Astrophotography - Reflector Or Refractor?

[Layor]

Hi All,

Well, I've gone and splashed out on an Atik 383L plus filter wheel etc from FLO. With lots of help from Steve.

It's going on my CPC800 but what I wondered was, are there any pro's and con's between using a reflector or a refractor scope?

Does one have an advantage over, say, DSO's or planetary imaging? And what about Dob's do they make any difference?

Just curious to know what other folk use.

Cheers, Layor.

[Tim]

Hi,

I use both 'fracs and reflectors for imaging. The refractors are easy to use, dont require too much skill, and give great results.

But Hubble is a reflector

If I only had one telescope for imaging, it would be a reflector of some sort, probably a SCT.

Cheers

Tim

[sgazer]

Refractors tend to be heavier and much more expensive for the same aperture/focal length (placing more demand on the mount..and your wallet!). It's also difficult/expensive to get a fast (f4-f5) frac with good colour correction, but they are lower maintainance requiring little adjustment. As for quality of the image, I don't think there's much in it, but again you'll be paying more for a comparable frac. Maybe the expensive Takehashis pull away from the reflectors a bit. You don't get diffraction spikes with a frac and potentially better contrast due to no central obstruction.

For planetary, a long focal length is best, so SCTs and Macs tend to be used.

[Quatermass]

I use both reflectors takemore playing around with but produce great results refractors are easy and quicker lighter as well great for wide field imaging.

Sent from my GT-S5670 using Tapatalk 2

[Layor]

Thanks for the info, its very interesting.

My CPC800 is an f11 so would using a focal reducer to bring it down to f6 or so make a big difference to DSO's?

Layor.

[Anweniel]

I believe the focal reducer will not only make things a little easier for your tracking wise hence making you able to take longer subs but also you should capture data 'quicker' and a faster f/ratio. Thats how I understand it anyway, not having an SCT I couldnt comment on experience only on reading.

[dmahon]

Reflectors generally add in spikes to the stars - this makes it difficult if not impossible to add to data over an extended period of time.

The focal reducer will make things much quicker for you. It's pretty much essential.

[fatwoul]

Layor - you're using an SCT, so you're already using both. ;-)

I'm all about sucking as much light onto the sensor as possible in a given time, so I am moving down the fast newtonian path, but that comes at the price of diffraction spikes and collimation.

I got some nice results from my Evostar 80ED, but it didn't get much use because of my photon hunger, so it got sold to someone with more refinement who will hopefully get more use out of it. The only refractor I have now is dad's Vixen 80M, which is nice for looking at planets, but doesn't get used for imaging anymore.

[Whippy]

Layor - you're using an SCT, so you're already using both. ;-)

*cough* SCT's don't refract...

Personally, I always used refractors mainly because they're easier to use and I want an easy life . On your CPC, I'd get a 6.3 reducer/flattener as it'll make your imaging easier by shortening the focal length and speeding up the scope.

BTW, have you got a wedge for the CPC? You won't get very far without one...

Tony..

[Stu]

Does the corrector plate on an SCT not refract?

Stu

[Whippy]

No. It's called a corrector plate because it corrects spherical abberations, not anything colour related. The Meniscus on Mak-Casses/Newts does something similar.

I've read that corrector plates do bring CA into the optical train but it's so slight that it's barely measurable, let alone visual.

Tony..

[Stu]

Surely it achieves that correction by refraction? It is a curved plate which works as a weak lens and lenses work by refraction? The fact that it introduces small amounts of CA tends to support that...

Stu

[todd8137]

Great topic answered my Qs

[steppenwolf]

Not sure where this is getting us but I'd have to agree, if the light passes through a piece of glass, it must refract!

As for Reflector v Refractor, it's a 'horses for courses' thing but colour aberration-free images are easier to achieve with a Reflector at lower cost. However, a fine (and, sadly, expensive) apochromatic refractor is 'a thing of true beauty' and it doesn't half take a good image too!

[Stu]

I understand it was a bit of a diversion but was just trying to clarify the 'SCT's don't refract' comment as I knew it to be wrong. You've now kindly confirmed this so all is well

Stu

[Whippy]

By your definition then, we're all using refractors as eyepieces, barlows flatteners/reducers all contain glass....

Have a look at this: http://telescope-optics.net/SCT.htm , no mention of CA...

Tony..

[Stu_2011]

I understand it was a bit of a diversion but was just trying to clarify the 'SCT's don't refract' comment as I knew it to be wrong. You've now kindly confirmed this so all is well

Stu

This is my understanding of SCTs as well, they are both reflector and refractor. The corrector plate is a lens and light is refracted, only by a tiny amount but it still refracts.

Now someone blow these clouds away so I can see Venus go across the Sun!!

Thanks

Sent from my iPad using Tapatalk

[Stu]

Thanks Stu

Very conscious that this thread is not a debate about SCT's so we should probably start a new one if it goes on longer.

The corrector plate is an inherent part of an SCT so is different too ep's, flatteners etc. It is a weak lens so the CA is barely noticeable, much like long f/l refractors. Aren't these scopes called compound scopes because they both reflect and refract which was the original point?

Stu

[Davey-T]

Thought I'd add my 2d as the original post seems to have got lost in the posts .

I don't think anyone mentioned that long FL SCTs are good for small things like the Eskimo Nebula and short fast refractors are good for big things like North American Nebula.

I have 10" SCT and 100mm Refractor and swap camera ,Atik314L,from one to the other.

Your camera has a larger sensor and if your bored waiting for clear skies you can work out the resolution you can expect with your camera, scope, focul reducer combination.

Davey-T

[nytecam]

I don't think anyone mentioned that long FL SCTs are good for small things like the Eskimo Nebula and short fast refractors are good for big things like North American Nebula. I have 10" SCT and 100mm Refractor and swap camera ,Atik314L,from one to the other.....Davey-T

Your 10" SCT has x6.45 the potential light grasp of the 100mm OG and, with a fast focal reducer, produces a very 'fast' and compact optical system of ~900-1200mm efl ideal for many DSOs.

[ollypenrice]

I image with refractors up to apertures at which it is no longer possible to afford them! At this point I swtitch to a reflector which my astro colleague Yves was good enough to afford...

The cheaper reflectors offer fast f ratios and do well when they are tickled up into perfect collimation and orthogonality. Refractors are much easier and more consistent. However, the larger the refractor is, the harder it is to get good colour correction at fast f ratios. They get slower as they get bigger. No such equation affects reflectors.

As an astronomy holiday provider I need to have systems which require the least possible attention before shooting. For that reason I went for refractors.

Olly