Eyepieces, Barlows, and well... filters

[LaFey]

I think the majority of the Barlows aren't threaded to accept filters, am I right?

When you have a non-threaded Barlow and still want to use filter how do you do it?

Common sense tells me I should screw the filter to the eyepiece, in the regular way and then insert the eyepiece+filter in the Barlow barrel.

Is this common practice? Does this affect the image quality since the eyepiece isn't in direct contact with the Barlow?

[iceman (Mike)]

It's true that filters will screw into the eyepiece and then put them into the barlow. It doesn't degrade image quality - it'll just change the focal point slightly so you'll have to refocus.

What type of scope and barlow do you have?

Some SCT/reflector owners might screw a filter into the diagonal, so they can change eyepieces without having to screw on the filter again.

Hope i've answered your question.. and btw, to the forum! All the way from Portugal! How did you hear about us?

[LaFey]

Thanks for the welcome!

I was searching the web a couple of months ago, for GSO dob reviews and found this community - plenty of useful articles if you own that scope (or dobsonians in general). Yesterday I was again on the hunt for this Barlow + eyepiece + filter question and I ended up here again. I read the existing articles and found my question wasn't addressed yet so I decided to register and give it a shot.

I have ordered a Orion XT-8 dob (previously I've owned a cheap 70mm refractor...) - I also ordered a Shorty-Plus Barlow and a filter pack (both from Orion*) which has the Moon variable polarizer. I read that (and I'll quote):

"With a variable moon filter on a 10 mm SWA Speers Waler eyepiece, the eyepiece doesn't fully bottom in the barlow. But, the 2 mm gap seems to cause no problems."

Common sense tells me this statement is true - have you got any similar experiences? I can't wait to test this myself...



*- No, I ain't an Orion bigot - I just get their material because they have an official retailer here with fair prices and excellent service.

[janoskiss (Steve H)]

Wecome LaFey, our first member from Portugal! No doubt one of the best places in the EU for astronomy.

The filter will raise the eyepiece by a few mm in the barlow. In practice this makes no difference (just a very slight increase in magnification).

[ausastronomer (John Bambury)]

Originally Posted by iceman

Some SCT/reflector owners might screw a filter into the diagonal

Mike,

In 30 years I have never found a need to use a diagonal in a newtonian (reflector), it doesn't suit me cause it gets your head all twisted up at funny angles

I think you meant SCT/MCT/Refractor

CS-John B

[iceman (Mike)]

Whoops, of course

[davidpretorius]

hi lafey!!!