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15-16" UC Dob: Summerian vs Obsession

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#1 PeteDavidsonTheFirst

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Posted 17 September 2021 - 05:18 AM

I'm in the market for an UC dob and am honing in on either the Obsession UC 15" or the Sumerian Canopus 16". They originate from opposite sides of the Atlantic, so doubt many (any?) have had a chance to directly compare. On the off chance someone has experience with both, how do they compare? Any significant differences in rigidity or other performance aspects? Thanks in advance for your thoughts.

 

 



#2 sixela

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Posted 17 September 2021 - 05:52 AM

They are very, very different. The Obsession UC is compact, but it cannot be called "light". The Sumerian Canopus is light (especially coupled with optics that are not too thick).

 

The UCs I saw had mechanical weaknesses (there's a thread about recent improvements, though) but it's a much more 'polished' scope, and they are all alike. They are also, for all practical purposes, mass-produced scopes, for better or for worse.

 

A Canopus is not a series production --Michael Kalshoven frequently tweaks them quite a bit; the woodwork is excellent but it's not not finished as if it was a piece of furniture, and things like attachments and bolts are functional but look a lot more 'crude'. They are also not as "sturdy" (though a lot more than Alkaid travel dobsons) but "overengineered/sturdy" doesn't go well with "light".

 

They're extremely popular over here because of Michael's excellent support, though -- an observing colleague bought a 5 year old second hand Canopus which had developed some problems and Michael refurbished it and absolutely refused to be paid for it. But obviously, it's easier for us in the Benelux to drive over to Sumerian. That wouldn't be an advantage if you were in the US.

I know quite a number of Canopus in the Benelux and France, usually with Nichol mirrors (a few with Huygens Optics mirrors that are excellent, but Huygens Optics has stopped serving the amateur community). The 18" I saw most recently is 66lbs heavy, while a UC weighs 90lbs. A 20" Canopus is less heavy and easier (though longer) to set up than an 18" UC. I have a picture of Michael setting up a 24" on his own --not with a winch or wheelbarrow handles but from pieces dragged from a car's boot (aka 'trunk') but that's really not what I'd personally call a one man job (the mirror box is less than 30kg but unwieldy).

 

The fact my 20" will be a Canopus, I think, tells where my preference lies (a UC is just too heavy and cumbersome for that size of scope compared to a Canopus for me, since I always observe after a drive and set it up alone); once I come back from holiday I'll give everyone here a tour of it after I took delivery and observed with it. But if I were wired differently, I could have a different view on things.

 

So: what do you find important in a scope? I could give you a less fluffy appraisal of what I see is different. And where do you live?


Edited by sixela, 17 September 2021 - 06:28 AM.

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#3 a__l

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Posted 17 September 2021 - 08:40 AM

I have a picture of Michael setting up a 24" on his own --not with a winch or wheelbarrow handles but from pieces dragged from a car's boot (aka 'trunk') but that's really not what I'd personally call a one man job (the mirror box is less than 30kg but unwieldy).

 

I am always curious when such weight is written.
For example, the weight of my 24" f/3.3 mirror is ~23 kg. I don't think this mirror is thick. It turns out 7 kg per box, mirror cell and 2 Alt bearings. That is, I can assume that at 30 kg the structure is very weakly and there is no point in seriously discussing it.

 

Or another option, the mirror is so thin and light and astigmatic that it also makes no sense in such a design.


Edited by a__l, 17 September 2021 - 08:52 AM.


#4 sixela

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Posted 17 September 2021 - 08:57 AM

I don't think this mirror is thick.

You think correctly. The Canopus I saw has an f/3.3 24" and the mirror weighs only 23kg. I also don't think that's thick.
 

 

That is, I can assume that at 30 kg the structure is very weakly and there is no point in seriously discussing it.

Since you are traditionally excel at assuming a lot without any actual data or experience (the Alt bearings can be separated and were not included, just as a data point), there is indeed no point in discussing it with you, especially since you haven't seen that 24" in operation nor have you seen the mirror box and 27 point cell. If I told you it works, you'd just resort to personal incredulity.

 

On the other hand, the point of this thread is to discuss Canopus and UC scopes, so you'll just have to forgive others for discussing them.

 

Can't post any pictures that aren't public yet, the official grand opening is on the 28th of October.

 

The one picture the owners posted is here (serendipitously, this is the mirror box, without the Alt bearings):

https://www.facebook...227010910724874

 

Mind you, that 30kg was off the top of my head. Might be more, but we were discussing the differences between a Canopus and an Obesssion UC and I'd really hate to drag a UC of that size out of a car, especially given the mirror thickness that Obsession usually favours.

 

Not that dragging that 24" Canopus mirror box out of a car wouldn't make me nervous (I picked 20" for my next scope because I feel more comfortable with that size), but at least it is possible to set it up yourself.

 

For the original poster: a 16" is obviously lighter; last weekend I saw the owner of a Sumerian carry the whole scope from the mirror box up in one piece down a small hill (he just had to fetch his platform plus rocker box later). You could also contact the owners of the 24" after the 28th of October to get their view on how the scope performs to get an informed data point (albeit that of owners, so I cannot exclude some bias).


Edited by sixela, 17 September 2021 - 09:50 AM.

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#5 sixela

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Posted 17 September 2021 - 09:26 AM

For some discussions of the UC design these are interesting:

https://www.cloudyni...3#entry11338072

https://www.cloudyni...changesupdates/

 

If you want to read some comments about Canopi, it would be good to know what languages you can read, but in English there's:

https://stargazerslo...opus-16-review/

 

and there are some other threads on that scope on that same forum.

 

There's also a thread on the 18" that is now in Belgium (and that I've used personally):

https://stargazerslo...8-inch-canopus/

 

but the truss connections to the mirror box and some other details have changed since (cfr. the picture of the 24" mirror box posted earlier).

 

If you read French then there are many other pointers too, if you're interested.

 

BTW, you might also consider Taurus telescopes:

https://www.tauruste...es.com/en/home/

 

They're also fairly light, although the UTA is not exactly compact. I'm not too hot about the ones with GSO mirrors, but the ones with 'premium' optics seem to perform well and I've heard a few satisfied owners. The 20" scope's f/ratio makes it less than practical --the main reason I didn't end up with one--, but the 16" is still a flat-footed scope.


Edited by sixela, 17 September 2021 - 09:37 AM.

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#6 MeridianStarGazer

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Posted 17 September 2021 - 02:12 PM

I am always curious when such weight is written.
For example, the weight of my 24" f/3.3 mirror is ~23 kg. I don't think this mirror is thick. It turns out 7 kg per box, mirror cell and 2 Alt bearings. That is, I can assume that at 30 kg the structure is very weakly and there is no point in seriously discussing it.

Or another option, the mirror is so thin and light and astigmatic that it also makes no sense in such a design.


I calculate your mirror edge thickness is 1.63". Sounds like something Gordon Waite would make.

#7 a__l

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Posted 17 September 2021 - 04:01 PM

You think correctly. The Canopus I saw has an f/3.3 24" and the mirror weighs only 23kg. I also don't think that's thick.
 

 

Since you are traditionally excel at assuming a lot without any actual data or experience (the Alt bearings can be separated and were not included, just as a data point), 

I have a more experience than you, as I made all my telescopes myself and experimented a lot with different materials.

Let's discuss your answer in more detail.

How are you going to install the mirror box into the rocker? Without Alt bearings? Therefore, the full weight of the mirror box is always taken into account. Otherwise, this information misleads the user.

 

 

there is indeed no point in discussing it with you, especially since you haven't seen that 24" in operation nor have you seen the mirror box and 27 point cell. If I told you it works, you'd just resort to personal incredulity.

 

I made for myself an aluminum-titanium mirror cell for a 24" scope with 18 points. It is very unlikely that the weight of 27 points will be less than 5-6 kg. Since thinner parts will be elementary weakly. Add the weight of the 8 clamps. I have an aluminum MoonLite. This is a little less than a kilogram (with 32 screws, stainless steel fixing).

How many fans on the side and bottom for a 24" mirror? The weight?

And how much will your box with dimensions > 650 mm (rough size) weigh and what wall thickness will it be? Even without Alt bearings? 1 kg?


Edited by a__l, 17 September 2021 - 04:19 PM.


#8 Jon Isaacs

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Posted 17 September 2021 - 04:30 PM

I have a more experience than you, as I made all my telescopes myself and experimented a lot with different materials.

 

 

Do you have any experience with the Sumerian Dobs?

 

That is what is important here.  

 

Sixela:  Some years ago, a friend was considering a Sumerian Dob, as I recall, part of the balance was either with springs or bungee cords. Looking at images of the Canopus, that seems to be the case.  How well does that work at high magnifications?

 

Jon


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#9 a__l

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Posted 17 September 2021 - 05:09 PM

Jon,  above we discussed general engineering ideas and how to make a mirror box for a 24 "telescope of 30 kg. This is just as important as "bungee cords".

In addition, such a design will clearly be less stable. I previously read about this on European forums, but I have no link right now.

 

Follow the link Sixela

https://stargazerslo...8-inch-canopus/

 

I didn’t like it right away, it was crumpled aluminum tubes (photo).... don't made that.

 

https://stargazerslo...that-never-was/

 

This review makes you think before buying it.

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Edited by a__l, 17 September 2021 - 05:14 PM.


#10 sixela

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Posted 17 September 2021 - 05:44 PM

Do you have any experience with the Sumerian Dobs?

That is what is important here.

Sixela: Some years ago, a friend was considering a Sumerian Dob, as I recall, part of the balance was either with springs or bungee cords. Looking at images of the Canopus, that seems to be the case. How well does that work at high magnifications?

Jon

On some Sumerian Alkaids part of the balance is with bungee cords to keep the weight of the scope down while ensuring that the Alt bearings still fit in the box. That is indeed a compromise but my 10" scope has to fit under an airline seat to be able to travel as hand luggage.

But on my personal Alkaid I ended up adding removeable counterweights that I stick on with 3M DualLock (which travel in my checked in luggage) since that is actually a lot better for stability and the smoothness of movement.

On the larger 16" Alkaids with a fast f/ratio the bungee cords is usually unnecessary, and I even have an observing colleague which uses the bungee cords to pull the top of the scope down when he removes the fairly heave optical finder because he doesn't want to bother with installing a counterweight at the top.

Canopus scopes are usually used without bungee cords. It's there for those 'in case of emergency break the glass' cases (usually if you changed the weight of whatever is on the UTA significantly, e.g. if you forgot your Paracorr), but you usually don't need them.

Jon, are you sure you were looking at a Canopus? A thread over here that was asking about a Canopus was diverted and pictures of an Alkaid were posted -- these are very different beasts. The Alkaid is a scope for someone who needs to put everything but the trusses in a minimalistic box so that he can travel with kids, family, luggage and the Alkaid (yes, cars in Europe are usually quite a bit smaller). It makes some compromises because of that, but none that I'd consider fatal (Tom Corstjens likes his a lot, and the fact it's not a Canopus doesn't seem to stop him from being our local Delos junkie and sketching god -- https://televue.com/...iece/#more-2717 ).

Edited by sixela, 18 September 2021 - 06:18 AM.

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#11 sixela

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Posted 17 September 2021 - 05:52 PM

https://stargazerslo...that-never-was/

This review makes you think before buying it.

Thanks for digging up an older thread about a 2014 scope that was not a Canopus, while ignoring everything in more recent and more relevant reviews except the one picture which you don't like. [I'll grant you one thing: the wood that Sumerian used to use in 2014 and is used on my 10" Alkaid is definitely not as good as the wood Sumerian now uses, in particular for the Canopus. That scope was one of the reasons. BTW, Sumerian took the scope back and fully refunded that customer.]

 

 

 

I didn’t like it right away,

There seem to be a lot of things you don't like. Except things you made yourself, these are always the bees' knees, because you have Seen the Light that others have failed to see ;-).


Edited by sixela, 17 September 2021 - 05:55 PM.

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#12 sixela

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Posted 17 September 2021 - 06:11 PM

Therefore, the full weight of the mirror box is always taken into account.

Then yes, for that last step of moving the mirror onto the rocker box it's more than 30kg (in fact I said earlier that it might be more than 30kg even without the bearings). So?

 

I do like the fact that you can remove the bearings, though. A 20" wouldn't fit in my Model 3 without that feature (a 18" does fit in the boot aka trunk, but there's not much spare room, as the boot isn't very high).

A UC-like design with foldable bearing might -- although the UC is not that low -- but I really do hate those foldable bearings with a vengeance, I'd rather just screw single-piece Alt bearings on while the mirror box is just beside the rocker box and then just lift it onto the rocker box.

 

Most people I know with 16" Canopus do leave the bearings attached, like this (this is a typical UK car, not that dissimilar to what most have here):

post-20507-0-55081900-1431804000.jpg

 

But a Model 3 (not a European car, but also not a behemoth) won't carry a 20" like that, especially not with someone in the front seat. So for larger scopes I find this configuration a lot more flexible (it's also lower since the mirror box descends a bit into the rocker box):

post-6880-0-98978500-1479937514.jpg


Edited by sixela, 17 September 2021 - 06:26 PM.

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#13 Bullgator

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Posted 17 September 2021 - 06:44 PM

Cheers to the OP



#14 a__l

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Posted 17 September 2021 - 08:28 PM

Thanks for digging up an older thread about a 2014 scope that was not a Canopus, while ignoring everything in more recent and more relevant reviews except the one picture which you don't like. [I'll grant you one thing: the wood that Sumerian used to use in 2014 and is used on my 10" Alkaid is definitely not as good as the wood Sumerian now uses, in particular for the Canopus. That scope was one of the reasons. BTW, Sumerian took the scope back and fully refunded that customer.]

 

 

 

There seem to be a lot of things you don't like. Except things you made yourself, these are always the bees' knees, because you have Seen the Light that others have failed to see ;-).

This is my specialty when I got my engineering education (a very long time ago). And I know what I'm writing about (no smiles). This should not be made with an aluminum tube. And this is not made by any serious manufacturer, except for amateurs.
What's the difference 2014 or not? The client paid the money and got what he got.

It seems with 30 kg and 24" we have removed all the questions?
Curious about how bungee cords behaves on frost, for example at -5 -10C?
I can't understand the material of the mirror cell? Is it plywood ????

 

Very similar to this. It cannot be done light weight. I would never buy a telescope with a plywood mirror cell. This has been discussed several times before. One of them is warm in front of the mirror. Other, cools down for a long time. The third does not hold its shape under prolonged load etc.


Edited by a__l, 17 September 2021 - 08:36 PM.


#15 sixela

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Posted 18 September 2021 - 02:03 AM

Well, that settles it: since you would never buy a scope with a plywood cell (or cell partly in plywood and partly in aluminium) those scopes aren’t for you and you need not discuss them.

But perhaps the original poster still wants to discuss them, which is why I’m attempting to write what I know about them the thread (and to cross-reference the threads about the UC too since the original poster is interested in these too).

Edited by sixela, 18 September 2021 - 02:10 AM.

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#16 osbourne one-nil

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Posted 18 September 2021 - 02:52 AM

But perhaps the original poster still wants to discuss them, which is why I’m attempting to write what I know about them the thread (and to cross-reference the threads about the UC too since the original poster is interested in these too).

I agree. Let's do that.  


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#17 Jon Isaacs

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Posted 18 September 2021 - 03:22 AM

Jon, are you sure you were looking at a Canopus

 

 

Alexis:

 

I am not sure what I was looking at. The Sumerian website does not seem to have detailed photos so I googled Sumerian Canopus.  It's entirely possible that I thought I was looking at a Canopus but was in fact looking at something else. I can't find the images I was looking at.

 

Jon



#18 Mauro Da Lio

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Posted 18 September 2021 - 05:29 AM

I have a recent Sumerian Alkaid 10", bought for travelling. I noticed that, compared to previous versions there are improvements. It is positive that Michael does not stick on a static design and improves it continuouslly.

The Alkaid is the lightest and most compact design: the 10" is the largest cabin luggage for many airlines. Nonetheless the truss in itself is quite rigid and it does not loose collimation. On occasion I transport the scope fully assembled by car, and it is still collimated after the travel. Of course lightness have a price but it is only in terms of (acceptable) vibration damping over say 200x when mounted on the rocker. There is an equatorial table for high power views though. For deep sky, between 40x and 200x it is perfect.

The 16" size might be preferable in the Canopus version though.

 

----

 

PS I am an engineer and I do not see any problem with crumpled tubes as long as they work a trusses (as it should be). Crumpled has no effect on push-pull capacity (they would have effect for flexure but the structure is a truss).

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Edited by Mauro Da Lio, 18 September 2021 - 05:41 AM.

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#19 Starman1

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Posted 18 September 2021 - 02:09 PM

Looking for an ultracompact scope with a single ring upper is going down the wrong path, in my experience.

This is very portable, and a lot better design:

https://www.waiteres...ade-telescopes/

Assembling an 18":

https://www.youtube....h?v=JEkLScsZ1yU

Assembly of a 20" f/3:

https://www.youtube....h?v=vn1OWJVPxw0



#20 a__l

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Posted 18 September 2021 - 02:31 PM

Well, that settles it: since you would never buy a scope with a plywood cell (or cell partly in plywood and partly in aluminium) those scopes aren’t for you and you need not discuss them.

Why is it not necessary?

The OP (anyone else) needs to understand what he will buy.
Have you not answered the bungee cords behaves on frost question?
And this is the way to solve the imbalance for this telescope. And it doesn't work as it should. This telescope has a relatively heavy UTA (plywood) and a light the weight mirorr box (due to the low height of the box walls). It is necessary to proportionally reduce the weight of the UTA. It can only be carbon and not plywood.

If the manufacturer really wants to reduce the weight of the heaviest part of his product.

 

https://www.cloudyni...vy-uta-on-dobs/

 

But carbon quickly raises the price.
Obsession takes these nuances into account, so it is not marketed as an ultralight telescope. And in this way it is made more competently.


Edited by a__l, 18 September 2021 - 02:47 PM.


#21 sixela

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Posted 18 September 2021 - 03:17 PM

Looking for an ultracompact scope with a single ring upper is going down the wrong path, in my experience.

Depends. The Canopus is not a single ring upper scope. In fact, it’s a lot more conventional than an Obsession UC.

The single ring scope is the Alkaid. A 10” fits under an airplane seat. A 16” is just a shallow box plus trusses, which some owners prefer when going on holiday with family.

None of the designs you showed are for the use case of an Alkaid.

They are more in the niche of a Canopus, and even Sumerian agrees a single ring design isn’t as good for that (hence the Canopus design). Interestingly, Obsession did pick a single ring design (and IMO not the best one either).

Edited by sixela, 18 September 2021 - 03:21 PM.


#22 sixela

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Posted 18 September 2021 - 03:25 PM

Have you not answered the bungee cords behaves on frost question?


Because as I had already explained the Canopus does not need a bungee cord. So it’s a red herring as far as the original question is concerned.

#23 a__l

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Posted 18 September 2021 - 07:37 PM

So it’s a red herring as far as the original question is concerned.

? I don't understand such answers. Let's take an objective approach to what is in reality.

 

Your link for 18" https://stargazerslo...8-inch-canopus/

 

Quote:

"I loaded the focuser with a 41mm Panoptic which is not an eyepiece that will ever appear in a slimmer magazine, this weighs just less than 1kg. Once the finder which is a 60mm model from Teleskop Services was placed in its very poor fitting but adequate shoe the secondary cage had increased its weight by about 20%, I can’t say this had a massive effect on the scope but I set the elastic balance system in any case. This is two pieces of elastic cord that can be wrapped around anchor points in different ways to offset the turning force, they can be used alone or together, simple but it works very well."

 

I don't think Pan 41 will be useful for this telescope, but N31 is for sure. There are Chinese eyepieces (ES) and more than 1 kg.

 

Here for 16" 

https://stargazerslo...-review/page/2/
balance issues identified for the N26 (0.7kg), so issues with the N31 will definitely.
The last post at link, quote:

"You can loop the tensioning cord various ways to get the required 'balance'.
It works on my Alkaid with the 31 Nag / Paracorr combo."

 

I will not search for links anymore, the problem with the 16" balance is obvious.

 

Ps. Also, I haven't seen a single photo Canopus with shroud. A wet or frosty shroud further exacerbates balance problems.


Edited by a__l, 18 September 2021 - 08:27 PM.


#24 a__l

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Posted 18 September 2021 - 07:58 PM

Interestingly, Obsession did pick a single ring design (and IMO not the best one either).

Yes, that's the truth. There is only one way out, 2 carbon rings and a price.
But Obsession has decided correctly with a secondary holder.
It doesn't use glue like on Canopus. Glue for a 16" telescope is a mass Chinese product (I can give links to the consequences of the fall of the secondary on the primary mirrors).
For 18" Canopus (photo) glue, this is nonsense.
I will not even discuss the issues of possible astigmatism in this case.
http://www.loptics.c...hop/shop42.html

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Edited by a__l, 18 September 2021 - 08:04 PM.


#25 sixela

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Posted 19 September 2021 - 01:02 AM

Your link for 18" https://stargazerslo...8-inch-canopus/


I don’t know what that owner was doing, but I can assure you that we were using that same scope (which has since changed owner) in France last week with a Paracorr plus either 31T5 or 21E without using a bungee cord (despite the presence of a RACI finder and a shroud).

 

Your photo (which comes from Sumerian since the truss wrapping is still missing) also does not have a bungee cord.

 

A French owner added a fairly **** finder on his scope. Despite that, no bungee cord:

blieux-2015-canopus-381-mm.jpg


Edited by sixela, 19 September 2021 - 04:03 PM.

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