Home made scope. (1 Viewer)

Paul,

First you need to know the focal length of the telescope objective in mm's. You can measure that reasonably closely by measuring the distance between the objective and the eyepiece fieldstop (probably a flat ring inside the eyepiece tube) when the scope is focused at infinity. Dividing that figure by the eyepiece's 22mm focal length will give you the scope's magnification. Multiply that number by the focal length of the camera's lens to get the effective focal length of the combination.

Henry

henry link said:

Paul,

First you need to know the focal length of the telescope objective in mm's. You can measure that reasonably closely by measuring the distance between the objective and the eyepiece fieldstop (probably a flat ring inside the eyepiece tube) when the scope is focused at infinity. Dividing that figure by the eyepiece's 22mm focal length will give you the scope's magnification. Multiply that number by the focal length of the camera's lens to get the effective focal length of the combination.

Henry

Click to expand...

Thanks Henry.

One more question. My Olympus C5050 has a focal length of 7.1 - 21.3mm which is the equivalent of 35mm to 105mm. Do I use the actual focal length of the camera or the 35mm equivalent to multiply with the scopes focal length ?

Cheers,
Paul.

I've found a place today selling 68mm coated lenses with a 360mm focal length so I've ordered one to add to this scope in place of the 50mm. I've also ordered an erecting prism to get the image up the right way. I'll report back once the parts arrive and I've tested them.

If all goes well then I'll build version 2 and refine the build quality and hopefully have a pretty good scope but it's working very well already. You may see them turning up on ebay in the near future.

This pic of a Robin was taken with this scope yesterday and it's my best photo so far. Range was about 30m.


Paul.

that is spot on!

with quality shots like this, you're sticking two fingers up at the 'top end' stuff - and getting great rewards! - brilliant work.

Getting better results from this home made scope now as I get used to this digiscoping lark. |:d|

Paul.

Just to give this discussion a new twist have a look at these sites.
The scope featured is modular (allowing mix and match) and seems to give good results when used for digiscoping.
http://www.sciencecenter.net/hutech/borg/
http://www.tomytec.co.jp/borg/bird/bird.htm
http://www.tomytec.co.jp/borg/bird/5syasin/50ed/50edyachou.htm

Hey Paul,

For the newbies among us (hehe. that being me!) might you be able to give us some more pointers on the construction of this piece. I've got an old tube from a reflecting scopy my great uncle assembled. It's mirror is in really bad shape though. I thought that tube might be a fun basis (with a diagonal and 2" eyepiece) for a scope project.

Cheers,

Sean

Hi Sean,
There's not a lot to it really. I've attached a photo of how my scope looks now. Firstly hold up your eyepiece to the lens and focus on something a fair distance away to get an idea of how long the scope will be. I started off with one length of strong cardboard tube. I cut this in half and then split one of the tubes along it's length. This allows it to expand and slide over the tube that isn't cut. I then taped up the split tube while it was over the other tube and made sure the tape wasn't too tight so they slide together with just the right amount of friction. Depending on the diameter of your lens you may need to mount it in something. I mounted mine in a lid from a coffee jar as it was the exact right size to fit my tube. I used a similar lid at the other end and mounted my eyepiece holder into that.

This gives you your basic scope but as you noted a diagonal is needed to get the image up the right way. I have fitted an amici prism to mine as I find this works much better than the mirror type designs. I tried a mirror diagonal and got a lot of annoying internal reflections but with the prism there are none. A mirror will only correct the image up the right way but it doesn't correct left to right so anything you look at which has text will be back to front. An amici prism is correct in all directions however. Also adding a diagonal may mean you need to shorten the length of the scope slightly. On mine I just shortened the tube that had the lens mounted in it by a few inches.

The link below sells a good selection of lenses at very cheap prices. Look in the objective lens section for some ideas. I've just ordered the fujinon copy lens to make a new digiscope. The lens is from an old photocopying machine and they are great for scopes, sometimes called copy scopes because of the lens source. It's only 55mm dia and I wouldn't go any smaller than that. The longer the focal length of the lens then the better the magnification will be from your given eyepiece. There's lots of other lenses for sale on the site with some up to 80mm dia. The second link shows some plans for copy scope designs using mostly plumbing parts with a lot of other info too.


http://www.surplusshed.com/
http://www.dma.org/~wagner/copyscop.htm

Paul.

Thanks Paul, for your extensive advice and work on this! I'll check those out.

Happy "tubing"!

Cheers,

Sean