I am very new to astronomy and astrophotography. My current goal is to photograph the moon on film. My current setup is a Skyline 8" dobsonian telescope and a Canon A1 with a T converter. I got a C type focusing screen and removed the prism but still can't get the moon in focus. I'm not looking for perfect focus or anything but currently I am just seeing a white blob that gets bigger and smaller as I turn the focusing knob on the telescope. It seems that the moon is most in focus when the focusing knob is turned all the way in, so I'm not sure how to fix it. Is there something I'm seriously doing wrong here?
Help with capturing the moon
Posted 12 October 2021 - 11:46 PM
Things will get bigger the more out of focus they are, in either direction. I think when you're getting smaller, you're getting closer and closer to focus. Unless you can get to a point where the white orb is at it's smallest and then starts to get bigger again, you're not actually able to reach/pass through the focal point.
You may not have enough in-focus to get it there. A barlow can help because it extends the focal point back a bit, but will also increase the focal length. If it were me, I'd try that to see if you can reach focus at all and see what that actually looks with your system. From there, you should have a good idea of what steps you need to take.
Posted 13 October 2021 - 10:56 PM
Your camera's focal point is 42mm from the front flange to the film plane plus what ever the length of the T-ring and coupler are.
In order for your telescope to focus you would need to move the main mirror up 1-2 inches.
Or try a barlow as stated above.
Since the scope was not designed with photography in mind a bit of rebuilding may be needed.
What prism did you remove?
And welcome to CN
Edited by TxStars, 13 October 2021 - 10:57 PM.
Posted 13 October 2021 - 11:08 PM
Thanks for the welcome! I removed the eye level prism from the camera so I look directly at the focusing screen now. Eventually I hope to buy a waist level finder but hoping that looking at the focusing screen will do for now. I ordered a barlow today, when it arrives I'll try that out. I also might look into getting another T ring adapter that is not as long if the barlow doesn't work. Thanks for the tips!
Posted 13 October 2021 - 11:16 PM
You have to use some sort of viewer waist level or other viewing devise in order to focus.
A loupe that is focused on the focusing screen would also work ,but without some lens you wont see anything in focus.
I know they made a waist level for the F-1, but have not seen one for the A-1
Edited by TxStars, 13 October 2021 - 11:49 PM.