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The influence of LTII focal reducer on bokeh
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PostPosted: Sat Jul 27, 2019 8:00 am    Post subject: The influence of LTII focal reducer on bokeh Reply with quote
Throughout the years we've heard many tales about how putting an additional glass between the lens and the sensor "just can't be good™".
Now, anyone who actually used a focal reducer knows it's pros significantly outweighs it's cons, but let's just drive a few more nails into the coffin where it hurts the most: bokeh.

Gentlemen, I'm going to prove it to you: focal reducer makes lens bokeh better.
Better than the one found with the same lens on the FF sensor, that is.


Without a further ado, I present you a Canon FDn 100/2.8.
I've shot with this lens wide open on LTII a lot in the past, and this is why I immediately could tell something is not quite right with FF body.
FF first, LTII second:




You might say: that's not that big of a difference, or "I don't really see anything".
And that's okay, the changes are quite subtle. Let me show you a much more obvious example: Canon FDn 50/1.4




LTII significantly reduces OOF outlining, which is a contributing factor in bokeh nervousness.
The effect tends to be much more prominent at the distance of full body portrait, I just had only the park bench to work with today.

There, you have it: additional glass made your lens better.


PostPosted: Sat Jul 27, 2019 8:39 am    Post subject: Reply with quote
A very interesting test you've conducted. I have long been one of the myth busters in favor of intervening optics and their not degrading optical performance -- and I have the results to prove it. The LT II is a well-designed adapter and does a good job at its task.

It's interesting, I guess, that the difference in results between the 100mm and 50mm are as dramatic as they are - that is, there is almost no difference in the 100mm test, while the 50mm test shows a definite softening of the OOF highlights. Now, given that the 50mm is half the focal length of the 100mm, it causes me to wonder immediately, what about an optic whose focal length is half that of the 50mm? Have you tried your LT II yet on a true wide angle -- say a 28mm or a 24mm? I mean, lenses in this focal range were really what the LT II was designed for, after all.

But can we have a bit more explanation of the testing? I take it you were using two cameras? One FF and one APS-C? I'd like to know which cameras were being used. Or were you using one of these FF mirrorless cameras that has an APS-C mode?


PostPosted: Sat Jul 27, 2019 8:54 am    Post subject: Reply with quote
cooltouch wrote:
Have you tried your LT II yet on a true wide angle -- say a 28mm or a 24mm?

I can do this test. My FDn 24/2.8 haven't sold yet and it does fit the bill of a lens with fairly noticeable outlining to dampen.
Here is a shot from the FF body which shows this behaviour:



cooltouch wrote:
But can we have a bit more explanation of the testing? I take it you were using two cameras? One FF and one APS-C? I'd like to know which cameras were being used. Or were you using one of these FF mirrorless cameras that has an APS-C mode?

I took a mini-tripod and two bodies: A7R and NEX-3N+LTII.
There wasn't much of a reason to do this though.
My initial findings were based on just putting a reducer on A7R.


PostPosted: Sat Jul 27, 2019 9:02 am    Post subject: Reply with quote
Nicely shown aidaho. Much appreciated Like 1 .


PostPosted: Sat Jul 27, 2019 9:09 am    Post subject: Reply with quote
Thanks for the additional info. Yes, well, the way I see it, it's always best to conduct a test with a camera where the item will be used for the effect it is supposed to achieve. Using a focal reducer on an FF camera is I suppose an easy way to make a super wide angle out of a wide angle, but tha wasn't its intended purpose -- or primary purpose, at any rate.

I've been mulling your results over some and I'm wondering if the heightened OOF blur might have something to do with the increase in apparent f-stop that occurs when using a focal reducer. It's increasing the f/stop by about 1 stop, correct? So that turns the 50/1.4 into a 50/1.0 in terms of light-gathering ability, at least. But could this also have an effect on the OOF highlights being softened as well, similar to the way an increase in actual aperture value would result in softened OOF highlights?


PostPosted: Sat Jul 27, 2019 9:23 am    Post subject: Reply with quote
cooltouch wrote:

I've been mulling your results over some and I'm wondering if the heightened OOF blur might have something to do with the increase in apparent f-stop that occurs when using a focal reducer. It's increasing the f/stop by about 1 stop, correct? So that turns the 50/1.4 into a 50/1.0 in terms of light-gathering ability, at least. But could this also have an effect on the OOF highlights being softened as well, similar to the way an increase in actual aperture value would result in softened OOF highlights?

In my understanding, booster somehow cuts off the outer part of the bokeh-ball.
This hypothesis is based on my anecdotal experience in shoothing though, so I might be very wrong in my understanding of the phenomena.

I've known about this behaviour for some time and in my experience it doesn't really depend on focal length, just on the level of lens OOF outlining in specific situation.
FDn 100/2.8 has a rather low outlining at close distances, but a very significant one at the long ones.
Thus close-ups look similar, but in full body portraits the difference is unmistakable.

I will however do a test with 24mm as you suggested. Maybe we will see something else.
Also, I still have an EF LTII and I can adapt Zuiko 50/1.4 and Zuiko 135/2.8 with additional adapter inbetween.
Now 135/2.8 is criminally smooth on it's own, but I think I'll bother to check Zuiko 50/1.4: it's has famously uneven OOF outlining, and that would be interesting to check out in this comparison.


PostPosted: Sat Jul 27, 2019 9:44 am    Post subject: Reply with quote
A7r sensor has known deficiencies with some mf lenses, especially at edges.

Intervening optics typically degrade edge performance; center, not so much. Unless you can prove otherwise.


PostPosted: Sat Jul 27, 2019 10:19 am    Post subject: Reply with quote
visualopsins wrote:
Intervening optics typically degrade edge performance; center, not so much. Unless you can prove otherwise.


I have actually debunked this myth. Years ago, I posted here a rather extensive test I conducted, in which I evaluated two teleconverters -- a Vivitar 7-element macro 2x TC and a Tamron 01F dedicated 2x TC. The lens I used was a Tamron 90mm f/2.5 macro.

Comparing the images I captured with these two teleconverters with images taken without TCs, I showed that the images with the TCs were actually revealing more detail than those taken without the TCs. I was taken to task by one member here over the fact that they didn't display twice the resolution since they doubled the image. I felt then and feel now that this guy's position was pointless and absurd for any number of reasons. But at least I proved my point that a good TC does not degrade an image and can, in fact, slightly enhance it under certain conditions.

However, given the task a focal reducer is asked to perform, it isn't surprising that performance on the edges suffers somewhat, although with a well-designed focal reducer, center performance shouldn't be affected at all.

Last edited by cooltouch on Sat Jul 27, 2019 10:28 am; edited 1 time in total


PostPosted: Sat Jul 27, 2019 10:27 am    Post subject: Reply with quote
Rode my bike to the park to get more data.

Canon FDn 24/2.8:



Pretty much no difference.
I notice the outlines on FDn 24/2.8 are quite thick and they did become thinner with LTII.
I think I like the FF bokeh a tiiiiiny bit more in this example.



Olympus Zuiko 50/1.4:



Oh boy, it might as well have been two different lenses.


PostPosted: Sat Jul 27, 2019 12:12 pm    Post subject: Reply with quote
cooltouch wrote:
visualopsins wrote:
Intervening optics typically degrade edge performance; center, not so much. Unless you can prove otherwise.


I have actually debunked this myth. Years ago, I posted here a rather extensive test I conducted, in which I evaluated two teleconverters -- a Vivitar 7-element macro 2x TC and a Tamron 01F dedicated 2x TC. The lens I used was a Tamron 90mm f/2.5 macro.

Comparing the images I captured with these two teleconverters with images taken without TCs, I showed that the images with the TCs were actually revealing more detail than those taken without the TCs. I was taken to task by one member here over the fact that they didn't display twice the resolution since they doubled the image. I felt then and feel now that this guy's position was pointless and absurd for any number of reasons. But at least I proved my point that a good TC does not degrade an image and can, in fact, slightly enhance it under certain conditions.

However, given the task a focal reducer is asked to perform, it isn't surprising that performance on the edges suffers somewhat, although with a well-designed focal reducer, center performance shouldn't be affected at all.


This one? http://forum.mflenses.com/teleconverter-comparison-tamron-01f-vs-vivitar-macro-t38993.html
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