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Old Mar 13, 2010, 8:41 AM   #1
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Default How do I use my A350 and Minolta AF 50mm 1.7 in low light?

Hello everyone, I am having trouble using my Minolta AF 50mm 1.7 lens.

The problem:
1) when I use the lens in low light the images I take are generally blurred.
2) when I use the lens in low light the auto focus takes ages to work, if it does at all, and my subject has moved in the meantime.
3) should my camera select an ISO other than ISO400 or is this normal (regardless of bright sunlight)?

I do not know whether I am expecting too much or whether I am simply not using the lens, or the camera, correctly. I am using a Sony Alpha 350.

I have read through most of the articles regarding the Minolta AF 50mm 1.7 lens on this forum and elsewhere on the internet and I could not find a similar scenario, so please accept my apologies if I have missed anything.

I have had the lens for about 12 months and I certainly do enjoy the shallow depth of field and sharpness of images that I have taken with the lens. These however have all been in good (day) light.

When I use the lens in low (wedding ceremony/church/disco) light I encounter problems. I am loathed to use the camera's built in flash, to the point where I would rather not take a photo then have a very pale individual on the photo, with a shadow of the lens on the bottom. Perhaps a flash is the answer to my problem, but of all the comment on this lens I have yet to see one that says "great low light performance with a flash". Surely that would be true of most lenses!

I generally shoot in aperture priority and use the widest lens aperture 1.7. By doing this the camera resolves the shutter speed and almost invariably the camera shake warning on the Super SteadyShot (SSS) flashes. I take the photo as steady as I can, gently brushing the shutter button to depress it enough to take the photo. I tend to have my arms tucked in and lean on fixed objects as much as possible to keep myself steady. If the camera focuses quickly, then once the photo is taken and I review it on the lcd the photo looks soft and very blurry. Occasionally the point of focus is in focus but generally it isn't.

I presume the SSS flashes a warning because the shutter speed selected is greater than 1/50 or (1/80 for the cropped sensor - which would be correct because 75mm is the "effective" focal length?). I have tried the camera on manual mode and experimented with various shutter speeds, all with blurry photos.

I also generally use auto ISO and the camera tends to select ISO400 regardless of whether there is good lighting or low lighting for this lens. I have tried experimenting with the ISO but the photos look very noisy above ISO400 and disappointingly noisy at ISO400. Should the camera select a lower ISO in bright light?

I use a local AF area mode and multi segment metering mode.

I have read a lot of good reviews of this lens, and of 1.7 aperture lenses generally, but the quality of my photos generally disappoint me. The lens is better than my standard zooms, but I cannot take great photos with it in low light.

How should I be using my Minolta AF 50mm 1.7 in low light? Am I expecting too much or can someone please help me?

Thank you so much for any help, if you need any more information please let me know.

Paul
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Old Mar 13, 2010, 9:15 AM   #2
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First, the camera shake warning is an indication that the camera is shaking, not that the SSS can't handle it. Certainly any attempt to keep the camera steady is good, but your attempt to do so, or lack thereof, may or may not have anything to do with the less than desireable results you're getting.

Since you haven't attached examples of the photos you're not satisfied with, it's hard to advise you on how to correct any kind of problem, but motion blur due to camera shake is highly directional, and the blur is almost always vertical more than horizontal. If the blur you're seeing is directional and covers the entire image, that would certainly be motion blur due to camera shake.

Second, the 50/1.7 is a sharp lens and focuses fast, but it still may be a cause for your blurry images. Any time you double the ISO, you halve the exposure time, and a large aperture allows the use of shorter exposure times and lower ISO settings, but other issues may be to blame. For instance, a lack of sharpness in large aperture lenses could be caused by Focus Shift. Also, the edge sharpness of the 50/1.7 isn't great, and that may be what you're seeing. It's also possible that you're not giving the lens adequate time to obtain a focus lock by not half-pressing the shutter button long enough before fully pressing it.

It would be most helpful if you could post some of the images you're not pleased with, and especially some 100% crops of those images, so as to isolate the areas of concern.
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Old Mar 13, 2010, 9:39 AM   #3
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Turn DRO off at higher ISO speeds to reduce noise levels (as it will try and brighten the shadow areas, which is "pushing" the exposure, resulting in higher noise levels).

You'll need to set something above ISO 400 to get faster shutter speeds without a flash indoors. Note that if you stop down the aperture a bit from wide open, you'll get sharper images (IOW, I'd go f/2.2 to f/2.5 if lighting permits, increasing ISO speeds as needed).

As for AF, turn the Focus Assist option off so that you're not using the built in flash for that purpose (unless you're using an external flash with a better red pattern AF light built in). For whatever reason, in lower light, the camera's Autofocus works better without the built in flash acting as a focus assist light. Also, check your AF settings. Note that the Center focus point is more sensitive in lower light (versus letting the camera try to pick one).
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Old Mar 14, 2010, 11:49 AM   #4
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Thank you both for your swift responses TCav and JimC – I am really keen to understand what I am doing wrongly.

Thank you TCav, I had not heard of focus shift, but this does not seem to be the cause as I refocus with any changes to aperture and use the viewfinder rather than live view. I will watch out for this in future though – sadly I do not think my problem is this technical!

Thank you for also pointing out that the SSS warning’s presence does not mean the photo will necessarily be blurred. I wasn’t sure whether the camera shake indicator made an assessment of the situation or whether it displayed the hand and exclamation mark based on some algorithm of the shutter speed being less than the reciprocal of the focal length of the lens (or similar) – the latter is obviously the case. I have attached the camera to my tripod today and seen the indicator SSS warning when there is definitely no camera shake (normally when using the tripod I have the SSS turned off).

I have searched the internet for examples of motion blur due to camera shake and this is almost certainly what I am experiencing. Is the shutter speed that I am using the cause? Movement of the subject also causes blurring which suggests to me that the shutter speed is the cause.

Please would you confirm whether this makes sense? If that’s confirmed, what I want to know is should my lens and camera be able to cope with being hand held in the situations I am taking photos in. I certainly appreciate that it is brighter in low light then my kit 18-70mm f3.5-5.6, but I hoped it wouldn’t be necessary to use a higher ISO setting because of the noise. I also am not in a position to purchase a flash unless it is vastly discounted from the RRP.

Thank you, JimC, for confirming that ISO speeds greater than ISO400 are required to shoot indoors without a flash; I may be asking to much of my equipment. Outdoors I do generally try to shoot at a maximum of f2.8, with this lens, to get sharper images and this sometimes increases the ISO speed accordingly. I generally cannot tell the difference between 100 and 200 ISO with my eyes. I also shoot in raw+jpeg, in most circumstances the jpeg is fine but I have used the raw to process the files myself where there is noise or variance in exposure across the photo. I also try and expose to the right to retain detail and reduce image noise from processed images. I do use DRO but use the raw file where this is not satisfactory.

This is normally okay but it is when I go inside that I struggle – it is starting to look like this may be because I am expecting the camera to take better photos and refusing to increase the ISO to lower the shutter speed.

I stopped the camera from using the flash to focus out of frustration, on my part and my subject’s, rather than for any technical reason. Thanks for pointing his out; I will ensure I certainly don’t use it in future. I try to compose my photos on the rule of thirds so rarely use the central point for the portrait type photography that I am taking in low light. I do tend to select a non-central point of focus myself rather than let the camera decide. Using the central point could improve my experience and I will certainly give this a try, thank you.

What are my options to reduce the blurring:
i) use a tripod,
ii) use a flash,
ii) decrease the shutter speed and increase ISO.

Are there any other options? What I think I could do is take a darker, but sharper photo and adjust the EV level +2.0. Will that help me take a sharp, albeit dark image, and then increase the exposure after the event? Hopefully 2.0 will be enough compensation. What do you recommend?

I have attached some photos that I have taken with this lens to illustrate what I am experiencing and why I am concerned.

The first photo of me taken outdoors in aperture priority mode with f2.8 [1/4000 and ISO 400 was automatically chosen]. Should the camera need to choose ISO400? This is why I suspect it may be the lens

The second photo is one I am pleased with taken in a festival in Swizterland, but there were a few blurred ones and I has to ask them all to be very stationary! Aperture priority mode with f2.2 [1/4 and ISO 400 was automatically chosen]. What is your view?

Photo 3 and 4 illustrate the frustration I have when my subject moves. The lady is almost in focus in one and then is moving slightly for the other. (the sign above the guy’s head shows the whole photo is not blurred because of this motion. Aperture priority mode with f2.2 [1/6 and ISO 400 was automatically chosen].

Photo 5 and photo 6 were taken at the same place. Obviously there is more light on the photo with two ladies but in a well lit room should the photo of the single ldy be blurred? We were out for dinner so I was probably resting on the table – and I guess I would have tried for their eyes as the point of focus. Aperture priority mode with f1.7 [1/2-1/4 and ISO 100 was automatically chosen].

Is the lens performing well and am I expecting too much without a flash? Thank you so much for your help.
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Old Mar 14, 2010, 11:50 AM   #5
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photo 6
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Old Mar 14, 2010, 3:04 PM   #6
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Quote:
Originally Posted by paul2584 View Post
... Is the shutter speed that I am using the cause? Movement of the subject also causes blurring which suggests to me that the shutter speed is the cause.
Almost certainly not. I've gone over your images and I see no indication of motion blur due to camera shake. Camera shake happens in a single direction at a time, so the blur is directional. For instance, if the camera were shaken vertically, the horizontal lines would be blurred but the vertical lines would be sharp. That didn't happen in any of your images.

What follows are 400% crops from your photos. None show any motion blur. What they do show is focus errors. I think that, in low light, you may be having trouble with the very shallow depth of field that a large aperture lens will give you.
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Old Mar 14, 2010, 3:08 PM   #7
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This is what motion blur looks like. The lower left and upper right of the shapes are sharp, but the upper left and lower right of the shapes are blurred.
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Last edited by TCav; Mar 14, 2010 at 3:53 PM.
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