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]

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, :welcome: 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]

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]

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:poke:

I think you meant SCT/MCT/Refractor :rofl:

CS-John B

[iceman]

Whoops, of course :P

[davidpretorius]

hi lafey!!!