Jump to content

Canada's top-tier Telescopes & Accessories
Be as specific as possible when reporting issues and *ALWAYS* include the full version number of the application you are using and your exact *CAMERA MODEL*
  • 0

Barlow Lens Versus Eyepiece Projection



I currently use a 2" 2X "focal extender" for planetary, Moon and Sun imaging at prime focus. But, because I already had the equipment to do it, I tried eyepiece projection using the proper adapter and a 25mm orthoscopic eyepiece. The result was absolutely awful: stars that were outside the center of the field of view were shaped like teardrops which became larger the farther away from center they lay! Is this normal for eyepiece projection or could there have been something wrong with the eyepiece internally? I did not try other focal lengths of orthoscopic eyepieces on that night.


If eyepiece projection is NOT advisable at all for imaging, then would focal extenders/Barlows of greater power be the way to go? Does the quality of images decline as the power increases, such as 2X to 5X? I have a range of focal lengths in my collection of University Optics orthoscopics (purchased in the 1970's) and would be saddened not to be able to use them for imaging.  :(



Link to comment
Share on other sites

  • Answers 2
  • Created
  • Last Reply

2 answers to this question

Recommended Posts

AP Imaging with most any DSLR - especially the current Canon / Nikon 18-24MP Models - is already capable of reaching Seeing-limited Resolutions.  There is nothing more in terms of actual Detail which can be dredged up by using a Barlow, only the Image Scale and Focal Ratio are magnified - meaning the need for Longer Exposures and More of them - placing stress on the Mount Tracking and AutoGuiding System.


Except for Planetary Video Imaging, where Video Stacking can recover Detail beyond the normal Atmospheric Seeing Limits, the Best Solution is to take High Quality Exposures at Prime Focus (without any Barlow or Tele-Extender) and then to Crop the Resulting Image once all other Calibration and Stacking and Processing is completed.  That is how to produce the Best Detail and Large Image Scale.


Eyepiece Projection and Afocal Imaging and Barlows were more pertinent in the days of Film AP Imaging, when there was no ability to perform Calibration / Stacking / Stretching.


(btw:  Why is this posted in the Application Support-BackyardEOS Forum and not in the Main Forum-General Forum ??)

Link to comment
Share on other sites

Thank you, s3igell, for your suggestions. I can imagine that the fewer glass elements there are between the objective lens of a scope and the camera's sensor is a wise thing. It never occurred to me that increasing magnification would make tracking/guiding more critical. That's an excellent point. I haven't done much posting of questions via the Internet and especially on the new BYEOS site, and so excuse me for using the incorrect forum for my particular question.  {vJv}

Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...

Important Information

This site uses cookies to offer your a better browsing experience. You can adjust your cookie settings. By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to the use of cookies, our Privacy Policy, and our Terms of Use