Are RF's "Faster" than SLR's?

[mtbbrian]

I was out photographing last night, for the first time, with my V-Lander R2A and 35 f/2.5 lens and Tri-X pushed to 1600.
It seemed to me that the shutter speeds I was able to use were faster than what I remember using with an SLR and similar lens.

So my question is, are RFs because of their design "faster" than SLR's?
Brian

 

[remrf]

The viewing and focusing sustem of the camera have nothing to do with it. The speeds used are a reflection of the asa or speed of the film and the aperture of the lens when used. If the metering of a scene is different between an slr and an rf camera using the same speed film and the same f-stop then one of the other meter is out of whack.

 

[mtbbrian]

The shutter speeds were only a stop or so faster, nothing too unusual.
Brian

 

[alexz]

Given all similar circumstances, I would come up with following idea:
the light path through the lens to the film plane may be considerably longer in SLR (due to SLR fundamental design) then in RF, therefore in SLR it may be needed to compensate for added light energy loss comparative to RF light path length.
Physics states inverse square law of radiated energy (be it photonic one (light) or other kinds of radiated energy). Light energy weakens proprotionally to the squared distance.
Thus, given in both cases (in SLR and RF) the metering happens at the film plane, since in SLR the light has to pass a longer distance to the film plane, consequently the metering cell in SLR will collect less light energy then in RF, thereby suggesting "slower" exposure to compensate for this effect.

At the bottom line, it sounds to serve RF shooters to their benefit offering easier exposure then would be with SLR in similar situation.

Of course, all said is IMHO.

 

[erikhaugsby]

SLRs have mirror vibration. RFs have no mirror.

Aside from differences in film speeds or apertures, this is the only thing that changes the range of "usable" shutter speeds.

 

[wolves3012]

Given all similar circumstances, I would come up with following idea:
the light path through the lens to the film plane may be considerably longer in SLR (due to SLR fundamental design) then in RF, therefore in SLR it may be needed to compensate for added light energy loss comparative to RF light path length.
Physics states inverse square law of radiated energy (be it photonic one (light) or other kinds of radiated energy). Light energy weakens proprotionally to the squared distance.
Thus, given in both cases (in SLR and RF) the metering happens at the film plane, since in SLR the light has to pass a longer distance to the film plane, consequently the metering cell in SLR will collect less light energy then in RF, thereby suggesting "slower" exposure to compensate for this effect.

At the bottom line, it sounds to serve RF shooters to their benefit offering easier exposure then would be with SLR in similar situation.

Of course, all said is IMHO.

The inverse-square law applies to light from a point source, sorry to disappoint you. The focussed image from a rangefinder lens or SLR lens only suffers from atmospheric scattering in the path between the lens and film, so the difference would be utterly insignificant. There is absolutely no advantage from a rangefinder with respect to the original suggestion. In terms of lens designs, mirror vibration etc there obviously are differences which may of may not be significant.

Unless someone knows better...

 

[alexz]

No dissapointment at all, always glad to learn.
Can't argue regarding point source just because I do not remember the physical definition exactly, perhaps need some brushing up to refresh the knowledge...
Athmospheric scattering sounds fair, though not someting major in the scope of teh asked question.
BTW, why the aforementioned law doesn't apply to anything but point source ?
Also, talking about focusing on distant object - wouldn't we be able to approximate the effect by inverse-square law ? (sufficiently distant objects may be approximated as point source)..

THinking again, I seem having troubles to realize why the light energy wouldn't fall proportionally to the distance (or some distance function), perhaps not exactly as squared distance, but nevertheless... ?
Having somewhat longer light path througfh SLR lens to the film plane, wouldn't we expect light energy (or power) at the film plane to be lesser then in the case of RF where that distance is shorter ?

Thanks, Alex

 

[Sylvaticus]

What generation of camera or metering system are we talking about?

A handheld meter will surely not have any idea of which camera you you intend to shoot with. There are times when the exposure might be increased by some factor for an SLR according to tables, such as macro situations. But that's a special case that can't usually be reproduced on a rangefinder camera, and if it could you would presumably need the same factor.

If you have a handheld meter for a rangefinder camera and TTL metering for an SLR, you might see a difference. Two different meters might give different readings anyway. The TTL reading is for the light actually coming in, whereas the handheld meter reading is for light you think might be coming in. The TTL reading might be taken just an instant before exposure, whereas the handheld reading is taken a minute or so before, and light conditions might change in the interval (I've seen it happen, when taking a reading before composing and then seeing what actually gets set when the picture is taken). There are various methods for TTL metering, and, depending on how recent the SLR is, readings might be taken from different areas of the image field and with different weightings between them. All of which might theoretically lead to different exposure settings between different cameras.

And if the rangefinder camera also has TTL metering, there might be different readings for the same reason between different manufactures or metering models.

On the other hand, other things being the same, the differences (between TTL methods at least) ought to be random around the ideal exposure that any meter is trying to find. With varying success.

I thin I'll get off the bus here before I get too dizzy.

 

[BrianShaw]

Unless someone knows better...

It has been a while since my high school physics course, but I think you got it right.

Alex, your'e thinking too hard today. Perhaps there is a very minute theoretical difference in the length of light path between SLR and RF cameras, but if any affect that might have on light level reaching the film is measurable, it is of negligible consequence. There's a reason why most cameras are adjustable only in 1/3 stop differences... anything more "accurate" doesn't make a difference because of film latitude, processing/calibration differences, etc.

 

[BrianShaw]

I think I'll get off the bus here before I get too dizzy.

Even though this isn't my stop, I'll get off too! 😀

 

[wolves3012]

No dissapointment at all, always glad to learn.
Can't argue regarding point source just because I do not remember the physical definition exactly, perhaps need some brushing up to refresh the knowledge...
Athmospheric scattering sounds fair, though not someting major in the scope of teh asked question.
BTW, why the aforementioned law doesn't apply to anything but point source ?
Also, talking about focusing on distant object - wouldn't we be able to approximate the effect by inverse-square law ? (sufficiently distant objects may be approximated as point source)..

THinking again, I seem having troubles to realize why the light energy wouldn't fall proportionally to the distance (or some distance function), perhaps not exactly as squared distance, but nevertheless... ?
Having somewhat longer light path througfh SLR lens to the film plane, wouldn't we expect light energy (or power) at the film plane to be lesser then in the case of RF where that distance is shorter ?

Thanks, Alex

Why the inverse-square law? Simple explanation: Imagine a point source of light. The light leaves it in all directions but consider a given distance, say one metre, against two metres. The surface area that the light covers at 2 metres is diminished by 2 squared since it covers any area 2 times wider and 2 times higher, i.e 2x2=4 times (ok, this is a SIMPLE explanation, it actually relates to the surface area of a portion of a sphere).

Actually, there is another confusion for you. Someone can tell me if I'm wrong here but I seem to recall that the optical distance of a lens from the film isn't the same as the physical distance. For a 50mm lens the optical rear lens node is 50mm from the film, whatever camera and lens type. This would mean that SLR and rangefinder are identical.

The (slightly) longer light path in an SLR is side-tracking you; the light is being brought to focus on a given area (the film frame) and has been collected from a given area of the lens. If nothing else changes, then the length of the path is irrelevant (as I said before, scattering etc could make a minute difference). The light isn't diverging like a point source.

Incidentally, the inverse square law only applies to non-coherent light. Lasers produce coherent light and there is no loss of intensity with distance (ignoring scattering, which IS significant in air over large distances).

 

[clintock]

Maybe the slr you were comparing to had one of those semi-reflective mirrors that stay in place during the exposure. I think those cost a half stop or something close to that.
Canon made some of those, I forget what models.

 

[remrf]

The distance the light has to travel has no bearing on the issue because the manufacturer would take this into consideration when calibrating the light meter whether the camera in question was an slr or and rf. If not the meter in the camera would be worthless. The asa rating of the film would have little meaning otherwise.

Also ...a difference of a stop or two is very significant to me. I check my internal meters againts my Gossen Luna star F. If they differ then the one in the camera is the one that needs checking. The only internal meter I own that does not agree exactly is in my Yashica GS which has the replacement battery of a lower voltage. The internal meters in my X700's and my Maxxum 7000 are spot on.

How do I know my Gossen is right? Because it was checked againts a friends brand new Gossen Digi six when I got it and they agreed exactly for a given situation. Both in incident and reflected.

 

[tetrisattack]

Actually, there is another confusion for you. Someone can tell me if I'm wrong here but I seem to recall that the optical distance of a lens from the film isn't the same as the physical distance. For a 50mm lens the optical rear lens node is 50mm from the film, whatever camera and lens type. This would mean that SLR and rangefinder are identical.

An ordinary 150mm lens is focused at infinity when the distance between the lens's optical center and the recording plane is 150mm.

A 150mm lens designed as a telephoto would give the same angle of view, but when focussed at infinity, the optical center of the lens would be closer to the recording plane than 150mm. This is an advantage for long lenses, especially for view cameras.

"Retrofocus" is the inverse of a telephoto design, where the optical center is further out than the focal length of the lens. This is the only possible way, for example, to get a 15mm lens on an SLR with a film-to-flange distance greater than 15mm. This is why rangefinders typically have better wideangle lenses; not having to account for the mirror clearance of an SLR simplifies lens design.

 

[alexz]

Why the inverse-square law? Simple explanation: Imagine a point source of light. The light leaves it in all directions but consider a given distance, say one metre, against two metres. The surface area that the light covers at 2 metres is diminished by 2 squared since it covers any area 2 times wider and 2 times higher, i.e 2x2=4 times (ok, this is a SIMPLE explanation, it actually relates to the surface area of a portion of a sphere).

Actually, there is another confusion for you. Someone can tell me if I'm wrong here but I seem to recall that the optical distance of a lens from the film isn't the same as the physical distance. For a 50mm lens the optical rear lens node is 50mm from the film, whatever camera and lens type. This would mean that SLR and rangefinder are identical.

The (slightly) longer light path in an SLR is side-tracking you; the light is being brought to focus on a given area (the film frame) and has been collected from a given area of the lens. If nothing else changes, then the length of the path is irrelevant (as I said before, scattering etc could make a minute difference). The light isn't diverging like a point source.

Incidentally, the inverse square law only applies to non-coherent light. Lasers produce coherent light and there is no loss of intensity with distance (ignoring scattering, which IS significant in air over large distances).

Thanks, but I wasn't questioning the inverse-square law itself, it is obvious.
I would imagine that in simple terms as the point sourse radiating light energy (like any other electro-magnetic radiation), it gets spread as spherical surface and the energy/power of these can be related to that surface area. As the raditaion travels farther away from the source, the sphare (radiation front or wave front) becomes larger in diameter thereby increasing the surface area, so that the farther away the light travels - the larger will be its sperical front area (to keep the things simple we aren't talking about athmospheric distortions of the wave front shape).
However, we shall remember that the source emmits constant power which gets spread over the spherical wave front (or something like that).
I.e. it we take a single point on top of the spherical wave front and measure radiated power of one at two distance X1 and X2 from the light source, when
X1 < X2, the point energy of X1 must be greater then that of X2 - that is to keep the source energy as a constant (which we assumed initially).
Perhaps I'm haveing troubles making clear my point, but in simple words it probably can be extrapolated to instanteous electrical power or active element (resistance for instance) or better, the power drawn by active load from the electrical source : Psource = Vout*Iout. As load gets increased (less resistance) - Iout that is drawn from the source gets larger. However, the source has been designed to supply a limited output power, so that to keep that natural law - as Iout increases, Vout of the source decreases proprotionally (we do not take into account any non-linear effects) in which way Pout (max) remains constant.

Well, I guess I got too carried away ...🙂, perhaps this discussion gets way off the topic, if so I would be better to shut up and just listen to more photo-skilled fellows here to get back on the RF track....
I tend to agree that the dlight path distance diffeernces between SLR and RF are not significant enuogh to be "eaten up" by third stops...

 

[kaiyen]

Since I'm too sick to even think about physics and whatnot...I think you're dealing with metering patterns and designs, period. A full stop difference cannot be accounted for with the difference between lens designs because of the mirror in an SLR.

allan

 

[LOOP]

Best use of light with RF ?

Best use of light with RF ?

Don't you think taht the main difference betwwen SLR and RF is that most SLR are heavier than RF.So it gives with RF the opportunity in some situations to use 1/15 S so closing the lens more and then using the lens at the best of its ability.
Another great +point for RF is that you can come closer to the subject with better lens than with big SLR + zoom.
These points are more important than the distance light has to do in SLR vs RF...
🙄

 

[alexz]

Don't you think taht the main difference betwwen SLR and RF is that most SLR are heavier than RF.So it gives with RF the opportunity in some situations to use 1/15 S so closing the lens more and then using the lens at the best of its ability.
Another great +point for RF is that you can come closer to the subject with better lens than with big SLR + zoom.
These points are more important than the distance light has to do in SLR vs RF...
🙄

All those are valid points, no doubt, but the original question was more specific to deal with exposure metering in particular, not the general outcome of RF usage against SLR.

 

[uhligfd]

(Sorry, i had caps lock on and do not want to retype this all, sorry and forgive the caps.)

I AM WONDERING IF THAT SUDDENLY FASTER FILM OF THE ORIGINAL POSTER CAME OUT UNDEREXPOSED AFTER DEVELOPMENT.

IT SEEMS THE FILM EMULSION HAS CHANGED IN HIS RF. THAT IS SOME WEIRD CHEMISTRY. I WOULD WONDER THAT THE LIGHTMETER IN ONE OF THE CAMERAS SLR OR RF OR BOTH WAS OFF BY QUITE A BIT.

THAT IS ALL THAT IS PHYSISCALLY POSSIBLE, UNLESS ONE TaLKS ABOUT THE SPEED of snapping pics with rangefinders which is their real advantage.

 

[shutterfiend]

Focal length (angle) and the type of metering (single/multiple) has a part to play when using internal metering.

I have a minolta hi-matic 7s with a faulty meter ($15, included shipping) so I use a drem instoscope ($1 at a garage sale). My wife has a 20D ($900) with a Tamaron 17-50 f/2.8 ($450). I calibrated (Wow! I used the word! Almost contextually too!) my drem against the 20D with focal length set between 28-30mm (equivanlent to full-frame 45-50mm) and took a few pictures with both cameras. They were quite comparable! I'm trying to find a decent bargain on a negative scanner (It's hard finding them at garage sales!) so I can post a few pictures. There must be a cheaper alternative.