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03-27-2018, 12:40 PM   #1
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Attaching my k-20 to my Telescope

I recently had the good fortune to acquire a Meade 114-DS 4.5 inch reflector telescope, with the electronic Astro tracker unit...
What was particularly exciting was... It was in brand new condition and had all the parts AND... it was only $35.00! After unpacking and assembling it I was looking at object in the sky that my old scope would take me hours to set up. So after a couple of days I decided I wanted to us my K20D to take some pictures with...
I lined up what I wanted to look at, set the computer to do the tracking and put the camera up to the telescope eyepiece and spent nearly an hour trying to get an image... I was using manual focus and a 28 mm macro lens and the best I could get was tiny pinhole image in the camera, and that's wen I could hold the danged thing still enough...
The next day, I went to Amazon and ordered a "T" mount to fit the eyepiece (2")... I arrived today.
I take everything outside to set it up in the daytime and once I get everything assembled, the farthest away I can focus is 150 feet... the farthest!
So, here I am, stuck! I've doubled the cost of the telescope with the "T" mount and I can't get the camera close enough to the reflecting objective (the mirror you actually look at to see the image) to focus on the sky...
What I'm thinking is, I need to reduce the distance between the sensor and the mirror somehow... The "T" mount will accept a 49mm threaded filter on the opposite end so, I'm wondering if I should get a 49mm lens magnifier to put on it or is there something else I'm missing?

Any and all suggestions will be greatly appreciated!


Cheers, Bob!

Here is an example of the distances I need to be to get an image.



03-27-2018, 12:46 PM   #2
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I imagine you will need some sort if adapting lens, if you don't feel like mutilating the thing with a hacksaw and a pinch of DIY
As to what lens you'll need, I am not sure. It'll need to be concave...
03-27-2018, 01:20 PM   #3
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I don't know which adapter you have. Some of them you put the eyepiece in the adapter, some of them you keep the eyepiece in place. The eyecup is usually removable. Some you don't use the eyepiece at all. The later usually come with the telescope and are the right length for standard flange distance for t-mount.
03-27-2018, 04:14 PM   #4
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Your suspicions are correct. The focus allowance on Newtonian refractors like yours is very small. There are optics that will work. Since you canít get close enough for focus you may need a Barlow lens before the T adapter. My suggestion would be to get onto Cloudy Nights Forum (I am Pentax Syntax there also :-)) and do a search on the little Meade. Many in that forum will have your telescope and may have solved your problem. It wonít matter what DSLR they use as long as they use the T mount. That said, a Newtonian on an Alt/Az mount is going to be very limited in exposure time allowed due to field rotation even if tracking is perfect. The setup should allow some planetary imaging though.


Last edited by Pentax Syntax; 03-27-2018 at 04:25 PM.
03-27-2018, 06:05 PM - 1 Like   #5
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One thing you can do but it will change your magnification and the brightness of the image, is use a Barlow lens. The Barlow fits the 1 1/4" eyepiece holder, and will throw the point of focus out far enough for you to be able to focus at infinity with the camera. The Barlow lengthens the effective focal length of the telescope which may be a good thing if you're trying to take a photo of planets or small angular objects, but will go against you if you want wider coverage. A Barlow is an achromatic negative lens in a holder, similar to a focal length extender ("teleconverter") used with a camera but in a telescopic Barlow, the negative lens is located in a 1 1/4" tube which places it such that the focus point can be extended enough to reach a camera sensor attached to it with a T mount & 1 1/4" adapter.

Another alternative is to take your mirror mount out and shim the mirror, moving it closer to the eyepiece end of the scope. The downside of that is that you probably won't be able to focus on infinity objects with eyepieces after it's done (though you can get an eyepiece extension tube which will allow eyepieces to be used). Also, you will need to be familiar with aligning your scope (adjusting the mirror) since that will have to be done after adding any shims.

Some scopes use a very long rack and pinion focuser which allows both cameras and eyepieces to be used but it's a little uncommon with hobby scopes like yours. I would try the Barlow - you might need a little experimenting to get it to work, but it should allow a camera to be used. Be careful though since the camera will really be "hanging out there" and might get knocked off - also you'll probably need to hang some weights on the back end of the scope to counter-balance the camera since it will make the scope top heavy.

Oh, and there's one other method - eyepiece projection which uses a special adapter to hold an eyepiece and allow it to project an image into your camera. Again, it really cuts down on the image brightness and is best for photographing small objects like planets. There is an adapter formerly offered by Orion which does this for you.

Orion 8725 1.25in 2x Ultrascopic 3-Element Barlow | eBay

https://www.ebay.com/i/323156175565?chn=ps&dispItem=1

Last edited by Bob 256; 03-28-2018 at 08:25 AM.
03-28-2018, 02:13 AM - 1 Like   #6
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You can shift the primary mirror further up the tube. Pentax cameras are 45.46mm deep from the front of the lens mounting flange to the sensor so you need to add this to distance you want to move the mirror. An article on what needs to be done: Modifying a Newtonian Tube for DSLR Photography - IceInSpace
03-31-2018, 10:30 AM   #7
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Thank you for all the suggestions... The telescope did come with a Barlow lens tube, so I will try that before anything...
I have a Pentax 100-300 Zoom that I tried to "fix" (the pins didn't make contact...) off a 35mm film ZX I got cheap, so I may see if I can cannibalize that too...

What I like most about astronomy and astrophotography is... Things are always "looking up"...!
04-01-2018, 01:35 PM   #8
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QuoteOriginally posted by bobphoenix Quote
Thank you for all the suggestions... The telescope did come with a Barlow lens tube, so I will try that before anything...
I have a Pentax 100-300 Zoom that I tried to "fix" (the pins didn't make contact...) off a 35mm film ZX I got cheap, so I may see if I can cannibalize that too...

What I like most about astronomy and astrophotography is... Things are always "looking up"...!
The snag with using the Barlow is that it a) increases the focal length and b) it it increases the f/ratio. You need a good drive, and spot on polar alignment to make use of a) and an increased f/ratio will mean except for the stars themselves, the image itself will be a lot dimmer. That means you may need to crank up the exposure time and/or ISO. Longer exposures means your drive really needs to be up to the task.
A coma corrector might be a viable option though you might have to upgrade your focusing unit. SkyWatcher coma corrector for Newton telescopes up to f/4: Buy online | Primalucelab.com

04-03-2018, 10:42 AM   #9
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SOLVED...!!! (More or less...)
So, the latest is this...
I cannibalized the 100-300...! I took out the second element from the front (I think it's a condensing element). (see below)
I used super glued to fasten it to the front of the telescope adapter with the lens element inside the adapter... (I tried both ways first, before I made a commitment...) and it all seems to work... Now it is a matter of practice and technique...
BTW: The 2" Gosky adapter is threaded for a 49mm filter, but the carrier for the lens element is a fraction of a mm smaller then the outside of the Gosky tube. A perfect fit!

Because I am trying to use a "lens" (the telescope) that is well over 900mm, I am triggering the camera with a remote shutter release and I've set the shutter release timer for two seconds to allow everything to settle down before the shutter trips...

Here is a picture of the assembled parts and a picture of a house that was over a quarter mile away... (apparently, I really need to clean my sensor now!)


If anyone is going to give this a try... here is what I used...
A Gosky 2" telescope adapter with Pentax "K" mount ring... The Inside element from a Pentax 100-300 Zoom lens that was not working anyway... ($30- $40 on Ebay) and a squirt of Gorilla glue...





04-16-2018, 03:53 PM   #10
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QuoteOriginally posted by bobphoenix Quote
What I'm thinking is, I need to reduce the distance between the sensor and the mirror somehow..
Yes in the good old days Newtonian often had two sets of mirror mounting holes, one for visual observing and the other for photographic. Either that or a low profile focuser with an adapter for visual.

Clear skies!
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