Whaaat?

[goosesilverwolf]

I've just recieved some eyepieces for my telescope and noticed that they appear to have different letters/codes.

The ones for my own scope are F eyepieces, whereas the ones I've just been given are H and HM eyepieces. Does this actually mean anything?

[John]

H = Huygens type

HM = Hugenian Mittenzwey type

Both simple, non-achromatic eyepieces.

I suspect the F on your other eyepieces might stand for Focal Length which is a specification rather than an eyepiece design.

[newman]

Try them out, but tbh these are very old optical designs (dating back all the way to the 17th century) and are completely obsolete these days. The only reason they're still made is to fill the ultra cheap category. If you have a longer focal length scope, I suppose you could make due with them until you've had a chance to invest in something a bit more decent.

[rwilkey]

Hi there, there is a very good article on ep types here: Eyepiece - Wikipedia, the free encyclopedia

[goosesilverwolf]

Try them out, but tbh these are very old optical designs (dating back all the way to the 17th century) and are completely obsolete these days. The only reason they're still made is to fill the ultra cheap category. If you have a longer focal length scope, I suppose you could make due with them until you've had a chance to invest in something a bit more decent.

Thank you... I got them from my late auntie so they have sentimental value to them. I liked the adition of moon and sun filters for them. Shame the skies have been poor for gazing!

Hi there, there is a very good article on ep types here: Eyepiece - Wikipedia, the free encyclopedia

Thank you for that... I will be sure to have a look at that

[rwilkey]

Do not use any back fitting sun filters if you have one, they are not safe. The only safe solar filters are those specially designed to fit over the full aperture of your telescope at the front. Filters that screw into the eyepiece are VERY DANGEROUS to your eyesight.

[Merlin]

This is where those Huygenian eyepieces come in useful and why I keep a set. They can be used to project the Sun onto a screen or into a box.

There are no cemented elements in Huygenian eyepieces ( with the exception of achromatic Huygenians ), so there's no balsam to melt in the intense solar heat.

This type of eyepiece is best used with long-focus refractors, say, from f.12 onwards.

A well-made Huygenian eyepiece, used with a long-focus refractor, can give superb on-axis definition and lets plenty of light through.

[crazyjedi]

Nice family heirloom though