Jump to content


Strange image artifacts with Canon EF 18-55mm


Recommended Posts


I know that the Canon EF 18-55mm is not exactly an excellent lens to start with, but I was planning to combine it with my ASI178mm and a SkyWatcher Star Adventurer to do some wide field astroimaging.

My first tests are a bit disappointing however: images show some strange halo around stars, sometimes even "V" shaped.

Attached a test image.

I can't close the aperture right now, I don't have a Canon body, but I might borrow one: do you think this could help solving the issue?




Link to comment
Share on other sites

It will probably need stepping down a bit, at 18mm I use either f5.0 or f5.6. If you can't control the lens directly you could try a front aperture mask, I use step-down rings for this which screw into the filter thread at the front of the lens, a set only costs a few quid. Thirds-focussing can help, focus on a star a third of the way in from the edge of frame rather than one in the centre - this gives better focus across the whole frame.

The kit lenses are capable of quite good results, this is 20 minutes on the Milky Way at f5.0 with the STM kit lens, which i think is a little better than the earlier ones. Taken at a dark site with a modded DSLR.


The stars aren't perfect but aren't too bad either, it's a bit of a compromise between star-shapes and signal.

  • Like 3
Link to comment
Share on other sites

No problem. Screw together a set of step down rings like this until you get the desired aperture:


Then screw the whole thing to the front of the lens using the filter thread. Cardboard with a hole of the correct size in front would be the alternative.

Unfortunately, looking at it in more detail I don't think a front aperture mask will work with a wide angle lens as the front element is so much larger than the entrance pupil. I've only done this with telephoto lenses.

I'm not sure how you could set the aperture for a kit lens on your camera. Even a camera body may not help, as I believe the aperture is only set when a photo is taken! Only thing I can think of is to set the aperture in manual mode, take an exposure of several seconds and remove the camera battery. Not sure that's a good idea and it may not work as the body may detect the opening of the battery compartment and close the shutter.

Tricky one, hopefully someone else can help. When using camera lenses on astro-cams people usually use front-aperture masks if required.

Link to comment
Share on other sites

Yes, that's what I though... you would need a 5-6 mm ring to close the lens to the desired aperture, it's not possible.

I already saw a trick for closing the aperture with a canon body, basically you just need to remove the lens, or better to shut down the camera, while pressing the "depth preview" button.

I'm gonna try tomorrow.. if the guy owning the camera remembers to bring it to me :p

I'm also thinking of buying a second lens, like a Samyang 85mm, fully manual and, as far as they say, very good quality.

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.