Compression or camera issue?

[Roelf Wentholt]

I hope one of you can help me. I have the EX3 and recently bought the Nano Flash. Now I have this test shot, a long shot of the canal in Amsterdam where I live. If I look along the parked cars then I notice how, the further away they are, the more focus they loose. As if the camera or codec or nano flash is not capable of handling all these details. I have exactly the same problem when recording on the SxS cards. I had hoped to solve this with the Nano Flash but maybe I hoped for more then is possible.
Does anybody know how I could overcome this problem where large total shots become blurry? Does anybody know what causes it?

You can see the shots at this site of a friend of mine:
(Low rise example) http://www.jitty.nl/fotomacminds/voorbeeld.jpg
(Hi-res example) http://www.jitty.nl/fotomacminds/voorbeeld.tga

[Dan Keaton]

Dear Roelf,

Yes, this seems to be a focus or depth of field issue.

To prove this, set up a similar shot in manual mode, go to manual focus, set your aperture to wide open, , set the shutter speed to 1/50 or 1/60, then while recording, change the focus (manually) of the lens, first focusing on near objects, then focusing on the far object.

Then change you aperture to a higher number, then do the same.

Then change you aperture to a higher number, then do the same.


When you playback, or take the files into your editor, the focus will shift.

When you use higher apertures, more will be in focus at one time.

(Please forgive me if all of this is obvious).

[Tim Polster]

Hello Roelf,

I will take a stab at your question.

This sounds like a camera related issue, not a codec/recording issue.

1) What f-stop was the footage taken with? Maybe too much ND filter and the DOF was really shallow?

2) Maybe for your backfocus is out of adjustment. I realize this series of camera looks like it is all in one, but I had to adjust the backfocus on my EX-1.

You can search the EX forum here for how to set the backfocus. I watched a youtube video of a forum member here which outlined the process.

[Roelf Wentholt]

Originally Posted by Tim Polster

Hello Roelf,

I will take a stab at your question.

This sounds like a camera related issue, not a codec/recording issue.

1) What f-stop was the footage taken with? Maybe too much ND filter and the DOF was really shallow?

2) Maybe for your backfocus is out of adjustment. I realize this series of camera looks like it is all in one, but I had to adjust the backfocus on my EX-1.

You can search the EX forum here for how to set the backfocus. I watched a youtube video of a forum member here which outlined the process.

Ok thanx Tim, we will look in the back-focus right away!

Cheers

[Alister Chapman]

To me that whole frame grab looks soft. Was the iris open more than f8? Was it f8, f11 or f16? With the EX if you use a smaller aperture than f8 the picture will be soft. Ideally you want to be between f8 and f2.8. It's not a codec or recording issue of that I too an sure, it looks like a focus issue.

[Roelf Wentholt]

Hello Alistair, thank you for your respons. I was away for a while. Shooting with the Ex 3 avoiding the shots that I know look 'soft'. Tomorrow I'll do some more testing to see what causes this. To remove back focus issues I set up the camera with the Letus adaptor and filmed some of these total shots that seem to give problems. With that set up I ran into the same problem. So tomorrow I am going to test on different apperture settings. To me it seems I can get incredible focus and picture quality up to the point where there is too much information in the shot. But that would mean codec restrictions and you said this is not it. I trust your opinion so I am going to do some more testing.

[Dan Keaton]

Dear Roelf,

I can assume you that these are not codec restriction issues.

Our codecs, especially our 100 Mbps or higher Long-GOP mode can record an incredible amount of detail and handle lots of movement in the frame and camera movement.

We have proved the above via very careful real-world tests.

[Alister Chapman]

The Letus adapter will not necessarily address your back focus issue (if that's what it is).
The focus on the EX cameras and most cameras with fixed lenses is done electronically by the camera looking up data about the zoom position and focus in a database and then adjusting various elements within the lens, or moving the sensors forwards and backwards by tiny amounts. This make the design of the lens simpler and cheaper than a traditional broadcast lens. If the backfocus adjustment is out it is possible that the camera won't ever actually be in focus as the lookup table (database) for the lens may be incorrect. With an EX3 you should point the camera at a flat wall around 3m away. The camera must be at exactly 90 degrees to the wall. A wall with fine texture or a pattern works best as this gives the camera something to focus on. Then you should perform the backfocus routine for all 3 filter positions. This allows the camera to build the necessary lookup table to ensure focus is correct.

To me though the pictures still look like the iris is too far closed. Diffraction limiting is a big issue on high resolution cameras. With 1/2" cams like the EX the picture will be noticeably soft if the iris is closed more than f8, ideally you want the lens open more than f5.6. On 1/3" cameras the problem is noticeable at f5.6! Even 2/3" Broadcast cameras suffer at f11, with a 2/3" camera ideally you keep the iris more open than f8.

So with an EX if the iris is at f16,f11,or f8 you really need to add more ND to open the iris up, otherwise the pictures will be soft. This is not an EX fault, it happens with all cameras, it's just the higher the native resolution and the better the quality of the codec the more it becomes noticeable.

Generally, codec issues manifest themselves as picture blockiness or other artifacts rather than simply being soft and I see nothing in the frame grabs to suggest a codec problem, it is almost certainly optical.

[Roelf Wentholt]

Thank you Alistair, I did some more tests and indeed the improvement when I open the lens to 3.5 is very significant. So it may be as simple as that. I am nevertheless also going to follow your advise on setting the back focus. Thanks again, you are all very helpful!

[Roelf Wentholt]

Now I did the back focus test with the three nd filters, about three meters away from a wall with detail and a testcard in the middle. And I found yet more improvement. So it was both: too small aparture setting plus slightly off back focus. I am very happy now!

[Dan Keaton]

Dear Roelf,

Thank you for the update.

It is great to hear that your issue has been resolved.