Focusing the Edge

[Bob Dobber]

Hi all - hopefully someone can give me some ideas here, but I'm all out at the moment. Am convinced that this is "user error" but not sure what else I can do. Got the Edge 8 with Pegasus Focus Cube Zero and I've been having trouble with repeatibility of focus positions. Last night, for example, at around 34000 on the scale, I got good focus on my L-Pro filter, repeated this again, and got the best AF run in NINA I think I've ever had, certainly on this scope. My step size was (I think) tiny, 15, any more and when NINA moves out 3 or 4 times this, the image is so blurred it can't pick anything up to calculate an HFR value, so I think this step size is about right, but could be totally wrong somehow.

Anyway, after I got these two AF wins (rare at the moment), I kicked off a sequence in R filter feeling confident, and nothing again. The focus was no good and AF failed, so I thought I would go back to the L-Pro and 34000 to get back to a known point. Nothing. I re-found focus this time at around 33750 (250 away, when even about 50 already pushes focus way out) so I am really unsure why I can't repeat the focus point.

 

Questions in my head abound regarding the mirror locks - I gather I am meant to not lock the mirrors when focusing, but I undid them til loose. Should they still be reasonably snug, even if not tight? I compensated for backlash a little and as you can see from the screen grab below, it seems _capable_ of doing it, it's just what on earth happens in between to make it lose focus.

 

Pretty much about to admit defeat here, but I am clinging onto the assumption that I am not actually a numpty and it's just a misconception holding me back... 

 

Thanks for any help...

 

edit: here's my best AF result (in NINA)...

 

Edited May 5, 2022 by Bob Dobber

[+Ibbo]

Always do your final focus anti clockwise on an SCT.

 

 

 

have a look at this.

 

 

Edited May 5, 2022 by Ibbo

[Bob Dobber]

Just now, Ibbo said:

Always do your final focus anti clockwise on an SCT.

 

have a look at this.

 

 

 

Thanks yeah, I have tried it both ways actually, but have this evening made sure that I have the backlash on the correct side to ensure it always ends with an anticlockwise turn. The "Focus Cube Zero" is meant to be zero backlash, quite what that means in practice, who knows.

[+Graham]

Sounds like you are suffering from a condition known as mirror flop, a common thing with an SCT.

When funds allow you should consider getting yourself a duel speed focuser that screws onto the visual back of you SCT.

Then you can rough focus using the SCT's focus knob, lock off the mirror in this position and do all remaining focusing with the duel speed focuser.

Once rough focus has been obtained and the mirror locked off you will never have to adjust it again as you will do all fine focusing using the duel speed focuser.

This completely eliminates all your problems. 

Something like this which I have on the back of my 10 inch Meade.

 

 

 

[Bob Dobber]

6 minutes ago, Graham said:

Sounds like you are suffering from a condition known as mirror flop, a common thing with an SCT.

When funds allow you should consider getting yourself a duel speed focuser that screws onto the visual back of you SCT.

Then you can rough focus using the SCT's focus knob, lock off the mirror in this position and do all remaining focusing with the duel speed focuser.

Once rough focus has been obtained and the mirror locked off you will never have to adjust it again as you will do all fine focusing using the duel speed focuser.

This completely eliminates all your problems. 

Something like this which I have on the back of my 10 inch Meade.

 

 

 

 

Sounds expensive 😞

 

Is there any other cure for mirror flop? I was considering taking it to Orion for a service, wondering if someone who knew what they were doing could work magic...

 

[+Bino-viewer]

I thought the Edge HD scopes had those mirror support knobs on the back of the tube to hold the primary still and eliminate mirror shift etc ??

[Bob Dobber]

5 minutes ago, Bino-viewer said:

I thought the Edge HD scopes had those mirror support knobs on the back of the tube to hold the primary still and eliminate mirror shift etc ??

 

As far as I'm aware I'm *NOT* meant to lock off the mirror when I am imaging and likely to refocus unattended during a session?

Edited May 5, 2022 by Bob Dobber

[+Graham]

The very design of an SCT means mirror flop is unavoidable.

The Edge is a vast improvement on the Meade but it will still suffer from the condition.

It only takes a fraction of movement to introduce all sorts of issues especially if you are auto focusing throughout an imaging session.

 

An add on focuser can be picked up on Astro buy and sell for a reasonable price.

Edited May 5, 2022 by Graham

[Bottletopburly]

I’d read the thread on sgl about Orion optics before considering sending away for a service.

[Bob Dobber]

1 hour ago, Bottletopburly said:

I’d read the thread on sgl about Orion optics before considering sending away for a service.

 

Ummm, did a quick search, *which one* exactly?? 😉 😮 There seems a few!!

[Bottletopburly]

2 hours ago, Bob Dobber said:

 

Ummm, did a quick search, *which one* exactly?? 😉 😮 There seems a few!!

This one https://stargazerslounge.com/topic/393897-orion-optics-puts-uk-engineering-to-shame/#comment-4236875

[Bob Dobber]

11 hours ago, Graham said:

The very design of an SCT means mirror flop is unavoidable.

The Edge is a vast improvement on the Meade but it will still suffer from the condition.

It only takes a fraction of movement to introduce all sorts of issues especially if you are auto focusing throughout an imaging session.

 

An add on focuser can be picked up on Astro buy and sell for a reasonable price.

 

Thanks. I think people have been saying that an add on focuser for the Edge is tricky due to backfocus issues. Do you know of a solution that just works? The ones people suggest elsewhere seem to almost encase the reducer somehow...

[+Graham]

Rob you are now in the world of the Darkside.

You have just learned your first valuable lesson.

There are no "quick fixes" or solutions that "just works" because every set up and situation is different.

You will soon discover that a set up that works perfectly one night will produce nothing but frustration the next night.

Everything plays a part in this game.

Temperature, moisture content in the air, Altitude you are imaging at, What day of the week it is 😂 you get the idea. 

[Bob Dobber]

5 hours ago, Graham said:

Rob you are now in the world of the Darkside.

You have just learned your first valuable lesson.

There are no "quick fixes" or solutions that "just works" because every set up and situation is different.

You will soon discover that a set up that works perfectly one night will produce nothing but frustration the next night.

Everything plays a part in this game.

Temperature, moisture content in the air, Altitude you are imaging at, What day of the week it is 😂 you get the idea. 

 

Oh believe me I am fully aware of that after two fun packed years at this. No time at all I know, but in that time I've been through about 5 or 6 camera, 4 telescopes, colour, mono, filter drawer, this that and the other, and yes, apart from the original refractor I had (still regret getting rid!) none of the rest ever "just worked". That's the way in this hobby though: get to a point where you think you're winning then it's imperative that you then say to yourself "I think I need to change everything" so you're back to the very start again!

 

PS - I get the impression that many solutions for the Edge _are_ designed just for the Edge so maybe a bit more than other scopes, it seems to be one that products are designed specifically for...

Edited May 6, 2022 by Bob Dobber

[Bob Dobber]

Anyone wanna buy an Edge HD8? 😪 (only half kidding)