Homemade camera external viewfinder?

I am trying to design my own camera for a science project and for this camera I

want to try to use some lenses I came across from an old 35mm SLR... but I don't

want to use the "reflex"? type of viewfinder SLRs use because of the complexity.

Can I use this type of viewfinder:

 

http://www.photo.net/bboard-uploads/008WIh-18350884.jpg

 

Could I buy something like this and attach it to my homemade camera? How do these

types of viewfinders work? Will they work with all different focal length lenses?

Are they very accurate when composing your shot? Is there some name/term that would

help me google this type of viewfinder and to find out how they work, and how to

make one, or use one? Any info would be great.

A simpler answer would be a wire sports finder. Here is an image of a camera with one:

 

http://imagehost.vendio.com/bin/viewimage.x/00000000/richertd/D102697A.JPG?vvid=51692229&allow_mailing_list=1&allow_track_link=1&track=02365561ea-b1fb3&sp=0

 

Sorry about the long URL -- Mark

Thank you for the response, Mark Fisher. That is definitely an interesting alternative. The only thing I worry about is that from my brief research it seems like you would need different wire frame viewfinders and would have to swap them out for different lenses. I would prefer to have one viewfinder that fits all the lenses.. but I don't know if that is possible.

Look for universal finders or turret finders. There have been multiple frames wire frame sportsfinders too. The Soviet made turret covers 28, 35, 50, 85, 135mm. Zooming finders like the Linhof can range from 90-360mm (for LF 4x5"). There are a few finders available which include frames for 2 or maybe 3 focal lengths.

 

All external finders I know are pricy. I can't understand what the reason is.

 

I never cared much how accurate the framing is. - Linhofs universal finder seems to be a bit too much on the safe side. (OTOH a 4x5" neg offers some additional space)

 

My Soviet turret suffered from a lose mask inside and the repair guy had a hard time attemting to fix that.

 

I'd salvage a simple SLR finder without return mirror for your project, if I was you. Any kind of external finder combined with zonefocusing will suck.

I forgot some finders include parallaax correction others don't. Maybe useing a finder that was intended for a huge distance between coldshoe and middle of the lens (Linhof) is risky.

 

Sportsfinders with multiple wire frames might be a option too.

A wire frame with a sliding front frame will accommodate an infinite number of focal lengths.

 

Very wide optical finders which are affordable often distort.

 

For another optical approach, look to the Linhof optical viewfinder. It accommodates 75mm to MM for 4x5. It also auto-adjusts for parallax. You can easily work out the equivalents for your format. (They also have one for 6x9cm, but it tends to be expensive due to rarity.)

Thanks to everyone for your responses. A lot to research there. I plan on mainly using this camera for macro photography or portraits so what if I attempted to design the camera in such a way that the camera portion detached from the the lens temporarily.. and the lens is attached to the tripod. Then what if I attached something like this to the back of the 35mm lens temporarily to compose the shot..

 

vivitar tla/1

 

http://cgi.ebay.com/Turn-your-35mm-Canon-Lens-into-a-Telescope-No-Reserve_W0QQitemZ180053355607QQihZ008QQcategoryZ711QQcmdZViewItem

 

I'm thinking this way I could perfectly compose the shot without any parallax or anything.

 

Would it be possible to make something like this? Or would I have to buy one like the one shown in the link? Or would the one in the link even be accurate enough to compose the shot perfectly?

Lester Lefkowitz wrote a book on close-up/macro photography that suggests some DIY gear for macros. Check your library.