Orion ED80 is an APO?

Hello all,

Well, I just received an Orion 80mm f/7.5 ED Refractor (#9895 optical tube assembly). Everything I read about it online referred to it as an apochromatic. However, the instruction manual for it refers to it as an achromatic. Which is it? I went back a reread most of the articles looking to see if perhaps they said "APO-like", which I've seen elsewhere, but they say APO. Of course the skies are overcast and it is snowing, supposedly all night. Can anyone ease my mind as I can't see for myself right at the moment Walter

Your manual has a typo, the Orion 80ED is an APO for practical purposes. It won't quite have the color correction of a $2000 80mm triplet APO but it won't have a purple halo around bright objects like you would get with an 80mm F 7.5 achromat.

Joplin

Hi Walter,
Visually, it is pretty much APO, photographic it is not quite APO, depending on what you are imaging.
So, if you are a visual man, it will seem to be an APO when you use it. If you want photography, it will work well, but not perfectly.
Much cheaper than a high end APO though, so they are a deal really.

Rest easy. I have a Vixen ED80SF which optically is the same scope as the Orion ED80. As Joplin said, color correction is excellent. CA certainly won't be a issue except for the most demanding users. It is definately not an achromat.

The problem is that there is no commonly accepted definition for an apochromatic scope, although I believe Roland Christen has advanced a good one. Not to mention that the marketing dept.'s definition is typically looser then engineering's. So when you read a description on any given scope, you have to do a little research to be sure you know what you're getting.

Walter Wozniak said:

Hello all,

Well, I just received an Orion 80mm f/7.5 ED Refractor (#9895 optical tube assembly). Everything I read about it online referred to it as an apochromatic. However, the instruction manual for it refers to it as an achromatic. Which is it? I went back a reread most of the articles looking to see if perhaps they said "APO-like", which I've seen elsewhere, but they say APO. Of course the skies are overcast and it is snowing, supposedly all night. Can anyone ease my mind as I can't see for myself right at the moment Walter

based on modern definitions of apos given by several optical experts, a 3" refractor at f/7.5 and using S-FPL53/proper mating element fits most to all their modern criteria for being an apo.

btw, whether the scope`s an apo or not...or good for AP or not...doesn`t depend on whether it`s a doublet/triplet...as much as what ED glass/proper mating element is/are being used combined with aperture and f-ratio/focal length...

for ex., a 3" f/5 triplet Apo using the same ED element, S-FPL53 in this case, and proper mating elements...will have approximately the same performance/color-correction as a 3" S-FPL53 f/7.5 apo doublet...all else =...

careful inspection of this shows that by simply increasing the focal length of the 3" doublet past the triplet`s 400mm and up to 600mm...causes the apo doublet to be about = to the apo triplet in performance/color-correction...

i`m sure some readers already see the relationship here...that is, an apo triplet the same aperture/f-ratio using the same ED element/proper mating elements will have about 1.5x better color-correction than an apo doublet...all else =...so, given this, it means that the doublet`s f-ratio/focal length should be approximately 1.5x that of the triplet`s to get about the same color-correction, etc...all else =...

hope this helps, 8)

Jim