unable to get sharp focus with IR converted P21+ using IR filters

[mikeinlondon]

i had a p21+ adapted to take IR photos recently but when I use the camera with an IR filter the images are unsharp, but not i think to a focussing issue. the backs focus is recalibrated I understood

the images attached show the first image in each sequence taken without a filter, second taken with a heliopan R72 filter and third in each set with a Lee IR 87 filter (730nm)

the first image is always sharp (look at the car number plates) in the first set, but when i add a filter to get the IR effect (dark sky) the image softens

 

[mikeinlondon]

i had a p21+ adapted to take IR photos recently but when I use the camera with an IR filter the images are unsharp, but not i think to a focussing issue. the backs focus is recalibrated I understood

the images attached show the first image in each sequence taken without a filter, second taken with a heliopan R72 filter and third in each set with a Lee IR 87 filter (730nm)

the first image is always sharp (look at the car number plates) in the first set, but when i add a filter to get the IR effect (dark sky) the image softens

In addition I notice that there is not much difference in the leaf (white) detail ie it looks 'IR' white like i expect, but its mainly the sky that darkens. I like the effect with the Lee filter, but would like the sharpness without a filter. is there a way to process the original file to get dark skies or perhaps blenn the two images together to enhance the sharpness, although that would be a pain to keep doing

the process for each three was:

the filter holder was on the lens before focusing

the camera was set to focus then switched to manual focus

then the three test shots were taken


Mike

 

[coulombic]

In addition I notice that there is not much difference in the leaf (white) detail ie it looks 'IR' white like i expect, but its mainly the sky that darkens. I like the effect with the Lee filter, but would like the sharpness without a filter. is there a way to process the original file to get dark skies or perhaps blenn the two images together to enhance the sharpness, although that would be a pain to keep doing

the process for each three was:

the filter holder was on the lens before focusing

the camera was set to focus then switched to manual focus

then the three test shots were taken


Mike

This is another problem inherent to your type of conversion. You had yours converted to full-spectrum. In effect, it is not focusing specifically to NIR, but to visible light. Visible light and NIR do not always come to focus at the same point (the fact that light doesn't all focus at the same point is inherently the cause of many different aberrations, btw).

For you to obtain focus lock, you'll either need apochromatic lenses, or you'll need to look for the IR focus designation on your lenses. Many new lenses do not have this. Mostly, you'll need to use the pinhole camera effect, and just stop the hell out of your lenses to get the most DoF.

 

[mikeinlondon]

This is another problem inherent to your type of conversion. You had yours converted to full-spectrum. In effect, it is not focusing specifically to NIR, but to visible light. Visible light and NIR do not always come to focus at the same point (the fact that light doesn't all focus at the same point is inherently the cause of many different aberrations, btw).

For you to obtain focus lock, you'll either need apochromatic lenses, or you'll need to look for the IR focus designation on your lenses. Many new lenses do not have this. Mostly, you'll need to use the pinhole camera effect, and just stop the hell out of your lenses to get the most DoF.

Actually I asked for an IR conversion, not full spectrum so if anything i would expect the shots WITH the filter to be sharper if the back was Calibrated for IR focus surely

I am using Phase One 35mm and 80mm lenses, any don't really want to stop down too much as that also causes sharpness issues

Would it help to leave the AF on when the filter is on (i used af and then set it to manual to take the shots)

Mike

 

[mikeinlondon]

By tweaking in capture One I can get the unfiltered shot to look like this by mixing the B/W channels and adding contrast, but somehow some of the tones look wrong but its nearer that I thought i could get it and its sharp

Mike

 

[coulombic]

Actually I asked for an IR conversion, not full spectrum so if anything i would expect the shots WITH the filter to be sharper if the back was Calibrated for IR focus surely

I am using Phase One 35mm and 80mm lenses, any don't really want to stop down too much as that also causes sharpness issues

Would it help to leave the AF on when the filter is on (i used af and then set it to manual to take the shots)

Mike

What you asked for and what you received are not, in effect the same thing. If you have to filter your camera to get IR images, your camera is not actually converted to IR.

An easy way to clear this up is to look at the glass covering your sensor. What color is it? If it's anything other than black, you have a full-spectrum camera, end of story.

 

[coulombic]

Sorry, I came across as curt there. From everything you've posted about your camera thus far, I am led to believe that you have a full-spectrum conversion. Please, verify the color of the glass covering your sensor, and we'll go from there. If it is already black, you do not need any extra IR filters. Installing them will only diminish your optical quality.

 

[mikeinlondon]

Sorry, I came across as curt there. From everything you've posted about your camera thus far, I am lead to believe that you have a full-spectrum conversion. Please, verify the color of the glass covering your sensor, and we'll go from there. If it is already black, you do not need any extra IR filters. Installing them will only diminish your optical quality.

No offence taken!

the colour of the glass is clear, indeed the recess where the IR cut filer was is empty (with the glass returned to me), but I was told that is how they do IR conversions at P1. I understand that they also strongly recommend not putting an IR filter directly over the sensor, but i do not understand why. This necessitates putting an IR filter over the lens to cut visible light.

Regarding full spectrum and IR conversion I was advised that they do both and that the processes differ, but i asked for IR conversion.

If the back is indeed calibrated for IR focus, when i use an IR filter perhaps I should have left the AF on?

Mike

Mike

 

[coulombic]

No offence taken!

the colour of the glass is clear, indeed the recess where the IR cut filer was is empty (with the glass returned to me), but I was told that is how they do IR conversions at P1. I understand that they also strongly recommend not putting an IR filter directly over the sensor, but i do not understand why. This necessitates putting an IR filter over the lens to cut visible light.

Regarding full spectrum and IR conversion I was advised that they do both and that the processes differ, but i asked for IR conversion.

If the back is indeed calibrated for IR focus, when i use an IR filter perhaps I should have left the AF on?

Mike

Mike

Yeah, that's definitely not an "IR" conversion. Suspicions confirmed, unfortunately. You're rocking a full-spectrum camera -- cool for astro photography, but not much fun for anything else. I do not speculate the camera's focus has been changed to focus IR light. Rather, as it's sharpest without the filter, I very much suspect that your camera is still focusing in visible light.

You can try using AF with the filter on, but if my suspicions are correct (they are), your camera will endlessly hunt for focus because all it thinks it's seeing is black. Like trying to make a camera use AF with a 10-stop filter on -- just ain't happening.

You were not given what you wanted is essentially what it comes down to. My camera is converted purely to shoot in IR. The sensor is covered with black glass that permits wavelengths 830nm and beyond. Because it has been fully converted to shoot in IR, it autofocuses perfectly.

One other consideration that you must take into account stems from the whole "light not all focusing at the same point" thing. Basically, not all lenses work the same in IR. I don't think this is your issue, however, but it may become a consideration later.

In the meantime, if you have a lens with an infrared focus mark on it, you can use that in conjunction with your filter and you'll actually be good to go.

Otherwise, MaxMax.com converts cameras to true IR, and supports AF perfectly. I highly recommend them.

 

[mikeinlondon]

I just got back from a photo trip and as I had the above problem I decided to 'bracket focus' on shots that looked like they had potential and shoot at f16, but still nothing was truly in focus and all the shots I got look soft. This is a real disappointment for me as i am used to pin sharp focus with my P25+ (normal) back. I raised a support case with P1 but only got back the advice to not use an IR filter on the lens! The ticket is still open so maybe i might still get a response, but at the moment it seems I have no way of predicting if I can get a particular scene in focus at all!

This is very frustrating as I can see the potential from the soft images!

Does anyone know of anyone who owns an IR converted P1 back and has had success with getting focus nailed every time?

Mike

 

[coulombic]

I just got back from a photo trip and as I had the above problem I decided to 'bracket focus' on shots that looked like they had potential and shoot at f16, but still nothing was truly in focus and all the shots I got look soft. This is a real disappointment for me as i am used to pin sharp focus with my P25+ (normal) back. I raised a support case with P1 but only got back the advice to not use an IR filter on the lens! The ticket is still open so maybe i might still get a response, but at the moment it seems I have no way of predicting if I can get a particular scene in focus at all!

This is very frustrating as I can see the potential from the soft images!

Does anyone know of anyone who owns an IR converted P1 back and has had success with getting focus nailed every time?

Mike

First, focusing an IR-converted camera is very easy. Unfortunately, that is not what you have. If you are interested, MaxMax.com is an excellent conversion service for converting to real infrared, and maintaining accurate focus.

The following is an excerpt from the Wikipedia entry regarding Infrared Photography:

Focusing infrared



Infrared filters.
Most manual focus 35 mm SLR and medium format SLR lenses have a red dot, line or diamond, often with a red "R" called the infrared index mark, that can be used to achieve proper infrared focus; many autofocus lenses no longer have this mark. When a single-lens reflex (SLR) camera is fitted with a filter that is opaque to visible light, the reflex system becomes useless for both framing and focusing, one must compose the picture without the filter and then attach the filter. This requires the use of a tripod to prevent the composition from changing. A sharp infrared photograph can be done with a tripod, a narrow aperture (like f/22)[citation needed] and a slow shutter speed without focus compensation, however wider apertures like f/2.0 can produce sharp photos only if the lens is meticulously refocused to the infrared index mark, and only if this index mark is the correct one for the filter and film in use. However, it should be noted that diffraction effects inside a camera are greater at infrared wavelengths so that stopping down the lens too far may actually reduce sharpness.
Most apochromatic ('APO') lenses do not have an Infrared index mark and do not need to be refocused for the infrared spectrum because they are already optically corrected into the near-infrared spectrum. Catadioptric lenses do not require this adjustment because mirrors do not suffer from chromatic aberration.
Zoom lenses may scatter more light through their more complicated optical systems than prime lenses, that is, lenses of fixed focal length; for example, an infrared photo taken with a 50 mm prime lens may look more contrasty than the same image taken at 50 mm with a 28–80 zoom.
Some lens manufacturers such as Leica never put IR index marks on their lenses. The reason for this is because any index mark is only valid for one particular IR filter and film combination, and may lead to user error. Even when using lenses with index marks, focus testing is advisable as there may be a large difference between the index mark and the subject plane.

Unless you use the red mark on the lens, or APO lenses, you are pretty much out of luck, as far as focusing goes.

 

[mikeinlondon]

Hi Thanks for the info and I understand what you posted but my lenses do have an IR mark on them.

I also did a test and on a very bright subject without a filter it will focus, obviously, then when I add the filter I half press again and the focus point moves towards the IR mark on the lens. So it looks like the lens is re-focussing but the pictures are still soft, so I have been 'focus bracketing' ie manually using a wide range of focus points before and after what should be the focus point, but it never achieves focus properly and the images look soft

I suppose what P1 did is to remove the IR blocking filter and make the camera sensitive to IR light, but also visible light. By adding an IR filter on the lens the camera should only 'see' IR light. The camera focusses fine without the IR filter but with it I cant seem to get accurate focus at all with it on. They dont seem to recommend putting the IR filter on the back itself, though I am not sure why, as I see you can get Hasselblad's done here http://www.spencerscamera.com/store...Product_ID=81&Category_ID=1&Sub_Category_ID=1

Stopping down to f16 on this shoot maybe was too much and maybe caused lots of diffraction which I am guessing would be worse in IR. I was shooting with the Mamiya 35mm with the light to the side and the lens hood on.

Mike

 

[coulombic]

Hi Thanks for the info and I understand what you posted but my lenses do have an IR mark on them.

I also did a test and on a very bright subject without a filter it will focus, obviously, then when I add the filter I half press again and the focus point moves towards the IR mark on the lens. So it looks like the lens is re-focussing but the pictures are still soft, so I have been 'focus bracketing' ie manually using a wide range of focus points before and after what should be the focus point, but it never achieves focus properly and the images look soft

I suppose what P1 did is to remove the IR blocking filter and make the camera sensitive to IR light, but also visible light. By adding an IR filter on the lens the camera should only 'see' IR light. The camera focusses fine without the IR filter but with it I cant seem to get accurate focus at all with it on. They dont seem to recommend putting the IR filter on the back itself, though I am not sure why, as I see you can get Hasselblad's done here http://www.spencerscamera.com/store...Product_ID=81&Category_ID=1&Sub_Category_ID=1

Stopping down to f16 on this shoot maybe was too much and maybe caused lots of diffraction which I am guessing would be worse in IR. I was shooting with the Mamiya 35mm with the light to the side and the lens hood on.

Mike

I feel as if I'm starting to repeat myself here, but I'll go over this once more. First, as your camera has only been converted to full-spectrum, that's what it's still focusing. When you install any type of IR filter over the lens, your camera is, in effect, not able to focus anything via AF, as it's not perceiving any visible light. As to say, if you can't see anything through your lens with the filter installed, neither can your camera. Pretty simple.

Why it's blurry is also pretty simple -- IR does not come into focus at the same point as visible light. This is a common, well-documented phenomenon. It is the cause of many optical aberrations, as well, to include any green/cyan/magenta/yellow/purple fringing. You are attempting to focus your lens to light that you cannot see, and your camera's AF has not been calibrated to. You also have no IR designations on your lenses. It should absolutely not be a surprise to you that you can't get a sharp image while shooting filtered.

Diffraction affects IR earlier than visible light. You will see softening from diffraction after f/11, or perhaps even earlier than this. However, due to the type of "IR modification" for which you have opted, and the optics you currently posses, you are stuck with attempting to minimize the circle of confusion with your lenses to increase DoF. As to say, the Pinhole Camera Effect. Due to the earlier onset of diffraction with IR, your images will appear much softer through this means than normal, as well.

To restate: without APO lenses, or without red marks on your optics for different wavelengths of IR, your focus will be off. There is no way for you to scientifically, and repeatably, maintain accurate focus.

I really, really think you need to do some research on this topic. As it stands, I feel as if I am saying the same things over and over to you, but without proper understanding of the physics behind IR photography, you're somewhat confused. I also think that, instead of wasting your time with a full-spectrum camera, you should just shell out the cash and have it re-converted to real-deal Near-IR.

 

[mikeinlondon]

I feel as if I'm starting to repeat myself here, but I'll go over this once more. First, as your camera has only been converted to full-spectrum, that's what it's still focusing. When you install any type of IR filter over the lens, your camera is, in effect, not able to focus anything via AF, as it's not perceiving any visible light. As to say, if you can't see anything through your lens with the filter installed, neither can your camera. Pretty simple.

Why it's blurry is also pretty simple -- IR does not come into focus at the same point as visible light. This is a common, well-documented phenomenon. It is the cause of many optical aberrations, as well, to include any green/cyan/magenta/yellow/purple fringing. You are attempting to focus your lens to light that you cannot see, and your camera's AF has not been calibrated to. You also have no IR designations on your lenses. It should absolutely not be a surprise to you that you can't get a sharp image while shooting filtered.

Diffraction affects IR earlier than visible light. You will see softening from diffraction after f/11, or perhaps even earlier than this. However, due to the type of "IR modification" for which you have opted, and the optics you currently posses, you are stuck with attempting to minimize the circle of confusion with your lenses to increase DoF. As to say, the Pinhole Camera Effect. Due to the earlier onset of diffraction with IR, your images will appear much softer through this means than normal, as well.

To restate: without APO lenses, or without red marks on your optics for different wavelengths of IR, your focus will be off. There is no way for you to scientifically, and repeatably, maintain accurate focus.

I really, really think you need to do some research on this topic. As it stands, I feel as if I am saying the same things over and over to you, but without proper understanding of the physics behind IR photography, you're somewhat confused. I also think that, instead of wasting your time with a full-spectrum camera, you should just shell out the cash and have it re-converted to real-deal Near-IR.

Sorry if you feel you are repeating yourself i do understand what you are saying, but I did state above that I do have red marks on my lens, so that should help right? If not focus bracketing should help no?

Also I did not opt for a full spectrum conversion, I did ask for full IR, i was just told that P1 didn't recommend a filter directly over the sensor and that they would adjust focus for IR anyway and that was the way it should be done, as recommended by P1! They should know what works best shouldnt they?

Anyway sorry if I seem obtuse!

Mike

 

[coulombic]

Sorry if you feel you are repeating yourself i do understand what you are saying, but I did state above that I do have red marks on my lens, so that should help right? If not focus bracketing should help no?

Also I did not opt for a full spectrum conversion, I did ask for full IR, i was just told that P1 didn't recommend a filter directly over the sensor and that they would adjust focus for IR anyway and that was the way it should be done, as recommended by P1! They should know what works best shouldnt they?

Anyway sorry if I seem obtuse!

Mike

The red marks may or may not help for you. The red marks are usually calibrated for a specific filter, with a specific wavelength. If you don't have the filter the lens is calibrated for, well, the marks are then of little use to you.

Focus bracketing may or may not help, I can't say. You might arbitrarily nail the focus on one image, and then never hit it again during the set. What I'm getting at, essentially, is that you have very little means of scientifically obtaining focus. This is, naturally, the grounds for much frustration.

Regardless of what you asked for, you didn't actually receive it. You do not have an IR camera. You also don't seem to have a camera that focuses in IR. Rather, from the sounds of it, you have a full-spectrum camera that focuses in the visible light spectrum.

If I were you, I'd be demanding my money back. This nonsense of "P1 knows best" has to end. This is ultimately why I recommend doing some reading for you, as it seems clear that you have limited knowledge of the subject. If you went into this situation demanding a 720nm-sensitive camera that auto-focuses in IR, there would have been no ambiguity. Either they'd have performed the modification, or they'd have told you that it would void your warranty, and you'd be off to another shop.

I cannot speak, as far as why they do not "recommend" an IR filter be placed in front of the sensor, as opposed to clear glass. I can tell you, however, your IR images will never be as good as you want them to be with this setup. Either you'll not have it perfectly focused, or you'll have stopped it up so far, your images will be severely degraded due to diffraction. No-win situation with your current filter.

Also, if you want black and white infrared, I'd recommend something longer than 720/730.

 

[mikeinlondon]

Thanks for all your input!

Mike

 

[coulombic]

Thanks for all your input!

Mike

No problem, man. Hope this helps. If you're determined to keep your warranty, get an apochromatic lens for your IR use. It should focus right around the same point in both IR and visible light.

 

[mikeinlondon]

No problem, man. Hope this helps. If you're determined to keep your warranty, get an apochromatic lens for your IR use. It should focus right around the same point in both IR and visible light.

Not sure you can get APO lenses for Mamiya fit (apart from one telephoto I think which would be no good for landscapes), unless you know better...

Mike

 

[coulombic]

Not sure you can get APO lenses for Mamiya fit (apart from one telephoto I think which would be no good for landscapes), unless you know better...

Mike

Hmm. I can only think of two for Mamiya -- the 200mm f/2.8 APO and the 300. Both exceptional lenses; however, finding an IR filter for them might prove difficult (they're both the drop-in style filter).

Telephotos can make for very interesting landscapes -- kind of depends on what you're shooting, and what your style is. It is not a comprehensive or adequate solution to your IR problem, however. Ultimately, you really should just get your camera converted to full IR, and put this headache behind you.