Aperture frenzy or am I kidding myself.

[idbvideo]

I have a Celestron Astromaster 130 EQ MD which I want to use for astrophotography.

My toolkit includes the scope, x2 Barlow, T ring, Canon EOS 500D and a nice laptop.

I have used the scope to photograph the moon, not too successfully because of seveal reasons, one was the camera battery was a little low and would not use live view. I focused with the viewfinder and it ended up being a little soft. The other was that the exposure was a little off. But the main issue was the poorly alligned star finder. I had lined it up once and then it decided to go out of alignment, Oh I hate the RDF

OK thats the scene set. Now to the question - How much difference would 200mm dia OTA make over the 130mm dia OTA in terms of magnification? I know the light received at the camera/eypiece would be better.

The main reason for asking is that I wanted a goto mount and I may as well go up in size if it makes a difference for astrophotography, especially since the size of the moon in my photos was kinda small considering the 2x barlow.

Cheers n beers

Ian

[Capricorn]

Aperture does not denote the magnification.

If you are doing prime focus you do not have magnification, just an image size that again is independant of the aperture, it is dependant on the focal length. Double the focal length and the prime image is twice as big. Leave the focal length unchanged but double the aperture and the image is the same size, just brighter.

[GJBC]

My first part to the this is to say if you want to go down the astrophotography route you need a mount that is solid and track at least if you can mange to a GO To even beter. If you take a look around at some of the equipment people use to obtain their images you will see many use smaller apature scope but they will be different than what you have and ed80 or decent refractors. there are plenty of scopes out there that you can attach a camera to. not all will produce the same result. would 200 mm be better than 130 yep more light magnification difference not sure.... the eyepiece does the magnification.. the mirror gathers the light as you state

someone else will answer that one for you

i have used a reflector and refractor for imaging. The reflector for planets The refractor for deep space the reflector 10 inch the reflector used for deep space wide field with a dslr i never use a barlow as i am looking to keep the image train straight (ie any flex in the path of light to the chip) i will use a barlow with a web cam as the weight is less and it does not flex the barlow.

if you can go up in size i cant see it being against you but have a read up before you jump as aperture fever can get us all some times. i went from an etx 90mm to a mead 10 inch F4 for deep space then back to an intes micro mn68 6inch F8 for planets the the last one was a TMB105mm F6 for widefield imaging. so different scope for different things if i had to choose an all rounder from the above it would have been the intes but i cant praise the TMB enough for its optics way ahead of the rest.

bit of a ramble but hope it helps

[Squagnut]

As Capricorn said, the focal length is what gives you magnification, in conjunction with whatever EP you use. It's determined thus: FL of OTA/FL of EP = Magnification (thus, a 20mm EP in a 1000mm OTA will yield a magnification of 50x). If you're doing focal point imaging then regard that as using the same EP in either 'scope, the 130 and the 200. An Astromaster 130 has a FL of 650mm, while a typical 200 has a FL of 1000mm, so this will make an appreciable difference - appreciable, but not exponential.

The main point of a larger aperture in astrophotography is to keep exposure time down when imaging faint DSOs, so as to minimise the effects of tracking misalignment, vibration, and so on. If your main target is the moon then light-gathering is hardly an issue!

A rock-solid mount, as GJBC says, is important - I'd say it's more important than the optics.

[idbvideo]

Thanks guys. Useful stuff.

It looks like the 130 will do for now, but the mount is not that good. I think I will be going for an EQ5 mount, the EQ6 is out of the window price wise unfortunately.

I am going to have to wait until March anyay for the mount. Until then I think I will upgrade the finder.

[Tinker1947]

So, you need a Webcam/Refractor for Planets and the Moon, and a Camera/Reflector for DSO's in Prime Focus, there all sorts of tutorials on theses forums or on You-Tube, or just ask and somebody will set about typing a reply.

[Tinker1947]

Upgrading the Finder, a Telrad makes a very good Finder and along with Stellarium and the free Telrad Maps will set you on the right road.

Stellarium

Sky Maps

[LukeSkywatcher]

I find the difference between my 130mm scope (f/l 650mm) and my 200mm scope (f/l 2032mm) to be quite large in terms of light gathering.

One thing i have noticed with the 200mm scope is that with a 25mm EP (same one i use in the 130mm scope) is that the Moon practically fills my FOV, whereas with the 130mm it is quite small (read this as normal size).

I went for the 200mm because i put it out there that i may be looking to buy one in the future and i kind of talked myself into it over the space of a few days. Others helped obviously.

Not sorry i bought it. Best scope i have. I would have been very happy to stay with the 130mm for a few yrs yet but when i get it into my head that i want something i have a terrible habit of getting it ASAP.

I'm done buying scopes now. Unless of course they invent a 300-400mm scope that is as portable as the 200mm.

[umadog]

Remember that if you magnify more the mount needs to be far more stable and the polar alignment needs to be good. This means a more expensive mount. Partly for this reason it is a good idea for beginners to start out with low-power shots from short focus (wide angle) instruments. Sure the magnification is lower, but the shots can be just as pretty and they are easier to take well.

[LukeSkywatcher]

Sure the magnification is lower, but the shots can be just as pretty and they are easier to take well.

I think everyone here would agree that the lower mag shot would be more pleasing then a half baked attempt at high mag on a wobbly mount.

Good point you made there Umadog.

Not everything in astronomy is to do with high magnification. I much prefer widefield stuff (visually and photographically).

[umadog]

Hurray for wide-field: Starship Asterisk* • View topic - APOD Collection: M42: the Orion Nebula

I like the images on that page because they show you several ways of taking same object: there are different hues and different contrast regimes (with aggressive composite shots and histogram stretching in some cases). Also, these images highlight well what can be seen at wider fields.

[LukeSkywatcher]

Hurray for wide-field: Starship Asterisk* • View topic - APOD Collection: M42: the Orion Nebula

I like the images on that page because they show you several ways of taking same object: there are different hues and different contrast regimes (with aggressive composite shots and histogram stretching in some cases). Also, these images highlight well what can be seen at wider fields.

Wow..............

Those are some serious images. I've never seen Orion in so many different flavours and colours.