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06-17-2008, 11:16 PM   #1
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test shots w/ tamron 28-75 f2.8 **now w/ charts

I think I've figured out the wide to middle part of my k10 system... 12-24, tammy 28-75 f2.8, and I'll use the tammy 70-300 for when I need to go long (which is very infrequent I'm finding).

I received the 28-75 today and took a few test shots. btw, I think I might have a front focusing issue though... I'll test it more thoroughly tomorrow. But for now, here's some of the pictures (all taken w/out tripod).... now that I've posted these, I'm realizing I took most of the shots at 28mm - I should have got a prime ah well, there's more pics I took that I'll convert from raw later. c&c always welcome!

Camera: Pentax K10D
Exposure: 0.017 sec (1/60)
Aperture: f/3.2
Focal Length: 28 mm
ISO Speed: 100


Exposure: 0.013 sec (1/80)
Aperture: f/2.8
Focal Length: 55 mm
ISO Speed: 100


Exposure: 0.013 sec (1/80)
Aperture: f/4
Focal Length: 28 mm
ISO Speed: 100


Exposure: 0.2 sec (1/5)
Aperture: f/22
Focal Length: 28 mm
ISO Speed: 100


Exposure: 0.006 sec (1/160)
Aperture: f/7.1
Focal Length: 28 mm
ISO Speed: 100


Exposure: 0.006 sec (1/160)
Aperture: f/3.5
Focal Length: 75 mm
ISO Speed: 100


Exposure: 0.006 sec (1/160)
Aperture: f/7.1
Focal Length: 28 mm
ISO Speed: 100



Last edited by vagrant10; 06-18-2008 at 07:41 PM. Reason: updated test
06-18-2008, 04:26 AM   #2
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Good deal! Hope you enjoy your copy.

------

As an update to my other thread (Front-Focusing), I got my 2nd copy from amazon yesterday and again I have front-focus by a little bit (45 degree angle test chart), so I'm thinking it's my camera body and not the lens, as this copy is FFing by almost the same amount.

Oh well, I will keep the new copy -- It doesn't exhibit the "shift" that the other lens was doing when focusing at 75mm.

I'll probably just avoid very close macros at angles, or just focus bracket macro shots. Other than the FF issue (which very well may be my camera), I'm loving the lens
06-18-2008, 04:32 AM   #3
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These pictures look good to me. But from these pictures it's haed to tell if there's a FF problems. It's best to use a focus chart with a tripod to test for FF. Hope it turn out fine.
06-18-2008, 07:14 AM   #4
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From the quailty of shots you should have endless amount of enjoyment from it


cheers

06-18-2008, 07:40 PM   #5
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As I feared, I've got some pretty significant front focusing.... well I'm bummed. I did get it from Amazon though, so hopefully it won't be too hard to resolve. I went ahead and ordered the Sigma 24-60 2.8 last night and when I get it, I'll see if that's better. Another poster just received his tamron 28-75, and both his copies had this same problem. Looks like this issue is more the norm w/ the Amazon stock. I really liked the lens too... as you can see from the pics though, the amount of front focusing is pretty significant. I don't mind manually focusing, but I'd rather not be forced to do it all the time...


Exposure: 0.033 sec (1/30)
Aperture: f/2.8
Focal Length: 33 mm
ISO Speed: 100


Exposure: 0.033 sec (1/30)
Aperture: f/2.8
Focal Length: 28 mm
ISO Speed: 100


Exposure: 0.033 sec (1/30)
Aperture: f/2.8
Focal Length: 43 mm
ISO Speed: 100


Exposure: 0.033 sec (1/30)
Aperture: f/2.8
Focal Length: 75 mm
ISO Speed: 100


Exposure: 0.033 sec (1/30)
Aperture: f/2.8
Focal Length: 75 mm
ISO Speed: 100
06-18-2008, 08:40 PM   #6
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The problem with manually focusing this lens is that its focus throw is sooooo short, like 60 degrees. I received a copy today, bought from a wedding photographer, and it front focuses about 2mm on that chart (I guess it didn't mess up any weddings...or maybe it did and that's why he sold it ). 2mm is something I can live with though, and is probably "within spec", but yours looks more like 10mm, which might become an issue when shooting portraits at close range. I don't know, I haven't done the math, but you should check it out in the field, see if you can notice in a variety of situations (28mm, 75mm, near object, far objects, etc.). Of course, do all your tests at f/2.8!

Remember that it may be your camera, it may be the lens, or it may be the combination of both. This is one thing that the K20D definitely has going for it, with its focus adjustment for individual lenses.

Good luck, mate!
06-19-2008, 03:20 AM   #7
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Yep Vagrant10, that's exactly what both of my copies of the lenses from Amazon look like, though your FF at 75mm looks a little more severe than mine. I think I was hitting 14mm slightly fuzzy, instead of mostly clear like on your chart. Of course, it could be slight differences in how we hold the camera, as mine was hand-held or propped, not on tripod.

What serial number did you get? My first copy was 5049** and my second copy is 5043**, so it looks like I got two close together.

Since I didn't get this lens for macro, I'm just going to test some portraits with it -- if I can't get the sharpness I want, I'm going to return it. So far, though, snapshots of my daughter have been pretty darn good, so I think it's a keeper (and with manual focusing or focus bracketing, macro shots tend to turn out pretty good).

I'll definitely try some closer portraits, though, to look for softness.
06-19-2008, 06:47 AM   #8
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my lens has a ser# 5002** so mine was made before yours. sounds like a production/ quality control issue or perhaps an incompatability w/ pentax... pretty annoyed at the frequency of this prob.

06-19-2008, 07:14 AM   #9
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don't get fooled by lens charts

Guys

Don't get fooled by lens charts and perceived focusing errors.

There are a couple of things I note in the photos of lens charts and also a point that was posted from someone at pentax.

- none of the shots I see are square on the focusing chart, and as a result, it is difficult to tell what is really in focus because of this, each side of the frame is different.

- pentax or someone who spoke to pentax about focusing charts, recommends 30 degrees not 45

- depth of field is not linear with distance, focusing should be 1/3 in front and 2/3 behind the focus line

- we are all using lenses assuming that they are "flat field" lenses when looking at the focusing chart. Macro lenses are designed to be flat field, but this is not necessairly true of normal lenses. As a result, Lenses are not necessairly focusing at the same distance off the middle of the frame, but on an arc therefore, with only a focusing scale on the sides of the frame, you may perceive that the lens is front focusing when in fact it is not.

- many people are taking quick snaps of a focusing chart while hand holding the camera, this introduces 2 very distinct errors, first, it is almost impossible to hold the camera to chart DISTANCE accurately, and when you press the shutter you lock focusing, and second, you may have vertical shake, and at the instance focusing is locked, you are not exactly on the center of the chart.

my advise is forget the stupid chart and take photos of real subjects, not targets.
06-19-2008, 09:15 AM   #10
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QuoteOriginally posted by Lowell Goudge Quote
- we are all using lenses assuming that they are "flat field" lenses when looking at the focusing chart. Macro lenses are designed to be flat field, but this is not necessairly true of normal lenses. As a result, Lenses are not necessairly focusing at the same distance off the middle of the frame, but on an arc therefore, with only a focusing scale on the sides of the frame, you may perceive that the lens is front focusing when in fact it is not.
This is very true, and I should have mentioned that I don't focus on the central black line, but centre and focus the frame on the This text should be perfectly in focus text on the side, that way the number scale is running vertically across my frame through the middle.

Run another test, guys, and see how it goes. And remember that lenses don't always focus the same at all distances, so you may get a focus error when shooting something at 1 foot, but be spot on when shooting a subject further than 2 feet away. Lenses are nothing but compromises, and I would bet that with a lens such as this the compromise was made on close focusing, as that is likely to be the least used by photographers.

cputeq has the right idea; pick a willing subject and take some portraits at f/2.8 from a normal portrait distance. Focus on the eyes and see where the focus is in the picture; if the nose or ears are in focus, you have a problem, but if not, then you're sorted for life with a great lens.
06-19-2008, 10:40 AM   #11
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QuoteOriginally posted by Lowell Goudge Quote
Guys

Don't get fooled by lens charts and perceived focusing errors.

There are a couple of things I note in the photos of lens charts and also a point that was posted from someone at pentax.

- none of the shots I see are square on the focusing chart, and as a result, it is difficult to tell what is really in focus because of this, each side of the frame is different.

- pentax or someone who spoke to pentax about focusing charts, recommends 30 degrees not 45

- depth of field is not linear with distance, focusing should be 1/3 in front and 2/3 behind the focus line

- we are all using lenses assuming that they are "flat field" lenses when looking at the focusing chart. Macro lenses are designed to be flat field, but this is not necessairly true of normal lenses. As a result, Lenses are not necessairly focusing at the same distance off the middle of the frame, but on an arc therefore, with only a focusing scale on the sides of the frame, you may perceive that the lens is front focusing when in fact it is not.

- many people are taking quick snaps of a focusing chart while hand holding the camera, this introduces 2 very distinct errors, first, it is almost impossible to hold the camera to chart DISTANCE accurately, and when you press the shutter you lock focusing, and second, you may have vertical shake, and at the instance focusing is locked, you are not exactly on the center of the chart.

my advise is forget the stupid chart and take photos of real subjects, not targets.
When i tested my Tamron 28-75, and DA F 50, i used real life subjects and a tripod(incase some one askes.:-))The last thing i used was the chart and shot it at 45 ish, 60ish but never tried 30 ish degree's

My K10D and DA f 50 are no back from Pentax Canada, and this time the notes said the camer was cleaned and adjusted. Also adjusted BF to lens.

Have not had a chance to check it yet, but it looks like the DA F 50 may have been the culprit.
Obviously they will not check a 3rd party lens.

Dave
06-19-2008, 10:58 AM   #12
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hey guys, thanks for the heads up on the perils of chart testing. I'll give it another go today, both inside w/ flourescent light and outside in natural light. My test yesterday was on a tripod so I think the distances were pretty consistent, but I was thinking that since the paper was crooked that would have an effect... the thing that suggested to me that I had a front focuser is that some real world shots were front focusing (I put the lens cap on those rocks posted in the first series and focused on the Tamron and the pic showed that the letters were not the focal point). It wasn't huge, but I had heard that some lenses had this issue so I was looking for this prob. Anyways, I'll post my results later tonight.
06-19-2008, 11:30 AM   #13
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gimme your lens for free.99 with shipping included. mmmk thanks.
06-19-2008, 01:14 PM   #14
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QuoteOriginally posted by vagrant10 Quote
hey guys, thanks for the heads up on the perils of chart testing. I'll give it another go today, both inside w/ flourescent light and outside in natural light. My test yesterday was on a tripod so I think the distances were pretty consistent, but I was thinking that since the paper was crooked that would have an effect... the thing that suggested to me that I had a front focuser is that some real world shots were front focusing (I put the lens cap on those rocks posted in the first series and focused on the Tamron and the pic showed that the letters were not the focal point). It wasn't huge, but I had heard that some lenses had this issue so I was looking for this prob. Anyways, I'll post my results later tonight.
one thing you might want to try is whether there is a difference in focus depending upon whether you are starting from infinity or minimum focus. Remember the camera is looking for high contrast, and may make the decision differently depending upon where you start.
06-19-2008, 01:22 PM   #15
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I purchased mine not quite a year ago from B&H and it has a serious FF problem also. After buying it, a little research showed that this was a known issue then. If the ones shipping nearly a year later still have the same problem I can't help but wonder about Tamron's commitment to quality.
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