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Old 11-10-2014, 12:40 PM
astro.photo
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Astrophography Newbie

Hi All.

First off - great site. I have spent a bit of time reading trying to understand the basics and was lucky enough (I think) to pickup an old Australian Geographics 900x130 reflector telescope with EQ mount for a cheap price.

I am trying to take photos with a Canon DSLR but am running into a bit of a problem. I bought a Tmount kit for the camera as well as an adapter to mount the camera to the telescope but then I run into trouble. As i try to focus, the telescope focus hits the stop and wont retract any furthur. I have tried fitting a 3x Barlow to see if that works and it does to a certain degree but it magnifies too much.

So my question is, is there any way (other than buying a new telescope as funds are limited) to get the camera to focus?

Thanks in advance.
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Old 11-10-2014, 01:22 PM
raymo
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Many Newtonians suffer from this problem. First question is whether the
camera nearly focuses, or whether it obviously is quite a way off. Ideally,
you could post pics of your adaptor arrangement, because maybe you are doing something wrong, or there is another way to get your camera closer to the focuser. You can in the meantime use a 2x barlow of course.
Budget level 3x barlows are often optically very average. With many Newts that won't come close to focus, the only option is to modify the scope by moving the primary mirror further up inside the tube, but with others that come close, there are easier fixes.
Someone who is familiar with your particular scope will probably put you on the right track.
raymo

Last edited by raymo; 11-10-2014 at 01:25 PM. Reason: more text
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Old 11-10-2014, 01:39 PM
glend (Glen)
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Cheapest option is to move the mirror up, you can try doing this by allowing it to rise on the collimation screws to the limit of the travel, if that's not enough you could get longer bolts and springs but I would discourage cutting the tube to shorten it.

I'd try cranking out the mirror first and see if that gets you to focus, but it will push the visual eye piece focus further out to the point where you may need an extension to reach EP focus.

You need to work out how much more travel range you think you will need to reach focus with the camera, that informs your next step.





Good luck

Last edited by glend; 11-10-2014 at 03:36 PM.
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Old 11-10-2014, 06:08 PM
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So the first step is to determine exactly where the focal point is. Take out the eyepiece and point the scope at the moon. You should be able to focus it on a piece of cardboard held up to the drawtube. To get focus with your camera you need to be able to place the imaging centre at the point of focus that you have just determined, so as above, the position will guide you to the next step
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Old 11-10-2014, 07:04 PM
raymo
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We could be all jumping the gun here; his scope might well reach prime focus using the right adaptor setup. We need him to post a pic of his gear. Many newbie owners of Skywatcher Newts have problems because
they don't know how to use the supplied adaptors.
raymo
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Old 11-10-2014, 08:25 PM
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It would definitely be helpful to see a pic of the focuser assembly and threading.
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Old 12-10-2014, 07:21 PM
astro.photo
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Hi All

Thanks for the responses..

Will take some pictures and post and hopefully that will answer a couple of the questions...

Cheers
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Old 12-10-2014, 07:45 PM
astro.photo
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Here are some photos - hope they help!

Click image for larger version

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If you need anymore let me know...

Ta

AP
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Old 13-10-2014, 05:30 AM
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Have you tried a Barlow ?
The only realistic solution I see here is to move the primary up the tube. Probably about 25-30mm I'd guess, the CCD focal plane is well to the rear in the camera. Quite a way back from an EPs closest point.
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Old 13-10-2014, 08:03 PM
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Yes, some models have a few tricks that can save precious centrimetres, but you're only choice there it would seem is moving the mirror up the tube or changing focuser. You probably won't find a focuser that will help under the price of the telescope, so that's probably no help.

As far as moving the primary, you may be able to put longer screws in if cutting the tube isn't your thing.

Its likely you are going to get quite severe vignetting with the relatively narrow focuser, and moving the primary will make that a little worse.


What sort of mount do you have? You may only want to do short pics of the moon and planets perhaps?
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Old 14-10-2014, 06:58 AM
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We can all speculate here until the cows come home but until we know exactly where the prime focal point is it's just idle speculation.
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Old 14-10-2014, 10:36 AM
raymo
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Which is why I asked him if it nearly focuses, or is obviously way off, but
never got an answer on that.
raymo
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Old 14-10-2014, 07:13 PM
astro.photo
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Hi all....

I should remember to do two things:
1. Check my posts and
2. Answer the questions that have been asked !!

First off - thankyou to everybody who have responded!!!!

@raymo - the focus is almost there, I would think if I could turn the focus an extra 1/4-1/2 turn then it would be there.

@RobFo - I have got an equitorial mount and the photos I would like to take would be of the moon, Mars, Jupiter and Saturn (if I can get them). I would love to take some of the great starscapes that I see however I don't think I have the equipment to do it and unfortunately am saturated in light pollution to take long duration exposures. I have posted a photo of the assembly, would a better picture of the threads help?

@ghsmith45 - I will give it a go this weekend and report back!

I might give the screws on teh bottom a go - is there a recommended method that I should follow to minimize the possibility of error?

Thanks again for all your help..

AP
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