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SCT focus problem


jkm13
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10sec X 3

hello.

my first edgeHD 8" sct image for M42 was not good.

it's too blur. i can't make sharp star point.

i made collimation and it looks good.

but even observing always blur like my shot.

tried every focus range but never show sharp star.

what should i consider more?

many suggestion would be thanks!

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hi.

i collimate with celestron collimator. not guided.

but my problem is act never not make sharp star at any try.

simply to say when focusing clockwise would be blur -> sharp -> blur.

but in my case blur -> less blur -> blur. 

this happens in observing too. could be product's problem?

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If you find a reasonably bright star and centre it in the eyepiece as it goes in to and past focus you see a round set of concentric circles that grow and shrink as you turn the focus knob.

Look on You Tube for some help.

It's possible that the secondary mirror has moved but then it shouldn't collimate.

Dave

Think you need 250 ? posts before you get an edit buttom

Edited by Davey-T
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The focuser on my 11" SCT (brand new) was absolute rubbish, so get e Feathertouch (FLO Sell them) and a Bahtinov Mask and you will be sorted......

http://www.firstlightoptics.com/starlight-instruments-feather-touch-sct-microfocusers/microfocuser-for-celestron-cpc-800-6se-c8edge-8se.html

I've bought and fitted one of the to my EdgeHD8 and it has made a big difference. I couldn't get jupiter focused for imaging with the standard focuser.

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Hi JKM (or whomever) - Welcome to SGL. Focusing on SCT's seems to be problematic with both Meade and Celestron. Seems they spent all their money on the optics, but let the mechanical end drop off a cliff. So there are a number of work-arounds. You are already aware of the Feathertouch. Pictured below is another - much less expensive - upgrade. Of sorts. Placing a larger diameter wheel over the focus-knob allows for a MUCH finer focusing job. Fancy wheels (as pictured) are just 'glam' for show. Some people use lids off jars of peanut-butter! :p

It really does help.

As for you, Dave: The Meade focus problem has been known and howled about for well over 10 years. Meade won't lift a finger. Aside from the above indicated "upgrade," there is an excellent kit available to change-out the internal parts - or lack of - the stock focusing-knob. The result is nothing short of spectacular! Coupled with a wheelie, my thoughts of using an electrical-focus flew away. I've installed the kit on both of my Meade SCT's. Here you go:

http://www.petersonengineering.com/sky/ez_focus_kit.htm

You might wish to check out the other kits Pete Peterson has assembled. I use several of them. His clutch kit for the declination is a life-saver.

Clear & Sharp Skies,

Dave

post-38438-0-91300400-1421032044.jpg

Edited by Dave In Vermont
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actually, was playing around with focuser mods on an SCT this weekend too (on this beast - http://stargazerslounge.com/topic/233947-school-observatory-finished/).

We've got a two-speed crayford focuser on the back of a Celstron Edge 9.25", so now can adjust focus via either the woefully inadequate SCT focusing knob, or by the crayford which gives much finer adjustment.  Would I be right in saying that the best way to do it is to put the crayford in about mid-travel, adjust the SCT knob to approx focus and lock the mirror down, and then adjust to fine focus with the crayford?  Or is there another way I should be doing it ?

(hope this isn't a thread hijack...)

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That's the way I do it, the really annoying thing about SCT focuser is not knowing where the mirror is, unlike a refractor focuser with nice graduation markings.

When swopping kit on it you have to wind it in and out to find focus, I did toy with the idea of fitting a digital counter on the focuser knob for reference but never got round to it.

Dave

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Strangely, I have had not big issues with my SCT focuser. Still got the original one after all these years (>19). Maybe I have become used to its foibles.  Many people do have issues with the focuser, however.  One thing to bear in mind is that the tube must be at ambient temperature. Any temperature difference between inside and outside of the tube results in hermal convection inside, effectively causing horrible seeing. If the tube is stored in a warm room, waiting for 45minutes after it has been put outside in the cold is essential to get a sharp image. The difference is huge. This is one reason I store my tube in a fairly cold garage.

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At F2.2 the depth of focus must be in the low 1/100 ths of a millimetre . At this F number the only working solution is a robotic focuser I would have thought.

A.G

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Hi JKM (or whomever) - Welcome to SGL. Focusing on SCT's seems to be problematic with both Meade and Celestron. Seems they spent all their money on the optics, but let the mechanical end drop off a cliff. So there are a number of work-arounds. You are already aware of the Feathertouch. Pictured below is another - much less expensive - upgrade. Of sorts. Placing a larger diameter wheel over the focus-knob allows for a MUCH finer focusing job. Fancy wheels (as pictured) are just 'glam' for show. Some people use lids off jars of peanut-butter! :p

It really does help.

As for you, Dave: The Meade focus problem has been known and howled about for well over 10 years. Meade won't lift a finger. Aside from the above indicated "upgrade," there is an excellent kit available to change-out the internal parts - or lack of - the stock focusing-knob. The result is nothing short of spectacular! Coupled with a wheelie, my thoughts of using an electrical-focus flew away. I've installed the kit on both of my Meade SCT's. Here you go:

http://www.petersonengineering.com/sky/ez_focus_kit.htm

You might wish to check out the other kits Pete Peterson has assembled. I use several of them. His clutch kit for the declination is a life-saver.

Clear & Sharp Skies,

Dave

attachicon.gifFine Focus Knob.jpg

Check the mirror lock is not partially engaged

actually, was playing around with focuser mods on an SCT this weekend too (on this beast - http://stargazerslounge.com/topic/233947-school-observatory-finished/).

We've got a two-speed crayford focuser on the back of a Celstron Edge 9.25", so now can adjust focus via either the woefully inadequate SCT focusing knob, or by the crayford which gives much finer adjustment.  Would I be right in saying that the best way to do it is to put the crayford in about mid-travel, adjust the SCT knob to approx focus and lock the mirror down, and then adjust to fine focus with the crayford?  Or is there another way I should be doing it ?

(hope this isn't a thread hijack...)

I own a Celestron C6 and a JMI Motofocus. Should I go with the kit or (gasp!) with a featherTouch... is this overkill ? Also, the kit seems to be only for Meade, is that correct ?

What is the mirror lock you are talking about ? I don't seem to have that on mine...

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in this pic...

https://www.intercon-spacetec.de/fileadmin/user_upload/ics-editoren/pg-40-4C/4C110H_03-celestron-edge-hd-1100-ota.jpg

...the cylindrical knob with the orange base is the focus knob, and the two conical shaped grey knobs at the top and left of the tube in the pic lock the mirror down after you've focused to prevent mirror flop.  Or so I understand it, new to this kit myself, we've not even got it polar-aligned yet.

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I use a micro touch focuser automated through focus-max. This is an expensive solution but since I've implemented it I've never looked back. It has made true focus so much easier. If you take long subs unless you have a low expansion mirror you need to refocus frequently to avoid your images gradually going out of focus as the night progresses. I'm investigating a solution called Sharplock through an on axis guider which checks  focus every time a guide camera image is taken and if required will refocus.

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