Review Mini review of Tamron 90mm (A7R5 | MFO-1)

[BoltSnap]

I don't get your second question, but the MTF of the lenses drops significantly beyond f/16. There are several physical / engineering factors for this.

I am fasting, so please excuse my slow mental state

In this context, does one have to set the lens's aperture at exactly f/16? They can't set it to f/22 or f/11 (or anything else).

 

[DragonUW]

Ah, OK - BTW, have a rewarding fast.

With high-resolution sensors, it will always be a compromise. A lower aperture, such as f/22, will give you a higher DOF, but the overall resolution (read image quality) will suffer. Apertures between f/11 and f/16 are a sweet spot for modern macro, in my opinion.

 

[Barmaglot]

In this context, does one have to set the lens's aperture at exactly f/16? They can't set it to f/22 or f/11 (or anything else).

You can set it to anything in the range from f/2.8 to f/16. It's not a fixed-aperture lens, but it can't go any narrower than f/16, which is a bit of a weakness. Sony 90mm is already limited to f/22, which is wider than most other macro lenses' f/32. While it is true that very small apertures cause overall image degradation due to diffraction, in many cases it is a worthwhile tradeoff for the increased depth of field. On land, with static subjects and a tripod, it is often possible to focus stack so as to get the required depth of field without diffraction-inducing apertures, but underwater it is a great deal more difficult to pull off.

 

[hedonist222]

While it is true that very small apertures cause overall image degradation due to diffraction, in many cases it is a worthwhile tradeoff for the increased depth of field. On land, with static subjects and a tripod, it is often possible to focus stack so as to get the required depth of field without diffraction-inducing apertures, but underwater it is a great deal more difficult to pull off.

Agree with this.
I took it a step further to decide what works best for me when I had my Canon 5D mkII and Canon 100 f/2 L lens.
I found that I absolutely needed between f18 and f/26.
I then did tests on the same subject from f/18 to f/28 or similar.

I found that remarkable degradation took place beyond f/22 on the Canon lens. No issue because I was okay with f/22.

 

[Interceptor121]

The Tamron 90mm is a sharp lens but all Sony FE AF lenses 90 Sigma 105 are sharp
The difference is the focus speed and the ability to go beyond f/16 which this lens does not have
On land it wont matter much you can focus stack but underwater this is a limitation

I also do not understand how a diopter or any shape or form would improve autofocus
This lens has a focus limiter MOD to 0.7 this is sufficient to avoid the lens scanning the entire focus range
The Sony 90mm also has an even more useful limit to 0.5m the Sigma 105 has the same limit to 0.5m. With the new Sony firmware you can preset focus distance on some cameras with the Sony 90mm so the chances of going hunting are very low and by the way I never got this lens to hunt even in blackwater

If you instead want the lens to focus beyond which in underwater terms means 0.5x1.33=66cm than a diopter helps however am not sure there is any macro subject that requires that we are talking about a frame size of 20cm which would only be useful for larger fish portraits further away

this MFO-1 idea arrives just 10 years too late...

 

[Will&BilltheKrill]

I am making a guess here but since what the MFO does is correct for the refraction caused by the flat port, (this is the whole reason it improves image quality) it stands to reason that this correction also helps the camera’s auto focus “see better” and thus detect the subject/focus point more easily and quickly. Especially since the MFO doesn’t add magnification the way a traditional diaopter does.

 

[Interceptor121]

I am making a guess here but since what the MFO does is correct for the refraction caused by the flat port, (this is the whole reason it improves image quality) it stands to reason that this correction also helps the camera’s auto focus “see better” and thus detect the subject/focus point more easily and quickly. Especially since the MFO doesn’t add magnification the way a traditional diaopter does.

The adapter will not correct for the refraction at best it will correct chromatic aberrations which can occure with a flat port
RIP David Knight developed a nice model for it basically the issue of aberrations really is apparent when you are far away but drops considerably as you get close. Another factor is that modern macro lenses unlike old ones have focus breathing and at close range the effective focal lenght drops considerably and this improves the CA situation
Furthermore no single lens is the same and an adaptor that emulates a nikon device made 20 years ago is not going to fit well lenses with a different design
nauticam tests and performance metrics keep refererring to Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED as the benchmark while the world has moved on and mirrorless lenses are diffently designed

 

[MrTW]

Lost track of this post but planing a local shore dive on the weekend and will try the Sony 90mm this time.

Excellent points on the limitations of the Tamron. Never done blackwater but definitely something I want to do if I have the opportunity.

Not an expert here but my thought was that the MFO corrects some of the refraction of the flat port as mentioned by Will&BilltheKrill. Maybe just a placebo? I dont really know.

Fact for me thought, that unless I made a user focusing error about 90% of my shots came out razor sharp using the MFO on the Tamron 90mm.

Curious to see how the Sony 90mm compares although not fair as Western Australian shore diving vs Philippines is just a tiny bit different.

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[Interceptor121]

Refraction is only addressed by a dome a flat port doesn’t correct field of view
A flat port can generate additional chromatic aberrations as I have said however at very close distances this effect is small as modern macro lenses reduce their effective focal length
So in short the adapter would only help if you were shooting far away with a flat port
An eventually that is not so common