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10 hours ago, John said:

Thats odd - when I tested the Myriad 20mm I seem to recall it came to focus in my 12 F/5.3 OO scope at about the same place that the 21mm Ethos does - plus or minus a mm or two :icon_scratch:

Just spoke to John at OO. He said try moving the mirror forward or something but it confused me. (I’m not that good at adjusting the mirrors yet but will get used to it). He said he thinks it’s a faulty eyepiece but I’m going to buy a 2” focuser extension off him anyway. I had to not fully insert the eyepiece for it to focus, but like just on the edge barely holding it in. 

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To be "faulty" in that way the field stop and internal optical elements of thye eyepiece would have to be moved within the body of the eyepiece by a large amount which, as far as I can tell from what I know of the design, is virtually impossible unless someone has dismantled the eyepiece and re-assembled the elements (there are about 7 or 8 of them) completely incorrectly.

It would be very unsual for OO to blame their own scope though :wink:

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Worth trying to see if you can reach focus by pulling the eyepiece and extender out of their positions a little way to see how much you need.

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A faulty eyepiece is one of the least likely causes. If it's just a few mm away from focus then using the adjustment bolts to move the mirror is easy enough to try 

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Posted (edited)
9 hours ago, MSammon said:

He said try moving the mirror forward or something but it confused me.

Forward?

This confuses me too...

These scopes collimate easily- you have a cheshire? I think moving the mirror forward (towards top of tube) pushes the focus point out- wrong direction for you. If you move it back it should suck the focus in the other direction ( which is what you want). Tighten the collimation bolts until they lightly bottom out, back them off 1/2 turn each and collimate. Tightening the bolts shorten the springs, pulling the mirror back,then check your focus.

Of course I could be wrong- I'd hate to argue with OOUK...😀

Edited by jetstream
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9 hours ago, John said:

It would be very unsual for OO to blame their own scope though :wink:

😁

 

9 hours ago, MSammon said:

He said he thinks it’s a faulty eyepiece but I’m going to buy

🤣🤣

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Posted (edited)
13 minutes ago, jetstream said:

Forward?

This confuses me too...

These scopes collimate easily- you have a cheshire? I think moving the mirror forward (towards top of tube) pushes the focus point out- wrong direction for you. If you move it back it should suck the focus in the other direction ( which is what you want). Tighten the collimation bolts until they lightly bottom out, back them off 1/2 turn each and collimate. Tightening the bolts shorten the springs, pulling the mirror back,then check your focus.

Of course I could be wrong- I'd hate to argue with OOUK...😀

"If your mirror cell is the same as mine you can lower it a bit,therefore achieving focus."

Edited 20 hours ago by paul mc c

This is what i said in my post,the primary mirror cell has 2 sets of holes upper and lower where the three bolts are,if you caerfully take these out you can drop the cell and use the upper holes in the cell therefore possibly letting you use your eyepiece with out an adaptor.

Edited by paul mc c
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1 minute ago, paul mc c said:

If your mirror cell is the same as mine you can lower it a bit,therefore achieving focus.

Edited 20 hours ago by paul mc c

This is what i said in my post,the primary mirror cell has 2 sets of holes upper and lower where the three bolts are,if you caerfully take these out you can drop the cell and use the upper holes in the cell therefore possibly letting you use your eyepiece with out an adaptor.

Yes, thanks. Mine has 2 sets of mounting holes in the cell edges giving flexibility to the focus point. This in combination with adjusting the bolts gives a good range.

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Posted (edited)

When i purchased my 12 F4 i asked John to fit the Moonlite which was on my old scope.

It is a non standard 60mm drawtube version which together with the spacer options will focus just about anything.

I got the 60mm drawtube because i use a 'Powerswitch binoviewer' and it has a fair amount of focus travel between the 'low' and 'high' power settings.

The Moonlite also gives me a little bit more stability which i need with a 2.5kg load.

I've been pleased with my F4.

Great rich field, low power views with the bino and the scope fits nicely across the back seats as well.

30822666498_7c117222de_b.jpg

Edited by Tubby Bear

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Does the tube not cut into the light path with that setup? That's one advantage of extension tubes, you keep the draw tube short and out of the light path.

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Posted (edited)

Fully racked in, yes the focuser tube is just in the lightpath, but its not too bad. I certainly haven't noticed degraded views or anything. A 12" mirror compensates well.

And when i'm in mid or high power mode and racked out, no issues.

One problem with extensions is that with a big heavy 2" eyepiece in the 1kg range,

you can put quite a bit of strain on the focuser, especially if its not a terribly good quality one.

My old OO focuser was in that category.

Fully racked out with a 2" there was noticable sag on the tube, although you can't fully see it from this image.

More of a worry was the security of the eyepiece itself.

21144920368_1a720d2519_b.jpg

 

 

Edited by Tubby Bear

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I tested all my newts for focuser sag and the resultant miscollimation- in the OOUK's it wasn't just the focuser, it was the aluminum tube deflecting. Te good news is that this only happened with very heavy eyepieces. I made a weight simulating eyepiece/binoviewers for the tests. If anyone notices image degradation in fast OOUK newts with binoviewers this is the first place I'd look.

I really don't know why OOUK pushes the focus out so far requiring an extension adapter. If they ran the focus point closer in they could shrink the size of the secondary and eliminate the tube deflection IMHO.

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17 minutes ago, jetstream said:

I really don't know why OOUK pushes the focus out so far requiring an extension adapter. If they ran the focus point closer in they could shrink the size of the secondary and eliminate the tube deflection IMHO.

I guess it is related to imaging Gerry, so there is enough inwards focus for their requirements.

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It's not OOUK's fault. It's eyepieces / imaging devices / 3rd party focusers / the speed of light that are wrongly configured :wink:

 

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22 hours ago, John said:

If and when you decide to go for a Moonlite focuser, go for the 10 inch tube fitting kit. The 12 kit fits Skywatcher, GSO, and Orion (USA) tube diameters but Orion Optics tubes are a bit slimmer so the 10 inch kit is a much better fit I found.

Orion Optics tend to position the focal plane of the primary mirror further outside the tube wall than the other manufacturers I've mentioned here (the slimmer tube plays a part in that) which is why you need extension tube(s) or the Moonlite risers to get eyepieces to reach focus.

I can help the OP there.....

My old scope was a 10" F6.3

I've still got the Moonlite 10" fitting kit somewhere. He can have it gratis if he wants it.

(btw : i used the 12" kit on my 12F4 as i thought i should, and afaik it was and looks a perfect fit)

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Yep, I saw that one as well. I would have gone for it had I been in the country at the time...I knew it would be gone by the time I got back.!

Congrats on a great buy.

RL

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Add a foot long extension to the top of the main tube from, say, lightweight camping mat.This will keep stray light from entering the main tube.

Manufacturers persist in making their main tubes too short at the top, probably to make them look more portable.

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4 hours ago, Merlin said:

Add a foot long extension to the top of the main tube from, say, lightweight camping mat.This will keep stray light from entering the main tube.

Manufacturers persist in making their main tubes too short at the top, probably to make them look more portable.

Agreed. I use a "half moon" light shield around the top of my tube on the side where pesky local lights have been known to shine and it has improved contrast noticably on DSO's. 

 

 

oo12dob04.JPG

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Interesting spider design they did back then. I wonder why they discontinued it ?

 

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1 hour ago, Tubby Bear said:

Interesting spider design they did back then. I wonder why they discontinued it ?

 

It was an option that OO offered for a few years but not enough demand aparrently and it was harder to fabricate I believe.

I still get diffraction of course but it's spread evenly across the field of view. No "spikes" either side of brighter stars. They were fitted to the scope when I purchased it (used) and I've seen no reason to change them.

Martin Mobberly opted for the same pattern when he comissioned his 10 inch F/6.3 from OO:

https://www.cloudynights.com/articles/cat/user-reviews/telescopes/dobsonians-10-40/orion-optics-250mm-f63-spx-newtonian-r621

My scope is the 12 inch F/5.3 version of his.

 

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Great stuff.. hope you enjoy your views... Clear skies.

 

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i saw one of these last week very nice ,the chap had fitted encoders  and a moonlite focuser i think too very nice setup indeed 

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This is my focuser fully extended. As you can see they do a longer one. Just emailed John about upgrading mine.

064F0051-C29D-4AED-8789-1E4DE6FEFD01.png

0536B529-1332-40FA-B3BF-1D7C528F7BCD.jpeg

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