Omni XLT 120, 150 Refractor, 8" or 6" Newtonian

[Bomia]

Hi to Astro Seniors, I am narrowing down to the 4 model for my first scope after reading for the pass 2 month and also went a few stargazing session. While these scope are within my budget and are acceptable size to me since I am driving.

But above that, I am concern on the performance and what I would be able to see with them. I know I may not see everything with 1 scope but will hope it can cover as much as possible. Please give me any comment.

[Great Red Spot]

The two refractors are achromats, I assume. The 150 will throw up lots of false colour since it is at F5. The 120, at F8.3 will do better, but probably not good enough. Achromats of such apertures should ideally have a focal ratio of longer than F10.

The newtonians will exhibit no false colour since light is reflected rather than refracted. They should also be cheaper and lighter than equivalent refractors, eg 120R vs 8N, 150R v 6N. My vote goes to the newtonians.

[Bomia]

I was thinking of Newtonian initially, but saw acticles which mentioned that the false color are not major issue since filter can be used, and refractor would give more detail or resolution over the Newtonian.

The fact is I am starting to incline toward refractor as I read more, and am thinking of 150 over 120. Other than more light gather equal more resolution, it is also shorter, meaning I may only need to get a smaller dry-cabinet.

[Hardwarezone]

Why not get that 6se in the buy/sell section ?

attractive price
no false color
compact tube for dry-cabinet
electronic mount

[Great Red Spot]

A 150mm refractor gathers roughly the equivalent amount of light as an 200mm newtonian (taking into account the central obstruction). But a 150mm achromat "loses" light as the spectrums of light do not sufficiently focus a the same point. A filter works by removing the unfocused spectrums of light, thus preventing it from interfering with the focused spectrums of light. So you end up with something like a 120mm refractor (just a rough estimate) instead of a 150mm refractor. It is a whole different story if you compare an APO refractor with a slightly larger Newtonian.

[Hardwarezone]

Resolution remains the same between refractor or obstructed design (newt, sct , mct)
Obstructed design retains <high contrast detail> and suffers at <low contrast detail>

I'm a newbie too , can't explain what is <low contrast detail>

This article explains it well. There is a problem accessing it on my Singnet though, use a USA proxy and it will display correctly.
http://www.hoflink.com/~mkozma/obstruction.html

[Great Red Spot]

http://www.cloudynights.com/topic/50058 ... try6594331

See Eddgie's post.

[antares2063]

But above that, I am concern on the performance and what I would be able to see with them.

Hi Bomia,
If you are a visual observer like Great red spot and myself, just join a Mersing trip. The overwhelming light pollution of sg is the killing factor of what you can see rather than the quality of the optics system. Dont worry so much about the scope once you gotten one, but bring it out to what I jokingly refer to as its "Natural Habitat" to soak in and absorb more starlight. Once you have seen a how a small scope like my 4" perform in dark areas...fwah..mind blown.

edit: or since you drive you may join places like Sedili although i cant comment much as Ive never been there

regards,
Junwei

[kochu]

Hi Bomia,

150 mm f/5 Refractor is not all that bad.
Just ignore the edges while looking at bright planets . That is all
On the other hand it is a great one for observing DSOs and even for Imaging.
More over it is good value for money.
I had couple of them and have one in hand now..
Look at one of my images below taken from Singapore.

viewtopic.php?f=7&t=13093
Kochu

[Bomia]

Hi hardware zone, The reason why I am not getting 6se, it is not EQ mount and I like to consider AP in near future. And can teach me how to use US proxy?