A general question about all lenses.

[shefjr]

So I have read a lot on TPF about the sweet spot of a lens specifically in regards to the f-stop and stopping down a lens a couple of stops for a crisper image. So I guess my question is, does shutter speed, iso, and other factors affect a lenses sweet spot or is it GENERALLY going to always be the same f-stop no matter what?

My guess is there are too many factors to generalize the perfect sweet spot of a lens.
Thanks for your help as well as patience.

 

[fokker]

Only the aperture will affect this so called sweet-spot, although if it is a zoom lens it will have an ideal focal length as well.

Shutter speed has no bearing on lens performance, and will only affect the sharpness of the photo if you don't use a solid tripod at slower speeds.

ISO will always give the sharper and cleanest performance at its lowest native setting (100 for canon, 200 for nikon).

 

[analog.universe]

Only the aperture will affect this so called sweet-spot, although if it is a zoom lens it will have an ideal focal length as well.

Shutter speed has no bearing on lens performance, and will only affect the sharpness of the photo if you don't use a solid tripod at slower speeds.

ISO will always give the sharper and cleanest performance at its lowest native setting (100 for canon, 200 for nikon).

Exactly this ^

I'll also add that for some lens designs, the distance to the subject may affect the sweet spot. This effect has been reduced by floating elements in newer designs, but it still shows up in certain lenses. The effect is not generally as large as the effect caused by aperture or focal length however.

 

[shefjr]

Exactly this ^

I'll also add that for some lens designs, the distance to the subject may affect the sweet spot. This effect has been reduced by floating elements in newer designs, but it still shows up in certain lenses. The effect is not generally as large as the effect caused by aperture or focal length however.

So then I could test out my lenses at different apertures find the best f-stops for them and GENERALLY use that as the basis for using those particular settings.

 

[analog.universe]

Exactly this ^

I'll also add that for some lens designs, the distance to the subject may affect the sweet spot. This effect has been reduced by floating elements in newer designs, but it still shows up in certain lenses. The effect is not generally as large as the effect caused by aperture or focal length however.

So then I could test out my lenses at different apertures find the best f-stops for them and GENERALLY use that as the basis for using those particular settings.

Yeah, pretty much. It's likely that someone has already put those lenses through some tests and published the results online, so you don't have to do it yourself.

Check out Welcome to Photozone! and LensTip.com - lens review, lenses reviews, lens specification - Lenstip.com

 

[shefjr]

Yeah, pretty much. It's likely that someone has already put those lenses through some tests and published the results online, so you don't have to do it yourself.

Check out Welcome to Photozone! and LensTip.com - lens review, lenses reviews, lens specification - Lenstip.com

WOW! Those are some great links. Thanks for the help.

 

[KmH]

(100 for canon, 200 for nikon).

Not all Nikon DSLR's have a base native ISO of 200.

 

[shefjr]

Not all Nikon DSLR's have a base native ISO of 200.

Yeah my D90 has an iso L1.0 which I'm told is iso 100
I'm actually thinking about stepping up to the d7000. Except there is no sign of when there will more out for sale on the market.

 

[analog.universe]

Not all Nikon DSLR's have a base native ISO of 200.

Yeah my D90 has an iso L1.0 which I'm told is iso 100
I'm actually thinking about stepping up to the d7000. Except there is no sign of when there will more out for sale on the market.

The "L" and "H" ISO settings are not typically native analog gain settings, which is why 100 is not considered the base on that cam. 200 will technically give you better dynamic range performance than "L1". In the same way, the "H" settings don't get you a lower noise level than shooting at the highest analog setting and boosting in post, since "H" is not an additional gain setting, but a digital boost.

 

[shefjr]

An additional question about all lenses. I was shooting the super moon last night with the sigma 150-500 and in addition I put a 2X teleconverter on. I manually focused a crystal clear shot of the moon, set iso 100, set an acceptable shutter speed, and set up my aperture at the lenses sweet spot (the heart of my question). The images all came out really soft. I did play with the settings for about a half an hour at which point I decided to eliminate the 2X teleconverter because everything seemed soft. The photos then looked considerably clearer. One thing to point out here that I did do wrong is the mup (mirror up) function on the d7k. I didn't know it was on the dial of my camera :slapped my own hands for not knowing my camera better: I was looking in my menu for the mup function and didn't find it until I read through my owners manual this morning. Now that I have given you hopefully a clear idea of what I did, here are my questions.
1. Does a teleconverter change the sweet spot of a lens? If no proceed to number 2. (relative to my super moon shoot)
2. Would the mup function really cause the image at 1000mm to become really soft. (after writing this I feel like its a dumb question because it seems to me like it would) my logic a 2X would have double the vibration/softness. I'm leaving this up in case my assumption is wrong.
Thank you for any help and have a great day!

 

[chris]

There is probably some image deterioration due to the TC but it may also have resulted in a shutter speed that would give motion blur.

 

[c.cloudwalker]

So I have read a lot on TPF about the sweet spot of a lens specifically in regards to the f-stop and stopping down a lens a couple of stops for a crisper image. So I guess my question is, does shutter speed, iso, and other factors affect a lenses sweet spot or is it GENERALLY going to always be the same f-stop no matter what?

My guess is there are too many factors to generalize the perfect sweet spot of a lens.
Thanks for your help as well as patience.

Who cares about the sweet spot? Unless you have a sweet photo?

Forget about the sweet spot and shoot worthwhile images. Most people here who spend hours worrying about the sweet spot can't shoot an image worth talking about. Which is more important?

I've had images published that were far from technically perfect for the simple fact that they were interesting so, unless you are a retail photog where technique is more important than content, forget about the darn sweet-spot.

Cheers!

 

[Nikon_Josh]

So I have read a lot on TPF about the sweet spot of a lens specifically in regards to the f-stop and stopping down a lens a couple of stops for a crisper image. So I guess my question is, does shutter speed, iso, and other factors affect a lenses sweet spot or is it GENERALLY going to always be the same f-stop no matter what?

My guess is there are too many factors to generalize the perfect sweet spot of a lens.
Thanks for your help as well as patience.

Who cares about the sweet spot? Unless you have a sweet photo?

Forget about the sweet spot and shoot worthwhile images. Most people here who spend hours worrying about the sweet spot can't shoot an image worth talking about. Which is more important?

I've had images published that were far from technically perfect for the simple fact that they were interesting so, unless you are a retail photog where technique is more important than content, forget about the darn sweet-spot.

Cheers!

I need to hear more stuff like this, quotes such as this free the mind and allow a photographer to do what they do best. Take photographs instead of pixel peep!

 

[Overread19 7]

A few thoughts to consider:

1) As said the shutter speed and ISO of the camera won't affect where the lenses best performance can be found. However at a base technical level the ISO and shutter speed will affect the clarity of the shot, as will the lighting present at the time.
If you are going to test lens performance you ideally need:
a) Your cameras base ISO setting (typically ISO 100 or 200 - note this is the base setting not an enhanced low setting)
b) A shutter speed fast enough to avoid any shake from taking the shot (in general the faster the better).
c) A static subject
d) Lighting as constant as possible. Ideally you want a situation where your lighting is totally provided by flash so that its the same each and every time. This is important because part of how we see sharpness in a photo is based upon the contrast in the shot itself. If the lighting is changing the contrast spread over the photo can also change, and as a result evaluations will differ not because of the lenses performance but because of the lighting shift (note that big changes in base optical performance will still show - though you might have to view at 100% to see them)

2) The understanding of a lenses "sweet spot" is a valid bit of technical information. It can be put to good use when you've a situation where depth of field or other settings are not the driving force behind the shot - and thus you are able to shoot for maximum technical performance. In the real world you'll often find that working within theories of ideal performance isn't practical for getting the shot. The theory is worth learning and having in the back of your mind, but you need to prioritise them - eg avoiding handshake blur should be near the top of the list.
In the end understanding the sweetspot of lens performance is rather like understanding the "expose to the right" theory - its good to know, useful to use, but you won't get to use it every time.

3) When using a 150-500mm lens you'll see (esp if you shoot shots with widest possible aperture) that the base sharpness degrades as you increase the focal length. Images at wide open at 500mm will still be usable after processing; however you'll see that they are lacking in clarity to shots taken at the 150mm end. You can improve upon this by stopping down one stop from wide open*.

4) Adding a 2*TC does two things to your lens setup. First it reduces the effective aperture by around two stops. Normally the camera reports this to the user, however if it fails to do so the aperture will still be two stops smaller than said on the camera. The second thing it will do is magnify the image, this generally means that any weakness in the lens also gets magnified.
On a lens like the 150-500mm the use of a 2*TC is going to produce a soft result - the magnification gain is simply too great for the optics to perform to a sharp level of quality. Even if you stop one stop down from wide open you'll still be pushing the lens far beyond its working tolerance.
I should note that even a 1.4TC on such a lens will still produce results that most people consider too soft for a usable result. Good enough in a pinch, but generally not something they'd use (ps this also stands true for other superzooms on the market including options like the canon 100-400mm L).

5) Remember that increasing the focal length with a teleconverter puts additional pressure on the holding of the camera to ensure that the shake is not affecting the shot. At 1000mm you'd need at least 1/1000sec to handhold without handshake blur and often much faster in practice. On a tripod it also increases the requirement for a stable set of legs - you'll see improvement if you put a heavy weight (camera bag works well) on the hook on the tripod (most have a hook either on the midsection or base of the central column)
In addition the use of mirror lock up will help even more since it removes shake from the shot - but of course will only work if you're able to triggor the camera remotely - either using the built in timer or with a cable/wireless remote.

*almost all lenses don't perform their best wide open - however many can perform very well wide open and the difference between wide open and one stop down will differ on a lens to lens basis; some showing big gains others showing smaller ones.

 

[EDL]

and since it was the moon, also consider this:

Astronomical seeing - Wikipedia, the free encyclopedia