Differences in Refractor and Reflector for Astrophotography

[vignesh1230]

Well, i have had my celestron 130EQ Telescope for about 2 years now and i wanted to get into deep space imaging. Looked up some Deep Space imaging setups and what they got out of their equipment and this caught my eye.
http://www.mikesalway.com.au/2008/12/17/deep-space-imaging-equipment/
And I saw that his imaging scope was the Saxon ED80 and the specs were focal ratio of f/7.5 and a 600mm focal length.

Then i found out that the celestron was
Aperture 130mm (5")
Focal Length 650mm
Focal Ratio f/5

So i take it that i would get around the same amount of viewing(imaging) capability with my scope. Generally speaking.

I know i could be very wrong, but i was just asking.:)

Forgot to add that i NEED to add a Barlow if i was to use it for astrophotography or else it wont focus..

[whzzz28]

A barlow will x2 (if using a 2x) the f/ratio of the scope, so it will become an f/10 or focal length 1200mm.
The lower the f/ratio the more light the scope collects and the wider the field of view. The lower the f/ration the less exposure time is required to capture detail. So lower f/ratio is (arguably) better (depends on what you are trying to do).

The scope you linked will give different images than your reflector. Reflector's by design lose some percentage of light when compared to a refractor (refractor is straight through, no reflection; reflector reflects off two mirrors that diffract and absorb a little light).

There is another issue to think of. The focuser. You have already determined that you don't have the inward focus required to go without a barlow and this is where Astrograph reflector's come into play. They are designed to allow a camera to work with them.

There is also the quality of the focuser. Cheap focusers often can't support the weight of the camera, or are sloppy and move around as the scope moves (giving you a fuzzy image).
And finally with reflector's you need a coma corrector (for serious astrophotography) and field flattener. A well regarded set is the Baader MPCC which will do both.

Why do a lot of people use refractor's for imaging over a cheaper Newtonian? Image quality is better on a refractor, it is sharper and there is less light loss due to a straight through design. They also don't need to be collimated before each session and don't suffer from mirror flop or coma. You do however pay a lot of money for them as a result.

Also do you have an equatorial mount (motorized)? You really do need a good mount for DSO astrophotography. A manual mount just won't work.
I'd say the entry level is a Skywatcher HEQ5 Pro, but there may be cheaper mounts that will do an ok job if you keep sub times short.

So long story short, would i use the 130EQ for astrophotography?
If your not looking to spend any real cash on this, then sure it will work. It just won't work too well. The limitations above would require outlay to fix (new focuser(optional), coma corrector, mount) and if your looking to spend the money, i would recommend you start with a cheap refractor (ED80 can he had for ~$600, second hand can be good too) as you will get better results with it and the learning curve isn't as high.

Don't let that stop you though! Feel free to give your 130EQ a try and see how it goes.

[gregbradley]

106mm is a good aperture for refractors. They give very sharp widefield images.

Wide field is easier in all ways to do.

The downside is a good refractor in that price range is expensive as they are hard to make with exotic glasses. The Takahashi FSQ106ED is the classic widefield imaging refractor. But its around $5000.

You can use cheaper 80 to 100mm refractors like Orion 80 and 100mm ED. They work very well. They are good value for money but the focusers will be a little weak. 80mm will keep you going for some time.

Reflectors are also great for imaging. Generally larger than 130mm and that is their strength. A 200mm refractor is large, heavy and costs over $24,000. But you can get several 200mm excellent reflector type scopes for under $2000.

Greg.

[vignesh1230]

Well I could see if i could fit a low profile crayford to achieve prime focus (If at all possible). The current focuser actually feels quite strong, and i know many people used their cameras with it
http://celestronimages.com/details.php?image_id=11572&mode=search&sessionid=9bb077f52f8e995779d8774c8 7dd35f1
What i dont get is how he was able to see that, as its quite small while just looking through the telescope.

And yes i have a motorized mount, Its just not dual axis drive but just Ra.

I dont mind actually going for the ED80, just as long as i can save up enough money and my parents will allow me XD I just wanted to do basic astrophotography... I posted a moon pic a while back here which got me into it.

But should i get a
http://www.telescopesdirect.com.au/Celestron-Universal-T-Adapter-with-Integral-Barlow-Lens-1-25-in?sc=164&category=1061784
to start off for this particular telescope? or just move the secondary up the telescope to get the focal point to the sensor?

[silv]

here, (http://www.12dstring.me.uk/fov.php?object=42)you can choose your scope and your camera to get an idea of the field of view for M42, Orion nebula.
you can also switch to "visual" and choose your scope with the eye piece you were using when looking at M42. possibly, you'll be able to find out which eye piece with your current scope would give a wider field of view.

(the image detail in this website is not related to the detail you would actually see. it's only about the FOV.)

[silv]

re buying a low profile focuserL

did you actually test your scope and the focal point with your camera?

if not:
Shiraz has explained it so well to me, maybe you'll read post 13 (http://www.iceinspace.com.au/forum/showthread.php?t=93820) in this thread.
(note: you would take out the 1.25 part of your focuser tube to test this. but...read :) )

(Don't bother with the posts before post 13.
But maybe, some of the posts following 13 are beneficial for you, too.)

[vignesh1230]

Oh. I see youve been there too xD
Yeah i havent tested it out myself, but i heard others had the same problems and they just went with a barlow, although i think a low profile would work better in my case.. Ill try the method Shiraz told you (once this rain stops :sadeyes:)