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Obsession telescope upgrades?

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#1 Orion64

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Posted 14 June 2021 - 12:06 PM

Hello everyone

I have recently received my first obsession telescope. The 15" classic. I must say that it's been providing me with fantastic views. I've never had a telescope bigger than 10inch and never looked through larger than 12onches.

I have the collimation down, mostly. So the telescope is setup for some nice deepsky observations. On its way is the stellercat tracking and goto system. I also have a binotron with the 3d eyepieces in there.

My question now is, which issues have you guys found with using these scopes?

Speaking for myself, the secondary spider is not up to par, especially the adjustment knobs. They are way too Coarse and flimsy. Second, I don't like the secondary mirror inside it's cell. I guess it provides protection, but I like a nice secondary mirror sitting proud. It makes centering under focuser easier. This is why I'm getting a new carbon spider and Antares 30lamda secondary.

Then I'm not sure about the primary mirror quality. Maybe I should be more patient with cooling time? I purchased the scope second hand. So I'm also respotting the centre dot with a hotspot. I found the default centre donut was off about 4mm. The mirror is the default one that comes with the obsession scopes. It was made in 2004.

So what are your opinions and experiences? I would like to hear more
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#2 firemachine69

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Posted 14 June 2021 - 12:49 PM

Did you mount fans on your scope? It'll really help with cool-down.

#3 TOMDEY

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Posted 14 June 2021 - 12:55 PM

There is a possible good reason for an apparently off-center PM appliqué. The optical and mechanical centers of mirrors are not generally/necessarily in the same place. For paraboloidal roundels, the true optical center is (the alignment point) where axial coma becomes identically zero. At work we characterized all incoming parabs in autocollimation interferometry, ran our own macro to back-solve for the optical center... and then dotted them there. Commercial parabs like we guys buy or make --- the that offset is typically within half an inch on slow mirrors and a few mm on the faster ones. For some reason very few people here are aware of that. Probably because it's difficult to locate that elusive point. This also explains why the common Newt alignment tools and procedures give mixed results. So we blame the tools or other stuff... when it may well be that the mechanically-centered feature is simply not where the actual wavefront optical center is.

 

Thankfully, one (should) tip-tilt the Primary Mirror ever so slightly to drive out axial coma in a center-field star. That, as the final gesture/tweak in precision field-alignment. At that point you are done, and what the tools are indicating drops out of the equation.

 

I contrived this graphic to show how that works. The Zernikes morph as evaluation center is moved around. Even some of the optical engineers at work were pretty clueless regarding that unless they were assigned optical testing for a while.    Tom

Attached Thumbnails

  • 07 75 Zernike Best Focus and Newt and Herschelian alignments.jpg

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#4 greenstars3

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Posted 14 June 2021 - 01:13 PM

Orion64

 

 

I put a cooling fan on the side of the mirror box to take off the boundary layer and increased the size of the back fan for better cooling.

Cool down is the only major issue with the Obsession that I have, the 2 inch thick mirror takes a while to stabilize thermally.

Run your fan(s) at all times and give the scope some cool down time before use.  

My 15 inch classic is a 2007 modal and came with an OMI mirror and it works great.

I replaced the secondary mirror in mine (because it was pitted) with an Antares 1/20 wave but did not change the holder

Mine came with the StellerCat and goto but I have never used the system but I hear that it works great

Other than making sure to measure all the poles and making sure they were all the correct length and some cleaning and tune up, I  have not really modified the scope except for the addition of the side fan and getting a larger back fan.

I am very happy with the performance of the scope, as in all endeavors your mileage my vary

 

Robert  

 

edit: I put a variable speed switch on both fans so they could be adjusted as needed and my center spot was etched into the mirror by OMI by a small X 


Edited by greenstars3, 14 June 2021 - 01:25 PM.


#5 Starman1

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Posted 14 June 2021 - 02:05 PM

And, eliminate the seatbelt sling and replace it with a Glatter wire sling.  It makes a difference in astigmatism (though the thick mirror is less injured by the seatbelt),

and doesn't slide off the edge of the mirror.

But, I'm with the above post: fans.  At least 1 large and maybe 3 small ones behind the mirror, started at sunset to cool the mirror down, and maybe 2 small fans inside the box to blow across the mirror to cool that thick piece of glass.

Here is a calculator to evaluate the fan air movement you need to result in a cooled mirror in less than 2 hours:

https://www.cruxis.c...rrorcooling.htm



#6 CHASLX200

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Posted 14 June 2021 - 06:25 PM

Hello everyone

I have recently received my first obsession telescope. The 15" classic. I must say that it's been providing me with fantastic views. I've never had a telescope bigger than 10inch and never looked through larger than 12onches.

I have the collimation down, mostly. So the telescope is setup for some nice deepsky observations. On its way is the stellercat tracking and goto system. I also have a binotron with the 3d eyepieces in there.

My question now is, which issues have you guys found with using these scopes?

Speaking for myself, the secondary spider is not up to par, especially the adjustment knobs. They are way too Coarse and flimsy. Second, I don't like the secondary mirror inside it's cell. I guess it provides protection, but I like a nice secondary mirror sitting proud. It makes centering under focuser easier. This is why I'm getting a new carbon spider and Antares 30lamda secondary.

Then I'm not sure about the primary mirror quality. Maybe I should be more patient with cooling time? I purchased the scope second hand. So I'm also respotting the centre dot with a hotspot. I found the default centre donut was off about 4mm. The mirror is the default one that comes with the obsession scopes. It was made in 2004.

So what are your opinions and experiences? I would like to hear more

I had a OMI in my 2004 made 15" Obsession and it could do 1100x on the planets without breaking a sweat. But i also have some super steady seeing.  What brand of mirror do you have?  It should have had a test report with the scope i would guess.


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#7 Markovich

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Posted 14 June 2021 - 08:33 PM

I have an Obsession 15, bought it new in 2002. The original mirror from Torus/OMI was poor with a significant TDE, so Dave made it right and I ended up with a delightful Swayze mirror. Here are my thoughts/suggestions:

 

Fans are essential - instead of adding more fans, I went the easy route and use a big AC powered fan behind the scope , aimed at the mirror. Moves a LOT more air that way. Out in the field, I use a battery powered camping fan. Im big on keeping it simple.

 

Secondary- never had any real issues with the secondary mirror or holder. I have a Protostar mirror that Bryan gave me a few years later I bought the scope. Spider and holder are original. The original secondary mirror was fine.

 

Primary mirror- I must have been the exception but I had very few problems with the sling. Mind you, astigmatism only comes into play when the mass of the mirror is being fully supported by the sling, basically when you're observing low on the horizon. I did recently replace it with the Glatter Sling and do recommend it as it does keep the mirror in place better than the belt sling. 

 

I love my Obsession and only age or injury will force me to part with it. I consider it the best purchase Ive ever made. Id rather use the Obsession than any other scope I own, at any time. Setting up is a Zen like experience for me and I never tire of it.

 

Only mods Ive made were to add 10K encoders and a tablet stalk. I use an AstroDevices Nexus II and an iPad for push to and Im thrilled with the results.

 

 

Good luck with the scope!


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#8 CHASLX200

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Posted 15 June 2021 - 05:55 AM

There were a few bad mirrors that slipped out from OMI back around 2000 since they tested them wrong. I think the way they tested them was setup wrong. I think most were fixed. My 2004 made Obsession was great. Not sure how long the mirrors sit around as i think they buy them in big lots so they could have been made well before 2004.

 

Had a 12.5" OMI that was a 800x killer as well.  Never used fans with any of Newts, but i am in very warm FL so my mirrors are ready right off the bat when i take the scope out. Sometimes it is 87f at 10pm and the scope is kept in a hot room so no cooling needed. On cold nites with more temp drops i don't even bother to view. I only view planets at very high powers so a super good mirror is a must.


Edited by CHASLX200, 15 June 2021 - 05:58 AM.


#9 Astro-Master

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Posted 16 June 2021 - 06:04 PM

The Obsession 15" Classic is a great scope.  My friend Bob would always share views back when I only had a 10" LX 200 SCT.  The views through the 15" from the dark desert skies were so good I stopped bringing my 10" scope all together.

 

About three years latter I bought a used 18" Obsession Classic in 2005, its been the best scope I've ever owned, and is easy to transport and set up, with the wheelbarrow handles and ramps, even at age 74.

 

Now I share the views with my friend Bob who can no longer carry the 15" scope down his stairs with his bad hips.  I think the Obsession 15" and 18" scopes hit the sweet spot for size and portability, and are lifetime scopes. waytogo.gif   Thank you Dave for your wonderful scopes.  waytogo.gif waytogo.gif


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#10 George N

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Posted 17 June 2021 - 10:23 AM

The Obsession 15" Classic is a great scope.  My friend Bob would always share views back when I only had a 10" LX 200 SCT.  The views through the 15" from the dark desert skies were so good I stopped bringing my 10" scope all together.

 

About three years latter I bought a used 18" Obsession Classic in 2005, its been the best scope I've ever owned, and is easy to transport and set up, with the wheelbarrow handles and ramps, even at age 74.

 

Now I share the views with my friend Bob who can no longer carry the 15" scope down his stairs with his bad hips.  I think the Obsession 15" and 18" scopes hit the sweet spot for size and portability, and are lifetime scopes. waytogo.gif   Thank you Dave for your wonderful scopes.  waytogo.gif waytogo.gif

For years DaveK reported (old Obsession Users Group) that the 18 Classic was his most ordered/sold scope by far. However, then the UC came about - originally intended to be 'ultra compact' to fit in the new smaller gas-efficient vehicles people were buying, and then an aging population wanted 'no ladders'.

 

About 3 years ago I met a guy at Cherry Springs who had a new-to-him Classic 18 that he bought used for a surprisingly low $$. He reported calling Dave about it and being told "nobody wants that style of scope anymore. they are less than 15% of my sales" - and we all know where that led - Classic design discontinued.

 

As for the original topic - nice list of mod's here, that I have little to add to from my experience. One I've seen that is perhaps more 'extreme' -- a friend with a Classic 18 became unhappy with chasing the air temp with his otherwise excellent 2" thick OMI mirror - and sold the glass. He now has a Zambuto 18 F/4.0 1.25" thick primary that of course required some work to shorten the truss poles and re-balance -- but the result is a fantastic scope - that still tracks/slews very well with its previously installed StellarCat. I only need one step up a stool to view, and only at the very highest altitudes.


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#11 Markovich

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Posted 17 June 2021 - 01:00 PM

For years DaveK reported (old Obsession Users Group) that the 18 Classic was his most ordered/sold scope by far. However, then the UC came about - originally intended to be 'ultra compact' to fit in the new smaller gas-efficient vehicles people were buying, and then an aging population wanted 'no ladders'.

 

About 3 years ago I met a guy at Cherry Springs who had a new-to-him Classic 18 that he bought used for a surprisingly low $$. He reported calling Dave about it and being told "nobody wants that style of scope anymore. they are less than 15% of my sales" - and we all know where that led - Classic design discontinued.

 

As for the original topic - nice list of mod's here, that I have little to add to from my experience. One I've seen that is perhaps more 'extreme' -- a friend with a Classic 18 became unhappy with chasing the air temp with his otherwise excellent 2" thick OMI mirror - and sold the glass. He now has a Zambuto 18 F/4.0 1.25" thick primary that of course required some work to shorten the truss poles and re-balance -- but the result is a fantastic scope - that still tracks/slews very well with its previously installed StellarCat. I only need one step up a stool to view, and only at the very highest altitudes.

I would assume he also had to replace the mirror cell??



#12 CHASLX200

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Posted 17 June 2021 - 06:44 PM

I would assume he also had to replace the mirror cell??

I would guess so.  I don't think a sling will work good with a thin mirror. I am lucky i don't have a problem with my thick 18" as it is ready right off the bat in my warm weather in FL.



#13 starman876

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Posted 18 June 2021 - 08:21 AM

For years DaveK reported (old Obsession Users Group) that the 18 Classic was his most ordered/sold scope by far. However, then the UC came about - originally intended to be 'ultra compact' to fit in the new smaller gas-efficient vehicles people were buying, and then an aging population wanted 'no ladders'.

 

About 3 years ago I met a guy at Cherry Springs who had a new-to-him Classic 18 that he bought used for a surprisingly low $$. He reported calling Dave about it and being told "nobody wants that style of scope anymore. they are less than 15% of my sales" - and we all know where that led - Classic design discontinued.

 

As for the original topic - nice list of mod's here, that I have little to add to from my experience. One I've seen that is perhaps more 'extreme' -- a friend with a Classic 18 became unhappy with chasing the air temp with his otherwise excellent 2" thick OMI mirror - and sold the glass. He now has a Zambuto 18 F/4.0 1.25" thick primary that of course required some work to shorten the truss poles and re-balance -- but the result is a fantastic scope - that still tracks/slews very well with its previously installed StellarCat. I only need one step up a stool to view, and only at the very highest altitudes.

not many people want a large wood hulk to move around.   As people get older moving around all that weight gets harder and harder.   Even though I can still manage heavy objects without a problem I am now looking for an ultra light large dob.   I want a large dob that is steady and light weight.   I want to be ready when I get older and cannot manage a heavy dob that I have to stand on a ladder to use and move around like a wheelbarrow.   I want a large aperture scope that will take me into the future and can use with ease.    I bet the market will soon be flooded with the large scopes as people get older and cannot manage them anymore.  Ultra light dob sales are going to go through the roof in the next few years. 


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#14 Starman1

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Posted 18 June 2021 - 09:11 AM

not many people want a large wood hulk to move around.   As people get older moving around all that weight gets harder and harder.   Even though I can still manage heavy objects without a problem I am now looking for an ultra light large dob.   I want a large dob that is steady and light weight.   I want to be ready when I get older and cannot manage a heavy dob that I have to stand on a ladder to use and move around like a wheelbarrow.   I want a large aperture scope that will take me into the future and can use with ease.    I bet the market will soon be flooded with the large scopes as people get older and cannot manage them anymore.  Ultra light dob sales are going to go through the roof in the next few years. 

Steady and light, at least as far as I see in the field at star parties, are mutually contradictory terms.

 

It can be done, but it can't be done for the cheap prices people want to pay.

It might look a bit like this:

https://www.mallinca...truss-tube.html

only in a newtonian configuration.


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#15 Markovich

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Posted 18 June 2021 - 09:49 AM

Steady and light, at least as far as I see in the field at star parties, are mutually contradictory terms.

 

It can be done, but it can't be done for the cheap prices people want to pay.

It might look a bit like this:

https://www.mallinca...truss-tube.html

only in a newtonian configuration.

Yeah, Ive seen a few "ultralights" most notably a few years ago at the Grand Canyon star party. They were all shaky and even the slightest touch resulted in an unusable scope. There is something to be said for mass:) 


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#16 starman876

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Posted 18 June 2021 - 09:50 AM

Steady and light, at least as far as I see in the field at star parties, are mutually contradictory terms.

 

It can be done, but it can't be done for the cheap prices people want to pay.

It might look a bit like this:

https://www.mallinca...truss-tube.html

only in a newtonian configuration.

you could be right that the combination maybe hard to find. But like everything else in life compromises need to be made.   I had a 12" newt all carbon truss that weighed 28 lbs.   With the right engineering light and stiff can be obtained. 

 

zwo2.jpg


Edited by starman876, 18 June 2021 - 09:53 AM.

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#17 starman876

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Posted 18 June 2021 - 09:54 AM

Also this CFF is light for its size.

 

cff.jpg

 

 

however, neither scope is a dob si I need to drag out a mount and tripod. 

 

I should sell the CFF and buy an ultra light dob with the money.  However, no matter how hard I try to find a decent review of the Ultra lights of  Explorer or Hubble I just cannot find a decent review of either one.


Edited by starman876, 18 June 2021 - 09:57 AM.


#18 George N

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Posted 18 June 2021 - 10:52 AM

I would guess so.  I don't think a sling will work good with a thin mirror. I am lucky i don't have a problem with my thick 18" as it is ready right off the bat in my warm weather in FL.

I don't know if he changed the mirror cell - but I don't think so. Both before and after he had a Howie Glatter sling - and with Howie as a good friend, I assume Howie was involved in the install and certainly 'inspected' it (as he did with the one I put on my 20" F/5).

 

What I do know is -- the Obsession 18 Classic with Zam F/4.0 provides excellent views. The 9-inches or so shorter tube is really only apparent if it is set up next to a 'standard' Obsession 18. The owner at least believes that the cooling of the thinner mirror has been worth the expense and effort.

 

I hope a steel wire sling suspended from linear bearings works with a thin mirror - because that's how my on-order NMT 20" F/3.5 is coming - and it will have a Fullum fused thin mirror - slumped, so with a curved back-side. BTW - Ryan at NMT says that making the mirror cell is roughly 50% of the build time for him!


Edited by George N, 18 June 2021 - 10:56 AM.


#19 CHASLX200

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Posted 18 June 2021 - 11:09 AM

Also this CFF is light for its size.

 

attachicon.gifcff.jpg

 

 

however, neither scope is a dob si I need to drag out a mount and tripod. 

 

I should sell the CFF and buy an ultra light dob with the money.  However, no matter how hard I try to find a decent review of the Ultra lights of  Explorer or Hubble I just cannot find a decent review of either one.

Don't know why you would want a big DOB unless you live in dark skies and or have steady seeing for planets.  A big Dob is not any good in my skies for deep sky. But i sure have the best seeing to see planets at over 600 to 1100x.  No matter how big you go M13 will only look ok in bright skies.



#20 CHASLX200

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Posted 18 June 2021 - 11:10 AM

I don't know if he changed the mirror cell - but I don't think so. Both before and after he had a Howie Glatter sling - and with Howie as a good friend, I assume Howie was involved in the install and certainly 'inspected' it (as he did with the one I put on my 20" F/5).

 

What I do know is -- the Obsession 18 Classic with Zam F/4.0 provides excellent views. The 9-inches or so shorter tube is really only apparent if it is set up next to a 'standard' Obsession 18. The owner at least believes that the cooling of the thinner mirror has been worth the expense and effort.

 

I hope a steel wire sling suspended from linear bearings works with a thin mirror - because that's how my on-order NMT 20" F/3.5 is coming - and it will have a Fullum fused thin mirror - slumped, so with a curved back-side. BTW - Ryan at NMT says that making the mirror cell is roughly 50% of the build time for him!

I liked the cells Starmaster used much better. My cell was a mess when i got it and the guy before me never even used the sling and the scope sat for 10 years and he had no clue how to even use the scope the nite he brought it over as i had to go thru the whole thing to get it working right.

 

So far it has done fine on Jupiter.. Globs are cored out but look dim.


Edited by CHASLX200, 18 June 2021 - 11:13 AM.

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#21 starman876

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Posted 18 June 2021 - 12:24 PM

Don't know why you would want a big DOB unless you live in dark skies and or have steady seeing for planets.  A big Dob is not any good in my skies for deep sky. But i sure have the best seeing to see planets at over 600 to 1100x.  No matter how big you go M13 will only look ok in bright skies.

I do not like to take a scope to darker skies.  Just too much hassle.  I have had big dobs and I really liked the views through them even in my light polluted skies.  Now I want an ultra light so I can more easily use that dob without feeling I am moving a wheelbarrow around.  Also, a fast dob so I can easily view without needing a ladder.   I have seen views of the planets from my yard that felt like I was flying in low orbit over the planets and I did not need 600X to do that.  That requirement is something you need.   I can see the detail fine at lower powers.  Besides, at 1000x I cannot imagine trying to keep an object in view with a dob.  I know what it feels like at 400X and that is hard enough with using an equatorial without a drive.  You are constantly trying to keep the object in view and never have enough time to really observe. 


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#22 starman876

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Posted 18 June 2021 - 12:26 PM

Don't know why you would want a big DOB unless you live in dark skies and or have steady seeing for planets.  A big Dob is not any good in my skies for deep sky. But i sure have the best seeing to see planets at over 600 to 1100x.  No matter how big you go M13 will only look ok in bright skies.

I have seen M13 plenty of times in my skies and it always looks awesome.  The fun part is increasing the power until you feel like you are flying around inside of M13.   



#23 cuzimthedad

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Posted 18 June 2021 - 12:33 PM

We're veering off topic folks. Back to Obsession upgrades please.



#24 Bill Jensen

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Posted 18 June 2021 - 02:23 PM

One of the scopes I am considering for a bit more aperture at home is a 15UC.

 

It would get me to nearly the same aperture as a scope I have stored out west (16 f/4). My 10 inch Teeter works well for me on my back deck, but at our club's sites, I want a bit more reach. 

 

The 15UC is within the weight that I can manage, at 45 pounds for mirror and mirror box. The upgrade I would need if I purchased it or a similar NMT would be encoders to attach my Nexus.

 

I don't want a ServoCat added due to the extra weight involved in having the mirror box and rocker mated. I made that mistake when I bought a 15 classic with a SCJr on it, and I never was able to carry it. The 15UC or similar sized scope would live in the back of my SUV most of the year. 

 

I would have to add some fans (more than the one supplied) given the thick mirror. Dew prevention is also something I would need to add to the order plus perhaps the Markless fan and secondary wiring kits. 

 

I considered picking up a used 12.5 inch Classic, or another premium scope in that size, yet it does't give that much more than the 10 inch.

 

As much as I would like a 20 inch f/3.3 premium dob, that is not in the cards for limited storage and carrying capability . Not unless I can convince my spouse to agree to purchase some nice property 2+ hours from home and store the scope there! 



#25 Starman1

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Posted 18 June 2021 - 02:38 PM

I do not like to take a scope to darker skies.  Just too much hassle.  I have had big dobs and I really liked the views through them even in my light polluted skies.  Now I want an ultra light so I can more easily use that dob without feeling I am moving a wheelbarrow around.  Also, a fast dob so I can easily view without needing a ladder.   I have seen views of the planets from my yard that felt like I was flying in low orbit over the planets and I did not need 600X to do that.  That requirement is something you need.   I can see the detail fine at lower powers.  Besides, at 1000x I cannot imagine trying to keep an object in view with a dob.  I know what it feels like at 400X and that is hard enough with using an equatorial without a drive.  You are constantly trying to keep the object in view and never have enough time to really observe. 

The power of a big scope is in the delivery of photographic images of deep sky objects.  To see those views, though, requires dark skies.

If you're stuck in brighter skies, and you primarily look at the planets and the Moon, I see no reason to go larger than 10-12" because it is HIGHLY unlikely the seeing

will ever exceed the resolution of that aperture.  The really big dob is simply wasted in that environment.

The 60" at Mt. Wilson, for example, doesn't give any better image of DSOs than a really good 16-18" in dark skies.

 

So back to collimation, which affects high power images most: the ultralight won't hold collimation tolerances you need for high powers on a fast f/ratio.

Yes, it's possible to engineer and make your own ultralight and stiff scope.  But you aren't describing any commercial scope I know of.

So figure you're going to build it yourself.

 

There is a way around it, I suppose: get a commercial ultralight and start modifying it with larger diameter poles or braces between the poles, or guy-wires to stiffen the structure,

and perhaps mods to the cell and trunnions.  That might yield a stiff-enough scope without engineering the entire scope yourself.




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