huw_evans2

It's possible, Marco. I estimate that that shot was taken from about 50m, and at that range the depth of field would have been roughly 0.5m before and behind the subject. Viewing at f/8 (with the converter) it's hard to nail the focus very precisely. Then again, that much depth of field should be enough to keep the whole bird reasonably sharp if the optics are good enough. I'm not sure getting it a few centimetres either way would have improved the shot very much.

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Here's a larger 100% crop area from that shot so you can see the wing as well - it's completely unsharpened, so try out your own settings. For me it's a usable shot, but whereas with a really good lens I would normally be willing to up-size a D2X shot somewhat, with one like this I wouldn't be keen to go beyond the native resolution at 300dpi.

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<a href="http://www.huwevans.freeuk.com/Temp/SpoonbillRadipole01Crop2.jpg">Sample 2 - larger area 100% crop</a>

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In the final analysis I do think the lens can sometimes get adequate results with a 1.4x converter, but it's very much on the limit, and hard to achieve the required standard consistently.

With some reluctance (because I'm very fond of my 600mm f/5.6 EDIF) I have to basically agree with Bjørn and admit that I've struggled to get consistently acceptable results with it on a D2X. On my D2H, and before that on a D100, it was terrific, but on the higher resolution camera it usually seems to fall that bit short of expectations - there's always a certain softness there, it seems.

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There do seem to be some conditions when its failings don't matter too much, though, so it's not a complete disaster, and certainly given how cheaply this old lens can be had nowadays I'm not sure there's a better alternative anywhere near the price. It's also very much lighter and more compact than its modern f/4 autofocus counterparts, FWIW.

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Here are a couple of examples where I've had <i>adequate</i> results from it, but unless there are samples of the lens out there that are significantly better than mine I wouldn't expect too much more. Mine is a rather beaten up old sort, with a lot of miles on the clock, so it's possible. Both of these shots were taken wide open - performance doesn't improve much one stop down.

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<a href="http://www.huwevans.freeuk.com/Temp/GreyHeronRadipole08.jpg">Sample 1 - 600mm f/5.6 EDIF</a>

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<a href="http://www.huwevans.freeuk.com/Temp/GreyHeronRadipole08Crop.jpg">Sample 1 - 100% crop</a>

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<a href="http://www.huwevans.freeuk.com/Temp/SpoonbillRadipole01.jpg">Sample 2 - 600mm f/5.6 EDIF, plus TC14B</a>

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<a href="http://www.huwevans.freeuk.com/Temp/SpoonbillRadipole01Crop.jpg">Sample 2 - 100% crop</a>

Indeed, Mark - actually I think, given the price tag, the 70-200 HSM is a far better lens than it has any right to be. I can forgive the occasional QC problem for optics like that. :-)

That lens was known to have a slight compatibility issue with the D100 (and I think one or two of the film bodies), and indeed mine would lock up occasionally, giving an 'ERR' message on the LCD. It was cleared by powering down and back up again.

 

However, I have used the very same lens extensively with a D2H and more recently a D2X and never had a single problem. I was under the impression that of the digital bodies only the D100 had any problem with that lens. YMMV, of course.

 

OTOH, the lens I've shot with for the last four years was the second one I had - the first one had an aperture that was so badly calibrated that it was about 1/3 of a stop out at f/4, and got progressively worse until f/22, at which point it was a full stop out. The second one was also slightly out, but within 'acceptable' limits. So I'd recommend checking the lens very carefully before deciding to keep it.

I didn't even get an e-mail. I checked my address as advised earlier in the week and everything was okay, but still no e-mail. I tried the 'forgot your password' option and still no e-mail. There is a <a href="http://www.largeformatphotography.info/forum/sendmessage.php">Contact Us</a> link at the bottom of the main forum page, so I've tried that. Have to wait and see now.

I've got a couple of these and have partially disassembled them in the past - both front and rear components definitely have more than one element. I can't recall anything more specific than that. I don't know of any source for optical diagrams for them.

I use the 60mm Micro-Nikkor on a D100 and D2H, and I can't fault it - it's a very fine lens, with no significant aberrations or colour fringing that I can see. I've no idea about the Sigma though. I also use a Tamron 180mm Di macro lens for when I need greater working distance from the subject, and that too is a superb lens.<br>

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Here are a couple of samples with crops from the 60mm:<br>

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<a href="http://www.huwevans.freeuk.com/Pictures/Blackthorn_1567.jpg">Sample 1</a><br>

<a href="http://www.huwevans.freeuk.com/Pictures/Blackthorn_1567_crop.jpg">Sample 1, crop</a><br>

<a href="http://www.huwevans.freeuk.com/Pictures/DSC_1485.jpg">Sample 2</a><br>

<a href="http://www.huwevans.freeuk.com/Pictures/DSC_1485_crop.jpg">Sample 2, crop</a>

It does cover 8x10, quite adequately, though I suspect Bob Salomon might tell you that it's not designed to, and that the halation won't be right. I like it well enough though.

I have an FM3A and a couple of F2's, as well as an EL2 (labelled 'Nikon' but really the last of the Nikkormats), and I'd have to say that there is no comparison at all between the FM3A and the earlier cameras, which are vastly more solid. The FM3A is comparable with the other FM/FE series cameras. Of course it might still be tough enough for almost all purposes, but certainly if you're looking for the robust feel of an F2 it will disappoint.

'<i>...the APO Grandagon 55mm has a flange focal distance of 67.6mm. It seems that this is a retro-focus design...</i>'

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That doesn't mean it is a retrofocus design - it is quite normal for the flange focal length to be greater than the focal length. You know the lens is retrofocus when the <i>back focal length</i> (i.e. the distance from the focal plane to the nearest point on the glass when the lens is focussed at infinity) is greater than the focal length.

The difficulty in making deductions based on looking at an end product like a print is that there are generally many links in the chain, and so you cannot necessarily attribute what you see to a difference in one particular link.

 

Someone correct me if I'm wrong, but I think the Super Angulon XL lenses that Roger Hicks mentions use aspheric elements as part of the design. At the very least that means that they differ from the older SA's in more than just retrofocus/non-retrofocus design.

 

As with others I'm not aware of any retrofocus LF lenses that would be more directly comparable to the non-retrofocus designs we are used to. However the comparison can certainly be made in smaller formats.

 

The same caveat applies though - if you are seeing a difference how can you be absolutely sure that it is really due to the retrofocus issue, and not to other factors? With that in mind, I know that in the only cases I can cite from my own experience the non-retrofocus lenses produce negatives that are generally sharper, with visibly better acutance and contrast, than the retrofocus ones. I can't comment on the distortion issue, as I rarely put straight lines at the edge of frames.

 

So, all in all I prefer the negs I get from my Mamiya 6 and its 50mm lens to those I get from my RB67 with its equivalent. And I prefer the negs I got from my Contax G2 and its 28mm Biogon to the ones I get from my Nikon SLR wide angles. But there's the rub - some of the lenses for the RB67 have been severely criticised over the years, whereas the lenses for the 6 seem to be universally praised. So are my better negs due to the retrofocus issue, or are the 6 lenses just better designed, or made with better QC? And is the Biogon design always inevitably better than any retrofocus design, or is the Zeiss glass just generally better than Nikon's?

 

Actually I suspect all of those things are probably true. But the only thing I can say with any certainty is that despite having the choice of systems, I've never yet looked at a subject and worried about whether the wide angles in my bag were retrofocus on non-retrofocus.

The aperture coupling lever is only tensioned by a small spring. You can get at it by removing the black cowling that surrounds the rear of the lens. It might be necessary to remove the bayonet mount itself to do this - the lenses do vary somewhat in their precise construction. Generally all of this is quite easy with suitable jeweller's screwdrivers.

 

If the lever has gone slack that presumably means either the spring has broken, or has jumped off its mounts, or has stretched (unlikely). Obviously the solution to the problem depends on exactly what you find when you get the cowling off, but you might need to get hold of a suitable replacement spring. If it has simply come off its mount then putting it back on is a simple but rather fiddly job. A spring that has stretched, or deformed, or even broken, might be made sevicable again by teasing out a couple of coils of the spring to make a new hook on the end, so that it can be mounted again.

Certainly - I've used mine for that purpose quite happily for about ten years. The floating elements mean that it is adequately corrected at infinity, and if you are stopping well down as is typical in landscape work then I doubt you will have any problems. I'm not sure what it would be like wide open at long range though - I've never tried it.

I'm seriously confused here. I've visited the Photodo site many times, and have just checked it again, and not a single RB lens of any description has been MTF tested. Not one. Am I missing something?

I've never used an 'S' type Sironar, but if you look at Rodenstock's own MTF curves for the two types they don't generally support the idea that the S is sharper than the N except out at the extremities of the circle of coverage (and of course this is larger for the S).

 

For the focal lengths I have checked (150mm, 240mm, and 360mm) the N versions look to be marginally better from the centre out to maybe 2/3 or 3/4 of the way to the edge. Whether this would make much difference in practice is open to question, though.

Just to confirm what has been said, I have the 360mm Imagon and it is <i>much</i> bigger than the opening for a #3 shutter. Your best bet is something like a Packard shutter or, as I use, the old black card and ND filters. Rather conveniently a standard 77mm filter is a fairly close fit inside the disc, so you can quite easily cut the light down far enough to make the card method adequate.

With no disk at all you get just a very, very soft focus image, which can be quite nice in some situations, but it is rather extreme in general. Yes, the disks can be used fully closed, and can give quite a sharp image in this way, although obviously not in the same way that a conventional lens would - the result is still quite 'creamy'.

I think the point about shutter accuracy with respect to different apertures is probably a reference to the fact that, since the blades of a shutter take a finite time to fully open and again to fully close, the aperture in use can make a difference to the <i>effective</i> speed of the shutter, even if it is perfectly adjusted and totally consistent.

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For instance if you set f/64 the aperture will be fully uncovered sooner than if you set f/16, and likewise it will begin to be covered later. The shutter is then <i>in effect</i> slower with a small aperture than with a larger one, even though there is no real connection between the mechanisms. This could mean that using f/16 at 1/400s would transmit more light than f/64 at 1/25s.

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So goes the theory. In practice if you never use the faster speeds I cannot imagine that the problem would make any real difference. I have certainly never noticed it, but then I am fairly relaxed about these things.

Somebody <i>forced</i> you to read it, Triblett?

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Anyway, a last word from me. I've finally had a good look at the Rodenstock DoF calculator, and I was interested to note that like Merklinger, Martin Tai, and me, Rodenstock also, it seems, cannot cope with basic optical theory and elementary mathematical manipulation. Makes you wonder how they ever managed to produce all those lovely Apo Sironars and Grandagons.

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There's a vague notion lurking in the back of my mind - something about morons standing on the shoulders of dwarves, but I can't quite get it into focus. If only I'd known that '<i>the 'vertical' component of near DoF rears up in the air as the lens is stopped down, when the plane is steeply tilted</i>.'

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Anyway, that brings me to my final word on the subject, which is to suggest, Pete, that you go back to the word 'surprisingly' in your post of July 9th, 05:42am, and work from there. You seem not to have heard the cacophany of alarm bells that should have started ringing in your head at that point at least, if not long, long before.

No, Pete's graphs are not correct - the DoF calculations for rigid body cameras have no relevance to the situation we have when the film plane and the lens plane are not parallel. They would be correct for objects lying on the lens axis, but nowhere else.

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The attached diagram shows why. I'm afraid it is a bit rough and ready, but it illustrates the point nevertheless. It is meant to show the change in the DoF situation for an off-axis point source when you apply a rear swing/tilt and refocus to keep that source in the psf.

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The conventional formulae for DoF assume that the lens and film plane are parallel, and cannot be applied without extensive modification to the swing/tilt situation. If you move that point source out to the indicated DoF limit its CoC is very different, simply because the film plane is no longer where those formulae assume it to be.

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<img src="http://www.huwevans.plus.com/CoCDiagram.gif">

Actually I don't think I made things quite as clear as I should have:

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With the <i>largest disc</i> the cut off begins sooner, but ends later. With the smallest disc it begins later, but is completed sooner. I know that is somewhat counter-intuitive, but that is how it happens.

I have a 360mm Imagon which I use on 8x10, so it is not quite the same as your situation. However, what I would say is that although the disc in use may give a notional f-stop of, say, f/11, that clearly doesn't mean that the light passage through the lens is restricted to the same narrow channel that a conventional iris would give.

 

In short, as soon as even one of the outer holes begins to be covered by the lens barrel you will have some light fall off. Whether you feel that is significant is up to you. Because the disc fits right at the front of the barrel, when it is open you will get some light passing through right up to the point where the last hole is covered by the rear rim. However if the disc is closed the cut off will happen much sooner.

 

So, the absolute limits will be different for each disc, and according to whether it is open or closed - with the worst case being the smallest disc in the closed position.

 

I can certainly use my 360mm and not notice any undesirable uneven illumination, and that with any of the discs, so it may just be less of a problem than you fear.

My RB sits very happily on a Manfrotto 075B. IIRC I paid about UK£125 for it, but that was about 10 years ago. I don't think the price has changed dramatically in that time though.

 

As for how I like it, well the fact that I'm still using it after ten years says it all. I have absolutely nothing to say against it - it is an excellent, versatile, and very robust tripod.

Pete, what do you mean - '<i>Do some of the calculation for yourself for a change</i>'? I did, before I even entered this discussion. Scheimpflug is a corollary of the thin lens equation. The plane of focus transforms into a tilted plane. DoF limit planes transform into tilted planes.<br><br>

 

Who mentioned the 'focussing distance to the edge of the field'? I am simply pointing out a massive apparent error in your understanding.

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With regard to your easy 'proof' - the DoF with a 150mm lens focussed at 22m, even assuming a maximum aperture of f/5.6, will be so great that I cannot see any possibility of verifying field curvature in the way you describe - perhaps with some sophisticated instrumentation, but with what I have - no way, not even if I focussed a lot closer, unless you are claiming an <i>extreme</i> level of curvature. In that case, I return to what I said before - generations of photographers have been getting flat planes of sharp focus and nothing has changed.

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Perhaps you could be more specific about the measurements you took which you think prove curvature.

I'm sorry Pete, but I can only echo what Martin has said - '<i>you are really confused</i>'. The distances are measured <i>perpendicularly to the lens plane</i>, and hence the cosine factor.

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Your weekend example could be expressed a bit more clearly, but I can't see that there is necessarily anything wrong with your measurements - you just haven't demonstrated that the transformed plane of focus is anything other than a plane, which is what you now seem to be disputing. That it <i>is</i> a plane is a straightforward corollary of the thin lens equation, and for those who don't like doing the mathematics it is trivial to verify experimentally, and photographers have been doing just that for generations.