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 Post subject: need help on focusing
PostPosted: Wed Apr 17, 2013 2:59 am 
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I was out tonight, [or should I say this morning. 1.30 to 3.00am] and saw Saturn for the very first time.
Found Saturn through the finder scope and put in a 25mm eyepiece and focused in nice and sharp no problem, then tried it with a 18mm piece and re-focused got that nice and sharp.
but when I tried it with a 2x Barlow I could not find it for the life of me and I still had Saturn in the middle of the finder scope, is there something I'm doing wrong? Is the finder scope set up wrong.
It was the same with the CCTV cam, at no magnification I could find Saturn but when I tried to Barlow it I lost all together.

Should I align the finder scope with a Barlow and eyepiece on a star, because what I have done was to point it at a star with a 25mm eye piece in and get it roughly in the middle and then adjust the finder onto the cross hairs.
I have a 12.5mm illuminated eyepiece coming sometime this week and will try that.


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 Post subject: Re: need help on focusing
PostPosted: Wed Apr 17, 2013 7:00 am 
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John, the first suggestion I'd make is to practice with your Barlow on a daytime terrestrial target - a distant chimney-pot or TV aerial, rather than wasting those precious clear nights.

Inserting the Barlow-lens with any eyepiece will reduce the field-of-view (with a x2 Barlow you'll get around one quarter the area) and move the focus position some way. From your daylight tests you should get an idea of how far to turn your focus-knob.

If the Moon is in view, it should be easy enough to find this with your Barlow-lens fitted, and then focus on some craters.
Then when you're aiming at Saturn, before switching to the Barlow first centre the planet in the eyepiece (don't worry about the finder), and then take care not to nudge the 'scope when swapping the eyepieces over (a non-whackery mount makes this easier!).

If you're way out of focus then the image of the star (or planet) will be spread out into a large faint disk, so turn the sensitivity of your camera up to maximum (or use longer exposures), and you may see a part of this disk on your sensor, enabling you to get it centred and better focused.
:idea: But for high-magnification imaging with a small sensor (a webcam or your CCTV camera), a flip-mirror would be a very worthwhile investment. Then finding your target and getting it close to focus is "simples"!


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 Post subject: Re: need help on focusing
PostPosted: Thu Apr 18, 2013 11:25 pm 
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Hi Ross, did like you said and tried it at the church flag pole about 1/2 mile away.
well now i know which way to turn the focuser with the 2x barlow in.

It was only about 1/2 turn clockwise, then I tried it with a 3x, but i think i'll give that a miss because it was very fine to get into focus. Didnt try the cam will have a go another day.

i was wondering if I should change the finder, I think the one that is on is 6x30, maybe go for the 9x50. I've got a red dot finder attached to the arm of the finder and they are both lined up together more or less.


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 Post subject: Re: need help on focusing
PostPosted: Fri Apr 19, 2013 8:56 am 
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OK John, you'll also need to know how far to move the focus when switching from the eyepiece & Barlow to the camera & Barlow. Then once you've got the focusing sorted, your only problem will be pointing.
When using a 1/4" sensor on the back of a 1.2m telescope with a Barlow-lens, I reckon that you'll need to get within 5 arc-minutes of the target before you see it on the sensor. You'd need to be very lucky to manage this using a finder-scope - much better to centre the image in the main 'scope as you step up the magnification (or use a flip-mirror with a cross-hair eyepiece as I do).


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 Post subject: Re: need help on focusing
PostPosted: Fri Apr 19, 2013 11:50 am 
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John, when using web camera for imaging this I tend to do

First I find the object using an eyepiece that I know roughly achieves the same focus as the web camera. A good test would be to use a terrestrial object so play around in the daytime. Either way fined an eyepiece that roughly matches your web camera focus

After finding the object with the eyepiece make sure the DEC and RA knobs are locked off and the mount is tracking. I then insert the web camera into the scope and reset the web camera to all the defaults setting on the software (gain, brightness, contrast etc..). It's one less variable to think about at this moment in time such as "is the camera working?"

Sliding the web camera in and out to achieve some focus or watching for pixel change on the screen also helps tell me if the object is in view.

Still the screen produces a lot of noise, the object will be over exposed, but once I usually see the edges of the object I start playing with the focus adjuster. Only then do I start playing with the gain, brightness, contrast etc. until I see detail

Depending on the tracking I then move up-to the x2 Barlow and again I follow the above.

Now the above may not suit and you'll devise you own system but its all patience, practice and knowing your setup.

_________________
Celestron 11" Telescope
Eq6 Pro Mount
Eq5 Mount
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Cannon 1000D SLR Camera

I choose to image with an 11" SCT Celestron in this decade and do the other things, not because they are easy, but because they are hard......


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 Post subject: Re: need help on focusing
PostPosted: Sun Apr 21, 2013 2:18 pm 
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The new eyepiece came yesterday and I've been playing with it. its very similar to the cctv focal length.Tried what Carl said about sliding it in and out of the focuser but would need a small extension tube to get it parfocal with the cam.

what a did again this time with the new eyepiece was to get the tip if the flag pole in the crosshairs, and swap it with the cctv cam with the barlow and found the tip of the flag pole had dropped right down to the bottom in the fov.

So it looks like I need a flip mirror like Ross said and collimate the eyepiece with the cam.
I'm correct in thinking this will do. I've been looking at the starbrite flip mirror which as a helical eyepiece adjuster and you can adjust the flip mirror too


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 Post subject: Re: need help on focusing
PostPosted: Sun Apr 21, 2013 3:35 pm 
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Hi John

I think this is what your trying to do, the only difference is that in this case I have a DLSR rather than a WebCam/ CCD

I use a 24mm eyepiece parfocalled with camera so once I have the object in sight and in focus in the eyepiece all I need is a few test frames to fine focus the camera.
Attachment:
Flip Mirror.jpg
Flip Mirror.jpg [ 211.15 KiB | Viewed 8024 times ]


Bill


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 Post subject: Re: need help on focusing
PostPosted: Sun Apr 21, 2013 6:19 pm 
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jpinna wrote:
So it looks like I need a flip mirror like Ross said and collimate the eyepiece with the cam.
I'm correct in thinking this will do. I've been looking at the starbrite flip mirror which as a helical eyepiece adjuster and you can adjust the flip mirror too

This is how my planetary camera system is arranged:
Attachment:
planetarycamera.jpg
planetarycamera.jpg [ 29.83 KiB | Viewed 8017 times ]

My Parks Optics Barlow lens is on the front, and the extra separation due to the flip-mirror assembly gives it more magnification.
Then on the rear camera port I've added a 5mm extension T-ring, so that the camera is nearly parfocal with my eyepiece (a Celestron 25mm SMA with a cross-hair reticule in the back).
The other metalwork on the front of the camera is a webcam-to-T adaptor, which includes an internal 31.5mm thread for my IR-blocking filter.
My flip-mirror is a simple one with no adjustments, but it's accurate enough that I can always get the planet's image onto my CCD, with or without the Barlow up front.


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 Post subject: Re: need help on focusing
PostPosted: Sun Apr 21, 2013 6:25 pm 
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jpinna wrote:
it looks like I need a flip mirror

Some examples of DIY projects:
http://stargazerslounge.com/gallery/album/1910-diy-flip-mirror/
http://stargazerslounge.com/topic/136137-home-made-flip-mirror-gina-style/
http://www.cityastronomy.com/flip-mirror.htm


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 Post subject: Re: need help on focusing
PostPosted: Sun Apr 21, 2013 6:27 pm 
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Location: Little Lever
yes Bill, thats the one I've been looking at.

Just found out one of the problems I've been having, or should I say what I have been doing wrong.

What I've been doing was to put the eyepiece in the diagonal and focus up, then remove the diagonal and put the cam into the rear cell of scope and that seems to throw everything out.

So now I use the diagonal for eyepiece and cam and went back to Carl's advice and setup the eyepiece to the cam and I had a parfocal ring and now I have both focused and with the barlow too. Only thing I have to sort out the FOV when I change over to Barlow, so hopefully if i get a split mirror that will solve that problem. cheers guys


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