Flattener spacing

[ollypenrice]

Great that Ian posted this because I was about to say that I vaguely remembered some graphics from TS on this subject. I now remember that it was in an earlier post by Monisieur Bird that I first saw them. This time I'll have the wit to copy the link!

Another possible source of error on these scopes might arise from the front cell and its three pairs of push-pull adjusters. They might be sending the beam just a whiff off axis down the tube. 

Olly

[swag72]

I remembered this excellent graphic and did copy it I do seem to remember though that great pain was made to say that this was specific to the Ricarrdi reducer and not to others - Hence why I didn't post it earlier. Please correct me if I'm wrong

[blinky]

Yep, I never saw this effect, it seemed that I always got the same pattern which led me to keep making the spacing greater, in actual fact sticking it back to 55mm has improved it, along with rotating the focuser

[ian_bird]

I remembered this excellent graphic and did copy it I do seem to remember though that great pain was made to say that this was specific to the Ricarrdi reducer and not to others - Hence why I didn't post it earlier. Please correct me if I'm wrong

Hi.

I think it applies to any flattener - not just the Riccardi. I just mentioned the Riccardi because that is what I am using.

And yes - I have seen the "Too Far Away" radial pattern. Had to deliberately go too far away - but it was clearly there.

Cheers

Ian

PS - It's the guys at Teleskop Service who deserve praise for this. They sent it to me in reply to a query on the correct spacing for the Riccardi.

[ollypenrice]

Yep, I never saw this effect, it seemed that I always got the same pattern which led me to keep making the spacing greater, in actual fact sticking it back to 55mm has improved it, along with rotating the focuser

Having a change when rotating the focuser is not good news though. Something is off axis or tilted. In the real world of imaging you're going to need to rotate your chip somehow, by whatever means.

Olly

[ian_bird]

Great that Ian posted this because I was about to say that I vaguely remembered some graphics from TS on this subject. I now remember that it was in an earlier post by Monisieur Bird that I first saw them. This time I'll have the wit to copy the link!

Another possible source of error on these scopes might arise from the front cell and its three pairs of push-pull adjusters. They might be sending the beam just a whiff off axis down the tube. 

Olly

Hi Olly

Could I ask you a question? Can the front cell go out of alignment? That is to say - if it was aligned - can it lose that alignment. Say for example if I had been in the South of France and the front cell, Riccardi Flattener, focuser and ccd were all perfectly aligned and I was getting perfect images - and then I drove back to the UK. Could the transportation cause the cell to move? Or are they not that sensitive?

Or to put it another way - it was all working perfectly when I was at your place. Now I am home - I have perfect stars top and bottom on the left - and eggy ones top and bottom on the right.

Personally - I think the sky above Les Granges isn't completely flat. I think the stars on the right are closer than the ones on the left.

Occam who?

Love to Monique as always. Just had one of her salads. Mmmmm! - Monique Salad! My wife is a salad nutter - it's all she eats. And she begs me to make salad the way Monique taught me!

Cheers

Ian

[Earl]

I found that getting a variable spacer which povided a full range of movement was the best plan, but use it without any other things like oags, filter wheels.

The makes it easier to use and then work out what is needed for the reducer / flattener, then once you have it right add the other things in and you hae a number to work off for extensions.

Yes this is a little more expensive as you wont use it in the final setup, but makes getting these critical measurements far easier.

[Owmuchonomy]

Great that Ian posted this because I was about to say that I vaguely remembered some graphics from TS on this subject. I now remember that it was in an earlier post by Monisieur Bird that I first saw them. This time I'll have the wit to copy the link!

Another possible source of error on these scopes might arise from the front cell and its three pairs of push-pull adjusters. They might be sending the beam just a whiff off axis down the tube. 

Olly

I did as I was told Olly and checked for these adjusters. As I too don't often have my wits about me I couldn't see anything at the front cell other than 4 sets of 3 tiny Allen screw adjusters! It was a bit daunting for me to attempt a remedy so I will wait to hear from Altair first. I got out the SCT and did some guiding/imaging with that. I was quite chuffed with my efforts especially on M27.

[Owmuchonomy]

Hi

I was the person who posted the "too close" "too far" pictures. They came from Teleskop Service - and they work for me. I have seen both effects.

Too Close.

too close.jpg

Too Far.

too far away.jpg

It really does work! Honest. Well - it worked for my Riccardi Reducer/Flattener on my WO98.

Cheers

Ian

Beautifully brilliant. I see the top scenario in my set up which is reported to have +/- 5mm of tolerance with my sensor. Clearly not. Thank you very much for your input. I will go away and think on it.

[ollypenrice]

Hi Olly

Could I ask you a question? Can the front cell go out of alignment? That is to say - if it was aligned - can it lose that alignment. Say for example if I had been in the South of France and the front cell, Riccardi Flattener, focuser and ccd were all perfectly aligned and I was getting perfect images - and then I drove back to the UK. Could the transportation cause the cell to move? Or are they not that sensitive?

Or to put it another way - it was all working perfectly when I was at your place. Now I am home - I have perfect stars top and bottom on the left - and eggy ones top and bottom on the right.

Personally - I think the sky above Les Granges isn't completely flat. I think the stars on the right are closer than the ones on the left.

Occam who?

Love to Monique as always. Just had one of her salads. Mmmmm! - Monique Salad! My wife is a salad nutter - it's all she eats. And she begs me to make salad the way Monique taught me!

Cheers

Ian

Hi Ian,

The truth is that all these darned things are so fickle. A refractor shouldn't lose collimation in car transportation, certainly not. I suppose a focuser might develop a bit of tilt, as might a camera if given a bump, but I'd be more inclined to suspect a chance gremlin in the way it all fits together. That is, the various attachments. Does the Riccardi have any kind of fine tilt adjustment? The Tak FSQ reducer does have three tiny allen keys radial to the light path.

Olly

[ian_bird]

Hi Olly

Thanks for that. I did wonder. I suspect you are right - will check everything is cinched up tight and square.

No - the Riccardi does not have any adjusters. But there are three small screws in the corners of the sky. Do they do anything?

Now - all I need is a 100 mile long screwdriver!

Cheers

Ian

[Uranium235]

This thread confirms what I have suspected for some time (coma = too short, radial = too long). In fact it might be worth stickying because its such a common problem, which also applies to coma correctors (ive seen it from my newt).

[blinky]

I don't see the coma pattern and I had my spacing at about 58mm brought it back to 55amd it's much better

Sent from my HTC One mini using Tapatalk

[ian_bird]

Hi Ian,

The truth is that all these darned things are so fickle. A refractor shouldn't lose collimation in car transportation, certainly not. I suppose a focuser might develop a bit of tilt, as might a camera if given a bump, but I'd be more inclined to suspect a chance gremlin in the way it all fits together. That is, the various attachments. Does the Riccardi have any kind of fine tilt adjustment? The Tak FSQ reducer does have three tiny allen keys radial to the light path.

Olly

Hi Olly

I took it all apart (needed to swap out the filter wheel as I had busted the old one*) and re-fettled it all.

Worked perfectly! So thanks - you were spot on!

Cheers

Ian

* I tugged the scope cover down not realising it had snagged on the filter wheel USB cable. Snapped the port off from the circuit board. Turns out to be the best thing I ever did. The busted FW was the most cantankerous, unreliable, infuriating pile of junk ever. The new one just works!

[knobby]

Thanks all, what a great thread