Real basic Astrophotograpy question

[RichardG]

I have read Astophotography 101 and other articles and haven't read a real basic answer or question.
I have yet to try it and will most likely go with the web cam multi image method to start with.
I think I read somewhere a few weeks ago that when using a camera (SLR) you don't use a lens on the camera and you DO NOT use an eyepiece on the telescope. TRUE or FALSE
If you do not use an eyepiece, is the total magnification equal to the Focal Length of the telescope? For example my 5 inch reflector has a focal length of 650 mm. If this was on my 35 mm SLR it would be equal to about 20X correct?
I see Jupiter at like 200X with an eyepiece.

So, how do you get these real great deep space objects to look so large without an eyepiece to magnify the image in the focus tube?
If I get a web cam and adapter, do I have to remove the lens from the web cam and insert it into the focus tube (with adapter) or will it work with the factory lens $still in place?
Can I use a Barlow Multiplier to get a little more magnification?

Is there any way to use a 10mm to 20mm eyepiece in the focuser and get the camera to capture that image?
TIA

 

[bloodhound31]

Hi Richard.

You will have to remove the lens from your webcam, then screw on the adapter. Take the eyepiece out of the telescope and put the webcam in.

This is called "Prime focus"

You do the same with your DSLR. Take off the lens from the DSLR, screw on the t ring and adapter, take out the eyepiece from the telescope and slide your DSLR in.

The longer the focal length of the telescope, the bigger the image at prime focus will be.

If you use a barlow lens between your camera and the telescope, you can magnify the prime focus image by a fixed factor of 2x, 3x, 5x, or whatever the barlow lens is. You are however, slowing down your telescope by doing this, efectively increasing the amount of exposure time needed to capture the faint light.

Ok for the moon and bright planets, not so good for faint deep space objects.

You can also get a special tube that goes between your camera and the telescope, which you can put an eyepiece in. This is called eyepiece projection.

Have a squizz around on my site. I have written a few "laymans" pages on the subjects.

http://www.asignobservatory.com/index.p ... icle&id=43

Good luck mate,

Baz.

 

[RichardG]

Thanks so much. I was afraid that "Prime Focus" (new term to me) was the way it worked.
So, if I figure it correctly a 650 mm FL reflector should yeald close to 20X mag.
Didn't know I could use my barlow to multiply it. I understand slowing it down as I have used multipliers with telephoto lenses on my 35mm SLR for decades.

I wasn't sure if I would have to remove the lens of a web cam or not. I have one on order that is a tube shape and close to 1.25 inches in diameter. I hope it will simply slide into my focuser.

Thanks again for the great info. Hopefully I will get some images to assemble into something interesting by the end of the month. With your help, now I am a lot closer to making that a reality.

 

[RichardG]

First attempt. I got an inexpensive web camera, removed the lens, applied tape till it fit in a 1.25 OD tube. Inserted it in the scopes focus tube and connected it to the PC/video capture software.

I focused on a distant tree top, about 200 yards away. I can see pine needles and bark in an area about 6 inches across.

Guess my guess of 20X mag was off by a factor of about 150. This looks like it's about 250-300X mag.

First attempt to focus and track Jupiter was a partial success. I could get Jupiter and two of 4 moons in the FOV. The moons were sharp points of light, Jupiter was a bright, over exposed fuzzy white ball of light. No detail, no bands.

I captured several 10 second AVI's and used the stacking program with success, but a white fuzzy Jupiter isn't what I had in mind. LOL
I need to find software that can compensate or adjust the aperture, saturation, gamma, brightness and contrast of the cameras video signal. I figure it was the auto aperture function of the camera that caused the over exposure.
Next step, search for software. The Debut Video Capture Software and VirtualDub Software don't seem to be able to do that.