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View Full Version : What Magnification do you need to see detail on Mars?



Arcane
2007-Dec-20, 04:33 AM
So I was finally able to use the new telescope tonight. Got some awesome views of the moon, I could practically see John Glenn's foot prints in crystal clear detail. However, I set my sights on Mars on focused in on the little yellow feller and it still looked like a small yellow dot....?:doh:

I am using an 8" dob and I had a 10mm lens with the 2.8x Klee barlow. I don't know exactly how that breaks down in to magnification numbers, but I would think I should at least be able to have a pretty decent picture of Mars with it, or am I wrong?

Its hard enough to line up on anything with that magnification as it is. Course Iím just a newbie so what do I know.

RickJ
2007-Dec-20, 05:26 AM
Mars is a poor beginner's object even when closest as it is now.

Contrary to the pictures you see of Mars, visually it is a rather low contrast object. Most beginners see little but the polar cap(s) at first. It takes time to train the eye and brain to see the low contrast detail. One hemisphere of Mars is especially void of detail. Though if you were viewing at about 1 hour UTC tonight (7 p.m. CST) Syrtis Major, the highest contrast feature on Mars besides the polar cap was well positioned in the center of Mars but Mars was just rising making it too low to see. Wait for it to get high over head to get the clearest view, though by then Syrtis Major will have been replaced by some other features, but still ones of fairly good contrast. Mars rotates about 40 mintues slower than we do. By Christmas night Syrtis Major will be nearly centered on the disk of Mars about 5 hours UT (11 p.m. CST). Then assume about 40 minutes later each following night.

There are several places on the net you can see what is "up" on Mars for any particular time. One is at the Sky and Telescope site: http://www.skyandtelescope.com/
Scroll down to Mars Profiler.

There are better ones but I don't seem to have them bookmarked.

Also you may be pushing the power too much, a typical beginner error. Contrast is what you need. Too much power for the atmosphere's seeing conditions just ruins seeing low contrast detail. When the atmosphere is very steady and the image doesn't go in and out of focus constantly, highest contrast is at about a 1 mm exit pupil. You are running 0.6mm. You're eyepieces are limited but try the 20 and the Klee for a 1.2mm exit pupil. Or just the 10 for 1.7mm exit pupil size. It will be smaller, and yes it is already small, but you'll likely see more once you get used to it. You have to learn to grab that split second of fine seeing the atmosphere gives you every once in a while. The great photos are taken by taking hundreds of images up to 30 or so a second, then sorting out those few that give the moment of good seeing then stacking those, pushing the contrast way beyond what the eye sees, applying sharpening routines to that and the result by those good at it is a great image but not what you'll see at the eyepiece.

Use the moon that's out to judge your seeing. Looking at craters near the terminator see what power gives you the sharpest image and highest contrast and then use that on Mars.

Some nights have such bad seeing nothing is sharp and clear. That is especially true if the jet stream is overhead or a front has just gone through and there are still lots of variations in the temperature of the air with a zillion pockets of warm and cold air that haven't yet evened out. If the stars are twinkling like crazy (doing the jitterbug in my astronomy club's terminology) it's not a night for planetary viewing. I get nights where 50 power is the maximum the atmosphere will allow. Rarely can I go over 250x, 0.8mm exit pupil for your scope.

To determine the exit pupil size divide the focal length of the eyepiece by the f ratio of your scope (6 in your case) then if you use a barlow divide that by the barlow power ((20/6)/2.8=~1.2. To convert to power divide 200 (your mirror size in mm) by the exit pupil size (200/1.2=~167x. There are other ways of doing it as well. I find this the most useful.

Have you collimated the scope since it arrived? They never seem to arrive in collimation. Super accurate collimation isn't needed at f/6, a sight tube should suffice.

Rick

Arcane
2007-Dec-20, 05:36 AM
Thanks for the input. Yes, the first thing I did when I got it was collimate it and judging by my views of the moon tonight it is collimated properly.

However, my issue with mars isnt that I can't get detail or that it is blury. My issue is that it appears as a tiny dot, much like what you see when looking at a distant star. The planet took up no more FOV in the telescope than it did with the naked eye. Little dot with the naked eye, little dot in the telescope.

The magnification I was using should have at least made it a BIG fuzzy ball right? Not a tiny dot.

I am sure I was looking at mars since it is basicaly the only yellow object in that area and I used the Starry Night software to make sure I was looking in the right place.

I am confused.

Dave Mitsky
2007-Dec-20, 07:26 AM
Assuming that the focal ratio of your telescope is f/6, its focal length is 8 x 6 x 25.4mm = 1219 mm and the magnification produced with a 10mm eyepiece and 2.8x Barlow lens is approximately 1219/10 x 2.8 = 341x. Mars currently subtends a mere 15.9" (its maximum diameter until 2016), which is only about 1/4th the apparent size of M57 (the Ring Nebula) and 1/113th the average apparent size of the Moon. Even at a magnification of 341x Mars won't be all that big but you should see a clearly discernible disk.

You may find this site (http://www.dustymars.net/Observing_Mars.html) useful.

Dave Mitsky

JustAFriend
2007-Dec-20, 02:26 PM
...I could practically see John Glenn's foot prints in crystal clear detail.


Wow, he must've had REALLY long legs to be able to do that from his low Earth orbit...

:lol::lol::lol:

Arcane
2007-Dec-20, 06:43 PM
Wow, he must've had REALLY long legs to be able to do that from his low Earth orbit...

:lol::lol::lol:

lol yah, I MEANT to put Neil Armstrong, no idea why John Glenn got typed instead heh.

Arcane
2007-Dec-20, 06:55 PM
Assuming that the focal ratio of your telescope is f/6, its focal length is 8 x 6 x 25.4mm = 1219 mm and the magnification produced with a 10mm eyepiece and 2.8x Barlow lens is approximately 1219/10 x 2.8 = 341x. Mars currently subtends a mere 15.9" (its maximum diameter until 2016), which is only about 1/4th the apparent size of M57 (the Ring Nebula) and 1/113th the average apparent size of the Moon. Even at a magnification of 341x Mars won't be all that big but you should see a clearly discernible disk.

You may find this site (http://www.dustymars.net/Observing_Mars.html) useful.

Dave Mitsky

Yah see, when I was a kid I this really cheap department store special type telescope, it was one of those little tubes on a stand like Galileo had, cept probably 100 times worse, and I was able to see the rings around Saturn.

Now I have this huge telescope with pretty decent lenses and mars just looks like a Tiny dot? By Tiny I mean a pin point like a distant star. It really doesn't make sense specially seeing as Mars is a lot closer than Saturn.

I haven't had a chance to look at anything else yet and I will try Mars again tonight assuming itís not cloudy.

Thanks for the input.

Casus_belli
2007-Dec-20, 07:18 PM
You're not looking at Capella by mistake are you? Mars is brighter and should look different from a star.

RickJ
2007-Dec-20, 07:29 PM
As Dave said, it is about 1/113th the size of the moon so at 113 power it should appear as big as the full moon does to the naked eye.

Always start with your lowest power. That will give you at least a 1 degree fov. So if your finder is adjusted correctly Mars should be near the center when you look in. It will be very bright. Almost too bright. Then start increasing the power until the image begins to break down then back off to where it was still clear. There's nothing around Mars nearly as bright as it is so you'll have no trouble recognizing it. It far outshines the stars of Orion, Gemini or Taurus that are its neighbors. Could you have been way off target and looking at Aldebaren or Betelgeuse? Both are bright orange stars in the area.

Use the moon to check your finder alignment. By day you can choose some object along the horizon that stands out above it like a tall tree, steeple or power pole. Scan the horizon with the scope until you find it then adjust the finder to match. I used to align a lot of finders for folk at Hyde Memorial Observatory. There was a University clock about a mile away that had an illuminated dial at night. It was a perfect target for finder alignment. You need something unmistakable like that that is on the horizon so you can quickly scan and find it.

Rick

Veeger
2007-Dec-20, 09:24 PM
Something doesn't make sense, because even in a cheap telescope one can see the difference between a planet and star. Stars are pinpoints of light at any magnification, planets usually appear as illuminated disks, even if they are quite small in low power. The difference is obvious, usually.

I hate to mention the basics, but I would check the alignment of the finder scope on some distant object on earth before peering skyward, unless you choose some obvious alignment target such as M42 or Alcyone in the Pleiades.

-Veeger

Arcane
2007-Dec-20, 11:48 PM
Yah, I have aligned the finder scope as well as I can. If I line it up with the moon then put in 25m lens with the 2.8x barlow and I can still see the moon, so I assumed it is aligned pretty well. At least well enough that I wouldnít be looking way over at Betelgeuse when I am aiming it mars heh.

BUT, I suppose it is possible I was off enough to be peering at some distant star that is right next to mars that I couldnít see with the naked eye or the finder scope.

I will have to check again once the skyís clear up and make sure I wasn't just off by a hair and missing mars all together.

Thanks for the help guys.

Dave Mitsky
2007-Dec-21, 06:51 AM
Now I have this huge telescope with pretty decent lenses and mars just looks like a Tiny dot? By Tiny I mean a pin point like a distant star. It really doesn't make sense specially seeing as Mars is a lot closer than Saturn.



Yes, but the ball of Saturn subtends about 20" and its rings are almost 2.5 times as large, making its maximum apparent size (~46") about that of Jupiter's.

If you can't see a disk at 341x, then you are not looking at Mars. Mars is currently the third brightest natural object in the night sky and is located "above" the feet of Gemini, to the of east of M35 and south of M37 in Auriga.

Dave Mitsky

Arcane
2007-Dec-22, 08:50 AM
Ok, I saw mars tonight. I must have been using the 25mm the other night a long with the 2.8 barlow. Tonight I checked it with a 10mm and 2.8 barlow and it was still a small dot. It was bigger, and it was for sure mars because a star would not appear that big, but it was still very small.

Now, from what you guys have said, Mars is 1/113 of the size of the moon with the naked eye right? So if I used a magnification of 113 I would see in my scope, mars as the size of the moon I see with the naked eye?

That would mean mars would be pretty big in my scope, which it is not even with the 10mm and 2.8 barlow.

I could tell it was a disc and a planet, I could even see a slightly off color band on it. But basically what I saw was a yellow fuzzy ball that was about 1/10th the size of the moon I can see with the naked eye.

Mars did not take up all of my FOV or even remotely close to it even with the 10mm and 2.8 barlow. So this leads me to think I must be doing something else wrong.

When I look at the moon I am simply amazed at the detail I can see, It is almost like I am standing on the surface. I can see shadows of mountains and every crater in great detail. But when I look at Mars I see a tiny yellow dot with practically no detail at all.

The detail part I am not worried about, it may be because of collimation or a nearly full moon or atmospheric conditions or who knows, but I would at least like to see a Big disk in my FOV, even if it is blurry.

You say the magnification I am using is 300+X so I should see mars taking up my full FOV right? Or at least close to it, not a small yellow dot.

Thanks for the help guys, I hope I can get this sorted out. Or do i need to buy a higher magnification lens?

aurora
2007-Dec-22, 02:44 PM
No, there really isn't much to see visually through a telescope when looking at Mars.

You might, at best, see some subtle shading, and sometimes you will see an ice cap. But that is only when Mars is at its closest, which is about every 2 years.

You'll do a lot better if you can observe Saturn or Jupiter.

Edited to add: I really recommend the book Turn Left at Orion. You can probably find a copy at your local library, or you can buy a copy from many bookstores as well as Amazon. It's great because it describes how to find about a hundred of the best objects to look at through a small scope, and it has drawings of what the objects will actually look like (instead of color pictures taken by Keck or Hubble), and gives some description of what the object actually is. It contains a nice mix of the different types of objects that are fun to look at, and it is organized by season. There are other great books, but this one is my pick for people just starting to use a telescope.

Hornblower
2007-Dec-22, 02:54 PM
You say the magnification I am using is 300+X so I should see mars taking up my full FOV right? Or at least close to it, not a small yellow dot.


Not even close. At the present opposition it would be roughly the angular diameter of a penny at arm's length. That would be a very puny field of view.

The perceived size of an object can be deceptive when looking through a telescope. Try looking at Mars with one eye at the eyepiece and simultaneously look at a penny with the other eye.

Dave Mitsky
2007-Dec-22, 03:20 PM
Now, from what you guys have said, Mars is 1/113 of the size of the moon with the naked eye right? So if I used a magnification of 113 I would see in my scope, mars as the size of the moon I see with the naked eye?

That would mean mars would be pretty big in my scope, which it is not even with the 10mm and 2.8 barlow.

I could tell it was a disc and a planet, I could even see a slightly off color band on it. But basically what I saw was a yellow fuzzy ball that was about 1/10th the size of the moon I can see with the naked eye.

Mars did not take up all of my FOV or even remotely close to it even with the 10mm and 2.8 barlow. So this leads me to think I must be doing something else wrong.

When I look at the moon I am simply amazed at the detail I can see, It is almost like I am standing on the surface. I can see shadows of mountains and every crater in great detail. But when I look at Mars I see a tiny yellow dot with practically no detail at all.

The detail part I am not worried about, it may be because of collimation or a nearly full moon or atmospheric conditions or who knows, but I would at least like to see a Big disk in my FOV, even if it is blurry.

You say the magnification I am using is 300+X so I should see mars taking up my full FOV right? Or at least close to it, not a small yellow dot.


If you check my first reply, you'll find that I said the following:

"Even at a magnification of 341x Mars won't be all that big but you should see a clearly discernible disk."

Mars is quite small, even during opposition. It currently subtends a diameter of almost 16 arcseconds, about 113x the size of the Moon (~1800 arcseconds). At a magnification of 113x, the Martian disk will be similar in apparent size to the naked-eye view of the Moon. Why then does it seem to look smaller? It's because one doesn't compare the Moon to the entire dome of the sky when one looks at it but, subconsciously or not, one does compare an object in the field of view of an eyepiece to the entire field.

Observing Mars takes a properly collimated and athermalized instrument of sufficient aperture (at least 6 inches), good "seeing", the appropriate filters, practice, and, most of all, patience.

http://www.skyandtelescope.com/observing/home/12083136.html

You won't see Mars taking up the entire field of view unless you're employing an extreme and unusable magnification of over 11,200x (assuming a 50 degree AFOV Ploessl) and you won't see much in the way of surface features if the "bland" desert side of Mars is facing the Earth at the time that you're observing the planet.

http://www.skyandtelescope.com/observing/objects/javascript/3307831.html

Dave Mitsky

Casus_belli
2007-Dec-22, 03:57 PM
I've come across several threads on various forums exactly like this. We all see pictures of Mars taken from powerful telescopes and Hubble etc and expect to see the same through our own vastly cheaper and less powerful scopes. Its human nature.

From what I gather Mars is an extremely challenging target for a newcomer to image. If you see any detail at all count that as a major victory. As a newbie myself I count myself fortunate to have succeded where so many have failed

I spent hours at the ep with only occasional glimpses of features. However this past week has seen very calm conditions in this area and (and this is the most important bit) I learned how to coliminate properly.

My own scope is a 10" lightbridge with a f5 focal length. Improperly coliminated, distant fuzzies, the moon and saturn are easily seeable but Mars is far more demanding especially in a "fast" (low focal length) scope. Now that I've sorted the collimination out Mars reveals itself almost constantly.

Arcane
2007-Dec-22, 06:54 PM
To be honest I am a realist and I do not expect to get views that I see from hubble haha or any other bigger telescope. But I have seen people on this and other forums take some pretty decent pictures of mars with telescopes that are near the size of mine. And yes, I realize a time-lapse photo is going to show more detail, but the detail is not what I am really concerned about it. It's the size of the object in the FOV.


Hornblower, yep, a penny at arms length is about the size of what I saw. Really disappointing to be honest.

Thanks guys.

Kyle Edwards
2007-Dec-25, 01:25 AM
I am using an 8" dob and I had a 10mm lens with the 2.8x Klee barlow. I don't know exactly how that breaks down in to magnification numbers, but I would think I should at least be able to have a pretty decent picture of Mars with it, or am I wrong?


That's strange because I can see a clearly discernible disk and sometimes dark markings with my Orion 70mm refractor with a 2x barlow and 10mm Plossl. Are you sure that you had Mars and not Capella or Aldebaran?

Egregious Philbin
2007-Dec-25, 06:56 AM
My best detail tonite was with a 30 mm eyepiece at 83 Power.

Even with the barlow at 166, I got a good view of detail.

I was using a 2" eyepiece, which I find much better.

But, Magnification is not important, Aperture is!