astrophotography. I want to know that the focal length is to determine the field of vision?
I'm interested in astrophotography. I want to buy a camera for my telescope. You can find the field of vision, if you know the focal length of the telescope. But what is the focal length of a camera with a fixed lens? If I have a 50 mm lens, is the focal distance 50 mm? or do you need to know the distance from the camera of body image sensor and add it to the lens focal length? Thanks in advance...
If you have a 50mm... lens focal length. The focal length is the distance between the end of the lens and the image plane. If you look at a digital SLR, there is a symbol on the body (usually the top of the body and often near the viewfinder) that looks like a small circle with a line through IT... which line marks the position of the focal plane inside the camera.
There is a friction more... If you have a 'simple' goal, it would be the focal length. Many modern lenses are technically able to be physically shorter than the focal length they provide... because of the types of 'glass' and the configuration of optics. So the focal length is based on how long a simple goal should be to provide that same value (even if you were to physically measure it and not get this value.)
All telescopes list their focal lengths, but also among the specs of the telescope focal reports. I have a refractor of 540mm with an opening of 101mm... so it is 'roughly' f/5.4 scope. I have also a larger 14 "SCT with a focal length of 3556mm and it is a stretch of f/10.
The distance "flange to focal plane" on a camera Canon is 44 mm... in the grand scheme of things with a telescope, it will not substantially change the focal length of the image.
Depending on the scope, you can use either a "focal reducer" or a "barlow" to decrease or increase the focal length.
One last thing... many designs of 'Newtonian' type telescope is problematic for astrophotography. This is because most of the glasses and catadioptric telescopes are designed with the intention that a person would use a diagonal of 90º with their eyepiece. "The diagonal has a tendency to add"roughly"2" to the overal of the focal path length. If you are using a camera you take this "diagonal" and simply attach the camera for a shot "straight through". So even if you have lost the focal length 2 ", created by the diagonal... the camera adds"roughly"the same amount of back in.
BUT... When you use a Newtonian telescope of reflector design, the eyepiece is near the front and there is no "diagonal" in use. This means that when you add a camera, focal length gets longer, it would be with an eyepiece. Pull door-eyepiece tube has some development trips... but because the camera is the longest focal length, you end up having to run the focuser completely 'in' to shorten the length of the focal length to put the image in focus. And that's where you are having problems... very often on a Newtonian telescope, you exceed the limit of traction of focuser (you can't shorten the development any more that you have) and the image was just starting to focus... but it's still pretty fuzzy.
This problem not to poison all the reflectors of knighting... some can accommodate cameras and still come to focus. You really check the specific scope.
Tags: Canon Camera
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