Astrophotography help

lesbehrens (Les) · #1 30-01-2009, 10:41 PM

hi. well i am interested in starting in this field but no success yet.
i have tried modding my 10"dob to suit this field but result are close but not close enough.
is there a telescope where u don't need to mod the scope for a slr?
will a ccd cam be better for the 10" newtoian ?
please help....

les

Jeff · #2 30-01-2009, 11:51 PM

Hi les, with most dobs you need to either buy a lower profile crayford focuser(which might get you an extra 10mm or so), or more likely shift the mirror cell up up the dob tube (not as hard as it sounds .... with a cordless drill and a pop rivet gun).

Have you read iceman's article on photography with a dob?

Jeff

lesbehrens (Les) · #3 31-01-2009, 11:56 AM

hi. yes i have tried both options . i put a low profile focuser in but that didn't work so i then got longer bolts to move the mirror up. but each time i try something different i am always short of focus. i then thought i could still use it for visual but found out u can't Whit the mirror up and with the focuser.
i want to do both visual and photography but more visual so i dint want to do so many mods and mucking around.
would the ccd option be better?
or going for a refractor be better?
les

Hagar (Doug) · #4 31-01-2009, 12:01 PM

Really there is only a few telescopes designed for astrophotography. Your Dob isn't one of them. You will need to measure and move your mirror up the tube by quite a bit to allow a DSLR to reach focus. This is not as dificult as it sounds. Several articles are available which spell out the process.
The other option is of course an expensive one and that is to purchase a good APO refractor or a dedicated Astrograph. The Dob will work well but you will need to make the modd and you will require a Comma Corrector like a Baader MPCC or similar.
I made this modd to a 12" dobb some years ago, it only took an hour to complete, was quite simple and worked a treat.

Good luck.

lesbehrens (Les) · #5 31-01-2009, 12:21 PM

so again u agree that a refractor is the way to go?
les

renormalised (Carl) · #6 31-01-2009, 01:02 PM

Much better than the dob, if more expensive.

Hagar (Doug) · #7 31-01-2009, 01:14 PM

Hi Les, It really is a matter of the type of astrophotography you wish to persue. In my opinion a refractor makes a lovely imaging scope but the cost can be almost prohibitive. The use of a refractor requires a good quality scope of APO standard. These aren't cheap. If you wish to image galaxies you need a scope with a reasonable Focal length and a reasonable objective size. eg a 102mm objective as a minimum with a focal length of arround the 800 to 900 mm making it an f8 scope. If you want to capture nebulas which are often quite large you can get away with a much smaller refractor in about the 80mm objective class. Say an ED80. This scope will not be of a lot of use with small galaxies.
The fact that a refractor doesn't have a central obstruction does help in the imaging process but again a refractor is not the begining and end of it.

Quality is the next big hurdle in both glass type and general image quality. The ability to collimate a refractor is imperative to good imaging.
Glass lens type is next with FPL 53 lenses are really a minimum to give quality images without aberations and colour shift.

Cost. Quality with a refractor costs money. Takahashi, TEC and AP make some lovely telescopes for imaging but they have a similar lovely price. Cheaper versions are available from the likes of Skywatcher at a much reduced price.

In conclusion your dob will make an excelent imaging scope provided you modify the focal length to suit your camera and use a MPCC or similar. There is no need to spend big dollars on a refractor which gives a dedicated field of view for a big wad of cash.
Sounds a bit Irish I know but experiment with the gear you have and progress to specialised equipment as your experience increases and as you deside which way you wish to go down in the imaging slippery slide.
You may notice most imagers have more than 1 scope to cater for the differing focal lengths required.

The main thing you need to concern yourself with is your mount. A poor mount will never allow you to take long exposure images. A good mount like a good scope cost money, like everything to do with Astrophotography. Some compromises can be made in your scope but the mount is the most important thing to do with long exposure photography.

Keep experimenting with what you have and have a bit of fun. Hope this helps.

lesbehrens (Les) · #8 31-01-2009, 01:30 PM

hi. how would this scope go for astrophography? sky watcher 120mm x 600mm Achromatic OTA? i just want to learn first no big rush. would this be ok ?
les

renormalised (Carl) · #9 31-01-2009, 01:39 PM

Quote:

Originally Posted by lesbehrens

hi. how would this scope go for astrophography? sky watcher 120mm x 600mm Achromatic OTA? i just want to learn first no big rush. would this be ok ?
les

Great if you like B&W piccies but colours will show chromatic aberration. Although I have seen some achro's better than others. However, if you want to get into colour pics try to stay clear of achro's. The apo scopes are much better....but more expensive (always comes down to what you're willing to pay).

For an f/5 scope, the Skywatcher is one of the better ones I've seen colour piccies from. Usually, the shorter the FL and faster the scope, the worse the aberration.

Hagar (Doug) · #10 31-01-2009, 01:43 PM

Quote:

Originally Posted by lesbehrens

hi. how would this scope go for astrophography? sky watcher 120mm x 600mm Achromatic OTA? i just want to learn first no big rush. would this be ok ?
les

If you already have this scope by all means use it. You may find ip produces a lot of chromatic aberation on bright stars or the moon etc but will not resolve colour as well as an APO or semi APO scope. If you are going out to purchase this scope you would be better to wait a while until you can afford one of the ED refractors. An ED80 is probably one of the most under rated wide field scopes available at a very reasonable price. You could do a whole lot worse than an ED80.

renormalised (Carl) · #11 31-01-2009, 01:49 PM

Andrews is selling SWED80's, full kit including eyepieces, carrying case etc, for $699.....and since you have an EQ6 mount, there's your piccie rig

lesbehrens (Les) · #12 31-01-2009, 01:54 PM

how would the ed 80mm be for visual?
les

renormalised (Carl) · #13 31-01-2009, 02:00 PM

Good....see plenty in the 80mm. Maybe not quite as much as the 120 but you've got a much better pic scope there in the ED80. The difference in visuals won't be too apparent unless you start looking for really faint stuff, otherwise the colour correction and definition of the ED80 will be substantially better than the 120, since the 80 is an apo. Resolution wise there's a small difference, but nothing to be worried about.

lesbehrens (Les) · #14 31-01-2009, 02:08 PM

Quote:

Originally Posted by renormalised

Good....see plenty in the 80mm. Maybe not quite as much as the 120 but you've got a much better pic scope there in the ED80. The difference in visuals won't be too apparent unless you start looking for really faint stuff, otherwise the colour correction and definition of the ED80 will be substantially better than the 120, since the 80 is an apo. Resolution wise there's a small difference, but nothing to be worried about.

can u still see galaxies?
les

renormalised (Carl) · #15 31-01-2009, 02:11 PM

No problem at all....galaxies, globs, open clusters, planetary nebs, ordinary nebs, stars (double, multiple...any number!!!) etc etc. Name it and you can see it. With a good camera (DSLR or CCD/Video) you'll be able to see even more and a lot fainter than you could see with your eye alone.

Under good skies and seeing, your limiting magnitude (the dimmest you can see) with an 80mm scope is around 12.7, which will get you the vast majority of the NGC and IC catalogues, lots of the SAO stars, all the planets except Pluto, many asteroids, the ISS (

), whatever you want to look at.

lesbehrens (Les) · #16 31-01-2009, 02:13 PM

Quote:

Originally Posted by renormalised

No problem at all....galaxies, globs, open clusters, planetary nebs, ordinary nebs, stars (double, multiple...any number!!!) etc etc. Name it and you can see it. With a good camera (DSLR or CCD/Video) you'll be able to see even more and a lot fainter than you could see with your eye alone.

ok. u have convinced me to buy that.
thanks for your help everyone.
les

lesbehrens (Les) · #17 31-01-2009, 02:14 PM

no other attachements needed to atach a slr?
les

renormalised (Carl) · #18 31-01-2009, 02:21 PM

You'll need a T-adapter and T-ring specific for your camera (T-ring, that is). You may also need an extension tube if your camera doesn't reach focus on the refractor...you maybe too short and have to move the camera back a bit. Someone with an ED80 will be able to tell you if you need one...probably not, but it's best to ask.

AlexN · #19 31-01-2009, 02:22 PM

you'll want a 2" extension tube around 50mm long to get you to focus..

Other than that, it will be great, and with the shorter focal length of the ED80, it will be easier to learn with than the 10" newt.

lesbehrens (Les) · #20 31-01-2009, 02:43 PM

great thanks everyone
les