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#26 Sarkikos

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Posted 05 December 2012 - 06:53 PM

Yes, I agree that lack of contrast is a problem. There are a number ways to enhance perceived contrast for planets. Filters can help. So can an apodizing mask for Newts. Binoviewers are of benefit. Very close collimation is very important, and is often overlooked by observers. Thermal stabilization of the optics is necessary for a sharp image. We should also mention decent eyepieces.

But all these methods deal with the optical equipment. What about the observer's eyes?

If the observer says Jupiter is "too bright," that doesn't indicate the contrast in the image is too low but that the image appears too bright to their eyes. I'll take them at their word. IME, the best solution is not to dim the image but to improve the adaptation of the eyes.

Mike

#27 Scanning4Comets

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Posted 05 December 2012 - 07:48 PM

The title of this thread is "filters". The rest is obvious, (collimation, etc, etc, etc). Contrast is the key to all observing being it planetary or deep sky.

#28 Sarkikos

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Posted 05 December 2012 - 08:03 PM

The OP did mention that "Jupiter appears very bright." That raises a red flag for me. I am compelled to address it. The assumption was made that the cure for Jupiter's brightness is to use filters, but that isn't necessarily the only or the best solution.

Mike

#29 JIMZ7

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Posted 06 December 2012 - 06:54 AM

My past experiences with different scopes from 80mm to 203mm-the filters I liked the most were #80A-blue**#11-green/yellow**& #ND of different percentages. On a Discovery 12.5" f/5 Dob. with no filters Jupiter's belts were nicely viewed at 511x. :dob:

Jim :refractor:

#30 Jaimo!

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Posted 06 December 2012 - 09:24 AM

Mike,
If you look into a flash light to stop down your pupil diameter, couldn't you accomplish the same thing with a smaller scope? I find my 12" dob a little much for Jupiter, but great for deep sky, and typically get my best views at 6-8"...

Jaimo!


Maybe I should be pushing the magnification... I am typically hovering around 200-250x, with the increased magnification I should also have a reduction in light throughput. I'm still a Dob novice...

Thanks,
Jaimo!

#31 Sarkikos

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Posted 06 December 2012 - 09:47 AM

Jaimo!

In the experience of many observers - myself included - Jupiter doesn't take higher magnification as well as Mars or Saturn. When viewing Jupiter with my 10" f/4.8 Dob, I usually keep it at 250x or below. That's 25x per inch and 1mm exit pupil. If the eyes are kept near photopic - especially if other methods of enhancing contrast are used - very fine surface detail can be seen at this image scale. Don't let anyone tell you it can't be done, because I know for a fact that it can. (I think some folks just like to push the power.) For your 12" f/4.9, a comparable power would be 300x. Try for that if the seeing will allow.

But whatever you do, don't look directly into the flashlight! I have never said to do that. Just look at a reflection of the white light on a white piece of paper.

Mike

#32 dpwoos

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Posted 06 December 2012 - 05:44 PM

In the experience of many observers - myself included - Jupiter doesn't take higher magnification as well as Mars or Saturn.


I have no idea what it means for something to not "take" higher magnification. Sounds like an equipment problem to me. Care to elaborate?

#33 Peter Natscher

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Posted 06 December 2012 - 09:57 PM

Ditto on that technique! Jupiter through my 24" dob is too bright with one eyepiece, no filter and under 300X. Neutral density filters and especially binoviewing cut down enough light and glare to see the surface details. I usually stack 2" M&SG and 50% ND filters together front-side on the Mark V bino and use 350X-450X on good seeing nights to get the view I like.

Mike,
If you look into a flash light to stop down your pupil diameter, couldn't you accomplish the same thing with a smaller scope? I find my 12" dob a little much for Jupiter, but great for deep sky, and typically get my best views at 6-8"...

Jaimo!

But the smaller scope will lose resolution.
If dimming the image in a larger scope enables you to see more details (and sometimes it does), try a light #50 neutral density filter or a #82A light Blue. The ND won't change the color.

However, I've found coloration in bands and details to be greater in greater aperture. My best view of Jupiter in color was in a 28" scope with no filter.

And remember, double the power and the image is 1/4 as bright per unit area. My best views of Jupiter have all been over 300X.



#34 DeSoto Kid

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Posted 07 December 2012 - 06:40 AM

What about using a Kendrick focusing aid cover available for SCT,s etc.? The one for the C9.25 has 3 - 3" holes around the periphery of the scope entrance. Being close to the outer edge should not reduce resolution so much and being positioned on the outer half of the scope might reduce spherical abberation if present. The single equivilet in area of these 3 spheres would be a 5" sphere ... and all this with NO central obstruction. This would reduce quite a bit of the light coming in.

Bob (REC) mentioned that brightness of Jupiter was not so severe when he first beging observing. It my be a good idea to eliminate this phenomenon before it happens ...???

Wayne

#35 Sarkikos

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Posted 07 December 2012 - 07:11 AM

dpwoos,

In the experience of many observers - myself included - Jupiter doesn't take higher magnification as well as Mars or Saturn.


I have no idea what it means for something to not "take" higher magnification. Sounds like an equipment problem to me. Care to elaborate?


No, it is not an equipment problem. :grin:

Of course, any object can "take" any magnification you care to throw at it, in the sense that you can setup the equipment to have that magnification. But will the image show you any more surface detail than at a more moderate magnification? Some objects will, some won't. Jupiter is one of those that don't "take" high magnification well, as compared to Saturn or Mars or double stars, for instance. This is nothing new.

A largely ignored factor in the equation of how much magnification is needed to see a high level of fine detail is how well the observer's eyes have been prepared for observing planets. IME & IMO, many observers don't have a clue how to do this, or even that it will make a difference. If the eyes are properly prepared, the observer shouldn't have to push the magnification - with some exceptions, such as close double stars, subtle detail in Saturn's rings and Mars at a small apparent diameter. (I've pushed a 6 arcsec Mars up to 600x in my 10" Dob with good results.)

I'm not usually a big fan of huge image scale for its own sake, particulary since my best planet scopes don't track. What I'm after is finer detail. I can see that without crazy-high power when observing Jupiter.

Mike

#36 Sarkikos

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Posted 07 December 2012 - 07:48 AM

Peter,

Ditto on that technique! Jupiter through my 24" dob is too bright with one eyepiece, no filter and under 300X. Neutral density filters and especially binoviewing cut down enough light and glare to see the surface details. I usually stack 2" M&SG and 50% ND filters together front-side on the Mark V bino and use 350X-450X on good seeing nights to get the view I like.

Mike,
If you look into a flash light to stop down your pupil diameter, couldn't you accomplish the same thing with a smaller scope? I find my 12" dob a little much for Jupiter, but great for deep sky, and typically get my best views at 6-8"...

Jaimo!

But the smaller scope will lose resolution.
If dimming the image in a larger scope enables you to see more details (and sometimes it does), try a light #50 neutral density filter or a #82A light Blue. The ND won't change the color.

However, I've found coloration in bands and details to be greater in greater aperture. My best view of Jupiter in color was in a 28" scope with no filter.

And remember, double the power and the image is 1/4 as bright per unit area. My best views of Jupiter have all been over 300X.


Please folks, stop copying Jaimo!'s incorrect description of the "Bright White Light" technique. It will do no one any good to look directly into a bright flashlight! Instead, look at the reflection of that light onto a white piece of paper! :poke:

Peter: I agree on binoviewing and the use of M&SG filters. Yep, at around 24" or so you might be hitting the threshold at which you actually do need to think about dimming Jupiter's image a bit.

:grin:
Mike

#37 Sarkikos

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Posted 07 December 2012 - 08:03 AM

Wayne,

What about using a Kendrick focusing aid cover available for SCT,s etc.? The one for the C9.25 has 3 - 3" holes around the periphery of the scope entrance. Being close to the outer edge should not reduce resolution so much and being positioned on the outer half of the scope might reduce spherical abberation if present. The single equivilet in area of these 3 spheres would be a 5" sphere ... and all this with NO central obstruction. This would reduce quite a bit of the light coming in.

Bob (REC) mentioned that brightness of Jupiter was not so severe when he first beging observing. It my be a good idea to eliminate this phenomenon before it happens ...???


The brightness of Jupiter should not be a problem in a 9.25" aperture. If Jupiter appears too bright, your eyes are not prepared optimally for observing Jupiter. It is not a good idea to reduce the aperture in order to reduce the brightness of a planet. You will be decreasing the resolution while trying to solve a problem that doesn't really exist.

Placing a ring around the aperture might cover up optical errors. But reducing aperture because a planet appears "too bright" is not a good solution to the problem of "brightness" - which actually is not a problem at all in moderate-sized scopes.

Mike

#38 dpwoos

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Posted 07 December 2012 - 08:09 AM

dpwoos,

In the experience of many observers - myself included - Jupiter doesn't take higher magnification as well as Mars or Saturn.


I have no idea what it means for something to not "take" higher magnification. Sounds like an equipment problem to me. Care to elaborate?


No, it is not an equipment problem. :grin:

Of course, any object can "take" any magnification you care to throw at it, in the sense that you can setup the equipment to have that magnification. But will the image show you any more surface detail than at a more moderate magnification? Some objects will, some won't. Jupiter is one of those that don't "take" high magnification well, as compared to Saturn or Mars or double stars, for instance. This is nothing new.


You again state your claim that Jupiter (unlike Saturn, Mars, etc.) doesn't "take" high magnification, but still don't explain why you think that. I often view Jupiter (and other high mag targets) at 250x in my 10" because that seems to be what the seeing on good nights most often allows. However, I have also observed Jupiter in the same scope at 400x, and I am quite certain that I was able to see fine detail that was not visible at the lower mag, and as one would expect. Honestly, I have no idea how one can possibly maintain that there is some minimum exit pupil size (I take it around 1mm?) that shows all there is to see on this target specifically, especially given the seemingly infinite amount of detail visible?

#39 Sarkikos

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Posted 07 December 2012 - 08:34 AM

dpwoos,

You again state your claim that Jupiter (unlike Saturn, Mars, etc.) doesn't "take" high magnification, but still don't explain why you think that.


It's not a claim. It's an honest report of personal experience. An explanation of why it happens is another matter. Low contrast detail on Jupiter as opposed to high contrast detail on Saturn's rings? Larger image scale of Jupiter as opposed to the usually smaller image scale of Mars? I think those are good explanations.

I often view Jupiter (and other high mag targets) at 250x in my 10" because that seems to be what the seeing on good nights most often allows. However, I have also observed Jupiter in the same scope at 400x, and I am quite certain that I was able to see fine detail that was not visible at the lower mag, and as one would expect. Honestly, I have no idea how one can possibly maintain that there is some minimum exit pupil size (I take it around 1mm?) that shows all there is to see on this target specifically, especially given the seemingly infinite amount of detail visible?


Well, good for you. Or maybe not so good, if you actually need higher magnification to see what I'm seeing at more moderate power. My scopes don't track, so I try to avoid higher power if I can. I don't need a substantially larger image scale for Jupiter in order to see fine surface detail. I know through experience how to avoid that. To each their own.

Mike

#40 coutleef

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Posted 07 December 2012 - 09:51 AM

i agree with Mike here

Jupiter is the planet for which higher magnification is generally not as useful as for other planets. the most useful mag is around 160-180. while i use much higher mags with Saturn and mars, when i use high mags pn Jupiter, i do not see more detail but i loose some.

#41 Sarkikos

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Posted 07 December 2012 - 10:09 AM

Saturn is an odd ball planet. It has very high contrast features - the rings - and very low contrast - the globe. So while higher power can help bring out subtle detail in the rings when the seeing is good, it won't help as much with surface features. But in general I try to push the power for Saturn.

Mike

#42 Starman1

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Posted 07 December 2012 - 10:59 AM

A little math.

Jupiter at its largest is 50" across. If you want to see a detail 1/50 the diameter of the disc, and you want to bring it up to the 8' apparent visual threshold, that requires a magnification of 480/1 = 480X
Saturn's disc maxes out about 20". To see a detail 1/50 the size of the disc, brought up to the same 8' apparent threshold would require a magnification of 480/.4 = 1200X.
Looking at the comparison, Saturn requires a magnification 2.5X as great to see details the same apparent size as you see on Jupiter.

Hence, if you see enough detail on Jupiter at 150X, you will need 375X to see details on Saturn at the same scale.

It's purely size as to why Saturn requires and takes higher magnifications than Jupiter, to see details that is.

That's without getting into relative contrast and albedo and coloration contrast, etc., all of which influence magnifications used.

#43 coutleef

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Posted 07 December 2012 - 11:46 AM

great answer Don! it explains a lot

#44 Dave Ittner

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Posted 07 December 2012 - 11:50 AM

Don,

I always enjoy reading your posts and quite often learn something.

Can you explain why you chose 8' as the minimum size? If Jupiter is 50" at it's largest wouldn't that require a magnification of 576?

50"/60" = 0.833 of a degree
then
8' = 480"
so 480/0.833 = 576

My logic is probably wrong but thought I would ask even at the risk of looking stupid.

#45 Dave Ittner

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Posted 07 December 2012 - 11:56 AM

I know my logic is wrong but still am having a hard time wrapping my brain around this.

#46 Jaimo!

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Posted 07 December 2012 - 12:26 PM

Many thanks Don!

Sorry Mike, You are the only source of "using a reflection a flashlight off of a piece of paper to reduce your pupil size" as an observing technique I have ever heard. I'm just not convinced that it is the best method, constantly re-adjusting you pupil size throughout an evening. I would think that being dark adapted and using a filter would yield more consistent results. That being said, I will try it out for myself...

Jaimo!

#47 Starman1

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Posted 07 December 2012 - 12:46 PM

Don,

I always enjoy reading your posts and quite often learn something.

Can you explain why you chose 8' as the minimum size? If Jupiter is 50" at it's largest wouldn't that require a magnification of 576?

50"/60" = 0.833 of a degree
then
8' = 480"
so 480/0.833 = 576

My logic is probably wrong but thought I would ask even at the risk of looking stupid.

Books I read when I was young said that the eye could easily differentiate one dot from another, with good vision, at a separation of 6' apparent. But 8' was a lot easier.
8' = 8x60" = 480"
A detail on the disc of Jupiter 1/50 of the disc in width would have a width of 1". To make 1" appear like 480" requires a magnification of 480X.
I don't know why you used degrees. I was talking minutes.

However, those of us with relatively acute vision can see distinct points with separations of 4'. Hence, 240X would suffice to see a feature 1/50 the width of Jupiter's disc.

Complicating the issue is that some features we look at are <1/50 the width of the disc, and if distinctly different colors, separations can be less than the apparent 4' and still appear separate. Small kids sometimes have vision that can separate details of 1' apparent separation, and a lot of adults (myself included) can see as distinct points features separated by 3' apparent. And if the points differ in brightness significantly, all bets are off as to what magnification will be required.

I was able to see dark blue-green festoons hanging out over the edge of an equatorial band that appeared quite ocher in color. The festoons were <1/50 the diameter of Jupiter in size. The detail was amazing at 228X. However, I could see the shadows of those festoons on the sides of the cloud bank below them at 456X, and I could not see those shadows at 228X. Sometimes, magnification is necessary.
I should note that on that night the seeing actually exceeded the resolution of my 12.5" at times, so the instrument was aperture limited. That is exceedingly rare, and the images from that night are burned into my brain. M15 was resolved all the way to the center at 228X and small triangles of faint stars covered the very center--a detail I'd never seen before and haven't since.

#48 Sarkikos

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Posted 07 December 2012 - 01:47 PM

Jaimo!,

Sorry Mike, You are the only source of "using a reflection a flashlight off of a piece of paper to reduce your pupil size" as an observing technique I have ever heard. I'm just not convinced that it is the best method, constantly re-adjusting you pupil size throughout an evening. I would think that being dark adapted and using a filter would yield more consistent results. That being said, I will try it out for myself...


Again, please don't misinterpret this technique. It's not just about adjusting pupil size. When did I ever say that? There are also changes in the retina. Google "photopic mesopic scotopic" for more info.

Dark adaptation is the last thing you want for observing planets. Not that you would ever be deeply dark adapted when you view Jupiter, but you would tend to be at the mesopic level rather than closer to photopic. The photopic level is ideally where your eyes should be.

There are some threads on CN - mostly older threads, I think - that mention the importance of being around white light for planet work. I don't agree with all the old techniques and the theories of the old timers who used them, but they were on the right track.

For instance, there was the idea that twilight viewing of planets would increase the perceived contrast. Some thought this was due to do a contrast effect between the disk of the planet and the bright sky surrounding it in the FOV. I disagree. I think there is enhanced contrast because the eye is better adapted to viewing planets as a result of the brighter ambient light surrounding the observer. I don't deny, though, that the better image might also be due partly to better seeing at this time of day in many locales.

They also liked to have constant white light around them when viewing planets, particularly in observatories. I'm not sure this is such a good idea, because it is too easy for the light to become a source of glare in the optics or your eyes. You don't want to see a light in the corner of your eye or reflected off the eye lens while you're trying to discern fine surface details. (This is one reason I really don't like viewing planets at twilight. The "Bright White Light" trick will make the eyes function as if it is twilight at midnight, but without the glare.)

Observers can try the "Bright White Light" trick or not, as they wish. I have no horse in this race. It's just an interesting and - in my experience - worthwhile method of improving the perceived image of planets. Besides, it's very cheap! $3 will get you a great little bright white-light flashlight.

:grin:
Mike

#49 Sarkikos

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Posted 07 December 2012 - 02:17 PM

Don,

However, those of us with relatively acute vision can see distinct points with separations of 4'. Hence, 240X would suffice to see a feature 1/50 the width of Jupiter's disc.


Also, maintaining eye adaptation closer to photopic will help the eyes retain more of the visual acuity that they enjoy during daylight hours. This has helped me to see very fine details - such as structure within the GRS or "strings of black pearls" along the equatorial bands - without having to push the power above 250x. There is not much joy in trying to sketch Jupiter as it drifts by at 500x. :(

Complicating the issue is that some features we look at are <1/50 the width of the disc, and if distinctly different colors, separations can be less than the apparent 4' and still appear separate. Small kids sometimes have vision that can separate details of 1' apparent separation, and a lot of adults (myself included) can see as distinct points features separated by 3' apparent. And if the points differ in brightness significantly, all bets are off as to what magnification will be required.


Another problem with allowing the eyes to fall into the mesopic level is that color range and contrast is diminished. As you comment here, contrast in color and brightness levels can allow our eyes to discern very small features, smaller than some would think possible. That ability is diminished if our eyes are not properly prepared for planet observation.

Owls' eyes are for deep sky. Hawks' eyes are for planets.

Mike

#50 Jaimo!

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Posted 07 December 2012 - 02:19 PM

Again, please don't misinterpret this technique. It's not just about adjusting pupil size. When did I ever say that? There are also changes in the retina. Google "photopic mesopic scotopic" for more info.



I understand, but if you look at a white light your pupil will change size. You didn't have to say it, it's biology, it's how the eye works. However I don't understand the changes you are talking about with the retina. Photopic, mesopic & scotopic refer to the usage of rods & cones under different lighting conditions (and on a side note is a great explanation for averted vision, taking advantage of the cones). Is it that under photopic conditions, typical daylight conditions where the retina is using only rods, that planetary visual acuity increases?

Jaimo!






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