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Leaning Pics


1 Jan 2008 11:14PM
What I am referring to is not the actual performance (functional) testing and final inspection, but the parts manufacturing tolerances designed in.

For example, the focal plane, where film or sensor receives the rays of light, needs to be where the the rays of light are focused within tight limits.

If the positional tolerance of the plane is greater than the depth of focus with any particular lens then the image will not be sharp.

The tolerance of the focusing screen plane must also be within be within similar tolerance, to produce a sharp image.

The mirror has to maintain the same distance, from lens optical centre to the focusing screen, as for the lens optical centre to focal plane.

If these three items are within their specified tolerance then the final image will be sharp.

The the focusing screen needs to be 'level' with the focal plane within a given angular tolerance, otherwise the problem originally complained of arises.

It is probable that some these tolerances will be on a 'True Position Tolerance' which broadly means that as a group they have to hang together as a tightly toleranced bunch - no undue build up of tolerances being permitted.

Which is probably why mirror boxes are often made as a separate assembly.

These tolerances are somewhat tighter, I believe than normal engineering tolerances, though these may applicable other parts of the body.

The above is a somewhat simplistic view of the situation, but (hopefully) some use in understanding the issues involved, for the first day of the new year, at least!.

The situation is made more complicated by the auto-focusing requirements of modern day cameras and the use of digital sensor in lieu of film.

jas

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1 Jan 2008 11:21PM

Quote:Being serious (for once ), I do find it strange that, with today's automated assembly lines, they can't get something as critical as this right. It makes you wonder what else might be out of tolerance.


They must endeavour to get their Statistical Process Control in order!

Assuming the have got the design right in the first place.

Also, if the sensor is outsourced, its tolerance may not be within their direct control and may accepted on a batch sampling routine, although this somewhat 'old hat' nowadays.
1 Jan 2008 11:36PM
Well, good night everybody. Smile
I was just going to bed when I saw Pete's query on mfg tolerances! Grin

Thought that I was on the shop floor again after seven years + retirement! LOL!

jas
Pete e2
13 18.7k 96 England
1 Jan 2008 11:38PM
Thanks Jas. I knew you'd have some logical explanation to this. Much appreciated. sorry to pull you back out of retirement Wink
Tooth e2
9 5.8k 227 Ireland
2 Jan 2008 2:19AM
Good to get some straight answers Wink

sorry, off to bed .....
2 Jan 2008 10:06AM
I enjoy it really, Pete. Wink

Morning all! Grin
macroman e2
11 15.3k England
2 Jan 2008 11:15AM
All these manufacturing tolerances are just as important with a film camera, but this seems to be a recent prob with some digitals.

Are manufacturers relaxing their standards because they know that many 'togs will upgrade to the next model with it's new 'bells & whistles' every year or so?

DSLR's are almost becoming disposable items with some tehnophiles, who must have the latest model in the vain hope that they will take better pix.
KenTaylor e2
10 3.0k 2 United Kingdom
2 Jan 2008 12:59PM

Quote:DSLR's are almost becoming disposable items with some tehnophiles, pix.

It does appear that way although disposable income is now greater than it was 20 years ago. Without the desire to have the latest there would be less room for development.

Thank you Jas for that explanation which was most interesting while unfortunately the OP gave up some time ago. I recall that darkroom enlargers needed to be aligned in situ for optimum results although many ignored it.
Ken
6 Apr 2008 6:19PM

Quote:It's not just me that's had the problem other Pentax users have also had it. If you check out the Pentax Users web site you will see what others have said about it.
I'm surprised to hear that there does'nt seem to be anyone on this site with the same issue.



Yer have the same problem with my k100D you need to be real careful whem framing shots of sea and sky line or edge of buildings and uprights. Think it's just a case of trial and error mate till your happy with the result dont have any suggestions to what causes the problem in the first place though sorry.
17 Apr 2008 4:19PM
Does anyone know if pentax has corrected this problem in there new camera. I have just been to Durham to try out a new lens and found it very tricky framing some shots due to the tenency to lean of the verticle and horozontal planes. You have to be real careful and I found I needed to re take shots more than once.
Chrism8 e2
8 753 14 England
17 Apr 2008 4:28PM
I don't really see much of a problem with my K10D, When shooting landscapes ( without a tripod ) I'm no more than 0.5 of a degree out and I put that down to me rather than the camera, just adjust the horizon with software and give the shot a minor crop.
Pete e2
13 18.7k 96 England
17 Apr 2008 4:42PM

Quote:Does anyone know if Pentax has corrected this problem in there new camera

Yes the K20D has been improved, based on us telling them that it wasn't straight. See Matt's review of the K20D here
Numpty
6 33 Wales
17 Apr 2008 6:01PM
could be because they never used longitutude and latitude with a Henderson/graham accurate timepiece.
17 Apr 2008 6:36PM

Quote:QuoteGrinoes anyone know if Pentax has corrected this problem in there new cameraYes the K20D has been improved, based on us telling them that it wasn't straight. See Matt's review of the K20D here


There has been some debate regarding the sensor having a slight sloping to it. Aligning the top of the frame with something straight such as the top of a picture on a wall will give a result of a slightly lop-sided image. This is an issue with the *istD and the K10D and still remains apparent on the K20D. I have contacted Pentax regarding the problem and, at the time of publication, they are looking into it before giving me a response, so watch this space.

Still not sure by the above that the problem has been resolved.
Pete e2
13 18.7k 96 England
17 Apr 2008 7:28PM

Quote:Still not sure by the above that the problem has been resolved.

Yes it has been resolved. Sorry I thought my answer above said that.
Just in case: the Pentax K20D has a straight sensor. Or at least the one we have has, as reported on the video review.

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