Vignetting with StarMax 102 scope...

[dtrayers]

A forum member PM'd me and asked if I could send him some examples of the level of vignetting with my G3 attached to my telescope with the MaxView eyepiece and Digi-T adaptor.

I thought that more people may be interested so I posted my reply here (http://home.attbi.com/~dtrayers/scope/HTML/index.htm).


It's a pretty warm day today in Minnesota, and there's a fresh breeze from the south. I'm shooting across an unplanted corn field, so there's a lot of heat waves. I didn't try to get perfect focus. The subject is a tornado siren.

Note that I have an Orion StarMax102 telescope. It's a Maksutov-Cassegrain, not unlike a catadioptric telephoto lens.

For those not familiar with this type of scope:

http://www.berger-bros.com/telescopes/telescope_images/sk-makdigrm.gif

I make this point because anything less than about 15mm of zoom you'll start to see the front mirror, not to mention the vignetting gets pretty bad.

I show five images: full zoom (28mm), 20mm, 15mm, and full wide (7mm). I also included an image at full zoom without the scope. You'll see the siren in the center of the picture.

My scope is f/12.7 at 1300mm focal length. The MaxView eyepiece is 40mm. I would think that a different scope may have a different level of vignetting.

By my math, at full zoom, it's about a 91x magnification. 1300mm/40mm = 32.5. The G3 has a 35-140mm equivalent lens. 140mm/50mm = 2.8 32.5 x 2.8 = 91

FWIW... YMMV.

[BruceW]

Dave,

You forgot to include the URL.


Bruce

[dtrayers]

I embedded it in the "here" (http://home.attbi.com/~dtrayers/scope/HTML/index.htm).

In any case:

http://home.attbi.com/~dtrayers/scope/HTML/index.htm

[Outlaw]

Hey Dave
I would like to ask your advice. I have an 8 inch SkyView Orion reflector, I purchased the Orion SteadyPix SLR camera mount to do some afocal astrophotography and got some great pics of the moon thru my 32mm plossl. But I want to get serious and do some prime focus time exposure photography! Do you have any recommendations for a device to couple my G3 to the Skyview? I'm not really sure that anything Orion offers in there current catalog will work for me. Plus right now I am photographing from my back yard here in the city (San Jose Ca) so I have alot of light pollution as you can imagine, but your Jupiter photo has me fired up and I have decent light gathering power with the 8 inch! Im ready to go, just would appreciate any advice. Thanks in advance. P.S. dont get me wrong shooting pics of the moon is a blast. But planetary looks really interesting! Have you done any deep sky photography with the G3. Are we limited with exposure time keeping the shutter open on the G3? Man I have a ton of questions.

Outlaw

[dtrayers]

Hi Outlaw,

By no means am I proficient in astrophotography. Up to this point, I've just been playing around.

I suggest you check out Mike Weasner's site:

http://www.weasner.com/etx/menu.html

Even though it's pretty much devoted to the ETX scope, you'll find a lot of info there, and lot's of links.

But to answer your specific questions:

Like you, I also have the SteadyPix mount, but I found it pretty unsteady. I like the Digi-T mount with the 40mm MaxView. It's rock solid. One nice thing about the G3 is the rotating display. I don't bother with a diagonal. I can place the scope in any position and rotate the display so I can see it. I rotate and mirror the image in Photoshop if I want.

I also live in an urban area, so any deep sky photography is out. The G3 is limited to 15 seconds, so anything you'll do will probably have to be stacked multiple images. My Jupiter photos were pretty quick shutter times because I didn't have perfect tracking. If I took more time to polar align and adjust tracking speed, I would have used a longer exposure. The advantage of stacking is it tends to cancel noise.

Here's one more site you may find helpful:

http://home.earthlink.net/~tkurkowski/Photo_Basics/photo_basics.html

Good luck! I look forward to your pictures!

[Outlaw]

Thanks Dave,
I tried to take some pics of Jupiter thru my 8 in Skyview, but I just messed around a little bit. I have a bunch of trees along the north side of my backyard so I didnt have my tracking tuned on. Cant see the north star from my backyard so I can't get a good fix. I have to go to a more open area so I can get setup and do some more experimenting. I will check out the websites you were refering to in your post. Meanwhile when we get the moon back I will get some more practice in. Your right about the StarPix but it works pretty good for the moon and the price was right. Thanks for your advice.

Outlaw

[DigPic]

Dave, your images came out quite well....it is now on my list of experiments to try.

[DigPic]

Just a little cropping work and.....what vignetting?! ;)