Scarlet AL and backfocus, I need HELP

[Luca Orlandi]

Ok, I know there are tons of posts on this topic.
BUT, honestly I need real information, not speculation.

I did some tests with these lenses:

• Canon 24-70 f2.8 L @ f.5,6
• Canon 16-35 f2.8 L @ f.5,6
• Canon 50 f1.8 L @ f.5,6 (yes, the cheaper)

Here the test files: LINK - r3d snapshots

All ISO 800 - 24fps - 1/48 - 4K - Compression 6:1

With different distances from the subject: 1mt - 1,5mt - 5mt (and for 50mm f.18 - 0,50 mt).
The images are soft ... mmm ... blurred :angry:.

This is the response of the red support (@ my request):
"Thank you for contacting RED SUPPORT. The back focus procedure is the same whether you have a PL mount installed or the Canon mount. Please refer to our operations guide for a step by step instructions on performing a back focus adjustment. Thanks!"

WHAT? Have you found any info for the BACK-FOCUS (EF MOUNT without Red-focus) in the Operation Guide?!

Now,
I have to adjust the back-focus? Yes, No, What?
There's someone in Italy who can help me? Or a simple (and safe) procedure?

Thanks guys for Your Help!

L.

 

[Isak Dinesen]

The backfocus only matters if your focus is off when you zoom in and out. Say you focus with a zoom lens at 35mm, then zoom in to 70mm - if the focus is off at 70mm, then your backfocus is off.

Backfocus is essentially micro adjustments to focus - just like the focus ring on the lens. So if the backfocus is off, you can compensate by focusing on the focus ring.

If you can't achieve focus at infinity (where your focus ring can't compensate anymore) then your backfocus could be off as well (both zooms and primes).


BUT: Still lenses are not made at precise as cine lenses, so even though the focus is off when you zoom, it doesn't necessarily mean your backfocus is off. Some still lenses are also able to focus beyond infinity, so you can't use them to adjust the backfocus at infinity.

You should be able to focus at 1mt 1,5mt and 5mt even if the backfocus is off

 

[Ray Sullivan]

Hey Luca,

The focus looks ok to me, except for the 24-70@24 and 24-70@70.

They seem a little underexposed though, could that be the problem?

I would try again at different apertures and see what you get!

 

[Patrick Grossien]

Hi Luca, if you are concerned about back-focus, either try to find a fellow reduser with pl-mount and the RED focus do help you out,
but I'm not entirely sure if the swap back to the canon mount would change anything. Maybe Ketch could let you know who to talk to in italy.

Another possibility might be to contact gecko-cam in munich, if this is at all possible for you, as they could provide the procedure:
RED service centers

I used to correct back focus on broadcast cameras in the olden days. just a simple siemens chart and the "standard procedure".
but this was only needed, as Isak says, when the focus didn't hold up throughout the zoom range.

of course, if nothing else helps, you could try it yourself with a siemens chart and a known good lens of yours, although this is not advised!
and if it does more "damage" to the sharpness than good, you definitely have to go see a cam doctor about it to reset the back focus for you.

 

[Scott Crawley]

The 24-70 is soft @ 24 and 70mm at anything less than f5, at least in my experience and all the folks I know that own one verify the same. Under exposure does not cause softness but, if he were shooting in light levels that caused him to set lower than f5, then you could say that insufficient light was indirectly the cause of the lack of sharpness.

Hey Luca,

The focus looks ok to me, except for the 24-70@24 and 24-70@70.

They seem a little underexposed though, could that be the problem?

I would try again at different apertures and see what you get!

 

[Patrick Grossien]

BTW, you know that the camera doesn't do any in camera sharpening? maybe try adding some to see if that works for you.

the images don't really look bad to me, but I can't really compare them because I don't own those lenses. Only the 24-70 @ 24 - 1 and 1.5mt and @ 70 - 5 mt look soft.

 

[Luca Orlandi]

Thank you Guys - all comments are very useful to me.
You're saving my life! (adjust the back focus... panic for me .. Yes, it's only one screw :-D )
Tomorrow I will do more tests (with better exposure).

Thanks,

L.

 

[Luca Orlandi]

New tests with better light.

LINK

The 24-70 is little more sharper.
I look forward vs. comments... i hope my back-focus it's ok.
[h=3][/h]bye.

L.