Viewing Saturn from a 6 telescope

[yiuscott]

Viewing Saturn from a 6" telescope

Hello

I am not quite sure what resolution i am suppose to see if i look through saturn in my Orion 6" Newtonian reflector at 300X. Can anyone show me a picture of saturn from a 6" telescope that is not editted? Thank You

Scott

 

[freerangequark]

You'll know Saturn when you see it. It won't be very large in your field of view; fairly small infact... a dull yellow in color. The rings will be obvious at times and much more difficult to see if the viewing angle is edge on. I don't know what the current angle is relative to Earth.

 

[russ_watters]

At 300x, it's much bigger than that. More like this:

That's a simulation based on an image I took with a 4" telescope and a webcam. I desaturated it, lowered the contrast, and blurred it. So you should be able to see it at least as well. Some things to look for to make sure you are seeing what you should: the Cassini division (the division between the rings) and banding on the planet surface.

Btw, I calculated that pic to be 300x magnification based on an 18" viewing distance from a standard monitor.

 

[yiuscott]

Wow, nice picture.

I can see something similar to the picture above but i can't manage to take a picture like that. All my pictures comes out tiny and an example is the picture below. What settings do I need for the picture and do i need a motorized scope to take pictures?

P.S. - The picture i took is from a digital camera and the exposture is set at 1/8 sec. The scope is not a motorized scope.

 

[russ_watters]

My pic above was taken with a webcam. Webcams actually get better results than regular digital camers because the technique is to take a large number of frames and stack them with software such as Registax.

 

[yiuscott]

In order to stack lots of frames, the saturn must stay in the same spot within my eyepiece? So do i need a RA motor for that?

 

[russ_watters]

No, but it helps. There are people who are able to get a webcam to snap a few dozen frames while it crosses the field of view. Trying to track manually can work too, but it can also make it jump around. Registax will follow the planet around and line-up the separate frames, but there is a limit to the "jumpiness" it can handle. You can also align them manually, but that can take a while if you have a lot.

 

[yiuscott]

Thank you for the reply.

I used registax as you suggested (aligned and stacked some pictures together). Below is the picture of saturn after registax. The image certainly looks better than before but is still much inferior than other 6" pictures. I can see good quality images from my telescope but I can't manage to capture the quality images... Is this because of my digital camera or is it because I only used 1/8 sec exposture? Furthermore, is there anything I should note when taking a picutre of saturn?

 

[russ_watters]

Exposure is fine, magnification could be higher though (try a barlow). The problem is that you probably only stacked a small handful while with a webcam you can integrate hundreds of pictures and that's how you get the more detailed pics. You should be able to do better than the pic I posted above - your telescope is better than the one I used to take that pic (plus, like I said, I lowered the quality a little before posting it here).

 

[yiuscott]

Thank You for the reply.

I did stack around 200 frames to get this. But am i allowed to have extra magnification? I thought the therotical maximum limit to a 6" telescope is 300X magnification. I tried looking through 600X and it looks slightly blur.

 

[russ_watters]

The theoretical max is about 300x, but that photo you posted is not 300x magnification, it's more like 150. What method did you use to take it and what kind of camera did you use? Eyepiece? Barlow?

Most decent astrophotos are taken with a camera that has no lenses and no eyepiece on the scope. The telescope's objective lens (and a barlow) is all there is and the camera is located at its prime focus.

 

[yiuscott]

I just placed the camera to the eyepiece (I think its called the afocal method, but i am not too sure...). But i used a 2X barlow and a 5mm eyepiece. The camera i used was a normal digital camera for daily use (lumix fx8).

I can't really pull the lenses off the digital camera, does this mean that i need to buy a camera that allows me to do that?

 

[russ_watters]

That's what's great about webcams - it's easy to pull the lens off and modify them for astrophotography.

Among the problems with the afocal method, is the more glass you have between your sensor and your subject, the more distortion and lost light you get. With prime focus, it's just the mirror and the sensor (+ a barlow). Your results are actually pretty good for afocal.

 

[yiuscott]

I read from a website that using prime focus, the magnification is around your focal length divided by 50. Thats 750/50=15 for me. Even with a 2X barlow, that's only 30X. I don't think you can actually see saturn that well with 30X. Does this mean I have to get a 10X barlow lens or something? Or can i just zoom with my camera?

P.S. - Can any webcam work? Can one of those cheap webcams used for MSN conversations work?

 

[russ_watters]

Not sure what website that was, but at prime focus, the magnification depends on the size of the camera's sensor. Here's a calculator: http://www.thecgo.com/id28.html . Typical pixel sizes are 6x4um, but I'm not sure what the SPC is.

Still, you'd want to use a 5x barlow if you can find one. People also stack them.

Better webcams do work better. The Phillips SPC900 is the favorite of photographers.

 

[yiuscott]

I would also like to ask if 0.5seconds is the correct shutter speed for saturn? Does stacking two 0.25 seconds photo make the photo 0.5 seconds?

 

[russ_watters]

It really depends on your camera, but generally .5 is too high. Also, no, stacking averages frames, so they don't increase in brightness much, just in signal to noise ratio.

 

[yiuscott]

Thanks for your reply

I went into registax and randomly played with the wavelet filter bars, and the resultant image is actually better than before (picture attached below). I would like to ask if there is a definite setting that i should use for the wavelet filiter or is it trail and error?

 

[russ_watters]

Wavelets have been trial and error for me. They usually look like a bell curve when I'm done. Btw, try the "colorweight" settings in the "histogram" tab to balance the color...

I also have a Registax tutorial on my website that may be helpful: http://www.russsscope.net/staxtutorial.htm

 

[danielandpenn]

No, but it helps. There are people who are able to get a webcam to snap a few dozen frames while it crosses the field of view. Trying to track manually can work too, but it can also make it jump around. Registax will follow the planet around and line-up the separate frames, but there is a limit to the "jumpiness" it can handle. You can also align them manually, but that can take a while if you have a lot.

Awesome! How do I hook my webcam up to my telescope? My webcam has a USB type cord and I don't see anywhere I can plug that into my telescope.

 

[JeffKoch]

Interesting, the photos posted so far are much worse than my eyepiece view of Saturn, where (when the rings are tipped far enough) I can clearly see the Cassini division and sometimes even the Encke division with my 7" Mak-Newtonian. I've never tried astrophotography - are these images typical, or compromised in some way by time integration or poor collimation?

 

[russ_watters]

Sorry I missed your post a copule of days ago daniel - the webcam sends the pictures to your computer. You remove the lens from the webcam and place it where they eyepiece would otherwise be.

 

[russ_watters]

Interesting, the photos posted so far are much worse than my eyepiece view of Saturn, where (when the rings are tipped far enough) I can clearly see the Cassini division and sometimes even the Encke division with my 7" Mak-Newtonian. I've never tried astrophotography - are these images typical, or compromised in some way by time integration or poor collimation?

The posted photos were all by beginners with low-end equipment. I recently bought a better camera and with my C11 took the attached photo. It is maybe 75% as good as the best photos out there, though I'm still getting used to the color processing... Compare it with these pics from Chris Go, who is published in Sky And Telescope and is considered one of the best amateur astrophotographers around: http://saturn.cstoneind.com/ Note his pics are just in the order they were taken - the best on that page is probably the ones from Feb 8. He uses the same 11" scope as me.

I'm not sure I believe you can see the Encke gap with your eyes and that scope - it's 325 km wide, for an angular diameter of .1 arcsec. A 7" scope has a theoretical maximum resolution of .6 arcsec. Because of the contrast, it probably acts like it is a little bigger, maybe double that, but not 6x. Here's a photo that just barely shows it, taken with a 12" scope. Note the caption about how rare it is to capture it - it claims to be the first ever by an amateur. It's about as good as they get, though black and white: http://www.meade.com/gallery/15a.html
Here's that pic and others over the past few years from that guy's website. His are a better than Chris Go's and his best was actually taken with a regular webcam! http://astrosurf.com/legault/saturn.html

 

[JeffKoch]

I'm nearly certain I've glimpsed it, though at such low contrasts it's possible I've fooled myself by expecting what I should see - at the extreme limits of visibility, the brain is an important part of the problem (resulting in, for example, the canals of Mars). The moments of good seeing are very short, which is why I wonder if astrophotographers can take pictures as good as what the eye can see (for brief moments).

 

[russ_watters]

In the beginning of the thread, I describe the method astrophotographers use, which partially defeats atmospheric turbulence - taking hundreds or thousands of pictures, webcam video style and then combining the better ones into a single photo. Here's a more complete description of the processing process: http://www.russsscope.net/staxtutorial.htm