LF lens f stop opening equivalent in 35mm lens

[Corran]

I believe apparent DOF between 35mm and 4x5 is 4 stops not 2. e.g. f/16 on 4x5 mm has similiar DOF to f/4 on 35mm

No, it's different by 2 stops or 1/4th - there's the factor of 4 that you are thinking of. That's a rough approximation though since 4x5 has a different aspect ratio of course.

Rick already explained it above. A 135mm lens at f/8 has the same DOF regardless of format but on 4x5 (assuming it covers 4x5) it shows a much wider field of view. Therefore one would use different lenses to acquire the same FOV in different formats - in other words a ~35mm lens on 35mm film would be about the same as that 135mm on 4x5, and would only need to be stopped to ~f/4 to get the equivalent DOF rather than f/8.

[EdSawyer]

Rick's explanation (which is a good way of visualizing it) shows a 4-stop difference. (f/2 to f/8)

[Corran]

You and Rick are right, apparently my head is not in the right place today! I've done these calculations a million times but switched one of my factors this time, whoops. My apologies. I should get back to packing my house now rather than trying to math

[Bruce Watson]

...is there any change in the f stop from the LF lens to the 36mm lens to get the equivalent light to the film?

No. That's the basic concept of an f-stop. Unfortunately for your 35mm thinking, you may find that there is little overlap between the range of f-stops available. IOW, your 35mm lens may give you a range of f/1.4 - 16, while your LF lens may give you a range of f/11 - 64.

My advice is to give up the 35mm thinking. It'll only slow down your learning of LF. And it can be costly, in that if you buy the "equivalent" lens focal lengths for LF that you used in 35mm, you find yourself selling them and buying again lenses that you actually use in LF. For example, when I was a photojournalist using Nikons, I would never have been caught dead with a "normal" lens. Yet in 5x4 work, my 150mm lens is one of my most used lenses. Because LF is a very different animal than 35mm is. Just sayin'.

[Colin D]

Ok, I'll take it that there is a 4 stop difference b/w the formats. So when using the 35mm lens at f11, that is equivalent to f32, in 4X5.

[Vaughn]

Ok, I'll take it that there is a 4 stop difference b/w the formats. So when using the 35mm lens at f11, that is equivalent to f32, in 4X5.

Whoa! That was a jump from exposure to DoF! Don't worry about it. Set up the 4x5 focus on a bunch of different scenes, close down the aperature while looking on the GG and see the DoF increase in size. Shift the focus a little and do it again -- see how near and far come into focus, the far quicker than the near, etc. What you see is what you get -- have fun!

vaughn

[rdenney]

Ok, I'll take it that there is a 4 stop difference b/w the formats. So when using the 35mm lens at f11, that is equivalent to f32, in 4X5.

If you want the same exposure, use the same F number.

If you want the same depth of field (when using a lens that covers the same field), use an F number four stops more closed down. That results in a different exposure, so you will need to compensate with a longer shutter speed.

Rick "simplifying" Denney

[EdSawyer]

hey, no worries, it's all good. I have to think about it every time too. ;-) Good luck with the packing!

You and Rick are right, apparently my head is not in the right place today! I've done these calculations a million times but switched one of my factors this time, whoops. My apologies. I should get back to packing my house now rather than trying to math

[drew.saunders]

It looks like the Zeiss DOF and Bokeh article is no longer on the Zeiss web page, but Digiloyd has a copy: http://diglloyd.com/articles/ZeissPD...ield-Bokeh.pdf

In this article, all formats are "corrected" to a 3:4 ratio to clean up some of the mess of "focal length equivalents" when the ratios are quite different (such as the 2:3 vs 4:5). 4x5" and 9x12cm get merged into 90x120mm. See page 10 for the big chart with multipliers to get which aperture will get the same DoF on different formats. Being that this was done by a real engineer, actual circle of confusion numbers were used that are appropriate for each format, instead of just multiplying the f-number by the focal length "crop factor." That's a long way of saying that to compare 35mm to 4x5, you can use 4x the f-number to get the same DoF, as others have previously said, but when both are cropped to 3:4 ratio, the diagonal is 40mm vs 150mm, so you'd use 3.75 for the "crop factor" multiplier, so your 120mm on 4x5 is equivalent to a 32mm on 24x36, if you crop them both to 3:4.

[Colin D]

Whoa! That was a jump from exposure to DoF! Don't worry about it. Set up the 4x5 focus on a bunch of different scenes, close down the aperature while looking on the GG and see the DoF increase in size. Shift the focus a little and do it again -- see how near and far come into focus, the far quicker than the near, etc. What you see is what you get -- have fun!

vaughn

I'm going to be shooting indoors, portraits and still life mostly, the dof is quite shallow with the background. I can suck and see with the 35mm equivalent lens as it will be on a digibox and I have a fair idea of how my LF lens will perform, shouldn't be able to work it out.