Peterson EZ Focuser issues

[Rodstar]

:astron:

I have had a quiet night in with my scope, installing the Peterson EZ Focuser. I am a complete ignoramus about anything "gadgical", but the instructions were plain as day, and I didn't have any probs.

A couple of questions for those who have installed one in their Meade SCT before:

1. I am a wee bit concerned that I have not put enough grease on it. It does not feel "buttery smooth" as the instructions suggest it might. It is reasonably smooth, though. How have other people found it when they installed it? Does it smooth out fully after a bit of use, or do you think I should open her up and whack on some more grease?

2. I assume the "backlash" that this gadget is supposed to avoid is the tendency for the image to move a little out of focus again when pressure is taken off the focuser knob. If so, this has definitely addressed that problem. HoweverI still have the problem that when I am turning the focusing knob the object moves around a bit in the frame of view, as if the mirror is not quite stable. Is this something the EZ focuser should also address, or is this something we SCT owners just have to put up with?

Any advice greatly appreciated!


:cheers:

[rumples riot]

Sorry Rod this is one mod that I have not yet attempted. I can't really help. Is it supposed to stop image shift? If so I will have to look into it. I am so sick of image shift when I am focusing.
I hope that someone will have some knowledge to help you out.

[atalas]

Hey Rod is there any screws on it to change the tension?


Louie:confuse3:

[[1ponders]]

Hi Rod Apparently the EZ Focuser won't remove the mirror shift problem. It is inherant with most SCT focuser designs. The new RCX Meades get around it by focusing using the secondary mirror and not the primary. I found this quote on the EZ focuser site

quote
"Typically, another 8% of the focuser backlash is due to mirror shift. Your SCT’s primary mirror assembly rides up and down the scope baffle tube to achieve focus. The focus mechanism is attached to a point way out on one edge of the mirror assembly. If the mirror assembly doesn't fit tightly around the outside of the baffle tube, the mirror will "wiggle" a bit from side to side if you push and pull on one edge (which is what the focuser does). THIS WIGGLING IS WHAT WE CALL MIRROR SHIFT. You will be turning the focuser knob while the mirror is shifting, but since the center of the mirror isn't moving until the mirror has completely shifted, you will be experiencing focuser backlash during this period of time.

The EZ Focus kit does not address this secondary backlash source directly"

end quote

Glad the new kit does what its supposed to.

[iceman]

The image shift sounds like on a newt, when you adjust at high powers, and the image wobbles about.. With rack'n'pinion focusers you can adjust the tension to make focusing smoother, but then you'll get slop in the tube.

Premium crayford type focusers get around this with fine and course focus knobs, with 8:1 or 10:1 ratio, so there's less image shift when focusing.

Alternatively, motorised focusers should keep it smooth.. does it wobble about when you use your microfocuser?

[xstream]

Hi Rod, you'll find the mod a great improvement in focusing; unfortunately it won't help the mirror shift.
I also found after a month or two of use I needed to dissassemble, make the the Top Hat a bit smoother with emery cloth and re-grease. Since redoing a second time the focuser has never been better.

[rumples riot]

Mike, just to clarify, the image shift that occurs with a SCT is different from image wiggle in a Newt. What happens visually is that the image will move across the FOV and often out of the FOV. as already stated the mirror moves when doing coarse focus and it is this movement of the mirrror that causes the image to shift. This is very frustrating as you need to move the scope in RA and DEC to recentre the image. My scope has considerable image shift now after 12 months, so much so that in a 26mm EP it will shift from centre to almost out of the FOV. The pattern is a little consistent and this means I can account for it most of the time. The only time this becomes a real problem is under high magnification for planetary work when going from the EP to a powermate insertion. The coarse focus must be changed and the image will shift out of the field of view and so focus must be done incrementally interspersed with moving the scope so that the image stays in view.

However once the coarse focus is achieved the micro focusor works perfectly to get sharp focus. You don't get any image wiggle or movement. The reason for this is that the MF is screwed to the visual back of the scope and only moves in and out like a Newt Focusor. It does not have any relationship with the Mirror which must move to obtain coarse focus. The motors of the MF are very smooth and do not vibrate. The amount of travel that the MF has amounts to around 15mm at most from close in to full out. Unfortunately it has limited applications in relation to Prime focus photography. Mounting a camera on the MF will prevent the camera from passing through the forks and will result in either damage to scope or camera. So when imaging in prime focus the issue of image shift rears its ugly head yet again.

Hope that this explained image shift better.

[[1ponders]]

Paul I found I had that problem with my 8" so I fitted a socket over the focuser (used a slightly larger socket and firmed it using blue tac sonot to put too much strain if over ran the focuser)attached it to a battery drill with a torque setting and set it to the lowest setting and wound the focuser in and out all the way to spread the grease more evenly. It made a huge difference in mirror shift. Hardly moves at all in a barlowed 6mm eyepiece.

[rumples riot]

Might have to try this. Because the scope is permanently house out side under a tarp it might be getting a little stiff with the grease. I will do the in and out all the way.

Thanks for that Paul.

[Rodstar]

Thanks for all of those valuable comments guys!

It does sound like what I've done is fine...very reassuring.

Like you, Xstream, I might do a re-grease in a few weeks just to smooth things out a bit more.

Mike, as the others have said, there is no image shift with the microfocuser. I must say, though, that I much prefer manually bringing an image into focus. I love the sudden and dramatic act of bringing something from a blur into sharp focus...it takes the breath away with something like Omega Cent or 47Tuc. I am assuming that a crayford style focuser cannot be fitted to a SCT? Is it just for Dobs??

[h0ughy]

Hi RodStar,

This topic may explain the odd shape of your focus knob that i experienced on Saturday Night.:P :P

I have severe mirror shift in my scope, and focusing is becoming more of a problem of late.

How much was your Peterson kit? I have been talking to Mick Pinner and swapping Meade sob stories and Mick is putting me onto a focus fix for my scope. I can only try it and see. He is mailing me some information on this.

[[1ponders]]

Paul if you're going to give the drill option a go, the reason I used the drill is that I ran it all the way in and out 3 times. I tried to find the web page that suggested it but without luck. "They" suggested about half a dozen times if I remember correctly. I found no great improvement after 2 times but gave it one more for good luck :)

[Rodstar]

HOughy,

The EZ Focuser kit was $69 from Bintel.

It doesn't address mirror shift if that is what you are after. It only helps with smoothing out the manual focus.

The knob shape is the standard shape for focusers in LX200s of THIS century!!

See you at the next star party.

[mick pinner]

l bought the E-Z focuser kit from Bintel as well, paid about $65.00 when it arrived l noticed that the bearings were made by Timken so being curious l rang the local bearing supplier l use for work and guess what they cost $4.15c each all you need apart from these is a 1/4" threaded bolt 50mm long cost 85c, a small allen key and a tiny bit of graphite grease, if anybody is interested l can make a copy of the instructions and send them to you, by the way the kit works absolutely great in my 12" and by moving the mirror back and forth with the bolt inserted into the mirror lock hole it has virtually eliminated mirror flop everything is explained in the instructions.

[Rodstar]

Mick, when you speak of "moving the mirror back and forth with the bolt inserted into the mirror lock hole" you have lost me. Can you explain another way?

I would love to nail this issue of mirror flop. Seems to be a huge issue for all Meade SCT owners.

Looking forward your further comments.

[mick pinner]

hi Rod, as the mirror moves in it's normal focusing operations the grease which surrounds the mirror becomes uneven therefore allowing the mirror to flop from side to side, on the lx classic you hold the mirror in place by way of inserting the supplied bolt in the mirror lock hole while you remove the focuser, before you replace the focuser you move the bolt back and forth which in turn moves the mirror along it's full length of travel redistributing the grease evenly around itself and so placing even pressure on the mirror at all times, on all other models this is done with the focuser mechanism just before it is secured back into place.

[h0ughy]

My scope must be an antique, at it was last century's. I like quality, maybe if Ed looks the other way I'll borrow his new century scope!!:D

[Rodstar]

Thanks Mick, I'll give it a go this weekend, and let you know how I go....I've got a new scope (purchased in Jan 05), so I do what you have described with the focuser shaft.

HOughy, I have envy of Ed's scope too! A seed has been planted...maybe in 5 years or so I might start the journey of building my own Obsession.

[atalas]

Hey Rod ! Ed told me he spent two years building his.
Start now!


Louie:work:

[h0ughy]

Rodstar

If you want seeds then hang around George for a few more hours and you will be hooked. You will think of it while eating dinner, you will see bigger scopes when you drive, you start seeing things everywhere, it is insidious and uncontrollable then you finally commit. The Dark side is very powerful, feel the force........................:fight :

[Rodstar]

:astron:

Actually, today I made the fatal mistake of dropping into York Optical in Sydney.....I have discovered the Celestron C20 Astrograph, which costs a lazy $75,000...and so, my life mission has been established....convince my wife that our mortgage really isn't as big as it should be, and that we need a 20 inch, state of the art Dall-Kirkham design observatory quality telescope.

What do you think my chances are?

:whistle:

[h0ughy]

Rodstar,

I think you would be supernoved and then black holed!:P

But what a way to go:cheers:

[Rodstar]

Even if it led to divorce, I guess I'd have lots of IceinSpace friends?!

[h0ughy]

Yes too many:whistle: