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New Sub Forum needed - Astro scopes for Visual (1 Viewer)

polarizer?

Anyone ever try using a linear polarizer on the end of a 2 inch eyepiece holder? Would that improve contrast for visual use???

:h?:
 
goldenarrow said:
Anyone ever try using a linear polarizer on the end of a 2 inch eyepiece holder? Would that improve contrast for visual use???

:h?:
Click to expand...

There are different sources for the stray light.

Photographers like circular polarizers(sky light), usually up front.
A linear polarizer might work well on glare inside the barrel or the holder,
but you would be much better off in that case making the interior surfaces
flat black or doing irising.
If you have a reflector, a hood or extended dew shield would be good.
If there is any shine in a holder or guide tube that should be flattened.


For all scopes, if you can tolerate a little yellowing, a "sky filter"
cuts way down on atmospheric haze. For long views it can make the
difference between seeing something and not seeing it.
 
polarizer

OPTIC_NUT said:
There are different sources for the stray light.

Photographers like circular polarizers(sky light), usually up front.
A linear polarizer might work well on glare inside the barrel or the holder,
but you would be much better off in that case making the interior surfaces
flat black or doing irising.
If you have a reflector, a hood or extended dew shield would be good.
If there is any shine in a holder or guide tube that should be flattened.


For all scopes, if you can tolerate a little yellowing, a "sky filter"
cuts way down on atmospheric haze. For long views it can make the
difference between seeing something and not seeing it.
Click to expand...

The only reason for a circular polarizer is because digital sensors get messed up focusing , otherwise a linear should be fine for visual. I will have to report back when I get the chance.

Flocking everything black is a good idea. My scope is well flocked and also has a built in sun shield.

With my scope, irising would just make a slow f/14 scope so much slower and darker to make it unusable.

;)
 
Just to clarify, irising is usually done on a refractor without affecting f/ratio.
To achieve a similar effect on a reflector you would need a baffle 'can' shape,
where the diameter is wider than the scope aperture and there are two irises
top and bottom. Or...ribbed sides. Probably not done due to the size, but it could be
made as a lightweight fabric "pop-up" thing. Like one of those spiral-wire
cat tunnels sprayed black inside.

One thing about polarized light is that the optimum angle shifts with targets and sun.
Rotating would be very handy. Another thing: polarizers lose a lot of light, good and bad.
 
OPTIC_NUT said:
Just to clarify, irising is usually done on a refractor without affecting f/ratio.
To achieve a similar effect on a reflector you would need a baffle 'can' shape,
where the diameter is wider than the scope aperture and there are two irises
top and bottom. Or...ribbed sides. Probably not done due to the size, but it could be
made as a lightweight fabric "pop-up" thing. Like one of those spiral-wire
cat tunnels sprayed black inside.

One thing about polarized light is that the optimum angle shifts with targets and sun.
Rotating would be very handy. Another thing: polarizers lose a lot of light, good and bad.
Click to expand...

Thanks much about the irising for reflectors. Will look into it!
B :)
 
You probably already have the bottom step-in.
Too bad instruments these days don't come with the slide-out
hoods of yesteryear. Some spotters do.
 
goldenarrow said:
Question - do you think the MagicBall is more useful that a regular ball head? I was thinking of just using a panorama head/base under the gear head but not sure.

B :)
Click to expand...

I missed that, sorry.
I haven't much experience with tripod heads. I have the Manfrotto 3D, the Vixen Porta geared with micromotions and a lightweight regular ball, but I know there are better regular balls out there.
I have the big magic ball. It has one lever with two controls, friction and lock. It is very stable and quite versatile. I put one hand on the lever and with the other I handle the mount almost as a pistolgrip.
5ebypa9u.jpg

I tried this configuration for zenith astronomical use.
4uzu5eju.jpg
 
Very nice! Looks like a very well damped tripod.
I was thinking or having a ball inside 3 crossed dowels as a mount for a telescope.
 
handling ability

kkokkolis said:
I missed that, sorry.
I haven't much experience with tripod heads. I have the Manfrotto 3D, the Vixen Porta geared with micromotions and a lightweight regular ball, but I know there are better regular balls out there.
I have the big magic ball. It has one lever with two controls, friction and lock. It is very stable and quite versatile. I put one hand on the lever and with the other I handle the mount almost as a pistolgrip.
Click to expand...

Interesting, the biggest magicball can handle 10 kg, the smaller one 5 kg (same as my 410 geared head). I wonder how fine adjustments can be made with any ball head, including the magicball. Geared heads as well as astro heads with slow-motion controls are automatically locked in place as soon as you stop turning the controls, no need to twist lock anything. But the downside is that larger movements are more awkward, like following a bird in flight. I have a mid-sized Manfrotto 498 ball head but found it too floppy and sticky and difficult to follow birds. The head could use some cleaning I suppose!!

You have a very nice setup in the pictures, especially for wide field astro use or birding a shoreline.

:t:
 
I can hardly follow bird flight handheld unless they are far away. I use the mount for distant objects and when looking birds mating. For higher magnifications I prefer the Vixen Porta Mount (used with the 6" Maksutov mostly) and the Nexstar GOTO mount (used with the 6" Schmidt Cassegrain). They both have slow motion controls.
Birding is much more demanding from optics. Whereas color fridge never annoys me in stargazing it is quite obvious around the feathers and in particular the bill of birds in our sunlit enviroment. But it is minimized when I remind myself to stop testing the optics and look at the bird instead. I remember how obvious it was in the Orion 80ST. The WO 66ED is much better in this regard, similar to the Canon 18x50 IS. It isn't waterproof but I only use it from my balcony for birds (I live in a hill, looking at the sea) and it proved good for stargazing on the mountain with cold, wind and humidity but, of course, no rain.
I'll never forget Andromeda in full darkness and at zenith with that scope and an LVW 22mm. I also saw the USS Enterprise during it's last trip, anchored just in front of my house, 2 miles away. Nice to have a little spotting scope for many uses. But most of my eyepieces are mainly astronomical with pincushion on linear objects. Hyperion zoom is good for terrestrial but I gave it to my daughter. I hope I'll be able to get a Leica Aspheric Zoom or something spotting scope oriented some day.
 
Last edited:
Here is my WO 66ED on Vixen PortaMount, during the recent partial solar Eclipse.
a9eza5an.jpg

And that's the C4 Maksutov during the transit of Venus last year. Nice spotting scope that too and it takes a 0.63x focal reducer.
umyrama6.jpg
 
Sweet 'chunky' telescopes. You certainly have a great location for them to work out in.
Nice to see a good photo of the Vixen mount.
 
goldenarrow said:
I have a mid-sized Manfrotto 498 ball head but found it too floppy and sticky and difficult to follow birds. The head could use some cleaning I suppose!!

:t:
Click to expand...

I'm working (in my head) on a telescope-in-ball idea to smooth things
out for eagles. I looked at foam spheres, but there would be a lot of
work fiberglassing them. A nice hemispheric salad-bowl might do better,
nice solid enameled metal. Maybe in the crown of a crossed-sticks
tripod. Or someone could just start with a junker "AstroScan" ball
and base, shop the chimney down and scoop out for the scope.
 
ajyjamyp.jpg

Here's in spotting scope configuration. 16.67x with an ES68 24mm, 4mm exit pupil and 4 degrees TFOV.
8amydyty.jpg

With Delos 10 and 6mm higher powers of 40 & 66x, the later at 1mm exit pupil and 1 degree TFOV. Ethos 13 gives ~30x at over 2mm and 3 degrees but I don't like it for terrestrial.
 
Short APOs are in their own class, both spotter and astro.
The length advantage is obvious. Weight-wise they can be heavier than astros sometimes,
and the monster eyepieces bring up another issue: a longer focal length for the scope
makes it much simpler to get performance out of ordinary eyepieces. A normal Plossl
6mm would be tiny and have more aberration near the edges, so the Delos-type eyepieces
become important to getting decent performance. For an FL of 700mm, you can get a
Super-Plossl 10mm with a generous view. The focusing tolerance is also relaxed.
 
Last edited:
APO's have a nice view but I find them a bit heavy. Had a 80mm Celestron ED and even at 6 lbs., seemed too heavy for me to carry around to go birding. My current experiments with the 89mm Maksutov (4 lbs. and shorter) are promising but I have to see if that polarizer helps enough with contrast. If not, then I may revisit using a refractor for birding. We shall see. I have a chance next week (if work/boss/job does not interfere!!!) to go out with birders and use the scope. Portability is important to me for some reason. I think it is because I like the camaraderie of the birding group and roaming around with them outdoors to find the elusive birds.
 
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"zoom" with a barlow lens??

I have a Nikon Fieldscope zoom (MC model). Nice and sharp but the FOV is too narrow. I prefer to use the Brandon 32mm that came with the telescope.

I will experiment soon with a camera Live View screen as my "eyepiece". Might be very useful on Bird Walks in a group. I don't have an eyepiece I can attach it to, so the image will be upside-down during my experimentation. A barlow lens might be able to "zoom" the image. We shall see!

Today's experiment with the polarizer was positive. Nice contrasty image. But the sun had to be out to get the full effect. Hence, the camera Live View idea. The camera compensates somewhat for the darker image. Can't wait to try it out this weekend! I am such a fool for stupid ideas......

3:)
 
The best volkszoom is the Baader Hyperion zoom 24-8. Another good one is the William Optics 22-7.5. And the premium one is the Leica Aspheric. I have the Baader and had a cheaper 21-7. They were day and night.
 
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