dave_smith24 Posted March 6, 2008 Share Posted March 6, 2008 I purchased a used tamron 28-75 from keh.comive been reading stories about people having to go through a few before getting a sharp one. Is there a technique to check if my lens is flawed? thanks Link to comment Share on other sites More sharing options...
ken munn Posted March 6, 2008 Share Posted March 6, 2008 Classically, tape a sheet of newspaper to a wall and shoot it wide open. If you can read the text easily on the resulting image (especially towards the edges) you're OK. However, very few photographers take pictures of newspapers, so I usually just shoot a few pix of my favourite sort of subjects and see if I'm happy with the results. Link to comment Share on other sites More sharing options...
shambrick007 Posted March 6, 2008 Share Posted March 6, 2008 How do your pix look? Link to comment Share on other sites More sharing options...
dave_smith24 Posted March 6, 2008 Author Share Posted March 6, 2008 <a href="http://www.deaneolaes.com/test/">http://www.deaneolaes.com/test</a> <br><br> product is about 5x5" <br><br> taken with 30D about 3ft away, 75mm, iso100, f2.8, 1/250 Link to comment Share on other sites More sharing options...
PuppyDigs Posted March 6, 2008 Share Posted March 6, 2008 The main flaw on the Tammy 28-70 is the manual focus ring. It turns wildly during AF and you can easily snag a fingernail. I tried several and they all have this same defect. I suspect the designer actually neglected to include a clutch mechanism. My fav soft lens is the EF 135 2.8 SF. You can dial in 2 levels of softness for old lady portraits or elect tack sharp. Sometimes the light’s all shining on me. Other times I can barely see. - Robert Hunter Link to comment Share on other sites More sharing options...
marc_matteo Posted March 6, 2008 Share Posted March 6, 2008 Troy - You like Lipton Soup? I think it's way too salty. Link to comment Share on other sites More sharing options...
PuppyDigs Posted March 6, 2008 Share Posted March 6, 2008 Lipton Soup gives causes me to see "floaters"--large dust like artifacts that drift across my field of vision. Must be a crapload of preservatives in there. Sometimes the light’s all shining on me. Other times I can barely see. - Robert Hunter Link to comment Share on other sites More sharing options...
marknagel Posted March 6, 2008 Share Posted March 6, 2008 Troy, Looking at the picture it looks like it might be front focusing, not soft. It appears to be focused about an inch in front of the box. Front/Back focusing issues are what I found int he Tamrons and Sigmas I've owned. Mark Link to comment Share on other sites More sharing options...
dave_smith24 Posted March 6, 2008 Author Share Posted March 6, 2008 "Troy - You like Lipton Soup? I think it's way too salty." mix it in with ground turkey and you have a killer turkey burger.. "Looking at the picture it looks like it might be front focusing, not soft. It appears to be focused about an inch in front of the box." how do i fix/compensate for this? Link to comment Share on other sites More sharing options...
dave_smith24 Posted March 6, 2008 Author Share Posted March 6, 2008 this was focused manually btw Link to comment Share on other sites More sharing options...
bryantan Posted March 7, 2008 Share Posted March 7, 2008 Well, that's probably the problem. I doubt you can manually focus accurately on a 30D with the naked eye. Link to comment Share on other sites More sharing options...
lester_wareham Posted March 7, 2008 Share Posted March 7, 2008 A test method for optical sharpness http://www.zen20934.zen.co.uk/photography/LensTests/simplemethod.htm And for focus accuracy here (at bottom of page ) http://www.zen20934.zen.co.uk/photography/Canon%20AF%20System.htm Link to comment Share on other sites More sharing options...
trebor_navilluso Posted March 7, 2008 Share Posted March 7, 2008 Troy: A couple problems with your test shot here. First, you didn't shoot strait on. You have the camera higher than the box and are shotting down at an angle. To do this test properly you need to have the film plane square/parellel to the subject. This may just be due to the lack of DOF. Second, you need to fill the frame with the subject for this test. So shoot something larger or get closer. Remember your minimum focus distance too. Then look at a 100% crop. I prefer innitially to shoot somethign a bit more 3D like a teddy bear. It will give you more of a real world example (unless you shoot/copy art/documents). Lastly to check for back/front focus (which is fairly common to some degree) use this method. Line up 3 to 5 film boxes or batteries in a row. Set them a few inches apart from side to side. And starting from the left make each one farther back from the by 1". Select cetner AF point only and single shot focus. Aim for the center one. Make sure the 5 items fill the frame (nearly). And check that the center item has the clearest text. If the one behind is sharper that's back focus, and if the one ahead of it is that's front focus. If it's only 1" off it may not be worth fixing. I have an old Minolta 28 that backfocus 2" on my A100 but is fine on a film body. I'm leaving it be because it cost more than I bought it for to fix and at 28, 2" back focus isn't all that bad for a $100 lens. Link to comment Share on other sites More sharing options...
trebor_navilluso Posted March 7, 2008 Share Posted March 7, 2008 Come to think of it, I wouldn't be surprised if 3' is too close for 75mm on that lens. You said you used manual focus right? Shoot a new test as I described earlier both MF and AF and make sure you don't violate min focus distance (again bigger subject or wider focal length as needed). Tripod, calbe relaese or timer, MLU, and faster shutter or diffused flash to ensure int's not camera shake wouldn't hurt eaither. Link to comment Share on other sites More sharing options...
jason_hall4 Posted March 7, 2008 Share Posted March 7, 2008 Mix in some of that soup mix into a tube of sour cream and break out the chips. You can also go to this site and down load this chart to test for back focusing. Of course that is test out your AF system. http://www.focustestchart.com/ It is writen by a Nikon guy, but we don't hold that against him. Jason Link to comment Share on other sites More sharing options...
jason_hall4 Posted March 7, 2008 Share Posted March 7, 2008 You can probably skip to about page 11 and move on from there. You will need a printer to print out the chart. Jason Link to comment Share on other sites More sharing options...
alan_myers Posted March 8, 2008 Share Posted March 8, 2008 "Mix in some of that soup mix into a tube of sour cream and break out the chips." Yep, and it's even better if refrigerated overnight so the flavors can blend.... MMMMMmmmmm! Hardest part is waiting overnight to dig in. Lipton's chicken noodle is the best cure for a bad cold. Link to comment Share on other sites More sharing options...
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