New A700 problem - serious vignetting at full zoom

[mic291]

Hi there

Am new to the forum and would have liked my first post to be a little different....

I picked up my A700 2 weeks ago now and there appears to be a very serious vignetting problem with the 18-250mm lens when at 250mm or there abouts. I have been scanning the web however I dont see too many problems listed so I am getting worried that it may be a faulty lens which is not a great situation, given I bought the lens in Singapore and live in Sydney.

Any users seen similar issues?

Thanks
Mike

[David Kilpatrick]

Well, it does vignette quite a bit. If you set high contras and Vivid colour mode, for example, and shoot a plain sky view at full aperture - yes, it will show fall off. All these lenses do. Post an example, and I could say whether it looks like a mechanical fault or the normal degree of vignetting.

David

[mic291]

Thanks for the reply David as this is sending me crazy.

Looking at a few of the fotos, they are at F4 however I do see it at 5.6 also.

The strange thing is I was using this lens for about 3 months on an A100 and I do not recall seeing this at all which has been worrying me that its related to the A700. If this is the lens, and is normal then thats a very bad lens in my opinion.

Here is an example at F4
http://www.flickr.com/photos/mic291/2363713936

Here is an example at F5.6
http://www.flickr.com/photos/mic291/2362883465

As mentioned, I dont think I ever saw this when using the A100.

What do you think?

Cheers
Mike

[David Kilpatrick]

This looks sharply defined compared to any vignetting on the 18-250 we have. There are two or three possible causes. The simplest would be that you have a filter which interferes with the peripheral image, unlikely or you would have mentioned it. The second is that the lens has in some way become misaligned but this should affect sharpness. The third is that the vignette mapping of your A700 sensor, a built-in function required for all lenses, is not correctly encoded while your A100 was OK. This is possible, but it would show in the form of increased vignetting with all lenses.

It could also be that the combination of conditions, contrast and exposure made these effects very visible. I certainly have had similar results on film from the 28-300mm Tamron XR, and the 18-200/18-250 models do show strong vignetting - as do all lenses like this. But not as bad as your example.

David

[mic291]

Thank you David

Definately no filter or lens hood and more concerning for me was the focal length as both of those fotos were at approx 28mm.

I went through a series of fotos I took in Las Vegas recently with the a100 and the 18-250mm lens and there is some extremely minor, as in most people would not pick it vignetting but nothing like whats on the a700 fotos.

I will have more a play on the weekend and see if I get the same type of results. Will also test with my 50mm prime and see if anything appears on those fotos.

Hopefully I can find a standard lens to eliminate the camera.

From the sounds of it, I am probably better off getting one of the new Sigma f2.8 50 -150mm or 70 - 200mm lenses that are not as extreme.

Thanks
Mike

[David Kilpatrick]

For the long reach stuff, give the Tamron 70-300mm f4-5.6 a serious thought. It is a genuine f4 all the way to 135mm, then f4.5 all the way to almost 250mm - it's hard to tell, but it switches to f5 around 230mm maybe, and it only becomes f5.6 right in the last couple of mm of movement to 300mm - 290mm or something. I have been comparing it with the Apo 100-300mm and it is 2/3rds of a stop faster almost all the way. It is very inexpensive and surprisingly good. I will be writing a review of this lens shortly. It's not wonderful wide open, but nor is the 18-250mm, or even the 100-300mm Apo. For around £120/$200 it's a bargain and focuses down to 0.95m, allowing some good semi macro shots. There is zero vignetting and hardly any distortion, of course.

David

[mic291]

Thanks David

Just finished some testing with interesting results.

What I did was shoot a couple of A3 pieces of white pages as follows:

- I tested at 28mm, 50mm, 100mm and 200mm focal lengths
- EV as 0 for every test
- Adjusted f-stop from lowest, f/3.5 - f/20

Results:
- vignetting reproduced in every focal length, however its typically worst from 28mm -100mm but still noticeably bad to full focal length.
- vignetting is very bad from f/3.5 through to f/10 where once past f/10 it starts to become quite acceptable
- firing the flash does not make a difference and the vignetting is still very bad

Testing with my 50mm f/1.4 prime, regardless of f-stop is sharp and has absolutely no vignetting at all. Regardless of what I try, there is absolutely no vignetting.

The confusing part is I have been through 25+ fotos that were taken with the A100 and the 18-250mm lens and regardless of what f-stop or focal length, I simply cannot see any vignetting at all.

So tomorrow I am going to see if a camera store will let me test a Tamron 18-250mm lens so I can eliminate the Sony lens that I have.

Cant help but worry that my brand new A700 is faulty....

Mike

[David Kilpatrick]

Well, the A700 does have a different sensor with different microlenses. I'll try to check our Tamron 18-250 on the A700. It normally lives on the A200.

David