Quick and Easy Telescope Measurments?

[Willis666]

For my science fair, I need to take measurments (to scale) on a telescope, for example, I need to be able to point it towards the moon, and measure its radius. Now, my problem there is how will I measure this? Since my eye will be in the way, I can't use a ruler to find a crude measurement, so I was wondering how I can do this. I don't want to spend much money on this, so I don't want to buy an adapter for my camera to attack to my telescope. Can I just shove my camera lense into the lense of the telesope viewfinder, and take a snapshot? I asked my stepdad, but he doesn't know much about telescopes (was more interested in microphysics.)

So do you guys have any idea how I can do this? The pictures wouldn't have to be nice.

I can't just eyeball it, since for the project I'll be looking at some pretty far off objects.

If I'm not being clear on something, feel free to ask.

 

[Vorde]

The only way I can think of is to know the magnification of the particular lens you are using. That will be able to tell you how many degrees you see when you look through the lens. If the object is bright enough, you can project it on a white screen-like paper, and when it's projected it's easy to measure with a ruler.

 

[Willis666]

Alright, I'll look into that. I ordered the telescope tuesday, so it should be here by monday.

 

[russ_watters]

Can you take the lens out of a webcam and hold it up to the scope?

 

[tombruce95]

Whatever the set up .. and answer is not trivial:

.. Sensitivity of you measuring device may be affected by a number of environmental changes. Look at this carefully.

.. Recalibrate your system often .. or .. each time you suspect a change in the setup.

.. try to develop a procedure that can be repeated easily

.. whatever procedure you use, assert what the practical minimum resolution is for your set up. For example: use the separation of binary stars for various conditions of "seeing."

The following is suggested

-- Point the scope at some **distant** terrestrial object which can be independently measured.

-- or point the scope at pair of stars whose angle of separation is known.

-- or point the scope at a large crater on the Moon whose diameter can be found.

-- or pair of very small craters .. on the Moon whose separation can be found.

Try several procedures .. several times and look for consistent scale. However, If you change the set up (which might include a change of temperature -- hence a change of focal length) then you'll have to recalibrate.