Talk me out of buying an Avalon Linear

[Ajohn]

True Oly but a 25GT doesn't really reach the level of the mount that Lee "doesn't" want  to buy. It seems to me that people are happy with their larger mounts. I reckon that the main problem with the 25GT is the tripod it comes on. The 2" shouldn't be an option and well the clutches are different and in my particular case I am not at all keen on their idea of goto alignment but suspect it does allow a high degree of precision.

It's really difficult to get decent information on mounts. I did find one informative test on the Avalon Linear in French. In a pdf unfortunately so hard to translate the lot but 2 snipits.

Fig.7 and performed without homing has an amplitude of ± 7

           arcsec corresponding to the values given by

          Avalon. When the curve is observed, although it

           is difficult to determine with certainty, we would note

          repeatability over a period of 10 minutes (9mn and 50s).

          The curve is smoothly and very low spreads

           observed are probably due in large part to the

           turbulence.

          There is some flexibility on both axes when

imparts a rotation of the tube with both hands to each

end. The size of the tube and the wind are they settings

take into account?

The curve is pretty smooth compared with some that use gears for a lot of the speed reduction. Smooth curves make life much easier for autoguiding. I think the last part is related to the length and weight of scope that could be used with it. Homing is autoguiding. They used a CN212 scope on it and an SBIG STL 11000M camera. Also a G11 stand rather than the tripod it comes with. A pier I assume.

Then there is an autoguided test

Homing performed on M13

Laying 15 minutes with fluctuations

maximum of ± 2 arc seconds

Star height in FWHM

3.18 ''

More and more people seem to be using much shorter exposures than that. I do wonder if the Linear uses a worm drive on the RA axis. One thing that is noticeable on the rather high end mounts that do is that the worm wheels are rather large. There is a pretty simple reason for that. Say it's possible to get the teeth in the correct position to 2um. That represents a larger error at say a 50mm dia worm wheel than it would on a 150mm dia one. The 150mm one can have a lot more teeth too = less or even no gearing before the worm. Going back in time the ideal was considered to be a worm wheel of the same diameter as the scope that was being used.

I don't suggest mounts either only mention them. If I don't own it I can't really comment. My better mount is an old Meade LX750. I did think about changing it until I talked to some one who kept up to date on high end Astrophysics mounts.

Looking around and for an observatory at this price level I think I would be going for the EQ8. It's rare to see tests so thorough as those youtube video's. As these days I am more interested in light weight I would look at more mounts but it looks like the Linear would be the one I would buy. Not the sort of 1/2 fork ones they make though.

John

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[ollypenrice]

The Linear is an all belt system on both axes as I understand it. For all its popularity the worm and wheel does have its issues and needs accurate machining and a decent size, as you say. I've seen problems at various degrees of severity with the worm and wheel mesh on the following mounts that I've used or seen used here: EQ8, Takahashi EM200, EQ6, Meade LX200, Astro Physics 900, 10 Micron, iOptron iEQ45. That does add up to quite a lot! Most could be fixed but it may explain my preference for alternative drive systems. 

Olly

[Ajohn]

I couldn't find any real info on what is belt driven on the Linear Olly just going on looks. The dec axis does look all belt. Not easy to tell on the other but it looks like belt reduction to worm would fit and not sure about the other way round. The do show a shot which seems to be with the side cover off which looks like it would need a right angle drive eventually.

I'm getting the impression that manufactures aren't so careful on the dec drives. Take the EQ8. That appears to use a direct worm drive to the dec and a belt to worm on the ra. To discover that I looked at  a video by some one who  I suspect lives in one of the ex Russian satellite countries and a German video just swinging the head around. Dec was far more noisy. Neither were in English. The "Russian" video threw up what looked like an unguided plot at the end, pass on the amount but it was pretty smooth.

It's sad really that all we generally get in English is blase reviews that don't really tell potential buyers anything of any use at all. That applies to all sorts of things. For instance the only place I am aware of that will give me some idea of what a camera lens may be like really is in Poland plus one that doesn't add many lenses of late in Germany. Oddly Australia as well for some things in that area.

John

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[ollypenrice]

I couldn't find any real info on what is belt driven on the Linear Olly just going on looks. The dec axis does look all belt. Not easy to tell on the other but it looks like belt reduction to worm would fit and not sure about the other way round. The do show a shot which seems to be with the side cover off which looks like it would need a right angle drive eventually.

I'm getting the impression that manufactures aren't so careful on the dec drives. Take the EQ8. That appears to use a direct worm drive to the dec and a belt to worm on the ra. To discover that I looked at  a video by some one who  I suspect lives in one of the ex Russian satellite countries and a German video just swinging the head around. Dec was far more noisy. Neither were in English. The "Russian" video threw up what looked like an unguided plot at the end, pass on the amount but it was pretty smooth.

It's sad really that all we generally get in English is blase reviews that don't really tell potential buyers anything of any use at all. That applies to all sorts of things. For instance the only place I am aware of that will give me some idea of what a camera lens may be like really is in Poland plus one that doesn't add many lenses of late in Germany. Oddly Australia as well for some things in that area.

John

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My comments on the EQ8 have been called all sorts of things on here but never blasé!!! 

Olly

[Ajohn]

My comments on the EQ8 have been called all sorts of things on here but never blasé!!! 

Olly

LOL I didn't mean any comments people on here might make - just reviews in certain magazines that originate in more than one country but are in "english" and do not in real terms include any useful information.

As good as we generally get can be found as for instance by searching iOptron 25GT review on google. Sky And Telescope did one. It does mention that an 8" SCT is "probably" the heaviest scope that could be put on it. It also that it was "mostly" used with 4" refractors. The standard tripod was mentioned too - a common problem really.  No results though and no detailed information such as the fact that the worm and wheel are held in contact with a spring which means that there isn't any back lash in that area. A web search would reveal that people may benefit from re aligning the worm and wheel - down to "Chinese" assembly. A fairly common problem. They do however try to use decent sized worm wheels and have also tried to do something about the silly centre of gravity of typical GEM heads which were initially developed for use with long focus refractors mounted on very rigid piers. The position of the north leg on the tripods in relationship to the weight always causes me some amusement but at my latitude it doesn't matter. They have always been like that so why change. Some I have seen don't even allow settings for all latitudes. Some even push the centre of gravity further out than it need be simply to give more clearance on the weight

Anyway being serious just from curiosity I decided to see what I would buy if it was permanently mounted in an observatory within the budget that was implied. Given the OZ reports the EQ8 would be the clear winner for me but that's  me. While I would like an Astrophysics mount of similar proportions for a head only it would probably cost me 3 times as much just for a bare head that needs extras. The EQ8 seems to be available less stand for circa £2500. For lots of people that is very significant and is why skywatcher have produced it. I'm inclined to say good luck to them and hope to see some sensible engineering type rather than instrumental design appearing at some point. Doubtful really as certain aspects have always been like that and in some cases copied from other manufacturers so good luck to iOptron too.

John

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[leemr]

First off, I'd like to say thanks again to everyone who's contributed to the thread.

 I do wonder if the Linear uses a worm drive on the RA axis. One thing that is noticeable on the rather high end mounts that do is that the worm wheels are rather large. 

<snip>

Looking around and for an observatory at this price level I think I would be going for the EQ8. It's rare to see tests so thorough as those youtube video's. As these days I am more interested in light weight I would look at more mounts but it looks like the Linear would be the one I would buy. Not the sort of 1/2 fork ones they make though.

John

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The Linear is totally belt driven according to Avalon's product info page, where it says "...we chose to switch from the traditional worms and gears mechanism to a new transmission system based on pulleys and tooth belts, for both right ascension and declination."

I've already owned an EQ8, and while it was ok, to be honest I kind of felt like it was mostly just a big EQ6. I never really trusted it, though I didn't have any issues with it in the short time that I owned it. I sold it off because I didn't find performance to be any better than the previous EQ6 I'd owned (not the same as the one I currently own), I didn't need the payload capacity and I thought the money better spent on a new refractor.

Anyway, I've officially made the purchase of an Avalon Linear today, hopefully it'll be on the way from Germany very soon!

Thanks again.

[ChrisLX200]

First off, I'd like to say thanks again to everyone who's contributed to the thread.

The Linear is totally belt driven according to Avalon's product info page, where it says "...we chose to switch from the traditional worms and gears mechanism to a new transmission system based on pulleys and tooth belts, for both right ascension and declination."

I've already owned an EQ8, and while it was ok, to be honest I kind of felt like it was mostly just a big EQ6. I never really trusted it, though I didn't have any issues with it in the short time that I owned it. I sold it off because I didn't find performance to be any better than the previous EQ6 I'd owned (not the same as the one I currently own), I didn't need the payload capacity and I thought the money better spent on a new refractor.

Anyway, I've officially made the purchase of an Avalon Linear today, hopefully it'll be on the way from Germany very soon!

Thanks again.

Congrats on your new aquisition! I'm sure you'll be pleased with it and we look forward to seeing the images. Don't forget to post pics of the mount! ;-)

ChrisH