PDA

View Full Version : Minolta 50mm f1.7 - overexposure daytime



cgl88
05-11-2007, 06:30 AM
I have taken a couple of outdoor shots on full auto and am getting over-exposure problems. Take on a 50mm f1.7 lens:

http://x27.xanga.com/09bd766252333121931941/m87947295.jpg

Auto exposure: F/5 1/125 sec ISO-100, M=pattern metering, 0 step exposure compensation.


What setting should I be using to have the camera correctly calibrate the brights and darks? I have yet to try the kit and zoom lenses under the same condition.

coldrain
05-11-2007, 07:28 AM
The camera clearly has metered for the wall of the right building most of all.
Try to tell the camera yourself what to meter for, for instance with spot metering and then meter with that spot on what you think should be exposed correctly (and metering on a mid tone while doing so).
The buildings will become darker of course, when the green/light central part will get better exposed.

DonSchap
05-11-2007, 07:52 AM
My question is: What was the subject of the composition ... the bark of the birch trees? With this much range in the f-stops, this decision could be kind of brutal, as a digital camera only has 3 f-stops of dynamic range to play with.

If those trees are at f/22 or f/32 and the wall at f/5.6 ... you are going to have an unbalanced exposure. The walls really need to be around f/8 at the minimum, to show any definition, as you begin to close down your aperture to adjust for the trees. You could try "fill flash" to brighten up the nearby walls and help the f-range get a bit closer. It's just a thought. You're going to need some serious flash against that kind of sunlight.

cgl88
05-11-2007, 11:06 AM
Thanks Guys. I will keep working with these tough exposure situations, and will try those suggestions.

These shots are by no means artistic (i.e. what is the subject?). I just got this a100 machine and decided to take the hard road by shooting under high-contrast situations!

"... a digital camera only has 3 f-stops of dynamic range" - what do you mean by that? Is this in reference to exposure compensation?

DonSchap
05-11-2007, 12:06 PM
Okay ... it is explained this way ... so be patient.

You take a light meter (or your camera's built-in meter) and measure your subject. Let's say the meter says the bulk of your subject is at f/5.6 @ 1/125 sec @ ISO 400. Thats pretty bright, actually. You should have as good shot, overall.

So, as you are aware ... the f-stop scale goes up and down in increments.

Darker - requires wider aperture
f/1 - Black (doesn't change in intensity)
f/1.4 - Black (doesn't change in intensity) Black doesn't change
f/2 - Black (doesn't change in intensity)Black doesn't change
f/2.8 - Blackest black for this image
f/4 - gray
f/5.6 <- Exposure center (The lens' aperture is set to this reading)
f/8 - bright
f/11 - Whitest white for this image
f/16 - White (doesn't change in intensity)
f/32 - White (doesn't change in intensity)
Bright - close down aperture

Okay ... with only three f-stops for your sensor's dynamic light width, with your lens' aperture set to f/5.6, anything measuring f/2.8 or wider, on the light meter, will be effectively black to the sensor. Anything measuring f/11 or greater with be blown out or white. It is the same way for color film (3 f-stops range) ... so if you use the summertime high-noon sun as your source, you are usually dealing with nearly 7-f-stops of light to manage. Once again, stuff in the shadows quickly goes to black and anything hit directly by the sun ... blown out. Let the sun set a little, it's easier to manage the light.

You think this is bad, just try using transparency or slide film. It has only 1 f-stop range. If your exposure isn't "dead nuts, right on", you get either a black or white image. I hate that stuff. You have to bracket your shots, just out of self-defense and to not waste time having to re-shoot.

B&W film has the greatest dynamic light range of just about anything out there ... a full seven f-stops. Looking at the scale, you effectively would get this kind of range for your image.

f/1 - Black (doesn't change in intensity)
f/1.4 - Blackest black for this image
f/2 - dark gray
f/2.8 - getting gray
f/4 - slightly gray
f/5.6 <- Exposure center
f/8 - brighter
f/11 - brighter
f/16 - brighter yet
f/32 - Whitest white for this image

Is this making any sense? Yes, we are talking about the digital sensor ... and not film. And yes, you can set the lens to whatever exposure aperture you want to, but the sensor can only vary its relative sensitivity 1 1/2 f-stops higher and 1 1/2 lower to display your overall image. If your image's light range is wider than that ... the difference in the highlight and shadow detail suffer.

How we doing?

cgl88
05-11-2007, 08:32 PM
Hi Don, I think I understand it. I'm printing out what you explained and will read it several times.

One thing to note is that the other zoom lenses (f/3.5 to start) do not over-expose. The 50mm f1.7 has completely washed out shots, at shots like 1/125 f5 or f/320 f/4 under even brighter conditions (mid-day full sun-light). From what you wrote, the sensor needs to have a smaller aperture.

I've updated the firmware to 1.02 and have yet to test. If it is lens-specific, i'll simply have to apply -M-anual mode when this lens is used.

DonSchap
05-11-2007, 11:37 PM
Again, try to meter for your subject. That is the light level you want to set the camera at.

If your subject is shaded, you crank open the aperture (lower f/stop numbers) or slow down the time.

If you subject is getting a lot of light ... you close down the aperture (higher f/stops) or speed up the shutter-speed. Just remember that what ever you set the aperture to ... your surrounding area exposure will only have 1 1/2 f-stops above and below that setting.

This is a simulation with a standard image ... not an actual sequence. It is merely for discussion purposes.

Let's take a standard flash image ... 1/60 sec, f/2.8, ISO-400
24292

Then for some reqason ... you want to push it up a 1/3 f-stop to f/2.5
24293

and then that's still not enough ... so you push it to f/2
24295
The image is overexposed by allowing twice as much light to get in.

What happens if we went straight to f/1.4?
24296
As you can see, the sensor is becoming saturated with light. The definition of the image is being lost. The sensor only can accomodate light levels at the proper exposure and 1 1/2 to 2 f-stops above and below it. So, in essense, you are always trying to fit your entire image between a a range three f-stops.

DonSchap
05-12-2007, 12:19 AM
Another common problem is shooting from indoors, outdoors.

24297

These would be spot meter readings for this shot. You can see that the blacks become unchanging at f/1.4 ... and the whites pretty blown out at f/11.

It shows quite clearly the 3 f/stop dynamic range limitation of the sensor as it goes from black to white ... and how you lose definition quite rapidly. If the sensor could cover the full light intensity spread, you'd see the folds in his trousers ... the details of his face ... the detail of the paint job on the car ... the grandstand seats, outside ... etc.

I hope this helps clear up the entire idea a little more. As you work in these high contrast situations, you will begin to understand this inherent limitation to almost any digital camera.

cgl88
05-12-2007, 07:25 AM
Thanks Don. All of your posts have been very helpful. The last shot displaying all the best required f/stops within a single picture really illustrates your points.

DonSchap
05-12-2007, 10:09 AM
One of the best exercises I did, where I actually began to understand the relationship of the lighting, was to set up a composition, from the about 8AM-10AM in the morning, or from 3PM to 5PM in the afternoon, on a sunny (no cloud cover day). That way, I stayed away from the highnoon sun, where it is at its strongest and contrast is the worst.

These earlier periods incorporated various shade elements, so you could actually detect shade-detail and brighter reflections without blow out.

You have to have a spot-meter or spot-metering on your camera to do this effectively from a distance, otherwise you will need to run around in your composition, to each spot and take the general incident measurement.

Regardless of how you take these measurements:

On a sheet of 8x11 paper, draw the image you see in your camera's viewfinder.
Follow the average reading of the camera's internal meter, adjust your settings, snap the shutter and take your image
With your light meter, rapidly begin metering and marking each result on your hand drawing of all the significant areas of light change, ie, various shadow areas, highlights, main subject, etc, (much like I did in the race car image).
Just for grins, take the image again, just to make sure the lighting hasn't changed due to incoming clouds or some such.


By doing this exercise, you will begin to understand the relationship between the f-stop and intensities. You will note that even though the light meter can pick out all the changes in intensity, the actual image you took will not, because of the sensor's inherent limitation to do so.

Hopefully, afterwards, you will begin to rationalize your lighting more quickly, knowing right up fromt if a shot is "doable" or whether you've got some lighting issues you may have to adjust for. :)

Good luck and have fun with that SONY A100

BTW: Here's another image were the background is over exposed in preference to the interior of the vehicle and the subject. It works and looks quite natural.
http://i147.photobucket.com/albums/r289/donschap/fauna/trakker.jpg

cgl88
05-12-2007, 08:12 PM
Don, I just realized something when I checked out this particular lens - the Minolta 50mm f1.7's aperture was not connected. This got disconnected after I cleaned it. After fixing it, it turns out the aperture will not close again if opened to the widest. It might need a new spring. This is such a shame because it is a very nice lens.

The problem was of course over-exposure. The only way to get around it is to not use it or to shoot full manual. So I laugh a bit at how one thing led to your exercises/tips. I thought I knew quite a lot but I still have quite a bit to learn about exposure.

Will try your exercises and will hopefully post some results.

Lovin' the alpha...

DonSchap
05-12-2007, 09:35 PM
I know what you mean about return springs going bad. I recently purchased a pair of used TAMRON Adaptall lenses and both have issues with aperture return springs. The 200mm lens has a spring that may be too tight and will not allow the aperture to close all the way down, it (heh-heh) stops around f/11 and just sits there. The 135mm may not have its spring missing entirely as I can't get it to go from f/32 -> f/22 without having to go up to f/16 and then back down to f/22. That's simply not proper operation and I will not tolerate it.

Anyway, I turned both in for evaluation at the local depot level repair site and am having them gone over for evaluation and repair. I want my equipment to work exactly as designed. I really don't appreciate it having a will of its own! :mad:

Both have low light performance and is one of the main reasons I sprung (pun intended) for them. The 200mm is a f/3.5 and the 135mm is a f/2.5. I simply don't have anything for the SONY that can get to that aperture. My closest lenses are a Ozunon AF70-210mm f/4.5 and a TAMRON AF70-300 f/4-5.6 LD, which are good outdoors ... but really need a flash inside. The TAMRON AF18-250 f/3.5-6.3 XR Di-II LD can do the job with the flash, also.

Also, because they have an Adaptall mount on it and is also manual aperture and manual focus, it can be used for almost any camera mount, if you have the proper adapter. Kind of stretches the use of your lensing a little more, too ... if you are running short of funds.

Anyway, I digress, big time ... I sincerely urge you to get your 50mm f/1.7 repaired. It is a dynamite lens and will offer incredible low light performance, beyond any zoom. :D

cgl88
05-17-2007, 09:54 PM
Having the lens stuck at f1.7 isn't that bad. I just need to set the camera to A-priority @1.7.

Check it out:
http://xa3.xanga.com/14a8215455358123303054/m89086291.jpg

coldrain
05-18-2007, 03:33 AM
Having the lens stuck at f1.7 isn't that bad. I just need to set the camera to A-priority @1.7.

Get the lens repaired though, if you can. It is a very nice lens.

DonSchap
05-18-2007, 07:39 AM
Okay ... the two lenses that I spoke about in the above post are being serviced at a cost that totals to $180 for their repair and gets them back to full, clean operation. It was roughly $90 each. Replacing them would probably be about the same.

The replacement cost of your broken f/1.7 is around $30-$50 on ebay, which I quickly urge you to do, so you do not miss any photographic opportunities. Pitch the broken one, unless you want to save it for parts. The standard $90 cost of the repair bill certain isn't a reasonable idea for your particular lens, especially since you could replace it with such little fuss.

There are a ton of these lenses out there. I suspect almost as many lenses as there are camera bodies to mount them on. That's just not so with the two I turned in for repair/adjustment. Your lens was the "standard" Minolta lens sold, so it has a lot of work behind it. A 100&#37; production line, to be sure.

So ... off to ebay with you ...

Heck, get two! :D

cgl88
05-19-2007, 02:52 PM
Okay ... the two lenses that I spoke about in the above post are being serviced at a cost that totals to $180 for their repair and gets them back to full, clean operation. It was roughly $90 each. Replacing them would probably be about the same.

The replacement cost of your broken f/1.7 is around $30-$50 on ebay, which I quickly urge you to do, so you do not miss any photographic opportunities. Pitch the broken one, unless you want to save it for parts. The standard $90 cost of the repair bill certain isn't a reasonable idea for your particular lens, especially since you could replace it with such little fuss.

There are a ton of these lenses out there. I suspect almost as many lenses as there are camera bodies to mount them on. That's just not so with the two I turned in for repair/adjustment. Your lens was the "standard" Minolta lens sold, so it has a lot of work behind it. A 100% production line, to be sure.

So ... off to ebay with you ...

Heck, get two! :D

Thanks Don. I need to reward myself with some hard work I've been doing lately, by getting that replacement lens! I have seen completed sales on ebay for about $125 (max) for the 50mm. I'll shop for them now. In the meantime, I'll use the current lens because I had intended to use f/1.7 on it all the time anyway.

Man I am really happy with the alpha. All the negative points about it, I can live with. The camera is all about the photographer and his lenses!

unclebrudy
05-19-2007, 11:53 PM
I say before you buy another, take an hour or two and clean the aperture again, like REALLY clean it. Use an ultrasonic cleaner or some mild detergent. Use Pete Ganzel (http://www.pbase.com/pganzel/disassembly_repair_of_maxxum_50mm_lens)'s directions and clean it real well, because even a little oil can cause big problems. A couple of my 50's use to get stuck once wide open at 1.7, but operated freely from 2 to 22.

Try this: take the mounting ring off and operate the aperture spring mechanism independent of the aperture rod, and if it swings back and forth with snap, then the spring is probably fine and the blades just need some cleaning.

Let us know.

cgl88
05-23-2007, 09:10 PM
There is someone willing to sell it to me in my area for a good price. I've tried to clean the lens but did not get to the step of opening the aperture.

Is this a good deal?

what do i check for - How do I check that everything works? Check focus, aperture, continuous AF?

DonSchap
05-25-2007, 08:42 AM
I went over to the repair depot, yesterday, to retreive my two errant lenses. After inspection, they did a great job cleaning the years off the internals and tightening things up, but the aperture "return" still was not working correctly on the 200mm f/3.5 lens, so they took it back with a better understanding of the problem. The technician promised he'd have it working correctly and in short order. We'll see. :o

I am still pretty certain it is the "aperture return spring". Like anything, used enough ... it loses its tensile strength.

The tech also asked: "Why do you use these instead of the newer lenses?"

I said, ""Look at the widest aperture ... f/3.5! You can't get that kind of low light response, at that focal length, out of most sub-$600 lenses. (The Canon EF 200 f/2.8L USM is $659 on a good day and it's minimum focus distance is still 4.9') I got this lens for $100. Once it works correctly, it will offer some serious bokeh for 200mm shots and effectively get the very same shot ... for $500 less. I know it is manual focus, but with the number of fixed focal length images I do with this ... I think I still can get a razor-shot, when needed. Keep the USM on the zooms, where it is really appreciated. That is the true beauty of interchangeable lenses."

"I understand ..." he smiled and then returned to camera repair-land, where he came from.

DonSchap
05-25-2007, 07:13 PM
I received "the call" ... from the repair depot. The Adaptall 200mm f/3.5 was finished and operating as expected. I quickly got over there and confirmed this.

Once again, I do not yet have a "bright" lens for the SONY, so this baby is it, until TAMRON releases the SP AF70-200mm f/2.8 Di LD in the Fall.

Moving on ... :rolleyes: