Celestron Omni XLT 150mm Reflector vs Refractor

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Gary
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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by Gary »

Joshelerry wrote:Hi Guys, thanks for the many comments and advise here.. really appreciate.

1) CG4 mount was sold as a complete set with the 150mm both Refractor & Reflector series of the Celestron omni versions. Hence I suppose they should have consider this? I might not be really sure what it mean by getting "streaky stars" due to tripod mount capability because I thought there will not be much movement unlike photography?

2) As for the 6" series to be too heavy.. well, its not that we will be moving too much but of course almost most of the star gazing will be outdoor. I do forsee probably sometime to be overseas like Ubin, St John island which requires travelling by boat (therefore I cap at 6" to 8"). Malaysia maybe will requires drive in and hence with the boot should not be a big issue.

3) Brand wise, based on remarks here shouldn't be an issue with Celestron, Orion etc...

4) Refractor vs Reflector .... understand that reflector is not usable on daylike due to the reverse images which refractor can double up as some spotting scope. In this case it makes the refractor more versatile. But mainly I will use telescope for astronomy as it will be too heavy to luge around for bird/wildlife photography which I also am doing

5) The main point here is even though I will be a beginner but I know that I will be interested in this as this is something I like since young. Budget wise will not of course wan to blow out too much (maybe within $1.5k the most roughly). And based on experience with photography, I don't want to get the entry level and later on try to sell it and upgrade, this lose more money actually. And hence I want a scope that can not just view planets but also some deep sky objects (of course I know location matters but for me I will say over 95% of the time I will be viewing in locations in Singapore mainland). Therefore I suppose getting a f/5 6" scope will be quite around the mark?? Of course do take note that I will not be buying until I did some trying and testing....

(1) "Streaky stars" refers to astrophotography. For long exposures and highly magnified view of deep sky objects, the imperfections in tracking of the mount will result in stars captured being anything less than a pin point circular dot - e.g. a dash.

(4) Do also consider the third type of telescope design - catadioptric. Examples are MCTs and SCTs. A portable Maksutov-Cassegrain Telescope (MCT) can be a very versatile telescope for both stargazing and terrestrial viewing but at the expense of smaller field of view compared to refractors and reflectors.

(5) For basic lunar/planetary and some brighter/bigger deep sky objects (DSO) at shorter exposures, $1.5k may be a sufficient budget. For most of the stunning DSO photos you see in astronomy forums and magazines by veteran astrophotographers, $1.5k is too low. Some of the astrophotography accessory required in those setups will easily cost much more than that, let alone the telescope and mount.

(6) Good to know you will do some actual viewing/trying before buying. This will be the most important and useful part of your research.
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starfinder
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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by starfinder »

I would recommend that you consider a 120mm ED refractor such as the one by Skywatcher which I bought used and am happy with. The Skywatcher 120mm f/7.5 ED is quite light weight and being 120mm has good resolving power: looking through it you can tell that the 120mm lens presents its views with 'authority'. At a dark sky site, it provides excellent views of star fields and the brighter nebulae, and from Singapore it provides good sharp views of the planets such as Jupiter and Saturn.

A fairly sturdy mount would be required for it, such as the Vixen Porta which is an alt-azi mount. Do note the weight of any 100mm and above refractor as some are much heavier than others of the same aperture size.

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cloud_cover
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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by cloud_cover »

Hi Josh,
Regarding the utility of the CG-4 with the 6" reflector or refractor: I believe Celestron markets this as a visual astronomy setup, not a photography setup. The big difference is this: Your eyes will accept a great deal of vibrations or shake and still see a clear image. On the other hand, a camera is extremely punishing when it comes to shake. As a birding photographer I'm sure you appreciate this fact - the need for very high shutter speeds when shooting small and more distant targets at high focal lengths if you don't want to have less than tack-sharp pictures. This is also why professional photographers use some sort of support for their optics.
What this translates to is that the CG-4, while perfectly fine for observing visually, will under-perform at the focal lengths used by the 6" scopes you have mentioned.
Now I see you mentioned "not much moving": That's true when compared to daytime work where you will walk around and pan your shots for various targets. However, in the daytime we use very fast shutter speeds to compensate for any movement by the target (birds or animals) or the vibrations inherent in your hand. Personally I find shooting less than 1/60s at 50mm-70mm does sometimes produce image degradations (I'm not using a vibration suppression system) and for fast moving objects, I try to keep to 1/1250 and above. In contrast, when shooting DSOs (these do not include the Sun, Moon or Planets), it is common to use exposures ranging from 1min to up to 30mins. Now stars do move, to the tune of about 15° per hour. What will this mean to you? Lets say you choose to use a non-tracking tripod, using a 6" f/5 (750mm) telescope on a DX or APS-C sized sensor (Take the Canon D40 as an example): Your field of view seen by the sensor is about 1.1° by 1.7°, or to be precise, 67.6 x 101.5 Arcmin. In about 8.9 mins, objects would have moved entirely from one end of your sensor field (the long way) to the other so in a 1 min exposure, the object will have moved at least 10% of your sensor. The result is that stars look like lines rather than dots.
Also, the gears and motors of the mount are often not perfect - even the high end ones costing tens of thousands of dollars are not, although these imperfections are much, much reduced - hence the mount won't track perfectly. This means stars will still look like little dashes instead of dots. For example, over an 8 min period or so, a CG-4 is expected to inherently have a tracking inaccuracy of about 70arcsec, which translates to 45pixels on a D40 using the 6" f/5 scope. This is where periodic error correction training and autoguiding come into play - features, I think, not found on the CG-4.
Regarding "beginner" equipment: Very often the telescope itself if not the weak link - the mount often is. So if you're worried about future upgrading, then look into getting a better mount, no necessarily a better telescope (Although an Achromat is not the best choice for photography)
Having said that again, one thing I'd like to point out is that Astrophotography really is a separate hobby from Visual Astronomy. The subject matter is the same but AP is really a technical exercise in light gathering and the mounting/scope optimization is different from Visual astronomy.
Still, all the best in your scope hunt :) Do read up reviews and better yet, look at actual equipment before committing!
Last edited by cloud_cover on Wed Aug 21, 2013 9:08 pm, edited 1 time in total.
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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by beginner »

Cloud-cover,

Very well explain. Good work.

Regards,

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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by orly_andico »

Yes cloud_cover

You da man! [smilie=admire.gif]


I do understand the notion of "don't buy the lowest end and then upgrade later."

I have fallen victim to this so many times, it's not funny.

The problem, as cloud_cover says, is that visual astronomy and astro-photography are two very different goals. And astro-photography is a very punishing hobby, because the requirements for precision are so great. To do really well at astro-photography, you need to blow a small fortune on the mount. This is where economizing will bite you in the ass. Unfortunately buying the "right" mount right away is not practical for most people.. simply because the "right" mount is a very expensive proposition (and often heavy).

You certainly can use that CG-4 for astrophotography, but only at very short focal lengths, e.g. with 200mm camera lenses or less.

If you want to go some distance with astrophotography, but not spend too much, I think the best mount at this time is the iOptron ZEQ25. Which tan14 (Peter Lee) in HK is selling for 6570 HKD plus shipping and GST (so very close to your $1.5K limit).

Then you'd need a telescope. Suggest a short refractor, something under 500mm focal length. So something like a Megrez 90. The TS 80mm triplet that astrosiao is selling is a good deal. But it's right at $1.5K. Or the Stellarvue 102mm doublet that cknjj is selling for $1.2K (try to haggle a little [smilie=admire2.gif])

Now if you're willing to buy in the US.. a Celestron CG-5 can be had new for $550, or used for $400 (USD). Then buy an Orion 80ED for $350 (USD). You'd have to do the legwork of shipping them all in though. Another $300 for shipping and GST, I reckon.

The long and the short of it is, if you buy with the goal of astro-photography in the future, it will not be cheap. I would consider a ZEQ25 + 102mm doublet to be an entry level AP setup... so resist the temptation to go cheaper.

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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by Joshelerry »

Hi, yes astro-photography is in mind but of course inthis area I will not be looking for the "extreme pro" quality and hence is generally able to accept moderate end. In fact more interested in astronomy observing itself and because I am into photography itself, hence thought it will be a good idea that I can do some photo shoot as well.

1) The kind of astro-photography I'm talking about is those where you get an adaptor to match your camera (DSLR) directly into the hole where you hold the eyepiece. Not those where you try to shoot through the eyepiece itself (hope I get it right to not confuse). And as such the focal length/ focusing will be dependant on the type of telescope used?

2) Read a few websites and found that Orion & Skywatcher offers some reflectors & SCT types of scopes specially for astrophotography. Did view a youtube where it explain that the focal point for such telescope is higher and hence will not create cropped corners. It seems that Skywatchers have some interesting telescopes as well but can anyone advise where can I view this brand (shops in Singapore)?

3) Obviously to date, I'm leaning more onto reflectors or SCT types as it gives more aperture for the bucks. Because I will prefer to have a telescope that can "see further". The range from 6"-8" (no doubt 8" will be pretty heavy for moving from my house to car and to setup and vice versa!). So 6" is more prefered

4) Just a general question - based on your people experience (since you all have known many astronomy observers in Singapore by the gathering), do more people owns a refractor, reflector or Catadioptric? ... generally observation not actual facts definitely

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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by ggodetucsamoht »

Joshelerry wrote:Hi, yes astro-photography is in mind but of course inthis area I will not be looking for the "extreme pro" quality and hence is generally able to accept moderate end. In fact more interested in astronomy observing itself and because I am into photography itself, hence thought it will be a good idea that I can do some photo shoot as well.

1) The kind of astro-photography I'm talking about is those where you get an adaptor to match your camera (DSLR) directly into the hole where you hold the eyepiece. Not those where you try to shoot through the eyepiece itself (hope I get it right to not confuse). And as such the focal length/ focusing will be dependant on the type of telescope used?

2) Read a few websites and found that Orion & Skywatcher offers some reflectors & SCT types of scopes specially for astrophotography. Did view a youtube where it explain that the focal point for such telescope is higher and hence will not create cropped corners. It seems that Skywatchers have some interesting telescopes as well but can anyone advise where can I view this brand (shops in Singapore)?

3) Obviously to date, I'm leaning more onto reflectors or SCT types as it gives more aperture for the bucks. Because I will prefer to have a telescope that can "see further". The range from 6"-8" (no doubt 8" will be pretty heavy for moving from my house to car and to setup and vice versa!). So 6" is more prefered

4) Just a general question - based on your people experience (since you all have known many astronomy observers in Singapore by the gathering), do more people owns a refractor, reflector or Catadioptric? ... generally observation not actual facts definitely


it is always difficult and hard to understand on writing and readings......best choice do a physical check it out on the scope. I am holding a 8" newtonian, you can feel how it perform. I have also a 5" SCT which i might thinking of selling with its CG-4 mount. I am planning to visit a newly found site at kranji and since you driving might want to drop me a visit too. PM me if you interested, FYI i am a beginner who know nothing too....

Thomas

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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by Joshelerry »

Hi, can you explain the difference between SCT and Newt? Since you have both.

Also I saw this Celestron Newt Advanced VX 6" & 8", beside the aperture, their focal length is difference (750mm vs 1000mm) while I saw a SCT at around 2,000mm+. Can explain how does the focal length affects performance like magnification etc?

Thanks

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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by Gary »

Joshelerry wrote:Hi, yes astro-photography is in mind but of course inthis area I will not be looking for the "extreme pro" quality and hence is generally able to accept moderate end. In fact more interested in astronomy observing itself and because I am into photography itself, hence thought it will be a good idea that I can do some photo shoot as well.

1) The kind of astro-photography I'm talking about is those where you get an adaptor to match your camera (DSLR) directly into the hole where you hold the eyepiece. Not those where you try to shoot through the eyepiece itself (hope I get it right to not confuse). And as such the focal length/ focusing will be dependant on the type of telescope used?

2) Read a few websites and found that Orion & Skywatcher offers some reflectors & SCT types of scopes specially for astrophotography. Did view a youtube where it explain that the focal point for such telescope is higher and hence will not create cropped corners. It seems that Skywatchers have some interesting telescopes as well but can anyone advise where can I view this brand (shops in Singapore)?

3) Obviously to date, I'm leaning more onto reflectors or SCT types as it gives more aperture for the bucks. Because I will prefer to have a telescope that can "see further". The range from 6"-8" (no doubt 8" will be pretty heavy for moving from my house to car and to setup and vice versa!). So 6" is more prefered

4) Just a general question - based on your people experience (since you all have known many astronomy observers in Singapore by the gathering), do more people owns a refractor, reflector or Catadioptric? ... generally observation not actual facts definitely

(1) The attaching of camera into the visual back of the telescope for photography is known as prime focus astrophotography. Different celestial objects looks good (subjective to the photographer) with different field-of-view and/or magnification. So you may also want to read up about these different types of objects and then select a telescope system that is suitable for capturing them in the way you like it. This is also one reason why some people advise newcomers to just go visual first for sometime (e.g. 1 year), observe how these objects looked like and see which ones/types they have a stronger interest in. Then, when they want to purchase AP gear, they will have higher chance of buying something "right" for them the first time round.

(2) Try reading up on Astrograph telescopes.

(3) If you have not explored portable 8" dobsonian designs, you may want to research more about this. The commercially built ones may be expensive though. And it takes more hassle (not impossible) to make them do astrophotography. But hey, you wanted to "see further" right? Always a price to pay literally. :)

(4) I see more SCTs and Refractors. Having said that, you should choose a design/size that makes you happy regardless of what is popularly seen out there. For example, I prefer to use my dobsonian telescope nowadays as I am mainly a visual amateur astronomer.
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"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.

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weixing
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Re: Celestron Omni XLT 150mm Reflector vs Refractor

Post by weixing »

Hi,
Hmm... look at the topic title, I realized that I owned both the scope you mention and currently using a 6" SCT...

Below is the quick comparison (IMHO) of the 3 scope (6" F5 Achro, 6" F5 Reflector & 6" F10 SCT):
6" F5 Achro Refractor
Wide Field Scanning: Excellent.
DSO: Excellent.
Planet and lunar: Not good.
Astrophotography: Not suitable.
Portability: OK.
Ease of use: Excellent.
Ease of Maintenance: Excellent.

Remarks
Very good for low power, wide field viewing. Not that good at higher magnification (> 200x). If you more interested in non-planet and lunar objects, such as star clusters, nebula & etc, this is a very good scope for this purpose. Bring the 6" to dark skies once and the new owner comment that it's give the same view and contrast of a 210mm Takahashi Mewlon at low power. Least portable out of the 3 scope due to it's weight. Mount requirement is high for Alt-Az mount, but if using EQ mount, a entry mid-range (CG-4 and above) one will do. This scope cannot be collimated, so there is no easy way of collimation if the scope is out collimation. Basically, no maintenance is require.

6" F5 Reflector
Wide Field Scanning: Good.
DSO: Good.
Planet and lunar: Good.
Astrophotography: OK.
Portability: OK.
Ease of use: OK.
Ease of Maintenance: OK.

Remarks
Suitable for most type of observation. Performance depend on collimation (alignment of optics). Coma will be visible at low power and when doing prime focus astrophotography and since there is no coma corrector for 1.25" focuser, there is basically not cure for coma. Mount requirement is basically same as 6" F5 Achro Refractor. Collimation is require before any observation. There will be some maintenance require once in a while since all the optics are expose to the element.

6" F10 SCT
Wide Field Scanning: Not suitable.
DSO: Good.
Planet and lunar: Good.
Astrophotography: OK.
Portability: Excellent.
Ease of use: Good.
Ease of Maintenance: Excellent.

Remarks
Suitable for most type of observation. Due to the long focal length, the widest field of view is limited to about 1 degree. Performance will depend on collimation (alignment of optics). Mount requirement is the lowest because it's very light and small compare to the above 2 scopes. Collimation is require before any observation if necessary. Basically, no maintenance is require.

Have a nice day.
Yang Weixing
:mrgreen: "The universe is composed mainly of hydrogen and ignorance." :mrgreen:

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