Curved Vane Spider?

Rich,
The curved vane spider in my ten-inch Newt completely eliminates the
diffraction spikes on bright objects. I have compared views with a
regular spider in the same scope. It is definitely a more pleasing image
and you can see a little more detail on the moon and bright planets, but
but it is difficult to determine if there is better contrast with the
curved vane spider. Although it eliminates the spikes, it does it by
smearing them over the entire field of view. Here's the scope:
http://home.fuse.net/astronomy/Reflectors.html
After this experience, I wouldn't build a Newtonian reflector without
a curved-vane spider.
Clear skies
Larry Brown



Rich McMahon wrote:

I noticed in protostars recent add that they advertised a curved vaned
spider. There also was a Sky an Tel article on this. Has anyone tried
it. I know some folks have used a 3 over a 4 vane spider for planetary
and like it. But haven't heard about the results of the curved vane
spider.

Rich

"Larry Brown" wrote in message
...
Rich,
The curved vane spider in my ten-inch Newt completely eliminates the
diffraction spikes on bright objects. I have compared views with a
regular spider in the same scope. It is definitely a more pleasing image
and you can see a little more detail on the moon and bright planets, but
but it is difficult to determine if there is better contrast with the
curved vane spider. Although it eliminates the spikes, it does it by
smearing them over the entire field of view. Here's the scope:
http://home.fuse.net/astronomy/Reflectors.html

Hi Larry,
According to your blurb on the site, the diffraction spikes are still
discernable. Are you now saying they're not? (Not to put you on the spot or
anything, I'm just curious if there's been a change in your perception, or
if there's an error somewhere). Would you please clarify?

As for contrast, I'm a believer that spikes have an impact on the eye.
Until someone can prove otherwise, it simply makes sense (to me) that
introducing bright spikes of light radially beyond the target object will
change the eye's response. That "belief" aside, I simply hate spikes, just
as much as I hate astigmatism. Although not technically an optical aberation
(defect of focus) they are a general aberation nonetheless in that they are
not what one would normally expect from their vision. When using my Dob, I
am forced to consciously ignore them. With the SCT, I don't even have to
think on it. So, as you can see, I am really interested in knowing just how
effective a curved vane spider would be.

-Stephen

When using my Dob, I
am forced to consciously ignore them. With the SCT, I don't even have to
think on it. So, as you can see, I am really interested in knowing just how
effective a curved vane spider would be.

-Stephen

The only time the spikes bother me is when viewing a planet. Then I realize
that the integrated sum of the diffraction spikes are washing out some of the
planetary detail.

But I believe that curved vane spiders are no better than straight vane spiders
in this regard and may actually be worse because they are longer.

jon

"Jon Isaacs" wrote in message
...
When using my Dob, I
am forced to consciously ignore them. With the SCT, I don't even have to
think on it. So, as you can see, I am really interested in knowing just
how
effective a curved vane spider would be.

-Stephen

The only time the spikes bother me is when viewing a planet. Then I
realize
that the integrated sum of the diffraction spikes are washing out some of
the
planetary detail.

But I believe that curved vane spiders are no better than straight vane
spiders
in this regard and may actually be worse because they are longer.

Thanks Jon.

Makes sense that the longer vein would add some diffraction. I'd still pay
the price to get rid of the spikes though. Especially considering the extra
45mm of aperture between my 8" SCT and "10"" Dob.

Yet, another modification to add to the Dobber to make it behave more like
the SCT. ;-)

-Stephen

Stephen Paul wrote:
Yet, another modification to add to the Dobber to make it behave more like
the SCT. ;-)

-Stephen


Heh.....I was just going to ask why this isn't done. Would flat glass
work, or would it have to be a correcting lens, like an SCT?

Dave

The object of the curved vane spider is to eliminate the spikes seen with
the 3 or 4 vane spiders. In that, they are effective. However, the
diffraction of the light is still there and has now become a more area
appearance as the sum of the diffraction produces a spherical diffraction
shape. The advantage to this shape is that it is a lot dimmer than the
straight spikes from the straight edges of the spider. On an area object
like a planet or the moon, the total effect on the contrast is minimal
relative to the regular straight spider but on star points, the dim
diffraction ends up being basically invisible to the eye and thus a more
pleasing view of bright objects is obtained.

--
There are more Democrats on the Calif. Special Election than Republicans!
Go count if you don't believe me!
Bob May

Some experimenters have found that the length and thickness of the vanes
themselves contribute very little to optical problems. Here is a link to a
site where they experimented with different sizes:
http://www.deepskyobjects.ca/spider.htm
Clear skies
Larry Brown

Stephen Paul wrote:

"Jon Isaacs" wrote in message
...
When using my Dob, I
am forced to consciously ignore them. With the SCT, I don't even have to
think on it. So, as you can see, I am really interested in knowing just
how
effective a curved vane spider would be.

-Stephen

The only time the spikes bother me is when viewing a planet. Then I
realize
that the integrated sum of the diffraction spikes are washing out some of
the
planetary detail.

But I believe that curved vane spiders are no better than straight vane
spiders
in this regard and may actually be worse because they are longer.

Thanks Jon.

Makes sense that the longer vein would add some diffraction. I'd still pay
the price to get rid of the spikes though. Especially considering the extra
45mm of aperture between my 8" SCT and "10"" Dob.

Yet, another modification to add to the Dobber to make it behave more like
the SCT. ;-)

-Stephen

Heh.....I was just going to ask why this isn't done. Would flat glass
work, or would it have to be a correcting lens, like an SCT?

Dave

Flat glass does work, but it has to be optically flat and this is not a simple
task.

But of course adding the glass means you now have the same problem that SCT
suffer from, DEW. It also means the scope is more fragile, something else to
break.

jon

But of course adding the glass means you now have the same problem that SCT
suffer from, DEW. It also means the scope is more fragile, something else to
break.

jon



In which case why not then just make it a corrector and get it over with?
rat
~( );

email: remove 'et' from .com(et) in above email address

In which case why not then just make it a corrector and get it over with?
rat
~( );


How about just leaving things well enough alone and living with the spikes?

jon