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Using a DSLR on a Newtonian telescope Part 1 by phrostie
Using a DSLR on a Newtonian telescope Part 1
Let me start by saying I probably did all this the hard way.  I should have planned ahead better.  I should have read more before I started rather than after.  I spent a lot of time trying things that didn't work, until I found the things that did.  I like to think it was the road less traveled, but I suspect many of us all go through the same thing.

There are many telescopes that are better suited for astrophotography.
There are even Newtonians that are designed for this.
But that wasn't what I started with.  I started with a 10" f4.7 Dob, that I later moved to an equatorial mount.

When I started down this path everyone warned me that there were issues using a Newtonian telescope for astrophotography.

1.  They don't have enough focus travel for DSLRs.
2.  The large tubes create a lot of sail area and cause problems every time the wind blows.
3.  you can never balance the off center weight of the camera correctly.
4.  There is too much coma on the flat sensor of the camera.
,,,.

Honestly there was a LOT of other stuff people told me, but most of it ended up being more myth and urban legend than practical advice.
The 4 listed above were the ones that had the most truth. 

The wind and sail area is something you just have to deal with.  I've seen some of the more serious people build portable wind breaks out of PVC and tarps.  I plan to do this as well one of these days.  I just haven't gotten around to it yet.
So, my solution for the time being is to always setup down wind of my jeep.  It makes a decent wind break and I don't have the additional setup.

The issue of balance is largely exaggerated by the naysayers.    Yes, Make sure you have a mount that can carry the weight of your scope and gear.  Yes, you will need to balance your gear every time you set up.  But If you are planning to do astrophotography, You are better off to be balanced with your camera in place and switch to an eye piece as needed than to balance for your eye piece and then switch to a camera.  The weight of both cameras and eye pieces vary greatly.  Setup for what you plan to use.

Coma is not just a Newtonian issue.  It affects all types of telescopes.  It's more common with lower cost telescopes and is more pronounced on scopes with a fast f stop(low focal ratio).  Since many Dobsonians and Newtonians fall under this description they get a bad rap.  This is why fast scopes with low coma are very expensive.  If you zoom in on some of the stars in the corners of my images you see that they aren't as round as the same size stars in the center of the same images.  This is coma.  My scope simply wasn't designed to be used as an astrograph.  It can be used, but I know and accept the limitations of my equipment.  A number of companies sell coma correctors.  Someday I'll invest in one, but it's like the wind break.  I just haven't yet.

The focus issue is one that required the most effort to work around.  DSLRs locate the sensor further aft than your lens would have been by a considerable amount.  This is to make room for the mirror mechanism.  The stock focuser on many Newtonian scopes just doesn't have the travel to bring it in.  The trick is to reduce the distance between the camera and the telescope mirror.


First frame:
The first thing you'll need is a T-ring and adapter.   The T-Ring is something that will be specific to your DSLR and attaches where your camera lens normally would.  There are lots of after market T-rings.  Try to pick one that is as thin as possible.  Remember we're trying to reduce the distance to the sensor and every little bit helps.  The adapter I use is a 2".  For some reason they insist on adding an extension to the 1 1/4" adapters.  For my application, it's counter productive.  If you're using a filter, the inside of the adapter should be threaded.

Second & third frame:
On my 10" f4.7 I replaced the stock focuser with one with a lower profile.  It has an extension for using an eye piece.  This moves the camera most of the way to where it needed to be, but it was still a little short.

Forth frame:
To make up the last bit a friend suggested changing out the hardware in the mirror cell.  FYI, Ace Hardware carries the correct metric sizes.  Be careful with the thread length on the remaining thumb nut.  You want to be sure to keep a few threads engaged or risk having your mirror come lose.

So for those that are struggling to get that first image, I hope this helps.
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Sun and Flare by phrostie
Sun and Flare
500 frames
Lunt LS50THa
Orion 3X Barlow
QHYCCD5
Stacked in Registax.
Wavelets in Registax
Tweaked in Gimp.
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The Sun, Before and After by phrostie
The Sun, Before and After
I've been asked what stacking does and how do you bring out detail.
Stacking removes noise and background grain.

On the right is 500 frames of video stacked. 
The dark region to the far right is nice and clean of noise from the camera.

On the left is the stacked image run thru the Wavelets in Registax. 
Wavelets do to images what a high or low pass filter does to sound.
The end result is that distortion caused from our atmosphere is reduced.


This is the same dataset as Sun-day 2014-11-23 by phrostie
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Sun-day 2014-11-23 by phrostie
Sun-day 2014-11-23
Second Run with my 50mm Lunt.

500 frames
Lunt LS50THa
QHYCCD5
Stacked in Registax.
Tweaked in Gimp.
Wavelets in Registax
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Lunt First Light by phrostie
Lunt First Light
First light with my new 50mm Lunt.

500 frames
Lunt LS50THa
QHYCCD5
Stacked in Registax.
Tweaked in Gimp.
Wavelets in Registax
Loading...

deviantID

phrostie
Don Octavio Del Flores
United States
Current Residence: out there somewhere
Favourite genre of music: varies, right now it's Rock and Blues
Favourite photographer: My Friends, they're just better at it and I learn from them.
Operating System: Linux
MP3 player of choice: My Jeep
Shell of choice: BASH
Wallpaper of choice: Something from Deep Space
Skin of choice: hers
Favourite cartoon character: RoadRunner/Coyote (you can't have one with out the other)
Personal Quote: What's life with out a sense of adventure?
Interests
farewell to John Dobson.

A legend has passed from this world.

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:iconjordent17:
jordent17 Featured By Owner Dec 1, 2014  Hobbyist Photographer
Many thanks for the fav, good sir :D
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:iconphrostie:
phrostie Featured By Owner Dec 1, 2014
You're very welcome
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:iconjsh50:
JSH50 Featured By Owner Nov 9, 2014
Thank you for  faving Knaresbourgh, and the kind comments! :)
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:iconphrostie:
phrostie Featured By Owner Nov 9, 2014
No problem,

It's a really cool old bridge.
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:iconevotronic:
evotronic Featured By Owner Oct 18, 2014  Hobbyist Photographer
tnx for faving ;)
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:iconphrostie:
phrostie Featured By Owner Oct 19, 2014
You're very welcome
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:iconprincevlad39:
princevlad39 Featured By Owner Aug 21, 2014
Thanks for the fav
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:iconphrostie:
phrostie Featured By Owner Aug 21, 2014
very welcome
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:iconjxsnyder:
jxsnyder Featured By Owner Aug 19, 2014  Hobbyist Photographer
Thanks for the fave!  :D
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:iconphrostie:
phrostie Featured By Owner Aug 19, 2014
you're very welcome
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