Anyone Here Use a Hartmann Mask?

If so, I would be pleased to hear of your experience.

I plan to try one for focusing with an SLR (film or digital) at prime
focus on an 8" SCT.

Tell me where to stick it -- must it be placed immediately in front of
the corrector plate, or can it be placed over the end of the dew
shield?

TIA!

Davoud

--
usenet *at* davidillig dawt com

I use a variant of a Hartmann mask with my 10" LX200 for imaging, but it's
just as useful with a film camera. The one I use has triangle openings
instead of round. When all is perfectly in focus you see a clear triangle
in the eyepiece which can appear upright or reversed. This will tell you
whether you are inside or outside of focus.

Al


"Davoud" wrote in message
...
If so, I would be pleased to hear of your experience.

I plan to try one for focusing with an SLR (film or digital) at prime
focus on an 8" SCT.

Tell me where to stick it -- must it be placed immediately in front of
the corrector plate, or can it be placed over the end of the dew
shield?

TIA!

Davoud

--
usenet *at* davidillig dawt com

I use one with my c11 . It's a homemade version with 3 holes rather than 2
.. It doesn't matter if it's at the end of the dewshield or next to the
corrector from an optical point of view but there might be mechanical
problems depending on how the dewshield is attached and how heavy is the
mask .

Matt Tudor

"Al" wrote in message
et...
I use a variant of a Hartmann mask with my 10" LX200 for imaging, but it's
just as useful with a film camera. The one I use has triangle openings
instead of round. When all is perfectly in focus you see a clear triangle
in the eyepiece which can appear upright or reversed. This will tell you
whether you are inside or outside of focus.

Al


"Davoud" wrote in message
...
If so, I would be pleased to hear of your experience.

I plan to try one for focusing with an SLR (film or digital) at prime
focus on an 8" SCT.

Tell me where to stick it -- must it be placed immediately in front of
the corrector plate, or can it be placed over the end of the dew
shield?

TIA!

Davoud

--
usenet *at* davidillig dawt com

Davoud wrote:
Tell me where to stick it -- must it be placed immediately in front of
the corrector plate, or can it be placed over the end of the dew
shield?

Doesn't matter. Being an incorrigible cheapskate, I use a tree -- I
focus on a star through the leaves of the tree and when the images merge
I know I have focus.

Best,
Stephen

Remove footfrommouth to reply

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I have used one for many years now, and I swear by it. Some pointers.

Use a star. There is no ambiguity then.

You can place it over the corrector plate or the dew shield. If there's a
difference, I didn't notice.

Good Luck !
--- Dave

"Davoud" wrote in message
...
If so, I would be pleased to hear of your experience.

I plan to try one for focusing with an SLR (film or digital) at prime
focus on an 8" SCT.

Tell me where to stick it -- must it be placed immediately in front of
the corrector plate, or can it be placed over the end of the dew
shield?

TIA!

Davoud

"Davoud" wrote in message
...
If so, I would be pleased to hear of your experience.

I plan to try one for focusing with an SLR (film or digital) at prime
focus on an 8" SCT.

Tell me where to stick it -- must it be placed immediately in front of
the corrector plate, or can it be placed over the end of the dew
shield?

TIA!
Anywhere you want.
The 'downside' of putting it in front of the dew shield is purely
'mechanical' (can your dew shield support the weight).
A 'simple' mask, with round holes, tends not to work well to get the last
'tweak' of fine focus. Ones using shaped holes are better in this regard.
You can also use patterns designed to tell you which way the focus needs to
change.
One alternative that also works well for star focussing, is a simple piece
of aluminium 'strip'. This can be a lot lighter than the mask, and simply
hangs on the dew shield. It produces a single pair of diffraction spikes. If
there are two spikes each side, you are not in focus, and as you focus, the
spikes move together, become one, and then move apart again as you go
through the focus point. I use this as the ultimate in simple focus aids,
when working mobile, since a piece of bent strip, can just fit in the corner
of an eyepiece case, and is no great loss, if it gets forgotten.

Best Wishes

One alternative that also works well for star focussing, is a simple piece
of aluminium 'strip'. This can be a lot lighter than the mask, and simply
hangs on the dew shield. It produces a single pair of diffraction spikes.
If
there are two spikes each side, you are not in focus, and as you focus,
the
spikes move together, become one, and then move apart again as you go
through the focus point.

You mean just hang a strip of foil? How wide should it be? How is it hung?
If the scope is tilted, the strip will not just hang free. What do you mean
exactly?

Thanks

I made a Hartmenn mask with two holes out of construction paper for my
8" SCT. It helped a lot but I know the holes are not perfectly round and
not exactly centered on the corrector. So, Your suggestion of a strip of
foil sounds interesting.. I to want to hear more! Width, Length,
Placement,...

--
Michael A. Barlow
"Thomas M" wrote in message
news:d0o1c.55946$A12.10299@edtnps84...

One alternative that also works well for star focussing, is a simple
piece
of aluminium 'strip'. This can be a lot lighter than the mask, and
simply
hangs on the dew shield. It produces a single pair of diffraction
spikes.
If
there are two spikes each side, you are not in focus, and as you focus,
the
spikes move together, become one, and then move apart again as you go
through the focus point.

You mean just hang a strip of foil? How wide should it be? How is it
hung?
If the scope is tilted, the strip will not just hang free. What do you
mean
exactly?

Thanks

"Thomas M" wrote in message
news:d0o1c.55946$A12.10299@edtnps84...

One alternative that also works well for star focussing, is a simple
piece
of aluminium 'strip'. This can be a lot lighter than the mask, and
simply
hangs on the dew shield. It produces a single pair of diffraction
spikes.
If
there are two spikes each side, you are not in focus, and as you focus,
the
spikes move together, become one, and then move apart again as you go
through the focus point.

You mean just hang a strip of foil? How wide should it be? How is it
hung?
If the scope is tilted, the strip will not just hang free. What do you
mean
exactly?

Thanks
Basically you can use anything you want. Foil will be rather difficult to
work with unless conditions are completely 'wind free', I use one of the
aluminium strips about 1/16" think, and 3/8" wide, sold in home improvement
stores. You could use foil, by 'rolling' it to make the piece a little more
rigid.
The strip doesn't have to 'hang free', just cross the front of the scope. If
you have a straight wire/rod/strip, across the front of a telescope, you get
a pair of diffraction spikes displayed in the eyepiece. In the case of a
Newtonian telescope (which typically has two strips holding the secondary),
you get four spikes. The spikes appear as single 'peaks', when the scope is
in focus. If you have something like a bit of bamboo garden cane handy, try
the experiment of looking through the eyepiece at a star, and just holding
this so that it passes across the field of view of the scope. You will see
the spikes.

Best Wishes

I'm not trying to be picky, and I know the term Hartmann Mask now refers to
a mask for focusing, but wasn't the original use of the term restricted to
the mask used for testing optics by comparing inside and outside of focus
images?

Thanks

Chuck Taylor
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Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/
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