Dobsonian tracking

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Dobsonian tracking
Posted by CygnusXT10 on Friday, August 27, 2010 3:06 PM

I'm occasionally seeing advertisements for devices that help Dobs track. For example, in October's Astronomy issue there's one on page 66. Can anybody give any advice on these things? Has anybody here had any experiences using them on Orion SkyQuests?....especially the 10 inch?

"Why is there something rather than nothing?"

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Posted by chipdatajeffB on Friday, August 27, 2010 4:14 PM

I don't yet have that issue, so I don't know which design you mean.

If you mean the "platform" designs, I've used the Osypowski versions a good deal, and I've seen one example of the Dob Tracker. These platforms are essentially the same as a "Scotch mount" except that the base is horizontal. In general, these will support dobs up to about 25" aperture, and are rated for a specific weight range and area of the base. They track for 45 minutes to an hour, at which time you "reset" them simply by stepping on the high side of the base and pushing down, to move the base of the scope East.

I find the Osypowski platforms perform very well if matched to the size and weight of the scope.

Some of these platforms also are equipped with "drive controls" that slew the mount in RA (you aim the scope in DEC by hand).

The base and rocker assembly have a built-in latitude range (I've seen them from about 28 degrees to 42 degrees and don't recall seeing any outside that range ... I've read about one model that is adjustable in latitude, and you can get some latitude range adjustment by propping up the base under one end. The Osypowski platforms have generous-travel leveling screws on some models, which extends their latitude range a bit.

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Posted by Poppa Chris on Friday, August 27, 2010 4:27 PM

CygnusXT10

I'm occasionally seeing advertisements for devices that help Dobs track. For example, in October's Astronomy issue there's one on page 66. Can anybody give any advice on these things? Has anybody here had any experiences using them on Orion SkyQuests?....especially the 10 inch?

I've seen some Dob's in Orion's catalog that are advertised as full GoTo scopes with all the expected motors, software, etc.  The pictures look like exactly the same hand controller that came with my Celestron CPC.  Also, Celestron announced they are selling "Sky tracker" Dob's that look all the world like Orion's stuff.  I heard awhile back that there was some sort of merger or something between these companies, so there may be a lot to it. 

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

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Posted by CygnusXT10 on Friday, August 27, 2010 9:44 PM

Thanks for your responses Jeff and Chris. The company is called Equatorial Platforms and they're from Grass Valley California. I suppose it couldn't hurt to send them an e-mail for a free catalog. I don't think I'd buy a platform unless I heard from somebody that it worked well on an XT10.   Roger

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Posted by pastorg on Friday, August 27, 2010 10:26 PM

Here are the websites to Equatorial Platforms and Dob-Tracker platfoms in case you don't have them: www.equatorialplatforms.com  and www.supernorthstars.tripod.com.

pastorg

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Posted by DaveMitsky on Saturday, August 28, 2010 10:31 AM

Poppa Chris

I've seen some Dob's in Orion's catalog that are advertised as full GoTo scopes with all the expected motors, software, etc.  The pictures look like exactly the same hand controller that came with my Celestron CPC.  Also, Celestron announced they are selling "Sky tracker" Dob's that look all the world like Orion's stuff.  I heard awhile back that there was some sort of merger or something between these companies, so there may be a lot to it. 

Synta, the Chinese company that manufactures the Dobs that Orion sells, acquired Celestron several years ago.

Dave Mitsky 

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by tkerr on Saturday, August 28, 2010 11:13 AM

So much for More Bang For The Buck!

 What was John Dobson's intention when he designed the Dobsonian?   Wasn't it to make the Telescope more portable and lower Cost so that even larger telescope would be more affordable to the average person?  

Adding all this electronic and tracking gadgetry only defeats the purpose doesn't it?  

The greatest thing about a Dobsonian is its simplicity.  No calibration, no polar alignment, no star alignment, and no power supply or batteries necessary.  Just set it where you want it and you're on your way to a great night under the stars.  
With the addition of all that electronic nonsense you can't just set it up and go anymore. And then, If for any reason you decide to relocate during your observing session you cannot exactly do it so easily anymore.  
Oh, and let's not forget, as with all electronics the cost is not just higher, but the life expectancy of electronics isn't very long.  After a few years of use and those nice fancy electronic gadgets quit working, then what do you have?  A Plain ole Classic Dobsonian with useless electronics that will be costly to repair or replace, and only if they are even available still. Which BTW, Orion has been notorious for dropping items as well as any further support for them.  So why not just stick with the old faithful Stable and simple Classic Dobsonian in the first place? 

If you want a telescope on a GoTo mount why not just get a telescope on an EQ Mount.  The price difference between one of those Orion GoTo Dobs and a Celestron Newtonian on the CG5 GT mount is only a couple hundred dollars. And if you eventually decide you want to try your hands at Deep Sky Astrophotography, an EQ mount is much more practical and proficient for that purpose.

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Posted by Antitax on Saturday, August 28, 2010 1:34 PM

Maybe I'll have a push-to one day but not a go-to. Too many motors and battery drain for a job that I can do myself.

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Posted by zachsdad on Saturday, August 28, 2010 3:33 PM

CygnusXT10

Thanks for your responses Jeff and Chris. The company is called Equatorial Platforms and they're from Grass Valley California. I suppose it couldn't hurt to send them an e-mail for a free catalog. I don't think I'd buy a platform unless I heard from somebody that it worked well on an XT10.   Roger

A well built equatorial platform will work with any dob you can fit on it.  If you are comfortable using tools there are many plans availible on-line to build your own.

Here's one from a kit:

http://home.netcom.com/~tlsystem/cablet4.htm

 

Terry's Law of Cosmology: "Light travels faster than sound. That's why some people appear bright until you hear them speak."

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10" Orion Skyquest Classic dob

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Posted by CygnusXT10 on Saturday, August 28, 2010 4:13 PM

Actually Tim, photography is what I was thinking about. I was wondering how practical it is with a Dob. I know it's a hassle but spending a lot of money on a second telescope is a hassle too. Am I correct in assuming that equatiorial platforms on Dobs don't track very accurately? Roger

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Posted by tkerr on Saturday, August 28, 2010 4:41 PM

CygnusXT10

Actually Tim, photography is what I was thinking about. I was wondering how practical it is with a Dob. I know it's a hassle but spending a lot of money on a second telescope is a hassle too. Am I correct in assuming that equatiorial platforms on Dobs don't track very accurately? Roger

There are people who have captured some great astroimages using a Dobsonian on a tracking platform, especially lunar and planetary images.  The problem however is not that they don't track very accurate, but the inability to polar align. Over time you will get what is known as field rotation unless it has some kind of derotator. There is also software that can correct some of that, but then you're losing some of your image having to crop it.  And another problem is that, if memory serves me correctly, you have to reset the tracking platform every 20 or 30 minutes or so. 

I guess what it boils down to is, how much patience and dedication do you have to mess with it?    

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Posted by DaveMitsky on Saturday, August 28, 2010 5:19 PM

Tim,

DSO imaging is possible using a dual-axis equatorial platform.

http://www.equatorialplatforms.com/images.shtml

I'd be happy with any one of the images shown.  If someone already has a large Dob and is interested in imaging, this certainly seems to be the way to accomplish it.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by tkerr on Saturday, August 28, 2010 6:09 PM

DaveMitsky

Tim,

DSO imaging is possible using a dual-axis equatorial platform.

http://www.equatorialplatforms.com/images.shtml

I'd be happy with any one of the images shown.  If someone already has a large Dob and is interested in imaging, this certainly seems to be the way to accomplish it.

Dave Mitsky

 

Yes, I know that, and in my previous reply I even said I have seen people produce some great images with a Dob platform.   But, I also said it depends on how much patience and dedication you have to mess with it. 

How long can you go before you have to reset?  Every 15 to 20 degrees, some even less, compared to my EQ mount that I can start level at 0° and allow it to go past 90° beyond the Meridian before I have to flip it.   More time on target without having to worry about tedious BS. When it comes to astroimaging time on target is important to some of us.

No matter what anyone says, you cannot beat a EQ mount for astrophotography.  By the time you waist your money for some of those Dob Platforms you may as well have invested your money in a EQ mount anyways.
http://www.equatorialplatforms.com/pricing.shtml

I guess it depends on how foolish a person wants to be with their money. 

You can get a nice Losmandy GM 8 for $1300.00 compared to $1750.00 for a dual axis platform that can handle the same weight.  And for some reason I'll just bet that Losmandy EQ mount will out-perform that Dob platform, especially for astrophotography.

If a person is truly interested in astroimaging, at those prices I am sure people should be able to find a nice EQ mount that can be properly polar align and won't have to be reset after 20° of motion.

Have I ever used a Dob platform?  No! I wouldn't own one.

Have I ever seen one in use?  Yes!  and that is what convinced me to never own one.  

Dob platforms are all hype!  
just my My 2 cents

 

On Edit:

The purpose of a Dob is to make the larger Newtonian Reflectors more affordable with a stable durable and easy to use alt-az platform.   Spending more money for a tracking platform defeats that purpose and compromises the stability. At least the one I saw wasn't exactly stable when it was leaning in one direction or the other.    They Do Not Make the best platform for astrophotography, however can make observing easier.  
Rather than spending hundreds, possibly more than a thousand dollars for a Dob Tracking platform save your money and build your own if you really must have one, for observing.  You can find plans to build them with a simple google search. 

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Posted by chipdatajeffB on Saturday, August 28, 2010 6:10 PM

Astrophotography is difficult enough that you don't want to start out with a handicap, and a dob set up on an equatorial platform represents that sort of start. True, it can be done. And if you already have the dob, then adding a platform capable of handling a 10-inch is a matter of only a few hundred dollars.

... and you will not get an astrophotography mount with great tracking, low periodic error, and good photographic weight capacity for just a few hundred dollars ...

So there's no harm in trying.

But if you're looking for advice on a good way to get into astrophotography, the conventional wisdom is to start with a solid-performing EQ mount (spend as much as you can afford there) and work up the rest of the setup from there ... furthermore, since a 10-inch newtonian is also going to present additional challenges compared to a short-focal-length, moderate aperture refractor, you might reconsider the whole endeavor based on an XT-10.

I'm not dissing the XT-10. But they're designed for visual observing and in my opinion are not great learning platforms for beginning imagers.

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

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Posted by DaveMitsky on Sunday, August 29, 2010 1:03 AM

tkerr

Yes, I know that, and in my previous reply I even said I have seen people produce some great images with a Dob platform.   But, I also said it depends on how much patience and dedication you have to mess with it. 

How long can you go before you have to reset?  Every 15 to 20 degrees, some even less, compared to my EQ mount that I can start level at 0° and allow it to go past 90° beyond the Meridian before I have to flip it.   More time on target without having to worry about tedious BS. When it comes to astroimaging time on target is important to some of us.

No matter what anyone says, you cannot beat a EQ mount for astrophotography.  By the time you waist your money for some of those Dob Platforms you may as well have invested your money in a EQ mount anyways.
http://www.equatorialplatforms.com/pricing.shtml

I guess it depends on how foolish a person wants to be with their money. 

You can get a nice Losmandy GM 8 for $1300.00 compared to $1750.00 for a dual axis platform that can handle the same weight.  And for some reason I'll just bet that Losmandy EQ mount will out-perform that Dob platform, especially for astrophotography.

If a person is truly interested in astroimaging, at those prices I am sure people should be able to find a nice EQ mount that can be properly polar align and won't have to be reset after 20° of motion.

Have I ever used a Dob platform?  No! I wouldn't own one.

Have I ever seen one in use?  Yes!  and that is what convinced me to never own one.  

Dob platforms are all hype!  
just my My 2 cents

On Edit:

The purpose of a Dob is to make the larger Newtonian Reflectors more affordable with a stable durable and easy to use alt-az platform.   Spending more money for a tracking platform defeats that purpose and compromises the stability. At least the one I saw wasn't exactly stable when it was leaning in one direction or the other.    They Do Not Make the best platform for astrophotography, however can make observing easier.  
Rather than spending hundreds, possibly more than a thousand dollars for a Dob Tracking platform save your money and build your own if you really must have one, for observing.  You can find plans to build them with a simple google search. 

 

Tim,

Any method of DSO imaging is going to require dedication and patience. 

I certainly do not maintain that a platform is superior to a GEM.  However, the fact remains that Poncet tables do permit prime focus imaging to be done with Dobsonians and with very good results.

http://www.equatorialplatforms.com/image.of.month.shtml (The proof is in the pudding, as they say.)  

Are equatorial platforms a waste (proper spelling) of money?  Compare the cost of a GEM mount that will accomodate a 20" aperture to an equatorial platform that will do the same sometime.

Some of what you said seems to based on your having seen one platform in operation.  I happen to know several people with equatorial platforms who are quite happy with them.  One fellow that I observe with regularly uses one with an 18" Obsession and it works quite well, with no instability issues.  Observing planetary nebulae and other appropriate objects at 1000x or more with large Dobs is made possible with equatorial platforms.  Your entitled to your opinion, of course, but please don't be doctrinaire in your pronouncements.

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by DaveMitsky on Sunday, August 29, 2010 1:10 AM

chipdatajeffB

I'm not dissing the XT-10. But they're designed for visual observing and in my opinion are not great learning platforms for beginning imagers.

Agreed. 

Dave Mitsky

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by CygnusXT10 on Sunday, August 29, 2010 12:50 PM

Sice you're both in agreement that the XT10 wouldn't be a good Dob for such ventures, I think I'll accept that conclusion and forget about looking into the matter any further. I wouldn't want to risk putting more money and time into it than it's worth. Thanks for the time and advice guys. I sure appreciate it. Roger

"Why is there something rather than nothing?"

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Posted by zachsdad on Monday, August 30, 2010 8:53 AM

CygnusXT10

Sice you're both in agreement that the XT10 wouldn't be a good Dob for such ventures, I think I'll accept that conclusion and forget about looking into the matter any further. I wouldn't want to risk putting more money and time into it than it's worth. Thanks for the time and advice guys. I sure appreciate it. Roger

You can still use your XT10 for afocal, and webcam photography of the moon and brighter planets.  It's not as sexy as long exposure DSO photography, but can still give you some great results.

Terry's Law of Cosmology: "Light travels faster than sound. That's why some people appear bright until you hear them speak."

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15 X 70 celestron Skymaster binoculars

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Posted by sammiefields22 on Monday, September 20, 2010 3:43 PM

 Tracking add-ons are really expensive for a Dobsonian. Do you have a dobsonian already? If you want tracking, I'd advise against anything with an alt-azimuth mount.

 Although they cost a lot more and are less portable, I'd advise an equatorial mount. An SCT on an equatorial mount can track a deep space object accurately for hours.

 At the end of the day it all boils down to what your specific individual needs are. There's no such thing as a one-size-fits-all telescope.

Good luck
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Posted by DaveMitsky on Monday, September 20, 2010 4:45 PM
Cygnus XT10 currently owns a 10" Orion XT10 Dob.

Sic itur ad astra!

Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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Posted by Poppa Chris on Monday, September 20, 2010 4:55 PM

I know this is a bit off topic - but I have a simple ( for you astrophoto gents) question...

With an aperature of 279mm and a focal length of 2800mm, what is the TFOV in a DSLR at Prime focus with no eyepiece installed utilizing a standard T-adapter and T-ring?

I apologize in advance for posting this here, but didn't feel it warranted a whole seperate thread.

 

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

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Posted by tkerr on Monday, September 20, 2010 6:21 PM

Poppa Chris

I know this is a bit off topic - but I have a simple ( for you astrophoto gents) question...

With an aperature of 279mm and a focal length of 2800mm, what is the TFOV in a DSLR at Prime focus with no eyepiece installed utilizing a standard T-adapter and T-ring?

I apologize in advance for posting this here, but didn't feel it warranted a whole seperate thread.

 

 

I replied with the answer to you in PM.

However for anyone else who might have the same question for their telescope. 

You will need to know the size of the imaging chip as well as the size of the pixels and the array size .  Then you can use this application and it will give you the true field of view and the image scale. 

http://www.newastro.com/book_new/camera_app.php

Using my Canon EOS 50D with your telescope as an Example.

The Chip Size of the 50D is 14.9mm x 22.3mm
Pixel Size is 4.7 x 4.7 microns
Array Size 4752 x 3168

Using CCD Calc it tells me at that aperture and focal ratio with my Canon 50D at prime focus, the result will be an Image Scale of 0.35 Arcsec per pixel, with a Field of View of 18.3 x 27.5 Arcmin. 

You should be able to find the necessary camera info in your camera manual. Or you can find it in the table on this web page if your camera is a Canon EOS DSLR >>> Here

 

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Posted by Poppa Chris on Tuesday, September 21, 2010 8:36 AM

Well - This is a bit more complicated than I thought it would be.  Maybe I should have posted it to a seperate thread.

My camera specs are:

Canon EOS T2i/550D

FOVCF = 1.6x  Sensor = 22.3x14.9mm  Pixel = 4.3micro-m  pixels array 5184x3456 - 18.0 Mpixels

Viewfinder = .87x (95%) DLA = f/6.8

So, if I understand you correctly,  certain of the above parameters effect the FOV at Prime Focus, and this varies with the individual camera.  Your EOS 50D has the same chip size as my T2i but the size of the pixels and the pixel array differ.  Therefore, we would have differing fields of view with the same telescope?  I'm assuming that once I have this calculation made I can file it away as being a constant unless or until I get another camera or scope (or both - Mischief )

 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

PS: How can we move this discussion to "astrophotography" so I am not so much off of the original topic?  (Are you listening moderators?)

 

---Poppa Chris---

Denham Springs, Louisiana USA

"Second star to the right - Then straight on until morning!" - Peter Pan

Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars

 

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Posted by TeleNoob on Tuesday, September 21, 2010 4:13 PM

Back on the original topic, I would have thought, if the dob has got a bigger mirror (like 10 -12 inch or more) that the light collection would be fairly high, and so exposure times proportionately reduced. Thus the tracking error would also be, somewhat, reduced.

?

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Posted by tkerr on Tuesday, September 21, 2010 4:36 PM

TeleNoob

Back on the original topic, I would have thought, if the dob has got a bigger mirror (like 10 -12 inch or more) that the light collection would be fairly high, and so exposure times proportionately reduced. Thus the tracking error would also be, somewhat, reduced.

?

 

Larger aperture = greater resolving power and greater light grasp would increase (speed up) saturation, therefore reducing the time necessary for each exposure. 

You also have to consider the focal length / Focal Ratio.

Shorter focal ratio = wider FOV which would be more forgiving to tracking errors. 
Longer focal ratio = narrow FOV which would not be so forgiving to tracking errors.

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Posted by TeleNoob on Wednesday, September 22, 2010 3:28 AM

Thanks tkerr. But wouldn't they be good for imaging solar system objects? Webcam imaging where you would be taking fast frames of bright objects. At 1200 mm focal length they have the high magnification thats useful for planetary imaging. With a 10" mirror it would have really low exposure times. If the tracking is off a little bit it usually doesn't matter, as long as the planet is on the chip.

 

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Posted by tkerr on Wednesday, September 22, 2010 8:50 AM

TeleNoob

Thanks tkerr. But wouldn't they be good for imaging solar system objects? Webcam imaging where you would be taking fast frames of bright objects. At 1200 mm focal length they have the high magnification thats useful for planetary imaging. With a 10" mirror it would have really low exposure times. If the tracking is off a little bit it usually doesn't matter, as long as the planet is on the chip.

 

 

Tracking of any kind will always help, and for planetary imaging it won't take much. 

Due to the size and brightness of the planets and the moon, the amount of time per frame is relatively small regardless of what aperture your telescope is.
When using a web-cam or planetary CCD Camera your recording multiple frames(video) rather than taking long individual exposures like you would for a DSO. Each frame for your planetary video is only a fraction of a second. The amount of drift(tracking error), if any, between each frame would be very little and is easy to fix when stacking the individual frames in something like Registax. Additionally, the total amount of time spent to get enough frames for a good stack is usually very short compared to the length of each individual exposure for a DSO.  Less than a few minutes for a planetary image vs multiple minutes or hours for a DSO Image.  Therefore, polar alignment and tracking isn't nearly as critical for Lunar and Planetary imaging like as it is for long exposure DSO imaging.  
Where Aperture really makes the difference is in the Resolving Power, contrast, and amount of detail you will get as an end result.  
Focal length / Focal Ratio will have more of an impact on how tracking effects your imaging.


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Posted by TeleNoob on Thursday, September 23, 2010 12:28 AM

Thanks again. I was thinking of getting one of those motorized dobsonians for my Dad, who's retired and wants to have his own telescope. It would be for visual observing, not astro-photography. If it can locate the object, planet, nebula or some such, he can spend more time just looking at it.

The one I saw was an F5, I think. Had a 10" (250 mm) diameter and 1200 mm focal length. Or something close to that.

If he uses high magnification with it, on a planet for instance I figure as long as it tracks reasonably well it would keep the planet in the field of view longer.

 

 

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