Infrared and Sony

[digARTal]

I am a keen infrared image maker and recently jumped ship from Canon to Sony. One of the reasons for this was the access to full frame mirrorless as I love my wide angle lenses for infrared.

 

The problem is that I am having trouble finding suitable full frame lenses suitable for IR as most of the Sony lenses have "hotspots". I have tested a few lwnses and visited most "infrared" knowledge articles on the web based around camera company modifiers and infrared groups. The list of suitable Sony lenses seems quite limited so I have started experimenting with other brands and adapters.

 

Is there anyone else out there in infrared world that we can discuss what we have learnt? May even try and post a list of lenses but this will take time and money to test and develop.

 

To see some infrared images visit my infrascapes gallery at - http://markd.photography/markd/digartal-colour-places/ , although most of these are pre Sony but the gallery will expand as I have 3 Sony Aphas and 2 are infrared.

 

Thanks.

 

Mark

[Golem]

Not doing IR, but I have been working

on the hot spot thing. 2-3 stops down

from full open I find the hot spots are

absolutely gone. Even 1 stop down is

a drastic reduction, but 2-3 stops is

the full fix.

 

I also see the IR work by a friend who

uses old digital "bridge cameras" and

an "opaque" IR filter. These cameras

have cheap zooms, which surely have

hot spots at wider apertures, but the

results I've seen must have been shot

at the better apertures.

 

All of which causes me to think I must

be missing something in terms of what's

bugging you about the lenses you have

encountered thus far. Whazzup widdat ?

 

I use adapted lenses almost exclusively,

so I'd say that if you're getting what you

need from Canon EF lenses, just keep

using them, via adapter.

[mopswerk]

I like my older (manual) Voigtländer SLR lenses: I only have a MFT IR converted camera, but a hotspot should also show up there in the center (couldn't make out any, however):

* Voigtländer Ultron 40, Voigtländer Color Skopar 20mm and Voigtländer Apo Lanthar 90mm

I am using the Nikon mounts (aperture can be set mechanically via an adapter), but since electronic Adapters for EOS-Sony exist (aperture to be set electronically), I see don't any problems using the EF mount versions of the Voigts.

Apart from that, those lenses are Pancakes or quite compact for a 90mm, and it's a joy using them (almost Zeiss like)!

[Foothill Sonyman]

I have a NEX-7 crop frame camera converted to Lifepixel's "normal IR" of 720nm. I've used the Zeiss 24-70 FE lens with no hot spots. With the 18-200mm Sony E mount lens I have a center hot spot below about 35mm but not above @35mm focal length. I haven't done any testing with other lenses.

[Zé De Boni]

I have a SLT-99 converted to full spectrum. I still have the old Fuji IS, but I don't use it anymore. Nothing compares to the life view capabilities of a mirrorless camera.

Golem did not understand the hot spot that you mention. It is not light falloff, which can be improved with stopping down. In Infrared the hot spot is enhanced at smaller apertures. That is because it is caused by internal reflection on lens surfaces. Lenses are coated to avoid this reflection, but for obvious cost reasons manufaturers do that just for the visual part of the spectrum (each layer of a multicoating deals with one narrow part of it). So, most of the lenses behave in IR as if it had no coating. As the infrared reflection transits freely in the optical path bouncing on all surfaces, the flare ends up obvious when it reaches the image sensor. Closing the diafragm you may eliminate some amount of the flare, as you cut part of the reflection from elements behind it, but the small part that can pass through will form a hot spot proportional to the size of the f-stop. The effect is more obvious the longe the wavelenght is sellected by the filter you use, a 720 nm filter giving less noticeable problem than the 780nm and so on untim the 950 nm, which shows the stronger hot spot.

There are few lenses that are projected to work on the extended range of the spectrum. They are very expensiive and usually cover the range around the normal focal lenght. Zeiss has a line of lenses specially designed for IR, coming in Nikon mount. Check their site.

I tried all my Sony mount (and Mamiya 645) wide-angle to normal lenses and the only acceptable oneswere those with Nano-coating. Now, for IR use the Sigma Art 35mm f/1.4 and the Rokinon TS 24mm f/3.5 in the widest aperture that can give me good resolution, avoiding less than f/8. I have just ordered the Sony A 24mm f/2 and will try it next week on a trip (however I will just use the 720 nm filter). I have good expectations on it, moreover on resolution.

[Golem]

.........

Golem did not understand the hot spot that you mention.

It is not light falloff, which can be improved with

stopping down. In Infrared the hot spot is enhanced at

smaller apertures. That is because it is caused by

internal reflection on lens surfaces. .........

In "normal" photo conversations, a hot spot is a form

of vignetting, cured by stopping down. The reflection

you mention, by whatever name, is also familiar to me,

in the non-IR world, and sometimes called "the dreaded

blue spot" ... cuz the sensor reflects a blueish color of

the lens's exit pupil. It reflects it back onto the rear

surface of the lens, where it is again "seen" by the

sensor, all of which is exacerbated by small apertures.

 

Other than avoiding small apertures, I've found that it

is almost intolerable with some lenses and hardly ever

shows up with certain other lenses, even at the smaller

apertures. This will depend upon how severely curved is

the rearmost surface of the lens, and its distance from

the sensor. It also depends, to some degree, on all the

internal-to-lens reflections that may be visible within

the exit pupil.

 

If the anti-reflection coatings are not effective for

the IR band, acoarst the exit pupil reflection is much

stronger, but it should still vary with distance and

curvature as noted above. This means having many

lenses on hand to experiment with .... OK for those of

us with bagsfull of leftover lenses from long careers,

but hugely inconvenient for more recent practitioners.

[Zé De Boni]

Golem still don't undestand it. It is not about the blue spot either! To know about IR hotspot one needs experience with infrared photography, digital or film (it happens on film too!). I have tested the Sony Zeiss 16-35/4, Samiyang TS 24/3.5, Sigma Art 35/1.4, Sony 50/1.4, Sony Macro 100/2.8, Sigma Macro 70/2.8, Sony Zeis 85/1.4, Sony Zeiss 135/1.8. According to the filter sizes recquired, I tested each lens with the 720nm, 780nm, 850 nm and 950nm. The general rule that I have learned from these tests is that for each lens the IR hot spot is worsened in the same proportion of the wavelenght, which is explained by the fact that they were projected to work in visible light. Also, the ploblem is progressively more evident as you close the f-stop.

I do my tests for personal use, I am not a blogwriter nor am I paid to publish them. I have just realized that I can help digARTal, by pointing a direction to  solve the problem.

I still reccomend the lenses in my previous post (24 and 35) and add the Sony Macro 100/2.8 with restrictions to the list.

[dierk]

I used a converted NEX-7 (720nm) for several years.

Now I got my A7R converted to 720nm.

I did not really notice any hot spots with all my lenses?

My impression is, that you see these on IR color images but not or less noticeable with B&W.

The used lenses are in the description of the images.

 

regards

dierk