MattKing
Moderator
Maybe because it only works if the lenses used were made by the camera's manufacturer, and explicitly identified as working with the scale.
The idea about the ruler is good though.
Bellows Exposure calculation
-
A
- Thread starter smithdoor
- Start date
Recent Classifieds
-
For Sale PENTAX SPOTMATIC SPII
- Started by Peter Schrager
-
For Trade For Trade, Nikon D750 DSLR for Leica lllf
- Started by dankapsner
Forum statistics
Maybe because it only works if the lenses used were made by the camera's manufacturer, and explicitly identified as working with the scale.
The idea about the ruler is good though.
Thank you Matt for noting that the ruler idea is a good one, it's sort of seems obvious to me
But as far as the lenses are concerned yes each lens is different, but please correct me if I'm wrong because obviously I don't know as much about this stuff, but wouldn't all lenses have the same bellows distance? So correcting for it would be the same and would only depend on focal length? So you could easily have a scale that showed 65, 75, 90, 100, 127, 135, 150, 180, 210, 300, 350, 400, 500
It could be simply a little slide out that you pull out to measure and would have the chart right in the side just like the RZ/RB have?
If someone had an odd size, they could simply interpolate between the two different sizes and get relatively the correct compensation?
Or am I totally off base here?
MattKing
Moderator
Stone:
How would you deal with telephoto lens designs, or retro-focus lens designs?
The scale on the camera can only measure how far the lens board is from the film plane. The actual focal length of the lens is measured from the nodal point of the lens to the film plane (when focused at infinity) and with large format lenses, the distance between the nodal point and the lens board will vary with the design of the lens, its construction, and possibly the shutter used.
In many cases (telephotos, retro-focus design), the nodal point is actually effectively outside the physical body of the lens - it certainly isn't a consistent distance from the lens board.
How would you deal with telephoto lens designs, or retro-focus lens designs?
The scale on the camera can only measure how far the lens board is from the film plane. The actual focal length of the lens is measured from the nodal point of the lens to the film plane (when focused at infinity) and with large format lenses, the distance between the nodal point and the lens board will vary with the design of the lens, its construction, and possibly the shutter used.
In many cases (telephotos, retro-focus design), the nodal point is actually effectively outside the physical body of the lens - it certainly isn't a consistent distance from the lens board.
Well I guess I've been measuring wrong... In any case, it can't be too far off from that? Within an inch? I don't even know what retro-focus means...
MattKing
Moderator
For some telephoto lenses, the nodal point is a long way forward of the front element and way outside the body of the lens.
And retro-focus construction is most often used for wide angle lenses. In that case it results in the nodal point also being outside the lens itself, except in this case it is behind the rear element. - some times a considerable distance behind.
Unless you know where those nodal points are, you cannot measure the distance between them and the film plane, and therefore cannot use single measurements from a fixed plane to determine an exposure calculation.
That is when the various tools that involve measuring magnification (e.g. using a ruler in the field of view) are most useful.
And that is why you can't build a scale on the camera for this purpose.
EDIT: for certainty and clarity, I mention that a "telephoto" lens is not the same as a long lens - it is a lens that is shorter than its focal length.
A bit of random googling yields an example of the Nikkor 1200mm f/18 lens which is focused at infinity when the bellows it is mounted on is extended to just 755 mm - about 450 mm or 18 inches less than the focal length of the lens.
The lenses you are using may not be strongly telephoto, or strongly retro-focus, in which case the nodal points may all be near the middle of the lenses.
But in any event, a scale on the camera wouldn't work.
Last edited by a moderator:
Gotcha, okay that makes sense, but at least the ruler idea make sense still, however my question now is how the heck do I know what I have on my lenses that I own now, is there a marking point that I'm supposed to look for, I don't remember seeing any of those zeros with lines through them...
Stone: Why do you need a chart for the RZ67? Wouldn't the built in exposure meter read less light as the bellows expands and automatically compensate for the final exposure?
Alan, the exposure meter is in the mirror attachment, a piece that I don't use to shoot with, nor do I have anymore I sold mine because I never used it, it's too heavy and I like using the waist level finder better to take pictures with that camera. So it's of no help when exposing. That's why the pullout chart exists on the side.
But anyway I was referring to shooting with my 4 x 5, in terms of having to calculate exposure with bellows extension.
MattKing
Moderator
If your lenses are either telephotos or retro-focus designs, the "marking point" would be outside the body of the lens.
You need to use the other tools available for this purpose unless and until you determine where the nodal point is.
Wait I'm confused what other tools? The only tools available to me are my reciprocity timer, which asks me about the Bellas distance, however if the bells distance includes this extra space that is outside of the lens area, how can I tell where on the lens this point is? I don't see any special marking telling me where that point is like you do on a 35mm camera which has that zero with a line through it showing that that is where the film plane is, so how can I know?
That is a problem. Information like that is available but one must read and understand the specification data for the lens in question. Knowing if your lens is a telephoto design or not is essential to knowing this.
I highly doubt any of my lenses are telephoto's, even if I bought a "telephoto", it wouldn't be a real one per your specification that the link has to be longer than the extension or something like that.
I own a 75mm f/4.5 grandagon, a 90mm f/9 Schneider super angulon and a 150mm f/5.6 Schneider super angulon, and I plan to purchase a fujinon 300mm f/8.5 C lens to complete my "kit" but the 300 is a compact lens so I don't think that qualifies as a telefoto in your new-to-me definition.
None of those are telephoto lenses. Measuring from the lensboard has always worked out well for me, as for the filmplane it's where the groundglass is.
None of those are telephoto lenses. Measuring from the lensboard has always worked out well for me, as for the filmplane it's where the groundglass is.
Yes I know where the film plane is
And ok, good enough for me! Lens board to film plane it is!
And... Look what I just discovered on my camera!
However it only seems to be accurate when the rear extension is not extended, and the front extension focusing knobs are not extended either, so I guess it's useful in certain certain circumstances but it's poorly placed, it's also not accurate to the actual distance, but rather to where you can view the distance, what I mean by that is obviously as you can see there is a piece of plaster sticking out from further than the actual lens board area, so that number seems to correspond with the actual lens for distance from the film plane, not the actual physical distance from the number markings to the film plane.
Either way it's handy to have in a pinch, so long as you realize that it doesn't account for the front and rear extensions.
It's also poorly placed, it could've added some kind of track system on the side that would've made a lot more sense, but at least it's a start!
However it only seems to be accurate when the rear extension is not extended, and the front extension focusing knobs are not extended either, so I guess it's useful in certain certain circumstances but it's poorly placed, it's also not accurate to the actual distance, but rather to where you can view the distance, what I mean by that is obviously as you can see there is a piece of plaster sticking out from further than the actual lens board area, so that number seems to correspond with the actual lens for distance from the film plane, not the actual physical distance from the number markings to the film plane.
Either way it's handy to have in a pinch, so long as you realize that it doesn't account for the front and rear extensions.
It's also poorly placed, it could've added some kind of track system on the side that would've made a lot more sense, but at least it's a start!
Look on the side, or maybe even on both sides. Isn't there a blank scale that you can mark?
Yes, I was going to mark infinity spots for my lenses for night work (so I don't have to show up 3 hours before when there's still light to focus
MattKing
Moderator
By "other tools" I mean those tricks one can use with either a ruler or other standard item that you include in the scene, and then read the exposure adjustment off of the image on the ground glass.
Or you could use that fancy math you are trying to avoid
By "other tools" I mean those tricks one can use with either a ruler or other standard item that you include in the scene, and then read the exposure adjustment off of the image on the ground glass.
Or you could use that fancy math you are trying to avoid
Believe it or not I'm actually still confused, I don't understand what helps me about putting the ruler into the scene, I'm just not following, also I wouldn't think that reading a spot meter on the back of the groundglass would give me an accurate reading because the light is already diminished?
Just really not following you there
Also in a secondary "duh" moment, I was looking at my own picture of the 4 x 5, and I noticed that the scale read 100, 200 150, but the 200 was in orange, I've now realized that the 200 is the marking for when the rear part of the camera is extended. I guess the engineers at Toyo figured some things out even if I'm too blind to notice them
MattKing
Moderator
Stone:
You put a standard item into your scene, at the distance you are focusing to.
Then you measure the image of the item on your ground glass using a scale that allows you to read the correction factor directly.
Try this link for an example: http://www.southbristolviews.com/pics/Graphic/CloseUpCalc.html
and in particular the tool linked thereon (including instructions!): http://www.southbristolviews.com/pics/Graphic/SBVCALC.pdf
In case you are wondering, this sort of tool works because you can reduce all the exposure adjustment calculations into formulas that depend on image magnification (instead of focal length and bellows extension).
You put a standard item into your scene, at the distance you are focusing to.
Then you measure the image of the item on your ground glass using a scale that allows you to read the correction factor directly.
Try this link for an example: http://www.southbristolviews.com/pics/Graphic/CloseUpCalc.html
and in particular the tool linked thereon (including instructions!): http://www.southbristolviews.com/pics/Graphic/SBVCALC.pdf
In case you are wondering, this sort of tool works because you can reduce all the exposure adjustment calculations into formulas that depend on image magnification (instead of focal length and bellows extension).
Andrew O'Neill
Moderator
I just use a small tape to measure the bellows and then do a bit of math. I used to have one of those gizmos that Calumet put out, but I lost it. I liked it until I forgot to remove the target from the shot and had a big surprise when I got home!
Post #15 and 22. I followed my own advise. Printing and gluing to a file card took about 1.78 minutes. Add another 5 for the Elmer's to dry. Send me your mailing address and it is yours. That plus about 3 minutes of playing with it will clarify everything in your mind.
Post #15 and 22. I followed my own advise. Printing and gluing to a file card took about 1.78 minutes. Add another 5 for the Elmer's to dry. Send me your mailing address and it is yours. That plus about 3 minutes of playing with it will clarify everything in your mind.
Haha bribing me to shut up basically! Haha ok well played sir
No, I enjoy your conversation... until it gets repetitive. I promise you... try that "chip in the scene and measure the exposure adjustment with the ruler" technique and your next post will be, "I GET IT!"
| Photrio.com contains affiliate links to products. We may receive a commission for purchases made through these links. To read our full affiliate disclosure statement please click Here. |
PHOTRIO PARTNERS EQUALLY FUNDING OUR COMMUNITY:  |