Focusing different eyepieces

[Skills]

Whilst observing I'm frequently switching eyepieces, my eyepieces don't have the same focus point. On Saturn it's not a problem but when I'm trying m13 it gives me difficulty finding focus.

Any good tips? I presume I should try to remember how far to turn the focus knob, any clever methods?

Thanks

Adrian

[Ad Astra]

Some eyepiece sets are called "parfocal" - meaning that they all focus in pretty much the same place.... but if your eyepiece collection is like mine, you may have many different types.

No help for it but to adjust as you go - otherwise you will have to remember the change for every possible combo, and that can be a chore... which is how the manufacturers sell parfocal eyepiece sets!

Dan

[John]

You can get rings to fix on the eyepiece barrels - through some experiment you adjust the position of these so that all the eyepieces are at focus at the same point in the focuser travel. They are called par-focalisation rings and cost around £3 per eyepiece I think.

Personally I've put up with the slight inconvenience. After a while you just get to "know" how much adjustment each eyepiece needs and apply it without thinking too much.

[Skills]

Thanks John and Dan, parfocalising rings looks like something I might try.

Adrian

[NGC 1502]

Hi Adrian. Good advice already given.

Another method is this - It's hard to focus accurately on a 'fuzzy' so I offset to

a reasonably bright star, focus on that, then back to the faint fuzzy.

HTH, Ed.

[Ad Astra]

Excellent, Ed!

Pretty much sums up the technique I use, too. I'd never heard of parfocalization rings - I'll have to look them up. Don't think I'd use them for everything, but I have one or two odd-ball eyepieces that are far different from others that would benefit from that.

Dan

Hi Adrian. Good advice already given.

Another method is this - It's hard to focus accurately on a 'fuzzy' so I offset to

a reasonably bright star, focus on that, then back to the faint fuzzy.

HTH, Ed.

[Capricorn]

I have a set of eyepieces that are parfocal.

Problem is that they all have completely different focal planes, so they actually are not parfocal at all. Which is to put it mildly annoying as hell. I think that some of the cheap and mixed eyepieces I have have better coincident focal planes then these do.

[twotter]

I think I'm so used to adjusting the focus with every EP change that if I had a parfocal set I'd end up adjusting anyway

[Roy@Aldermaston]

I bought a set of four parfocal rings from Modern Astronomy for £16 with free postage - not the cheapest but a reliable service. One is in permanent use to match the focal point of an high powered eyepiece to the focal point of my CCD camera - saves a lot frustration when imaging.

Roy

[John]

I have a set of eyepieces that are parfocal.

Problem is that they all have completely different focal planes, so they actually are not parfocal at all. Which is to put it mildly annoying as hell. I think that some of the cheap and mixed eyepieces I have have better coincident focal planes then these do.

Some eyepiece series are more parfocal than others ......