GH3 Why is my best lens not perfectly sharp at long distance / infinity focus?

S

Stab

Well-known member
Hi guys,

I'm using the Samyang primes with the Speedbooster for 6 months now and I'm really happy with it.
But yesterday I noticed that I couldn't get a couple of shots 'sharp' with the 35mm 1.4 on the Speedbooster... I did not see this before actually.

This lens is razor sharp and when I focus on something nearby, I'm always amazed at the amount of detail I get in my shots with the GH3. I'm sure that I can reach inifinty focus with this lens on the Speedbooster, because I can also go 'beyond' infinity when I keep turning the focus ring. That means I've must have hit it before, right?

Take a look at this shot for example. I zoomed in at the couple a couple of times before focussing, but I couldn't get it sharper than this. It's not extremely blurry, but it's noticably soft and I don't know why.

This is around F2.8 or F4 I guess, had an ND filter on (which I also use in the perfectly sharp shots nearby). This shot is straight from the camera (50 mbps mov / 24p / contrast -3, sharpness -4, saturation -2)

What do you guys think?

soft ceremonie.jpg
 
It's tough to tell from this one, downscaled picture. I don't know if I can really offer any insight into the situation either. If you can focus sharply at infinity, you should be able to come back and focus closer. Did you have your lens wide open when you shot this?
 
Stab said:
Hi guys,

I'm using the Samyang primes with the Speedbooster for 6 months now and I'm really happy with it.
But yesterday I noticed that I couldn't get a couple of shots 'sharp' with the 35mm 1.4 on the Speedbooster... I did not see this before actually.

This lens is razor sharp and when I focus on something nearby, I'm always amazed at the amount of detail I get in my shots with the GH3. I'm sure that I can reach inifinty focus with this lens on the Speedbooster, because I can also go 'beyond' infinity when I keep turning the focus ring. That means I've must have hit it before, right?

Take a look at this shot for example. I zoomed in at the couple a couple of times before focussing, but I couldn't get it sharper than this. It's not extremely blurry, but it's noticably soft and I don't know why.

This is around F2.8 or F4 I guess, had an ND filter on (which I also use in the perfectly sharp shots nearby). This shot is straight from the camera (50 mbps mov / 24p / contrast -3, sharpness -4, saturation -2)

What do you guys think?

View attachment 83983
Click to expand...

Since I don't have a 'Speedboost'... I can't comment on what it may do to the optics of the primary lens. But just on general principles, any 'additional' optical elements may impact 'sharpness' either in actual resolution degradation, or in contrast degradation, which humans often mistake for 'sharpness'...

If I understand how the 'Speedboost' works, it is by altering the optics such that a shorter focal length is the result, this changes the effective aperture/focal length ratio, which yields the boost in speed.

Precision is of course the watchword in optics, and even very small errors, may result in 'fuzzy' images...
 
Yes true. But the Speedbooster actually improves detail and makes the lens sharper in the center. Also, this lens is razor sharp with all the shots I did, except for the ones that are focussed at (almost) maximum distance.

It could be the Speedbooster, but I'm not sure. This was shot at f2.8 I believe. For sure not wide open.
 
It does look a bit soft.
you need to check the lens collimation, the SB collimation and the camera flange depth.
These are all highly technical procedures that , to be done correctly, require both skill and equipment.
It could be much simpler explanation however:
The most basic check would be for any debris on the seating surfaces on camera mount, SB and the lens mount.
Also check if any mechanical play or slop developed between those 3 components.
Any of the above would cause the lens not reaching infinity focus.
hope that helps...
 
I would strongly suspect the Samyang lens. Samyang is a 3rd party low cost lens maker and like all of those will tend to not have the excellence of quality control the OEM makers do. Any optical faults will show up more easily with any kind of auxiliary optics.

I had a Rokinon (rebranded Samyang) 85mm T1.5 cine version of the Rokinon 85mm f1.4 for about a month. While it showed no obvious faults, when I replaced it with an Olympus 75mm f1.8 I saw that the Oly "ran circles" around the Rokinon in every way from better overall sharpness (although the Rokinon was OK), better inherent contrast, much better tonal values, and noticeably much less flare.

When I shot primarily with Nikon F, F2, and F3 I tried Vivitar in 2 lenses. The 70-210 zoom failed misterably in first tests so I got rid of it right away, the 20mm ultra wide was fairly good (but not excellent) so I kept it due to it's unique FOV. When I worked with Canon I stayed completely with Canon optics the quality of which never let me down.

Now I have Panasonic Lumix and Olympus m.Zuiko lenses for my m4/3 cameras and no 3rd party optics, nor do I take a chance with any kind of "auxiliary" optics.
 
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