 Irene Troy |
Tele-extender exposure problem This, I’m afraid, may check in as a “little too late to ask – dumb me” question; however, I recently purchased a 2X tele-extender for my Sigma 50-500mm lens. I have had two problems with the extender: the first is that it seems that the images made with the extender end up being way off in exposure and that the histogram on my Canon 5D does not accurately show the exposure with the extender attached. I saw something online (another site, but I cannot remember where) that mentioned this issue with tele-extenders and suggested that the camera’s ttl meter is somehow incapable of accurately measuring light through the extender. Is this true and if it is, is there a work around to more accurately expose images? Second issue: this may seem really idiotic, but I am having a hell of a time trying to attach the extender to the lens! Every time I try to attach the extender in the field I end up missing my shot because it takes so long to get the */!#** thing attached! Is there a secret to this or am I just hopelessly uncoordinated?
|
|
|
|
||
|
Mark Feldstein |
Most tele-extenders come with a product sheet that tells you how much exposure compensation you need to provide / build-in to your exposure readings. At least with film cameras, the general rule is that a 1X extender requires about 1 more stop, a 2X needs about two additional f-stops worth of light. I could tell you how to do that with a built-in meter on an SLR but since I'm digitally impaired, dunno about your Canon 5D. Maybe you have to extrapolate when using an x-tender. And assuming this is a bayonet lens mount of sorts, unless your camera's instructions tell you differently, I'd attach the extender to the lens first then the whole rig to the body. There are usually dots placed on the camera and lenses (or telextenders) that help you line up the hardware then a single, short twist of the whole rig locks it into place. If you don't have alignment dots or lines, you can make your own using a small drop of red nail polish. I can usually change a lens on a bayonet mount body in less than several seconds. If not, iit;s usually because I'm not holding my mouth right. Take it light Irene.
|
|
|
|
||
|
Bob Chance |
Irene: If you, to the best of your knowledge, are aligning the markings on the extender and lens properly, but still have difficulty mating your equipment, then perhaps the problem is deeper.
|
|
|
|
||
|
Irene Troy |
Thanks Mark and Bob for responding so quickly! Mark - I have no problem switching lenses in the field and can, like you, do it in seconds when needed. That is why I find this extender to be such a pain! Sure it has dots to line up to the dot on the lens, but for some reason it simply will not attach without much fiddling around. I am beginning to think that the extender may simply be mis-matched. The lens is a Sigma (a good brand) and the extender is also a Sigma and supposed to be engineered to this lens - "supposed to be" being the operative word. On the exposure end - I am puzzled as to why, when using the extender, metering seems so far off. The bit that I read on the other website about the camera;s TTL meter being unable to meter with an extender makes no sense to me, which is why I asked about it here. Bob, your suggestion to take the extender back to the dealer is probably the best idea - I will call B&H and talk with them today. Thanks!
|
|
|
|
||
|
Christopher A. Vedros |
Oh well, I was going to suggest that you probably need to have a Sigma extender to match with the Sigma lens, until I saw that you do have the Sigma extender. The reason I think you need to use the Sigma extender with this lens is that it is designed to work as a 200-1000mm lens with the 2x, not a 100-1000mm lens. It's something about not being able to double the wide end of the zoom below 100mm. Anyway, the Sigma 2x is programmed to limit the lens in this way, but I don't know if another brand like Kenko would match up like this. Here's a way you might be able to check to see if your 2x tele is getting good communication with the lens. Check the EXIF info on an image shot with the lens & 2x tele combo. It should identify the lens used as a 200-1000mm lens. If it says it was a 50-500mm lens, then something is wrong with the connections. When I use my Sigma 70-200mm lens with the Sigma 2x tele, the EXIF info will show it as a 140-400mm lens. Chris A. Vedros
|
|
|
|
||
|
Jon Close |
The Sigma 2x TC has a front element that extends into the rear of the lens. With the 50-500 you must have the lens zoomed to 100mm or longer to mount the extender, otherwise the lens's rear elements conflict with the TC's front elements. This is noted in the compatibility chart at http://www.sigma-photo.com/lenses/lenses_tele.php, and I would assume also in the instructions for the TC and the lens. Whether or not the combination reports the true aperture (f/8-13) or the lens's nominal setting (f/4-6.3), the combination should meter properly on the 5D without having to manually adjust the exposure 2 stops for the TC.
|
|
|
|
||
|
Irene Troy |
Chris and Jon - thank you for the valuable info and insights! I will check the EXIF info to varify that the lens is being recorded correctly. Jon, as always, you came up with the most likely culprit/explanation for the problem with mounting this lens. If this info is in the instructions for the TC, I somehow missed it. There is another explanation for the issue about metering that occured to me while viewing the images that were made last night: I may simply be attempting to meter in conditions when no TTL meter can accurately measure light. I was trying to photograph the moon rise and also earlier to photograph sunset and I know these two situations can be hard to measure through the camera. I set the exposure using my best hunch and ended up with a decent exposure. Every time I think that I am passed the novice learning phase, something happens to remind me that I am still a rank beginner! Thank you, everyone, for your help! Irene
|
|
|
|
||
|
This old forum is now archived. Use improved Forum here
Report this Thread |
||