Canon x3 lens sharpness & 16X Manual lens+adapter BACK-FOCUS issues

[Tony Davies-Patrick]

I’ve just been experimenting with the OPTEX Wide Angle X.7 Multi-coated converter fitted to the Canon 16X Manual lens.
I bought the Optex converter as a deal with the XL1s, along with the 16X manual lens, so I obviously would have preferred to keep it than buying the X3 lens, but I always strive to own the sharpest optics available to me (at decent prices of course) - although the ‘soft-focus’ issues of the Canon X3 lens made me have doubts if it would be worth buying one, and would I see the difference in quality compared to the Optex?

The first time I tried the Optex converter it looked a bit ‘fuzzy’ when attached to the 16X lens - (This surprised me, because the Optex is a big chunk of multi-coated glass and quite expensive to buy seperately, so I was hoping for decent quality ). If I pressed the rocker switch on the XL1s to zoom the 16X lens slightly out of full wide, it would snap into focus, but then it would be only showing a frame similar to the 16X lens set on its widest without the converter – so obviously not worthwhile!

I noticed when the 16X lens’ ‘back-focus’ was out of adjustment, the converter seemed to look slightly better at full-wide setting (By the way, the Optex 0.7 adapter is a ‘fixed’ lens converter at the wide-angle setting and will not maintain focus throughout the zoom range.).
However, I was still not happy with the ‘soft’ focus with the Optex attached. I thought that maybe the thickness of the 72mm UV filter could be making a difference, so I removed this, and although I noticed an extremely slight difference, the focus was still soft.

I removed the Optex conveter, double-checked and then carefully adjusted the back-focus of the 16X manual lens so that sharpness was maintained throughout the zoom range using the servo. I then reattached the Optex converter to the 16X lens. Result? – the focus looked even softer than before!

I then tried to adjust the back-focus of the 16X lens at its widest setting with the Optex wide Angle adapter screwed to the front. Hey Pesto! – The lens clicked into perfect sharpness throughout the frame! - Very little barrel distortion, great colour, and superb sharpness for a converter.

The only downside is that I I will need to adjust the back-focus every time that I attach the 0.7 Optex converter to the 16X manual lens, and then re-adjust the back-focus again when I remove the Optex converter for normal shooting.
However, at least I have the option of maintaining the very sharpest possible focus on both the 16X manual and the Optex converter – which is more important than the hassle of needing to adjust back-focus.

I feel that if I had actually purchased the autofocus 16X IS lens I would have experienced the same ‘soft’ focus problems with the Optex, and sold it without realising that back-focus was the problem.

This discussion on the back-focus problems of the 3X lens with the XL1, XL1s, and XL2, and the different plane of sharpness it seems to obtain with each body, would indicate to me that maybe lack of a back-focus adjustment could be a contributory factor into why the X3 lens is often soft at some settings within its zoom range. See here:

http://www.dvinfo.net/conf/showthrea...r&pagenumber=2

The lack of ‘fine-tuning’ with the autofocus lenses, and the results of turning what I at first thought was a ‘soft’ converter lens into a sharp one, simply be adjusting back-focus on the 16X lens, has given me even more doubts about buying the 16X, 3X or 20X AF lenses.

[Richard Alvarez]

Tony,

For what its worth, this is mentioned on the OPTEX website.

____

The adaptors are easy to use; simply set the lens to its widest angle of view, attach the required clamp ring to the lens and then
screw on the adapter(s), on broadcast lenses you must use the back focus or macro adjustment to achieve focus. No exposure compensation is required as there is no significant light loss through the high definition multi-coated glass elements.

N.B. This adapter does not allow the zoom to be used and only works at the wide end of your broadcast lens. Use of this adapter with the Canon XL1/S 16x standard lens will permit zooming of 10x (approx) through the zoom range.

[Tony Davies-Patrick]

Thank you for that information, Richard, and it WAS worth a lot!

I didn't get any instructions with converter when I bought it with the package, and never assumed that I needed to adjust the back-focus continually, and even the guy I bought it off said it didn't work in zoom mode at all on the 16X manual.

However, I've just given it another trial, and by re-adjusting the focus using the back-focus pin instead of the actual focus ring on the 16X lens, as I zoom in, the lens+ adapter clicks nicely into focus.
Great stuff! now I at least have more scope with the set up. When I'm working in a boat, for example, I can just leave the
Optex converter attached to the 16X manual lens most of the time, and just focus using the back-focus knob in conjunction with the rocker switch. Then, when I'm back on land and need the full scope of the 16X telephoto, I just remove the Optex.
Things are looking more rosy! I'll give the set-up a thorough work-out on boats etc, over the coming weeks.

[Chris Pettit]

I have a standard XL1sII servo lens with the Optex x.7 wide angle adaptor and although I have no sharpness problem, I do have flare problems when working into the light (which is quite often). A flag works well when mounted on a tripod but not when hand held and I have wondered about buying the X3 wide angle lens. Are there fewer flare problems with this lens?

I have also wondered about buying the x16 manual lens for its better focus 'feel'. But it sounds as if I would have all the same flare problems if I used the Optex x.7 with it.

Any comments?