Pentax 100mm Macro

Don't forget that the human eye has a variable amount of accuracy. Tests done in the 1970s showed that the point of focus varied quite a lot each time a photoapher manually focused a camera.

This might be as accurate as you can hope to get.

Looking through the viewfinder at the tape you can actually see that the eye has a "depth of field" everything between say 90mm and 110mm looks in acceptable focus. It's less of a problem at 2m and beyond because you can't see the difference because of the depth of field in the finished image.

shim

Just had a look at this site and the depth of field for a 50mm lens at f/2.8 and 1.5ft (450mm) distance is only +-3mm. I've repeated the test with the 100mm Macro at double the distance and the results are the same..... Back focusing on manual and AF by 5-10mm which means the K10D is about as much use as a chocolate fireguard. I think I'll start looking for a Canon

shim

You can't back focus on manual. But the eye isn't accurate enough to judge. The focusing screen has to be in the right position if any of your pictures hope to be sharp - the amount of depth of focus is very small indeed.

The mirror also has to be in the right place.

The AF system could back focus, but that's another matter altogether and is true of all marques.

in relation to front/back focus has anyone ever asked the manufactures what tolerance they work to when assembling the cameras? 3mm over 450mm is a tolerance of 0.66% would seem very good to me

I don't know where your getting the 3mm tolerance from..... that's the depth of field that you have to play with plus or minus... the camera for it to even be of merchantable quality should be able to focus within that depth of field so that you get a sharp photograph. The K10D and the two expensive Macro lenses I've tested it with quite clearly aren't up to that. I can get a sharp photograph by focusing and then moving the camera back 8mm on a focus rack, but I shouldn't have to do that. Tolerances now days with state of the art manufacturing are usually very tight. I've got a Leica Disto distance meter that's accurate to +- 1.5mm over about 50m and Leica have laser scanners that can take millions of measurements of a building and produce 3D drawings within minutes. I am not surprised that Pentax have closed their UK Surveying Equipment down where tolerances of 5mm in a mile are not uncommon.

shim

If you are having to move the camera back 8mm then there is something wrong with it. My macro shots are dead sharp with my K10D/Sigma 50mm and we have quite a few macro enthusiasts on here posting dead sharp images. If it is still under warranty, send it back. or get it fixed.

I am assuming you have never removed the focus screen?

Cheers, Kris.

I’m asking the question is being able to focus to +-3mm over 450mm i.e. a tolerance of 0.66%, acceptable or not? I take your argument that it's not.

The other point I was making is that it's not stated anywhere, that I can find, the manufactures expectation for there products in terms of focusing accuracy.

A lens could be described as having pin sharp performance or crisp but it’s of little use if, as you say, it can focus 10mm front to back of the target, but still be within the manufacturers limits.

These tests should be done on a proper rig in a laboratory, so we don't know the experimental error either.

The only thing we can know is if our images are sharp or not.

Hi Kris, Without looking up the exact calculation 50mm goes into 450mm 9 times and if it's similar triangles something must be out by about 1mm inside the camera, I haven't been near the focus screen, but will have a good look to see if it has moved. I had a glance and it doesn't look all that impressive the way its constructed, I might have to have a look later tonight.... our binmen come tomorrow

shim

Ran through the same test again today on the K10D and also on the *istDS. Instead of moving the box away from the tape everytime I notched it over the top of the tape on the other side leaving about 10mm sticking over and under the tape at the 100mm mark which is red. I used a small dentists type inspection mirror to make sure that I was exactly on the 100mm mark at the top of the tape. (I've put a small red arrow on the pics to indicate this point) I manually focused the 50mm A f/2.8 Macro on the lettering on the box immediately above the mark. Everything was square and the camera was level. The tape was at 45deg to my line of site. The distance was 460mm to the theoretical film plane on the camera.

The 3 results for the K10D were worse than yesterday at 15mm (10mm allowing for the 45deg tape angle). That's the bottom window in the pic below (the white balance was set wrong, but the colours don't matter). I did 6 tests with the *istDS moving the camera slightly for each one and ALL of them were dead right almost to the mm..... so no error with that camera. See top window on pic below.

[IMG]http://i545.photobucket.com/albums/hh387/penbx/Compare_StaristDS_K10D.jpg[/IMG]

Just a quick test outside (pic below)with the *istDS and I'm not having the problems I have with the K10DS which is now out of guarantee. I can't believe the amount of Pentax gear that is being turned out faulty. Canon here I come.

[IMG]http://i545.photobucket.com/albums/hh387/penbx/Frosty.jpg[/IMG]

shim

How much do you want for the 100mm macro

Hi Mike, I've still got a lot of film gear such as 2 Z-1P's, 2 Super A's, 2 MX's about 15 lenses etc. so I think I'll be doing more film than digital for the forseable future. It may take me some time to sort out what Canon to buy plus were in a heavy recession here. With Canon having a thinner body than anyone else adaptor's are available for just about everything. Most of the Takumars etc. going for high prices on ebay are because Canon owners are buying them along with the East German Zeiss stuff.

I feel really gutted with Pentax spent £1400 on the *istDS and K10D and I haven't got a decent camera between the pair of them.... plus they are both worthless compared with what they originally cost.

shim

What peeves me about this ridiculous thread is that you waited a year until the camera was out of warranty before noticing there is something wrong and are now not even prepared to send it back to Pentax to see if there is something simple which can be done to fix the problem. We know that the K10D is capable of really good, sharp images, so if you have a bad example get the thing fixed. It is unlikely the repair will cost as much as jumping ship to another brand. K10Ds sell for about 300 quid second hand so even spending 150 quid will be a good investment.

Sadly, poor QC is common across many fields as a means of cutting costs including ipods, Blackberrys as well as cameras and so on. The golden rule in this day and age is test out the item immediately and if you are not happy return it during the warranty. We do have a generous two years

Sorry if I sound a little less jolly and polite than normal but this has rubbed me up the wrong way a little.

I'll shut up now.

Best wishes, Kris.

Best read up on all the faults Canon have as well before you jump ship, they were selling cameras for £5000 that couldn't focus properly, so don't think jumping ship will solve your problems.

Agree with Womble, get it fixed or repaired, and just because it's out of warranty don't think you can't do anything about it, if it's not fit for purpose, you have more rights than you may think.