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FORUMS Photography Talk by Genre Astronomy & Celestial Talk 
Thread started 19 Jul 2010 (Monday) 08:55
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How big should I be seeing stuff?

 
swag72
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Jul 19, 2010 08:55 |  #1

Apologies for the really dumb question. My 120ED came out for the first time ever yesterday and the moon was absolutely awesome. The decided to find something else to view. Looked on the computer and found I could see Saturn. So .......... I found it, BUT ............. For some reason I thought I'd be seeing it much bigger in my 8mm eyepiece. All I could see was a white circle with 'ears'. I thought I'd be seeing it much bigger than that. So, have I done something wrong? Do I need more realistic expectations? Mars was just a red blob - So disapointing.

Help me have enthusiasm in such a brand new venture, before it all gets packed away and never somes out again!


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Jul 19, 2010 09:26 |  #2

8mm is a HUGE magnification! You might be better using a 25mm or even a 40 mm eyepiece. The image will be smaller, but much sharper and more detailed. A 120mm ED is not really designed for planetary work as the focal length is not long enough. It is more designed for wider field and objects of larger angular distance, like nebulae and some of the larger galaxies.

Planets have tiny angular distances and you are trying to magnify such a tiny thing with an eyepiece. This is where the QUALITY of an eyepiece can really affect the outcome and destroy the image.

Also, at the moment, Mars IS just a red blob.

Baz.


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swag72
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Jul 19, 2010 09:45 |  #3

Cheers Baz - If I got a Barlow would that help? Also, If I took a photo, I could crop it and make it bigger?


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Nighthound
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Jul 19, 2010 10:49 |  #4

There are limitations in magnification from the telescope and eyepiece optical quality to atmospheric conditions on any given night. As Baz mentioned over magnifying, beyond optical limitations will always result in poor detail/resolution. Only on the steadiest atmospheric nights (about 3 nights a year-average) will I push magnification and that extent depends on the telescope I'm using. Start at high mag and back down until you begin to start to see the best detail possible. Glad you're enjoying the new scope, congrats.


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swag72
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Jul 19, 2010 12:01 |  #5

The issue I have is that with Saturn for example, if I start at high magnification and work down, it's so damn small to start with that I can't see any detail particulary anyway. I am quite despondant about this aspect if I'm honest.


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DonR
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Jul 19, 2010 17:56 |  #6

I will disagree with the others a little here. Assuming your 120ED is f/7.5, i.e., the Synta Skywatcher 120ED or equivalent, your focal length is 900mm, which is enough to get decent views of Saturn on a good night. With the 8mm eyepiece, your magnification is 112.5, which is a little low for Saturn, because as you noticed, Saturn is quite small at that magnification. Nevertheless, assuming your optics are in good condition, you should be able to see some detail with that magnification on a good night. On a poor night you won't see any detail at all, and on an average night you won't see a great deal of detail.

The optical resolution of a telescope depends on its aperture (greater aperture means greater resolution), and based on the resolution there is an upper limit to usable magnification. Telescope manufacturers usually state the maximum usable magnification as about twice the aperture in millimeters, or 50 times the aperture in inches. Truthfully, though, this much magnification is very rarely if ever possible. In my experience, magnification of 40 times the aperture in inches (about 190X for your ED120) is more realistic, and even this magnification requires exceptional viewing conditions. You would achieve close to 190X with a 5mm eyepiece, or a 10mm eyepiece with a 2X barlow.

I suspect your experience so far has been hampered by poor atmospheric conditions, compounded by your lack of experience. Keep it up, look for local astronomical seeing forecasts that cover your area, and even on a night when you aren't seeing much detail, keep watching the planet for a while. On an average night, you will find that there may be moments of good seeing mixed in with generally average or poor seeing. Part of learning to view the planets through a telescope is developing the patience to wait for those moments and catch as much as you can when they occur.

On a night several years ago I pointed my telescope at Saturn and was amazed by what I saw - crystal clear, crisp, steady detail like I didn't think was possible with an 8" reflector. It was one of those nights I had heard about, and I spent several hours just viewing Saturn. The next day I visited a local astronomy store and everyone was buzzing - "Did you see Saturn last night? WOW!".

If you want to invest in optics for planetary viewing, I would recommend a good eyepiece more than a barlow. A 5mm orthoscopic eyepiece can be had without breaking the bank, or if you can swing it, a Televue Radian or Nagler is hard to beat. If you decide to get a barlow, keep in mind that a 2X barlow with your 8mm eyepiece will rarely if ever give good views - its just too much magnification for a 120mm telescope. Also, if you decide to get a barlow, you should look for an "ED" barlow to match your telescope's optics.

Don




  
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Adrena1in
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Jul 20, 2010 05:37 |  #7

Must admit, my first views of Saturn were through a 1200mm scope, and though I was impressed, it was very small. Best eyepiece I had was a 10mm, giving 120x magnification.

Viewing conditions have to be very good to push the magnification super-high. Earlier in the year I tried to view Mars when it was at opposition, so effectively the largest it would appear. First time was rubbish...was just a blurry red blob and I got very disheartened. Next time it was fantastic, and I pushed the magnification to around 400x through my Celestron C11. Could see the polar caps and the different colours of red making up the surface.

Saturn's not been so great this year, what with the rings being almost side-on to us. Plus you need to get very "close" in order to make out the different colours in the planet's surface. Again, I've had it at 300-400x mag. a few times and it's been good.

What you want to do is give Jupiter a go. Soon it'll be getting quite high in the sky, and it's got plenty to keep you interested. Wider angles will get in the major moons, and then zooming close will show you the belts, (or belt), and Great Red Spot. I saw it the other night, but it was low down and it was a cloudy night, so not ideal. Can't wait for the winter months! ;)


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anishmangal2002
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Jul 20, 2010 08:48 |  #8

swag72 wrote in post #10563358 (external link)
Apologies for the really dumb question. My 120ED came out for the first time ever yesterday and the moon was absolutely awesome. The decided to find something else to view. Looked on the computer and found I could see Saturn. So .......... I found it, BUT ............. For some reason I thought I'd be seeing it much bigger in my 8mm eyepiece. All I could see was a white circle with 'ears'. I thought I'd be seeing it much bigger than that. So, have I done something wrong? Do I need more realistic expectations? Mars was just a red blob - So disapointing.

Help me have enthusiasm in such a brand new venture, before it all gets packed away and never somes out again!

Get an astronomy book! There are much bigger and better things out there than Saturn.

And yes it does look disappointingly small at first. Were you able to spot some of its satellites (That might help you cheer up a bit). If not, the night wasn't probably good enough for viewing with an 8mm eyepiece anyway.


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swag72
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Jul 20, 2010 09:00 |  #9

anishmangal2002 wrote in post #10570143 (external link)
There are much bigger and better things out there than Saturn.

Examples? What would you recommend?


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anishmangal2002
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Jul 20, 2010 10:43 |  #10

swag72 wrote in post #10570201 (external link)
Examples? What would you recommend?

There are many excellent beginner books on astronomy. 'Turn left at Orion' is the book I have.

Objects of interest currently might include...

Planets:
Venus (the brightest object in the sky currently after sun and moon) - with good optics, you should be able to make out its gibbous shape. Also, when Venus is close to the earth is has a big beautiful crescent shape.
Jupiter (try to make out the cloud bands on a clear night)
Saturn ;-)a

When you're past the above, go for the following list. They should be a good exercise in star hopping.

M13
M31 Andromeda (If you're willing to stay up till late, best watched in dark skies. Its almost as big as the moon)
M6, M7 (should be easy finds)
M25
M39

More suggestions please :-) ?


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DonR
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Jul 20, 2010 14:11 |  #11

swag72 wrote in post #10570201 (external link)
Examples? What would you recommend?

The moon and major planets are easy to find. Of the planets, Jupiter is the largest and shows the most detail, but there's something special about Saturn if you are able to see it on a good night with sufficient magnification. Your telescope, with a decent 5mm or 6mm eyepiece, is capable of showing you good views of Saturn when the atmosphere cooperates. Even with your 8mm eyepiece there will be a lot to see on a good night. Even the distant planets Uranus and Neptune are within your grasp, although it won't be possible to see any detail on them. Uranus appears very close to Jupiter right now, and through your telescope it will appear to be a blue spot, hardly distinguishable from a star. On a good night with high magnification you will be able to tell that it is an extended object rather than a star-like point. Venus may amaze you the first time you see it, but IMHO it gets old fast, showing absolutely no surface detail.

Most DSO's, with the exceptions of a few like M42, M31 and perhaps M13, can be challenging for a beginner. In addition to the need for reasonably dark skies (with the moon absent), the dark adaptation of the observer's eyes is very important, and even then the beginner will have trouble at first locating and identifying many DSO's. Currently there are dozens of Messier objects visible every night, but most of them will require some experience to easily locate and identify, most of them will be impossible to see without proper dark adaptation, and some of them will be impossible to see without pretty dark skies also.

I would add M5, M15, M16, M8 and M20 to the list of good starting targets visible now, but none of these will likely be instantly recognized by a beginner. The necessary experience can be acquired alone, but it's quicker and less frustrating to start with an experienced observer - at least you will know that the object you seek is in the field of view when the experienced observer can see it. Each time you manage to see one of these objects, it becomes easier to see them the next time.

I assume that you are interested in astrophotography since you posted in this forum. Gaining some experience with the telescope is a prerequisite, and after that there are several decisions to make, such as what kind of camera to use, what kind of objects to seek, guiding considerations, etc. But the good news is that you will be able to see much more using the camera as your eye once you get the hang of it.

Don




  
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swag72
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Jul 20, 2010 14:27 |  #12

Thanks for that Don - I am interested in that you commented on Venus - Well, when I looked at that it was nothing but a bright pin prick. Certainly nothing worthy of comment. I really think I must be doing something wrong. I expected to be able to see some form of detail on a planet, or at least recognise it as such, Venus just looks like a star.

This is pants, I am clearly doing something VERY wrong.


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anishmangal2002
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Jul 20, 2010 15:25 |  #13

swag72 wrote in post #10572111 (external link)
Thanks for that Don - I am interested in that you commented on Venus - Well, when I looked at that it was nothing but a bright pin prick. Certainly nothing worthy of comment. I really think I must be doing something wrong. I expected to be able to see some form of detail on a planet, or at least recognise it as such, Venus just looks like a star.

This is pants, I am clearly doing something VERY wrong.

Hmm, what eyepiece are you using? You'd need similar eyepieces for viewing venus and saturn. You won't see any surface detail on Venus (with your telescope, and without any filters, and Venus being quite far currently). What you should see is a gibbous bright white disk (probably something like this (external link) and about the same size as Saturn.

Can you do a quick star test (external link) on your scope's optics.


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swag72
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Jul 20, 2010 15:51 |  #14

I was using an 8mm and 17mm eye piece. What you have shown is pretty much what I was seeing, albeit tiny in the eyepiece. And yes, it probably was about the same size as Saturn. I was expecting to see some kind of detail on Saturn. Jupiter, for example, when I see it, I have an idea in my head that I should be seeing some spot details ............... Won't be seeing anything if it's as damn small as Saturn!!

Star test ............... Mmm, looked at that ............... More confused. I think I'll put the scope away for a while and probably forget about it.


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DonR
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Jul 20, 2010 16:09 |  #15

swag72 wrote in post #10572111 (external link)
Thanks for that Don - I am interested in that you commented on Venus - Well, when I looked at that it was nothing but a bright pin prick. Certainly nothing worthy of comment. I really think I must be doing something wrong. I expected to be able to see some form of detail on a planet, or at least recognise it as such, Venus just looks like a star.

This is pants, I am clearly doing something VERY wrong.

Well, Venus shouldn't look like at star at 112X magnification. When properly focused, a star in your refractor should look very much like a single point of light. Venus should be distinctly larger, close to the size of Saturn's disk, and since Venus is about 63% illuminated now, it's shape should resemble the current moon, more than half illuminated by less than full.

Are you able to resolve stars to practically single points as seen through the shortest eyepiece you have? If so, the telescope and eyepiece optics would seem to be OK. If through your 8mm eyepiece you still can't distinguish the shape of Venus from that of a bright star, perhaps a neutral density filter like a "moon filter" would help. Venus is very bright, which is one of the reasons you can't see any surface detail - the other reason is that there is very little surface detail, since Venus is covered by a thick and fairly uniform layer of clouds.

Here's another question, and I don't mean to get personal, but it could be applicable. How is your visual acuity? I have cataracts - my eye doctor says they are not yet developed enough to warrant surgery, but they definitely affect my viewing. Less light reaches my retina, and star images are distorted so that they are smears rather than points. That's another reason I seldom look through the eyepiece anymore, spending just about all of my astronomy time taking photos. But although I haven't looked lately, I think I could still distinguish the shape of Venus at 112X.

Don




  
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How big should I be seeing stuff?
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