I was going through your article HOW TO in the July 2011 issue of SP. I read an article about the use of linear polarizing filter in front of circular polarizer to make a variable ND filter. I and one of my friend tried this and found it very useful in daylight photography when needing very slow shutter speeds. But some people say that attaching two filters degrade the image quality. Please offer your valuable comments.
Dr. Lovekesh, via E-mail
Yes, using two PL filters can work as a variable Neutral Density filter though you should ideally have both of the circular variety. And yes, using more than one filter can always degrade image quality. To what extent depends on various factors.
Full Moon Shots
When I photograph a full moon, my photos always get overexposed. The size of the moon in the photo is also very small. I am using a Pentax K-5 with its 18-135mm lens. What should I do?
Arihant, via E-mail
Let’s discuss the focal length first. At the longest end, your zoom lens has an equivalent focal length of approximately 202mm (135 x 1.5). This is by far way too little to provide a decent size moon photo. You will have to borrow a longer lens (say, about 500mm, which will effectively be around 750mm on the K-5). Alternately, get one of those 20x – 30x bridge camera. You will require a very steady tripod. Don’t use a very slow shutter speed or you’ll have an elongated moon!
Now let’s discuss the exposure part. Unless you, more or less, fill the frame with the moon, your camera meter will read more of the dark sky rather than the moon itself (in spite of the fact that the moon is a very bright object). The meter ‘sees’ very little light reflected from the dark sky and hence orders the camera to provide more light, thus overexposing the moon. Hence I suggest you use the manual exposure mode and reduce the exposure till you can see the required details in the moon on your camera’s LCD.
Results Not sharp
I have a Canon 550D with 18-55 kit lens. I have purchased a Sigma DC 18-200mm lens with image stabilisation but I m not satisfied with the Sigma results. Pictures are not as sharp as those from the Canon 18-55mm. Kindly suggest a lens. Someone told me that if I choose a long range lens like 18-200mm, I will not get good results. Should I go for one long range lens or two lenses, one like 17-85mm and the other like 70-300mm? Please suggest a flashgun also.
Amit Kumar, via E-mail
From your description, I think that there is nothing wrong with your Sigma lens. When you use a longer focal length lens, not only is the image magnified, the camera movement is also magnified. The 18-200mm lens on your APS-C size sensor Canon 550D gives you approximately 29mm – 320mm equivalent. This means that at the longest focal length, the magnification (over a standard 50mm lens) is 6.4 times, and any camera movement is also magnified 6.4 times!
Please use the same lens as mentioned below and report back to me:
1. Set your Sigma lens to 200mm (320mm equivalent with your Canon 550D).
2. For hand-held photography, set the shutter speed not less than 1/320 sec. If the light level is low, you may need to use higher ISOs.
3. Take pictures.
Note one more thing. With wider apertures like f/5,6 or f/4, and at close distances, the depth of field (zone of acceptable sharpness) will be very small. Hence take your time to focus as accurately as possible.
Repeat the above experiment using a good tripod. When using the tripod, you could also try slower shutter speeds, but take care not to shake the tripod during the exposure.
I suggest you get a Canon dedicated flashgun. They currently have 5 flashguns (plus 2 ring-type). Which one you should buy depends on the kind of work you do and the amount you are willing to spend. If you want one for general day-to-day photography (not wedding photography), you could get the 270EX II or the 320EX.
Adobe RGB or sRGB?
I always use Adobe RGB as my colour space, but on a recent shoot I accidently set it to sRGB instead. Also, the pictures have been shot in JPEG. I have processed the images but am not sure how much of image quality I may have lost.
(Name withheld on request)
He who makes mistakes, learns. We know that Adobe RGB has a wider colour gamut compared to sRGB. This does not mean that Adobe RGB has more colours. It simply means that the range of colours is greater in Adobe RGB. The number of colours included depends on the bit-depth. In spite of this, sRGB has more than adequate range for many photo situations. So please don’t worry too much.
Your query specifically relates to “how much of image quality would be lost”. That would be hard to tell unless you make a similar size picture of the same scene (keeping every parameter the same) but using Adobe RGB. Even then, for many situations, and with careful editing, you would be hard-pressed to observe a noticeable difference. The advantage of Adobe RGB is that it offers you a greater leeway in editing.
Confused
I am a bit confused. Should I buy the Nikon D90 or the Canon 550/600D? Nikon offers 3200 ISO and 12-megapixels; Canon offers 12800 ISO and 18-megapixels. Both are available at Rs.50,000 (approx.) with full kit. How does it help getting a 18-105mm lens over a 18-55mm lens? Canon also has a 18-135mm. Is it better? I can increase my budget up to 65,000-70,000 if the suggested camera is good enough. My prime focus is nature, monuments, architecture, wildlife and portraits.
Vishal Chouhan, New Delhi
12-megapixel is good enough for most day-to-day photography but 18-megapixel allows you to crop areas of the picture without as much loss as you would get in an equivalent crop from a 12MP model.
I wouldn’t bother about the difference in ISO offered by the two makes of cameras you mention. In day-to-day photography, we rarely, if ever, use such high ISOs.
You have mentioned the 18-55mm kit lens, the 18-105mm and the 18-135mm. They offer the same angle of view (and hence the same size image) at the wide-angle end, but at the longer end, the 18-135mm provides greater image magnification.
All the three models are good, but in terms of technology, the Nikon D90 is now quite old. I suggest you handle all the three models and see which model you are more comfortable with. Then decide. Also check whether the focal range that you will need in the future is offered by the manufacturer you choose.
You have mentioned in your mail that you would like to get the camera from abroad. Keep in mind that you may lose the warranty if you do that. Since you are a beginner (and more likely to misuse/damage the camera), I suggest you spend a little more but get the satisfaction of a service back-up. In other words, buy the camera in India.
