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Dragon focus Issue?

Harcharan Singh

Harcharan Singh

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Website
www.editfxstudios.com
Hi
We are facing focus issues with our Ultra
Prime lenses specially 16mm.24mm,32mm
and 50mm on all our Dragon cameras.But 85mm,100mm
and 135mm are okay.
All the lenses are okay with our EPICs.
Is anyone else facing same kind of issue
or is there any solution to it.
Thanks in advance.
Harcharan
 
Focus

Focus

Hi
No adjustment done on focus.
There is a focus adjuster near the mount
of camera but never used it.
Can we get some help from you?
Thanks
Harcharan
 
Yes Harcharan. There is a small screw on the top of the camera that needs to be removed, near the front. Then there's another screw that adjusts the back focus underneath that. Turning that either way will change your back focus.

If your back focus off it could be the difference of your scales reading accurately or inaccurately. It also can have some negative impact of the "optimal" quality of the image.

A good way to check if your back focus is spot on or not is to grab a few lenses and measure out 15 feet from the optical center of the camera. If it reads something off (and it can be way off if it's out of whack) you need to adjust it.

This is of course assuming the lenses themselves are within spec.
 
Focus

Focus

Hi
Thanks .
But dont you think this adjustment
in anyway will harm the lenses
which are showing proper focus?
Harcharan
 
The issue of backfocus and unprecise lenses will have similar effects.

If some of your lenses are ok, and others not, it is hard to determine on a forum... :)

If you have a wide lens and set it to infinity and point it at infinity fully open, that should be sharp... :)
If the sharpness gets better "beyond or before" the infinity mark, that could suggest you are off.

then check with the next-widest in a similar fashion.
If the tendency is similar, you may have a back-focus issue.

If it's different, you most likely have lenses out of whack.

It's a good place to start to check if backfocus is off (given that you have a lens you trust)
 
Focus..

Focus..

Hi
Thanks for your replies.
We have 4 sets os Ultraprimes
which are perfect on EPIC with no
focus issues.
But same lenses with focal lengths
16mm,24mm ,32mm and 50mm are not
showing proper Focus shooting at 6K. But
with resolution at 5K the focus on Dragon is
also okay.
Harcharan
 
Wait.

you are saying that a focus mark at say, six feet is in focus with the camera set to 5k and out of focus with the camera set to 6k?

that one is quite strange....

battistella
 
That does indeed sound intriguing...

How do you check focus?
And are the marks on the lenses correct on the Epic AND on the Dragon (at 5k)
16mm should get soft/vignette at 6k.
But I guess that is not what this is about.
 
Hi
We know the 16mm issue..
But we are having focus issue.
And it is in all our 4 ultraprime sets.
and all our Dragons..plus minus a little
Bit...will check tommorow with tips given
And revert back.
Thanks
Harcharan
 
David Battistella said:
Wait.

you are saying that a focus mark at say, six feet is in focus with the camera set to 5k and out of focus with the camera set to 6k?

that one is quite strange....

battistella
Click to expand...
Yes
 
Hm...

Can you share 3 R3D's of a focuschart?
If you don't have a focuschart... well... something else, like a wall with tons of details.

Snaps.

1: Epic @ 16mm, wide open 6ft 5KFF
2. Dragon @ 16mm, wide open 6ft 5k
3. Dragon @ 16mm, wide open 6ft 6kFF

Same lens.
 
Harcharan Singh said:
Yes
Click to expand...


Wow. Ok. I'd advise sharing r3ds and a log file with red support right away.
The weird thing also is that it's only the wider lenses. If you can share r3ds here as well that would be good.

the distance the lens is projecting onto the sensor (back of the lens to the sensor plane) does not change so the focus should not change.
Does the compression change? Is it on the r3d or just in the monitor?

Battistella
 
I suspect curvature of field and coverage. Are you confirming focus center frame? 6K FF is outside of the optimal coverage in field and edges on these primes. In terms of matching the general image performance from MX 5K. Dragon should be set to 5.5K for the same FOV.

Though the last time I shot with the 32mm UP I didn't experience any real issues.
 
Please post the results of the investigation Harcharan. I have some theories about how the larger imaging target might be adding distortion by scattering light from the outer edges of particular elements in the lens. IIRC the wider focal lengths you are having issues with are Distagons, while the 50mm and up are planar design.

Cheers - #19
 
Focus

Focus

Hi
Will do the tests today and post the snapshots?
Thanks
Harcharan
 
Sounds like a back focus issue. Wider lenses have a shallower depth of focus which would make a back focus issue more pronounced than longer lenses. Depth of focus not to be confused with depth of field.

Nick
 
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