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NEBULA Photography with a Cheap DSLR & Lens


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Nice video and info. The big deal here is the polar alignment and motor, which is barely mentioned in the video. Note that the sky turns once every 24 hours (actually more like 23 hrs and 56 minutes because of the Earth rotating around the Sun).  When you look through a telescope, note the magnification is usually somewhere between 30-240x magnification and is lucky to hold 1° of sky in view.  Since there are 86,400 seconds in day and 360 degrees the sky turns in a day, then an object would stay in a typical low-mag viewfinder 86400/360 = 240 seconds. So something that began centered in the viewfinder would go out of view in half of 240 seconds, or 2 minutes.  In good telescope like mine, it doesn't last a minute1

So, to do photography, you need a motor that turns one of the supports at a rate of 1 revolution every 24 hours!

The mount in the video has a barely mentioned motor that turns the post holding the camera arm at a rate of once every 24 hours.  In order to keep a star steady in the viewfinder, the post must be pointed at Polaris, the North Star - he refers to it in the video as something like the "polar aligning" after it gets dark. The North Star is close enough to dead north that all the other stars appear to revolve around it each night and if you had a camera set on the north star, all the other stars would make rings around it. Below is an example I just found from somewhere like southern Mexico - the center of the circles is where the North Star is and the trails are where each star around it circles.  The North Star - day and night, stays in virtually the exact same place in your sky (within about 1/3°) and it's height above horizontal is equal to your latitude, which is in about the mid-30°'s to close to 50° north for most people in the USA and southern Canada. It looks like about 10° in the picture so that's WAY south. Your fist held fully extended extends across about 5° of the sky. So you have to point the telescope mount's post that the motor controls right at the north star so when you move the camera on the 2nd arm to focus on one of those circling stars, the camera will keep following the star in it's circle, keeping it a dot, not a trail for the camrea.


So the main post is pointed at the north star and the second arm that the camera is on is carefully rotated to find the star or feature you want - in the video's case the Orion and Horsehead Nebulas.

You don't have to go to that expense to get great star shots.

There was a California amateur astronomer in the 1960's who developed cheap mounts for large (he made 17" mirror scopes) amateur made telescopes name John Dobson.  Many of us amateur telescope makers have put ours on cheap, wood and teflon and lazy susan Dobsonian Mounts.  In order to cheaply get the viewfinder to keep the star in the viewfinder, an amateur astronomer name Haig, in the 1970's, came up with a cheap way of moving the telescope over a period of a 15 minutes or so basically using a box with a hinge on one end of a flat lid that a clock motor slowly raised - turning the telescope enough to keep objects in the viewfinder and allow at least a several minute timed astrophotograph.

In 1988, a guy named Dave Trott improved on it and invented what he called the "barn door drive" (below). Trott says, "This is the double-arm “barn door” drive which I invented many years ago....This device is designed to make it possible to photograph the stars with an ordinary camera, a couple of boards, some hinges and an inexpensive clock motor. The one in the photograph [left or 1st below] is my Type-3 barn door. A simple device like this can produce stunning photographs like the Milky Way [at bottom]."

Source: http://davetrott.com/inventions/double-arm-barn-door-drive/

The 2nd pic shows the double arm where the small one on the left would have a clock motor underneath it that turns something like a 1/4" bolt that runs through a stationary tee-nut in the small board, causing the boards to rise as the motor/bolt turned. The setup, as shown, would be set up to best track the star being observed as it moved along it's circle. The camera or telescope would be placed on the large board.  The graph in the 3rd pic shows that the double-arm reduces error to just around 4 seconds (around 1/90 of a degree) over 50 minutes.  That is small enough to allow sharp pictures over that period of time as shown by the photo at bottom taken with a double-barn door mount of the Milky Way.

DoubleArm1a  image.png.f94b0c819d79badb0f336e896671155e.png image.png.c7822ab052a986bd68207e14c2649467.png

DoubleArm2 milkyway


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I have a 16" piece of 1 5/8" thick double-annealed pyrex glass and may make a telescope with it. If I do, it will be an f/4 (focal length of 64") Newtonian so that I could look in the eyepiece without standing on a latter or stool. the I have a 12" and two 8" diameter paraboloidal mirror Newtonian telescopes whose mirrors I made, on Dobsonian mounts.  I ground and figured the mirrors to within 2 millions of an inch of perfection myself.  Amateur made mirrors general are better performing than commercially made ones, though the difference is getting negligible.

You need something like 10" or more if you want the light gathering power to so some spiral galaxies, the dust storms on Mars, and some nebulas, especially if you live in a light-pollution-filled urban area.

I'd rather take advantage of all the computerization and buy the telescope below, but only if I seriously get back into astronomy. Notice it doesn't have a post pointing to north star for alignment because once it determines its position, it's computer controls its motors to keep it tracking an object as the Earth turns.

To go from the 11" to the 14" it almost doubles in price and this would do most of what I want.

Source: https://www.bhphotovideo.com/c/product/818689-REG/Celestron_11009_CPC_Deluxe_1100_HD.html/overview

It has finder stuff so the telescope will automatically turn to what you want to see and you can get eyepieces that feed live video to your television on cold nights and that aid in astrophotography where the pictures build up and store directly on your computer.


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