Depth of Field - 4x5

[Bill Glickman]

Scot, you sure picked a hot topic! Some very good input by the above posters. Just a bit of compilation here.... there is 2 practical ways to get proper DOF after knowing your near point and far point.

The first method will bypass using the desired cc desired on film....as Ellis and others point out, use the camera as a focussing guide, this technique is reasonably sound. The benefit of this system is you do not need to know the distance to your near and far point, you just need to be able to foucs on them and set then set the standard accordingly - and then the f stop. The drawback is, this does not take into consideration the potential enlargement capability of the exposed film. If your enlargement factors are small, (less than say 3x) this method is very fast and sufficeint.

To be more exact, you will need to figure the cc desired on film to accomodate your potential enlargement size. A good goal is .3mm to print, so if you want a 10x enlargement, then use a .03 mm cc in your DOF formula as found on many of the links offered above. With this, you can either make your own DOF focus chart on a piece of paper and carry it in the field or do the math in the field...or of course carry a DOF adj. guide...the chart is the most practical. The benefit of this approach is the exactness of accomplishing your desired enlargement. The drawback is, you need some way to find distances in the field. For example if your chart says focus at 200 ft., you need some way to determine how far away is 200 ft so you can pick an object and focus on it. A little pocket golf rangefinder works fine up to 2000 ft.

So there is many ways to skin a cat when it comes to this, you can choose what works best for you... Polaroids are great if you only want a 4x5 size print, it's a great cross check. But you can not tell from a positive polaroid how much enlargement potential it offers. As mentioned by a few posters above, polaroids with a negative will offer the benefit of knowing enlargement potential if you have a loupe with you... Best of luck!

[Glenn Kroeger]

Scott.. previous posts span the full range of circle of confusion COC tolerance... Brian's suggestion is about 10x the focus range, i.e. a focus range of 3mm gives about f/32. This assumes a very small COC. Alan's post suggests about 3x the focus range, i.e. a focus range of 2.8mm gives f/8. That will produce a pretty large COC. I have a chart, I think came from Linhof, that suggests a factor of about 5x for 4x5, and 8x for roll film sizes... so, I have been using a factor of 6x with good results.

Thus, for a 2.5mm focus range, I use f/16, for a 5mm focus range I use f/32... etc. I agree that a slight bias toward the front will assure a sharp infinity which seems important in subjective impressions of the image sharpness.

[John Hennessy]

The differences in rail extentions and corresponding f/stops suggested by Glenn Kroeger and Brian Ellis are very useful and realistic for decently sharp prints with any degree of enlargement. Brian Ellis's note says his numbers come from the Linhof chart and Bob Soloman offers the Rodenstock calculator. Actually Ellis's numbers have been (and should have been) sharpened somewhat over the Linhof chart and if you use the Rodenstock gadget, set the format to 6x9 when using 4x5. And Allan Fontanilla's suggestions will produce a circle of confusion the size of bagel.

You need to balance all this effort to get the right f/stop against the problem of defraction. If you're not satisfied until you get down to f/45 or f/64 then your image will be blurry due to difraction anyway. So back off and decide of tilts and/or swings will solve the focus problem with a smaller more reasonable f/stop. That's why we use view camera after all. If that doesn't work, back up and/or use a shorter lens and plan on enlarging more. If that doesn't work, plan on contact printing or think of the image as the one that got away!

[QT Luong]

If you want to understand some of the number which have been thrown in this thread, I insist that you read the article I mentioned previously. I spent a fair amount of time to make sure to get things right there.

Brian's method uses a CoC of 0.05mm. This will ensure a sharp 11x14 at minimum viewing distance. Allan's method uses a CoC of .17mm. This is appropriate only for a contact print. Glenn's method uses a CoC of .078, which is more in line with what I personally recommend. While those linear approaches are useful for determining whether a certain focus spread is acceptable, their drawback is that they doesn't take into account diffraction.

[Brian Ellis]

John is correct - the numbers I gave are stopped down one stop from the numbers on the Linhof chart, in part because it's so easy to remember them that way (1.6 mm difference = F 16, 2.2 mm difference = F 22, etc.) but more importantly because Linhof's numbers assume an enlargement to 8x10, whereas I often enlarge to 11x14.

[Jules Hancock]

Does using a 5x7 camera affect the depth of field calculator? Truley a beginner, so forgive me if this is obvious to everyone but me? Thanks.

[Scott Mittelsteadt]

Hey!! I just wanted to thank of all you who took the time to respond to my question. I got a lot of great advice, and I hope spend quite a bit of time seeing which methods work best for me. Its great to have this forum....and I can't tell you how much this novice appreciates having the wealth of information that you all provide...at my Internet fingertips.

Thank You!!