Best place for filters?

Hi, everyone!
I've been using an MK-67 (with 2" Intes diagonal, 1.25" and 2"
eyepieces and 2" Barlow) for a few years now, and I'm considering
getting some filters (UHC, colour), finally.

I'm wondering where in the optical train would be the best spot
to put them, to keep their imperfections from deteriorating
sharpness and contrast as far as possible.

I've got filter threads:

- on the diagonal (facing the OTA),
- on the back of the 2" - 1.25" adapter,
- on the Barlow,
- and obviously on the eyepieces.

Apart from convenience aspects (like the ability to change eyepieces
while keeping filter in place if it's mounted in the diagonal),
what would you suggest? Is there any noticeable difference at all?
Should filters be kept away from the focal plane? Kept close to
the focal plane?

Cheers
Steffen.

"Steffen Kluge" wrote in message
...
Hi, everyone!
I've been using an MK-67 (with 2" Intes diagonal, 1.25" and 2"
eyepieces and 2" Barlow) for a few years now, and I'm considering
getting some filters (UHC, colour), finally.

I'm wondering where in the optical train would be the best spot
to put them, to keep their imperfections from deteriorating
sharpness and contrast as far as possible.

I've got filter threads:

- on the diagonal (facing the OTA),
- on the back of the 2" - 1.25" adapter,
- on the Barlow,
- and obviously on the eyepieces.

Apart from convenience aspects (like the ability to change eyepieces
while keeping filter in place if it's mounted in the diagonal),
what would you suggest? Is there any noticeable difference at all?
Should filters be kept away from the focal plane? Kept close to
the focal plane?


Hi Steffen,

If they are on the focal plane, you will see every bit of dust on them.
However, with most eyepieces, the focal plane is in a ways from the filter
threads.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

According to Chuck Taylor :
Should filters be kept away from the focal plane? Kept close to
the focal plane?

If they are on the focal plane, you will see every bit of dust on them.
However, with most eyepieces, the focal plane is in a ways from the filter
threads.

In other words, it's good to screw them into the diagonal, so
dust and imperfections won't show? Why are most people putting
their filters on the eyepieces, I wonder?

Cheers
Steffen.

Steffen Kluge wrote in message ...
According to Chuck Taylor :
Should filters be kept away from the focal plane? Kept close to
the focal plane?

If they are on the focal plane, you will see every bit of dust on them.
However, with most eyepieces, the focal plane is in a ways from the filter
threads.

In other words, it's good to screw them into the diagonal, so
dust and imperfections won't show? Why are most people putting
their filters on the eyepieces, I wonder?

Probably for conveniece since it's more of a hassle to remove a diagonal
just to change filters.

One solution would be a filter wheel or slider (either holding 4-6 filters)
and keeping one slot open (i.e., no filter) for a clear view.

StefferKluge posted:

I'm wondering where in the optical train would be the best spot
to put them, to keep their imperfections from deteriorating
sharpness and contrast as far as possible.

I've got filter threads:

- on the diagonal (facing the OTA),
- on the back of the 2" - 1.25" adapter,
- on the Barlow,
- and obviously on the eyepieces.

The best place is on the eyepiece. This way, the edge of the filter will not
vignette the field any more than is absolutely necessary. Placing it farther
forward may or may not intrude on the incoming light cone. The second best
place is on the 2" to 1.25" adapter if you have 2 inch filters and want to use
them on 1.25" eyepieces. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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