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Premium 1/10PV 8" Newtonian vs mass market 8" Newtonian.

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#1 N3p

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Posted 19 July 2019 - 11:57 AM

Hello I have this question about the quality of telescope and looking for some opinions. I currently own a Synta SW BKP 200DS - 200x 1000 F5 Newtonian and it's not bad at all, for the price it must be a real challenge to beat, just like the Orion Dobs and other affordable tubes with good reputation.

 

But, I am sure I could benefit from higher quality mirrors today with another premium 8" telescope. I have one in mind right now which has precise mirror tested 1/10 PV, it's F6 instead of F5 and even a bit lighter then my current one, for visual only. I read that a well built 8" Newtonian with very precise mirrors, precise collimation, might very well surpass a 10" in contrast and for the overall quality of the views.

 

Even light gathering because of the better coating and the overall precision of the parable of the mirror, more light is supposed to be concentrated at the right place in the system.

 

A premium 8" matching a mass market 10" in brightness with less weight and size, that's a serious selling argument for me right now.

 

My question is the following:

As anyone replaced their regular 8" Synta Newtonian with a higher quality 8" Newtonian and how was your experience? My current telescope I paid approximately 1100CAD for it with a EQ5 and the telescope, the OTA alone was around 700CAD with taxes. The new telescope I have my eyes on would cost me over 2100CAD for the OTA and rings only (that is including a couple of bills for border duty) and the primary is 1/10PV.

 

It's an important expenditure for me and I would like to test first it if would be a great upgrade, if you want to share your story with me.

 

NOTE: Getting a larger telescope then 8" is not what I want, I already think a good 12" Synta would easily beat a premium 8"  I am interested by the 8" because if it's low weight especially.

 

Please feel free to tell me what you think.

 



#2 TOMDEY

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Posted 19 July 2019 - 12:39 PM

The short answer is that a good Premium telescope will probably perform noticeably better than an average cheap mass-marketed one. Somewhere between better and way better. But that's actually a statistical statement. Occasionally a too-good-performing cheap one somehow slips through their QC system... and occasionally a Premium scope will be deficient. The Premium scope is almost always worth the Premium price differential. That is to say --- if you don't want to mess around --- just buy the better scope and enjoy it!    Tom


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#3 gwlee

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Posted 19 July 2019 - 01:01 PM

I owned a Synta 8”f6 Dob along with a custom 8”f6 Dob with a Zambuto mirror for several years. The differences in the views were subtle, requiring side-by-side viewing on rare nights of excellent seeing to confirm. On the other hand, the improvements in the views offered by two inches additional inches of inexpensive aperture were obvious. 

 

If an 8” scope is the largest you want to handle, and you want improved views, premium 8” optics will provide a marginal improvement at about 10x the cost. An inexpensive 10” scope will cost about 2x and the improvements in its views will be obvious. However, premium scopes usually come with premium mechanics in addition to premium optics, and the mechanical improvements are usually obvious under all circumstances. 

 

So, my preferred approach these days is to empirically determine  the largest scope that I am comfortable using at an observing site, and then upgrade or replace its optics and mechanics as much as my budget allows


Edited by gwlee, 19 July 2019 - 01:13 PM.

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#4 howardcano

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Posted 19 July 2019 - 01:26 PM

Make sure that "1/10 wave Peak-to-Valley" rating is on the wavefront, not the mirror surface.  Also, make sure the seller has a good reputation.

 

I went a different route, and had my first Synta 8" F/6 mirror re-ground by a respected glass-pusher, as its initial figure was quite poor.  To fill in the gap while this was in process, I purchased a second Synta 8" F/6 (yeah, seems like a stupid idea, but the second one was reasonably good).  The total cost was lower than buying a complete specialist-built scope, but of course I had to do a little work myself.

 

I've decided to hold onto both scopes for now.  I've set up the one with the great mirror using a better mirror cell, low-profile focuser, and smaller secondary, optimizing it for high magnifications, while the second scope is for lower mags, with a larger fully-illuminated field.

 

Like you, an 8" Newtonian is at my limit for weight and size.


Edited by howardcano, 19 July 2019 - 01:30 PM.

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#5 Starlease

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Posted 19 July 2019 - 01:44 PM

Put a Zambuto mirror in my 10" dob and it outperformed my 14" claimed 1/8 wave dob for planetary details seen. Little tiny details on Mars seen in 10" were invisible in 14".


Edited by Starlease, 19 July 2019 - 01:44 PM.

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#6 N3p

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Posted 19 July 2019 - 02:34 PM

Put a Zambuto mirror in my 10" dob and it outperformed my 14" claimed 1/8 wave dob for planetary details seen. Little tiny details on Mars seen in 10" were invisible in 14".

That is serious results. The 14" is it a mass market Dob?

 

Make sure that "1/10 wave Peak-to-Valley" rating is on the wavefront, not the mirror surface.  Also, make sure the seller has a good reputation.

 

I went a different route, and had my first Synta 8" F/6 mirror re-ground by a respected glass-pusher, as its initial figure was quite poor.  To fill in the gap while this was in process, I purchased a second Synta 8" F/6 (yeah, seems like a stupid idea, but the second one was reasonably good).  The total cost was lower than buying a complete specialist-built scope, but of course I had to do a little work myself.

 

I've decided to hold onto both scopes for now.  I've set up the one with the great mirror using a better mirror cell, low-profile focuser, and smaller secondary, optimizing it for high magnifications, while the second scope is for lower mags, with a larger fully-illuminated field.

 

Like you, an 8" Newtonian is at my limit for weight and size.

Red: Thanks for this advice, nice project.

 

I owned a Synta 8”f6 Dob along with a custom 8”f6 Dob with a Zambuto mirror for several years. The differences in the views were subtle, requiring side-by-side viewing on rare nights of excellent seeing to confirm. On the other hand, the improvements in the views offered by two inches additional inches of inexpensive aperture were obvious. 

 

If an 8” scope is the largest you want to handle, and you want improved views, premium 8” optics will provide a marginal improvement at about 10x the cost. An inexpensive 10” scope will cost about 2x and the improvements in its views will be obvious. However, premium scopes usually come with premium mechanics in addition to premium optics, and the mechanical improvements are usually obvious under all circumstances. 

 

So, my preferred approach these days is to empirically determine  the largest scope that I am comfortable using at an observing site, and then upgrade or replace its optics and mechanics as much as my budget allows

Red Oh: Ok it varies from person to person.



#7 nirvanix

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Posted 19 July 2019 - 02:35 PM

Put a Zambuto mirror in my 10" dob and it outperformed my 14" claimed 1/8 wave dob for planetary details seen. Little tiny details on Mars seen in 10" were invisible in 14".

Your 14" dob at 1/8 wave is about 1/4 wave at the wavefront - just diffraction limited. It's possible in extremely good seeing that your 10" would show more detail, but on an average night I doubt it, unless there are other issues that you haven't thought about like cooldown, collimation, mounting of optical components, or maybe the claim of diffraction limited of the 14" isn't true.

 

People are always looking for fairy dust they can sprinkle into their telescopes to make them defy the laws of physics. Someone let me know if it works. smile.gif


Edited by nirvanix, 19 July 2019 - 02:37 PM.

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#8 N3p

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Posted 19 July 2019 - 03:20 PM

I find it hard to tell if it would be really worth the money now, ordering a 2100CAD  8" tube I can't even see physically or try before I buy.

 

Especially when considering the fact that my current Synta gave me pretty a high level of satisfaction to this day. I don't feel it would be right to upgrade it's mirrors. 



#9 Pinbout

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Posted 19 July 2019 - 05:52 PM

Replacing the 2ndry will probably be the best bet

 

but you should learn how to star test 

 

https://youtu.be/QxUQJjjsdW4

 

the thickness of shims should be checked on abberator program to get the star 10~ defocused 

 

I just grabbed some 1/8” alum for demo purposes

 

use an eyepiece the same focal length as the mirrors focal ratio.

 

6mm eyepiece for a f6 scope- that produces a 1mm exit pupil, perfect for star testing.

 

do this and post what you got then we can tell you if it will make a difference

 

the first thing you look for is 2ndry shadow size differences 

 

my mirror has had very little 2ndry shadow difference cause I made it to very high accuracy. laugh.gif


Edited by Pinbout, 19 July 2019 - 05:59 PM.

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#10 Pinbout

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Posted 19 July 2019 - 06:01 PM

If your star test looks like this

 

https://youtu.be/tAD-2r6gW9A

 

you can use the primary as a paper weight 



#11 Pinbout

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Posted 19 July 2019 - 06:03 PM

Most likely your test will resemble something like

 

https://youtu.be/MFmFpuST67M

 

then the answer is yes better mirror will provide better views when seeing will allow it.


Edited by Pinbout, 20 July 2019 - 10:13 AM.

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#12 N3p

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Posted 20 July 2019 - 09:37 AM

Replacing the 2ndry will probably be the best bet

 

but you should learn how to star test 

 

https://youtu.be/QxUQJjjsdW4

 

the thickness of shims should be checked on abberator program to get the star 10~ defocused 

 

I just grabbed some 1/8” alum for demo purposes

 

use an eyepiece the same focal length as the mirrors focal ratio.

 

6mm eyepiece for a f6 scope- that produces a 1mm exit pupil, perfect for star testing.

 

do this and post what you got then we can tell you if it will make a difference

 

the first thing you look for is 2ndry shadow size differences 

 

my mirror has had very little 2ndry shadow difference cause I made it to very high accuracy. laugh.gif

Thansk for the information and the idea to test my current mirrors. I tried the star test once but I thought it was only to test collimation, i will definitely give it a shot to check the shadow size now. Cool shim tip also.

 

If your star test looks like this

 

https://youtu.be/tAD-2r6gW9A

 

you can use the primary as a paper weight 

LOL a paper weight :p

 

I can't really tell what was wrong with that primary mirror currently nside that second video. I think the outside ring is wrong but it's just a wild guess, I don't have a clue.

 

I will try to film the airy disk of my star test as soon as I can, I can do that with a simple digital camera?



#13 N3p

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Posted 20 July 2019 - 09:45 AM

With my telescope right now I can't put the secondary very concentric with the focuser without adjusting the focuser angle itself. Visually the angle is noticable. For that reason I am not too attracted to the idea of replacing the mirrors in my current tube.

 

There is something wrong with my telescope, as I said before in other threads, the tube is not perfectly round and I highly suspect it's because of that I need to move the angle of the focuser.

 

I like the idea of reusing the synta tube.. but frankly mine it's poorly constructed.



#14 Pinbout

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Posted 20 July 2019 - 09:47 AM

 

 

I can't really tell what was wrong with that primary mirror currently nside that second video. I think the outside ring is wrong but it's just a wild guess, I don't have a clue.

I will try to film the airy disk of my star test as soon as I can, I can do that with a simple digital camera?

Your guess on outside is correct

 

this mirror is waaaaaaay over corrected - larger shadow inside under , larger shadow outside over.

 

some of those vids are from my iPhone so a digital camera is fine

 

just no Barlows - they add to the correction reading.  



#15 Woj2007

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Posted 20 July 2019 - 09:54 AM

Although I didn't do it with 8", but with 10", I think the mirror exchange was a large improvement for visual observations. Views through my GSO 10" were good, but star tests have shown some astigmatism. Following the advice on this forum, I exchanged the secondary mirror for Antares, but the astigmatism was still there. So, I decided to exchange the primary for the 1/10 pv. The difference is considerable. With GSO mirror, the views were very good, now they are great. I can see many more crispy details on Jupiter, Saturn, Mars or the Moon. Things that were 'soft' before are sharper now. And it happens even on the nights with poorer seeing, I just have to wait for the moment in between smile.gif

For low-power, wide-field DS objects, probably there is no difference, but color: GSO coating produced a greenish touch, OOUK makes it more white/ flat.

With GSO mirror, I often used the aperture mask to see planets sharper. After exchange, in my opinion the aperture mask only makes things dimmer and less sharp, so I guess the scatter light before was bigger with the standard mirror. 

Overall, I have learnt the lesson saying that the exchange for a better mirror was worth it, the telescope is used now more often for the sheer joy of visual hunt for details.


Edited by Woj2007, 20 July 2019 - 06:50 PM.

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#16 Asbytec

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Posted 20 July 2019 - 10:11 AM

 

Even light gathering because of the better coating and the overall precision of the parable of the mirror, more light is supposed to be concentrated at the right place in the system.

 

A premium 8" matching a mass market 10" in brightness with less weight and size, that's a serious selling argument for me right now.

 

You did not say what scope you were looking at, but in terms of light grasp I'm not sure some 10% difference in coatings will make it compete with any 10" aperture. Surface area matters a lot (exponentially so as the square of the area). The light concentrated in the right place is contrast, not light grasp. Some improved contrast due to premium fabrication is what you will be paying for.

 

You said your current scope is not bad, but how good is it? The question being how much improvement will your money get you? Do you see astigmatism or any other aberrations of note (like Danny's paper weight above)? All that said, you cannot go wrong with a (truly) premium mirror in a good tube with a nice mount.

 

As for collimation due to your crooked (or whatever) tube, the focuser does not have to be square. All, you need to do is get the secondary centered under it best you can. I do not have eyes on the problem, but I trust you know better than me and know what you're doing. So, square the focuser and see if that helps (if you have not already) with collimation and performance of your not bad scope. 

 

Are your average seeing conditions pretty good or are you often under the jet stream up in Canada? Can you see the Airy discs often? If not, seeing may turn your premium 8" Newt into a run of the mill 4" APO, shudder at the thought. smile.gif


Edited by Asbytec, 20 July 2019 - 10:22 AM.

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#17 ed_turco

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Posted 20 July 2019 - 10:23 AM

Hello I have this question about the quality of telescope and looking for some opinions. I currently own a Synta SW BKP 200DS - 200x 1000 F5 Newtonian and it's not bad at all, for the price it must be a real challenge to beat, just like the Orion Dobs and other affordable tubes with good reputation.

 

But, I am sure I could benefit from higher quality mirrors today with another premium 8" telescope. I have one in mind right now which has precise mirror tested 1/10 PV, it's F6 instead of F5 and even a bit lighter then my current one, for visual only. I read that a well built 8" Newtonian with very precise mirrors, precise collimation, might very well surpass a 10" in contrast and for the overall quality of the views.

 

Even light gathering because of the better coating and the overall precision of the parable of the mirror, more light is supposed to be concentrated at the right place in the system.

 

A premium 8" matching a mass market 10" in brightness with less weight and size, that's a serious selling argument for me right now.

 

My question is the following:

As anyone replaced their regular 8" Synta Newtonian with a higher quality 8" Newtonian and how was your experience? My current telescope I paid approximately 1100CAD for it with a EQ5 and the telescope, the OTA alone was around 700CAD with taxes. The new telescope I have my eyes on would cost me over 2100CAD for the OTA and rings only (that is including a couple of bills for border duty) and the primary is 1/10PV.

 

It's an important expenditure for me and I would like to test first it if would be a great upgrade, if you want to share your story with me.

 

NOTE: Getting a larger telescope then 8" is not what I want, I already think a good 12" Synta would easily beat a premium 8"  I am interested by the 8" because if it's low weight especially.

 

Please feel free to tell me what you think.

I hate to burst your bubble but a ten inch telescope, unless unspeakably horrible, will always outperform an eight inch telescope.  Laws of physics, you know  :)


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#18 25585

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Posted 20 July 2019 - 10:41 AM

Hello I have this question about the quality of telescope and looking for some opinions. I currently own a Synta SW BKP 200DS - 200x 1000 F5 Newtonian and it's not bad at all, for the price it must be a real challenge to beat, just like the Orion Dobs and other affordable tubes with good reputation.

 

But, I am sure I could benefit from higher quality mirrors today with another premium 8" telescope. I have one in mind right now which has precise mirror tested 1/10 PV, it's F6 instead of F5 and even a bit lighter then my current one, for visual only. I read that a well built 8" Newtonian with very precise mirrors, precise collimation, might very well surpass a 10" in contrast and for the overall quality of the views.

 

Even light gathering because of the better coating and the overall precision of the parable of the mirror, more light is supposed to be concentrated at the right place in the system.

 

A premium 8" matching a mass market 10" in brightness with less weight and size, that's a serious selling argument for me right now.

 

My question is the following:

As anyone replaced their regular 8" Synta Newtonian with a higher quality 8" Newtonian and how was your experience? My current telescope I paid approximately 1100CAD for it with a EQ5 and the telescope, the OTA alone was around 700CAD with taxes. The new telescope I have my eyes on would cost me over 2100CAD for the OTA and rings only (that is including a couple of bills for border duty) and the primary is 1/10PV.

 

It's an important expenditure for me and I would like to test first it if would be a great upgrade, if you want to share your story with me.

 

NOTE: Getting a larger telescope then 8" is not what I want, I already think a good 12" Synta would easily beat a premium 8"  I am interested by the 8" because if it's low weight especially.

 

Please feel free to tell me what you think.

Review of a SW 8" F6 that was given a 1/10 mirror.  https://neilenglish....r-skyliner200p/


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#19 N3p

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Posted 20 July 2019 - 11:05 AM

You did not say what scope you were looking at, but in terms of light grasp I'm not sure some 10% difference in coatings will make it compete with any 10" aperture. Surface area matters a lot (exponentially so as the square of the area). The light concentrated in the right place is contrast, not light grasp. Some improved contrast due to premium fabrication is what you will be paying for.

 

You said your current scope is not bad, but how good is it? The question being how much improvement will your money get you? Do you see astigmatism or any other aberrations of note (like Danny's paper weight above)? All that said, you cannot go wrong with a (truly) premium mirror in a good tube with a nice mount.

 

As for collimation due to your crooked (or whatever) tube, the focuser does not have to be square. All, you need to do is get the secondary centered under it best you can. I do not have eyes on the problem, but I trust you know better than me and know what you're doing. So, square the focuser and see if that helps (if you have not already) with collimation and performance of your not bad scope. 

 

Are your average seeing conditions pretty good or are you often under the jet stream up in Canada? Can you see the Airy discs often? If not, seeing may turn your premium 8" Newt into a run of the mill 4" APO, shudder at the thought. smile.gif

RED: I will test the mirrors again and log the results carefully. With a low power EP ES 24mm 68d and 34mm I see a slight elongation of the planet in one quarter of the EP close to the edge that's about the only thing I can see. I think it's minor.

 

BLUE: Ah ok ? Then if this is not required, my collimation is pretty good from what I can see inside my cheshire sight tube. The secondary round shape is fitting almost perfectly in the CST. But I also need to use my collimation cap in the process, because I can't see the primary mirror clips with the CST. With the CAP clearly, the secondary is not concentric with the inside diameter of the focuser's tube.  crazy.gif  I hate that.

 

I adjusted my spiders 2 days ago there was a 2mm difference between the 2 diameters. The secondary has an angle with the central axis of the telescope itself but yesterday the angle was suppressed, perhaps because of the spiders adjustment, i am not 100% sure.  I still need to give the focuser an angle to get the secondary concentric inside the CST, just like before spider adjustments.

 

The tube is now a bit rounder too but still visually not perfect. It's not Turing well in it's rings. The rings are not exactly round either so.. it's hard to tell if it's because of the tube, the rings or both.. 

 

25585

Thanks there is a lot of text there lol, I might spend 3 hours working on my collimation before but I'll try reading it soon.



#20 howardcano

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Posted 20 July 2019 - 01:24 PM

Review of a SW 8" F6 that was given a 1/10 mirror.  https://neilenglish....r-skyliner200p/

It's always interesting to hear about the ones with the good mirrors.  My sample of that exact same model had the paperweight.


Edited by howardcano, 20 July 2019 - 01:25 PM.


#21 gwlee

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Posted 20 July 2019 - 01:58 PM

Red Oh: Ok it varies from person to person.

I find that it takes side-by-side testing over many nights for me to tease out the subtle differences between two good quality scopes of the same aperture unless there’s something obviously wrong with one of them, such as improper collimation, insufficient cooling, over tightened mirror clips, etc. 

 

 

 

 

 

 


Edited by gwlee, 20 July 2019 - 02:23 PM.

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#22 Asbytec

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Posted 20 July 2019 - 02:59 PM

I see a slight elongation of the planet in one quarter of the EP close to the edge that's about the only thing I can see. I think it's minor.

But I also need to use my collimation cap in the process, because I can't see the primary mirror clips with the CST. With the CAP clearly, the secondary is not concentric with the inside diameter of the focuser's tube. crazy.gif I hate that.

A slight elongation of the planet might be due to eyepiece field distortion. I am no expert of eyepiece aberrations, but sounds like pincushion (rectilinear) or barrel (angular magnification) distortion is causing it.
https://www.handprin...html#distortion

It does not sound like astigmatism. Astigmatism (maybe from the eyepiece) plus a little coma (from the scope) stars begin to look like little stellar seagulls toward the edge. If you do not see astigmatism on axis, it's likely form the eyepiece toward the edge. It's related to distortion and flat fields, somehow.
https://www.handprin...tml#astigmatism (Scroll down a little)

Seeing the clips is one thing, collimation is another. If you focus all the way in and all the way out the reflected image of the primary will change apparent size. If you lose the clips (the edge of the primary, really) at any point, it just means you're vignetting a little. But, the scope can be collimated, regardless. If the clips are not centered, i.e., one is missing while the other two are visible, then one of the signatures for good collimation is not right. Probably need some more secondary adjustments as the focuser axis is not aimed at the center mark, or maybe some rotation of the secondary is needed. Also, the collimation cap is used to collimate the primary, it's not used to center the secondary. However, the site tube is. I'd trust your site tube.

Not sure of the accuracy of your primary center mark, either. But, once you set the focuser axis (site tube cross hairs on the center mark), you can collimate the primary with the collimation cap. Then tweak the primary on a star. Not hard. Your focuser axial alignment has the largest tolerance and can be off by as much as 6mm, but the primary pretty much needs to be spot on. It needs to hit very close to the center of the FOV.
https://garyseronik....pe-collimation/

Yes, I hate it too. But, really all that matters for axial alignment is the cross hairs on the primary center mark indicating good focuser alignment and the primary center mark centered in the Cheshire for good primary mirror alignment. If your secondary is off center in the focuser axis, it just means your fully illuminated field is off center. Ideally, that is not the case, you want to see the bottom of the focuser draw tube, the secondary mirror surface, and the reflection of the primary all concentric. But the scope's axes can be aligned. In any case, once collimated it should perform noticeably better.

Work on that while you're considering a premium scope. No hurry, right? No impulse buying hoping for a miracle? You're scope may be pretty good, but premium is as good as it gets. It just depends on how much you are willing to spend and how unhappy you are with your current scope. Or how demanding you are as a connoisseur of fine things. Newts do take some care and preparation to work well, and premium scopes are no different. You still have to cool and collimate them, too, and hope for good seeing. Your current scope may be just fine, and a premium scope /should/ be a little better. But, once your scope is up and running, I think you're in a better position to decide if it's time to get a premium one.

Oh, if you have to, shim your focuser so you can better center the secondary. Throw some small washers under the mounting screws.

Edited by Asbytec, 20 July 2019 - 03:39 PM.

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#23 N3p

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Posted 20 July 2019 - 05:06 PM

A slight elongation of the planet might be due to eyepiece field distortion. I am no expert of eyepiece aberrations, but sounds like pincushion (rectilinear) or barrel (angular magnification) distortion is causing it.
https://www.handprin...html#distortion

It does not sound like astigmatism. Astigmatism (maybe from the eyepiece) plus a little coma (from the scope) stars begin to look like little stellar seagulls toward the edge. If you do not see astigmatism on axis, it's likely form the eyepiece toward the edge. It's related to distortion and flat fields, somehow.
https://www.handprin...tml#astigmatism (Scroll down a little)

Seeing the clips is one thing, collimation is another. If you focus all the way in and all the way out the reflected image of the primary will change apparent size. If you lose the clips (the edge of the primary, really) at any point, it just means you're vignetting a little. But, the scope can be collimated, regardless. If the clips are not centered, i.e., one is missing while the other two are visible, then one of the signatures for good collimation is not right. Probably need some more secondary adjustments as the focuser axis is not aimed at the center mark, or maybe some rotation of the secondary is needed. Also, the collimation cap is used to collimate the primary, it's not used to center the secondary. However, the site tube is. I'd trust your site tube.

Not sure of the accuracy of your primary center mark, either. But, once you set the focuser axis (site tube cross hairs on the center mark), you can collimate the primary with the collimation cap. Then tweak the primary on a star. Not hard. Your focuser axial alignment has the largest tolerance and can be off by as much as 6mm, but the primary pretty much needs to be spot on. It needs to hit very close to the center of the FOV.
https://garyseronik....pe-collimation/

Yes, I hate it too. But, really all that matters for axial alignment is the cross hairs on the primary center mark indicating good focuser alignment and the primary center mark centered in the Cheshire for good primary mirror alignment. If your secondary is off center in the focuser axis, it just means your fully illuminated field is off center. Ideally, that is not the case, you want to see the bottom of the focuser draw tube, the secondary mirror surface, and the reflection of the primary all concentric. But the scope's axes can be aligned. In any case, once collimated it should perform noticeably better.

Work on that while you're considering a premium scope. No hurry, right? No impulse buying hoping for a miracle? You're scope may be pretty good, but premium is as good as it gets. It just depends on how much you are willing to spend and how unhappy you are with your current scope. Or how demanding you are as a connoisseur of fine things. Newts do take some care and preparation to work well, and premium scopes are no different. You still have to cool and collimate them, too, and hope for good seeing. Your current scope may be just fine, and a premium scope /should/ be a little better. But, once your scope is up and running, I think you're in a better position to decide if it's time to get a premium one.

Oh, if you have to, shim your focuser so you can better center the secondary. Throw some small washers under the mounting screws.

Red: I will work on my collimations there is absolutely no rush, I agree. Still I am  a bit disappointed with the choices we have left for lightweight solid tube Newtonians between F5 and F6 in Canada.. it seems like the visual observers are left behind...

 

Bluc: My focuser is adjustable so.. I am not sure the shims are really necessary.


Edited by N3p, 20 July 2019 - 05:06 PM.

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#24 Chesterguy1

Chesterguy1

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Posted 20 July 2019 - 05:29 PM

After owning a really fine 8” CZ mirror for several years I am always impressed by the views when the mirrors are properly collimated and when the primary mirror has reached thermal equilibrium. Is it better than a mass market 8”? I can’t say because I have no way to compare. It’s also really light for the given aperture (better construction/thinner mirror) without giving up stability.

What I can say about my premium reflector is that the mechanicals beat the pants off my venerable, but flawed 10”. The focuser, balance, bearing smoothness, primary mirror cell, secondary mirror holder are superior in every way. The entire tube is flocked and the cradle design allows the tube to be easily turned and/or moved north south. My definition of a premium scope (which includes the mirror) is one that both offers expected mirror performance while the structure disappears as one uses it. A premium scope is more than a premium mirror and a premium mirror will fall short of full potential if one has to battle with the other parts.

Chesterguy
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#25 areyoukiddingme

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Posted 20 July 2019 - 08:03 PM

I have two 8ers to compare, one Zambuto 8" F7, the other a generic "Skywatcher" 8" F6. 

 

But the comparison is necessarily through memory . . .

 

I visit family a couple of times per year in Australia. Got tired of lugging my C6 and refractor through airports. So last time back I bought an 8" F6 "Saxon", which is the same as the Skywatcher 8" solid tube.

 

About a year ago I came across an ad where a guy had the parts for an 8" F7--the primary being a Zambuto quartz, and the secondary a 1/30 wave Antares. Moonlight single-speed focuser. A solid tube (flocked), and splashed out for an Aurora precision cell. I run it alt-az on a Skytee 2 mount.

 

How do they compare?

 

I wasn't expecting miracles with the Saxon. A solid diffraction limited scope was all I was wanting.

 

First object was Sirius at high elevation in quite good seeing. Within 2 minutes of setting up the scope on first light I easily split the pup. Done. This is a good scope!

 

Star test isn't perfect (I am no expert on this). My recollection was a brighter ring on the outside on one side or the other of focus. So I'm guessing a less than perfect edge. But it performs very well indeed, and more than met my hopes. I haven't spend much time on planets with this scope (it does perfectly fine). When down under I'm more interested in the Southern objects--Magellanic clouds put up a ton of detail in this scope. 

 

But what about that Zambuto? Well, as far as I can tell it is as close to perfect as you can get in an 8" mirror. Star test looks identical to my eye on either side of focus.

 

The mirror is up and ready to go with just a couple minutes of running a fan, and puts up etched views of the planets and moon (it has a very small secondary, and is optimized for planets). A particularly memorable view was of the double double from Mt Pinos (parking lot must be close to 8k ft). Perfect dots and diffraction rings. An observing friend with a lot of experience called it the best view of the double double he'd ever seen.

 

But how would this thing compare to a 10". Well, I think you'll get a more sharp/contrasty view out of the 8" premium, but so long as the 10" is decent, it will resolve more detail, those details will just look a tad softer.


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