How do I use a TC????

fordpop · 23 Oct 2009

No, it's not a wind up......

I was reading with interest a thread t'other day in which desantnik commented on regarding how to use a TC and the need to stop it down to avoid stop focus, or something along those lines.

Now I come to try out the advise - do you think I can find it........

I only ask, because I used a 1.4x and 80-200 f2.8 at the Oulton BSB round and was far from impressed with it - soft focus issues - but maybe Im not using it right?

Cheers

HoppyUK · 23 Oct 2009

TCs are always a compromise and rarely a substitute for the real thing. You need a very good lens and a top quality TC to get good results. They work best with longer lenses, and often stopping down to a higher f/number helps with sharpness and vignetting.

You always lose one stop of light with a 1.4x and two stops with a 2x. If this takes you over f/5.6 you will lose AF with most cameras too. No free lunch.

andrewc · 23 Oct 2009

Plus focussing speed is much reduced.

fatphotographer · 23 Oct 2009

I have found that they don't offer the best results with zooms, and the 80-200 is an older zoom as well, which won't help. AF will be slower, and that will be made worse by the speed of moving vehicles. TCs are a comprimise. They are better suited to prime lenses, but by the time you buy a fast prime to match your TC, you will be defeating the object of looking for a cheap way of getting extra focal length!! No easy answer.
BTW, have you calibrated the lens with the TC attached?

fordpop · 23 Oct 2009

have you calibrated the lens with the TC attached?

No I haven't - this is what I mean really - do I need to do anything other than put it between the lens and the body and shoot away.

I understand the principals of IQ loss, slow AF, better on primes etc etc that was not my question, but the results I got from brief trials where simply shocking.

I had given it up as a bad job, but the post I cannot find lead me to believe there maybe a little trick or two to their actual use.

I tried PM to desantnik but in box is full:shrug:

Cheers

fatphotographer · 23 Oct 2009

The D3, D700 etc have a focus calibration setting in the menu, I presume that the D300 does as well. Google "focus test chart" "focus calibration chart" and you will come up with a few pieces of paper to print off and check your kit against. You definitely DO need to calibrate the lens for use with the TC, the body should recocnise the fact that it is attached and apply the correction for you. This will help a bit, but will not get around the fact that there will be a loss of performance / quality, when using a TC with a zoom.

HoppyUK · 24 Oct 2009

fatphotographer said:
The D3, D700 etc have a focus calibration setting in the menu, I presume that the D300 does as well. Google "focus test chart" "focus calibration chart" and you will come up with a few pieces of paper to print off and check your kit against. You definitely DO need to calibrate the lens for use with the TC, the body should recocnise the fact that it is attached and apply the correction for you. This will help a bit, but will not get around the fact that there will be a loss of performance / quality, when using a TC with a zoom.

Just don't use anything invloving an A4 sheet of paper shot at 45 degrees and very close distance (even though that is what google will come up with). It will lead you astray.

Some good info on this thread on how to check focus accuracy http://www.talkphotography.co.uk/forums/showthread.php?t=166932 You don't need any special chart.

hollis_f · 24 Oct 2009

HoppyUK said:
Just don't use anything invloving an A4 sheet of paper shot at 45 degrees and very close distance (even though that is what google will come up with). It will lead you astray.

Some good info on this thread on how to check focus accuracy http://www.talkphotography.co.uk/forums/showthread.php?t=166932 You don't need any special chart.

But a good chart, set up parallel to the focal plane, can make it a lot easier to tell if the focus is better or not. I use this one.

HoppyUK · 24 Oct 2009

hollis_f said:
But a good chart, set up parallel to the focal plane, can make it a lot easier to tell if the focus is better or not. I use this one.

That's a lens resolution test chart (and leaving aside it's general suitability for that, or not) it is not very good for checking focus error.

Sure you need a good flat target with clear, bold graphics set up square to the camera, at a sensible distance, like 50x focal length, but then you also need some way of showing where the focus actually is - ie in front or behind, and how far.

You don't need anything sophisticated for this. I use a cereal packet and a ruler propped up to one side - a bit like Tim's test in the link I posted above.

It's easy, real world, relevant, and extremely accurate. No need to download anything or make it complicated

fatphotographer · 24 Oct 2009

HoppyUK said:
It's easy, real world, relevant, and extremely accurate. No need to download anything or make it complicated

The proccess / results are the same, focus on a point and have a guide to see if there is a sharper area in front or behind - I didn't think printing a sheet of A4 from a 300kb file was a big issue in this day and age.

HoppyUK · 24 Oct 2009

fatphotographer said:
The proccess / results are the same, focus on a point and have a guide to see if there is a sharper area in front or behind - I didn't think printing a sheet of A4 from a 300kb file was a big issue in this day and age.

The process/results I have described is not the same.

fatphotographer · 25 Oct 2009

HoppyUK said:
The process/results I have described is not the same.

Do you not think so?

Put something in front of the camera to focus on, and then have a measuring device in front and behind the point of focus to quantify the results....

Whether it is a peice of card with Kelloggs on it or a piece of A4 with a black line....a tape measure at an angle or measurements on the A4 page that is at an angle.....neither here or there really

We have both offered advice, hopefully he can gain from it

Cheers

Gary

HoppyUK · 25 Oct 2009

fatphotographer said:
Do you not think so?

Put something in front of the camera to focus on, and then have a measuring device in front and behind the point of focus to quantify the results....

Whether it is a peice of card with Kelloggs on it or a piece of A4 with a black line....a tape measure at an angle or measurements on the A4 page that is at an angle.....neither here or there really

We have both offered advice, hopefully he can gain from it

Cheers

Gary

In the post of mine that you replied to, I was referring to the use of a resolution chart as a target, which as described has no way of assessing front or back focus.

The other popular focus test target that is downloaded is a sheet of A4 paper, shot at very close distance, and at a 45 degree angle. Apart from being very prone to user error, there are various problems with this that lead many people to believe they have a focus problem when they don't, and to subsequently recalibrate their lenses. This can then result in them being out when used at normal focusing distance.

The process that I have described, and posted a link to, is different. And better.

Cheers

fatphotographer · 25 Oct 2009

Sorry, your first reply to my advice was..

HoppyUK said:
Just don't use anything invloving an A4 sheet of paper shot at 45 degrees ...... It will lead you astray.

I have had good results with the focus chart method ... if you see your method as better, then fine.... I see them as very similar means to the same end.

HoppyUK · 25 Oct 2009

fatphotographer said:
I have had good results with the focus chart method ... if you see your method as better, then fine.... I see them as very similar means to the same end.

With respect, I think that is bad advice. Other methods are better, and easier.

If it works for you that's fine, but not everyone is so lucky with a variety of lenses. If you ask a camera technician to explain why so many cameras sent in for focus calibration are found to be perfectly okay, they will tell you that many of them have been subject to that test. It is notorious in warranty workshops.

This link from Canon (second question down) explains why an angled target is unreliable, and recommends a minimum distance of 50x focal length, which rules out anything as small as A4 paper.

http://www.digitaljournalist.org/issue0812/tech-tips.html

hollis_f · 25 Oct 2009

HoppyUK said:
That's a lens resolution test chart (and leaving aside it's general suitability for that, or not) it is not very good for checking focus error.

Sure you need a good flat target with clear, bold graphics set up square to the camera, at a sensible distance, like 50x focal length, but then you also need some way of showing where the focus actually is - ie in front or behind, and how far.

It depends on what you're trying to do. If you're trying to acertain whether your lens is back, or front, focussing, and by how much then, yes, the angled rule next to the target is required.

But, if you're doing Micro Focus Adjustment then the angled rule isn't required. You just need the flat target, shoot various MFA adjustment values and see which resulting image is sharpest. Like what Chuck recommends in your linked article.

For MFA the target needs to cover only the central AF point. At 50xFL an A4 sheet covers roughly one-quarter the field of view of an APS-C camera. That should be easily enough to give the AF mechanism a good target.

desantnik · 25 Oct 2009

fordpop said:
I was reading with interest a thread t'other day in which desantnik commented on regarding how to use a TC and the need to stop it down to avoid stop focus, or something along those lines.

Now I come to try out the advise - do you think I can find it........

I only ask, because I used a 1.4x and 80-200 f2.8 at the Oulton BSB round and was far from impressed with it - soft focus issues - but maybe Im not using it right?

As this was kinda addressed at me.. you tried to PM me but my inbox was full and I was away - sorry!

What I was talking about was that when you use a TC you need to avoid using it wide open as the TC softens it quite dramatically even on a good quality lens. You probably need to come down one whole stop for a 1.4x or 1.7x and probably getting on for two stops with a 2x - thats not talking about how the TC effects maximum aperture size, but how you actually dial in your shot.

For example, 70-200 f2.8 with a 1.4x TC. You instantly loose one stop to the TC, so you have a f4 lens now, however for best results you need to shoot at f5.6 or smaller.

I do this by shooting in manual, as in motorsport, the shutter speed is by far and away the most important value to control, but at the same time you need to watch that aperture! Using the ninja magic that Nikon provides me, auto-ISO is how I control the exposure

Good results with zooms and TC's? Hmmm sometimes, its a bit random I've found. It does work, but I've rarely got anything to write home about from it to be honest. (I'm just looking at some shots I took on my hols that was 70-200 and 1.7x and they are all a bit blurgh)

fordpop · 26 Oct 2009

OK guys, thanks for all the replys...

I think the best think I can do is spend some time doing a proper test/calibration using some of the advice above and then take it from there.

Cheers

desantnik · 26 Oct 2009

Calibrate With a zoom??? I wasn't going to comment against some of the things said above, but don't waste your time doing that.

By all means calibrate a prime if you think it needs it, but a zoom???