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Disappointed of my celestron 8SE

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#1 EEBA

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Posted 25 February 2020 - 08:33 AM

Hi everyone, I am new to the hobby and I got super excited and got a brand new 8SE. I have using the telescope in my light polluted neighborhood. First two weeks I was able to see orions nebula [which is beautiful] and sirius. During these 2 weeks, I noticed the Sirius is not sharp I as thought. I have a smaller etx 70 meade, which is not powerful, but the stars look sharp. Yesterday, I went back to the store where I bought my telescope and I explained my concern to the them. I was told, it was the sky conditions. Also he said , if I go to a better area out of the city it will improve. Today I went about 20 miles away from the city to a place called "baldy mountain' the sky look nice a decently dark. I was able to see Venus[ not to sharp] orions nebula[same as before], and Sirius without improvement. I am not experiencing collimating but the star test looks uniform to me at using the 8mm eyepiece. I was using my 8-24 baader zoom. And I believe is a quality eyepiece. Also, I removed and tested without the diagonal, but sirius look the same. Did anyone have this issue before? What can it be?

Enrique

#2 coopman

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Posted 25 February 2020 - 09:03 AM

When you defocus bright stars, are you seeing concentric rings? If so, then you are reasonably collimated. It could be the seeing/sky conditions. A dark sky does not necessarily mean that it's going to be a good night for observing. Is your scope acclimated to the outside temperature? If not, it will not perform good.
SCTs will not show really sharp pinpoint stars like refractors do because of their rather large central obstruction. You will notice that when trying to focus on stars, just before you achieve what would be a nice sharp focus, it starts going out of focus again.

Edited by coopman, 25 February 2020 - 09:06 AM.


#3 whizbang

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Posted 25 February 2020 - 09:05 AM

The sky conditions you heard about is "seeing".  It is upper altitude calm or turbulence.   It has a huge impact of image quality.

 

Sirius is the brightest star in the sky.  It worsens all the internal reflections in your scope and eyepieces.  Have you tried dimmer objects?

 

M45, M44, M35, M37, M33, Iota Cancer, Tegman, Eta Cass, and Mintaka.  Also the "37" cluster NGC 2169 and the Owl cluster NGC 457.

 

Your scope is probably fine.  Sirius is a tough object, especially if seeing is marginal.



#4 sg6

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Posted 25 February 2020 - 09:05 AM

I have had similar. Basically I have never had a "good" view from or through an SCT.

 

About 8 years ago I bought some new BST Explorers (Paradigms) and tried out the 2 I had received that day - it was a Tuesday. Jupiter was SE and in the ETX 70 (yes I have one) it was sharp, equitorial band and a North and a South, and all 4 moons each a different color. OK it was small but sharp.

 

Next night the conditions were identical (to me at least) club put their 14" SCT on Jupiter. It was bigger but garbage. Their 8" produced the same. The ETX sharp, just small.

 

Around a year ago there was a post asking the same question, basically why are SCT's poor.

 

Now the club ones may have needed a good collimation, they are work horses for another aspect.

 

There is one person here in the UK who has a business both repairing but also just collimating and setting up SCT's. Now it might be a bit of a hobby business but I think they make a living from it. So could be that SCT's need attention on a regular basis.

 

Will ask why an 8SE?

Just I tend to think that once you are outside of the 8"-10" and f/5 newtonian and 5" f/8 refractor specifications you are into slightly specialised scopes. And as a rule the more specialised the more work/effort is required.



#5 Heitman

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Posted 25 February 2020 - 09:13 AM

I get very good views through my Celestar 8 mounted on that same mount. Make sure it has had plenty of time to acclimate, and yes, check the collimation. It doesn't take much to make the image soft. 



#6 db2005

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Posted 25 February 2020 - 09:18 AM

Don't despair... An 8" SCT will require good collimation, good sky conditions and ample time to reach ambient temperature. My C8 normally needs at least 2 hours of time to cool down before reaching its full potential.

 

This is the reason why I like to use my 3" APOs more... they are ready to deliver crisp performance at a few moments' notice. If I were in your shoes I would bring a small 80mm refractor along to use while the SCT is still acclimatizing. When my C8 is ready, and the sky conditions are good, and the scope is in good collimation, I am always rewarded with magnificient views of DSOs and clusters.



#7 coopman

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Posted 25 February 2020 - 10:37 AM

A lot of SCT users are now wrapping their OTAs with reflectix or some similar insulation to minimize the acclimation issues. You can buy reflectix material from Amazon.

#8 wrnchhead

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Posted 25 February 2020 - 12:49 PM

Can confirm collimation is critical to top performance. I got a used C8 Ultima with problems. It did ok, but the day I nailed the collimation, I was stunned at the difference in sharpness. Specifically looking at M13 that day, I will never forget it. 


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#9 EEBA

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Posted 25 February 2020 - 04:20 PM

I considered all these aspects as probably cause of lack of sharpness. Seeing condition, cooling time in the ambient, and collimation. I think all three were ok yestarday and still sharpness was no great. Some of you are telling me the this is normal for SCT scopes. Perhaps this is how this scopes can do. Perhaps I had higher expectations from a 1200 dollars telescope? If this is the case, I think the money was not worth it.

#10 descott12

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Posted 25 February 2020 - 05:05 PM

I considered all these aspects as probably cause of lack of sharpness. Seeing condition, cooling time in the ambient, and collimation. I think all three were ok yestarday and still sharpness was no great. Some of you are telling me the this is normal for SCT scopes. Perhaps this is how this scopes can do. 

Since you said it was much sharper the first time, that means your scope is capable of good views. So something has changed...either your scope or the external conditions.

 

Don't give up. I love my Celestron 8" SCT. It is a very good scope and very flexible for all sorts of viewing (including EAA).



#11 Lola Bruce

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Posted 25 February 2020 - 05:29 PM

Bottom line for your scope 2034mm focal length (I have the same C8 optical tube) an 8mm is beyond max magnification for all but the rare best of nights. 10mm is the most common good night eyepiece. For a given night back off until the target is sharp, that will be your best magnification for that nights conditions. The C8 (optical part of your scope package) is a good performer. Exceptional for the price point. I also have a Mewlon 250 one inch larger diameter, it usually will go to an 8 or 7mm on a given night. Problem is for that performance it is over ten times as expensive and without a mount.

 

In ten years I have enjoyed maybe a dozen great nights and three OMG nights. We view through an atmosphere that is fickled. On the common  poor seeing night a wide angle refractor may seem to do better but if you do the math for a given magnification they will be very close. And on that rare night the C8 will strut it's stuff.

 

Enjoy you have a nice scope but yours nor mine are a Hubble.

 

Bruce


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#12 coopman

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Posted 25 February 2020 - 05:46 PM

It is true that a lot of SCTs that are in use are not accurately collimated.  It is absolutely critical to their performance. 


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#13 Anony

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Posted 25 February 2020 - 05:56 PM

I considered all these aspects as probably cause of lack of sharpness. Seeing condition, cooling time in the ambient, and collimation. I think all three were ok yestarday and still sharpness was no great. Some of you are telling me the this is normal for SCT scopes. Perhaps this is how this scopes can do. Perhaps I had higher expectations from a 1200 dollars telescope? If this is the case, I think the money was not worth it.

 

What magnification were you using with the SCT and refractor? Equal playing field? Meaning were the magnifications equal?  If just testing the same eyepiece in each scope, that could result in too much mag for the SCT, hence the lack of sharpness.

 

Someone else here can do the math, but guessing it'd be something like 32mm in the SE vs 16mm in the refractor to be somewhat equal magnification?



#14 EEBA

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Posted 25 February 2020 - 06:23 PM

It gives me hope that a lot celestron 8SE owners love and say it is a great scope. Perhaps while I see and believe the donut in the stat test looks isometric to me, I might be missing something. I was able to take orions nebula picture with my dslr. It is 3 pm in LA California. In a few hrs venus and Sirius will be up. I will post the pictures to get feedback.
Regarding to the comparison with the small refractor, the magnification was way less for example refractor x80 very sharp looking at Sirius, while 150x plus looking with my C 8SE.

#15 Anony

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Posted 25 February 2020 - 06:54 PM

It gives me hope that a lot celestron 8SE owners love and say it is a great scope. Perhaps while I see and believe the donut in the stat test looks isometric to me, I might be missing something. I was able to take orions nebula picture with my dslr. It is 3 pm in LA California. In a few hrs venus and Sirius will be up. I will post the pictures to get feedback.
Regarding to the comparison with the small refractor, the magnification was way less for example refractor x80 very sharp looking at Sirius, while 150x plus looking with my C 8SE.

 

Use 80x (or whatever number conditions allow, 25-50x is fine too) through both scopes and see how they compare. Higher magnification doesn't necessarily mean a target will be sharper, quite often if conditions are bad, it'll make things worse.

 

When the moon comes out to play again, give it it a try there,  use equal magnifications on both scopes, then crank up the SE until things start to get worse.


Edited by Anony, 25 February 2020 - 06:57 PM.


#16 bandazar

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Posted 25 February 2020 - 06:57 PM

If you are into sharp views and don't have the patience for cool down, then maybe a refractor is something you'd probably be better off with.  I have seen one c8 with very good views.  But you have to know what you are doing in regards to collimination and cooldown.  Most people who had bad c8's from personal experience did not colliminate their telescopes, or they had a misaligned diagonal, or lived in an area that just was bad for sct's.



#17 AhBok

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Posted 25 February 2020 - 07:44 PM

One reason is the 200m SCT is more affected by seeing than the 70mm is simply because it is a much larger aperture. Also, a small refractor gives pretty views of tiny stars, but the 8” will show you much, much more. I’ve owned nice large triplet Apos, large dobs with excellent mirrors and several SCTs of most sizes and SCTs are capable of excellent views. You need to view many more objects and a much larger variety of objects under varying seeing conditions before drawing conclusions about the quality of your scope. M42 looks good through most scopes and Sirius is too bright to draw many conclusions, especially from a beginner. Also, continue to ask for help, but keep in mind most of what you read is heavily biased (even mine!). Give it time. It takes a while to develop good observing skills. I’ve been at it for over 50 years and am still learning.
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#18 EEBA

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Posted 25 February 2020 - 10:29 PM

I came back of spending 2 hrs testing different eyepieces and magnification. Found out my C 8SE tonight gives me sharp image of Rigel up to 130-150x. Also, I was using as target the trapeze of orions nebula. I think is a good reference for testing. My best outcome tonight was using the 15 mm eyepiece, which yields 130x. It was very enjoyable to see that clear. Also, I again did the star test. I used high power eyepiece as advised. It looked almost perfect. Maybe barely noticeable off. I dont know I I can improve what is now. I might make it worse. Ah, I almost forget, I saw venus as well, it was not sharp. All in all. It seems that my celestron works 130 to 150 range ? I wish I gives more and more. Thanks all of you for taking your time to help me.

Enrique

#19 Napp

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Posted 25 February 2020 - 10:47 PM

Your scope is capable of higher magnifications IF atmospheric conditions allow.  I have had nights when my 16 inch DOB was limited to 150X.  Unfortunately, Venus is not going to be sharp.  The lower an object is the more atmosphere you are looking through.  You don’t state your location but the farther north you are the worse the view of Venus.  Try looking at Venus as soon as you can spot it even in daylight.  The higher in the sky the better and a brighter sky cuts down on the glare.



#20 EEBA

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Posted 25 February 2020 - 11:09 PM

Yes Naap, I live in California and I was looking for venus in day time. I found it a little high in the sky. Lol I was looking for stars before it gets dark.

#21 sanbai

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Posted 25 February 2020 - 11:14 PM

Sirius is a very challenging target. It's very very bright, it will show all defects, and it's low in the sky for many people. These season I've only achieved once to see it's companion. It was a night with a good seeing, Sirius was close to the meridian, and it was after midnight. Many days is just like fireworks.

More examples. One night (early time) I was looking to epsilon lyrae double double, late in its season. It wasn't looking nice in my C8edgeHD. I was almost panicking about the quality of my scope (less than one year now) and collimation. But collimation looked ok. I slewed some degrees up in the sky to a more challenging double. It was looking nice. The problem was the atmosphere, especially for low altitudes.

The same was happening with Jupiter, there was a point when I just stopped observing it, it was too low and the seeing gets pretty bad at this point.

People tend to say that new C8 are of good quality (for a SCT design). Reflectix can help, I use it. It also prevents dew to certain extend (so far I don't miss heaters).

#22 Noah4x4

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Posted 26 February 2020 - 04:07 AM

You only need look at my Cloudy Nights signature to understand the issue.

 

After reading wonderful stories in the forums about the visual observing success of others that I never enjoyed at home under dire light polluted skies,  I spent a fortune on expensive optical upgrades such as Williams diagonal, Televue Delos eyepieces etc. Then realising I could not beat light pollution, I then spent even more on travel and accommodation to dark sky sites.  Frankly, I still didn't ever see anything better than the faint fuzzies depicted in the book, Turn Left at Orion and more often than not I saw nothing due to cloud and suffered from poor seeing due to atmospheric conditions. Simply compare the view that you get at the zenith to one low on the horizon to see the difference 'atmospheric soup' can make.

 

Disappointed by the limits, I invested another small fortune on DSLR, wedge and pursued Astrophotography. Now I was, at last, seeing challenging stars and DSOs in the colourful paradigm that I wished to see them. But it was tedious to set up, polar align etc and my patience was thin, notably as more often than not, clouds would roll in to curtail my session. I needed something that would deliver these results faster.  My solution was EAA using Hyperstar. I now have boxes full of expensive redundant kit purchased along this journey. I have not looked through any of my £450 eyepieces in two years, whilst light pollution has worsened as they have built 6,000 new houses close to mine in that same time.

 

For visual astronomy to reveal what I suspect you want to see you will need ideal dark skies. The only place I have ever seen such conditions was in the caldera of Mt. Tiede, Tenerife and the Galapagos Islands. There are, of course, places in the United Kingdom, but I have given up visual astronomy because of travel and accommodation expense. EAA is now delivering what I originally expected. Under severe light pollution, it is probably  the only solution if frustrated. Just don't waste too much money improving optics if your local conditions mirror mine. Dire!


Edited by Noah4x4, 26 February 2020 - 04:09 AM.

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#23 EEBA

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Posted 26 February 2020 - 06:30 AM

Thanks Noah, I have been in the hobby less than 2 months, and it is hard and frustrating. But I cannot jump from knowing nothing to EAA, at least i think i should get the basics.
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#24 Noah4x4

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Posted 26 February 2020 - 07:07 AM

Thanks Noah, I have been in the hobby less than 2 months, and it is hard and frustrating. But I cannot jump from knowing nothing to EAA, at least i think i should get the basics.

Absolutely! I was not suggesting otherwise. But if you are going to optimise enjoyment and not waste huge amounts of money pursuing impossible goals it is important that your expectation is managed at each level.

 

I mistakenly threw far too much money too quickly at my frustrations. Hence, my advice is take things as far as you can with your existing kit. Then if still dissatisfied, carefully think about each next step. If extreme light pollution is a problem, try getting to dark sky sites. Astronomy is a wonderful journey, but very expensive if you take the wrong  turn. The jump from visual to EAA is massive. Just be aware that it is an option. Perhaps join your local astronomy club and look through the scopes of others. Above all, take your time, and keep your wallet in your pocket until certain that next spend will eliminate your frustration.



#25 Asbytec

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Posted 26 February 2020 - 07:07 AM

"Perhaps while I see and believe the donut in the stat test looks isometric to me, I might be missing something."

If you're seeing an out of focus "donut", I'd dare say you are way too far from focus the evaluate collimation. We do not collimate on shadows of the secondary in the center of a donut, we collimate on diffraction close to and in focus.

For that, use high magnification of 200x or more and defocus slightly, as close to focus as seeing conditions will allow, until you see one or more diffraction rings (not a large donut) with the Poisson spot at the center.

Adjust the secondary collimation screws to center the diffraction rings on the Poisson spot at center. Then bring the star into focus and, best you can given seeing conditions, make the in focus star as symmetrical as possible. The first diffraction ring should be fairly uniform if you're lucky enough to see it well. The three 'Cs' matter for sharp images: collimation, cooling, and C'ing.

You can also watch the tendency for the in focus star to 'flare' to one side more so than evenly and symmetrically. But, if seeing is not cooperating or the scope is thermally unstable, chances are seeing errors are larger than collimation errors and the image suffers both, anyway. It won't be sharp in this case.

Edited by Asbytec, 26 February 2020 - 07:08 AM.

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