I am using the Nikor 800 and 1200 mm tele lenses. These are the first teles I e ver owned and therefore am not aware of how exposure compensation is calculated. I don't beleive the normal exposure compensation formula works for teles? Doe s anyone have an exposure compensation formula that works for telephotos? I pla n to work at far distances, so exposure discs will not work. Thank you in adva nce.
Bill,
I have a Fuji 600 mm tele, and do not do any exposure compensation for distant subjects. Are you refering to compositions in which the bellows extension increases more than several cm beyond the extension required for focus at infinity?
Bruce
Yes Bruce, when focussing on something a bit closer than infintiy I was wondering how to calc. the amount of exp. compensation.
Bill, What you are concerned about is something called exit pupil factor. You can actually see some difference in the apparent size of a given aperture by sighting through the lens first from the front, then the rear. Every tele has a different EPF, but you'll be relieved to know that it only comes into play in any appreciable way, when the object size on the gg is greater than 1/10th the actual object size. What this means is that in landscape work, where, with lenses that long you are usually quite some distance from the subject, it won't typically be a problem.
Bill ; I am sure that Robert is correct, but your question interested me in case you were going to use these lenses for macro work.
The basic principle with any lense used for macro work is that to get 1:1 magnification, both the subject and the groundglass need to be at twice the focal length of the lense being used. Easy to apply with a normally designed lense, but less obvious with a telephoto design where the front nodal point is in front of the lense, thus permitting a smaller flange focal length / bellows draw.
Looking at my Nikkor LF lense catalogue - the flange focal length of the Nikkor 1200mm f/18 is 755.7mm. Hence, if you want to get 1:1, the bellows draw would be 1511.4mm (2 x 755.7mm), and the subject would be 3288.6mm from the lense (2 x (1200-755.7) + 2400).
I think that the exposure compensation would then be 2 stops, following a normal calculation. Anyway, I hope this isn't a digression from the intent of your original question.
Finnegan,
Would it be inconvenient for you to either post or email me the specs on the Nikkor-T lenses? I keep an extensive spreadsheet on all lenses, and am missing most of the vitals for the 500 thru 1200 lenses. I am looking for: image circle wide open, flange focus distance in mm, weight in gm, and length in mm. I have the other info.
Finnegan, are you saying that all lenses that have bellows draw at 2x lenght vs infinity are producing 1:1 on the gg? IF so that is very interesting.
So I guess the same basic principle applies here, double bellows draw vs. infintiy - yields 2 stops exp. compensation, just like any non tele lens, right? Thank you all for your input.
Bill ; 1:1 is produced when the distance from the lense of both<i/> the subject <i>and the groundglass are at a distance that is twice the focal length of the lense. This won't apply when the subject is at some distance from the lense, not least because your subject would not then be in focus. For most distance work, I think that Mr Zeichner's comments will apply.
I forget to add to my earlier post - the calculation example is similar to what I use when I use my Fuji 400T for close up photographs. I think that the calculation is correct, but if it is technically wrong, I would like someone to point out to me where any error may be. Cheers
Bill ; I have a question for you. For each exposure, are you then measuring the bellows draw, and if the draw > lense focal length, are you then calculating an exposure factor? So far I have only applied such exposure compensation when doing close up photographs.
FW.... I have not attempted it yet, that is why I made the post, I got stumped :-) My goal was to know either how to calc. the following two items... first, if a subject is 150 ft. away, how much exposure compensation do I need. Or, if the bellows is racked out to 1000mm, how much exposure compensation would I need. Either of these would solve the exposure compensation dilimna.
On my non tele lenses, I have listings for each lens for focus distance / exp. comp., and bellows draw / exp. comp. This way I know for each lens, what is the closest subject I can focus on with the amount of bellows or rails I have with me... I would like to do the same with these teles... I find it much easier to compensate for bellows extension by knowing the subject distance vs. measuring the bellows draw. I just grab my laser range finder, and in 1 second I know the submect distance in feet, then I look at my trusty charts and apply the proper exp. compensation. Now, how do I do that for the teles? I never saw formulas in view camera books for this?
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