SAL70400G

[henniebez]

I bought this lens in Singapour. I was so excited, but in the bush I don't seem to get sharp images on 400mm F5.6. i am using a tripod with remote switch, and without one I have shoot at faster than 1/1500sec. Saterday the lens also didn't want to move past 100mm to 70mm. On sunday the lens moved past th 100mm mark again.

I have send Sony South Africa an email. They have responded quickly, but they told me that they will not look at the lens themselves. They would rather post it to singapour-free of charge- Seeing that Singapour offers international warrantee.

I have ruled out back focus- With the 100mm macro the focus is perfect!

What do you think? Is it risky to send through Sony back to Singapour?

[david antony]

Are you leaving "super steady shot" on while using tripod?

[David Kilpatrick]

I am sure Singapore is safe, probably has Japanese techs working there. The 70-400mm should be safe to handhold with SSS at any focal length at 1/1500th. The issue is more likely to be focus and depth of field.

David

[UrsaMajor]

I have ruled out back focus- With the 100mm macro the focus is perfect!

If I properly understand the issue of front focus and back focus, I do not think that back focus can be completely excluded just because one other lens has correct focus on this camera - although I agree that the performance of the 100m lens reduces the chance that back focus is occurring.

As I understand the subject, back (or front) focus can occur due to the combination of error in the camera and error in the lens. Each can be within its own acceptable variation from nominal, but if both are near the tolerance limit in the same direction, the combination can result in back or front focus. If the camera is in error in one direction and the lens in error in the other direction, you can end up with the errors partially or completely cancelling each other. It is possible that the 70-400 and the camera are in error in the same direction, and the 100mm is in error in the other direction. The probability of this combination of errors is low, but it does exist.

If possible, you might want to see how other lenses perform on your camera and/or how your 70-400 performs on another camera before you ship the 70-400 off to Singapore.

With best wishes,
- Tom -

[henniebez]

I got the lens back from Sony. They were not able to find any fault. They said they have run some diagnostic tests. I have ask them to show me the test.

They took four photos of leaves with different f-stops.

I dont know. I am not satisfied, seeing that my photos is not sharp at all. The main guy also phoned me, telling me that the reason could be heat waves, which is impossible, seing that the photos were taken just before sunset and the bird was like 15 meters from me. He also stated that I need to shoot at f8 @ 400mm.

On receiving the lens they told me they can't send the lens away if there was no proof of any fault

So I need help, to check if the lens is sharp or not.

Any recomendations on how to test the focus. Please a bit more scientific- Speaking of which the technician aren't aware of that you are able to work out the depth of field.

[David Kilpatrick]

The simplest way is to test focus at a very fast shutter speed - 1/1000th or faster at 400mm - on a support like a bean bag which will minimise any possible vibration. Turn SSS off. Use autofocus, and when the lens has locked on the subject, switch to MF. Now take a shot. Next, adjust the lens manual focus in small increments first one direction then the other.

Do the same with a lens you trust to focus perfectly.

Compare the results, and see whether the manual adjustment in front or behind has produced a sharper picture than the AF.

David

[henniebez]

Thanks

I will do it tomorrow.

[henniebez]

I have test the lens. The lens was sharp. Then I have put the filter back on, and the photos ware not sharp at all.

The filter is a pro-digital Kenko UV filter. All the trouble, while meantime it is something as obvious as a filter.

Is it possible that the filter has a defect? I foought that I bought a good filter.

Hennie

[Dusty]

Anytime you put anything in the focal path of the lens it has the possibility of disrupting things. Whether it's a filter of a heat shimmer it doesn't matter.

I would take the filter back to where you bought it and ask them to swap it out. If you still have the same problem, swap it for another brand. Quality control is not always perfect, so you may just have a bad example, or they may have had a bad run and didn't catch it.

Dusty

[Birma]

Check out the filter test here http://www.photoclubalpha.com/forum/vie ... =27&t=2354. Hoya came out as best in the test, but Kenko were not dreadful (joint 6th place). Glad you have got to the bottom to the problem. I guess there is a lesson for us all in being aware of the possible impact of filters.

[David Kilpatrick]

Had you said there was a filter fitted, I think most people would have advised you to test without it. However, a Kenko UV is a pretty good filter - I use a plain (£20) Kenko UV on my 28-75mm. It actually comes from exactly the same factory as Hoya filters, because Kenko is a Hoya brand. You must have got a rogue filter, a really bad example, to make that kind of visible difference.

I guess the safest option would be to order a Sony Carl Zeiss UV or lens protector.

David

[FramerDave]

The Sony protector filter is Zeiss T* coated but slim design. You can put lens cap on it but cannot stack another filter. With 70-400 you don't need slim design in case you want to screw on a polarizer. Hoya HMC or pro digital 1 is the way to go.

[David Kilpatrick]

You should never stack a polarizer over a UV filter - always remove the UV then fit the polarizer. Even the most efficient lens coatings have problems when two surfaces are lined up parallel like that, and most polarizers do not employ multicoating on the rear surface. Most UV filters now use single coating on the front surface and multicoating on the rear. Some like Hoya Pro SHMC use multicoating on both surfaces. I have not checked the Zeiss T* but I imagine they are multicoated front and back.

Even so, it's a bad idea to stack filters and the filter choice should be based on getting the very highest quality.

David

[bossel]

Do we still need UV filters? I read somehwere it's less useful with digital than film. It seems some use UV filters just to protect their lens front elements but I don't. Given what we've learned in this thread, it's maybe not a good idea? I do use a polarizer from time to time, that's all.

[David Kilpatrick]

I have not been using a UV on my Sigma 70-200mm. I've been very careful but the front element does now need cleaning. I prefer never to clean the lens directly, I'll buy a new cleaning cloth to do this, and I will be fitting a UV permanently. Really, it is not worth the risk. UV filter - £30-50. Lens - £600. You never know when a splash, load of wind-blown grit, or even someone's hand will manage to get inside a lens hood and touch the lens.

My worst was Indian green monkeys at the Agra Fort, green monkey poo all over my 20mm from their filthy little hands.

David