There are thousands of 'opinions' and 'lots' of experience examples regarding fine tuning of both prime versus zoom lenses but as you only mention your zoom why not just concentrate on that?

Firstly how have you come to the conclusion that your zoom 'may' be out?

For the past month both my cameras and all lenses now live in a humidity controlled cabinet, https://www.bhphotovideo.com/c/product/1282132-REG/ruggard_edc_80l_electronic_dry_cabinet_80l.html all other odds and ends in sealed plastic boxes.

Living by the sea with very high humidity (97% today) I'm now a much happier man.

That's exactly it.

The light is what it is, if you can take advantage of positioning, good, if not, just learn how far you can push things in camera and be reasonably confident you can pull it back in post should you get a worthwhile capture.

Some thoughts.................

The image shows a fair amount of noise, ISO400.
A flower that that may be subject to movement caused by breeze is not an ideal test subject.
You do not say if this was shot hand held or on a tripod.

Put the camera/lens on a tripod, shoot in Raw, focus on a static subject that contains fine detail/edges manually using Live View if you have it, use shutter delay or delay timer with remote if you have one, shoot at base ISO at widest and one and two stops down.

If the sharpness is not acceptable after undertaking basic Capture and Output sharpening the lens is no use to you.

Thank you for the update, it's always good to hear when a problem cause has been found.

Now we can see the Exif that eliminates that possibility, time for some static testing.

I have a Nikon setup and with my TC 1.4 on both a 70-200 and 80-400 it requires max fine tune adjustment but even without it you could easily see by the grass where the focus was but there's a massive difference between left and right sides here.

It appears in this shot that the guy centre and the guy far left (sharp) are basically on the same focus plane, suggesting 'movement' may be your problem with this example.

I suggest you undertake testing with a static subject using a tripod to assess results, which may also show any possible front or rear focus issues with the TC attached.

Having recently been experimenting and learning star/star trail photography one of the main concerns regarding lens selection that many talk about is the 'coma' that it exhibits. 'Coma' causes the stars at the edges of the frame to no longer be round but appear triangulated like flying saucers.

There seems to be a consensus that the Rokinon/Samyang primes are favoured so it may be worth you investigating this further whilst comparing options.

On the assumption that you 'only' have the D300 and the 18-200mm and this combination is not Auto focusing, apart from the AF switch positions already mentioned have you 'inadvertently/unknowingly' changed settings to make the AF/ON rear button (BBF) activate AF and not the Shutter button?

Here it is once again 'rationally'.

Your superimposed lines are meaningless on the examples you have given to 'support' your case because they are so poorly aligned and minor misalignment's at source will be greatly exaggerated at their vanishing point.

For info, linear perspective analyses are valuable IF undertaken with a degree of accuracy.

Now, where's the answer to the location of a difference of "inches" which you stated 'supported' your assumption that it 'proved' the perspectives between images were different?

I tried the 'theory' for myself, have provided examples. Have also shown that your 'nitpicking of the results is flawed, but have not asked anyone to accept my word. Should you have actually read any of my posts you would note that I have remained non-committal.

I'm still awaiting your explanation of where this "inches" difference is. Can't you explain it, or do you expect me to take 'your word'.

You can't have things all your way, if you are going to make definitive statements in a discussion you need to be able to back them up. I await your explanation.

I would have hoped that if you are so qualified you would have been able to give a credible, technical and quantitative reasoning as to why the perspective has altered between two images. I'm sorry but a few poorly aligned drawn lines prove nothing to me.




You are correct, "placed" and "not extremely accurate" are what you have produced.

I do not refuse to do anything. As a practical and technical person I understand the futility in attempting to place lines on these images and make conclusions as to differences in perspective/vanishing points. Your own examples have clearly demonstrated the obvious, it's a far too inaccurate method.

But what I have done is given two real world examples that demonstrate the actual results obtained. I consider this a far more 'accurate' real world representation of a test especially when it reveals the alignment (equivalent to your line effort) between three points of, 3.5m, 720m and 14900m camera to subject distance spaced within the framing.



It was a very simple question, so why have you not answered it? Where is this "inches" difference?



So you would prefer others just accept what you say and disregard your errors? There is a major difference between 'an explanation of perspective' and trying to produce 'evidence' that there is a difference of it between two images.

Angry? you seem to want to read things into my posts now.

You have still not answered b) how you consider a 'line' placed against a couple of decking boards and projected some distance represents accuracy.

And yes, I certainly do question your methods and it does not require an expert on 'perspective' to know that your example results of the placement of coloured lines aligning against parts of those images are extremely poor and do not provide any acceptable reasonably accurate evidence of 'perspective' change in this circumstance with relation to vanishing point.

Here's another pictorial example of your 'poor' alignment you have based conclusions on.

And as for this one, quote "BTW, that the post itself is of a different size in the two pix, a matter of inches, is further proof, if you understand perspective, that the images are distorted." Really, where are these "inches" difference?

(Download)

I don't think there are any 'arguments' here.

It appears mainly a frustration by many to get from Bob some realistic evidence or technical reasoning to support his statement, because all he has put forward so far are some very dubious red and blue lines on others images proving nothing.

But they are not difficult questions, and a lack of a straightforward response will raise further questions.

Hopefully, it's not that the consequences of sloppy work with respect to a result are not appreciated.