Focussing for Infrared film with a Mamiya C3

[neilt3]

I have a digital camera that I converted for full spectrum and Infrared photography , but after getting back into using a lot more film again , including building a permanent darkroom , I've treated myself to some Infrared film .
Found the Rollei Infrared IR400 for what seems like a nice price here ; http://www.firstcall-photographic.co.uk/rollei-infrared-ir400-120-iso-400/p994 , so bought some 35mm and 120 roll .

With regards to focussing , the 35mm will go in Minolta Dynax 9 and the older lenses I have all have the IR index mark on them , so that O.K.
Likewise one of the 120 rolls will be going into a Bronica ETRSi . Again that has an IR mark on the lens .
Most shots will be with a 720nm filter , although I might try some of my other ones to see how the film behaves with them .

The third roll I want to try in a TLR .
That will be going in my Mamiya C3 .
I believe some of the later cameras had a mark on the side showing the correction needed , but this one doesn't . Has anyone here used this camera for Infrared , and if so , how did you account for the different focus point ?

On SLR lenses IR focusses a bit closer than visible light so would racking the lens out another 1/8" a good idea , and rely of DOF to take care of the rest ?

Although most of what I do will be landscape with a 65mm lens using a small aperture , I want some things I have in mind to do to have quite a narrow DOF with a 180mm lens , and it would be nice to have in focus what I want .

The TLR cameras seem ideal for IR as the filter can be left on the taking lens leaving the viewing lens clear .
Any suggestions are welcome .

Regards , Neil .

 

[MattKing]

The Rollei film is more a near-IR film than a true IR film like the late, lamented Kodak HIE.

And those marks for IR focusing were designed for the wavelengths that HIE was sensitive to.

As the wavelengths you are working with are mostly visible light, you can probably just focus normally. Maybe favour slightly the near over the far.

 

[neilt3]

Thanks' for replying .
Up until now with Infrared I've used a digital camera with live view , so what you see is what you get . Very easy .

I probably focus with visible light then just back off a touch , same with the SLR's then , rather than using the Infrared marks on their lenses then .
I'll see how I get on .

 

[Ai Print]

I did a test with Rollei IR400 using a Hasselblad 501CM with 60mm, 100mm and 180mm lenses. What I found is that the correct focus mark for IR was about half way in between the red IR line and the regular focus line with the recommended R72 filter. Since I use the same filter for EFKE IR820, I use the same correction for that film and thus far, it seems to work well.

IR 400 is a very sharp film so it is worth putting in the effort to get the focus as spot on as possible so backing it off a bit would be a good idea, doing a test to get it dialed in, even better. Having said this, I bet in using the R72 filter with IR400, you could do the half way in-between thing for all lenses that have the IR mark and be good to go.

By the way, IR400 with a R72 is about ISO 6. It builds up contrast even faster than HIE or other IR films do so be aware of that and again, test it out to see what you like best.

It's a killer film, I hope they keep making it, here is it in 4x5...

 

[Sirius Glass]

The film will focus close enough the the visual wavelengths that you can just focus normally.

 

[Ai Print]

The film will focus close enough the the visual wavelengths that you can just focus normally.

As per what I wrote above, that is not what I found.

I actually lost a couple of great shots that were deliberately shot nearly wide open and then decided I had better do a test.

 

[neilt3]

As per what I wrote above, that is not what I found.

I actually lost a couple of great shots that were deliberately shot nearly wide open and then decided I had better do a test.

Thanks for the extra information and taking the time to reply . That's a very nice example shot .
I have found on APS-C digital using such as an 85mm lens near wide open there was significant focus shift , so with 35mm and especially 120 this should be more severe . As the light being focussed is at 720nm rather than visible light , the medium used to capture it shouldn't make a difference .

I'm looking forward to enlarging these quite a bit when I set up my darkroom , so I'd like to get it right without wasting too much film !

So a couple more questions ;
On the SLR's the lenses have IR indicator marks and you suggest adjusting to a mid way point .
As there are no markings on my Mamiya C3 TLR , how do you suggest I compensate ? The two main lenses I will be using on it are the 65mm and 105mm . Possibly also a 180mm .
Like wise , I also have a 5"x4" camera , and if I like the results I might get some IR film for that too .
For a landscape shot's should it just be backed off a touch from infinity focus ? Would the same apply to something that is approximately 50 - 60 feet away ?

Thanks again . Neil .

Edit ; just to add , on the Rollei data sheet it says to treat the film as ISO 25 with a Heliopan RG715 or Kodak Wrattan 88A , as these are approx. 720nm , what is the advantage to shooting at ISO 6 ?

 

[Ai Print]

The massive development chart gives two times for the developer I often use and that is HC-110 dilution B, ISO 12 and 25, I pre-soak for about 3-5 minutes. I found it gave me rather thin negatives so I standardized it as ISO 6 quite some time ago, your mileage may vary.

As far as how to mark your lenses, I will take a look at my 60, 100 and 180 and let you know what the regular compensation mark is at for infinity for the mark does not change as per distance implying that it is the same focus shift correction regardless of distance from the focused subject.

Then, you can have a starting point for your tests which you certainly should do given the style of how you read focus on the TLR, obviously to be shot wide open. And I do think the filter you are referring to will be 720NM although I standardized on a Hoya R72 type across all my formats to keep consistency, even have one in 95mm for my 40mm CF FLE which has a big correction factor in terms of how far to turn the focus ring.

Now then, be aware that as nice as 4x5 is, the film base on the Rollei is super thin, about half that of the roll film which means it is less than half of an average sheet film base...it is a royal pain in the rear end to handle during loading / unloading and equally as tough to process. I have not tried tray developing but the only way I have not had the film become dislodged is developing it in a Jobo 3010 drum which holds a total of ten sheets in pairs of two in 5 cylinders. I load a total of 5 sheets, one per each cylinder instead of two because the darn things can become dislodged and often stick together otherwise. They seem to do good in their own cylinders so souping in batches of 5 in a run keeps them safe, for me using rotary anyway and that is the only way I develop 4x5 ( 5x4 UK ) because I hate uneven development, surge marks and streaks that I get doing if any other way.

It's a nice film in 4x5 with great results but a supreme pain to load and unload in the holders, not hard to accidentally load two or more sheets in the one slot if one is not careful and unlike other 4x5 films, you can't use IR goggles for obvious reasons.

A couple years ago I did a louped test of the focus point in 4x5 and a 350mm lens with the R72 filter on it and if I recall, the correction at infinty was about 1.3mm closer focus with that lens, so I made a mark on my focusing bed and fudge the other lenses from there, the wider the lens, the more the correction on the focus bed. The shot I attached above is with a 180mm likely at F22. You could do that test too although it is rather tedious requiring looking at the subject in full sunlight on the ground glass with and without the filter on but somehow making it dark enough to see it under the darkcloth in order to make a note.

So I will get you the corrections from my Hasselblad lenses later, you can base your tests with your C3 off of those in sets of three shots, no correction, half way and then my lens's IR correction since it is the same format.

More later,

Dan

 

[MattKing]

Correct me if I am wrong, but I believe that the focus shift decreases as the focal length increases.

 

[Ai Print]

Correct me if I am wrong, but I believe that the focus shift decreases as the focal length increases.

Correct, hence the IR mark on a fisheye being much more of a differential than one on a 200mm.

 

[MattKing]

Correct me if I am wrong, but I believe that the focus shift decreases as the focal length increases.

Correct, hence the IR mark on a fisheye being much more of a differential than one on a 200mm.

Thus, given the same subject field of view, the focus shift while using the shorter focal length lenses that are used with a small digital sensor (the OP's previous experience) would be greater than while using the longer focal length lenses that are used with larger film formats.

 

[Ai Print]

Thus, given the same subject field of view, the focus shift while using the shorter focal length lenses that are used with a small digital sensor (the OP's previous experience) would be greater than while using the longer focal length lenses that are used with larger film formats.

Well sure, but with MF and LF he is still going to be dealing with enough focus shift that he will need to calibrate it, I did and it made all the difference in maximum sharpness.

 

[neilt3]

All good information and much appreciated .
As I'm new to 5x4 I'll be getting used to using regular B+W film with it first before trying IR in it .
Both the 35mm and 120 SLR's should be fairly straightforward to focus , I'll try a few different levels of exposure on the 35mm to see how it behaves .
It's the focussing on the Mamiya C3 with the absents of any IR markings that causing the most head scratching .
I have a few more days in work this week and then off to the Pembrokeshire coast of Wales for a week , looking forward to it .

 

[grahamp]

The C3 is very like a view camera, in that the focusing is linear (not helical). You might want to look at this LF Forum thread http://www.largeformatphotography.info/forum/archive/index.php/t-40217.html which does it to death. It will depend on the film sensitivity, the filter transmission, and the lens focal length. None of the Mamiya C lenses are 'APO', unfortunately.

 

[neilt3]

The C3 is very like a view camera, in that the focusing is linear (not helical). You might want to look at this LF Forum thread http://www.largeformatphotography.info/forum/archive/index.php/t-40217.html which does it to death. It will depend on the film sensitivity, the filter transmission, and the lens focal length. None of the Mamiya C lenses are 'APO', unfortunately.

Thanks for the link , I've had a read through that and seems to give a bit more insight on the correction needed for the larger formats .
It's been a dull day over here today but I've had a play around with the C3 with the 105mm lens on and an R72 filter on .
I was just about able to focus on the rooftops down the road with the filter on , and the difference between filter on or off seemed to fall in line with the suggested 1/70 of the focal length adjustment .
I'm not sure if that will work with the shorter focal lengths used on medium format ( compared to 5x4) , certainly with 35mm there is a much greater difference in the correction needed between different focal lengths . That's clear to see on my Minolta zoom lenses that have a few IR marks on for each end of the focal range .
The shots that I have planned for next week with this film are relying of the weather being fairly bright , so the adjustment should be easy enough to make after I put the filter on , after focussing first without it on .
It should be easy enough to work out what should work best when I'm set up for the shot's , so we will see .