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 Orion 3x Barlow for 8" DobNow viewing all messages in this thread. | View previous thread :: View next thread |
| Eyepieces, Binoculars, BinoViewers, and Filters -> Barlows | Message format |
Julie46825 |
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Member Junky Posts: 37  Location: Fort Wayne, IN | |||
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| jimbo |
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Admin Posts: 2616    Location: Boiling Springs, SC | |||
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| mosheriffic |
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Admin Posts: 5325  Location: Marysville,Wa 48.07N-122.21W | I'm in total agreement with Jimmy.  The 400mm limit is assuming perfect seeing conditions, which rarely if ever happens. Can you see things at the higher than practical powers?....Sure you can, but even though you are in tighter on an object, the detail and contrast gets fuzzy. I own the Orion 3x barlow. It was used with my 600mm FL 120ST and did allow me to effectively view and image the Moon and Saturn. Just for grins, last night I combined it with a 10mm in my 2032mm FL SCT for 609x. I was exploring various Lunar features. There were moments when I could make out good details, but mostly the image was very fuzzy and dim. One of the biggest misconceptions in astronomy is confusing more magnification with seeing more detail. The best views I've had of any object, are with my 17mm Ultima-LX. It gives a modest 120x with my scope, and has a 70 degree AFOV. You might concider saving your pennies for a better eyepiece, thats a purchase you won't regret. Here are two images taken last night through the 3x barlow @ 609x: the first is crater Copernicus; the second is crater Tycho. Edited by mosheriffic 7/14/2008 1:03 AM Attachments ----------------  copernicus1.jpg (70KB - 2 downloads) Tycho1.jpg (55KB - 3 downloads) | ||
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| Julie46825 |
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Member Junky Posts: 37 Location: Fort Wayne, IN | |||
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| JohnM |
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Forum Support Admin Posts: 6043  Location: Wyoming Wind River Range | |||
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| EHHaggis |
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Member Junky Posts: 25 Location: San Jose, CA | |||
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| EHHaggis |
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Member Junky Posts: 25 Location: San Jose, CA | mosheriffic - 7/13/2008 9:36 PM I'm in total agreement with Jimmy. The 400mm limit is assuming perfect seeing conditions, which rarely if ever happens. Can you see things at the higher than practical powers?....Sure you can, but even though you are in tighter on an object, the detail and contrast gets fuzzy. I own the Orion 3x barlow. It was used with my 600mm FL 120ST and did allow me to effectively view and image the Moon and Saturn. Just for grins, last night I combined it with a 10mm in my 2032mm FL SCT for 609x. I was exploring various Lunar features. There were moments when I could make out good details, but mostly the image was very fuzzy and dim. One of the biggest misconceptions in astronomy is confusing more magnification with seeing more detail. The best views I've had of any object, are with my 17mm Ultima-LX. It gives a modest 120x with my scope, and has a 70 degree AFOV. You might concider saving your pennies for a better eyepiece, thats a purchase you won't regret. Here are two images taken last night through the 3x barlow @ 609x: the first is crater Copernicus; the second is crater Tycho. :) I have several reactions to your comments and pictures. My first concern is that digital images are NOT comparable to eye views. I guarantee you that the exposure time in your Lunar pictures was longer than the less-than-100-millisecond fluctuations of the air that the eye can detect! As one watches a highly magnified view of the Moon or planets, we can quantify detail and sharpness of image in slices of time that are about 100 ms (or even less.) So, the eye viewer may THINK that the sky is "perfectly steady and clear" because, on average, we are seeing pretty sharp views, fluctuating constantly over a true range from nearly perfect to horribly blurry--but the eye/brain combination tends to mentally focus on, and recall, the 'sharp moments'. After all, that's what we are straining to do! But, the camera system is brutally honest--though over a long average of time. It does not have a mechanism to isolate perfect moments; it just averages everything, and you lose the 'sharp moments'...unless you are using exceptionally short exposure times with a VIDEO capture system; throw away the bad frames; and stack only the good-to-nearly-perfect ones. I have had the experience of viewing incredible details on Mars that just took my breath away; but then setting up my imager and getting LOUSY pictures! Ditto for Jupiter--maybe it's even worse with that planet. If I just stuck with visible observing, I would conclude that it was a night of "great seeing". So, I would NEVER, ever try to "test" optics for visual observing...with imaging or photography! These are really two entirely different methods of observation, one using the special techniques of the trained eye (and brain); the other using the objectivity of the electronic sensor (which is not nearly as good in resolving fine detail as highly trained photopic vision processes.) Second reaction: "limits" to optical observing are really just conventions that can, in some cases, date back 150 years or more. The Dawes Limit, for instance, has almost NOTHING to do with the way the eye works on lower contrast perception and discrimination of higher or lower frequency detail. So applying the old "50x per inch of aperture maximum magnification" alleged RULE is really very, very simplistic--and in the case of planetary observing, can cause you to fail to take advantage of best opportunities, being "afraid" you'll break the "rule" and suffer so-called empty magnification. These "rules" break down IMMEDIATELY when you have vastly better optics than those old 19th century observers used (MOSTLY in the moist UK skies, when Rev. Dawes, George Biddle Airy, and other "authorities" came up with their iron-clad rules.) If you ever used, over time, an AstroPhysics or Takahashi refractor for hundreds of hours, in pristine high altitude skies with laminar airflow (ahem--where I observe!) then you won't pay the SLIGHTEST attention to any of these "rules" !! I have a lowly 3" f/9.2 Bushnell reflector, with spherical primary mirror, that is SO GOOD and SO SHARP that I can regularly use it at 350x for Saturn and Mars. An acquaintance has a 3.5" aperture Questar, and one of the two or three best and most detailed views of Jupiter I have experienced SINCE 1957, has been with that scope--at 100x per inch of aperture, or 350x: at a city park here in San Jose, one memorable night. Rules. BAH! Steve W. Edited by EHHaggis 5/17/2012 4:55 PM | ||
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| mhmeyers |
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Veteran Junky Posts: 278 Location: WA | My god, I love this forum!  I can't believe that rule is THAT old and still spoken as if it is unbreakable. Makes me want to purchase that 3mm lens I've been looking at. | ||
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| lightbridge_driver |
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Elite Junky Posts: 957 Location: Mohave Desert AZ/CA border | |||
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| lightbridge_driver |
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Elite Junky Posts: 957 Location: Mohave Desert AZ/CA border | |||
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| craytab |
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Veteran Junky Posts: 204 Location: Bethlehem, PA | lightbridge_driver - 5/29/2012 11:48 AM I missed this post ..sorry.. For a Dob I would not even bother with a Barlow, Get instead a Parks Silver series 7-21 mm zoom eyepiece. with the dobs mount, you can simply zoom the eyepiece on the object, and keep it centered, there is no good reason to buy a barlow with a Dob and have to mess with it in the dark, remove the eyepiece, install the barlow and reinstall the eyepiece and try to keep it centered while doing all that. What? No barlows for Dobs?  I use a barlow with my dob every night I am out. Combine a good barlow with a set of good wide field EPs and you have double the set of good wide field EPs! I use the 2x 1.25" Ultima barlow mostly with my 11mm ES 82 EP giving me 218x which is often the most mag I can use in my local seeing conditions. If I were to just get a zoom ep I would be missing that nice wide 82 degree FOV that is maintained even in the barlow. In fact, I believe as you zoom in the FOV gets more tight with a zoom ep, or is it the other way around? Either way, many folks use barlows with dobs. They work great for most people! | ||
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| lightbridge_driver |
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Elite Junky Posts: 957 Location: Mohave Desert AZ/CA border | It's simply a matter of making things easier. I use my zoom eyepiece particularly for planets, craters. One can have it set at 21 mm, and zoom in while guiding the dob and increasing magnification. Things are much easier to find with the wide field , then simply zoom in. For those kind of objects There is no need for wide field anyway. I do have several barlows and focal reducers, but for an unguided dob, I like my zoom lens. If you try it, you will think 'Wow, that is easy"  Edited by lightbridge_driver 6/7/2012 5:38 PM | ||
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