Achromat - home made?
 

AFter researching, it seems that achromats are really three macro lenses put together. Two to make () and a third to top it off ()) . And in my search I found that telescopes have achromats in them - so I wonder if it would be possible to either buy a cheap charity shop kids telescope and get the achromat from it or pull together macro lens to make a achromat. Anyone try this? Any thoughts?

Bob Hart
 

Mandy.

A kid's telescope eyepiece may be too small a diameter. The SW5042 lens set for the Tasco telescope comes out at about 44mm at the front element and it is only barely wide enough for the 24mm x 18mm frame. This was my experience with the PD150 which has a 52mm front element on its built-in lens (58mm filter mount). For smaller camcorders with a 37mm front end, a smaller telescope or binocular eyepiece may work but I have my doubts.

As with the SW5042, you may find your home made achromat lens may have to be within 12mm to 18mm of the groundglass. This is great for a very short path but there are issues with edge softness in my version though I got round it by framing a little tighter on the gg. Brightness across the image was even without any fall off. Also with the SW5042, I had to severely modify the mount for the glass and place it as close as I could get to the front element of the camcorder's own lens to get the 44mm diameter path to work satisfactorily.

If you later choose to make a prism path to erect the image, you will have to use something else with a longer path to the gg, probably something in the ballpark of 5+ to 7+.

The music video .mov file on www.dvinfo.net/media/hart was shot through the SW5042 lens set. Any of the "mtatk?.JPG" images there were shot through this lens set.

http://www.surplusshed.com/pages/cat...elenses_1.html

At $7.50 plus shipping, I wouldn't bother trying to make my own. http://www.surplusshed.com/pages/item/l1590.html

Court

Very true.
The focal length is 170mm, which I think isn't going to be a strong achromat - isn't it the shorter, the stronger?

The problem is this : I live in Canada and although $7.50 is very inexpensive, I have to factor in shipping to Canada, money exchange and wait time. So $7.50 end up being like $20+ for something that might be marred, marked or scratched - a second that might be in the end, useless - whereas making one, I can scrour places today and find what I need. Yes, maybe it will be a waste of time, but it will be a grand adventure and learning experience.

I didn't realize that you lived in Canada, so yea, it'd probably take some extra time for it to get there. I ordered one and I can tell you that it's not marked up - brandnew without a scratch. It wouldn't bother me if it did have a scratch though. I'm just using it for proof of concept.

Good luck.

Court

What is the strength on it? +4 +2 +10?

These are diopters, just like reading glasses, they indicate level of magnification/closeup capability.

Radek

It's the second link that I have above.

Court

Ok, I have clicked the right link, but I don't see anywhere that shows the strength of the dioptre. Am I missing something? I am comparing it to Macros that have the +1 +2 +4 +7 +10 beside them. Is it listed somewhere, because I can't see it.

You can determine the diopter rating by this equation:
Diopter = 1/[Focal length in meters]

D=1/0.170 ==> 5.88 (for the lens in the link in my post)

Court

That is great, thanks you. +5 will do just fine! Do you have any still from your system using the achromat you got from Surplus shed?

I've not really started yet. I just got the ground glass in today, so maybe this weekend I'll give it a crack.

Court

Opinion:

Not everything should be homemade. If you find yourself making something only because it will save you $20, $30, whatever - you're most likely ripping yourself off...Dont forget your time is worth something too.

I try to ask myself what the TRUE cost of something is. If I do that I almost always end up making what I NEED but does not exist and purchasing a professionally made product for the rest.

Looking at Surplusshed.com again, this little item came up:
http://www.surplusshed.com/pages/item/l3034.html

It is called a 52MM SPOTTING SCOPE OBJECTIVE - does anyone know what that means and can they explain it in layman's terms?

It's the same thing that I picked up, just with a larger focal length.
http://www.surplusshed.com/pages/item/l1590.html

It's just a convex lens, in this case a doublet, which corrects for two different light wave lengths - most likely red and blue - so that your resulting image is closer to being color correct. In otherwords, it's correcting for aberration.

You can get triplets as well, but the price goes up. That would correct for red, blue and a wave length inbetween. They are some that correct for more wave lengths, but the price is way up there.

This lens I got from them appeared to me to be new. Was shipped very protected and seems to be pristine.

Court