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Extension tube for Celestron Astromaster 70EQ


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Which extension tube would fit my telescope? This is my main problem:

I have a Celestron Astromaster 70EQ and these cameras: Canon EOS 1100D, Canon EOS 450D and Canon EOS 7D. I've also got a T-ring and a T-adapter. When I connect the camera to the telescope with both the T-ring and the T-adapter I am getting a very strange view of Jupiter. It seems like it's only a BIG grey dot - it's totally zoomed in without me doing anything else than connecting the T-ring and T-adapter after taking out the eyepiece. When I look into the telescope with the eyepiece I am getting a nice view of Jupiter and it's moons - far away, but I guess I could zoom in in Photoshop and getting a nice photo out of it if I could take a photo like that...  The planet is really about 50 times bigger when using the T-adapter and totally unsharp. Attaching a photo so you can see what the problem is. Got a question if it really is Jupiter or the spider vane? After reading about spider vanes I am starting to believe that myself.

Got a tip in here that I should get an extension tube. Today I'll recieve a 2xbarlow - not sure if that would be enough so I guess I need an extension tube as well. I am quite new to this so have a lot of questions... :) I do have three different extension tubes for my CAMERAS, could I use them insted of buying one that would fit on the telescope?

I've got a webcam since two days ago and have managed to get a couple of videos of Jupiter but really want to figure out the problem with DSLR ;)

Thanks in advance!


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Usually the problem is that there is insufficent inward travel when using a DSLR.

So I would guess that what you see is the spider vane and the secondary not jupiter.

A DSLR on the scope is probably a bad idea, the camera is too big. Additionally people normally image Jupiter (and other planets) with a webcam not a DSLR. Sort of it is a camera but not the best camera for the job.

Webcam is smaller and lighter so less problems with weight and it can get to the focal plane of the scope.

Next, a webcam at the focal plane will likely have too small an image so people add a barlow in to increase the image size that is on the webcam. Also note that often the scope of choice is a Mak or SCT which with the longer focal length delivers a bigger image.

I would suggest your arrangement should be: Scope, barlow, webcam.

Whether a 2x or 3x barlow is a case of try and see what delivers the best.

As you say "vanes" I presume it is a reflector so be aware when in focus and with the brightness of Jupiter you can expect to get an image of Jupiter with 4 diffraction spikes. These may lose detail of Jupiter. Other then another scope Mak/SCT/Refractor that is a property of the scope design.

As in most aspects a poor barlow will deliver a poor image, however I suggest you get one to try the principle out and get something so you can go and process the resultant video in a software package. People seem to stack in one, process wavelets in another and sharpen in yet another. But I believe Registax will do all so consider that as at least a first play.

Unfortunately "imaging" is not a simple case of attach camera to scope press button and get picture.

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Thanks for your answer! Now the Moon is lovely and looked great with my new eyepiece. Too big with the barlow though but I expected that anyway. Didn't buy the barlow for the Moon ;) Tried the webcam again and all I could see on the screen was BLACK!!?!?! So frustrating... :( Why is it so difficult for me to get photos when it seems like anyone can get nice photos? I must be doing something wrong...

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Figured out what seems to be the main problem when using the DSLR. When the camera is without a lense and I only have the T-ring and T-adapter connected, it will only show all light sources as big white circles. Tried to point the camera towards a lamp outside and all I could se in the live view was a big white circle. The camera is set to bulb-mode. This happened when I connected the camera to the telescope as well and pointed at Jupiter. It doesn't help focusing with the knobs either. Anyone experienced the same?

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The reason why you cannot get the camera to focus is because there is insufficient inwards focuser travel as stated previously. To get a focused image you need to either, move the primary mirror farther up the telescope tube (not recommended) or use a Barlow lens to move the point of focus of the telescope outwards so that the camera can produced a focused image.

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Yes, but this seems to happen just pointing the camera towards a lightsource - even without the telescope connected to it. Is it because it in fact there is no lens attached to the camera? I am totally new to this, so therefore I have a lot of questions... :smiley: The lamp hanging outside my house looked like a HUGE white circle, not even close to a lamp. 

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