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aser hisham

which telescope to choose?

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@Nyctimene the 3 inch was disappointing because at the beginning (2 years ago) i had some very unrealistic expectations , i thought that the magnification was all that mattered then after looking up the important things about telescopes i wanted to build one so i have been studying up on telescopes for a year but someone i know built one and it didnt work quite well so i decided to buy one instead of risking it , but the problem wasn't cooling down or collimation . it performed well on the moon but terribly on the planets , i didnt see jupiter's belts , saturn wasn't bad , mars and venus of course showed nothing . i actually saw jupiter through a celestron 8 inch sct which made me realise how terrible my telescope was so i know the range of the details that will be shown 

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I would go with the reflector.  It's the most cost effective, I assume it will have a wide field of view (around F/5), will cool down quicker than the Mak and give chromatic aberration free views.  The Mak is probably best for planetary and lunar viewing, but is a lot more expensive, requires a longer cool down time (up to an hour?) to get the best out of it and will have a narrower field of view (F/10 to F/12) making less effective on the bigger DSOs.  A long focus refractor would be a close contender for planetary and lunar views, but it will be a beast to mount and you will therefore need to spend more on the mount.  One thing to consider is whether you want to split double stars or not, the diffraction spikes from the secondary on the reflector might get in the way, but it will be a strong all rounder.

 

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double stars wont be an issue , the major with the reflector is mainly collimation and cleaning  ,  there is no place where i van have my scope collimated  or cleaned so i wil have to collimate it on my own and i wont be able to clean it and dust is a monster which is a big problem so i am leaning towards the maksutov and the refractor .

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I think a 6" version of what I have should produce views almost as good.  Although I only got my first telescope last December and therefore cannot comment on the other designs the Dobsonian mount is nice and simple to set up - you will be ready to view in moments and if you are in an area with little technical assistance to hand I cannot see any unsolvable problems with a Dobsonian mounted tube. 

Regarding the collimation - a Cheshire collimator will cost only around £20-£25.  If you have time to find my relevant threads you will see that was in a absolute mind warp about the prospect of actually touching screws and doing collimation.  I tried various options, but then did what everyone had been telling me and downloaded Astro baby's collimation guide (which is easy to find using Google) it's slightly misaligned on the page in places, but is absolutely brilliant and I followed it to the letter with a Cheshire collimator and very quickly understood what I was trying to achieve and with that understanding came the doing which was actually fairly easy.  It also helps if you watch some you tube of people adjusting a reflecting telescope for collimation - don't worry about what or how they do it, just fast forward to the twiddling with the screws stage and you will have the confidence to fiddle with your own screws (my apologies if that doesn't sound quite correct, but I'm sure you understand what I mean) - oh, yes, and work on the tube with it horizontal in the mount so you don't drop anything on the tube.   I liked this video (below) - they use a laser (I tired a laser, but got on better with the Cheshire and it matched Astro baby's guide), but its the confidence  fiddling with your own screws bit that its valuable for - watch this (below) and then use Astro baby's guide with a Cheshire device and it all becomes clear.  

Cooling - I find that it doesn't take long to cool my tube down - I just sit it outside about an hour before it gets dark, and I store it with the supplied plastic reducing cover and this keeps the mirror clean - in fact reading on SGL apparently mirrors have to become quite dirty before they cease working and I don't intend to touch mine during my ownership of the telescope (assuming no-one tips a cup of coffee over it!)

In short I would think that there would no detriment to getting a 8" reflector in a Dobsonian mount.

DISCLAIMER - I am NOT an expert I only got a telescope last December and knew nothing prior to this - the above is just my own experiences as a new owner

 

Edited by JOC

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31 minutes ago, aser hisham said:

double stars wont be an issue , the major with the reflector is mainly collimation and cleaning  ,  there is no place where i van have my scope collimated  or cleaned so i wil have to collimate it on my own and i wont be able to clean it and dust is a monster which is a big problem so i am leaning towards the maksutov and the refractor .

Why suggest the reflector in the first place then if you are so dead set against it?

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30 minutes ago, aser hisham said:

@Nyctimene i really want your opinion regarding what i told you

Well, I must confess, that I am somewhat confused. In case, the 3" was performing well on the moon, it should at least show the two main equatorial belts of Jupiter and Saturn's ring at a moderate magnification. Is this 3" the one built by your friend, or is it another commercial one? Have there been seeing problems when viewing Jupiter?

As far as the dust is a problem (as mentioned in one of your posts); I'd lean towards a frac.

Take yourself time, please.

Stephan

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6 hours ago, aser hisham said:

hello guys , I've been looking for a good telescope for a while , I previously had a 3 inch reflector but it was frustrating , I ended up with through choices and I really need your help .

I found a 6 inch reflector , a 6 inch refractor and a 6 inch  maksutov cassegrain but it's a price problem , the maksutov is triple the price of the reflector , and around 1.5 the price of the refractor , so i wanna know is the maksutov worth it ? and if not should i buy the rreflector or the refractor ? bearing in mind that the refractor is double the price of the reflector . thank you very much , your help is appreciated . i also looked around and pictures compared sizes andsaid that the image of an 80 mm refractor =that of a 150 mm reflector is that true ?

 

What is your price range?  Can you post links to the specific scopes you have investigated already?  I have no idea what is available in Egypt.

Maks and SCTs cost more than newtonians because they have large corrector lenses and moving primary mirror focusing.  They are more compact, but have larger central obstructions which can reduce contrast.  SCTs suffer from this more than Maks.  The other downside to CAT (catadioptric) designs is that they tend to have high focal ratios and long focal lengths limiting wide field views.  However, since you're mostly interested in solar system objects, this isn't much of an issue.  The Mak would be the preferred design of the two for planetary observation due to its generally smaller central obstruction and better correction over a wider field of view.

Refractors, in particular ED and APO types, tend to cost vastly more than any equivalently sized reflector or CAT due to the cost of the exotic glass in the objective.  It's worthwhile, though, to get at least an ED over an achromat for seeing low contrast detail on planets unless you go to at least f/15 or higher with the achromat.  Then you're dealing with an extremely long tube which can vibrate in the least little breeze.

There's really no substitute for aperture when it comes to seeing planetary detail.  A well figured 12" newtonian will completely blow away any 4" to 6" design on most nights once the mirror has reached equilibrium.  Among 6" scopes, the Mak or a high quality Newt will probably work best.  If you can manage the weight and bulk of a 10" Newt in a Dobsonian mount, it will show far more detail than a 6" Mak on planets for about the same money when you figure in the cost of a mount for the Mak.  However, it will be far less portable.  It's all about compromises.

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13 minutes ago, Starpaw said:

Why suggest the reflector in the first place then if you are so dead set against it?

im not deadset against it , I'm just worried about the cleaning and collimation so they make it less favorable

 

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@Nyctimene the 3 inch was not the one my friend built , he built a 6 inch one , the 3 inch showed the moon well according to my limited understanding but jupiter no matter which eyepiece or with or without the barlow it never showed detail but i did see the galelian moons a couple of times

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Hello again Aser,

From what you have said the Maksutov is a strong contender as it has a closed tube (no issues with dust/sand), they also keep  collimation very well and have no chromatic abberation like Achromats do.

It will be the easiest of all the three types of scope you listed to equatorially mount - this is very important when observing at high powers.

As the 6" Mak has a long focal length you will be able to use longer focal length eyepieces to achieve planetary magnifications - for Jupiter x180 is good so assuming the Mak has a 1800 focal length you would need a 10mm eyepiece.

Checkout the drawings made by Asbytec in the sketching section of Cloudynights - he uses a 6" Mak.

Edited by dweller25

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Hi - a Maksutov is  a very good design for lunar and planetary observations - a longish focal length reflector is a close second - a refractor will only be good at magnfiication if it is apochromtic,  which is at cost- I would go for  a reflector or maksutov - Tony

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21 minutes ago, aser hisham said:

@Louis D http://www.egy-telescopes.com/152-750eq.html this is the link for the refractor unfortunately there are no liks for the other i will tell you the details tomorrow though

Your choices are clearly more limited than some of us have.

If you post links to the options that are available to you, we can give some opinions on them rather than to reccommend scopes which simply cannot be sourced where you are.

 

Edited by John
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35 minutes ago, aser hisham said:

@Louis D http://www.egy-telescopes.com/152-750eq.html this is the link for the refractor unfortunately there are no liks for the other i will tell you the details tomorrow though

Yes, I found that vendor just before your post.  They appear to be your only option.  They don't seem to have any larger Maks in stock.  Perhaps they can order something for you.

If you want to primarily look at planets, don't get that short tube refractor.  The false color will limit details at high powers.  It's mostly useful as a low power, richest field scope.

They do have two 8" SCTs, a Celestron and a Meade.  Both would be far better than the short tube refractor on planets.

Interestingly enough, they aren't carrying any Dobsonian mounted Newtonian reflectors.  However, if sand is a perpetual issue, they might not be the best choice.

Check out this video comparing a 6" refractor to a 6" reflector on Jupiter to get some idea of the views in each.

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@@Louis D they do have the scts but they are not on the website but i will get the details and send them tomorrow because the store is closed and regarding the video , the  chromatic abberations are really a worry of mine

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Buying a decent telescope in Egypt by all accounts is not easy and not simple! In fact, I believe private ownership of a telescope was illegal in Egypt until a few years ago. If you live in or near Cairo, I think there's an astronomy society at the American University so perhaps one of the members can give you some good local advice.

I've never used or seen the Voyager telescopes, but to me a 150mm refractor for 520 or 720 dollars (depending on focal length) seems worryingly cheap given that I would expect prices to be much higher than Europe or the USA. I would certainly try to find someone who has one and ask their opinion, or even ask them to let you try it! The Voyager price list does however offer the Celestron 8" SCT and although it's considerably more expensive, it is a known brand with a very good history and a loyal following for this particular model. At the end of the day it might be the better option if you can find the money!

I wouldn't compare an 80mm refractor to a 150mm reflector - but as a rough rule, I might compare a 120/130mm refractor to a 150mm reflector, or a 150 to a 200. BUT other factors will come into play such as lens and mirror quality. Chromatic aberration (CA) or fringing is a problem especially with faster achromatic refractors, however it will be less present with longer focal length. 1200mm will give less noticeable CA than 750mm. I don't know how old you are, but the good news is at CA becomes less of a problem as our eyes age.

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I would take a 6 inches reflector of good quality, they are inexpensive but effective. Collimation is not a big deal, after some practice it's easy to execute. You clean the mirror once in a few years and that also is not really hard if you follow the procedure.

For me, the 6" is the best bang for the buck.

 

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This may be an option...

https://www.edfa3ly.co/

If so, let us know, and then we can make improved recommendations and suggestions.

A Newtonian, or open-reflector, is 100% colour-free, yet does require the most maintenance, and in the form of collimation.  But collimating a Newtonian is not the monster that's generally thought of at first.  Once it's accurately collimated, it then only needs minor tweaks now and again; nothing major.  In enhancing it after it arrives from the factory however, it can be a bit work-intensive, but it will then reward the observer, and tinkerer, with wonderful views.  Enhancing one is always an option however, as it will perform quite well as it comes.  

A Maksutov is the closest of the mirrored telescopes akin to a refractor.  The Maksutov has been described as being "refractor-like" in performance, and the design born of the long-focus refractor...

https://stargazerslounge.com/uploads/monthly_11_2014/post-4043-0-58438000-1417365975.jpg

That's what a 6" Maksutov would look like if its light-path were unfolded to its full length, and with that refractor being a 5" f/15.

Maksutovs take the longest amount of time to acclimate to the outdoor conditions; about an hour before all powers are available for use.  Some if not many owners store them outdoors in a protective yet un-insulated container or shed, and ready to observe with at a moment's notice.

A Schmidt, given the design's larger apertures, simulates a long-focus Newtonian, but without the spider-vanes, yet with the largest of secondary obstructions.  Secondary obstructions of the mirrored designs reduce contrast and sharpness, and akin to being as a "cataract" in the center of the telescope's "eye".  Only a refractor's aperture is unobstructed, among consumer telescopes, and offers the sharpest and most contrasty images, particularly the long-focus achromats, and apochromats, and over all other designs. 

In all of the mirrored designs' favour, especially in the case of a Newtonian, the telescopes are practically colour-free.

Short, fast achromats, like this 6" f/5...

https://www.firstlightoptics.com/startravel/skywatcher-startravel-150-eq5.html

...are exclusively for the dimmer deep-space objects of the night sky, and excels at such.  But point it at a bright object, and the false-colour may not be to your liking, to put it mildly.  

Voyager carries this 5" f/6... http://www.egy-telescopes.com/127-700.jpg

There would be a little less false-colour, but perhaps still not to your liking.  The shorter an achromat per its aperture, the greater the false-colour when viewing brighter objects.  The 6" f/5 is quite short for its aperture, and again, can be quite colourful.    

Voyager also offers a 6" f/8...

http://www.egy-telescopes.com/152-1200eq.html

False-colour would be considerably less evident when viewing brighter objects with that one.  It would be rather undermounted on the EQ-4 however; a bit shaky and wobbly.  It would need at least an EQ-5 mount, for visual use; if for imaging with a camera attached to it, then an even larger EQ-6.

Edited by Alan64

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32 minutes ago, aser hisham said:

unfortunately after phoning the store , there are only the refractor scopes available and the website @Alan64 suggested cannot get the telescope so i think this one is the only option please tell me your opinions http://www.egy-telescopes.com/152-1200eq.html

If the false color bugs you a lot on bright objects, you can try various "violet fringe killer" filters.  Some are nothing more than a light yellow filter.  The Baader Yellow, 495nm Longpass filter is a very strong yellow filter that squashes just about all the violet fringing.  Here's a daytime example of what effect it has.  Here's another color-corrected example.  Here's some side-by-side daytime photos showing the effects of various other fringe-killer filters (ohne Filter means without filter).  The Baader Contrast Booster seems to work pretty well among these to maintain a decent color balance by eliminating yellow.  This can be advantageous in an urban setting because a lot of light pollution is yellow.

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4 minutes ago, aser hisham said:

@Louis D so even the f8 will have chromatic abberation?

 

Absolutely.  That video is from an f/8 achromatic refractor (a Sky-Watcher 150mm f/8 Achromat Refractor according to the comments).  Even at f/15, there will be some.  You'd have to switch to a much more expensive 152mm ED refractor to eliminate most of the chromatic abberation at f/8.

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post-849-0-30515700-1462896353.jpg

This graph is useful in illustrating the level of chromatic aberration you can expect to get at different apertures and focal lengths.  As you can see, to have minimal or no CA on a 6" scope, it would have to be F18, which would weigh an absolute ton.

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