What is a quintuplet?

[GalaticBoba]

Just wondering...

From my reading broadly speaking, (I know there are exceptions), a doublet has two lenses, second lens re focuses blue and red light to reduce chromatic aberration. ED and fluorite coatings are often used here to further reduce CA. Marketing often use Achromatic as a selling keyword.

Triplets have an additional lens which focuses 3 wavelengths further reducing CA. Marketing often calls these Apochromatic.

Quadruplets builds upon the triplet and adds a fourth lens which flattens the FOV useful in AP.

So what does the 5th lens do in a quintuplet?

Edited September 22, 2021 by GalaticBoba

[happy-kat]

You can have doublet Apochromatics such as skywatchers ED range. And doublets that are achromatic

Edited September 22, 2021 by happy-kat

[GalaticBoba]

1 minute ago, happy-kat said:

You can have doublet Apochromatics such as skywatchers ED range.

I know there are exceptions, when fluorite is used in doublets these are often called Apo's.

[happy-kat]

I had edited my post as I added achromatic as well, which are not apochromatic but both can be doublets.

Achromatic are not corrected on blue.

[John]

Often these multiple element systems have the lenses arranged in more than one group, so you can find a doublet or a triplet set much closer to the focuser of the scope.

The TAL Apolar 125mm had 6 elements with just a singlet as the furthest forward and no low dispersion glass types used. It was pretty much apochromatic as I recall. I would not want to have to collimate one though !

Point 7 above is the focal plane, not a further element.

 

[GalaticBoba]

11 minutes ago, John said:

Often these multiple element systems have the lenses arranged in more than one group, so you can find a doublet or a triplet set much closer to the focuser of the scope.

The TAL Apolar 125mm had 6 elements with just a singlet as the furthest forward and no low dispersion glass types used. It was pretty much apochromatic as I recall. I would not want to have to collimate one though !

Point 7 above is the focal plane, not a further element.

 

I see, so a quintuplets could actually be similar to quads and triplets just with lenses grouped together. I would assume in the above diagram 2, 3 and 4 are for CA and lenses 5 and 6 are for flattening the image.  

[Louis D]

Many modern quintuplets are triplets up front with a doublet corrector somewhere between it and the focal plane.

Edited September 22, 2021 by Louis D

[GalaticBoba]

Thanks all, this makes sense now. Google couldn't find this answer.