Tag Archives: D40

Variable ISO – a useful exposure tool

Thom Hogan posted some interesting ideas on his site yesterday, pertaining to the question of how we, as photographers, deal with setting exposure. Basically, in the film days, we were stuck with one ISO rating for an entire roll of film (and some of us habitually used only one type of film), so at that time, ISO was essentially a fixed value. To adjust exposure, we then had to adjust shutter speed and aperture.

Today, ISO can be varied from frame to frame, and on some cameras, there is quite a wide degree of choices available. Hogan’s idea, then, is that having a selection of finely adjustable aperture settings may not really be necessary. We pick one of our two or three preferred apertures (wide open, optimal sharpness, or maximum depth-of-field prior to diffraction), then vary the shutter speed and ISO (if needed) to get the exposure we want. The point then is that we don’t really need a whole slew of apertures to choose from.

This talk of varying the ISO brought to mind something similar that I’d been considering writing about. I got a longer lens late last year, a 300mm, which on my reduced size sensor equates to a 450mm field of view. That’s long enough to make it a significantly different animal compared to other lenses I’ve used. Furthermore, it does not have vibration reduction. On the other hand, while it’s a somewhat hefty lens, it’s weight is well within reason for hand-held use. The problem then becomes ensuring that the shutter speed doesn’t go down far enough to result in problems. In practice, I discovered that I was most comfortable keeping it around 1/800 of a second or higher. That speed allows me some leeway, meaning I can get away with sloppier shot discipline, basically. If I went down to 1/500, I would have to be very careful to hold it steady as I released the shutter, and the overall percentage of blurred shots would be higher regardless. Another thing I ran into relates to a peculiarity of my camera (a Nikon D40): higher shutter speeds sometimes seem to result in weirdness. This is sort of hard to describe, and I’ve never really been sure what the hell is going on when it happens. I suspect it has something to do with the electronic shutter that this camera uses, in that it can sometimes create some weird artifacting effects at higher shutter speeds. The anti-aliasing filter may also be a factor, or possibly the lossy compression, even though it makes no sense at all that shutter speed would interact with either of those things. I don’t honestly know what it is. However, the practical implication of it was that I realized it would work very well if the shutter speed was at 1/800 all the time, at least for hand-held shooting with this lens. Well, there’s an obvious solution to that, isn’t there? Shoot in shutter-priority mode.

The one question was what would happen when the lens opened all the way up. It’s only an f/4 lens, which is not fast enough for shady conditions or heavy cloud cover at 1/800. So I turned on AutoISO, a feature I hadn’t used on my camera in a couple of years, and which I had never ever tried in shutter priority mode. I actually wasn’t even sure it would do what I needed it to, which was to keep the camera at the base ISO of 200 until the lens was wide open, then raise the ISO upward if there wasn’t enough light. Turns out, this is exactly what it does, and it works very well. I totally recommend it, at least for Nikon bodies with this type of AutoISO, and similar non-VR long lenses. It would work with VR lenses, too, if I had some particular reason for not wanting to use the VR, such as bokeh optimization.

On other camera bodies, such as the D7000 which I will have in the not too distant future, it wouldn’t be necessary to do it this way. The D7000 has more flexible AutoISO settings. On the D40, when using AutoISO in the more typical aperture priority mode, the highest setting allowed for “minimum shutter speed” is 1/250th of a second, which is not fast enough for a lens like this. On a D7000, I am not sure what the “maximum minimum” is, but I know it’s at least 1/1000th of a second. So on a D7000, I could just leave it in aperture priority mode, set up AutoISO to allow a minimum shutter speed of 1/1000th of a second, and viola!, I’d be set to go. That camera also does not have an electronic shutter, so that particular weirdness would presumably be gone, meaning I’d have no reason to avoid very high shutter speeds.

In the mean time, though, I have accumulated quite a collection of 1/800 second shots, many of them at f/4 and weird ISO values like 520 that result from the AutoISO setting. I’ve so far only run into one instance where the camera maxed out at ISO1600. The resulting shots were about one stop underexposed, but actually looked pretty good anyway.

That, of course, leads to the other big consideration with this, which is how high can you push the ISO? There was a time when I would not have been willing to use ISO1600 on a D40. However, more recently, I’ve come to realize that the noise inherent in that setting is really not all that bad. The amount of detail lost is pretty minimal, and the noise reduction in Lightroom 3 does a pretty good job at keeping the noise under control. As long as the photo isn’t extremely underexposed, the result is a somewhat grainy looking picture, sort of like Ektachrome 400, back in the day. (Although, frankly, a D40 RAW image at ISO1600 has better color than Ektachrome 400 ever did.)

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So, what lens should I get? :)

I’ve been itching to upgrade my lens collection lately, but of course it’s a challenge for a person in my position to figure out which way to go. By “my position”, I mean “not having a lot of money”, and also “not having much in the way of lenses to begin with.” That means almost anything would be an improvement.

Here’s the current situation: My camera body is a Nikon D40. For lenses, I have the Nikon 18-200mm VR, and a non-functional 18-55mm, where the autofocus doesn’t work. For those not familiar with the 18-55, the manual focusing on that lens is especially tricky, in that you turn the lens only about 1/8th of a revolution to go all the way from closest focus to infinity. Combined with the difficulty of using the D40 viewfinder for focusing, it makes the lens virtually unusable in many situations. I have been meaning to send it in to get it fixed, but haven’t gotten around to it yet. If I got it fixed, it would serve as my “macro” lens—it doesn’t focus to 1:1, but I don’t need to focus that close anyway. I find that at 55mm, it focuses close enough for my purposes. Here is an example:

False Sunflower

(Actually, that pic was taken after the autofocus failed, so it is clearly possible to get good results on manual focus. But it took a bit of extremely careful, minute rotations of the lens barrel to get that shot into good focus. Autofocus probably would have been easier.)

The image quality of the 18-55 is also better, in general, than that of the 18-200 VR. Even the barrel distortion at 18mm isn’t as bad, although it is certainly obvious enough to be seen, if there are straight lines in the shot.

So, given my current situation, I’ve been thinking about a few specific expansion options. There are four that come in under $1000 (I would not feel comfortable spending a huge amount of money right now—in fact, I probably am not going to go with any of these, since I really shouldn’t be spending anything right now, heheheh). They are:

10-24mm f/3.5-4.5G ED AF-S DX – A good DX landscape lens, which would give me some wider angle options than what I currently have, and better quality overall. A possible drawback to this choice is that I am not sure whether I would actually need to go this wide. The widest lens I have used on a regular basis was on my old Konica SLR, a nice little 24mm prime. In general I found it to be a bit wider than I needed it to be, except for in a few limited circumstances. It should be noted, however, that in the years I used this lens (roughly 1994 through 2005), I didn’t have as much idea of how to use a wide lens as I do now. I guess the best thing to do would be to actually try out a superwide lens before committing to buying one.

16-85mm f/3.5-5.6G ED VR AF-S DX – A general purpose replacement for the 18-200, to be used primarily for landscape shots. It would give me a bit more reach on the wide end, would force me to narrow my mental focus while in the field (by depriving me of instant access to the longer focal lengths), and would probably give me better image quality than the 18-200. One question with this lens is whether, by getting it, I would be making myself even less likely to ever try a superwide lens. The 16mm wide end would put me at an equivalent angle of view to the 24mm lens on my old camera.

Another question relates to the fact that it is a DX lens. It can be argued that the best Nikon camera body for landscapes is currently the 24 megapixel D3x, which happens to be an FX camera. In that case, the 24-70mm f/2.8 would be a better option. That, however, is getting pretty speculative, given the great expense of that equipment.

70-300mm f/4.5-5.6G IF-ED VR AF-S – This would extend the reach and overall quality on the long end. I’ve been really interested in bird shots lately, and let’s face it: The 18-200 is not a very adequate lens for that purpose. It’s not long enough, and the quality at 200mm is not the best. I’ve gradually learned, through trial and error, that my best birding configuration with this lens is to set it to 200mm and f/6.3 (opening up all the way to f/5.6 seems to result in lower quality), and hope for the best. At that aperture, I find that I often need to bump the ISO up to 400 (or even 800) to get an acceptable shutter speed. I also find that autofocusing doesn’t always lead to the best results, although I think this is more due to trying to focus on something that’s too small in the frame. When a bird only fills part of the center focus point, the camera will often focus on what’s immediately behind the bird, instead of the bird itself. I’ve learned to try and get the bird positioned right at the top center part of the marked focus area in the viewfinder, since that seems to be where the focus point looks, but even with that, I often find I’ll get better results if I go through the trouble of manually adjusting the focus. I haven’t been able to detect any clear focusing error in the lens itself, luckily—it seems to be entirely due to just pushing the lens beyond what it’s designed to handle. Being able to zoom in more would certainly help.

The reason I hesitate with the 70-300VR is that it’s not really the 300mm option that I want. What I really want is the 300mm f/4D ED-IF AF-S, along with a 1.4x teleconverter, which would take me up to 420mm f/5.6. This would be the same as having a 630mm lens on a film SLR, which is more telephoto power than I thought would ever be within reach for me. I practically drool at the possibility. :) The problem is that this combination would cost me close to $2000, and it would not give me VR, which I find very helpful during focusing and framing. Assuming Nikon updates this lens with a VR “G” version at some point, I’d expect the price would go up by at least a couple hundred dollars, plus there are rumors of further upcoming adjustments in pricing thanks to the excessively high value of the Japanese Yen. So it’s unknown whether getting that combination will be a likely possibility over the next few years, thus I am considering the 70-300 VR as a “best I can do for the foreseeable future” option. (I still need to look at 3rd party offerings, too, admittedly.)

35mm f/1.8G DX – This lens is tempting for two reasons. One is that it’s just cheap, compared to Nikon’s other lenses. The other is that it’s a prime lens, roughly in the “normal” range (I actually consider it on the long side of normal, since the “normal” lens on my old camera was a 40mm, and this 35mm comes in at about 53mm equivalent, when adjusting for the D40’s crop factor). Using a lens like this would be an interesting creative challenge. Part of it would involve leaving the other lenses at home, which would force me to work with just the one, single focal length. I wonder what I could come up with? I wonder if I would hate it? It’s been a long time since I was limited to just one focal length.

I also think this would be a handy lens to have for trips to museums and the like. It’s much smaller than the 18-200, which means security people would be less likely to look askance at it. :) (If my 18-55 worked properly, this reason would go away.)

Drawbacks to this lens? Other than the concern that using a prime lens would drive me absolutely nuts, the main issue would be the lack of a distance scale. Probably I would just have to learn to make do with the native autofocus capabilities of the camera, inadequate as they are, and fancier stuff like what I was talking about in this previous entry, simply wouldn’t be possible. On the plus side, since it is a 35mm lens, rather than an 18mm, I’m thinking that would be less of a big deal. The other problem with this lens? Nobody has it in stock!

So, there they are: my current options. Comments appreciated, especially if you happen to have switched from the 18-200 to one of the lenses listed here, or have opinions on third-party telephoto alternatives.

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