Sony SAL 1650- Parfocal? For sure?

Shawn, I just tried a 3rd SAL1650 and found it to be parfocal.
I tested both the Zeiss Vario-Sonnar 24-70mm f/2.8 and SAL1650 while shooting dance video... and have decided to keep both.
 
paulcurtis said:
Fair point :)

How are you getting on with them?

cheers
paul
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Probably the best decision I've made in the last ten years. Was going to go with af100's . VERY VERY glad I went this way.
I actually like the fact I have to use vari NDs. (just set f stop to what I want and adjust exp) Only thing I still won't get used to is the
viewfinder on the top????? (that's just proof crack is bad for you IMO)
 
kerrigan said:
Shawn, I just tried a 3rd SAL1650 and found it to be parfocal.
I tested both the Zeiss Vario-Sonnar 24-70mm f/2.8 and SAL1650 while shooting dance video... and have decided to keep both.
Click to expand...

Glad to hear you got a parfocal copy in the end. I just feel bad for the next guy who buys your returned lenses...

I've decided to hang on to my alpha mount Tokina ATX-Pro 28-70 f/2.6-2.8 after all. I was going to trade it for another sal1650 but the deal fell-through and I found that I need this range for dance recital shoots as the 16-50 is too wide. At first I didn't like it because it is really prone to lens flare but that isn't a big concern in a theatre as there is no light spilling onto me at my camera position.

I'm sure the Zeiss 24-70 is really nice and sharp but I found that it wasn't parfocal - can you confirm?
 
I will try my Zeiss 24-70 this weekend as well. Shawn raises a good point with regard to the lenses that were not parfocal in that someone will get them and if they are shooting still perhaps it makes no difference. But if they are shooting video it obviously does. Bill was the inspiration for this thread to begin with, it was a conversation I had with him about the 16-50 that caused me to post here. I wonder what Sony has to say about the quality control on the lenses? It seems to me that as we all await the arrival of new firmware for our cameras and our $500.00 LA-EA2 adapters built for these lenses to be used on our cameras, that there should be some assurance that we won't have to try three lenses to find one that does the job. Any chance someone can as Sony about this?
 
My guess after my experience with the lens and the feedback from other users is that the issue is with the A-nex adapter. Any manufacturing tolerance variation is compounded when an adapter is introduced. Too bad there's no back focus adjustment possible like on broadcast lenses. As I've been using my Sal1650 quite often I'm seeing the back focus issue as almost negligible under most shooting schenarios. Now I can concentrate on other things I dislike about the lens such as the very short focus throw. Come on Sony how about a purpose built video lens of the same specs??
 
I don't really understand how an adaptor or manufacturing tolerances would affect whether a lens is parfocal or not. I would have thought a lens has to be designed to be parfocal in the first place. The adaptor might make reaching infinity or MFD an issue, or if it's not straight then focus across the plane would differ, but that's about it.

cheers
paul
 
What I'm saying is perhaps the Sal1650 IS designed to be parfocal but the interplay between it and the adapter throw it off slightly. That would indeed also throw off the m.o.d and infinity (at least the focus scale). It's easy to check this. If you have access to a broadcast lens and camera, simply change the back focus very slightly. You may still be able to hit infinity but now your lens won't hold focus during a zoom. This is essentially what is happening with the adapter on the Sal1650. That's my educated guess at least.
 
paulcurtis said:
I don't really understand how an adaptor or manufacturing tolerances would affect whether a lens is parfocal or not. I would have thought a lens has to be designed to be parfocal in the first place. The adaptor might make reaching infinity or MFD an issue, or if it's not straight then focus across the plane would differ, but that's about it.

cheers
paul
Click to expand...

For the lens to hold its focus it must be a VERY specific distance from the sensor. Any variation anywhere in the optical system will deviate from parfocal. An adaptor will certainly have an impact on the flange depth of the system. In high end cinema lenses, this is accomplished with shims because the lenses are almost NEVER perfect even if they are $25,000. In almost all of the broadcast lenses, it is done with a mechanical screw we all know as the back focus adjustment. This also extends to the camera itself. The flange must be at a very specific distance from the sensor which is almost always accomplished with very precise shims. In the case of the FS100 and Sony lenses - there are no shims and nearly no effort to get a precise optical distance from lens to sensor. It is literally a crap shoot unless you collimated the individual lenses and the camera. I don't think it is a design problem with the lens or the adaptor - it is a manufacturing issue. These things are cheap and the there is no money to shim every lens, same goes with the camera itself.
 
So what you are saying is there should be a back focus adjustment on the FS100 or the LA-EA2 that the lens is mount on should have this feature?
 
I wouldn't say that should be a feature on a camera at this price point. Precision is expensive and the goal of FS100, LA-EA2, and the E-mount lenses is to be inexpensive while being reasonably acceptable. Part of saving money is compromise. If I made a living with an FS100, I would shim the mount and my lenses/adaptors. It's a DIY way to get it all to work really well without spending much money. There is some skill involved and/or a learning curve. The alternative is to buy a far more expensive camera - but I think shims are cheaper ;-)

The FS100 is a good camera - a great one if you take the time to tweak it a bit.
 
Thanks. Your points are really appreciated and I have to admit that I had completely forgotten about back focus since my good old Iki.
 
IanD said:
What I'm saying is perhaps the Sal1650 IS designed to be parfocal but the interplay between it and the adapter throw it off slightly. That would indeed also throw off the m.o.d and infinity (at least the focus scale). It's easy to check this. If you have access to a broadcast lens and camera, simply change the back focus very slightly. You may still be able to hit infinity but now your lens won't hold focus during a zoom. This is essentially what is happening with the adapter on the Sal1650. That's my educated guess at least.
Click to expand...

What I'm curious about is AFTER the fireware update if my 1650 will become parfocal. What I mean is, last night I was reading something about the la ea2 adapter and how the translucent mirror works with af to make the AF soo fast.
What I read said something about the adapter "having priority" during the af cycle. My take on it was that the adapter actually assists with the focus function throught the "mirror" and because this is done electronically, it speeds up the af till the lens af gets into play.
Since it was late last night I didn't give it much thought but the more I think about it today, that makes a little more sense to me now.
I'm wondering if once the fireware update electronically "matches" the adapter to the camera/lens combo, if all of a sudden the "backfocus" corrects itself for whatever the model lens installed?

Just cause I've always wondered just what the "translucent mirror" actually does?????? If I'm losing a third of a stop, there better be a good reason to put it between the sensor and the glass.
 
good to know, maybe the DUCLOS cinemod nikor 17-35 would be a better option, of course we are talking 2000+ bucks tho......lol. But as far as cine style zooms go, looks pretty good.
 
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