vasilis

<p>to Michael, I am not discounting your experience at all. A zoom lens will have a more complicated bf/ff signature because out of focus - in focus regions are affected by focal length. So any AF adjustment will not help you because it will work one end of the zoom but not the other. <br>

But what I said was not about experience, and again I am not discounting yours, it was about how the lens-camera system works. Let's leave zoom lenses aside that are more complicated and we do not undestand them maybe and think of a prime lens. The camera will decide where the lens is focusing properly, the lens does not affect this decision in any way, and then the camera will take the picture. It cannot be the lens's problem ....</p>

<p>To Laurentiu,<br>

I understand that AF was off in other models, what surprised me was that manual focusing was off. Also the article from the lens rentals, I do not understand it. A camera may front-focus or back-focus, but a lens cannot. Meaning a lens may have a problem with a non planar focal surface (most of them have by design) or by being decentered etc.. However it cannot have the problem of front-focusing or back-focusing: the camera decides and stops the lens when it is in focus in autofocus mode, or your hand stops the lens when you think it is in focus in manual focus mode. If afterwards, the picture is soft it means that the distance mirror-sensor is different to the distance mirror-AF sensors or mirror-viewfinder (in the case of manual focusing). What I do not understand is why the camera industry thinks that we should be tolerating cameras that font-focus or back-focus, there is a general acceptance, that this is so common that it is ok!. I do not understand that, absolute 100% correct focusing is a basic requirement for any camera.<br>

Also for the focusing aid, the only way to do it is to focus in the center and then pan and hope that you have not changed your distance to the object!</p>

<p>Hi Garry,<br>

Now, I remember why I have not posted for so many years in photo.net or any other photographic forum. People are so happy to give plenty of wisdom or credentials. Well, if we are applying for a job my credentials are that I have a BSc in Physics, an MSC in Optical fibres and a PhD in optics and lasers. I am an academic with research in optics, lecturing electromagnetism, also I use cameras in the lab, attached to microscopes for laser beam profiling. When I write down that the k7 had focusing problems, I know that it had and this was not my question. I do not care if you shoot pentax or whatever for the last 7000 years, if you own 10, 20 or 50 lenses. The reason I wrote the post was not to be lectured on the difficulty to do a correctly focusing camera, it was only to see if other people have experienced similar problems with pentax.<br>

I am sorry for taking the space and thank you very much!<br>

Vasilis</p>

 

<p>Peter, all your comments are valid and as you would expect the testing in the shop was not scientific, but it was enough to make the dealer mad! However the errors that you describe or the difficulty to manual focus would make the tests to give random results meaning that the focus point would be random, but what happened was that all the lens-body combinations manual or auto focus gave the same consistent slight front focus which was apparent at low apertures (1.4 - 2.8). On the other hand live view focus gave correct focus (as you would expect). Now, for this to happen, the only logical assumption is that the distance between mirror and focusing or phase sensors is the same whereas the distance mirror-sensor is slightly different.<br>

I am not saying that all pentax k7 have the same problem but I would be interested to see if other customers, especially in the UK had the same experience. Don't think I am happy to have this adventure, I would very much prefer for the K7 to work, if not for anything else, this zeiss planar was an amazing lens!<br>

Vasilis</p>

 

<p>Whatever I wrote to the post was true, I have tested 4 pentax k7 bodies, 1 of them had a malfunctioning e-dial and I did not check the focusing and 3 of them exhibited front focusing. This is my experience, your conclusions from this story maybe are different than mine.<br>

I do not really care if other companies have the same problem, fine focus adjustment solves the problem for the focusing in the auto focus sensors but not in the manual focusing case. If you believe that a camera that does not manual focus properly is acceptable and you would have kept it, then probably we have different expectations from cameras. The reason though that I wrote the post is to see if other people had a similar experience.</p>

 

<p>Hi all,<br /> It has been a long time since I have last contributed in photo.net. The reason I am writing is my adventure with Pentax k7. I live in England and at the beginning of November I decided that my cameras needed a total upgrade, I had a nikon d70 with some lenses, flashes etc (24-120, 50, 10-20, sb600). I decided that I would like to go for something different and try Pentax k7.<br /> I started the process of selling things in ebay, I bought the first pentax k7 from Amazon, which had a non-functioning main e-dial, with also a tamron 17-50mm 2.8 and a afg340 flash unit. I returned the k7 to amazon and then got a new one from amazon. The k7 came and seemed to be functioning ok except I found the focusing, to be not slow, but unreliable. Meanwhile we had our newborn son, so although I did snap photos of him I never took the time to look at the photos in any detail.<br /> But I was not exactly happy with the setup, I started realizing that the 17-50mm focused at different focal planes at 17mm and 50mm. I suspected that this was due to camera because I can not understand how a lens can back-focus or front-focus since the camera decides focusing. I sent the lens back, starting to be prepared for the worse. I found in a shop called SRS a Zeiss 1.4 manual planar lens and I ordered to check the camera. Since it had 1.4 aperture and was fixed focal length I thought that it would show problems with the camera. The lens arrived and the camera front focused using the manual focus and also front focused using the autofocus, autofocus and manual focus agreed with each other but the sensor did not agree with them. This would mean that the sensor plane is at a different distance from the mirror than the autofocus and the focusing screen is! I called the shop (SRS) and they told that I should bring the camera to them and test it. I visited the shop where the responsible confirmed my theory; we tested a different lens, the camera was doing the same thing. Then we opened two other pentax k7 cameras and tested lenses on them and they all behaved the same way. They front-focused enough to be detected at apertures 1.4 up to 2.8 at 50mm! We concluded that pentax has released a series of pentax k7 bodies with wrong distances in the sensor plane! Most people will not complain because at 2.8 you can tune it with the AF fine tune and at 3.4-5.6 where the kit lens is it is not apparent.<br /> SRS is maybe the most important dealer of pentax cameras in the UK, I have to note that the sales person that was dealing with me had for his personal use a nikon (although this is just a juicy detail). I bought there and then a used nikon d300 returning back to the company with which I was at the beginning but with significant losses as all my nikon items are sold to ebay. I returned the pentax k7 to amazon and they refunded me, I am still waiting a refund for the lens and now I have to find what I will do with the flash.<br /> Now with the Nikon d300, I do not have all the nice things that I would with pentax (eg vibration control) but I have a camera that reacts to your inputs in such a way that you can trust it. This sounds like a very general criticism but it is absolutely true! I am writing to communicate my sadness towards pentax as in paper their cameras seem fantastic on paper but with their quality control they have lost a customer probably forever. Mainly though I am writing to see if other people had the same experience, it seems like a significant number of pentax bodies could be affected, although it may be a characteristic of the bodies imported in the UK!<br /> Vasilis</p>

<p> </p>

this is a joke?

I have a 24-120 and now that you mention it, I have as well the impression that this lens moves more than others. And as you said maybe to a point that it seems too much to be normal. BUT, as the previous poster said, if it has correct focus and image quality I would not let it trouble me.

As you have said they are almost the same all of them. For me how you feel them on your hands should be the most important. KM 5D has the same high iso performance with the d70 (I have them both). Rebel XT I do not have it but from what I have heard should be slightly better. But as I have said differences are minimal in image quality so for me handling is the most important thing.

hey can I sign up now? hey can I sign up now? heeeeeey

Peter, people in the road are needed, even if they have a childish view of the world.... they work for us that we stay at home.... :-)

I would like to play this game of "print swap" as well, but I do not know the rules (I did not follow the game from the beginning). What should i do to play ? :-)

to be honest for most people the 18-200 will be much more useful than the 28-70. There is no better lens. If someone wants one lens to do it all then the 18-200 is definetely better. It is all a matter of personal taste. I like shallow depth of field but the 28-70 2.8 for me is useless on a digital camera (and extremely useful on a film one). With the range it has (42-100) on a digital camera is like bying an expensive and not very bright prime.

 

If we were talking for the 17-55 2.8 (or something similar) then things are different.

<img src="http://d6d2h4gfvy8t8.cloudfront.net/3527783-lg.jpg">

<img src="http://d6d2h4gfvy8t8.cloudfront.net/3382529-md.jpg">

Nice thread the one you mentioned Eric ;-)))

You are a breath of logic in this forum. come baaaaaaaaaack!

Thank you, and you are right Takaaki had always good nightmare staff... he left from photo.net as well?

<a href=" title="Photo Sharing"><img src="http://static.flickr.com/34/73853792_0c09447f31_o.jpg" width="751" height="563" alt="IMG_0248" /></a><p>

 

<a href=" title="Photo Sharing"><img src="http://static.flickr.com/34/73853822_c6ce3206b5_o.jpg" width="718" height="539" alt="IMG_0249" /></a>

I would get the tokina 12-24 instead of the sigma. And if you are interested in VR (I am) you should get the 24-120VR instead of the 18-70. I would also go to a shop to handle the camera before I do all that.

I know that these things about novels and music sounds off topic. But every time someone reads a novel he gives the time for it like he enters a museum. So maybe these forms of art are not affected that much from our oversaturated age.

 

Eitherway, the problem is that the amount of information that we accept each day is enormous compared with past eras. We give our time in accepting and rejecting information automatically and almost no time to thinking. This rejection process goes to automatically erase information about wars, people that are hungry etc. Sometimes I doubt what is more bad, watching the news or watching commercials. Most people if they see a picture of a dead child from hunger they will just automatically erase it in a msec and continue. Each one of us has seen thousands of pictures from wars and human distress and this is the perfect way to become a cynic.

 

Photography is based (partially) on directness and surprise and cynicism is its worst enemy, how can you surprise a modern cynic?

Bruno, you cannot compare a museum to the web. It is normal that something in a museum will get more attention if it is a painting or a photograph. If you put paintings in a rating queue then it will be the same thing. Apart from that I think that you have a point because our age is oversaturated with images ... Paintings and photos apart from that are a parallel process, all the signals come at the same time. Music and novels, for example, are serial and they "require" a certain amount of time and attention.

I do not think that it makes a difference for photography, actually nowadays is a step backwards like using an old typewriter instead of a modern computer. But if someone likes to collect beautiful things and has enough money I think they are very pretty.

Nothing bad with creating a more "aesthetic reality", photography and generally arts are not necessarily for recording the truth. All arts and in the end a lot of other human activities are trying for "completeness" or "truth", but this target is difficult or impossible to achieve. Paintings and photos try by images, music by sounds, novels by using words etc.. the goal always is to let know someone else what you felt at the time (more or less). For my part I think that the most sophisticated tools are not pictures but language and music.

I just bought a LaCie last weekend. If I have seen your posting I would have gone with your suggestion.