Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Reflectors

Pages: 1 | 2 | 3 | 4 | 5 | (show all)
BillFerris
Post Laureate
*****

Reged: 07/17/04

Loc: Flagstaff, Arizona, USA
Re: Big dob for objects with structure and detail? new [Re: alexvh]
      #5914400 - 06/11/13 01:07 AM

Quote:

So at the same magnification M31 will look the same regardless of aperture?




What you'll notice if you have an opportunity to observe a galaxy like M51 (the Andromeda Galaxy isn't a good example because it's extremely large and nearly edge-on) through a range of apertures under a dark sky, is that objects and details appear more obvious to the eye as aperture increases. Also, subtle details which are at or beyond the threshold of visibility in a smaller scope will be visible at the eyepiece of a larger scope. By delivering a more intense light packet to the eye, a larger aperture allows you to discern more subtle contrasts. In other words, increasing aperture lowers the threshold contrast at which an object will be visible to the eye. The bottom line is this translates to improved views.

That said, many observers can get more out of the scope they have by investing in the time it takes to drive to darker skies to observer, by spending more time at the eyepiece to study an object and by learning to use a range of magnifications to tease every bit of detail from an object. A person often doesn't need to buy a larger scope to see more. Developing their technique and spending more time under a dark sky can deliver more of everything.

Bill in Flag


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Big dob for objects with structure and detail? new [Re: BillFerris]
      #5914463 - 06/11/13 02:30 AM

Bill,
You said, "By delivering a more intense light packet to the eye, a larger aperture allows you to discern more subtle contrasts."

Just to be clear...

For extended objects, a larger aperture by itself does not deliver a more intense light packet.

At given exit pupil, all apertures deliver equally intense light packets.

At given aperture, a lower magnification (larger exit pupil) delivers a more intense light packet.

If a more intense light packet is what's required to see subtler contrasts, then one would tend to go to lower magnification/larger exit pupil. Of course, as we know, this is not generally the case, as object size on the retina is also very important, and so a higher power is often preferred to a lower power.

Threshold contrast is controlled fundamentally by the exit pupil; larger pupils allow to detect subtler brightness variations, because visual system noise is reduced.

Threshold detail is fundamentally controlled by the aperture. A larger aperture provides a larger image at given exit pupil/surface brightness.

To say that a larger aperture lowers threshold contrast is really saying that a larger aperture reveals more detail. Which is axiomatic.

Suppose we have two galaxies which are intrinsically identical, but one is 10X more distant. The nearer one is 20' across, and the farther is 2' across. both have identical surface brightness, but in integrated light the farther one is 1/100 as bright, or 5 magnitudes fainter.

A 2" scope is trained on the near galaxy, and a 20" scope on the distant galaxy. At the same exit pupil, both views will be identical; the 10X bigger scope exactly compensates for the 10X larger distance. The larger scope is *not* lowering the threshold contrast; the perceived surface brightness, brightness profile and visible extent are the same. The larger scope is merely presenting detail commensurate with its aperture.

If the larger aperture in this example lowered the threshold contrast, we should expect to see more detail and a larger extent in the galaxy it's trained upon.

My questions to you, bearing in mind the specific experiment outlined...

Will the views be the same or different?

If different, why?

If not different, how then can it be said that the larger aperture lowers threshold contrast?


I don't like the phrase "lowering threshold contrast" because it too easily connotes the magical and incorrect notion that contrast has increased. Particularly for the less knowledgeable.

If through a small aperture I can discriminate a patch of nebulosity only when it is 10% or more brighter than the sky, can I expect to see through a larger scope a nebula that is 9% brighter than the sky, and with an even bigger scope, a nebula 8% brighter than the sky?

No. No matter the aperture, the same contrast limits apply. And so threshold contrast is not altered by aperture.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jpcannavo
scholastic sledgehammer
*****

Reged: 02/21/05

Loc: Ex NYCer, Now in Denver CO!
Re: Big dob for objects with structure and detail? new [Re: robininni]
      #5914726 - 06/11/13 09:48 AM

Rob
I also enjoy the more detailed "showcase" objects. One thing to realize, though, is that the list gets longer with larger aperture - assuming observing conditions are sufficiently good.

Another thing to appreciate is that it doesn't take a long list of deep sky objects to keep you busy. I just got back from a one night 6 hour stretch under pristine Rocky Mountain skies at the RMSS. I must tell you that I spent that 6 hours with just a few objects. You mention M51 - I spent nearly half the night on M51 alone! But not all in one stretch, but rather going back and forth between M51 and just a few other objects. Each time back to M51 I would try to see more than I had just seen a 1/2 hour ago. Later in the evening I did the same with the M17 and M20. Oh, BTW do add NGC 4565 to your list, its right up at the top - it will seem almost photographic in detail with your aperture under dark skies with good seeing.

But, that having been said, this sort of experience is not everyones cup of tea. To illustrate, birding comes to mind. For me, it is remarkably similar to the endeavor we are discussing here. Telescopes (granted smaller) are used, illusive targets are hunted down and, often, remote/highly selected observing locations are sought. And, it also involves glimpsing and seeing stuff that you can see more clearly and conveniently in a magazine. Yet - it doesn't grab me! Why, I don't know, it just ain't my cup. It's particular "poetry" doesn't speak to me, perhaps in the way Haydn doesn't but Mozart does.

Getting deeply gratified by deep sky observing is a combination - for me - of several things. Part of it is straining to catch more detail that I already know is there, I know the photons are reaching me, if I can just see them! But clearly thats not enough! If it were I might as well sit in a darkened room straining to look at familiar photographs! So for me, it is also the unique flavor of the experience. The dark, the spooky night, the remote location, the complete forgetting about everything else, the quiet, the knowledge that I am peering far beyond this terrestrial realm, the finickiness of my spaceship (the scope!), and the morning and many, many days after; revisiting and savoring through memories of the views while anticipating the next visit to the same object; "Did I rally see the connecting bridge to M51 as clearly as I could? next time I'll push the mag more, or shut off tracking and let it drift into view..."

There is a gratification to this endeavor that few other things give me. And, I often find myself in a meta mode of sorts, reflecting on just what that gratification is - what it is like. So, for example, several nights ago while peering into the dark at M51, straining to see how much detail I was actually seeing, I actually asked myself: In what sense am I enjoying this? Is this more intensely pleasurable then say really good meal when very hungry? Without digressing endlessly into some phenomenological account and philosophical analysis on the nature of pleasures, I will say this. In some way the "peak" hedonic value of the M51 experience is less intense. But while the "rush" of the meal leaves me with little once it is over, the "M51" pleasure (as stated above) stays with me for weeks, months, years as I savor the memory of the entire experience and plan, prepare and look forward to the next.

My advice is to slow down, slowly draw up your list of fav objects. Start an observing notebook. Keep returning to these objects - as you would some good friends. Try to get know them well, and better and better. In the process you will discover if the poetry of the deep sky really does speak to you, or if your cup of tea lies elsewhere.

Joe


Post Extras: Print Post   Remind Me!   Notify Moderator  
robininni
scholastic sledgehammer


Reged: 04/18/11

Loc: Stephenville, TX
Re: Big dob for objects with structure and detail? new [Re: jpcannavo]
      #5914761 - 06/11/13 10:14 AM

Joe,

Very deep! Thanks for such a revealing post of your observing habits and philosophy. I agree with everything you said. And the notebook is a great idea for me. I should have already started that.

Thanks,

Rob


Post Extras: Print Post   Remind Me!   Notify Moderator  
BillFerris
Post Laureate
*****

Reged: 07/17/04

Loc: Flagstaff, Arizona, USA
Re: Big dob for objects with structure and detail? new [Re: GlennLeDrew]
      #5915064 - 06/11/13 01:23 PM

Quote:

Bill,
You said, "By delivering a more intense light packet to the eye, a larger aperture allows you to discern more subtle contrasts."

Just to be clear...

For extended objects, a larger aperture by itself does not deliver a more intense light packet.




Glenn, you're redefining my statement to mean something I did not say. Quite simply, a larger aperture delivers more light from an extended object to the eye than a smaller aperture will. This is a simple, undeniable fact. If you point a telescope of a given aperture at a galaxy, the galaxy will have an apparent magnitude at the eyepiece. If you point a second telescope with 60% larger aperture at the same galaxy, the galaxy will have an apparent magnitude one full magnitude brighter. This real benefit of increased aperture--delivering more light from an extended object to the eye than a smaller aperture delivers--is what I'm referring to when I write that a larger aperture delivers a more intense light packet to the eye. I neither said nor implied that increasing aperture produces an increased surface brightness. Why you would respond as though I had is beyond understanding.

Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
robininni
scholastic sledgehammer


Reged: 04/18/11

Loc: Stephenville, TX
Re: Big dob for objects with structure and detail? new [Re: BillFerris]
      #5915075 - 06/11/13 01:32 PM

Quote:


If you point a telescope of a given aperture at a galaxy, the galaxy will have an apparent magnitude at the eyepiece. If you point a second telescope with 60% larger aperture at the same galaxy, the galaxy will have an apparent magnitude one full magnitude brighter.

Bill




As long as the magnification remains constant that statement is true, right?

Rob


Post Extras: Print Post   Remind Me!   Notify Moderator  
BillFerris
Post Laureate
*****

Reged: 07/17/04

Loc: Flagstaff, Arizona, USA
Re: Big dob for objects with structure and detail? new [Re: GlennLeDrew]
      #5915076 - 06/11/13 01:33 PM

Quote:

I don't like the phrase "lowering threshold contrast" because it too easily connotes the magical and incorrect notion that contrast has increased. Particularly for the less knowledgeable.




The concept of threshold contrast and aperture's role in determining threshold contrast are perfectly understandable to those who bring an open mind to the table. And since threshold contrast is central to the activity of observing and detecting faint, extended objects, it's important to expose new observers to the concept. It would be easier if I didn't have to reply to posts that skew my words into something I never wrote.

Bill in Flag


Post Extras: Print Post   Remind Me!   Notify Moderator  
auriga
Pooh-Bah


Reged: 03/02/06

Re: Big dob for objects with structure and detail? new [Re: jpcannavo]
      #5915087 - 06/11/13 01:39 PM

Joe,
Another very worthwhile post. It gives a sense of the wonder of observing and the aesthetic and philosophical meaning of observing the skies. Poetic. Thanks for posting.
And I agreei in general with your sentiments. Except about birds. I am not a "birder" but from what I hear, birds are not "illusive, they really exist.
But for some deep sky objects there is perhaps some doubt, as in the famous "AintNo List."
Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
Galicapernistein
super member


Reged: 09/24/07

Loc: Detroit Michigan
Re: Big dob for objects with structure and detail? new [Re: jpcannavo]
      #5915285 - 06/11/13 03:40 PM

Quote:

Rob


But, that having been said, this sort of experience is not everyones cup of tea. To illustrate, birding comes to mind. For me, it is remarkably similar to the endeavor we are discussing here. Telescopes (granted smaller) are used, illusive targets are hunted down and, often, remote/highly selected observing locations are sought. And, it also involves glimpsing and seeing stuff that you can see more clearly and conveniently in a magazine. Yet - it doesn't grab me! Why, I don't know, it just ain't my cup. It's particular "poetry" doesn't speak to me, perhaps in the way Haydn doesn't but Mozart does.


Joe




For me, birding and astronomy reinforce one another. Looking for the only surviving members of the dinosauria clade as they return from the other side of the earth is as much fun to me as looking for a distant galaxy. 230 million years ago small, upright reptiles emerged, grew big, and eventually took over the world. All we have left from those times are tough little feathered remnants. There are only a few galaxies a quarter of a billion light years away that I can see in my scope, but I can see the descendants of those ancient reptiles every day. But then, I listen almost exclusively to Bach, so to each his own.


Post Extras: Print Post   Remind Me!   Notify Moderator  
robininni
scholastic sledgehammer


Reged: 04/18/11

Loc: Stephenville, TX
Re: Big dob for objects with structure and detail? new [Re: Galicapernistein]
      #5915341 - 06/11/13 03:59 PM

Quote:



For me, birding and astronomy reinforce one another. Looking for the only surviving members of the dinosauria clade as they return from the other side of the earth is as much fun to me as looking for a distant galaxy. 230 million years ago small, upright reptiles emerged, grew big, and eventually took over the world. All we have left from those times are tough little feathered remnants. There are only a few galaxies a quarter of a billion light years away that I can see in my scope, but I can see the descendants of those ancient reptiles every day.




I'm not into birding, but I can appreciate the similarity with some aspects of astronomy. I find it fascinating to stare at galaxies of sizes and at distances we can assign numbers to, but we really can't humanly comprehend. Then to think God created the immense universe and everything in it, which is also, beyond all comprehension, and that what we occupy in this reality is immeasurably small just fills me with awe.

Rob

Edited by robininni (06/11/13 04:13 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Big dob for objects with structure and detail? new [Re: robininni]
      #5915387 - 06/11/13 04:26 PM

+1 on taking your time. Last Saturday I was out from 8pm - 1am and only viewed Saturn and the Lagoon Nebula. Saturn was an eyepiece swapout exercise. A person there was considering buying an Intelliscope and had just purchaed a 5mm Radian. We used the Radian in the dob on Saturn for about 30-40 minutes, then pulled back to the 11T1 (Gawd what a sharp image). Finally used the 7T1 and was completely blown away....the view was razor sharp and the Cassini division was a nice dark black, probably the best view of Saturn I've had. We tried the 5mm radian and my 5mm Pentax XW, but the seeing just wasn't up to that for either eyepiece, the views were good, you could still see the Cassini division, but it was a little blurry. Alone, I broke out the 30mm Pentax and the 24mm ES82(nonwaterproof) and the OIII filter and spent at least an hour or so viewing with these two eyepieces with and without the OIII. I was never a big filter fan; but this OIII has convinced me there really is something to them.....the background stars disappeared, but the nebula's dark lanes and glowing whisps just popped out....I'll definitley be using the OIII a lot more.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Fred1
Carpal Tunnel
*****

Reged: 09/19/07

Loc: Somewhere in the Orion Spur
Re: Big dob for objects with structure and detail? new [Re: robininni]
      #5915426 - 06/11/13 04:52 PM

Quote:

Quote:


If you point a telescope of a given aperture at a galaxy, the galaxy will have an apparent magnitude at the eyepiece. If you point a second telescope with 60% larger aperture at the same galaxy, the galaxy will have an apparent magnitude one full magnitude brighter.

Bill




As long as the magnification remains constant that statement is true, right?

Rob




Rob, I think what you want is the same mag for the number of inches of aperture. e.g Comparing an 18" F/4.3 to a 25" F/4. Figuring 15x per inch, then the 25" would be at 375x and my 18" would be at 270x. I believe this will give you best comparison for contrast and detail retrieval for such objects. This is just for illustration purposes only and not figuring in Paracorr use. If I'm off base, I'm sure someone will chime in.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Big dob for objects with structure and detail? new [Re: Fred1]
      #5915848 - 06/11/13 09:13 PM

To alter threshold contrast is to change the brightness ratio which can be perceived. This is exit pupil dependent, not aperture dependent. A small scope at a larger exit pupil permits to discriminate lower contrast than a big scope at a smaller exit pupil.

And so it is completely true to say that a *small* scope does lower threshold contrast as long as the exit pupil is larger.

This is fundamentally why I object to the simplistic statement that a larger aperture lowers threshold contrast.

The context in which the concept of threshold contrast is usually invoked centers around the visibility of a *specific object*, and at the *threshold* of perception of detail. This is really no more than stating that a larger aperture delivers a brighter and/or larger image, which permits to perceive more detail. The completely expected result; no surprises here.

But consider such an object as the Califiornia nebula, which is large and resolved at very low power (certainly 10X, if not less.) Which unfiltered scope do you suppose makes the nebula stand out more prominently against the sky?

A 3" at a 6mm exit pupil, or a 12" at a 6mm exit pupil? Equal image surface brightness makes for equal ease (or difficulty) in detection. Both instruments deliver images having the same contrast ratio. Being already well resolved in the small scope, the bigger scope (at the same exit pupil) offers mo real advantage for detection.

How about a 3" at a 6mm exit pupil and a 12" at a 3mm exit pupil? The dimmer view in the latter makes for a more difficult detection. The larger aperture *by itself* has not lowered threshold contrast. The smaller exit pupil has *raised* threshold contrast. In this instance, the large scope is a liability.

To say that increasing aperture lowers threshold contrast in an absolute sense can be true only when the exit pupil is increased. Otherwise, when restricting to describing the aspect of a given object, we're really restating--in a potentially misleading way--the well known fact that increasing aperture increases detail seen.


Post Extras: Print Post   Remind Me!   Notify Moderator  
gatorengineer
Carpal Tunnel
*****

Reged: 02/28/05

Loc: Hellertown, PA
Re: Big dob for objects with structure and detail? new [Re: GlennLeDrew]
      #5915879 - 06/11/13 09:32 PM

I have always looked at and understood contrast alot differently than what is stated above...

A junk mirror (in this case rough) will have poor contrast

A perfect mirror in a lousy structure will have lousy contrast. (stray light leakage)

A perfect mirror with a poor eyepiece will have lousy contrast.

A perfect mirror in an urban setting will have lousy contrast. (relative to that scope in dark skies)

A perfect mirror in an uncollimated scope will have lousy contrast.

(Larger CO also means that there are photons not getting to where they should but that is a slightly differnt story).

A perfect mirror in poor seeing will have lousy contrast. (Trap E and Trap F, dont come and go night to night.....)

Simple explanation is photons getting to where they arent supposed to be. This is the cause of poor contrast, and many inexperienced observers get lost in the sauce, but simply put this is it.

Space is black because there is no scattering of photons.

So any talk about contrast needs to start with an assumption of a sound structure, a smooth primary, a quality multicoated eyepiece (using the birder analogy, Swarovski, and Leica coatings are what make the difference), goodd seeing and a well collimated (and cooled) system.

Optics after that are a straight signal to noise ratio. the larger the antenna (mirror) the more signal is gathered relative to noise. Meter class scopes you can see color in DSO's, why because the signal is higher and the cones can pick it up....

Why use avert vision because there are more rods off of the center axis of the eye....

For extended objects the object will always look brighter in a larger scope, at the lowest useable magnification for that scope than any smaller scope (Period). This is the cause of aperature fever, which is known to beset many in the hobby.


Post Extras: Print Post   Remind Me!   Notify Moderator  
BillFerris
Post Laureate
*****

Reged: 07/17/04

Loc: Flagstaff, Arizona, USA
Re: Big dob for objects with structure and detail? new [Re: robininni]
      #5915913 - 06/11/13 09:56 PM

Quote:

Quote:


If you point a telescope of a given aperture at a galaxy, the galaxy will have an apparent magnitude at the eyepiece. If you point a second telescope with 60% larger aperture at the same galaxy, the galaxy will have an apparent magnitude one full magnitude brighter.

Bill




As long as the magnification remains constant that statement is true, right?

Rob




It's true for any magnification producing a true field large enough to present the whole galaxy. It's true for all celestial objects...stars, clusters, nebulae, etc. Of course for point sources like stars, there is no magnification limit.

Bill in Flag


Post Extras: Print Post   Remind Me!   Notify Moderator  
BillFerris
Post Laureate
*****

Reged: 07/17/04

Loc: Flagstaff, Arizona, USA
Re: Big dob for objects with structure and detail? new [Re: GlennLeDrew]
      #5916016 - 06/11/13 10:45 PM

Quote:

To alter threshold contrast is to change the brightness ratio which can be perceived. This is exit pupil dependent, not aperture dependent.




Increasing aperture does lower threshold contrast and this is easily demonstrated. Simply observe the same galaxy cluster on the same night under the same dark sky with at least two scopes of different aperture. This can be done at any dark sky dark party. Observers will see more galaxies in the larger aperture. Some of those galaxies will be the same size as galaxies seen in smaller apertures but they will have fainter integrated magnitudes than were visible in the smaller scope. These fainter magnitude galaxies have lower surface brightnesses than their brighter counterparts. By definition, they will be lower contrast objects that were made visible by increasing aperture.

Increasing aperture reduces the threshold contrast at which objects become visible to the eye. Folks interested in learning more about the role of aperture in the visibility of faint extended objects can read the article in my signature.

Bill in Flag


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Big dob for objects with structure and detail? new [Re: BillFerris]
      #5916079 - 06/11/13 11:30 PM

The example of bringing small objects formerly below the detection threshold into visibility by application of a larger aperture is more analogous to the case for stars.

How about the case where an object is already large and resolved, such as the huge California nebula? One can enjoy a more obvious detection in a finder or RFT than through a light bucket.


As to space being black and not scattering photons... Deep images show the galactic disk region to be suffused with clouds and general 'cirrus' which does scatter light. It's not important to visual observers because natural airglow and zodiacal light vastly dominates.

As to the gain in signal to noise afforded by a larger aperture... The gain in signal does not go to increasing contrast, for both the (extended) object and the sky are brightened equally. The signal gain goes to increased detail.

A meter class scope only reveals color in some DSOs more readily because the larger image it provides covers more retina at given exit pupil. The surface brightness and contrast in that large scope is no higher than that for a smaller scope (at the same exit pupil.)


It is not required to limit discussions of contrast to 'ideal' conditions. As long as the variables, such as sky and instrument quality, are the same, the results are meaningful and valid.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jpcannavo
scholastic sledgehammer
*****

Reged: 02/21/05

Loc: Ex NYCer, Now in Denver CO!
Re: Big dob for objects with structure and detail? new [Re: GlennLeDrew]
      #5916174 - 06/12/13 12:34 AM

I hate retyping: an earlier post is somewhat informative here: Aperture and extended detail

Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Big dob for objects with structure and detail? new [Re: jpcannavo]
      #5916373 - 06/12/13 05:46 AM

Joe,
I read that post of yours at the time, and am in full agreement. Your idea of examining a photo from different distances in dim light--I did that years ago.

My argument against the *universal* statement that an aperture increase lowers threshold contrast might be summed up this way.

Imagine a rather larger aperture working at a somewhat smaller exit pupil. Magnification has increased, and the view has somewhat lower surface brightness. Therefore the larger scope has a *higher* (worse) threshold contrast because of the dimmer view. Yet in spite of this, it still reveals more detail simply by virtue of the increased image scale. The improvement afforded by magnification has increased faster than the worsening of threshold contrast.

And just what is threshold contrast? An example...

At a 7mm exit pupil, an object might be detected when about 4 magnitudes fainter than the sky. This is fairly low threshold contrast. Reduce the exit pupil to 1mm, and now an object must be no fainter than the sky by about 1 magnitude in order to be glimpsed. This is fairly high threshold contrast. The foregoing would apply equally for all apertures.

The only way a larger aperture lowers threshold contrast, then, is when the exit pupil is increased. If all observers only used ever larger exit pupils when increasing aperture, the the generalization that an aperture increase lowers threshold contrast would hold. But observers tend to employ the same range of exit pupil in all their instruments, and so it cannot be universally stated that an aperture increase lowers threshold contrast.

My seeming belabouring of the point might come across as arguing semantics. But it goes to a *fundamental* understanding of all the variables. I am taking great pains to quell any misapprehension that increasing aperture by itself improves contrast.


Post Extras: Print Post   Remind Me!   Notify Moderator  
robininni
scholastic sledgehammer


Reged: 04/18/11

Loc: Stephenville, TX
Re: Big dob for objects with structure and detail? new [Re: GlennLeDrew]
      #5916556 - 06/12/13 09:16 AM

Glenn,

For what it's worth coming from a relatively inexperienced guy, I totally follow you and it makes complete sense that improving the threshold contrast (I'd just call it making an object seem brighter) by increasing aperture is actually all about having increased the exit pupil for the same or possibly even higher magnification.

Rob


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | (show all)


Extra information
14 registered and 13 anonymous users are browsing this forum.

Moderator:  ausastronomer, Knuklhdastrnmr, Phillip Creed, JayinUT 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 3080

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics