Why do we need bigger scopes?

[cloudsweeper]

2 minutes ago, jetstream said:

Thing is the light coming from the extended object does not change.

Yes, but the amount you gather does change.

[JeremyS]

21 minutes ago, jetstream said:

The brightness adds up?

Yes. The eye/brain can integrate exposures to an extent.

[vlaiv]

Ok, I accept that size makes difference for same exit pupil, but I have a sense that it's given more credit than it deserves.

How about objects that have features that are half the size of the whole object? Anyone looked observed something like that? Usually faint nebulae will be prime candidates for that.

Say NAN for example.

I marked two regions that are prime candidates for this - they look like they have same brightness and one is about x4 larger than the other in surface.

Did anyone ever see one and not see the other? If size explanation holds - this will happen at least in some cases.

Edited October 5, 2021 by vlaiv

[Stu]

18 minutes ago, jetstream said:

Thing is the light coming from the extended object does not change like using more LEDs in a flashlight.

No, but if you are able to maintain the same surface brightness over a larger area by using a larger scope, does the analogy not hold? What’s your take on it Gerry?

[jetstream]

10 minutes ago, vlaiv said:

Did anyone ever see one and not see the other?

I always see both, but I had a great view of them in the H130 the other night...

[Stu]

13 minutes ago, vlaiv said:

Ok, I accept that size makes difference for same exit pupil, but I have a sense that it's given more credit than it deserves.

How about objects that have features that are half the size of the whole object? Anyone looked observed something like that? Usually faint nebulae will be prime candidates for that.

Say NAN for example.

I marked two regions that are prime candidates for this - they look like they have same brightness and one is about x4 larger than the other in surface.

Did anyone ever see one and not see the other? If size explanation holds - this will happen at least in some cases.

You are showing two very large objects there Vlaiv, I think the point is more likely to be relevant to smaller, fainter galaxies which can be enlarged enough by larger dobs (whilst maintaining that SB) in order to be seen. With a smaller scope, you might not be able to get the to a size where they can be perceived.

[vlaiv]

This size / contrast thing should work in single scope with zoom eyepiece.

When we change magnification - we don't change contrast between the two - object and background. If we have threshold object - at some magnification (barely detected) - if we zoom out - it should disappear from view.

We don't need constant exit pupil for this to happen.

I'm fairly certain that this will happen far less often than is suggested.

[Stu]

2 minutes ago, vlaiv said:

I'm fairly certain that this will happen far less often than is suggested.

Give it a try on some small galaxies and let us know!

[vlaiv]

2 minutes ago, Stu said:

You are showing two very large objects there Vlaiv, I think the point is more likely to be relevant to smaller, fainter galaxies which can be enlarged enough by larger dobs (whilst maintaining that SB) in order to be seen.

My experience was with x2 larger magnification and galaxies in Markarian's chain at about x20 and x40.

These are about 2' x 1' to maybe 3'x2'. This means that they were quite small in both scopes - around 1° when magnified.

[jetstream]

2 minutes ago, Stu said:

but if you are able to maintain the same surface brightness over a larger area by using a larger scope, does the analogy not hold

I'm not sure- is the surface brightness "fixed" for each object? Were delving into increasing an objects brightness in a telescope -where many say contrast is fixed between the skies brightness and the surface brightness of the extended object. The exit pupil deal is for our own perception of the object- however contrast remains fixed. Re; Aceys thread years ago.

[jetstream]

I wish some members debating this could look through my 15" and 24" side by side and then apply the theories.Actually do the 10,15 and 24 . Because contrast in fixed between the objects brightness and sky brightness no scope should be able to magnify brightness, many say.

[Stu]

2 minutes ago, jetstream said:

I'm not sure- is the surface brightness "fixed" for each object? Were delving into increasing an objects brightness in a telescope -where many say contrast is fixed between the skies brightness and the surface brightness of the extended object. The exit pupil deal is for our own perception of the object- however contrast remains fixed. Re; Aceys thread years ago.

 Contrast is fixed, regardless of magnification, I agree, or at least that’s my understanding! As you increase the mag, you dim both target and background SB.

The thing I don’t have the language to describe is this issue of maintained SB in a larger scope at higher mags ie larger image scale. If the brightness per unit area is, say, a and in a smaller scope the target covers b units squared, the ‘total brightness’ coming from the target is a x b. In the larger scope, perhaps it is three times the area, so the ‘total brightness’ is now a x 3b. Does that make any sense?

[Stu]

4 minutes ago, jetstream said:

I wish some members debating this could look through my 15" and 24" side by side and then apply the theories.Actually do the 10,15 and 24 . Because contrast in fixed between the objects brightness and sky brightness no scope should be able to magnify brightness, many say.

So, if you view them all at the same mag, what’s the result Gerry? Presumably the overall image appears brighter in the larger scope?? I’m not totally sure what you are saying, are we all missing the point somewhat?

[jetstream]

1 minute ago, Stu said:

Does that make any sense?

Nope,

How about this one the "majesty factor" I truly believe that a larger AFOV helps viewing objects like the Veil-tested that one out the other night. What does an increased AFOV do to things?

[Stu]

Just now, jetstream said:

Nope,

🤣🤣

So, teach me. Why not, and what is the actual result? 🙏🙏

[Stu]

1 minute ago, jetstream said:

How about this one the "majesty factor" I truly believe that a larger AFOV helps viewing objects like the Veil-tested that one out the other night. What does an increased AFOV do to things?

Don’t bring another factor into this, it’s confusing enough as it is! 🤣

Is this not related to being able to perceive the edges of the object more easily with a larger fov; so, not looking through the object but seeing it set against the darker sky and being able to catch the edges where there is contrast??

[Stu]

Well, I’ve got a 4am start so need to leave you chaps to play this one out! I’ll catch up on it sometime tomorrow.

Enjoy👍

[jetstream]

3 minutes ago, Stu said:

Is this not related to being able to perceive the edges of the object more easily

I was looking at the western Veil the other night and features centred in both the plossl and 100deg showed better in the 100 deg. Theres a reason many use 100's on the nebs IMHO. Who knows - wife is home and going fishing 👍

[StarryEyed]

In a image software package processing the background so it fades allows the target to stand out. The eye has a limited sensitive if you magnify an image so the background starts to be less notice fades away the target will standout. This is true of any telescope magnify the image enough and your eye will eventually see nothing. Stick a CCD on it for a couple of days and you will get a deep field image. There is still light there but not to the eye. Its why zoom lens are so much fun and contrasty refractors so nice to look through. They are easy to tune to the conditions and your eye. The bigger the better. Seven years ago I stopped caring about the technical things Ive had terrible eye sight all my life as I get older they get worse. But when I look through any telescope Im grateful my eyes work and for the joy the views give me.  This is the most important thing. 

[JeremyS]

4 minutes ago, jetstream said:

 wife is home and going fishing 👍

Is there a correlation?
 

🤣

[globular]

29 minutes ago, jetstream said:

I wish some members debating this could look through my 15" and 24" side by side

Great offer. I accept. I'll bring my rods too. 

[John]

What an interesting discussion 

I've no idea what the answer to the original question is

I'm sure glad that I have my 12 inch dob as well as my refractors though

 

Edited October 5, 2021 by John

[jetstream]

1 hour ago, globular said:

Great offer. I accept. I'll bring my rods too. 

Yes, fish during the day, astro by night. Just got back- a pair of huge golden eagles were watching us fish and then decided to go for a cruise. Man they are big birds, dwarfing the bald eagles also seen. Finished off with a long boat ride.

[Stu]

3 hours ago, jetstream said:

Yes, fish during the day, astro by night. Just got back- a pair of huge golden eagles were watching us fish and then decided to go for a cruise. Man they are big birds, dwarfing the bald eagles also seen. Finished off with a long boat ride.

Wow, sounds amazing!

[cloudsweeper]

8 hours ago, Stu said:

 Contrast is fixed, regardless of magnification, I agree, or at least that’s my understanding! As you increase the mag, you dim both target and background SB.

 

Not sure about that, Stu.  Does it not depend on the relative SBs?  A brighter fuzzy will dim less than the background, and this is why the exit pupil range of say 4 - 2mm is desirable for contrast.  Only at even lower exit pupil does the target dim a lot more.

Doug.