Jump to content

740427863_Terminatorchallenge.jpg.2f4cb93182b2ce715fac5aa75b0503c8.jpg

Canon lens question.


Recommended Posts

Hi, my Canon EF200L lens has arrived and is destined for use with a CCD camera via a Geoptik adapter.

This means that I need to set the aperture on a Canon camera first, then take off the lens without switching off the camera to leave the lens stopped down to whatever I have selected. Fine.

So I did this on my 1000D (AV mode, aperture priority, set to f32 to test the principle, remove lens with camera switched on...

...and when I look down the lens it looks, to my untutored eye, the same as it did wide open. I was expecting to see the iris creating a much smaller aperture. Should I see a radical difference?

Any ideas?

Olly

Link to comment
Share on other sites

The lens isn't stopped down until you press the shutter button or DOF Preview button Olly.. To get the lens to stop down and stay stopped down, with the camera on, press the DOF preview, then, whilst continuing to hold the DOF preview, remove the lens. You should find the lens stays stopped down. I'm not 100% convinced there isn't some risk to the electronics in doing this, but it works.

Link to comment
Share on other sites

You could always make an aperture mask to fit over the objective
This is a very good idea for a second reason as well - unless you only shoot at full aperture with the attendant increase in aberrations, the 8 diaphragm blades of the iris on this lens will cause multiple diffraction spikes on bright stars that are not to everyone's taste. An aperture mask as Angus has suggested would avoid these. Edited by steppenwolf
Link to comment
Share on other sites

You could always make an aperture mask to fit over the objective in order to get the same effect without any chance of damaging anything.

That is not a bad idea at all. It could also be round, avoiding diffraction effects. But what about its distance from the chip, I wonder, and its positioning with regard to the lens elements?

Olly

Link to comment
Share on other sites

I use the twisted lens trick a lot to avoid aperture flicker when shooting time lapse videos. i.e press the DoF button and slightly untwist the lens to lock the aperture at the selected value. It is a common method of improving the time lapse quality and I've yet to hear of any problems caused by technique

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
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • 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.