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Archive 2017 · TAP "Decentered"?

  
 
AdaptedLenses
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p.1 #1 · p.1 #1 · TAP "Decentered"?


Adapter doesn't seem to be obviously out of square, but maybe is? Is there anything else I'm not thinking of that might cause this? Same A7II and CV 50/1.5 LTM with Fotodiox adapter. Sharp image was taken on a VM-E, the other on a TAP using AF. Centers seems comparable, edges, left especially, not so much...












Jun 06, 2017 at 05:11 PM
arduluth
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p.1 #2 · p.1 #2 · TAP "Decentered"?


Testing this close to a brick wall is very demanding in terms of guaranteeing that the sensor is parallel to the subject. I wouldn't draw any conclusions without using an infinity scene.

Also, I'd test with multiple lenses just in case. Your lens could have a defect that the VM-E is countering. Testing with a few more lenses will tell you if the problem is the lens or the adapter.

All that said, it's certainly possible.



Jun 06, 2017 at 05:20 PM
AdaptedLenses
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p.1 #3 · p.1 #3 · TAP "Decentered"?


True but repeated with same, extreme difference at f/2 and f/2.8, just posted these to be sure. And at 6', f/2.8 should have 8" of DOF, so shouldn't be this apparent. Also saw the defect at infinity initially.

Still, get your point. That's the only M lens I have currently but have some others via adapter, Ill see what else I can test.



Jun 06, 2017 at 05:37 PM
genji
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p.1 #4 · p.1 #4 · TAP "Decentered"?


The images you've posted are about three bricks wide. A standard American brick is either 8 inches or 7 5/8 inches wide so the horizontal field of view is about 2 feet and the focused distance is therefore about 3 feet. As arduluth said, very demanding in terms of aligning the sensor parallel to the subject. The framing is slightly different too whereas, if the camera was mounted on a tripod, I would have expected the framing to be almost identical given it's the same lens but a different adapter. Also, did you use manual focus with the TAP?


Jun 06, 2017 at 10:22 PM
retrofocus
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p.1 #5 · p.1 #5 · TAP "Decentered"?


I would repeat the test with the TAP adapter with manual focus. The top image seems unsharp on both sides equally and also on top and bottom. Only the center brick is sharper but not as sharp as in the second image. My first guess is that the AF was not spot on here.

In general the brick wall test works pretty well. I tested a few wide angle lenses in the past with this kind of test setup, and even if the sensor plane is not 100% parallel to the wall (you simply adjust the best you can to have the sensor parallel to the wall) you can tell if a lens is decentered or not.



Jun 07, 2017 at 07:14 AM
LightShow
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p.1 #6 · p.1 #6 · TAP "Decentered"?


I would do some more testing to confirm the behaviour, testing on the VM-E to see if I can duplicate the results, testing on the TAP to see if it is field curvature/focusing distance, alignment with the wall(also at infinity) and on a tripod to reduce any variance in technique, and I also agree with using manual focus, a calliper or micrometer will be useful to rule out adapter uniformity, even shooting the camera upside-down may yield useful data, nothing like throwing money at user error(not that that's what's happening).


Jun 07, 2017 at 09:41 AM
genji
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p.1 #7 · p.1 #7 · TAP "Decentered"?


retrofocus wrote:
I would repeat the test with the TAP adapter with manual focus. The top image seems unsharp on both sides equally and also on top and bottom. Only the center brick is sharper but not as sharp as in the second image. My first guess is that the AF was not spot on here.

In general the brick wall test works pretty well. I tested a few wide angle lenses in the past with this kind of test setup, and even if the sensor plane is not 100% parallel to the wall (you simply adjust the best you can to
...Show more

One thing you can do to increase the likelihood of getting the sensor plane parallel to the wall is to gaffer tape a small mirror to the wall, compose the shot so that the mirror is at the center of the frame, and then make sure you can see the (out of focus) reflection of the camera through the viewfinder.



Jun 07, 2017 at 06:51 PM
AdaptedLenses
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p.1 #8 · p.1 #8 · TAP "Decentered"?


Took some more shots tonight, again with the CV 50 and a Super Tax 55. The CV does show some field curvature, but i square up 1PP shots all the time and with brick walls you can choose not to trust me but they're going to be pretty darn close. At f/1.5 I'd agree but saw the same fall off at 2.8.

Used a tripod tonight, but I don't see the point of MF to test the TAP. If it can't AF accurately it's got a problem even if I'm reading the cause wrong...

Thanks for the thoughts, hadn't thought of that mirror tip before.



Jun 07, 2017 at 08:15 PM
genji
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p.1 #9 · p.1 #9 · TAP "Decentered"?


Mathieu18 wrote:
Took some more shots tonight, again with the CV 50 and a Super Tax 55. The CV does show some field curvature, but i square up 1PP shots all the time and with brick walls you can choose not to trust me but they're going to be pretty darn close. At f/1.5 I'd agree but saw the same fall off at 2.8.

Used a tripod tonight, but I don't see the point of MF to test the TAP. If it can't AF accurately it's got a problem even if I'm reading the cause wrong...

Thanks for the thoughts, hadn't thought of
...Show more

I would use manual focus in order to determine whether the problem is with the hardware (uneven adapter thickness, etc) or the firmware (faulty autofocus). If it was the former, I'd return the TAP for replacement. If the latter, I'd revert to a previous version of the firmware and test again.



Jun 07, 2017 at 09:08 PM
ZoneV
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p.1 #10 · p.1 #10 · TAP "Decentered"?


Take a wood or houses or something big with fine structures more than 50m away. Thats OK as infinity. You could make the images with the camera tilted to have the trees whatever goes diagonal through the image.

Those short adapters with helicoid add perhaps more tilt than good for faster lenses.



Jun 08, 2017 at 01:02 AM
AdaptedLenses
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p.1 #11 · p.1 #11 · TAP "Decentered"?


Sets from last night look better, AF accuracy in AF-S isn't ideal looking at the set, and curvature is playing a roll. I prefer AF-C and believe I've seen that tip elsewhere. I'll have to try in sunlight when this rain ends and I don't need 2 sec delay for slow shutter. Using the 2 sec timer only allowed AF-S. First couple times when switching to the TAP adapter racked focus AFTER taking the first shot, hadn't seen that behavior before.

I'm wondering if the curvature is worse when the lens is at Infinity and on the TAP, but believe the lens is unit focusing so it shouldn't make a difference?

Genji, fair thought on MF. I might downgrade for FW 4 and see how it behaves regardless.

Anyway I'll keep playing with it, thanks again for the thoughts.



Jun 08, 2017 at 08:25 AM
arduluth
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p.1 #12 · p.1 #12 · TAP "Decentered"?


Yes, field curvature is typically worse (or more visible) at infinity. Even for unit focusing lenses.


Jun 08, 2017 at 10:51 AM
AdaptedLenses
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p.1 #13 · p.1 #13 · TAP "Decentered"?


Right, meant if it's unit focusing, doesn't matter if you prefocus and let TAP fine tune, or if you set lens to infinity and let TAP handle all the focusing adjustments. A FLE lens set to infinity but focused to 3-4' with TAP could in theory have worse performance? Don't think that's the case with this lens but I'd need to get a tripod out again to double check that. Unfortunately I can't start shooting brick walls on a tripod in my office, otherwise co-workers will think I've lost my mind...


Jun 08, 2017 at 11:22 AM
JimBuchanan
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p.1 #14 · p.1 #14 · TAP "Decentered"?


While the below post attempts to explain the lens weight limit as a vertical force, the take-away feature of the TAP is that support of the M lens mount has no helical which would act as a more precise way to control parallelism of lens and camera sensor. Rather, the TAP is constructed similar to a standard of a bellows unit where the standard or in this case the TAP lens mount rides on a larger rail controlled by gears and a secondary rail for stability.

At first glance, the corner out-of-focus could be a horizontal misalignment, but I suppose a vertical misalignment (as in a heavy lens) could cause the same.
https://www.fredmiranda.com/forum/topic/1452716/11#13842437



Jun 08, 2017 at 11:26 AM





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