Back focus, am I soft??

Alastair Traill · October 22nd, 2010, 07:01 AM

Quote: -
does the auto focus switch have to be set to AUTO?? It isn't mentioned in the above video. Could be a major duh moment on my part!!!!!

It may not be mentioned in the video but it is mentioned on page 33 of the manual (see above). According to the manual it should be on.

What I have not seen mentioned is what aperture one should aim for. I would guess the camera's task would be easier if the adjustment could be undertaken at full aperture and thus minimum depth of field.

Darren Ruddock · October 22nd, 2010, 08:58 AM

Hi Alistair,

Ah, thanks for that conformation. That shall be included in my next attempt this weekend.

I too have wondered about the aperture. If conducting the adjustment outside surely ND filtering is needed so the whole thing isn't blown out and the sweet spot for F stop can be obtained. As far as I know the adjustment should be done with no ND's in.

Alastair Traill · October 22nd, 2010, 03:31 PM

Hi Darren,

Placing a filter behind the lens effectively shortens the light path and changes the focal point. However when neither ND filter is used there is a clear "filter" in place, at least in my EX3. I would assume that this is to ensure the same apparent length of optical pathway whether there is an ND in place or not meaning that filter selection is unimportant.

However I suspect aperture selection could well have an effect. Any comments?

Luben Izov · October 22nd, 2010, 03:47 PM

Hey Darren,
Please, just be sure that your camera is on full auto focus and let the camera do the job. I said that in my previous post. Full auto focus is the only thing that is required from you, plus light on the card. No ND filter at all. Plane, clean lens with/out clear filter (UV or IR like 486 Digital UV/IR), thats all. Good luck with it. Post how did go please.
Cheers

Darren Ruddock · October 23rd, 2010, 09:45 AM

Cheers fella's,

All good input. Will be testing again tomorrow hopefully (friends birthday this evening so I may be somewhat delicate tomorrow!)

I will follow all your advice. Something I totally forgot was to remove my T1 filter. Wonder if it makes a difference??

Will try and post results forthwith!

Vincent Oliver · October 23rd, 2010, 10:00 AM

Keep the aperture as wide as possible to avoid depth of field sharpness.

Not sure why the Andy in the video recommends using 1080 60i, I can't see what difference that will make, especially if you normally shoot 24, 25 or 30p.

Any suggestions?

Darren Ruddock · October 26th, 2010, 10:29 AM

Hi guys,

Attached are the latest stills after back focus adjustment.

This time I removed my T1 filter and had the focus switched to the AUTO position! Also had ah F stop of 4.

I think the shots look a little better but still not sure.

Let me know what you guys think.

Much appreciated

Andy Wilkinson · October 26th, 2010, 11:10 AM

Yep, better lit and sharper. Look OK to me.

Darren Ruddock · October 26th, 2010, 12:07 PM

Cheers Andy,

I can definitely see an improvement. I think sometimes you look at something so much you can get lost!

This does seem better though!

Andy Wilkinson · October 26th, 2010, 12:17 PM

Hey, stop pixel peeping and spend the time to make some nice films/have fun with your camera!

Darren Ruddock · October 26th, 2010, 12:48 PM

Great advice for us all Andy!!

Daniel Epstein · October 26th, 2010, 03:56 PM

I sympathize with your problems trusting backfocus for the camera to the cameras electronics.You can still get a chart to see if there are any problems which show up.
I know the procedure I use for lenses with manual backfocus is critical to getting the right result. I use a backfocus chart from Arri, expose the chart with the f Stop wide open (either decrease the amount of light on the chart if it is too bright or use ND if the ND is built in) focus zoomed all the way in and then pull out full wide. Adjust to maximum sharpness. If you use a smaller F Stop then your results will not be correct when the lens is wide open. You have to be close enough to the chart so the pattern on the chart shows up clearly so depending on the size of the chart you may have to move closer to it but on zoom lenses you still should be farther than minimum focus but not necessarily ten feet away.
For Lenses with extenders do the back focus with out the extender. Check the result with the extender in to see if your lenses extender has problems or needs adjustment as the extender can give you a different result if it is not correctly aligned.

Pietro Jona · October 27th, 2010, 07:54 AM

Anyone knows where I can download a Siemens Star to print?
The guy who had it last time I checked backfocus lives far from me..

Darren Ruddock · October 27th, 2010, 02:13 PM

Hi Pietro,

I got my charts from here..

Free Charts

I coloured mine in after printing just to give them more contrast

Pietro Jona · October 27th, 2010, 02:17 PM

Darren

thank you very much.

pietro

October 22nd, 2010, 03:47 PM	#19
Luben Izov Major Player Join Date: Nov 2009 Location: White Rock Posts: 254	Full Auto Focus Hey Darren, Please, just be sure that your camera is on full auto focus and let the camera do the job. I said that in my previous post. Full auto focus is the only thing that is required from you, plus light on the card. No ND filter at all. Plane, clean lens with/out clear filter (UV or IR like 486 Digital UV/IR), thats all. Good luck with it. Post how did go please. Cheers

October 23rd, 2010, 10:00 AM	#21
Vincent Oliver Trustee Join Date: Sep 2004 Location: Chislehurst, London Posts: 1,724	Keep the aperture as wide as possible to avoid depth of field sharpness. Not sure why the Andy in the video recommends using 1080 60i, I can't see what difference that will make, especially if you normally shoot 24, 25 or 30p. Any suggestions? __________________ Eyes are a deaf man’s ears. Ears are a blind man’s eyes

October 26th, 2010, 10:29 AM	#22
Darren Ruddock Regular Crew Join Date: Sep 2008 Location: Southend, UK Posts: 165	Hi guys, Attached are the latest stills after back focus adjustment. This time I removed my T1 filter and had the focus switched to the AUTO position! Also had ah F stop of 4. I think the shots look a little better but still not sure. Let me know what you guys think. Much appreciated Attached Thumbnails

October 26th, 2010, 11:10 AM	#23
Andy Wilkinson Inner Circle Join Date: Sep 2007 Location: Cambridge UK Posts: 2,853	Yep, better lit and sharper. Look OK to me. __________________ Andy K Wilkinson - https://www.shootingimage.co.uk Cambridge (UK) Corporate Video Production

October 26th, 2010, 12:17 PM	#25
Andy Wilkinson Inner Circle Join Date: Sep 2007 Location: Cambridge UK Posts: 2,853	Hey, stop pixel peeping and spend the time to make some nice films/have fun with your camera! __________________ Andy K Wilkinson - https://www.shootingimage.co.uk Cambridge (UK) Corporate Video Production

October 22nd, 2010, 07:01 AM	#16
Alastair Traill Major Player Join Date: Nov 2008 Location: Melbourne Australia Posts: 626	Quote: - does the auto focus switch have to be set to AUTO?? It isn't mentioned in the above video. Could be a major duh moment on my part!!!!! It may not be mentioned in the video but it is mentioned on page 33 of the manual (see above). According to the manual it should be on. What I have not seen mentioned is what aperture one should aim for. I would guess the camera's task would be easier if the adjustment could be undertaken at full aperture and thus minimum depth of field.

October 22nd, 2010, 08:58 AM	#17
Darren Ruddock Regular Crew Join Date: Sep 2008 Location: Southend, UK Posts: 165	Hi Alistair, Ah, thanks for that conformation. That shall be included in my next attempt this weekend. I too have wondered about the aperture. If conducting the adjustment outside surely ND filtering is needed so the whole thing isn't blown out and the sweet spot for F stop can be obtained. As far as I know the adjustment should be done with no ND's in.

October 22nd, 2010, 03:31 PM	#18
Alastair Traill Major Player Join Date: Nov 2008 Location: Melbourne Australia Posts: 626	Hi Darren, Placing a filter behind the lens effectively shortens the light path and changes the focal point. However when neither ND filter is used there is a clear "filter" in place, at least in my EX3. I would assume that this is to ensure the same apparent length of optical pathway whether there is an ND in place or not meaning that filter selection is unimportant. However I suspect aperture selection could well have an effect. Any comments?

October 23rd, 2010, 09:45 AM	#20
Darren Ruddock Regular Crew Join Date: Sep 2008 Location: Southend, UK Posts: 165	Cheers fella's, All good input. Will be testing again tomorrow hopefully (friends birthday this evening so I may be somewhat delicate tomorrow!) I will follow all your advice. Something I totally forgot was to remove my T1 filter. Wonder if it makes a difference?? Will try and post results forthwith!

October 26th, 2010, 12:07 PM	#24
Darren Ruddock Regular Crew Join Date: Sep 2008 Location: Southend, UK Posts: 165	Cheers Andy, I can definitely see an improvement. I think sometimes you look at something so much you can get lost! This does seem better though!

October 26th, 2010, 12:48 PM	#26
Darren Ruddock Regular Crew Join Date: Sep 2008 Location: Southend, UK Posts: 165	Great advice for us all Andy!!

October 26th, 2010, 03:56 PM	#27
Daniel Epstein Trustee Join Date: Jan 2006 Location: New York, NY Posts: 1,267	I sympathize with your problems trusting backfocus for the camera to the cameras electronics.You can still get a chart to see if there are any problems which show up. I know the procedure I use for lenses with manual backfocus is critical to getting the right result. I use a backfocus chart from Arri, expose the chart with the f Stop wide open (either decrease the amount of light on the chart if it is too bright or use ND if the ND is built in) focus zoomed all the way in and then pull out full wide. Adjust to maximum sharpness. If you use a smaller F Stop then your results will not be correct when the lens is wide open. You have to be close enough to the chart so the pattern on the chart shows up clearly so depending on the size of the chart you may have to move closer to it but on zoom lenses you still should be farther than minimum focus but not necessarily ten feet away. For Lenses with extenders do the back focus with out the extender. Check the result with the extender in to see if your lenses extender has problems or needs adjustment as the extender can give you a different result if it is not correctly aligned.

October 27th, 2010, 07:54 AM	#28
Pietro Jona Regular Crew Join Date: Jul 2003 Location: italy Posts: 172	Anyone knows where I can download a Siemens Star to print? The guy who had it last time I checked backfocus lives far from me..

October 27th, 2010, 02:13 PM	#29
Darren Ruddock Regular Crew Join Date: Sep 2008 Location: Southend, UK Posts: 165	Hi Pietro, I got my charts from here.. Free Charts I coloured mine in after printing just to give them more contrast

October 27th, 2010, 02:17 PM	#30
Pietro Jona Regular Crew Join Date: Jul 2003 Location: italy Posts: 172	Darren thank you very much. pietro