IR focus correction with Rolleiflex TLR

[m.c.fitz]

<p>Can anyone help me with this? There is no mark on the focusing knob of the Rolleiflex to adjust for focus when using IR film and filter. Last year in spring I used a couple of rolls of Ilford SFX 200 and had no problem with focusing issues, but that film is near infrared, not infrared, and as I understand it, the focus shift doesn't affect the SFX.<br>

I have a couple of rolls of Rollei infrared now, and am not certain how to compensate for the focus shift. The lens is a Zeiss Planar and the filter is a Heliopan IR filter. In searching for information it sounded as though some lenses had focus correction integrated in them during the manufacturing process. Is that possible?<br>

Is stopping down the lens as much as possible sufficient? <br>

Any guidance or suggestions would be quite welcome, thank you.</p>

[Brian1664876441]

Most lenses require that the focus be adjusted closer for IR than for visible, although there are exceptions.

 

http://www.photo.net/medium-format-photography-forum/000viO

 

I found this old thread on photo.net. That would have been my first guess for IR- move the focus closer, use the right-side

F5.6 DOF mark for the IR index.

 

Some lenses are better than others, most are between F4 and F8.

[dhbebb]

<p>The easiest solution if you can find one is the fiendishly clever original Rollei IR filter, which has an optical correction in it to bring the taking lens plus filter to the same focus as the view lens.</p>

[glen_h]

<p>Traditional achromatic lenses made with positive crown glass and negative flint glass, have fairly known IR characteristics. But many now use fancier glasses, so it isn't so simple.</p>

<p>https://en.wikipedia.org/wiki/Achromatic_lens</p>

<p>Note in the graph at the bottom of the page, that the apochromat has pretty much the same focus as the visible. </p>

[dave_s]

<p>Some of the discussion <a href="http://www.apug.org/forum/index.php?threads/infrared-focus-point-for-hasselblads.55598/">on this web page</a> may be useful. They talk, among other things, about the Hblad Planar (admittedly a different Planar, because it's retrofocus). Some users don't adjust focus at all.</p>

<p>When all is said and done, you may have to test, or at least bracket, if you want optimal results.</p>

[m.c.fitz]

<p>Thank you all for your replies, suggestions and links to other threads and information. All of it has given me plenty to read and take into consideration.<br>

I had pretty much come to the same conclusion as Dave S suggested, I'm going to have to do some testing.<br>

Thanks again, if I get any satisfactory results, I'll share them here.</p>

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