Help me choose my next lens

[Mechcozmo]

I'm trying to decide between two lenses. The decision sort of boils down to mm and f-number... not sure what to go with. I use a Pentax K10D, which has a 1.5x crop.

Pentax 40mm f/2.8 Limited Linkety
Pentax 50mm f/1.4 Linkety

So... the 50mm has better low-light capabilities, but the 40mm gives me a bit wider view and is physically much smaller. What suggestions, thoughts, etc. do you guys have?

 

[furious]

What will you be using your lens for mostly?

And is the price difference a problem?

I personally would get the 50mm.

 

[miloblithe]

How important is size? Those pancake lenses are neat, but if you're rarely taking gear far, they seem less attractive.

 

[Coheebuzz]

About the focal range, personally i find the 50mm on a crop to be a bit too long for indoor shots. If your subject is a person in a small-ish room then you *may* not be able to fit him in the frame.

The 40mm would be better for framing in these situations but it's also a whole 3 stops slower, more expensive and it's also a digital only lens - too many drawbacks for me so in this case i would go for the 50mm.

 

[miloblithe]

Isn't it 2 1/3 stops?

As for the field of view with a 50mm lens on a crop camera, excellent for portraits, very tight for a scenery.

What lenses do you have so far?

 

[jpfisher]

Did you look at the FA 43mm f/1.9 Limited? It might be a good comprise for your needs -- it's a faster lens, well-built, and in between the two focal lengths you are looking at.

It's also the only FA Limited that I don't currently own, so I can't give you any first-hand info... but if it's anywhere near the quality of the 31mm or 77mm Limited you won't be disappointed.

 

[Abstract]

Isn't it 2 1/3 stops?

It's 2 stops. The 40 mm is 2 stops slower, or it allows 4 times less light in at max aperture. It goes from f/2.8 --> f/2 --> f/1.4.


And I'd go for the 50 mm f/1.4. I think it's too long for indoor shooting, but if I could ONLY go for one of those two lenses, I'd get the 50 mm. A 40 mm f/2.8 lens is nice, but I can shoot at 40 mm f/2.8, along with many other focal lengths, using my 24-70 mm lens, so buying a lens that can shoot at f/2.8 and 40 mm isn't particularly a good use of money, IMO. You'd be better off getting a zoom lens that covers 40 mm focal length if f/2.8 is good enough.

Also, I think a 40 mm may be even less useful than the 50 mm. It's still not wide enough to shoot indoors, but now it's also not long enough. That, plus isn't particularly fast.


If you're going to get a lens shorter than 50 mm, get one that can shoot at 28 mm, 30 mm, or 35 mm, and at f/2 or faster. That would be fantastic.

 

[miloblithe]

It's 2 stops. The 40 mm is 2 stops slower, or it allows 4 times less light in at max aperture. It goes from f/2.8 --> f/2 --> f/1.4.

Oops. I was adding the 1/3 stop between f/2.0 and f/1.8 twice.

 

[wmmk]

Yeah, as Abstract said, a 35 f/2 would be great. You could either pick up the FA 35/2 now, or wait for the DA 35 SDM, which will focus faster and might end up being f/1.4.

 

[ChrisA]

Isn't it 2 1/3 stops?

No. f-stop is the ratio of the diameter over the focal length. so f-stop is proportional to diameter. The standard stops are set up so the the _area_ (remember pi*r^2) doubles with each standard stop. 2.8 is double 1.4 so the area is 4x larger, 4 is 2 to the 2nd power, the area is doubled twice, so two stops.

Historically an "stop" was a piece of metal with a hole in it placed in front of the camera lens to reduce it's diameter. Today we use an adjustable iris or a leaf shutter that opens only to a given set size. The diameter of the iris is calibrated to have to effect of the old external stop So now we saw the aperture is the effective diameter over the length of the lens

 

[ChrisA]

I'm trying to decide between two lenses. The decision sort of boils down to mm and f-number.

Most of the time you can always adjust the framing by walking closer or backing off. Unless there is a physical barrier that's the best way. But no matter where you walk to an f/2.8 lens will always be an f/2.8 lens. I'd go for the faster lens.

If you are shooting people indoors the smaller DOF is a great way to remove clutter from the background. f/1.4 also extends your flash range and makes bounce off a far wall possible. I like the tighter shots too. I have a 50mm f/1.4 on my Nikon.

 

[Mechcozmo]

Because some people asked... my only other lens is the Tamron 18-250mm f/3.5. Very nice, but somewhat slow. Great quality pictures from it, plus an awesome zoom range.

What will you be using your lens for mostly?

And is the price difference a problem?

This would be a walkaround sort of lens, for times when I need a more open aperture or better quality glass. The price difference between the two isn't that great, so it wouldn't be a problem.

About the focal range, personally i find the 50mm on a crop to be a bit too long for indoor shots. If your subject is a person in a small-ish room then you *may* not be able to fit him in the frame.

The 40mm would be better for framing in these situations but it's also a whole 3 stops slower, more expensive and it's also a digital only lens - too many drawbacks for me so in this case i would go for the 50mm.

OK.

Did you look at the FA 43mm f/1.9 Limited? It might be a good comprise for your needs -- it's a faster lens, well-built, and in between the two focal lengths you are looking at.

You forgot to mention, it is $500 vs. the ~$200-$260 range we were looking at. I'll keep that lens in mind for when I have the money for it...

Also, I think a 40 mm may be even less useful than the 50 mm. It's still not wide enough to shoot indoors, but now it's also not long enough. That, plus isn't particularly fast.

If you're going to get a lens shorter than 50 mm, get one that can shoot at 28 mm, 30 mm, or 35 mm, and at f/2 or faster. That would be fantastic.

So your vote would be for the 50mm and later down the line get some sort of wide-angle zoom? Good point about the 40mm being a sort of awkward focal distance to have in a prime.

Most of the time you can always adjust the framing by walking closer or backing off. Unless there is a physical barrier that's the best way. But no matter where you walk to an f/2.8 lens will always be an f/2.8 lens. I'd go for the faster lens.

If you are shooting people indoors the smaller DOF is a great way to remove clutter from the background. f/1.4 also extends your flash range and makes bounce off a far wall possible. I like the tighter shots too. I have a 50mm f/1.4 on my Nikon.

Don't have an external flash yet. I'm mostly outdoors, so not too worried, but I'd like to get one eventually. But the fact that the lens will always be faster is a good one.

I think I'll order the 50mm then. Although maybe there is a local camera store that has it and will match Amazon's price?

Sidenote: My SanDisk 2GB card is away, for it was only showing as 1GB. Hopefully it will return to me soon...

 

[jpfisher]

You forgot to mention, it is $500 vs. the ~$200-$260 range we were looking at. I'll keep that lens in mind for when I have the money for it...

The 43mm is $470, but there is a $100 mail-in rebate that is good through the end of this month. The DA 40mm and FA 50mm each have a $50 rebate.

Have you plotted out the focal length of the pictures you have taken so far with your current zoom lens? I believe there is software out there to do this -- it might be worth a shot to see what focal length you tend towards.

I generally carry a 50mm f/1.4 in my bag, but it's very seldom that I actually use it. Generally when I'm in a situation where I need the extra light, I also need a wider angle -- I find that I'm using the 31mm in those situations. When I'm really cramped it's the 14mm, and outdoors walking around I'm more comfortable with the 77mm. YMMV, of course -- if you find yourself with a lot of shots taken at 50mm than that would be the way to go... but if you drift towards the wider end of things it may be worth considering saving for a little longer and going with the 43mm.

 

[Abstract]

So your vote would be for the 50mm and later down the line get some sort of wide-angle zoom? Good point about the 40mm being a sort of awkward focal distance to have in a prime.

Sort of. My vote is to get the 50 mm f/1.4 if it's only between these two lenses. Ideally, I think you'd want an 18-50 mm f/2.8 (or a 24-70 mm f/2.8 type lens that I own), and then one fast lens such as a 35 mm f/2, 50 mm f/1.4, or something similar.

Personally, I'd go with a wider 28, 30, or 35 mm f/1.4, f/1.8, or f/2 instead, and then get an 18-50 mm f/2.8 (or 24-70 mm f/2.8) later on. Or maybe get the zoom lens first (more versatile) and then get a 50 mm f/1.4 or 30 f/2 prime later. I think 28-35 mm is a better range for shooting people when indoors, and indoor shots in general, while the 50 mm is definitely better for shooting outdoors. My choice would depend on what you plan on shooting. When I want to take low-light shots, it tends to be of people, and I need a wider lens to take indoor group photos, or photos of a room, etc.

I'm also making this recommendation as someone who owns a 50 mm f/1.8, but wants to buy a Sigma 30 mm f/1.4, as I don't use the 50 mm f/1.8 as much as I thought I would. Of course, lots of people swear by the Nikon 50 mm f/1.8 and f/1.4 lenses, and find them VERY useful, so what do I know?

 

[Mechcozmo]

Have you plotted out the focal length of the pictures you have taken so far with your current zoom lens? I believe there is software out there to do this -- it might be worth a shot to see what focal length you tend towards.

There is, but it is Windows software. I found a Linux shell script but wasn't able to hack it to work on my Mac.

I generally carry a 50mm f/1.4 in my bag, but it's very seldom that I actually use it. Generally when I'm in a situation where I need the extra light, I also need a wider angle -- I find that I'm using the 31mm in those situations. When I'm really cramped it's the 14mm, and outdoors walking around I'm more comfortable with the 77mm. YMMV, of course -- if you find yourself with a lot of shots taken at 50mm than that would be the way to go... but if you drift towards the wider end of things it may be worth considering saving for a little longer and going with the 43mm.

Only problem is that I'm leaving on a trip and would like to bring this lens with. Fundraising time's up. But point taken about looking into wider lenses.

Or maybe get the zoom lens first (more versatile) and then get a 50 mm f/1.4 or 30 f/2 prime later. I think 28-35 mm is a better range for shooting people when indoors, and indoor shots in general, while the 50 mm is definitely better for shooting outdoors.

I'll try to see what sort of Pentax lenses are out there in my price range. Most of the wide zoom lenses that I can find are really expensive, and I don't see any with an aperture bigger than f/2.8.

I'm also making this recommendation as someone who owns a 50 mm f/1.8, but wants to buy a Sigma 30 mm f/1.4, as I don't use the 50 mm f/1.8 as much as I thought I would. Of course, lots of people swear by the Nikon 50 mm f/1.8 and f/1.4 lenses, and find them VERY useful, so what do I know?

You know enough to make me hesitate before buying this lens. Gee, thanks.

 

[jpfisher]

There is, but it is Windows software. I found a Linux shell script but wasn't able to hack it to work on my Mac.

Aaah, gotcha -- I guess you could really go crazy and write your own script to read the EXIF. Lightroom lets you filter by lens, but not (to my knowledge) at what length a zoom lens is set at when a picture is taken... but as you're in a time crunch, that doesn't do you much good.

Only problem is that I'm leaving on a trip and would like to bring this lens with. Fundraising time's up. But point taken about looking into wider lenses.

Well, worst case you find that you bought the wrong one and you take a slight hit reselling it.

I'll try to see what sort of Pentax lenses are out there in my price range. Most of the wide zoom lenses that I can find are really expensive, and I don't see any with an aperture bigger than f/2.8.

The fastest, widest lens in the current line-up is the FA 31mm Limited f/1.8 -- but it's also pushing the $800 mark after you get the rebate. I lucked out on one in perfect condition on eBay for $750 a few months ago. There is a FA 35mm f/2 that is a little more reasonably priced -- if you can find it. Other than that, on the wide end you're looking at the DA 14mm f/2.8 and the DA 21mm f/3.2 for primes.

You know enough to make me hesitate before buying this lens. Gee, thanks.

Well, if you don't using the camera in manual mode, you can probably find an old 50mm f/1.4 for fifty bucks or so... you'd have to set the aperture, shutter speed and focus manually. Call it retro digital.

 

[Mechcozmo]

Aaah, gotcha -- I guess you could really go crazy and write your own script to read the EXIF.

I'm working with the guy who wrote the script. Maybe, just maybe, there will be an OS X shell script. Don't keep your hopes up... but who knows?

The fastest, widest lens in the current line-up is the FA 31mm Limited f/1.8 -- but it's also pushing the $800 mark after you get the rebate. I lucked out on one in perfect condition on eBay for $750 a few months ago. There is a FA 35mm f/2 that is a little more reasonably priced -- if you can find it. Other than that, on the wide end you're looking at the DA 14mm f/2.8 and the DA 21mm f/3.2 for primes.

Well, if you don't using the camera in manual mode, you can probably find an old 50mm f/1.4 for fifty bucks or so... you'd have to set the aperture, shutter speed and focus manually. Call it retro digital.

Hell, I've used a Nikon FE. I know what to expect from manual.


I managed to get the script to almost-work. Enough to pull the focal lengths out of it. Here's the graph:

There are quite a few 40mm pictures. But also, if you add up the 49mm and 52mm pictures, you get 16 which happens to be the fourth-most used focal distance. Just one behind 3rd place. I'm leaning towards the 50mm, but the 35 is intriguing. However, the 50mm is probably more common and therefore easier to procure.

 

[miloblithe]

There are quite a few 40mm pictures. But also, if you add up the 49mm and 52mm pictures, you get 16 which happens to be the fourth-most used focal distance. Just one behind 3rd place. I'm leaning towards the 50mm, but the 35 is intriguing. However, the 50mm is probably more common and therefore easier to procure.

Actually, it seems that your chart here is including the crop factor of your camera, so your 18-250 lens is charted out between 27-375. So a 50mm lens would be pretty close to that 72mm mark that you seem to shoot at a hell of a lot.

On the other hand, the 40mm lens (60mm equiv) looks like it's more in the middle of your preferred range of 40-72.

Hmmm. Is there a cheap, high quality, 24-45 zoom out there? No. I guess there isn't.

 

[Mechcozmo]

Actually, it seems that your chart here is including the crop factor of your camera, so your 18-250 lens is charted out between 27-375. So a 50mm lens would be pretty close to that 72mm mark that you seem to shoot at a hell of a lot.

On the other hand, the 40mm lens (60mm equiv) looks like it's more in the middle of your preferred range of 40-72.

Hmmm. Is there a cheap, high quality, 24-45 zoom out there? No. I guess there isn't.

Err... good point. I thought that since the graph took into account the crop, it could be directly compared to the markings on the lens. Actually, the markings on the lens needed to be multiplied by the crop factor to be compared to the graph!

I'm thinking the 50mm lens because it is fast and because it is pretty close to what I've shot at. Maybe in the future I'll get that 35mm lens, sort of even out the wide-angle collection. But hell, that's the future!

 

[Abstract]

Get the 50 mm f/1.4, if only for the speed.

See? I'm not a pain in the ass this time.