Problem with auto focus

[sparkie1263]

I was having a problem with my 70-300 locking on focus. I did not test my other lenses yet. It keeps searching and stops way out of focus but if I just tap the shutter release button it locks dead on. The only change I made was I added a CLP filter so I took that off and it seems a little bit better.

[BLWNHR]

CP filters take about half a stop of light out and this can be enough to slow the AF system on an already slow lens. I have the same issue with my CPL on the Bigma.

[sparkie1263]

Thats what I was thinking. I don't want to up the iso just to use the filter. I will try it again on a sunny day.( it was real overcast today)
Thanks Frank

[DonSchap]

I thought we had discussed the drawbacks of dark lenses and CPLs ... maybe it was longer ago than I thought. Gee, where does the time go?

[sparkie1263]

Don my memory fails me. LOL I do remember you saying that a while back.Time to save some cash and buy some glass. I hate running into all these brick walls. Good thing I did not buy that TC I would br real upset. I would have to shoot only on sunny days or at iso 1600.

[BLWNHR]

High ISO still won't make any difference, it is the light coming into the lens that is lost, this slows the AF system. This is all before the light hits the sensor meaning ISO is of no consequence.

[sparkie1263]

Thanks for explaining that.

[DonSchap]

One aspect to the DSLR is they usually do not suffer with fast glass (f/2.8 or better). You can add all the bells and whistles, but when you shoot through consumer glass (f/4 or worse), you do not get much in the way of elbow room for doo-dads.

[sparkie1263]

Thanks again