Canon 5d mk3 mirror/shutter vibration

[5haan_A]

Hi,

Im not sure if the mirror/shutter vibrations is causing some of my star shapes to be quite weird. 

Is there a way to fix this.

 

Im currently getting to grips with some wide field shots and I am borrowing a canon 5d mk3 to practice with. Worth adding that the lens used is just a standard canon one.

The action of the shutter and mirror closing and opening is very substantial to say the least, and I'm wondering if this is what is causing some weird srar shapes to pop up on the APT preview.

 

I'll see if I can attach a screenshot as an example.

Edited June 25, 2020 by 5haan_A
further info provided

[5haan_A]

Apologies for the phone pictures of a screen, the laptop I captured off isn't allowed to connect to the internet.

 

First screenshot stars look fine perhaps out of focus but not too bad.

Second screenshot, same image but further along towards the edge of the image very weird looking star shape. 

 

I dont understand it. This image I think was an exposure of 5 seconds so not very long. The camera is mounted on a SA but I wouldnt think guiding issues cause that sort of star shape.

 

 

 

[5haan_A]

Ah sadly I think my widefield shots are going to come to an end. Weird star shapes are a secondary concern now.

 

The camera just unscrewed itself from the SA mount and fell lens first on to the floor. It was completely unexpected and I dont understand how a screwed on camera could fall down.

There are some deep scratches on the optical glass and dents on the lens cap ring. The lens in question is a canon 16-35mm f.28 ef usm 2. The camera itself is working, thank god.

I did a quick Google of how much the lens costs. Used is about £690 brand new is double that. Oh dear!!

The camera was kindly borrowed to me, lens included. I cant return it back in its current state, so now I'm in a bit of a pickle. 

 

 

 

 

[wxsatuser]

These star shapes are most likely normal for the lens.

Sometimes called the 'flying bird' a mixture of coma and astigmatism.

Often stopping down will correct some of it.

As to the damage, it could be repaired but a red ring lens will most likely not be cheap.
May be the owner has insurance?

[5haan_A]

20 hours ago, wxsatuser said:

These star shapes are most likely normal for the lens.

Sometimes called the 'flying bird' a mixture of coma and astigmatism.

Often stopping down will correct some of it.

As to the damage, it could be repaired but a red ring lens will most likely not be cheap.
May be the owner has insurance?

Thanks for the reply.

 

What is stopping down?

 

I did some research on aperture, something that I have never had to think about properly with a dedicated astro camera attached to a telescope. I had set my lens on APT to max aperture, so the lowest number possible and perhaps I could experiment with pushing that number up a little bit to see what happens. 

 

Re the lens I have come across a company online that does lens repairs. I am going to give them a go. It won't be cheap but still better than returning in its current state. 

 

Best,

 

 

[Physopto]

If the lens is scratched you can forget repairs. The optics come as a matched set glued and aligned in the factory. I very much doubt that any repair could sort that out. If it could be done I recon it would cost more than a complete replacement unit.

I would look around for a replacement in perfect condition second hand.

Derek.

Edited June 27, 2020 by Physopto

[wxsatuser]

3 hours ago, 5haan_A said:

Thanks for the reply.

What is stopping down?

 

Stopping down is just decreasing the aperture, in this case go from f/2.8 to say f/4 or 5.6 and this can sometimes cure the abberations.