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Hi all,

I just came back from HK - shopping/friend's wedding trip.
I was all excited at the possibility of buying a few lenses but stoped at 1. the Sigma 30mm f1.4.

First impressions...nicely constructed, more solid than I thought it would be and fairly quick to focus...but!!! to my dismay..it has a huge backfocus problem. It is probably focusing 3 cm behing what I am targetting the focus point on!!! which as you can imagine makes this lens pretty useless at f1.4.

I have the Nikon 18-70 and the 50 f1.8 and never had this as an issue...so I suspect that it is a lens issue rather than my D70. I chose sigma as they have international warranty.

Does anyone have experience with this issue? I am not even sure who I contact for warranty issues like this? and is it a widely known problem or will the distributer simply try to get out of their obligation to fix it...

So much for buying lenses OS .....I think I may have a once bitten twice shy attitude to things in future...

All in all its a shame cause I was looking forward to using the low light capabilities for my honeymoon through france

Hi jyt,
in theory it isn't possible for lenses to have a back-focus (or any focus inaccuracy) problem on an SLR. Focus accuracy is determined by the exact matching distance between matte screen or AF sensor and film plane in the camera body. The only thing that happens with (long) lenses is that the mechanical stop at infinity isn't always actually infinity focus but past infinity.

That said, I can speculate about other sources of bad focus. The AF electronics in the body can play up (which should be visible in the view finder), the focusing motor of the lens can pick up some sort of electrical spike when the camera communicates with the lens prior to exposure, the lens can whack itself out of focus when operating the diaphragm,...

I guess you have to get it checked out.

Cheers
Steffen.

Joe, this link may be handy http://www.dslrusers.com/viewtopic.php? ... ht=kennedy

Joe,
Few things:
- Check the D70 with other lenses, I'm sure you did it.
- Try the 30/1.4 on other camera body to see if it's backfocus with other body.
- If it's not backfocus, then body and lens required to calibrate.
- Nikon or Nikon Authorized Service Center may not look at your problems coz the lens is third party lens, and it's the case they always use for their excuses.
- Send the lens back to HKG, where you bought it from and ask for credit.
- I wonder why didn't you try or test the lens while you're in HKG pre & post purchased.
- CR Kenedy the local Sigma player may not want to talk to you about the lens.

Hi jyt,

I have read many posts about the backfocus issue you talk about. If you do a search on FredMiranda there will be ample posts. Most people sent their lens back to the shop where purchased.

Since you purchased in HK, I'd check with the local importer and see what they can do. It might cost some $$$, but might be cheaper than sending to HK and trying to deal with them?

This is a great lens, here is one of my samples @ f1.4:
http://www.dslrusers.com/viewtopic.php?t=14850&highlight=

There is an inherent problem with auto focus in modern lenses which can be up to 43% out!!

Have you tried manual focus as this would be the way that I would first test the lens. With a 30mm prime and especially in low light manual is the way to go.

Look upon it as being similar to a lightmeter - does a lightmeter always give accurate results - no - the same with focus.

thanks for your comments.
I tried CR Kennedy today..and they were not interested in assisting me with the problem...actually it was a pretty poor attitude displayed by them.

What I dont get is how can sigma say that the lens has international warranty when that is not the case.

The warning in CR Kennedy's website is so wide that they would not honour sigma warranty even if I was a resident in HK and purchased legitimate (not grey import lens) and moved here to AUST during the warranty period. There is little value in an international warranty...and effectively provides no support for legitimate purchases overseas.

I can understand it where the refuse to honour the warranty for things purchased in Aust from grey importers but I just cant understand the rationale if you were overseas and purchased it legitimately.

anyway ... sorry to ramble on really peeved off at sigma...
I have started my letter writing campaign via email...will let you all know how I go.

Thanks
Joe

Joe,
Sorry to say this:

It's Sigma. and it's stench!:(

Nikon & Canon supports their International warranty.

A bit like how HK smelt I suspect!!!

I will post a couple of shots from the lens anyway...let me know what you guys think...mostly taken with high f stop though

cheers

Joe - you have to realise that CR Kennedy is NOT Sigma - they are only an importer - if you have an argument it should be directed to Sigma direct. It could be that CR does not get compensated by Sigma for lenses purchased outside of Australia.

HSM focussing on a 30mm lens is, IMO, totally useless. I believe that they do this to titillate prosumers and it does not only apply to Sigma

jyt wrote:A bit like how HK smelt I suspect!!!

cheers

Not HKG or Sigma's policies but it's CR Kenedy's policies, even they mentioned, they will match the price in fighting against the grey import (they wish) but they could not match with my two recently inquiries of two Sigma lenses which I pointed them to eBay's site.

They have stall at PIW 06, good to have a protest and question at their stall in those days.

removed

Sorry, forgot to open a new topic,
Gerard

jyt wrote:... Sigma 30mm f1.4.

First impressions...nicely constructed, more solid than I thought it would be and fairly quick to focus...but!!! to my dismay..it has a huge backfocus problem. It is probably focusing 3 cm behing what I am targetting the focus point on!!! which as you can imagine makes this lens pretty useless at f1.4.
...Does anyone have experience with this issue?

Joe, all is not lost, read through this thread:

http://www.dslrusers.com/viewtopic.php?t=14119&start=0

I initially thought I had a problem with my 30mm f/1.4 Sigma, but it turns out it was a problem with the D70, which was easily fixed with an Allen key.
Check the photo there- I had a 3 metre backfocus problem, not merely 3cm!
Of course it all depends at what range you are focussing, but it was completely useless at infinity @f/1.4, everything so far out of focus it was impossible to tell what was in the frame.

Gordon
oops, I just ordered a D200

Thanks for the info Gordon...Wish I had seen this thread earlier

I actually managed to convince CR Kennedy to take a look at the lens under warranty...I explained the problem to them and they did not advise that it was the combo with my D70 that was causing he problem.

I guess when it comes back, I can look at doing the adjustment myself if there is still a problem.

One question though...my 50mm 1.8 is bang on focus...if I adjust that nut so that the 30 mm is sharp what happens to that?

I thought I might run into a problem with my 105, which seemed to be OK before the adjustments, but it is still just fine after the adjustments too!
Keep an eye out for a few macro photos of toadstools I took yesterday, I'll post them today sometime.

Gordon

sirhc55 wrote:HSM focussing on a 30mm lens is, IMO, totally useless.

I can't understand this statement. Sure HSM gives you quick focussing, but that's not the point. It gives you full-time manual focus override (same as Canon's ring-USM [and Nikon's AFS (M/A)?]).
Personally I love this, as I have AF separated from the shutter button.