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Nextar 8se optical tube issue

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#1 hisrael3

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Posted 14 September 2019 - 10:31 AM

I purchased an 8se ota about one year ago. Initially the images were excellent. However over the last few months the images have become very blurry. Although I am s novice, I did check the collimation and also did the star test, and all seemed ok without the need for any adjustments. I compared with images from my explore scientific 5” refractor last night,& this confirmed that the blurred images on the 8se had nothing to do with atmospheric conditions or the lenses I was using.

Has anyone experienced this? At this point, my inclination is that this 8se ota is defective. However, maybe there is something else I should try? Otherwise how would I get this repaired, checked out without spending a fortune in shipping?

Any suggestions would be most welcome.

Thanks

Howard

#2 deansjc

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Posted 14 September 2019 - 10:58 AM

As a fellow 8SE user who has spent a fair bit of time trying to get the most out of this scope, I would be interested in seeing an image or two, perhaps from both scopes.  "Blurry" can cover a range of issues relating to focus, collimation, and particularly coma which is an inherent "feature".  f

 

Are you using a reducer, filter?  How does visual look?

 

To your question, a slow degradation in image quality is odd.



#3 junomike

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Posted 14 September 2019 - 11:15 AM

I suspect thermal issues as the temperature is dropping at night, enough to cause issues  such as blurry images with a camera or visually.


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#4 ishorx

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Posted 14 September 2019 - 01:34 PM

if the images were excellant to begin with i find it difficult to understand them drgrading in a year.....unless someting came loose ,such as secondary,but you did a startest,which you say is good.is there condensation in the tube that fogs up?...is it the same with all eyepieces?did a baffle tube become loose



#5 hisrael3

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Posted 15 September 2019 - 11:45 AM

Thanks for your input
It’s not the temperature or the lens. I used the same lenses at the same time with my 5” refractor and the images were good.

Unfortunately, I’m too much of a novice to answer some of the other questions.

#6 hisrael3

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Posted 15 September 2019 - 11:46 AM

I don’t know what coma is(other than when I come home exhausted after a long day of work)

H

Don’t think it’s condensation.
Same problem with all eyepieces.
Baffle loose, not sure of what this is or how to check or fix

Edited by hisrael3, 15 September 2019 - 11:50 AM.


#7 Steve C.

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Posted 15 September 2019 - 12:04 PM

I would try the OTA on a terrestrial object and see if you have the same problem. I suppose it's possible that you're not achieving best focus for some reason.



#8 JMP

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Posted 15 September 2019 - 06:01 PM

There have been many comparo's between a 4-5 inch refractor and a C8 over the years. The refractor often wins unless the so called seeing is very good. A C8 is more sensitive to seeing than the refractor. Falling temps during the evening can be an issue, harder for the reflector to keep up. The moving mirror can be an issue because the focuser pushes and pulls on one side causing the mirror to tilt slightly.

 

When you check collimation there is coarse collimation, looking at the out of focus donut, then there is fine collimation looking at the difraction rings at very high power in focus. Some people just don't like SCT's because the stars never come to a sharp focus unless the seeing is unusually good and the telescope has an hour or two to cool to the temperature of the night air. Sometimes my C11 never seems to cool enough. Also note that the C8 has a much longer focal length than your refractor so you need to use a lower power eyepiece in the SCT. For example if your refractor has a focal length of 900mm you would use a 9mm eyepiece for 100X but the SCT would use a 20mm eyepiece for the same magnification.

 

Before you try to send your scope out for repair you should try to find an experienced local person to help you check it out. There may be something minor like fine collimation that can be tuned up for best results. Or maybe just always finish your focus adjustments by turning the knob counter-clockwise.

 

Jeff P

Eugene, Oregon




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