Dumb question on 2x III + 300/2.8 II

Today I went out with my 300/2.8 IS II and 2x III. I had great lighting and some very cooperative subjects. Unfortunately, upon returning home I noticed that my images were not sharp on the intended focal point. Instead, the sharp spot was a bit in front on all my photos. I will say, if the combo is properly MA'd, it would be one heckuva sharp combo.

So here's my questions:

Is it either party's fault (lens, teleconverter) or is it just the pairing of these specific parts that is off?

I'm thinking I could purchase another 2x III and see if it is sharper on the intended point of focus...or I could try my luck with autofocus microadjust (a process I never had fun doing, and was never confident in my work).

Thoughts?

birder_herper wrote in post #17975166
Today I went out with my 300/2.8 IS II and 2x III. I had great lighting and some very cooperative subjects. Unfortunately, upon returning home I noticed that my images were not sharp on the intended focal point. Instead, the sharp spot was a bit in front on all my photos. I will say, if the combo is properly MA'd, it would be one heckuva sharp combo.

So here's my questions:

Is it either party's fault (lens, teleconverter) or is it just the pairing of these specific parts that is off?

I'm thinking I could purchase another 2x III and see if it is sharper on the intended point of focus...or I could try my luck with autofocus microadjust (a process I never had fun doing, and was never confident in my work).

Thoughts?

If the TC is giving sharp results, then it is doing its job. The TC is just a passive player in the overall AF equation, with the lens and the camera doing all of the real work.

Do the micro-adjust, and live happily ever after. The cameras keep separate memories for the lens with and without TCs.

MFA exists solely so you don't have to repeatedly try to get a 'sharp' copy. You paid for it. Why not use it?

John and Bassat- thanks for the responses.

I have gone ahead and done a test. To answer your question, Bassat, the difficulties I had in performing the test are exactly why I am considering buying another copy and comparing. If I were to guess, I'd say +8 to + 12 might be the range I am looking at here. But my results were all over the place. Perhaps I'm the only one that has inconsistent results doing manual microfocus adjustments. Plus/minus zero was front-focusing...+5 was an improvement...+8 was better yet...then +12 and +14 were front-focusing badly once again (what the heck???). That was just in one series of testing, but no series was very conclusive and despite using LensAlign, a tape measure, etc it was often hard to pinpoint what exactly was sharpest. It's easier to see the correct focus spot on a duck or goose, but those don't sit perfectly still to run a test. So I guess I need to borrow a taxidermist's work for the afternoon.

I don't have the 300 F2.8 Mk2 - I use the Mk1, but I have found the 2 x Mk3 and 300 F2.8 to be a very good combination. Mine seems to focus spot on as do all my other lenses and digital/film SLR Canons, perhaps I am just lucky?

It sounds like (as others have suggested) that you have a MFA issue. I looked into the "Dot Tune" method to confirm that my cameras/lenses were spot on - which seems to be the case.

Remember though that when making focus micro adjustments you are working on the law of averages so repeat the procedure a few times and note the results - then dial in the average offset and you should be good to go.
Let us know how you get on.

MFA is really nice. Unfortunately, it can't fix inconsistency.

Please correct me if I have read your post wrong. You say that this combination front focuses, then as you move the focus further (+) then things improve but when you moved the focus further (in the + direction) it reverted to front focusing. That sounds odd to say the least. I do not know of any way that an extender would cause this phenomenon though I understand how an extender can effect the actual point of focus.
All I can suggest is that you try the Dot Tune method (I know it has worked well for others) and if this doesn't work then perhaps a word with Canon may be in order. If we lived closer you would be welcome to try my Mk3 extender as a comparison - do you know anybody local who has one that you might try for comparison? Most photographers are pretty helpful.

I don't know what body you have, but if it is one that is compatible with Magic Lantern then you might want to consider installing and using ML. ML has a Dottune module which will automate running the Dottune MFA method. It runs the test multiple times, and averages the result for you. The default is four runs, but you can set it to do from 1 to 10 runs. The other advantage of using ML is that it offers an expanded range of MFA adjustment values. Instead of the usual +-20 range you get with the stock Canon software, ML covers a range of +-100. Running the test is really easy too. Simply mount the camera on a tripod, or secure it so that it cannot move. Switch your lens to MF and using Liveview ×10 manually focus the test target. Then simply run the Dottune test from the ML menu. Wait a few minutes while the test runs, and ML even sets the correct average value for the lens. You do have to enable the Dottune module in the modules section of the ML menu before you can use it. It is so simple to use, that as long as you can find a flat surface with some decent contrast on it (a road sign would be excellent for example) you can run a Dottune on location before your shoot. I was playing with my Sigma 150-600 on my 50D at the weekend, and I had a few issues with consistency when using it at practically MFD (9.2') and at 400/600mm, but I think that was more to do with my target than the system itself. When I moved back to 20' to run that series it seemed to work really reliably every time. I used the default 4 runs per test, but repeated them five times. I was doing the tests at the distances/focal lengths that Sigma use for the 16 point MFA using the dock. I didn't get the time to finish the whole series of tests, add them to the lens with the dock, and retest. For the Sigma 150-600 C the MFA combinations are 150mm, 250mm, 400mm, and 600mm at 9.2', 20', 40' and infinity.

Alan

Thanks again, fellas.

BigAl- DotTune sounds very interesting. I've heard of Magic Lantern but never tried it out (or really understood what it was). Would installing it decrease the value of my 1D Mark IV if I ever decided to sell it? Since it downloads to a memory card (correct?) should I try it on a less desirable card in case it messes up the card (i.e. I have tons of cards, some I rarely use as they are 4gb or 8gb whilst I prefer my 16 and 32's)?

1D series is NOT supported by Magic Lantern.

I have the 300 2.8 II and the 2x III. I've used them with a couple of 70Ds, a 7D2, and a 5D3. In general, the bare lens didn't need MFA with any of the bodies. However, with all of the bodies, adding the 1.4x III or the 2x III did require MFA. I use the Spyder LensCal as a starting point. LensCal is basically just a tape measure, but I got it free with a Spyder monitor calibrator. Therefore I use it. It has worked well for me to get a really good starting point for MFA.

After using LensCal, I do adjust in the field. Each time I go out, I take a few test shots that are representative of what I'll be shooting that day. I look at them carefully to ensure that the focus is spot-on. It usually is, although I find that the 7D2 might need plus or minus 1 step on any given day. My 70Ds and 5D3 (which I don't own anymore) rarely required any further adjustment once I was happy with MFA.

Regards, Jim