Dobsonian And Mount

[Frostyricho (Stephen)]

Hi members of IIS,

I was wondering with an Dobsonian if you can take it off the mount and put it on to a equatorial and use it as a huge reflector. And also i thought if i was to get the mount would i have to put more counterweights due to the fact of how heavy the dobsonian is. This would be good for in the future when i start to do astrophotography as i can then put a motor drive and track stars or other objects. I know that to do good astrophotography photo's i will need a few hundred dollars put into it. Thats why im planning to keep this telescope for a few years and upgrade it slowly by slowly with a new DSLR camera and also new mount.

I don't know do you guys think this is a good idea.

Kind regards,
Frostyricho

[brian nordstrom (As avatar)]

Yes it can be done , what size is your OTA ? that dictates what size mount you will need , I do think that a 'Few Hundred' wont cut it , more like a 'Few Thousand" .
Brian.

[Frostyricho (Stephen)]

Well i haven't gotten the telescope yet but im getting it in a few days. It is an 8"inch Dobsonian. But im not going to do it now as i said in the future. Plus also eBay there is heaps of sales on there. Just nee to shop around a bit to find the best prices and also talk to other people on here about it.

[barx1963 (Malcolm)]

Yes it can be done.
Just a small point, by definition if you remove the OTA from a dob and mount it on an EQ mount it is no longer a dob. A dobsonian is a type of newtonian, so what you have then is a equatorially mounted newt.
Anyways, back to the question. Yes it can be done... but, there are a number of provisos:
1. At you correctly surmised a solid OTA of a larger dob will be heavy and will require an appropriate mount. Probably a 10-12" will need an EQ6 or equivalent as a minimum.
2. Most dobs are not setup for imaging. For visual use you can get away with a much smaller fully illuminated field, so the secondary tends to be smaller. So if imaging a new secondary may be required. Also many dob OTAs will display a fair bit of coma which would need a corrector (Paracorr or similar). Both these first 2 points apply especially to deepsky imaging rather than planetary BTW. Also the focal plane is usually inside or just outside the focuser, rather than where the sensor on a camera tends to be, necessitating either shortening the tube or moving the primary mirror up the tube.
3. Cost. All the above adds up top a fair bit of cost.

There is an article here http://www.iceinspace.com.au/63-201-0-0-1-0.html on imaging with a plain dob and no EQ mount.

Cheers

Malcolm

PS. just so I am clear, I am not trying discourage you, just making sure you are aware of some of the pitfalls that you may encounter before you spend your hard earned cash!! If this the way you want to go then go for it!

[barx1963 (Malcolm)]

Originally Posted by Frostyricho

Well i haven't gotten the telescope yet but im getting it in a few days. It is an 8"inch Dobsonian. But im not going to do it now as i said in the future. Plus also eBay there is heaps of sales on there. Just nee to shop around a bit to find the best prices and also talk to other people on here about it.

Just be careful with Ebay scopes, there are lots of poorly loked after ones coming up all the time and i wouldn't part with my $$$ without a physical inspection. Most sellers here on IIS are reliable ( you can check their past history a bit). If you are wanting new I can strongly recommend Bintel for their customer service and advice to beginners.

Malcolm

[Frostyricho (Stephen)]

Originally Posted by barx1963

Just be careful with Ebay scopes, there are lots of poorly loked after ones coming up all the time and i wouldn't part with my $$$ without a physical inspection. Most sellers here on IIS are reliable ( you can check their past history a bit). If you are wanting new I can strongly recommend Bintel for their customer service and advice to beginners.

Malcolm

Well thats why I probably would go with someone selling in my region so that i can go to them and check the condition of the item. Also thats why you pay with Pay Pal so if your item is faulty and no one told you that there was damage on it the item you can get your money back.

[Frostyricho (Stephen)]

Originally Posted by barx1963

Yes it can be done.
Just a small point, by definition if you remove the OTA from a dob and mount it on an EQ mount it is no longer a dob. A dobsonian is a type of newtonian, so what you have then is a equatorially mounted newt.
Anyways, back to the question. Yes it can be done... but, there are a number of provisos:
1. At you correctly surmised a solid OTA of a larger dob will be heavy and will require an appropriate mount. Probably a 10-12" will need an EQ6 or equivalent as a minimum.
2. Most dobs are not setup for imaging. For visual use you can get away with a much smaller fully illuminated field, so the secondary tends to be smaller. So if imaging a new secondary may be required. Also many dob OTAs will display a fair bit of coma which would need a corrector (Paracorr or similar). Both these first 2 points apply especially to deepsky imaging rather than planetary BTW. Also the focal plane is usually inside or just outside the focuser, rather than where the sensor on a camera tends to be, necessitating either shortening the tube or moving the primary mirror up the tube.
3. Cost. All the above adds up top a fair bit of cost.

There is an article here http://www.iceinspace.com.au/63-201-0-0-1-0.html on imaging with a plain dob and no EQ mount.

Cheers

Malcolm

PS. just so I am clear, I am not trying discourage you, just making sure you are aware of some of the pitfalls that you may encounter before you spend your hard earned cash!! If this the way you want to go then go for it!

Yea with shortening the tube and moving the mirror up the tube more will be something i don't want to do as it can completely ruin my telescope. I've seen a few guys do it but they are experienced and im not that experience. Im just a kid that wants to look at objects within our solar system and out of our galaxy.

Also i want to ask what is a coma in a astronomy perspective. I've heard of it but never taken any interest in it. I wish dobsonians came with adjustable mirrors to move up and down the tube. Would make life easier with astrophotography.

I HAVE SO MANY QUESTIONS TO ASK GOSH. Ill do it over time hahahah:shi p2:

[barx1963 (Malcolm)]

Coma is an aberation that is inherent in newtonian telescopes. It results in stars towards the edge of the field starting to look like little comets with tails pointing outward. In a correctly collimated newt, the centre of the image where coma is not present is central in the focuser, so stars and objects that you are looking at are not affected, but stars near the edge are. Hence for visual use it is less important ( at least I think so) as I am only really looking at the object in the centre but when imaging it can make an image less appealing. For planetary imaging, the object of interest is usually in the middle anyways so coma can be less of a factor there.
Newts with faster focal ratios (f5 and faster, eg f4) have a smaller coma free area, which is why you hear people say that fast scopes are less tolerant of poor collimation.
Moving the mirror is often not that complicated. the cell that it sits in rides on (usually) 3 bolts and some springs. Simply replacing them with longer bolts and strings can often do the job.

Malcolm

[raymo]

You don't need to move the primary mirror if you buy a
Skywatcher Flex Dob. They work just fine at prime focus
straight out of the box, unlike many other brands.
raymo

[MichaelSW (Michael)]

You can even build your own mount as this ATMQ member has done. Uses his rig for visual only. Photo from Queensland Astrofest.

[Frostyricho (Stephen)]

Originally Posted by MichaelSW

You can even build your own mount as this ATMQ member has done. Uses his rig for visual only. Photo from Queensland Astrofest.

Heheheh Michael
I don't think my scope is going to be like that one. That is insane thats thousands of dollars and i dont have that money. Thats going to be when I'm older and i have the money.

[Frostyricho (Stephen)]

Originally Posted by barx1963

Coma is an aberation that is inherent in newtonian telescopes. It results in stars towards the edge of the field starting to look like little comets with tails pointing outward. In a correctly collimated newt, the centre of the image where coma is not present is central in the focuser, so stars and objects that you are looking at are not affected, but stars near the edge are. Hence for visual use it is less important ( at least I think so) as I am only really looking at the object in the centre but when imaging it can make an image less appealing. For planetary imaging, the object of interest is usually in the middle anyways so coma can be less of a factor there.
Newts with faster focal ratios (f5 and faster, eg f4) have a smaller coma free area, which is why you hear people say that fast scopes are less tolerant of poor collimation.
Moving the mirror is often not that complicated. the cell that it sits in rides on (usually) 3 bolts and some springs. Simply replacing them with longer bolts and strings can often do the job.

Malcolm

Oh wow i never you could get longer bolts and put it in to make it closer to the secondary mirror and eyepiece. But don't some dobs have fixed primary mirrors.

And now i know what coma is. Thanks for telling me. Such nice people on here.

[Frostyricho (Stephen)]

Originally Posted by raymo

You don't need to move the primary mirror if you buy a
Skywatcher Flex Dob. They work just fine at prime focus
straight out of the box, unlike many other brands.
raymo

Raymo that scope is way out of my price range. And plus I've already found my self one.