deal if you have a refractor, but with any reflector or catadioptric, you will get a dark patch in the middle of the FOV.  In some cases, that may be acceptable, but mostly you will be unhappy with it.


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#9 nyx

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Posted 19 November 2019 - 02:58 PM

It is true that you just lose some light if the exit pupil is larger than the pupil of your eye.  But the light is not lost evenly across the field of view. 

 

The light that is lost is the light that would have filled in the shadow of the secondary mirror.  Not a big deal if you have a refractor, but with any reflector or catadioptric, you will get a dark patch in the middle of the FOV.  In some cases, that may be acceptable, but mostly you will be unhappy with it.

Very interesting, thanks! I own a dobson, so that would apply in my case. 



#10 Redbetter

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Posted 19 November 2019 - 03:43 PM

From 5mm eye pupil to 7mm exit pupil does not seem to have a noticeable negative effect on image brightness, nor does a shadow appear in a typical obstructed scope.  For a refractor it will have no effect on the surface brightness other than maximizing it.  That's right, it maximizes it.  Why?  Because everything below 5mm (if the eye only dilates that wide) produces lower surface brightness.  At 5mm and beyond the brightness will be limited to 5mm. 

 

What it does do is reduce the image scale.  And if your eye can't allow in the full light cone, it is effectively reducing the aperture, but not the surface brightness. 

 

On the flipside, if one assumes their pupil dilates to 5mm, and uses an eyepiece achieving that, but their eye actually dilates to 6mm, then they are operating at 25/36 ~ 70% of the max surface brightness their eye can achieve at night.  For low surface brightness targets (e.g. diffuse nebula, particularly with filters) one can do better with excessive pupil than with "safe" exit pupils. 

 

Unless one is looking at something large and exceedingly bright, like the Moon or daylight observing, the central obstruction is not going to be visible going to 7mm with a 5mm dilated pupil.  Why?  Because the central obstruction still doesn't block enough of the aperture to produce a visible shadow.  Typical Dobs are in the 25% obstruction range (less for the larger ones),  8" SCT's are in the 35% range and 127mm Maks are around 40%.   So take a 35% obstructed SCT, if you could get 7mm pupil with it, the shadow would be 7*.35 = 2.45mm.  That is the equivalent of roughly 50% obstruction at 5mm dilated pupil, which still works. 

 

But in daylight or on the Moon you might see the obstruction, even with an eyepiece that is essentially that of your pupil.  Why?  Because your pupil constricts under bright light.  It is no longer 5mm or 7mm.  It will likely be 2mm or less, possibly a lot less.  At 2mm dilated pupil with even a 5mm exit pupil and 35% obstruction, the obstruction of the exit pupil would be 1.75mm.  The effective obstruction becomes 88%.  Yep, that is noticeable. 


Edited by Redbetter, 19 November 2019 - 08:42 PM.

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#11 aeajr

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Posted 19 November 2019 - 07:20 PM

Eyepiece Exit Pupil and Astigmatism
http://www.televue.c...=54&Tab=_Choose

 

Incorrect article deleted and correct article posted at post 13.


Edited by aeajr, 20 November 2019 - 08:38 AM.


#12 Jon Isaacs

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Posted 20 November 2019 - 08:16 AM

So, when shopping for eyepieces, should one take the theoretical exit pupil limits into account or just shop for the "best" eyepiece, even if it means that you may be losing some of the projected image?

 

I think this is the relevant question.

 

If you are shopping for a single low power, wide field eyepiece, I think it's wise to measure your dark adapted pupil diameter and keep that in mind when choosing an eyepiece.

 

There are situations where an oversized exit pupil can be justified by the wider field of view one might gain but in general, the higher magnification will be more useful than the wider field of view.

 

This is true even if your eye does dilate enough to take in the entire exit pupil. A classic example is a 41 mm SWA (68°) versus a 31 mm UWA (82°.)  The SWA offers a 10% wider field whereas the UWA provides 30% greater magnification, the UWA will nearly always show more.

 

And don't rely on tables, measure your dark adapted pupil. One study of age versus dark adapted pupil included 30 people in the 60s. The average dark adapted pupil was 5.6 mm but the range was from 3.5 mm to 7.5 mm... which one are you?

 

Jon


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#13 aeajr

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Posted 20 November 2019 - 08:29 AM

I posted the wrong link earlier.  I edited that post and removed the link.   Sorry.   This is the article I meant to post.

 

A very good discussion, by Al Nagler, about eyepieces and magnification for those who want to go a little deeper. He discusses our eyes, our telescopes, focal ratios, exit pupils, the atmosphere and things related to choosing magnification.  A good read and not too technical.  It is a general discussion and not specific to any eyepiece or any brand of eyepiece.

http://www.televue.c...page.asp?id=102

 

 

Quoted from the article related to exit pupils.

 

What we can physically fit into our eye as an exit pupil and what is appropriate may not be the same. Furthermore, they differ for reflectors and refractors. A refractor has no limits on how low the power can go and how large the exit pupil can be. This idea is heresy to many, so let me explain. Consider a 4-inch f/4 refractor with a 55-mm eyepiece. The exit pupil has a diameter of about 14 mm. Since you can only use about 7 mm, some would say that half the aperture is wasted and you are really using a 2-inch telescope. They would say you are wasting light and wasting resolution.

 

However, the truth is that while you are wasting potential aperture, you are not wasting light because your eye is fully illuminated, and you have the brightest possible image that you can ever have at that low magnification. Think of using 7 x50 binoculars in the daytime when your eye's pupil is only 3.5 mm. Does the image appear dimmer than it does in 7 x25 binoculars, which has a pupil that matches your eye's? Of course not. Also, the resolution reduction for a 2-inch telescope compared to a 4-inch is totally invisible at that magnification.

 

If a 14-mm exit pupil at 8x doesn't cost you anything in brightness or resolution, does it have any benefits? Sure. At 8x, a 2-inch eyepiece will produce a true field 6° or more in diameter. If you want that large a field to view the Milky Way, for example, why not have it! I'm not arguing that it is particularly wonderful to have an 8x scope, but the concept is valid.


Edited by aeajr, 20 November 2019 - 08:33 AM.

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#14 aeajr

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Posted 20 November 2019 - 09:42 AM

When I started with visual astronomy, I read that when using an eyepiece that provides you an exit pupil greater than your pupil actually is, you lose "visual" information. Now, I understand the basic concept of exit pupil and how it relates to telescopes and eyepieces, but I have no idea how it looks like in practice.

 

So my question is: if your pupil is 5mm big and the eyepiece gives an exit pupil of 7mm, does it mean than what you see through the eyepiece is similar to an eyepiece that gives you an exit pupil of 5mm? For the sake of the example, let's assume that both views have the same FoV at the end.

 

Clear skies!

This question is primarily related to low power eyepieces which, in general, are being used to optimize field of view.  This would either be to assist in star hopping as a finder eyepiece or to take in wider vistas or larger DSOs.

 

My observing site is very light polluted, so my eyes never fully dark adapt.  I have never measured them but even if they can hit 6 mm, I doubt they ever get wider than 4 mm because of the light pollution.   

 

My low power wide field eyepiece for my 12" Dob has an exit pupil of 7.6 mm and a FOV of about 1.75 degree at 40X.  I use it for observing and as a finder eyepiece. 

 

As per Al Naglers article above, I am not wasting light as my eye is fully illuminated.  But if I were to limit my eyepiece selection to my assumed 4 mm exit pupil then my 20 mm 82 degree AFOV eyepiece would be the optimized eyepiece.  That provides  a 4 mm exit pupil at 76X and 1.07 degree FOV.  If I were to stick to the optimized exit pupil I would lose a huge amount of field of view.

 

So, consider the purpose of the eyepiece and what you want to achieve with that eyepiece.  I may be wasting aperture with that 38 mm 70 degree AFOV, but I am gaining a huge amount of FOV which is my primary purpose for that eyepiece.  In this case the eyepiece is optimized to the task and the goal I have set for its use. 


Edited by aeajr, 20 November 2019 - 09:44 AM.

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#15 Jon Isaacs

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Posted 20 November 2019 - 10:18 AM

If a 14-mm exit pupil at 8x doesn't cost you anything in brightness or resolution, does it have any benefits? Sure. At 8x, a 2-inch eyepiece will produce a true field 6° or more in diameter. If you want that large a field to view the Milky Way, for example, why not have it! I'm not arguing that it is particularly wonderful to have an 8x scope, but the concept is valid.

 

 

The brightness of an extended object like a galaxy or nebula is no dimmer with an oversized exit pupil but theyre smaller, most often making them more difficult to see.

 

Stars are dimmer. This is because the brightness of a star only depends on the actual working aperture of the telescope.  An oversized exit pupil reduces the effective aperture of the scope. Your hypothetical 14 mm exit pupil dims the stars by a factor of 4.

 

In theory the resolution is also reduced but your eye has poor resolution at large exits pupils so it's inconsequential. 

 

So, consider the purpose of the eyepiece and what you want to achieve with that eyepiece.  I may be wasting aperture with that 38 mm 70 degree AFOV, but I am gaining a huge amount of FOV which is my primary purpose for that eyepiece.  In this case the eyepiece is optimized to the task and the goal I have set for its use.

 

 

 

 

When compared to an eyepiece like the ES 30 mm 82 degree, you are gaining about 6% In terms of the true field of view. I consider this relatively small. On the other hand, the 30 mm provides 27% more magnification which I consider significant and will definitely show small objects better and serve as a better finder as well as working at full aperture so stars are brighter. 

 

My eyepiece collection includes both the 41 mm Panoptic and the 31 mm Nagler, my dark adapted pupil is closer to 8mm than to 7mm. As a finder at F/5, I always use the 31mm Nagler, the magnification is more helpful than the slight gain in field of view.

 

Jon



#16 stargazer193857

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Posted 20 November 2019 - 11:18 AM

When I started with visual astronomy, I read that when using an eyepiece that provides you an exit pupil greater than your pupil actually is, you lose "visual" information. Now, I understand the basic concept of exit pupil and how it relates to telescopes and eyepieces, but I have no idea how it looks like in practice.

So my question is: if your pupil is 5mm big and the eyepiece gives an exit pupil of 7mm, does it mean than what you see through the eyepiece is similar to an eyepiece that gives you an exit pupil of 5mm? For the sake of the example, let's assume that both views have the same FoV at the end.

Clear skies!


True except it stays 5mm even as you move your eye around. You'll have less blackout risk. For reflectors, the dark center will be bigger, but that is only an issue during the day time or at very large exit pupils. Some people with astigmatism will have a worse view at the larger exit pupil, but the larger eyepiece might let them use their glasses.

#17 stargazer193857

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Posted 20 November 2019 - 11:28 AM

Difference will be the brightness. The 7mm dia means 2 mm falls outside the pupil, whereas a 5mm means it all squeezes in.

However if the same scope then the magnification of the 5mm is more then the 7mm so the image on the eye is bigger and so dimmer. confused1.gif

I would just accept that some falls outside the pupil. Now if that is disaaterous to you go for the smaller exit pupil. Otherwise just accept that some is lost and look at the view.


Brightness is not determined by how much light falls outside the pupil. It is determined by what percentage of the pupil is lit. In a refractor, these two would be equally bright, if the pupil is kept dead center of the eyepiece.

Magnification only dims an object if raised high enough to shrink the exit pupil smaller than your pupil.
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#18 stargazer193857

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Posted 20 November 2019 - 11:30 AM

I believe your understanding is correct. You would only be collecting about 1/2 (actually 25/49) of the the light coming out of the eyepiece. Hence you gain nothing by having the 7mm exit pupil compared to the 5mm exit pupil.

In fact you probably lose, since the 5mm exit pupil eyepiece will have a higher magnification than the 7mm exit pupil eyepiece, and if there is enough light coming from the target, you might see more detail in the higher magnification image than in the lower magnification image.


The 7mm has a wider field of view. And you can move your eye around without losing brightness.

#19 Kipper-Feet

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Posted 20 November 2019 - 02:50 PM

Attention nyx, you've got mail.  Kindly look inside the Inbox of your Personal Messenger.



#20 aeajr

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Posted 20 November 2019 - 04:52 PM

When I started with visual astronomy, I read that when using an eyepiece that provides you an exit pupil greater than your pupil actually is, you lose "visual" information. Now, I understand the basic concept of exit pupil and how it relates to telescopes and eyepieces, but I have no idea how it looks like in practice.

 

So my question is: if your pupil is 5mm big and the eyepiece gives an exit pupil of 7mm, does it mean than what you see through the eyepiece is similar to an eyepiece that gives you an exit pupil of 5mm? For the sake of the example, let's assume that both views have the same FoV at the end.

 

Clear skies!

So, we go back to your original question about, does it look similar?

 

Similar in what way? 

 

Any two dissimilar eyepieces will yield different results and different views in some way.   

 

Assuming your pupil opens to 5 mm, will an eyepiece that produces a 7 mm exit pupil produce a dimmer image than one that produces a 5 mm exit pupil?  No.

 

As long as the eye, the pupil, is fully illuminated they will be equally bright, at least to the extent that you can likely notice. 

 

However the eyepiece that produces the 7 mm EP will have a numerically higher focal length and thus a lower magnification.  So, from a magnification point of view, it will look different, but not because of the exit pupil, because of the magnification. 

 

Reflectors

 

As has been pointed out to me, we should address the difference between refractors and reflectors. With  reflectors, Netwonian telescopes, you have a central obstruction.  You do run into limits on how low you can go in magnification.  At some point you begin to see a shadow of the central obstruction.  I don't know if this is directly related to exit pupil, but I don't think so. 

 

If you look at the specs for most Newtonian scopes (Dobs and non Dobs) you will usually see a "lowest useful" magnification.  This is typically calculated based on a 7 mm exit pupil.   I presume this also applies to SCTs and Maks, but I am not sure. 

 

What happens if you put in an eyepiece that goes lower than that mag?    Maybe nothing bad, or maybe you see the shadow of the central mirror.   

 

That 38 mm/70 eyepiece that I use in my Apertura AD12 yields 40X.  The published lowest useful mag in a scope of those specs would be 43X, yet I have no problems at all. 

 

I have had 3 Newtonian scopes. 

  • 4" F5
  • 8" F5.9
  • 12" F5     

 

I have used that 38 mm/70 degree in the 8" (6.44 EP)  and 12" (7.6 EP) with no noticeable shadow of the secondary mirror.  I use this eyepiece often. 

 

However, if I use a 25 mm (6.4 EP)  in the 4" F4 I start to see the central shadow.  A 32 mm can't be used in this scope.  I typically don't go longer than 20 mm in this scope. 

 

While this does not directly relate to your question, it is something to be aware of.  If you buy a reflector, plan for no wider than a 7 mm EP you should be safe in most, but perhaps not all. 


Edited by aeajr, 20 November 2019 - 05:16 PM.

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#21 sunnyday

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Posted 20 November 2019 - 04:56 PM

I posted the wrong link earlier.  I edited that post and removed the link.   Sorry.   This is the article I meant to post.

 

A very good discussion, by Al Nagler, about eyepieces and magnification for those who want to go a little deeper. He discusses our eyes, our telescopes, focal ratios, exit pupils, the atmosphere and things related to choosing magnification.  A good read and not too technical.  It is a general discussion and not specific to any eyepiece or any brand of eyepiece.

http://www.televue.c...page.asp?id=102

 

 

 

merci monsieur 

thanks



#22 nyx

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Posted 20 November 2019 - 05:33 PM

If you are shopping for a single low power, wide field eyepiece, I think it's wise to measure your dark adapted pupil diameter and keep that in mind when choosing an eyepiece.

Is this a "visit the eye doctor" thing or something I can do at home?

 

This question is primarily related to low power eyepieces which, in general, are being used to optimize field of view.  This would either be to assist in star hopping as a finder eyepiece or to take in wider vistas or larger DSOs.

To be honest, this will be the eyepiece I plan on using when viewing big targets, like the M42 or similar. By the way, I am using this in order to calculate the optimal eyepieces for my telescope (304/1500).

 

The biggest target would be M31, but I doubt I can find a suitable eyepiece to fit the complete Andromeda Galaxy without hitting the exit pupil limit, except maybe the 30ES100, which is way over my budget anyway.



#23 aeajr

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Posted 20 November 2019 - 05:39 PM

OK, so you have an F4.9 scope of some kind.  I don't recall you telling us what type of scope it is and you don't have a signature so we can only guess.  I would speculate that it is some kind of a Newtonian reflector.

 

So, if we stick to the 7 mm EP, that means your longest eyepiece should be about 34 mm.  

 

Assuming a 34 mm 70 degree AFOV you will have 44X and about 1.59 degree FOV.  Close enough for discussion purposes.   That is about half the width of the Andromeda Galaxy.

 

If you want to view M31 in full, you have the wrong scope.   To view M31 in full you need a shorter focal length scope.  

 

I have an F5 80 mm refractor that gives me 12.5X and 4 degree FOV and 6.4 mm EP with a 32 mm Plossl. It only takes 1.25" eyepieces. 

 

 

 

 

Tips:

Top right of the screen you will see your screen name with a little down arrow.
Go to My Settings.  This is where you can make a number of changes.


SIGNATURE:   I recommend you create a signature (my settings)
where you can list your telescope your eyepieces or whatever you wish.  My
signature is at the bottom of this post.  A signature helps people help you
because they know what you have.  We get a lot of requests from people
saying, "I am new, what eyepieces should I get?"   Now we play 20 questions
to find out what telescope they have, what eyepieces they already own, etc..


BUDGET: When asking about things to buy it is good to provide a budget.   An
eyepiece can be $30 or it can be $300.  If we don't know your budget we
don't know how to advise you.  In fact, consider rephrasing your question
to, "I have $200 to spend on eyepieces.  I have the following telescope and
eyepieces.   What would you suggest?"   Give it a try.


LINKS: If you are asking a question about a specific product I suggest you
provide a link to that product so we know exactly what you are talking
about.  For example, Orion sells the Starseeker IV 150.   Well, it turns out
there are two different telescopes that could be described by that name.
One is a 150 mm Newtonian reflector and the other is a 150 mm
Maksutov-Cassegrain.   Or someone says they just got a 4” Celestron GoTo
scope and wants to know what eyepieces to get.   Well, Celestron makes a
number of 4” GoTo scopes.   If there is no link then people will answer
based on the one they think you are asking about rather than the one you
want to know about.


Part of what makes Cloudy Nights so great is that people are very happy to
help one another.  These tips just make it easier for us to help each other
or to understand what is being discussed in the thread.  I hope you find
these tips helpful.


Glad you decided to join us in the sky.   smile.gif


Edited by aeajr, 20 November 2019 - 05:45 PM.


#24 havasman

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Posted 20 November 2019 - 05:48 PM

So, when shopping for eyepieces, should one take the theoretical exit pupil limits into account or just shop for the "best" eyepiece, even if it means that you may be losing some of the projected image?

No. You should measure your maximum dark adapted exit pupil so you're neither guessing or taking some unreliable info as a hard and fast rule.

Close yourself up in a bathroom with a towel under the door as necessary and wait with a camera and a set of calipers preset to 7mm for 20 - 30 minutes. Take a pic in the mirror with the calipers held near your eye. Be sure any red eye reduction pre-flash is OFF.

Then choose your widefield eyepiece. And look to your expected highest useful mag for your gear, site and preferences and see what focal length you may want for that. Decide on the density of population you may need between the two extremes. Cost usually factors in here. Populate the kit with wider spacing at the large exit pupil and and higher density at the higher mag end for best support of your observing. Check to see if your American Express card needs CPR.  wink.gif



#25 nyx

nyx

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Posted 20 November 2019 - 06:09 PM

OK, so you have an F4.9 scope of some kind.  I don't recall you telling us what type of scope it is and you don't have a signature so we can only guess.  I would speculate that it is some kind of a Newtonian reflector.

 

So, if we stick to the 7 mm EP, that means your longest eyepiece should be about 34 mm.  

 

Assuming a 34 mm 70 degree AFOV you will have 44X and about 1.59 degree FOV.  Close enough for discussion purposes.   That is about half the width of the Andromeda Galaxy.

 

If you want to view M31 in full, you have the wrong scope.   To view M31 in full you need a shorter focal length scope.  

 

I have an F5 80 mm refractor that gives me 12.5X and 4 degree FOV and 6.4 mm EP with a 32 mm Plossl. It only takes 1.25" eyepieces. 

 

 

 

 

Tips:

Top right of the screen you will see your screen name with a little down arrow.
Go to My Settings.  This is where you can make a number of changes.


SIGNATURE:   I recommend you create a signature (my settings)
where you can list your telescope your eyepieces or whatever you wish.  My
signature is at the bottom of this post.  A signature helps people help you
because they know what you have.  We get a lot of requests from people
saying, "I am new, what eyepieces should I get?"   Now we play 20 questions
to find out what telescope they have, what eyepieces they already own, etc..


BUDGET: When asking about things to buy it is good to provide a budget.   An
eyepiece can be $30 or it can be $300.  If we don't know your budget we
don't know how to advise you.  In fact, consider rephrasing your question
to, "I have $200 to spend on eyepieces.  I have the following telescope and
eyepieces.   What would you suggest?"   Give it a try.


LINKS: If you are asking a question about a specific product I suggest you
provide a link to that product so we know exactly what you are talking
about.  For example, Orion sells the Starseeker IV 150.   Well, it turns out
there are two different telescopes that could be described by that name.
One is a 150 mm Newtonian reflector and the other is a 150 mm
Maksutov-Cassegrain.   Or someone says they just got a 4” Celestron GoTo
scope and wants to know what eyepieces to get.   Well, Celestron makes a
number of 4” GoTo scopes.   If there is no link then people will answer
based on the one they think you are asking about rather than the one you
want to know about.


Part of what makes Cloudy Nights so great is that people are very happy to
help one another.  These tips just make it easier for us to help each other
or to understand what is being discussed in the thread.  I hope you find
these tips helpful.


Glad you decided to join us in the sky.   smile.gif

Awesome tips as usual :)

 

My first scope was a TS Photon 6" f/5. I still have it, but am currently selling it. My new and only scope is a Taurus 300 12" truss dobsonian. I got it about a month ago (had to wait like 4 months for it). I am hoping to write a review about it one day. For now, I can only say that it is an very well thought scope.

 

I use a Telrad to navigate the night sky and a TS Optics 50/204mm finder-telescope with a 17mm 50° Plössl, which gives me a FoV 4.17°, about the same as the outer circle from my Telrad.

 

One day I will beat my laziness and update my signature too! :)




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