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Newtonian quality

TareqPhoto
24 Feb, 2018 22:23
Hi,

I want to ask about how good is TS/GSO 8" newtonian?

I will buy a newtonian of 8" F5, and almost the only one i found is this TS/GSO one, so is it good one as optical quality?

I didn't ask if it is good against another scopes or newtonians, i only ask about this only quality.

Thank you very much!
glennb44
28 Feb, 2018 02:20
I have had a few newtonians, 18inch, 6inch.
Collimation must be perfect. Setup the secondary,  laser to the centre of the primary, adjust the primary to get the return beam perfect.  Then star test first and fine adjust the primary at low magnification and finally at high power
Use a bright star. Near zenith. Test by checking the out of focus disc against known fault diagrams.   Look at the disc both sides of focus.   It might show astigmatism or turned down edge or bad zones.
Did the scope come with a set of written specifications?   Like is the mirror 1/4 wave, 1/16th wave or better.  What is the secondary mirror spec?   I bought a 1/25th wave secondary and the views I got were much better than with the old mirror.
I read that the GSO scopes recently improved and actual claims of better than 1/16th wave for  the primary are proving to be pretty true.  I came across a 10in GSO 3-4 years ago the had bad astigmatism.
Visual checks that rely on seeing being optimal & given perfect collimation include looking at double stars for resolving power, looking for the rille on the bottom of the lunar Alpine Valley and looking for the Enke division of Saturns rings.   If you can see these then the optical quality would have to be pretty good.
Hope this helps.
Glenn  smile
TareqPhoto
28 Feb, 2018 07:37
glennb44
I have had a few newtonians, 18inch, 6inch.Collimation must be perfect. Setup the secondary,  laser to the centre of the primary, adjust the primary to get the return beam perfect.  Then star test first and fine adjust the primary at low magnification and finally at high power
Use a bright star. Near zenith. Test by checking the out of focus disc against known fault diagrams.   Look at the disc both sides of focus.   It might show astigmatism or turned down edge or bad zones.
Did the scope come with a set of written specifications?   Like is the mirror 1/4 wave, 1/16th wave or better.  What is the secondary mirror spec?   I bought a 1/25th wave secondary and the views I got were much better than with the old mirror.
I read that the GSO scopes recently improved and actual claims of better than 1/16th wave for  the primary are proving to be pretty true.  I came across a 10in GSO 3-4 years ago the had bad astigmatism.
Visual checks that rely on seeing being optimal & given perfect collimation include looking at double stars for resolving power, looking for the rille on the bottom of the lunar Alpine Valley and looking for the Enke division of Saturns rings.   If you can see these then the optical quality would have to be pretty good.
Hope this helps.
Glenn  smile
Thank you very much!

Is the collimation needed every time we use the newtonian outside or it is done once per while?
superelch
28 Feb, 2018 10:32
Hi Tareq,

i have a GSO 8" newtonian F/5 about 5 years. It's a good qualitiy scope with a really good price-performance ratio !
The only thing i would change is the 2" Crayford focuser. It is not stable enough for a CCD or CMOS cam.

If you want, you can take a look on my gallery with many pictures taken with my GSO newtonian.

Thomas

https://www.astrobin.com/users/superelch/
Edited 28 Feb, 2018 10:36
TareqPhoto
28 Feb, 2018 13:35
Thomas Richter
Hi Tareq,i have a GSO 8" newtonian F/5 about 5 years. It's a good qualitiy scope with a really good price-performance ratio !
The only thing i would change is the 2" Crayford focuser. It is not stable enough for a CCD or CMOS cam.

If you want, you can take a look on my gallery with many pictures taken with my GSO newtonian.

Thomas

https://www.astrobin.com/users/superelch/
Your gallery and someone else here is what made me to think about Newtonian, mainly this GSO, there is someone else who is using Lacerta Newtonian 10" F4, but as long i saw similar amazing results from this GSO by you and another one i decided why not give it a try.

Now i may go with another brand, which is Meade as i found one brand new at very nice low price, and i want to know if all Newtonians has similar mirror quality if they are at cheaper price less than $400, i am talking about 8" F5, changing focuser is just very easy if i can find sompatible, that is why i wanted to go with cheap one and i upgrade parts later, and many said that the focuser is the weakest part here, so i can think about a FeatherTouch or MoonLite one if i can find one compatible with whatever 8" F5 newt i will buy, and hopefully it will be that Meade i found.
glennb44
01 Mar, 2018 04:10
Tareq Abdulla
Is the collimation needed every time we use the newtonian outside or it is done once per while?

Depends….mostly on the freedom of the mirrors in the mirror cells  +   how far different the current object of interest is from the spot where you collimated the scope.
I usually would pop in the laser and check the hit on the primary and the return beam   +   check the look of the out of focus disc of a star nearby the objec of interest.  A quick enough check.  Nightly =  best results…..less then less than best results.   (Now I have a SCT I will still check things using a star test - much simpler with mirror locked.)

Please advise - what primary mirror  and secondary mirror specifications in writing sellers provide to you?  If they dont have this info then why buy?
Maybe you should buy a small SCT - modern optics =ACF or Edge.   Why buy an antique style telescope?

GlennB
Edited 01 Mar, 2018 04:12
TareqPhoto
01 Mar, 2018 06:49
glennb44
Tareq Abdulla
Is the collimation needed every time we use the newtonian outside or it is done once per while?
Depends….mostly on the freedom of the mirrors in the mirror cells  +   how far different the current object of interest is from the spot where you collimated the scope.
I usually would pop in the laser and check the hit on the primary and the return beam   +   check the look of the out of focus disc of a star nearby the objec of interest.  A quick enough check.  Nightly =  best results…..less then less than best results.   (Now I have a SCT I will still check things using a star test - much simpler with mirror locked.)

Please advise - what primary mirror  and secondary mirror specifications in writing sellers provide to you?  If they dont have this info then why buy?
Maybe you should buy a small SCT - modern optics =ACF or Edge.   Why buy an antique style telescope?

GlennB
I buy due to low price, it is like a deal, so wanted to go with that, and no information or details about the mirror, and it is -if i go with it- a discontinued scope, so i was hoping that it is still a great scope regardless it is discontinued, i don't know how bad it will be if the mirror isn't as it should be.
glennb44
01 Mar, 2018 22:29
Tareq Abdulla
i don't know how bad it will be if the mirror isn't as it should be.

This is a link that will show you how bad it can be if the mirror isn't as it should be.
http://www.rfroyce.com/compimag.htm
Have a search for RFRoyce mirror and Zambuto mirror too.
Maybe buying the deal is like buying a car without any information?

GlennB
TareqPhoto
02 Mar, 2018 17:35
glennb44
Tareq Abdulla
i don't know how bad it will be if the mirror isn't as it should be.
This is a link that will show you how bad it can be if the mirror isn't as it should be.
http://www.rfroyce.com/compimag.htm
Have a search for RFRoyce mirror and Zambuto mirror too.
Maybe buying the deal is like buying a car without any information?

GlennB
Ok, let's start by this Newtonian as i found one in stock and i liked the design and the color, you can read the details in their site, what do you think about it?

Meade 8" F5

Look at the scope, i found it OTA only without the mount.
glennb44
02 Mar, 2018 23:59
Looks just fine.
Theres no claim about optical quality.   I cant find reviews other than one that is positive for planets and moon at low magnification.  No bad comments is good.
Good name brand.

What is the purpose you have for the scope?

GlennB
TareqPhoto
03 Mar, 2018 02:20
glennb44
Looks just fine.Theres no claim about optical quality.   I cant find reviews other than one that is positive for planets and moon at low magnification.  No bad comments is good.
Good name brand.

What is the purpose you have for the scope?

GlennB
1. Far deep targets such as some galaxies or small targets.
2. To have a natural spike, without modifying a Mak or SCT or refractor or adding that by an app.
3. Lower price.
……..
……

..
.
4,5,6. You can say to collect more equipment, to have an experience with different scopes, any reason you want.
Edited 03 Mar, 2018 02:21
robertjones
03 Mar, 2018 08:03
I think it is important to know the optical quality especially with so many new stuff coming out in 2018.
Edited 05 Mar, 2018 18:43
iamsiggi
03 Mar, 2018 15:38
I start 3 Years and some Month  before  and One Question I answer too before I decide to start or let it bee was:
I'm not willing to buy twice - that's to expensive.
At reading a lot of postings and at websites for beginner it was clear to me, a CS with the normal Mount is the wrong Instrument..
I Only have to decide: APO or "old fashioned" ;-) Newton.
The Newton give the most brightness for money - and that is what I need for DeepSky Objects.

Happy that I found a "pimped" 200/800  Newton from SkyWatcher  - "Newton ohne Namen"
So I'm happy with the focus stability over the night. I check every time the collimation, but I don't need recollimation since month…
But with an Laser It's quick done if I need. On my F/4 New
On forum I read that someone try to get his GSO carbontube Newton with the PK7 Mirror focus stable too. So he changed the focuser to Lacerta Octo. Finally he found the problem: The Mirror made from PK7 glas. Finally he changed the mirror from Skywatcher made from Pyrex…..

On deep Sky photography you need a lot of light, so you need a fast system. I need 4 Minutes or more exposure time at each frames. So you need also an Guider. Cheap but tricky with Laptop an Freeware…. or easy with MGen - also build by Lacerta. And you need a very good mount. Absolut minimum is EQ5 better EQ6 and belt driven…..
What you also need - a suitable flattener - that's have to fit for your System. You need an adapter to you camera to and perhaps some extensions rings to find the correct distance to you camera sensor.

On APO or normal Newton, you need to refocus when Temperature change, so perhaps you need an Automatic focuser to ….
Siegfried
Edited 03 Mar, 2018 15:43
TareqPhoto
03 Mar, 2018 16:02
robertjones
I think it is important to know the optical quality especially with so many new stuff coming out in 2018.

With Newtonian there are no many details about mirror or optical quality details, the one with details are so expensive, for that i better go with a refractor then, but i wanted a Newtonian, and i looked at images from different newtonian s here on AB and they produce really nice images, so they are good enough, my ST80 with Ha filter producing good enough images means newtonian should do better then, and i will be a better corrector and collimator.
TareqPhoto
03 Mar, 2018 16:04
Siegfried
I start 3 Years and some Month  before  and One Question I answer too before I decide to start or let it bee was:I'm not willing to buy twice - that's to expensive.
At reading a lot of postings and at websites for beginner it was clear to me, a CS with the normal Mount is the wrong Instrument..
I Only have to decide: APO or "old fashioned" ;-) Newton.
The Newton give the most brightness for money - and that is what I need for DeepSky Objects.

Happy that I found a "pimped" 200/800  Newton from SkyWatcher  - "Newton ohne Namen"
So I'm happy with the focus stability over the night. I check every time the collimation, but I don't need recollimation since month…
But with an Laser It's quick done if I need. On my F/4 New
On forum I read that someone try to get his GSO carbontube Newton with the PK7 Mirror focus stable too. So he changed the focuser to Lacerta Octo. Finally he found the problem: The Mirror made from PK7 glas. Finally he changed the mirror from Skywatcher made from Pyrex…..

On deep Sky photography you need a lot of light, so you need a fast system. I need 4 Minutes or more exposure time at each frames. So you need also an Guider. Cheap but tricky with Laptop an Freeware…. or easy with MGen - also build by Lacerta. And you need a very good mount. Absolut minimum is EQ5 better EQ6 and belt driven…..
What you also need - a suitable flattener - that's have to fit for your System. You need an adapter to you camera to and perhaps some extensions rings to find the correct distance to you camera sensor.

On APO or normal Newton, you need to refocus when Temperature change, so perhaps you need an Automatic focuser to ….
Siegfried
Not understanding much of you said???

I think i will go with what i found, i looked at many newtonian, and only cheap ones i can get, the expensive one are geat but if can't afford then it is no point thinking too much. i think all cheap newtonians will be in same quality then.
glennb44
05 Mar, 2018 23:49
Tareq Abdulla
i think all cheap newtonians will be in same quality then.

A good option would be a used newtonian from a trusted astro society/club member that you can try before you buy?  Approach the club president and ask. I think you could get a fine instrument cheaper than the Meade.

Can you try before you buy the Meade?

Can you return it if it proved flawed?

GlennB
TareqPhoto
06 Mar, 2018 00:03
glennb44
Tareq Abdulla
i think all cheap newtonians will be in same quality then.
A good option would be a used newtonian from a trusted astro society/club member that you can try before you buy?  Approach the club president and ask. I think you could get a fine instrument cheaper than the Meade.

Can you try before you buy the Meade?

Can you return it if it proved flawed?

GlennB
Unfortunately testing it locally is not possible or not available, even if an astro society/club has all scopes i can't ask, i reached or approached a president club once before and he was like not helping or showing kind of superiority, i didn't like the attitude at all, so i stopped going there at all and i won't, he even said that he doesn't allow scopes to be for public, only one scope for public to test or observe through which is C9.25, but anything else it needs private or special request and who knows what it requires, i think we have to pay little money to be allowed to test them, sorry but i don't like this kind of approach, i will risk buying a Newtonian than going to waste money even driving and entry fees to test something, no thanks!

I think i can't return it if it proved flawed, but let me say something, i bought a camera that is cheap, it is working great, suddenly i damaged it and now i can't return it because it wasn't the item fault and i even can't sell it, the scope will be nearly the double price of that camera, if it is flawed it won't be a big lose as the camera as well, the scope is always has a way to fix or improve it somehow, while the camera it needed to be fixed by a technician that i can't think to send the camera for, not worthy.

I will update later if i get that Meade, i hope it won't cost me much, i saw amazing images from GSO newtonian, also from SkyWatcher 200PDS, and both are closer in prices with SW slightly more, so if those cheap were great, the why not Meade and Celestron Newtonians?
glennb44
06 Mar, 2018 00:37
Tareq Abdulla
so if those cheap were great, the why not Meade and Celestron Newtonians

Yes, I agree they have a good name.

Your experience with the club is shocking.  Very sorry about that.

Glenn
 
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