Building a Plossl eyepiece

[Chriske]

Did not know where to post, so I also posted in the eyepiece section.

Hi,

Just finished building an eyepiece and I was surprised it worked, and it worked rather good as a matter of fact. It was a quick test using a refactor with a 1 1/4 focuser, handhelding that eyepiece. So I could not see the entire FOV.

From what I've read the acromats should be placed as near as possible, front lenses pointing to each other, so I did.

I made a holder in which I could change the spacing between the two. Observed a large post at about 300m distance : in both occasions, lenses very near and also at about 60mm apart the result is just the same.

How is that possible...?

Lenses 50mm diameter(was a binocular) F=180mm

 

Thanks...

[John]

I've replied to your other thread on this:

 

[davidc135]

8 hours ago, Chriske said:

Did not know where to post, so I also posted in the eyepiece section.

Hi,

Just finished building an eyepiece and I was surprised it worked, and it worked rather good as a matter of fact. It was a quick test using a refactor with a 1 1/4 focuser, handhelding that eyepiece. So I could not see the entire FOV.

From what I've read the acromats should be placed as near as possible, front lenses pointing to each other, so I did.

I made a holder in which I could change the spacing between the two. Observed a large post at about 300m distance : in both occasions, lenses very near and also at about 60mm apart the result is just the same.

How is that possible...?

Lenses 50mm diameter(was a binocular) F=180mm

 

Thanks...

Would the 2 binocular lenses, each of f= 180mm, together have a fl of 90mm? You would be using a very low power. 

Also, how much of the 50mm plossl aperture would be used? If spherical aberration is proportional to the 4th power of aperture that might explain the wide spacing tolerance.

David

[Chriske]

David,

I'll be using that 'Plossl' in combination with a 150mm refractor f15.7.
So primary image of the Sun will be about 24mm. I'll project the image of the sun on a white screen. I'll be refocusing until I have a very large sun on that screen.

So if the combined FL of that Plossl is 90mm it has no effect on the projected image. Visual observing would indeed give me a very low magnification. But I will not use it for visual observing at all.

The most important reason why I use these large lenses, and as a Plossl combination, is to avoid heating up that eyepiece while projecting the sun.

Thanks for the input. Still have to learn about these self-made eyepieces...;-)

[Chriske]

Thanks John,

Nice tool..!