APS-C to FF aperture question.

I'very got an EF 24-70 F4 that I've been using on a 7D2 but I'm taking it to an aviation nightshoot tomorrow on my 5D4. I realise that moving from APS-C to a full frame sensor means I will have to up the aperture to get the same DoF, but I want to know about the likely change in terms of sunburst effects on lights. On the 7D2 F11 used to give me a great effect on lights, will I need to go past this on the 5D4 to get the same effect or stay at F11?

I can't say about the 5D4 because I haven't gotten there with it but typically I'd generally get my best sunbursts on the 5D3 at F/16. I say generally because there were often exceptions depending on the lens I was using. Hope that helps.

Thanks for that, it does sound as if I'll have to stop down a bit.

I don't understand how sensors size would affect sunbursts. Aren't their properties governed exclusively by the lens f stop?

I get the best results at f/16 for most of my lenses with both a FF and an APS-C sensor. As for the quality of the burst and at what aperture you'll get a starburst effect depends on the lens and the light source. Smaller and brighter light sources tend to give better star patterns.

frugivore wrote in post #18149328
I don't understand how sensors size would affect sunbursts. Aren't their properties governed exclusively by the lens f stop?

This.

The property of the starburst is based on the aperture blade count and their shape as they close down at different stops.

Changing sensor sizes won't effect the starburst look, only the lens's blades, their shape, and it's different at each aperture stop.

Very best,

frugivore wrote in post #18149328
I don't understand how sensors size would affect sunbursts. Aren't their properties governed exclusively by the lens f stop?

One does need to keep in mind that the star diffraction pattern is a fixed size, and so it is a greater percentange of the frame's dimensions by a factor of 1.6
That is, if the star were 2mm in absolute size on sensor, it is 2/24 of the FF frame height but 2/15 of the APS-C frame!!!

For example, in this shot that dhornick posted on POTN, the starburst is 7mm in diameter, on a 24mm frame size (6D).
https://photography-on-the.net …hp?p=18138749&i​=i72057115

The starburst would still be 7mm on the sensor with APS-C camera at the same aperture, but instead of being 30% of 6D frame height it would be about 45% of the APS-C frame height, since the small sensor captures less area.

Wilt wrote in post #18149364
One does need to keep in mind that the star diffraction pattern is a fixed size...

That is not the case. Star pattern size is not of uniform size. It is dependant on relative size and intensity of the source light on the sensor. Take, for example, a row of street lamps. If the closest one was of relative size and brightness as in your example, it would have a large star pattern. As the lights recede in distance their relative size diminishes therefore their corresponding star patterns would diminish. Likewise if the light intensity was lower.

Here is an example...

-Duck- wrote in post #18149452
That is not the case. Star pattern size is not of uniform size. It is dependant on relative size and intensity of the source light on the sensor. Take, for example, a row of street lamps. If the closest one was of relative size and brightness as in your example, it would have a large star pattern. As the lights recede in distance their relative size diminishes therefore their corresponding star patterns would diminish. Likewise if the light intensity was lower.

Here is an example...

You misinterpreted what I said. In your photo, you can measure (at one light) the diameter of the starburst pattern, and you can measure the diameter of the light itself. BOTH objects cast an image which has a fixed size on the sensor, regardless if a FF sensor captures them both or an APS-C sensor captures it. That image size is entirely dependent upon the FL of the lens casting the image on the sensor, the star pattern is also dependent upon the aperture, but the image is nevertheless is the same specific diameter (for the FL and aperture), regardless if it falls on the FF sensor or the APS-C sensor.

When you took the photo with your 6D, the closest light was about 2.67mm on the sensor, and the star pattern coming from it (caused by the aperture) was about 2X or about 18.67mm in diameter. If you had shot at same camera position with an 80D, using same lens same aperture, the light would still be 2.67mm in diameter and the starburst would still be 18.67mm in diameter.

In fact, even if I shot with a 4x5 sheetfilm camera using the same 43mm FL and the same aperture, the streetlight would still be 2.67mm on film and the starburst would be the same 2X diameter (assuming I could mount the same Canon 24-70mm at 43mm and same aperture, so the starburst would be the same)

THAT is the point I was intending to make.

Thanks to everyone for the replies, I think some proper experimentation is in order.

Wilt wrote in post #18149476
You misinterpreted what I said...

I understand now. Thanks for clarifying.