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AbsoluteApril
11-17-2011, 02:18 PM
I recently moved up from pocket point and shoots to my first DSLR, I picked up a Pentax K-R. Obviously still have a lot to learn about how to use this camera but my main issue right now is depth of field. It's great for artistic shots but I cannot seem to get the camera to focus on the entire snake, head and body, it's just one or the other. I have been shooting on 'auto' or 'pet' (which, as I understand it, faster shutter speed to account for movement of the subject).

Any tips or advice?

here are some examples:
http://i332.photobucket.com/albums/m331/Hisba/snake%20pics/More%20Amazon%20Tree%20Boas/Tigress9_24_11.jpg

on these staged shots, the camera always wanted to focus on the wood (grrrr)
http://i332.photobucket.com/albums/m331/Hisba/snake%20pics/More%20Amazon%20Tree%20Boas/Ammo9_25_11b.jpg

http://i332.photobucket.com/albums/m331/Hisba/snake%20pics/More%20Amazon%20Tree%20Boas/Goose9_25_11a.jpg

thanks from this camera noob

Ophion
11-17-2011, 02:57 PM
That is the major downside of shooting on auto modes - it is going to pick the best for what the camera sees in the situation. Camera do not know exactly what we want, nor what exactly what is going on. When you put the camera on a pet mode it likely is going for a shutter priority. Stopping motion is the first priority - everything else is a lesser priority still considering there should be decent exposure (not an underexposed pitch black image or overexposed white image).

This is where you're juggling three main pieces that control your overall and exposure (and where I hope I don't lose you or hope you don't feel I'm dumbing it down too much! :) ).

1. Shutter Speed (as you know) - how slow or fast the shutter in the camera is opening and closing to expose for the image.
2. Depth of Field (DoF or F-stop) - The amount of light the lens allows into the camera. (possibly confusing part) The less available light, the smaller the f-stop number and the smaller the visible depth of field (or sharpness, what you are getting in your images). The more available light, the larger the possible f-stop number, the larger the visible depth of feild.
3. ISO - Lower ISO number allows for less light, while higher number allows and tells the camera there is more light. (when there may not be) Really high ISO numbers (1600+) start to create noise as the camera is having to 'guess' at what information was supposed to be there in low light situations.

So, what is happening is your camera is likely upping your shutter speed and since it does not see your depth of field as a priority it keeps it at a low number. (likely only compensating enough with ISO to get a decent exposure) If you would like the entire subject in focus I would say it is time to start playing on manual and playing around with your ISO, shutter speed and F-stops. Hopefully that helps a bit and I will try to add a bit more later if this is still a bit vague.

AbsoluteApril
11-17-2011, 04:05 PM
I have been reading up on ISO and Fstop and never once made the connection that F-Stop is Depth of Field for some reason, so THANK YOU! That helps out my understanding a lot more. I'll mess with it this weekend and see how it goes on Manual. :)

hhmoore
11-17-2011, 04:12 PM
I hadn't either, April. I have a similar problem, mainly when working with my macro lens...but it seems to strike at random times with my general purpose lens, as well. (Don't really have the problem with my 70-300, but I have to be too far away to pull off snake shots, lol. They'd be gone by the time I got in position and focused)

WebSlave
11-17-2011, 04:26 PM
Actually the LARGER the F-stop number, the smaller the aperture, and less light is allowed in, requiring a slower shutter speed if all other factors remain constant. The smaller the size of the aperture (which paradoxically means a LARGER F-stop number) the WIDER the depth of field.

Generally if you are looking to control depth of field, you need to shoot in aperture priority, not shutter priority. And flash, maybe more than one, is a necessity for inside shots when you seek wide depth of field results. Using a tripod will help reduce the amount of assisted lighting necessary, because aperture and shutter speed are inversely proportional. The larger the F-stop number, the smaller the shutter speed number necessary to get a proper exposure because LESS light is allowed in through the lens.

Also bear in mind that the type of lens used and the distance of the lens to the subject has a large bearing on depth of field as well. The closer the lens is to the subject, the more narrow the depth of field will be. That's why you might want to have several different focal lengths of macro lenses. You can more easily control the working distance from the subject by simply using the best lens for the job at hand. The Nikon macro lenses I used were 60mm, 105mm, and 200mm. You can get the same framing of a subject from any of those lenses, but the WORKING distance for each lens will be entirely different. For adults I used the 60mm. For baby snakes, the 105mm worked best for me. I rarely ever used the 200mm lens but it would be my choice to try to get a photo of a small butterfly that might get spooked if I got too close to it.

KelliH
11-17-2011, 05:18 PM
If your camera has an aperture priority mode it can help to start with that mode while you are learning. :-)

Ophion
11-17-2011, 05:33 PM
Actually the LARGER the F-stop number, the smaller the aperture, and less light is allowed in, requiring a slower shutter speed if all other factors remain constant. The smaller the size of the aperture (which paradoxically means a LARGER F-stop number) the WIDER the depth of field.

Actually we said exactly the same thing, but with different wording. (I had to go double check, I wrote it really fast before class!) I just wanted to avoid the larger/smaller combo without spending time and making things more confusing. When f/2.8 is a huge aperture and the lens is wide open allowing in a lot of light, but the number is low. However, f/64 is stopped way down and the lens has a tiny opening allowing the smallest amount of light in, but the number is high.

The aperture priority would certainly help as suggested if you want to focus on that aspect. Just keep in mind that while on any priority setting it will allow you to adjust that priority (the shutter speed or aperture), but will choose the other. So, if the images come out blurry because the shutter speed is not high enough, you may need to compensate with more light or upping the ISO. (or try the scary full manual mode)

Also just a general thought on focus. Where you focus can play a big part of what is in focus or remains sharp. Where you place the focal point the area of sharpness will fall about 1/3 in front of that point and 2/3 behind that point. (not the exact science numbers, an idea to keep in mind) Sometime it can be frustrating even if you know you should have everything in focus, part of it may be where you place the focal point.