Question regarding fast lenses

[isusdfr]

I have a Pentax K100d and a pentax 18-250mm f3.5-6.3 lens. I am thinking of purchasing a pentax 50-135mm f2.8 lens.

I dont know if this question can be answered but here goes..

with my lens at the moment, sitting in my office pointing the camera out the window at 135mm I get a shutter speed of 1/125 of a second. If the conditions are all the same can you estimate what shutter speed i would be getting from the 50-135mm lens? Being a f2.8 I would assume that it would be faster but is there a calculation as to how much faster.
I would like to know whether the shutter speed difference is going to be worth forking out $1500.

I do oftern find that when taking pictures around the 100mm-150mm range that I get such low shutter speeds that objects that are moving are blurry because i cannot get a decent shutter speed

thanks

David

[kiwi]

The lens you currently have is variable aperture, so, when you are at 135mm I am not sure what actual aperture that will be on your lens. I'll guess at F/5.6

Basically though each time you improve a stop you double the shutter speed

So, if at F/5.6 at 1/125, then F/4 will be 1/250s and F/2.8 at 1/500s with the same exposure

This is quite a good explanation:

http://en.wikipedia.org/wiki/Exposure_(photography)

The other benefit with a fixed aperture lens is that it stays the same as you zoom which means you don't have to change any other settings to compensate

The other variable in exposure is your ISO setting. Maybe you can increase your ISO to achieve the result you are after.

[gstark]

Hi David,

I have a Pentax K100d and a pentax 18-250mm f3.5-6.3 lens. I am thinking of purchasing a pentax 50-135mm f2.8 lens.

I dont know if this question can be answered but here goes..

It can, but we'd need more information, such as the mode that you have set on the camera, and the aperture setting that was in place at the time that the reading was taken, the ISO value that was in place ...

with my lens at the moment, sitting in my office pointing the camera out the window at 135mm I get a shutter speed of 1/125 of a second. If the conditions are all the same can you estimate what shutter speed i would be getting from the 50-135mm lens? Being a f2.8 I would assume that it would be faster but is there a calculation as to how much faster.
I would like to know whether the shutter speed difference is going to be worth forking out $1500.

With respect, I think that you're asking the wrong questions.

I do oftern find that when taking pictures around the 100mm-150mm range that I get such low shutter speeds that objects that are moving are blurry because i cannot get a decent shutter speed

Ok ... what shutter speeds are you getting? And what might you consider to be a "decent" shutter speed? Have you considered bumping your ISO?

There's a few points that should be considered here, and the first of those would be technique, along with a smidgeon of theory. How you hold your camera and lens is important, and can have a significant affect upon how your images come out. This is very true when using longer glass, and that's where the smidgeon of theory comes into play.

As a general guide, the minimum shutter speed that you should be using would be the reciprocal of your selected focal length. Thus, with a focal length of 135mm, the slowest shutter speed you should use would probably be in the realm of 1/125 or 1/160. For a focal length of 250mm, 1/250 would be the lowest shutter speed.

But that then brings us back to technique. With good technique, you might be able to extend those values down to 1/60 or 1/125 respectively, but that does require deliberate attention on your part to how you hold the camera, your breathing, and often several other matters.

Modern lenses with IS/VR capabilities can sometimes help to bring these values even lower: I've taken handheld images at down to a half second, but that's the exception, not the rule.

With that out of the way, let's now explore your needs: what do you photograph, and how?

[isusdfr]

Yes it is f/5.6 at 135mm, thanks for the help

[isusdfr]

The shots that i take that i am usually disappointed in are those that are taken in low light with a moving subject. example, trying to take a shot of my 9 month old son inside the house when he does something funny. i dont always have the time to increase the lighting. So i usually bump up the iso to 1600 and take some snaps but because he is rocking or moving his arms about the shots are always blurry. Most of the time the shutter speeds are around the 1/20 to 1/50 of a second mark. The shots are usually taken around the f5.6-6.3 mark.
Also i take alot of shot of reptiles, frogs etc in displays which are usually very dark and i find that if the animal is moving at all I find that the shot comes out blurry, once again evern when using a high iso, the shutter speed is too slow. I am using a monopod and the camera has built in shake reduction so the issue isnt me moving when the shot is being taken. Hope that helps a bit

Hi David,

I have a Pentax K100d and a pentax 18-250mm f3.5-6.3 lens. I am thinking of purchasing a pentax 50-135mm f2.8 lens.

I dont know if this question can be answered but here goes..

It can, but we'd need more information, such as the mode that you have set on the camera, and the aperture setting that was in place at the time that the reading was taken, the ISO value that was in place ...

with my lens at the moment, sitting in my office pointing the camera out the window at 135mm I get a shutter speed of 1/125 of a second. If the conditions are all the same can you estimate what shutter speed i would be getting from the 50-135mm lens? Being a f2.8 I would assume that it would be faster but is there a calculation as to how much faster.
I would like to know whether the shutter speed difference is going to be worth forking out $1500.

With respect, I think that you're asking the wrong questions.

I do oftern find that when taking pictures around the 100mm-150mm range that I get such low shutter speeds that objects that are moving are blurry because i cannot get a decent shutter speed

Ok ... what shutter speeds are you getting? And what might you consider to be a "decent" shutter speed? Have you considered bumping your ISO?

There's a few points that should be considered here, and the first of those would be technique, along with a smidgeon of theory. How you hold your camera and lens is important, and can have a significant affect upon how your images come out. This is very true when using longer glass, and that's where the smidgeon of theory comes into play.

As a general guide, the minimum shutter speed that you should be using would be the reciprocal of your selected focal length. Thus, with a focal length of 135mm, the slowest shutter speed you should use would probably be in the realm of 1/125 or 1/160. For a focal length of 250mm, 1/250 would be the lowest shutter speed.

But that then brings us back to technique. With good technique, you might be able to extend those values down to 1/60 or 1/125 respectively, but that does require deliberate attention on your part to how you hold the camera, your breathing, and often several other matters.

Modern lenses with IS/VR capabilities can sometimes help to bring these values even lower: I've taken handheld images at down to a half second, but that's the exception, not the rule.

With that out of the way, let's now explore your needs: what do you photograph, and how?

[kiwi]

is there a cheap 50mm 1.8 prime for Pentax ?

For those indoor shots I'd suggest using bounced flash at the mo.

[Pa]

i see you are using a monopod i think that might counteract the on board shake reduction try it with that feature turned of

[isusdfr]

Yeah, that is something that i only just read about , dont use the in built shake reduction when using a tripod/monpod because it looks for shake and actually causes shake when it cannot find it.

i see you are using a monopod i think that might counteract the on board shake reduction try it with that feature turned of

[gstark]

The shots that i take that i am usually disappointed in are those that are taken in low light with a moving subject. example, trying to take a shot of my 9 month old son inside the house when he does something funny. i dont always have the time to increase the lighting.

But you can probably pop the built-in flash. That will give you a shutter speed of somewhere around 1/125- 1/160, but more importantly, your effective shutter speed would be more like 1/20000, and you could use f/8 and ISO 200. As has been suggested, if you can bounce the flash (harder with the built-in flash, but there are ways), then you'll start to see better results.

Also i take alot of shot of reptiles, frogs etc in displays which are usually very dark and i find that if the animal is moving at all I find that the shot comes out blurry, once again evern when using a high iso, the shutter speed is too slow.

Again, absent a fast lens, consider using your flash. If you're using a flash, be alert to your environment: do not, for instance, shoot directly into a glass casing when using your flash: the light will just bounce straight back at you. Shoot at an angle, and you'll go through the glass.

Before using flash, RTFM. Learn how to pull the flash's power down, and practice pulling it down by anything from 1/3 stop to 2 stops: using a reduced power flash can be a very effective way of adding extra light to your images.

And always be wary of using your flash when shooting animals; be considerate towards them.

[ATJ]

I agree with the use of flash, especially with the reptiles and frogs. Note that while shooting at an angle through glass can avoid the reflection of the flash, refraction through the glass can distort the image. Depending on how close the subject is to the glass, another trick is to shoot straight on, but put the camera as close to the glass as possible. This means that any reflection won't reach the lens. I do this all the time with aquarium photos (where refraction is a lot worse) and get no reflection.

Perhaps you'd be better off buying a flash rather than a lens. A flash in the hot shoe is a lot higher than the pop-up flash and that can be enough to eliminate reflections.

[aim54x]

I agree with the use of flash, especially with the reptiles and frogs. Note that while shooting at an angle through glass can avoid the reflection of the flash, refraction through the glass can distort the image. Depending on how close the subject is to the glass, another trick is to shoot straight on, but put the camera as close to the glass as possible. This means that any reflection won't reach the lens. I do this all the time with aquarium photos (where refraction is a lot worse) and get no reflection.

Perhaps you'd be better off buying a flash rather than a lens. A flash in the hot shoe is a lot higher than the pop-up flash and that can be enough to eliminate reflections.

I was given the tip of using a rubber lens hood and adhering that to the glass and then flashing away to my hearts content!

[gstark]

I was given the tip of using a rubber lens hood and adhering that to the glass and then flashing away to my hearts content!

Yes, that will certainly work very well as well. The issue then becomes one of finding a rubber lens hood; these used to be very common, but lately seem to have become somewhat less so. Mind you, I think I have seen a range on the site of one of Poon's suppliers, so I will see what we can get in this regard.

[ATJ]

I was given the tip of using a rubber lens hood and adhering that to the glass and then flashing away to my hearts content!

That will work, but I rarely find I have an issue, especially when using separate flash mounted on the camera.

[Murray Foote]

Hi David

I'm not seeking to disagree with the comments of people using flash, though for the sort of images I take I don't use flash and I don't even own one. In the worst case, if you use flash as the single light source mounted on the camera you will get a very poor quality of light. There will be a distance for correct exposure, everything closer than that will be overexposed and everything further than that will be underexposed. It is likely to be better to use the flash as a supplementary light source with one or more flashes placed away from the camera.

Another alternative is to use household lamps to make a crude studio lighting setup in your living room, set up your camera (perhaps even on a tripod triggered by remote release), put your son in there (or set them up around him), interact with him and wait for the right moment.

I think the place to start, though, is shutter speed. What shutter speed do you need to avoid subject movement blur? I find I usually need at least 1/80 sec for available light shots of musicians. Perhaps if you son moves more quickly it may be 1/125 sec as you suggest - but try a range (or assess your shots) to find out. Then the question becomes - do you really want to avoid shutter movement. Try some shots with really slow shutter speeds. Moving hands and feet may be good but often you want at least eyes and part of the face in focus. You may want to consider taking similar images at different shutter speeds and combining them in Photoshop.

Also, I second the suggestion of a 50mm f1.8, which is probably quite cheap, especially second-hand. If he is moving about, you might also want to compose a bit loosely, expecting to crop a bit, so that if he moves suddenly he still stays in the frame.

Regards,
Murray

[ATJ]

I'm not seeking to disagree with the comments of people using flash, though for the sort of images I take I don't use flash and I don't even own one. In the worst case, if you use flash as the single light source mounted on the camera you will get a very poor quality of light. There will be a distance for correct exposure, everything closer than that will be overexposed and everything further than that will be underexposed. It is likely to be better to use the flash as a supplementary light source with one or more flashes placed away from the camera.

This is true only if you have little experience with using flash and to be perfectly blunt know little about using flash. There are numerous ways to get fantastic light using a single flash mounted on the camera.

[dviv]

I'm not seeking to disagree with the comments of people using flash, though for the sort of images I take I don't use flash and I don't even own one. In the worst case, if you use flash as the single light source mounted on the camera you will get a very poor quality of light. There will be a distance for correct exposure, everything closer than that will be overexposed and everything further than that will be underexposed. It is likely to be better to use the flash as a supplementary light source with one or more flashes placed away from the camera.

This is true only if you have little experience with using flash and to be perfectly blunt know little about using flash. There are numerous ways to get fantastic light using a single flash mounted on the camera.

Agreed,

And even more if you have a hot shoe flash with a short TTL cord

[Murray Foote]

That's probably fair comment. I haven't used flash for over 20 years and I've never used flash with TTL metering. There's obviously also bouncing flash off the ceiling or using a diffuser. Any other of the numerous ways?

[ATJ]

Bouncing off walls. There are some devices that will both bounce and diffuse at the same time. Most of the light gets bounced up or to the side but some light is allowed straight through.

Here's a snapshot I took at Christmas using bouncing off the ceiling.



This is "straight from the camera" and exported from Lightroom with nothing other than a bit of sharpening and the watermarks. It is not the best photograph in the world but far from "a very poor quality of light" in my opinion. It is right up there with the sorts of shots that David was wanting to take.

[Murray Foote]

OK, thank you. Point taken.

I think he should probably experiment with the various approaches and see what works best for him.