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JOC

A box of (lesser) green and black - or what you can achieve with SGL classifeds

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12 minutes ago, JOC said:

You don't ūüôā¬†

In fact I find the hardest thing in astronomy is knowing how big/small the object is that I'm looking for.  

 

When it comes to the fainter DSO objects you can be looking straight at it ,and not realise it. Its basically invisible to the eye, sometimes adverted vision can help .Light pollution can really destroy the ability to find the fainter DSO ,and this is where a true dark site really comes into its own. A true dark site and good transparent Sky's can really really help in finding the fainter DSO and obviously aperture and good eyepiece's can also help. But if you really want to find the fainter DSO then you do need to travel to a true dark site, where the fainter DSO will pop to the eyes far more easily ,when in light polluted Sky's can be invisible to the eye.

 

 

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12 minutes ago, JOC said:

I've often thought a useful thing would be a novices list of say 20 interesting things to see up there (and roughly the right time of year to view - say before midnight) and the sort of magnification that they support to get the best view - most novices could then do the maths for their own F/L and work out what their best EP's would be to get close to that 'magnification' out of what they own.

Thank you.

This is a great idea, but is there a chance that the listed parameter magnification could be changed to exit pupil for extended objects?

This is because magnifications can change enough with (f ratio and aperture) that we could well be out of the range to view the extended objects- nebula in particular, espc with filters.

An example of this is with the f7.5 SW120ED- I use a 42mm Vixen LVW on the Veil with and without filters- the same eyepiece in my 10" is not so good for this. the "optimum" mag for the 120ED is 21x and for the 10" 44x at the same 5.6mm exit pupil.

This also illustrates "image scale" as related to me by mod @swamp thing years ago.

Anyway, the concept is excellent for the list :thumbright:

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By the way, I love this photo (it's the one I've hanging on my wall). A good way to visualise where/how big the HH is in relation to that part of the sky and the Flame Neb/Alnitak. 

Credit: Rogelio Bernal Andreo, Oct 2010.

 

RBA_Orion_HeadToToes.jpg

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4 minutes ago, Second Time Around said:

What a spectacular photo!

Mind-blowing, isn't it! I took one look at full-resolution, saw it was open license, and immediately took it on a memory stick to the print shop and said 'could I have this on your largest print please'.

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8 minutes ago, Ships and Stars said:

PS JOC apologies if I was explaining things you've known for ages,¬†I get excited talking about the Horsehead and that's it, I'm away with the fairies¬†ūü§£¬†

Def. the best place to be atm.  

I don't know a great deal (except maybe about the mistakes that novices make when setting up Goto units!!!¬† ūüėČ )¬† I am still very much a novice at this, despite my fancy intermediate set of EP's and don't get to view things very often so any help is useful.

2 minutes ago, Timebandit said:

When it comes to the fainter DSO objects you can be looking straight at it ,and not realise it. Its basically invisible to the eye, sometimes adverted vision can help .Light pollution can really destroy the ability to find the fainter DSO ,and this is where a true dark site really comes into its own. A true dark site and good transparent Sky's can really really help in finding the fainter DSO and obviously aperture and good eyepiece's can also help. But if you really want to find the fainter DSO then you do need to travel to a true dark site, where the fainter DSO will pop to the eyes far more easily ,when in light polluted Sky's can be invisible to the eye.

I've discovered this with the Ring nebula, but at least if I have a list of magnifications I know that I am at least not missing things due to being too close or too far away and that all I've got to do is the 'see' it.

3 minutes ago, jetstream said:

This is a great idea, but is there a chance that the listed parameter magnification could be changed to exit pupil for extended objects?

This is because magnifications can change enough with (f ratio and aperture) that we could well be out of the range to view the extended objects- nebula in particular, espc with filters.

As a novice it is good to have things explained in terms of things that I Immediately comprehend - now I guess this is about me, but maybe does apply to other folks.  I immediately comprehend apparent 'magnification' its the focal length of my scope in mm divided by the length of EP in mm.  This is why I get about x120 out of 10mm and about x240 if I can get to 5mm, but in the UK that's about as good as it gets despite the  theoretical maximum of the scope.  I can easily go and look up what exit pupil is and I'd understand it, but as I read it I see no direct read-across to my own kit and equipment because I have nothing to hang it on in terms of a tangible focal length of scope or EP.  In the same way in programming I'm OK if I can attach a macro or routine to an object (say a macro button), but to hook it to a theoretical 'variable' that hangs somewhere in the great void of computer land is something that I struggle with far more.  For me 'Exit pupil' is not a tangible 'something' I can't think in those terms and tbh just take what I am told at face value when folks go on about it.  Yet, explain something to me in terms of apparent 'magnification' I see that in terms EP length and telescope FL and can relate this immediately to how people with different size scopes would perceive things.  I realised a long time ago that these seemed the most important two things in getting things the right size in the EP.  I've largely now discounted mirror size - I realise now that is really only important for gathering more light needed to see more distant objects.  At least within what I am conscicously understanding about telescopes.

That is probably not very well explained, but 'exit pupils' unless I really study up goes 'whoosh' straight over my head.  I hope the reason why that is personally the case for me makes sense.

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24 minutes ago, Ships and Stars said:

A good way to visualise where/how big the HH is in relation to that part of the sky and the Flame Neb/Alnitak. 

I can find it easily in that its about 10 O'clock on the edge of the larger red/pink circle within the lower colour arc

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3 minutes ago, JOC said:

As a novice it is good to have things explained in terms of things that I Immediately comprehend

Well, if exit pupil is not directly used then a list of f ratios and mag ranges needed for nebula viewing might be an asset.

Inadvertently, optimum exit pupil will be stumbled upon and then reflected in the eyepiece of choice by the individual. If an understanding of eye illumination can be had the sky really opens up IMHO and much quicker.

Using S&S image I'll relate (if its ok) whats possible with basic equipment using eye illumination as a component of the observation.

Of course this is completely off topic ^^- but I'll say this- the eyepiece class that the Morpheus sits in is high.

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I have a list of favourite objects if anyone wants to include them.

M42

The Ring Nebula - (best DSO object up there IMO, but needed averted vision)

The blue snowball - that's a rather cool object

The catseye nebula - def. saw that

The Owl Nebula - pretty sure I've caught that too

The cigar nebula - if memory serves I may have found that too.

M81 or M82 - I'm pretty sure I got either/both

Lyra - double double star - on a good night I can get that to budge into 4 stars - real sense of accomplishment, but it took 5mm to do it.

Polaris double star

Jupiter

Saturn 

The moon - though we probably don't need instructions for that!

Andromeda - never yet seen more than the middle.

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7 minutes ago, JOC said:

I have a list of favourite objects if anyone wants to include them.

Very interesting that all your objects listed can take high mag (low exit pupil), knowing this allows suggestions for other, fainter observable objects if members would like to pursue it.

Have you tried your 31mm Baader on M31?

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1 minute ago, jetstream said:

Have you tried your 31mm Baader on M31?

Not so far - in fact it's been largely unexperimented with due to it being for 'larger objects' and I haven't had much success chasing these at all (i swear blind that damn veil is a figment of the imagination - mind you at the other end of the scale so is E and F in the trapezium - though apparently they might show with slightly less magnification from what folks have shared with me over the last few days) so I've tended to stick with what I know I can find.

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Just now, JOC said:

Not so far - in fact it's been largely unexperimented with due to it being for 'larger objects' and I haven't had much success chasing these at all (i swear blind that damn veil is a figment of the imagination - mind you at the other end of the scale so is E and F in the trapezium - though apparently they might show with slightly less magnification from what folks have shared with me over the last few days) so I've tended to stick with what I know I can find.

JOC, you will see at least one dust lane with the 31mm Baader.

You can easily see the Veil with a high transmission tight OIII from your home-using the 31mm.

I might humbly add that M31 is one of the largest objects (in EP) in the sky to observe.

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3 hours ago, John said:

I finally managed to spot it with my 12 inch scope a while back. No "horse head" shape I'm afraid - just the vaguest slightly darker "bite" out of another very faint strip of nebulosity.

 

 

Hi John.

Did you use any type of filter to see the horse head? Is it another low mag target.

Baz

 

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6 minutes ago, Barry-W-Fenner said:

Hi John.

Did you use any type of filter to see the horse head? Is it another low mag target.

Baz

 

Here is my report of that Baz:

https://stargazerslounge.com/topic/304416-barnard-33-the-horsehead-nebula-at-last/

I would say that its more of a "right" magnification target to get an effective exit pupil that maxmimises the impact of the H-Beta filter (which is also a highly desireable tool for this task). Even when all these things and the observing conditions fall right I've found it probably the most challenging target that I've managed to see from home. It took me a few years to manage to see it as I've mentioned in the report.

 

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4 hours ago, JOC said:

For me 'Exit pupil' is not a tangible 'something' I can't think in those terms and tbh just take what I am told at face value when folks go on about it.

All I can say to make exit pupil tangible is to point your scope at something bright like the sky and pull back from the eyepiece and notice how the illuminated spot shrinks with increasing magnification.  If I had to guess why 2mm is the sweet spot, that's the size of most people's irises in the daytime, so that's where your vision has adapted to having the best acuity over time.  As far as why tiny exit pupils are uncomfortable, it's like a pinpoint of light shining into my eyeball illuminating every floater individually in there.

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22 hours ago, JOC said:

  I can easily go and look up what exit pupil is and I'd understand it, but as I read it I see no direct read-across to my own kit and equipment because I have nothing to hang it on in terms of a tangible focal length of scope or EP. 

In terms of numbers it is just your EP focal length divided by your scope focal ratio, so in your f6 dob your 6.5mm gives about 1mm, your 12.5mm about 2mm and your 17.5mm about 3mm. Thinking in terms of exit pupil is probably the most important thing in visual astronomy, in fact it is almost the only important thing. 

22 hours ago, JOC said:

I've largely now discounted mirror size - I realise now that is really only important for gathering more light needed to see more distant objects. 

No. Each object has an ideal exit pupil size. Increasing the aperture allows you to view the object at a larger magnification while keeping the exit pupil size the same. The horse head requires a large (4-5mm) exit pupil and a good level of magnification, hence why you need a large scope to observe it. With a smaller scope you have to choose between getting the right exit pupil or the right magnification, and so you will struggle to see it. 

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4 minutes ago, Ricochet said:

No. Each object has an ideal exit pupil size. Increasing the aperture allows you to view the object at a larger magnification while keeping the exit pupil size the same. The horse head requires a large (4-5mm) exit pupil and a good level of magnification, hence why you need a large scope to observe it. With a smaller scope you have to choose between getting the right exit pupil or the right magnification, and so you will struggle to see it. 

but if you look at it from mirror size they are more than linked - following that argument the larger mirror allows a larger exit pupil and from what I gather the more faint the object the more advantageous it is to view it through a larger exit pupil as more light will hit the optic nerve.  i.e. the larger mirror permits you to increase pupil size you need to see faint objects.  It seems to me that whether you look at the larger mirror as something that gathers more light or something that allows a larger exit pupil its all about being able to see the more faint objects which need more light to hit the optic nerve.  Thus supporting my statement that increasing the size of the mirror appears to be a means to an end to see more faint objects (even if by dint of this you are doing so by increasing the possible pupil exit size that can be used). 

HH still sounds a 'way out there' target for me though. Though @John did write

19 hours ago, John said:

maxmimises the impact of the H-Beta filter (which is also a highly desireable tool for this task)

Which kicked off a rummage in my filter bag as I thought I had another of these talked about filter types lurking I've turned up a pristine H-Beta filter with Explore Scientific written on it.  Who knows...it might help?

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10 minutes ago, JOC said:

but if you look at it from mirror size they are more than linked - following that argument the larger mirror allows a larger exit pupil and from what I gather the more faint the object the more advantageous it is to view it through a larger exit pupil as more light will hit the optic nerve.  i.e. the larger mirror permits you to increase pupil size you need to see faint objects.  It seems to me that whether you look at the larger mirror as something that gathers more light or something that allows a larger exit pupil its all about being able to see the more faint objects which need more light to hit the optic nerve.  Thus supporting my statement that increasing the size of the mirror appears to be a means to an end to see more faint objects (even if by dint of this you are doing so by increasing the possible pupil exit size that can be used).

A larger scope will not necessarily improve the ability to detect an object if the magnification at the optimal exit pupil becomes too high.  An example of this would be Barnard's Loop.  It wasn't even discovered until the advent of photographic plates because it's too large and diffuse to detect with the eye in pretty much any telescope.  Had it been 100 times farther away, it might have been detected earlier.  However, Barnard's Loop is easy to detect with night vision gear and a low magnification lens.

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On 30/03/2020 at 09:24, JOC said:

I've largely now discounted mirror size - I realise now that is really only important for gathering more light needed to see more distant objects. 

JOC, I'm no expert and didn't want to disagree with you on a lot at once. The easiest thing to do is just "follow" the advice, but if your like me a deep understanding of something is almost mandatory.

@Ricochet is right. But, I'll describe something else that many discount, but what a few believe later.

1 hour ago, Ricochet said:

No. Each object has an ideal exit pupil size. Increasing the aperture allows you to view the object at a larger magnification while keeping the exit pupil size the same. The horse head requires a large (4-5mm) exit pupil and a good level of magnification, hence why you need a large scope to observe it. With a smaller scope you have to choose between getting the right exit pupil or the right magnification, and so you will struggle to see it. 

This is correct but I might add that the "ideal" exit pupil is an individual thing, however each object has a "typical" range.

INCREASING APERTURE DOES NOT MAKE DSO EASIER TO SEE BY ITSELF.

After you follow the path of realization on this, objects will "fall" into the eyepiece, limited by your sky.

JOC are you onboard to explore this fact?

 

 

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4 minutes ago, jetstream said:

JOC are you onboard to explore this fact?

Certainly, it's a sad person who can't learn something new each day.  So what you are suggesting is that within a certain setup - say my 8" F6 1200mm FL Dobsonian I could through my EP's and put stickers over all the mm markings and re-write them with exit pupil size and I could still pick the EP that was going to give me best performance on certain targets if I was aware of the targets rough size (small, medium or huge) in the sky?

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I can make it simpler than this-your 31mm Baader gives 5.16mm exit pupil and is perfect for diffuse nebula like the Veil, Monkyhead, Rosette, Eagle, Swan neb. etc...and the list is long.

If you can temporarily assume that a 2mm exit pupil is good for many galaxies then your super 12.5mm Morpheus puts you in the strike zone.

Object size in the eyepiece is a defining parameter, eventhough there is a range.

Clark and Blackwell have VG info on detection.

https://clarkvision.com/visastro/omva1/index.html

No real need to go to the trouble understanding this but its interesting.

What are your thoughts now about eye illumination (exit pupil)?

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Clark

"Optimum Magnified Visual Angle

A low-contrast object is more easily detected if it is larger. For an extended object such as a galaxy viewed in a telescope, magnification does not change the contrast with the background, because both the sky's and the object's surface brightnesses are affected equally"

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4 hours ago, jetstream said:

What are your thoughts now about eye illumination (exit pupil)?

That my 31mm is better for bigger objects and my 12.5mm is going to be better for Galaxy hunting, but once found I might be able to get closer.  However, that tells me nothing new and I am still not looking at it from the perspective of exit pupil - it just applies the common sense that the larger the object the less 'magnification' is needed and the smaller the object the closer I need to get to it.  The exit pupil is still zooming over my head. Though this:

4 hours ago, jetstream said:

A low-contrast object is more easily detected if it is larger. For an extended object such as a galaxy viewed in a telescope, magnification does not change the contrast with the background, because both the sky's and the object's surface brightnesses are affected equally"

is understood and common sense suggests that this has to be the case.

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48 minutes ago, JOC said:

is understood and common sense suggests that this has to be the case.

Then your all set to go.

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Fine set, range of eyepieces for your 8" F6 dob.

The Globular's are coming, your mid-power from 14mm, 12mm to higher power 6.5mm perhaps 5mm, will be superb. the 17mm will act as a finder. 

What to look forward to

M3 located  in Canes Venatici

M5 located in Serpens

M13 and M92 located in Hercules

M53 located in Coma Berenices

Abound within those constellations there are also a number of NGC cat globular's, such as NGC 6229 in Hercules.

Perhaps there ought be a SGL announcement:

"The Globular's are coming soon; to a back garden near you"

I think I am starting to become a little lock down crazy.

 

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