Is this possible?

[Darkplague]

I was thinking about buying this lens from ebay but couldnt find any info on it anywhere.

http://cgi.ebay.com.au/ws/eBayISAPI....3434&rd=1&rd=1

Do you think it is possible to make a cheap refractor out of it??

The lens is a Besco E.F series 3, 6" diameter. Unfortunately this means nothing to me at all (

HELP!!!!

[mercedes_sl1970]

Not sure if this site helps?

http://alag3.mfa.kfki.hu/astro/GiantLenses/127mm.htm

Good luck.

Andrew

[Terry B]

Originally Posted by Darkplague

I was thinking about buying this lens from ebay but couldnt find any info on it anywhere.

http://cgi.ebay.com.au/ws/eBayISAPI....3434&rd=1&rd=1

Do you think it is possible to make a cheap refractor out of it??

The lens is a Besco E.F series 3, 6" diameter. Unfortunately this means nothing to me at all (

HELP!!!!

The person selling it answered a question saying both surfaces are concave and it seems to make objects smaller. This would be a -ve lens and opposite to a refractors lens. Make one heck of an eyepiece though.

[bojan]

This is probably not complete lens system... Most likely it is part of bigger zoom or something similar
Forget it, you can not do anything usefull with it :-)

[monoxide]

lol, id have to buy a whole weight bench to chain to the back of my dob if i used that for an eyepiece

[Darkplague]

I was going to make it into a refractor however now reflecting on it, it is more trouble than its worth.

Just thought that it might be a really good lens to use , one of those rare items that could be that "gem" that somebody doesnt know they are selling.

Who knows, this lens might be worth a lot and be super accurate, however its too much of an unknown.

[Darkplague]

Originally Posted by Terry B

The person selling it answered a question saying both surfaces are concave and it seems to make objects smaller. This would be a -ve lens and opposite to a refractors lens. Make one heck of an eyepiece though.

Yes I read that too, but looking at the picture through the lens, the objects behind it appear smaller, which is what you want at the focuser end no???

[Darkplague]

Originally Posted by bojan

This is probably not complete lens system... Most likely it is part of bigger zoom or something similar
Forget it, you can not do anything usefull with it :-)

Bah, you had to spoil my party!

I just thought I could make a nice 6" refractor with it, for relatively cheap. The price is still at $41.

[davewaldo]

I have a large telescope objective and at close range it makes objects seem smaller. I have a feeling that lens on ebay would work as a telescope. I had my eye on it also but thought I would give it a miss. The surface of the lens looks a little "chunky" also.

But I also agree that if it is infact "concave" that it would not work.

[bojan]

Originally Posted by davewaldo

I have a large telescope objective and at close range it makes objects seem smaller. I have a feeling that lens on ebay would work as a telescope. I had my eye on it also but thought I would give it a miss. The surface of the lens looks a little "chunky" also.

But I also agree that if it is infact "concave" that it would not work.

There in no way negative lens (and this is what is is) can work as an objective of the telescope.
Telescope lens does sometimes make objects smaller, but then it also inverts them (that means, what we see then is the real image of the object behind the lens, formed in front of it, provided the object is farther away than the focal point).
In this case, it is obvious that the lens is negative, and I am sure it was only part of the bigger system.
What may be possible is to add positive, strong and large lens in front of it
so that this negative lens could act as some sort of barlow..
But I would not recommend it, because, this lens, being designed for a specific optical system, can perform in terms of abberations etc, ONLY in the system it is designed for. So it would have been an expesive game to play with it, considering the size of the whole thing, and no guaranties it would work properly, if at all

[Darkplague]

Originally Posted by bojan

There in no way negative lens (and this is what is is) can work as an objective of the telescope.
Telescope lens does sometimes make objects smaller, but then it also inverts them (that means, what we see then is the real image of the object behind the lens, formed in front of it, provided the object is farther away than the focal point).
In this case, it is obvious that the lens is negative, and I am sure it was only part of the bigger system.
What may be possible is to add positive, strong and large lens in front of it
so that this negative lens could act as some sort of barlow..
But I would not recommend it, because, this lens, being designed for a specific optical system, can perform in terms of abberations etc, ONLY in the system it is designed for. So it would have been an expesive game to play with it, considering the size of the whole thing, and no guaranties it would work properly, if at all

The item has ended now so I cant be tempted !!

I know it would have been a long shot to do anything useful with it, but it doesnt hurt to ask questions

[bojan]

No worries mate, we all have questions.. this is what this forum is for, among other things
So we helped you not to waste money

[Geoff45 (Geoff)]

Originally Posted by Darkplague

I was thinking about buying this lens from ebay but couldnt find any info on it anywhere.

http://cgi.ebay.com.au/ws/eBayISAPI....3434&rd=1&rd=1

Do you think it is possible to make a cheap refractor out of it??

The lens is a Besco E.F series 3, 6" diameter. Unfortunately this means nothing to me at all (

HELP!!!!

You can get a good refractor or you can get a cheap refractor. You cannot get a good, cheap refractor.
Geoff