[nmcleod1993]

I was shooting with a borrowed Sigma 100-300 F4 APO EX DG, and it didn’t seem sharp at all. I was using it with a 1.4 sigma converter, and I was wondering could the converter “mess” with the in body stabilization, or is my copy just less sharp? I’ll post pictures when I get home from work.

[csa]

I have the Sigma 300 F4, and always use it with a 1.4TC. Images are quite sharp from it, so I'm thinking possibly it might be the lens, in your case.

[chrism888]

Its possible, it could also be front or back focussing or just you or the subject or a combination of all 4 !! I've an early version and its an excellent lens, you'll need to keep the shutter speed up cos when combined with the 1.4 conv and if you've a crop factor camera the effective focal length will be around 630mm so you'll need at least 1/800 sec to stand a chance of a sharp image.

[mikesbike]

I have read that SR, of any variety, is less effective at much longer FLs.

[SSGGeezer]

I prefer the IBIS rather than the OS in my Sigma 120-400 HSM OS. If both are on there will be softness, and too slow shutter speed as previously noted is also a likely culprit. Try both methods of stabilization an use a shorter exposure time and then post an image or three here if you still have issues.

[vonBaloney]

When using the Sigma TC, the SR will be using a lower value than it should because only the recent Pentax 1.4x TC will communicate the effective focal length to the body. (And that might not even be true when using it with Sigma lenses -- anybody?) So if you are shooting at 300mm x 1.4 = 420mm, the camera will still be correcting for 300mm, so it will be less effective. However if your shutter speed is high enough (or you just turn SR off and make sure you are stable or shooting with a very fast shutter) your images should still be pretty good, even with the TC. That lens -- if there is nothing wrong with it -- is sharp as hell at all focal lengths and apertures. Back/front focusing could also be an issue (especially with TC, it may need an adjustment for that). So I'd try it under ideal conditions without the TC before deciding it is crap or there is some lens issue like de-centering.

[CarlosU]

I have the lens and, when everything goes right, it is one of my sharpest lenses. In my case, the most common cause of poor sharpness with the lens is back/front focusing. I have spent a lot of time carefully adjusting AF for that matter with my K5 and K3. The problem is reduced to an extent but persist. AF fine adjustment with my other lenses seems to be more effective. Otherwise the lens is quiet sharp.

[nmcleod1993]

Its possible, it could also be front or back focussing or just you or the subject or a combination of all 4 !! I've an early version and its an excellent lens, you'll need to keep the shutter speed up cos when combined with the 1.4 conv and if you've a crop factor camera the effective focal length will be around 630mm so you'll need at least 1/800 sec to stand a chance of a sharp image.

What do you mean front or back focusing, can I fix it? When you say 1/800 is that for handheld shooting or with a tripod?

[nmcleod1993]

Here are four pictures, would you consider them sharp?

---------- Post added 10-31-18 at 05:44 PM ----------

or here is a full res version on drive:
https://drive.google.com/open?id=1XI5zPSVRmY1fiZS45b2reHc12Lm1aQ5A

[CarlosU]

Are any of those pictures taken with the 1.4 TC?

[nmcleod1993]

Are any of those pictures taken with the 1.4 TC?

The two of the hawks are with the 1.4 TC the other two are just with the 100-300

[CarlosU]

I don't have the Sigma TC but a Kenko 1.5 TC. That is the sharpness I would expect from my combination, which I seldom use by the way.
Since there is some loss of sharpness when using the TC, I would say your lens is OK. Do a test without the TC and that should give you a more clear idea of the lens quality.

[nmcleod1993]

I don't have the Sigma TC but a Kenko 1.5 TC. That is the sharpness I would expect from my combination, which I seldom use by the way.
Since there is some loss of sharpness when using the TC, I would say your lens is OK. Do a test without the TC and that should give you a more clear idea of the lens quality.

How would you suggest I test the sharpness?

---------- Post added 11-01-18 at 10:47 AM ----------

I don't have the Sigma TC but a Kenko 1.5 TC. That is the sharpness I would expect from my combination, which I seldom use by the way.
Since there is some loss of sharpness when using the TC, I would say your lens is OK. Do a test without the TC and that should give you a more clear idea of the lens quality.

So when you say OK, are you saying that my lens is not as sharp as this model should be?

[CarlosU]

How would you suggest I test the sharpness?

Shoot a fine detailed target in good light. Focus carefully, preferably in live view. Use a tripod and shoot with 2s delayed self timer. Shoot first at max aperture and then close one stop for each additional shot until f11. Examine the results at 100%. When I have some time today I can upload some 100% crops samples from my lens so you can see what kind of sharpness you could expect from the lens, at least from my copy.

So when you say OK, are you saying that my lens is not as sharp as this model should be?

On the contrary, what I meant was that your results with TC are on par with how this lens should perform with a TC.
This are quotes from Photozone site when they tested the lens in Nikon mount. Unfortunately they didn't do it in Pentax mount but the results should be the same.

" The Sigma AF 100-300mm f/4 EX DG HSM APO is one of the most impressive Sigma lenses tested to date. It is able to deliver a near-flawless performance with great resolution figures"

"The Sigma AF 100-300mm f/4 EX DG HSM APO delivered excellent resolution figures in the MTF lab matching the best zoom lenses in its range as well as many fix-focal length lenses"

"Combined with the Sigma AF 1.4x EX DG converter there's a drop in performance in the center but more so towards at the borders. However, the results remain generally on a very good level although it may be advisable to stop down a little here for an extra kick in terms of contrast."

Here the link for the complete test

[nmcleod1993]

Shoot a fine detailed target in good light. Focus carefully, preferably in live view. Use a tripod and shoot with 2s delayed self timer. Shoot first at max aperture and then close one stop for each additional shot until f11. Examine the results at 100%. When I have some time today I can upload some 100% crops samples from my lens so you can see what kind of sharpness you could expect from the lens, at least from my copy.



On the contrary, what I meant was that your results with TC are on par with how this lens should perform with a TC.
This are quotes from Photozone site when they tested the lens in Nikon mount. Unfortunately they didn't do it in Pentax mount but the results should be the same.

" The Sigma AF 100-300mm f/4 EX DG HSM APO is one of the most impressive Sigma lenses tested to date. It is able to deliver a near-flawless performance with great resolution figures"

"The Sigma AF 100-300mm f/4 EX DG HSM APO delivered excellent resolution figures in the MTF lab matching the best zoom lenses in its range as well as many fix-focal length lenses"

"Combined with the Sigma AF 1.4x EX DG converter there's a drop in performance in the center but more so towards at the borders. However, the results remain generally on a very good level although it may be advisable to stop down a little here for an extra kick in terms of contrast."

Here the link for the complete test

Sounds good I'll do that tonight and post my results. I would appreciate if you take a peak to see if the sharpness is what you would expect. And very cool I really appreciate all of your time