Achromatic vs Reflector

[Sconesbie]

I haven't researched these ones (Achromatic). I'm looking at options to replace my scope that was nicked.

What are the benefits/negatives of Achromatic vs getting a new reflector scope? I'm still looking at the $400 mark. Astro Petes has this one for $425 including freight.

http://www.astroanarchy.com.au/telescopes/Skywatcher_102x500_Refractor.html

I had a 4" / 900mm Skywatcher on EQ1.


Regards
Scott

[Wavytone]

Pros of reflector - zero chromatic aberrations, bigger aperture for a given budget; fast f-ratios possible on a budget;

Cons - collimating the optics from time to time; central obstruction reduces image quality at high power (for f-ratios 5 and under); diffraction spikes on bright objects; mirrors are more likely to collect dust requiring occasional cleaning; may need a coma corrector (f/5 or less) and/or flattener for imaging.

Eyepiece position... depends on what you prefer.

Stretching your budget a tad = http://www.astroanarchy.com.au/telescopes/StarDiscovery_130x650.html

Or http://www.iceinspace.com.au/forum/showthread.php?t=174423 and wait for a small mount to turn up.

[Ukastronomer]

Please remember to check out PRE owned from reputable dealers for better gear for your money

The problem with "cheap" driven do it all mounts is that you are then spending the greater portion of the money on a mount and not better optics.

ALSO remember you will more than likely want 2" eyepieces in the future, check the scope is capable of using them.

[Renato1]

Hi Scott,
It depends what you want to do with your telescope.

I have a 102x500 Achromat which I use for wide field viewing at low power, which is easy to take outside and setup in a couple of minutes. It's great for that. But at high power on planets, it needs a yellow or yellow-green or chromatic aberration filter to get rid of the blue light that mucks up the view. And it's pretty useless for viewing galaxies except at the darkest of sites.

I don't like the AZ3 mount which comes with it much. The 6X30 finder, is pretty good for finding stars and planets so long as you remember the trick of keeping both eyes open.

For less money, that site has the 6" dob which gives you twice the light gathering power, and much better views of planets - once you've mastered collimation (or how to adjust the three back screws to get a bulls-eye pattern in an out of focus star image). And you may have to leave it outside for half an hour or more before the temperature in the tube settles down to get the very sharp views on planets.
http://www.astroanarchy.com.au/telescopes/dob_6_FullTube.html

But, to hunt down galaxies and faint nebula and planetary nebula, the 8" dob that store has is dearer, but ridiculously better than the 4" achromat.
http://www.astroanarchy.com.au/telescopes/dob_8_FullTube.html
Though it comes with an 8X50 finder, to my mind also needs 1X red-dot finder to make life easier finding objects. It does have a 2" focuser, which the 6" model doesn't.

Over the years, I've spent a very large amount of time looking through a short tube refractor (for the wide field views) and through an 8" telescope for the deep sky views. Yes, you can make do with one or the other, but ideally you'd want both types of telescope.
Regards,
Renato

[Ukastronomer]

100% which is why most people end up with two or three different scopes

[Sconesbie]

Thank you Renato. I've got a 10" dob at home and the views are cool through that. I was assessing another dob instead of one on EQ mount this time and looks like I might do that. A six inch will do the trick. I need something I can load in the car when we head away and bring it home again. I'm not leaving the new one at the shack any more.

[Renato1]

Yes - the operative word I think being the "we" in "when we head away". I used to happily take my little 80mm/ 500mm focal length refractor away with me when I was single, but after getting together with my wife, I had to get a smaller 66mm William Optics refractor for taking away when travelling.

Now it depends how big your car is. If it can take a 6" dob without others complaining, that's probably the best way to go. Though you do miss out on the wide field views of the refractor.

I remembered what I didn't like about the AZ3 mount with my 100mm achromat. Basically my setup with the Achromat connected to Celestron Delux Slow Motion control, in turn attached to the top of a solid tripod was just much easier to use than with the achromat on the AZ3, especially as when using the solid tripod it is simple to raise or lower the height of the telescope to suit one's chair.

Unfortunately, that Celstron slow motion control is no longer available, and the Orion version very poor in comparison.
Cheers,
Renato

[Hoges]

I have the 4" F5 Acromat - And I'd have to say that I'm not overly impressed by it. An ED80 is a much better choice imho. They turn up here s/h fairly regularly. Put it on something like a vixen porta mount and you've got a light weight setup that's robust and easy to pack into the car, and you can use it as a birding/spotting scope as well. It certainly won't show the detail a 6" reflector will, but I am often surprised at the things I can see in mine.

[doppler]

Acromats get better the longer the focal length, f15 is the sweet spot.

https://stargazerslounge.com/topic/308127-chromatic-aberration-in-refractors/