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View Full Version : Whole Plate Image Circle and Lens Focal Length Equivalents to 35mm?

audioexcels
2-Aug-2007, 14:26
I will leave this one to the techies as I'd love to know first, the minimum IC for 6.5X8.5 and also what an equivalent lens to 35mm of say, 115-120mm would be on the format? Is there a way I can calculate a rough estimate of any lens length for 6.5X8.5that would be the equivalent to a lens put on a 35mm camera?

Thanks all!

Jason Greenberg Motamedi
2-Aug-2007, 14:39
Standard lens (and thus minimum IC) is about 260mm. For 35mm equivalent divide (or multiply) by 6.2.

Ole Tjugen
2-Aug-2007, 14:45
Do the maths: SQRT(6.5^2 + 8.5^2) = about 10.5 inches, or 260mm.

Do you want the equivalents based on short side, long side or diagonal?

Short side - 35mm is a little less than 1 in, 6.5 a little less than 6.5 in (image area): Multiply by 6.5.

Long side - 1.5 to 8.5 in - multiply by a little less than 6.

In other words there are no exact equivalents - it all depends on what you want. Other film sizes are worse, except maybe 5x7".

For whole plate, "six-ish" is a good factor.

audioexcels
2-Aug-2007, 15:00
So basically the Grandagon 115mm is roughly 19mm or so equivalent? Is this right? Seems VERY WIDE:):):) I know people have noted a 120 on an 8X10 as being the equivalent of 18mm, but this wouldn't be right if the 115mm and even 120mm are right around 19-20mm on Whole Plate.

Thanks for the quick and excellent responses.

One more good one...what would 4X10's image circle (minimum) be and what multiplier/dividing number on it for the equivalent to 35mm?

It's no wonder why people have these larger "telephoto" lenses that are really not telephoto at all when on a larger format. Thinking of something like a 300-450mm lens on 8X10 and it seems like it's basically a "normal"...

Nick_3536
2-Aug-2007, 15:05
4x10 has a normal of 270mm. But the difference in format shapes makes comparing hard.

For full plate instead of looking at 35mm look at something like 6x7. Or maybe Fuji's 6x8 camera. 35mm is a much better match in shape for 5x7 then any of the squarer formats.

BTW 300-360mm is considered normal for 8x10.

Paul Droluk
2-Aug-2007, 15:17
Funny, I just recently finished a focal length interchange chart for 35mm vs. Whole Plate, which shows equivelant FL's in both the horizontal and vertical axis. You can find it here... http://www.fotomancamera.com/technical.asp

audioexcels
4-Aug-2007, 11:03
Funny, I just recently finished a focal length interchange chart for 35mm vs. Whole Plate, which shows equivelant FL's in both the horizontal and vertical axis. You can find it here... http://www.fotomancamera.com/technical.asp

Does this perfect coincidence of a post mean I get some free whole plate holders to test out...and give a review for them???:):):)

Thanks a lot Paul. I printed out every chart. It gives me the idea of what backs I want to have on the camera and what lenses I will end up with.

Thanks also to everyone that has posted. I'm going to use these figures as well though Paul's charts are awefully convenient than me calculating things:D

audioexcels
22-Dec-2007, 00:08
Do the maths: SQRT(6.5^2 + 8.5^2) = about 10.5 inches, or 260mm.

Do you want the equivalents based on short side, long side or diagonal?

Short side - 35mm is a little less than 1 in, 6.5 a little less than 6.5 in (image area): Multiply by 6.5.

Long side - 1.5 to 8.5 in - multiply by a little less than 6.

In other words there are no exact equivalents - it all depends on what you want. Other film sizes are worse, except maybe 5x7".

For whole plate, "six-ish" is a good factor.

Ole,

I was doing your square root calculation to determine IC per 6.5X8.5, but I come up with a lower number. Square root of 8.5, for example, is 2.9. For 6.5 is 2.55.

Trying to figure out what I am doing wrong.

Ole Tjugen
22-Dec-2007, 06:07
It's SQRT((6.5 x 6.5) + (8.5 x 8.5)).

You have to work it from the inside out - do the multiplications, add the results, and take the square root of the sum.
There's no square root of 8.5 anywhere there. :)

audioexcels
22-Dec-2007, 10:30
It's SQRT((6.5 x 6.5) + (8.5 x 8.5)).

You have to work it from the inside out - do the multiplications, add the results, and take the square root of the sum.
There's no square root of 8.5 anywhere there. :)

LOL...;)

You know I keep wondering about going something like 5.5X8.5 as weird of a format as that sounds and so I'm trying to gather numbers here. I want to maintain the nice 5X7ratio, but gain a little more film resolution for digital processing.

I raised this with Sandy because I know he shoots pretty much exclusively 5X7, but I had a peculiarity with how well 5X7 stacks up to a larger size (why I have considered for so long whole plate aside from being able to contact a slight larger size). I also considered 8X10 for a while, but with the Arca system, I don't see a point because I would want to make a primary size, and if anything, I'd have 8X10 or even larger=maybe 5X12 or even 7X17;):) for my panoramic work. I want my primary to handle the Schneider 72XL which covers 5X7 well, but can be made to cover a little larger format and so I'm trying to see what format would be best suited for my work and that it could be well possible that I do stick to 5X7.

I ask this question about resolution because until I can get a higher end digital scanner, I'm limited in that area and need the larger film on the flatbed to maximize my final sized print potential.

Primary work is color, but b/w is a dominant commodity because I love it as well...and it is a lot cheaper unless you go the aerial route for your color film.

Too much congestion here, but basically...my thinking is like this:

5X7 if I can make equally good looking prints in both b/w and color vs. the much larger 8X10 and even whole plate. Would use a 4X5 reduction back that is super light so I can use up a ton of 4X5 waiting for me in the freezer, and just because it is so cheap compared to 5X7...though strange ratios of 5.5X8.5 or even 6X8.5 are appealing also due to the extra surface area.

And then something panoramic like a 7X17 or even 6X15.5 (More funky ratios).

Thanks and I'll now re-adjust my calculations to get the ic required for each format.

audioexcels
22-Dec-2007, 10:52
It's SQRT((6.5 x 6.5) + (8.5 x 8.5)).

You have to work it from the inside out - do the multiplications, add the results, and take the square root of the sum.
There's no square root of 8.5 anywhere there. :)

Hey now...I got 10.7...where are you getting 10.5...close enough says online calcuations.

For 10X8 I get 12.8=325mm=12.5mm's more than the LF forum's measured area, though I have seen this 325mm number out on websites, so maybe I and others are missing something here...LF forum says 312.5=12.5 difference

8.5X6.5=271mm or so=basically the same deal as the above..about a 11mm difference than what others have been posting for WP (260mm).

Here's 13cmX18cm: 218mm=9mm's off LF Forum's 208.7 figure.

Now lastly 9cmX12cm: 162.5mm...LF forum says 153.7mm...again, 9mm's off.

Maybe I need to just subtract 9-11mm's for every conversion I've been doing, with more mm's off the larger I go;):)

Any idea what I am doing wrong here? Are the online calcuators incorrect?:)

Ole Tjugen
22-Dec-2007, 10:56
The difference is in the part of the film edge covered by the holder - and the difference between npominal sizes like 13x18cm and the real standard size of the film, which is always a few mm smaller so that it would fit a film sheath in a plate camera!

Subtract 3mm from each measurement and you get the real film size, subtract another 4mm and you get close to image size.

audioexcels
22-Dec-2007, 11:19
The difference is in the part of the film edge covered by the holder - and the difference between npominal sizes like 13x18cm and the real standard size of the film, which is always a few mm smaller so that it would fit a film sheath in a plate camera!

Subtract 3mm from each measurement and you get the real film size, subtract another 4mm and you get close to image size.

Perfect...I think I will take the time to do correct calculations, but for now, I will go with my 9-11mm's off thing;)...seems to be a decent mean/average for the size I am looking to shoot anyhow.

Crazy how much more surface area the WP has. Gotta definitely look at 5.5X8.5...I think that would be a neat format...and still let me use the 72XL:)

About 246mm for the 5.5X8.5 format...72XL borderlines it:)!

Try 5X8 now=230mm's or so..not too shabby for the 72XL to handle...along with a 90mm...would be quite a nice little kit for handling wide shots and even being able to use some other lenses that wouldn't cost much for the format...hmmmm...

BTW...I dunno how the person shot this lens on 4X10 with relatively good success. I did read where someone said actual measured IC they were getting from the lens was 250mm...which is still a far cry from the 20 more mm's of IC needed for 4X10.