help with moon flares

Question

I recently switched from a cropped sensor, APS-C Sony to a full frame sensor Sony.

When I would take pictures of the moon with the cropped sensor, I would get this:

15s, f1.4, ISO 1000. And this is not a full moon, not sure what phase but the motion of the moon just makes it seem more full.

Now when I take pictures of the moon with the full sensor camera, I get this:

and this:

These are also 15s, f1.4, ISO 1000, but with full frame. Why does the moon now look like some sort of Phoenix bird when I take it with the full frame sensor? How can I get the same look of the cropped sensor with the full frame sensor? What am I doing wrong? (also when I'm taking these pictures, I'm focusing on the stars, and then waiting for the moon to rise. Is it a matter of focus??)

I use Rokinon lenses, APS-C was a 21mm/1.4, FF was a 24mm/1.4

Answer 1

It might be an effect of "coma" aberration. As I understand, it might be especially bad with fast lenses at large apertures. Here Ken Rockwell talks about coma on his Nikkor 50mm f/1.2 lens, with images and examples.

The solution (partial) is to shoot at smaller f-number, or switch to different lens. In another article Ken suggest that aspherical elements can be introduced to correct coma, as done in Nikkor 58mm f/1.2

Answer 2

The flare you are getting from the light looks to be following the curvature of your lens. It looks like you might have smudged something on it.

Clean the front and rear glass element.

Are you using the same lens both times? Have you added a filter to the front of the lens? Try shooting your full frame in the crop frame mode and seeing if you get the same result.

Answer 3

I would not expect different lenses to have the same flare characteristics.

A: Is your lens clean and smudge free?

B: If you use a filter is it clean and smudge free.

C: If you use a filter do you get the same problem without it.

D: Does it change a lot stopped down 2-3 stops?

E: Go outside with a couple of beanbags on a sunny day. Support the lenses so they throw a reflection onto something in the shade a few yards away.

• If the reflections are equal in intensity (adjusting for size of spot) then the front coatings are about the same in efficiency.

• Repeat this test with filters if you use them.

F: Put the moon in various places in the frame. Does your phoenix change orientation, shape? If it's fairly constant but oriented differently at a give distance from the centre of the frame, then it's likely a characteristic of the lens. If it changes much, it's more likely crud somewhere.

If the front element is fairly flat, you can get more reflection happening back and forth between the lens and a filter. Curved elements tend to shift the bounces off the sensor. This is why some lenses only show flare when the bright object is near centre, but not if it's off to one side.

G: Try other lenses. Good camera stores will often rent lenses.