RB67 Pro SD - 65mm or 75 mm for 35mm equivalent on 35mm?

Hi folks,

Usual noob disclaimer here: maybe i'm getting stuff ass-backward, so be gentle!

I have a few 35mm lens shots that i did on my Nikon F2, and i now want to repeat these with my RB67 Pro SD (for higher resolution).

My conundrum is which lens to get for the RB, the 65mm or the 75mm?

From googling, it seems the 75mm is listed as 36mm equivalent, so in principle, that's closer to the Nikon 35mm lens.

But 6x7 is a different aspect ratio from 35mm film cameras.

So does that mean that if i go for the 75mm, i'll actually loose some width in my shot? Or will i gain more height?

Sorry if this makes no sense and looking forward to your reactions!

(PS - below is one of the pix i want to re-take, if this helps)

I use a simple method which compares the length of a 35mm frame (nominal 24mm x 36mm) with the length of the format you are comparing, in this case, 56mm x 68.4mm. That information comes from
Michael Butkus Jr.'s website.

The nominal aspect ratio of a standard 35mm frame is 3:2, or 1.5:1; for your RB, it would be 1.22:1. What I do is compare the focal length of the taking lens, namely 35mm, with the length of the frame, nominally 36mm. Divide 35 by 36, and multiply the product by the nominal length of RB format, 68.4mm, and my math says that it would be a focal length of 66.5mm. So, (35/36) x 68.4 = 66.5.

If you shoot with your RB and the 65mm lens, from exactly the same position, with the same angle, you should have slightly more field coverage than with the 35mm lens on your Nikon F2.

What this method does not do is to address the height difference of the two different formats; you will no doubt find, that with the above mentioned lens set, that you will have more coverage with the RB, top to bottom, than with the Nikon. Think of the greater top to bottom coverage as a bonus!

I have that issue when I am out scouting for images; I bring a Nikon F and a 55mm macro lens, as the only 4x5 lens I current own, that is actually functional, is a 191mm Wollensak; which using my method, calls for a 57.3mm lens on my Nikon.

The 90 mm on the 6x7 frame is almost exactly the diagonal, which would be equivalent to a 43 mm on the 35 mm frame. I treat the 90 as a "normal" even though the 127 got the most use on most of these cameras (because they were used in a studio environment shooting torso portraits or full body portrait equivalent). To emulate a 35 mm on the 35 mm frame, then, you'd want 7/8 of the "normal" focal length and 75 mm would be closest. I haven't seen a 75 for these cameras, though. A 150 with .45x filter would be the closest I can come with my kit...

Terrence Brennan said:

I use a simple method which compares the length of a 35mm frame (nominal 24mm x 36mm) with the length of the format you are comparing, in this case, 56mm x 68.4mm. That information comes from
Michael Butkus Jr.'s website.

The nominal aspect ratio of a standard 35mm frame is 3:2, or 1.5:1; for your RB, it would be 1.22:1. What I do is compare the focal length of the taking lens, namely 35mm, with the length of the frame, nominally 36mm. Divide 35 by 36, and multiply the product by the nominal length of RB format, 68.4mm, and my math says that it would be a focal length of 66.5mm. So, (35/36) x 68.4 = 66.5.

If you shoot with your RB and the 65mm lens, from exactly the same position, with the same angle, you should have slightly more field coverage than with the 35mm lens on your Nikon F2.

What this method does not do is to address the height difference of the two different formats; you will no doubt find, that with the above mentioned lens set, that you will have more coverage with the RB, top to bottom, than with the Nikon. Think of the greater top to bottom coverage as a bonus!

I have that issue when I am out scouting for images; I bring a Nikon F and a 55mm macro lens, as the only 4x5 lens I current own, that is actually functional, is a 191mm Wollensak; which using my method, calls for a 57.3mm lens on my Nikon.

Click to expand...

deleted reply, see below

Terrence Brennan said:

If you shoot with your RB and the 65mm lens, from exactly the same position, with the same angle, you should have slightly more field coverage than with the 35mm lens on your Nikon F2.

Click to expand...

Sorry, just to clarify: you mean in the width, right? Is so, them i will have quite a lot of excess in the height?

And with the 75mm, i won't cover the width (but probably the height will just be covered?

I would expect that a 65mm lens would give a greater field coverage than the 75mm lens on your RB, just as a 35mm lens on a Nikon F2 will have a greater field coverage than a 50mm lens.

Before you splash the cash for a lens, be sure about field coverage it exhibits; you can usually find info on angles of view from the manufacturers' websites.

Terrence Brennan said:

bout f

Click to expand...

Terrence Brennan said:

I would expect that a 65mm lens would give a greater field coverage than the 75mm lens on your RB, just as a 35mm lens on a Nikon F2 will have a greater field coverage than a 50mm lens.

Before you splash the cash for a lens, be sure about field coverage it exhibits; you can usually find info on angles of view from the manufacturers' websites.

Click to expand...

Of course, but what i'm asking is: which lens will be closest to replicating my shot which was done with a 35mm lens on a Nikon F2?

Two different focal length lenses on two different formats are equivalent at precisely one common subject distance (from the subject to first nodal point of the lens) and this happens if, and only if, both formats receive the same field of view from the plane of focus for finite subject distances or the same angle of view along corresponding format dimensions: length, width, or diagonal for any focusing distance, finite or infinity.

Strictly speaking, this only happens for two different formats of the SAME aspect ratio. For two formats of different aspect ratio the correspondence can only be established for one of these dimension pairs at a time. As the common subject distance varies, then so too must the focal length of the second lens vary for the equivalence to hold.

You might want to think about how we use a camera to make an image. Like most film camera owners, I use it to make a negative that I’ll enlarge to some standard print size, most often 8” x 10”, 11” x 14”, or 16” x 20”. An 8” x 10” or 16” x 20” print have aspect ratio 5:4 =1.25.

By first determining the largest aspect ratio you will ultimately print and calculating the largest rectangle of that aspect ratio contained within each of the two formats, you will get a more useful equivalence.

The largest 5:4 rectangle in the 24 mm x 36 mm format is 24 mm x 30 mm. The RB67 makes a negative of 56 mm x 69.5 mm. The largest 5:4 rectangle it contains is 55.6 mm x 69.5 mm.

Using the standard EFL (Equivalent Focal Length) equation [Note: this is given at infinity focus]

f2 = f1(n2/n1)

Where f1 = the original focal length, f2 = desired equivalent focal length, n1 = chosen dimension of the largest rectangle in the first format, and n2 = the corresponding dimension of the second format.

To find the EFL on the RB67 camera compared to a 35 mm lens on the 35 mm format, I’ll work with the minor dimension of each rectangle. Then

f2 = 35 mm(55.6 mm /24 mm) = 81 mm

The closest RB67 lens focal lengths are 75 mm and 90 mm.

If you chose to work with the major dimension of each rectangle,

f2 = 35 mm(69.5 mm /30 mm) = 81 mm

When used from the same subject distance, calculating the EFL in this manner is exact. Prints made by enlarging either of the given rectangles on film will have the same angle of view and see the same field horizontally, vertically, or diagonally.

Of course, the two different formats of different aspect ratio will record more or less than the other outside of the rectangular section as described. But, for enlarging at the same aspect ratio, this recipe gives an accurate equivalent focal length for the second format.

Great, it seems the 75mm is a good choice for what i want to do.

I already have the 50mm and that feels really wide, so i think the 65 would have still felt too wide.

Thanks for taking the time , just ordered the lens from Ebay Japan, fingers crossed!

FWIW, I use a 35mm most frequently on 135 film, and I found 65mm on the RB67 to "fit my eye" similarly.
When you are trying to make comparisons between different formats with different aspect ratios, there will be no focal length that gives entirely the same result.
If you are more "focused" on the long dimension of the frame, any calculations will give different results than if you are more "focussed" on the short dimension.
I tend to print to something close to a 4:5 aspect ratio. Which means I tend to use approximately 24mm x 30mm of the 135 frame

Why not just crop to your specs?

Arthurwg said:

Why not just crop to your specs?

Click to expand...

I want to make the most out of the 120 (and my scanner's) resolution in order to make a really big print, so i don't want to crop unnecessarily, i want to get the lens that best fits the 35mm field of view. Anyways, the 75mm is ordered, I'll post my results back here once i get the lens!

The 75 should be good. I don't have a 65 myself, so I'd probably shoot on 50 mm and crop. 120 has oodles of resolution, and my scanner will pull 80+ megapixels out of 6x7.

With your post #9 in mind, I would also mention that I had no trouble justifying a 50mm lens as well for the RB67 - it gives significantly different results from the 65mm.
This was taken using either the 50mm or the 65mm - probably the 65mm - and would have been different in the print or scan if the floating element ring was set in a significantly different position:

Here is a different way to think of the issue, that nullifies difference in the aspect ratios of different camera formats: Use the SHORT DIMENSION OF THE FRAME as the basis of Angle of View for a given lens FL

• 24mm lens on 24mm tall (1:1) 135 format is same Angle of View as 56mm lens on 56mm (1:1) tall 6x7 frame of the RB67.
• 48mm lens on 24mm tall (2:1) 135 format is same Angle of View as 112mm lens on 56mm (2:1) tall 6x7 frame of the RB67.
• 96mm lens on 24mm tall (4:1) 135 format is same Angle of View as 224mm lens on 56mm (4:1) tall 6x7 frame of the RB67.

Since you like 35mm FL (1.458x) on the 135 format camera, the 'same angle of view' would be offered by 81.67mm on the RB67, so choose the 76mm lens FL.
65mm FL on the RB67 would be similar to using 28mm FL on 135 format.
After all, if you shot portraits with the different formats and made 10"x8" or 20"x16" prints, you would be fitting the portrait sitter in the narrow direction of the image and cropping off the excess frame length of the neg in makin the final print!

For the same horizontal FOV, you'd need a 35*70/36=68mm lens and then crop to 3:2 to mimic the Nikon. You'll gain height.

For the same vertical FOV, you'd need a 35*56/24=82mm lens but you'll get a 4:5 crop of the Nikon picture. You'll loose width.

Dazzer123 said:

Of course, but what i'm asking is: which lens will be closest to replicating my shot which was done with a 35mm lens on a Nikon F2?

Click to expand...

Dazzer123 said:

I want to make the most out of the 120 (and my scanner's) resolution in order to make a really big print, so i don't want to crop unnecessarily, i want to get the lens that best fits the 35mm field of view. Anyways, the 75mm is ordered, I'll post my results back here once i get the lens!

Click to expand...

Hmmmm, since you've already ordered the 75, my opinion is a bit late. Hopefully, that lens gives you what you want.

I think the simplest answer, related to Terrence's reply in post #2 and his method, would be to use the 65mm--which is an excellent lens; I've never owned/used the 75, but I can vouch for the quality of the 65--and then crop the top and bottom. That way, you could have the identical 3:2 (1.5:1) ratio as your 35mm shot, and you'd get the *full width* of the 6x7 frame. You would only lose the part of the image that wasn't included in your original shot anyway, while getting the entire benefit of the 7cm (68.4mm, actually) width of the image.

So, with your Nikon F2, your image was 864mm squared, while with the RB67, cropping only the top and bottom of the landscape-oriented frame, you'd get 3120mm squared of image area, with the resulting greater number of pixels after scanning--and the perspective of the image should be practically exactly the same as that produced by the F2's 35mm lens.

65mm lens on the RB67 matches 35mm lens on the F2 on the width of the view - 54.5 degrees width when focused at infinity for both. Of course, you get more height with the RB67. 46.6 for the RB67 vs 37.8 degree height for the F2.
DOF angle etc