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Old December 17th, 2010, 08:35 AM   #1
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Effective focal length of DSLR lens

I've been prompted to ask this question because I own a Sony A100. a CZ16-80 and even more older Minolta glass that will fit the A55 which appears to be a serious contender in the wedding market. Since I'm a tyro here could you forgive and answer the following basic questions, please.

What is the effective focal length of a 16-80 zoom on a DSLR shooting video at 16:9?

Do DSLRs typically have sound monitoring outlets, headphone sockets etc?

Many thanks
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Old December 17th, 2010, 09:18 AM   #2
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I don't really know if the A55 could be called a 'serious contender' for weddings.

The SLT design does result in some light loss which is not ideal for weddings. Apart from that, there is no manual control. It has a microphone jack but I'm not sure about headphones - not that it really matters becuase you can't control the audio at all.

If you got some older minolta glass you'd like to use then possibly consider a micro 4/3rds camera - they are adaptable to just about an old lenses.

As for the effective focal lenth of the lens, it will be about 24-120 in 3:2 stills mode, and fractionally more cropped in 16:9 video mode.
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Old December 17th, 2010, 09:55 AM   #3
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John, can you explain what you mean by a micro 4/3rds camera? Sorry if I'm being thick.
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Old December 17th, 2010, 11:27 AM   #4
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Hi Phillip -

Not sure I'd consider the A55 or the A33 as a serious contender either, but I don't really consider any time limited camera as a primary for event work, for the simple reason that I don't want to be stressing on clip length limits due to either file size, or in the case of some of these cameras (and particularly the A55) HEAT. I know that some are shooting weddings with DSLRs, but to me it looks like more stress than it's worth.

That said, for short glamour/DoF shots and secific purposes, the A55 might well be a contender - I'm looking at adding one in just for the stills, with video as a bonus, plus it should be a nice "small" camera.

A55 has a mic input, I haven't been impressed by the audio I've heard from the onboard mics, don't think there's a headphone out, don't think any SLR's have headphone outs - small bodies don't leave a lot of room for amenities!

Not sure exactly how you'd do the math for 16:9 (1920x1080). The usual way of referring to APS-C sensors is that they have a 1.5 crop factor, making as John stated the effective lens range of your 16-80 approximately 24-120, but that'd be for a 4x3 frame.

The light loss is fairly minimal, Sony claims 1/3 stop IIRC, while it may be slightly more, but the A55 sensor is supposed to be pretty sensitive in low light (about a stop faster than the a33) - won't know until I get hands on one (Christmas budget, and they are hard to get right now!).

Micro 4:3, "four-thirds", m4:3 are referring to a relatively "new" interchangeable lens mount format used by Panasonic and Olympus primarily, notably the GH1 and GH2, which are quite popular - the advantage is they can have adapters for various lenses (similar to the NEX series) because of the shorter flange range, so potentially many lenses are available, with the cost of an adapter.

SInce you've already got some nice older A mount glass (me too!), you're doing the math and thinking you can save a bundle over buying a whole new "system". I'm considering the A55, and the A580 (traditional DSLR design, same sensor, but you lose the fast focusing, and gain that portion of a stop back) - they would replace older A350 bodies, so they'd primarily be for the still capability, but I think they'd also be used for video enough to make them worthy additions.
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Old December 18th, 2010, 07:47 PM   #5
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Sorry, Phillip.

I was referring mainly to the GH1 and the just-released GH2. There is also the AF100 Pro camcorder but that's in an entirely different league to the video capable DSLRs.

Mirco 4/3rds is a system using a 4/3rds sensor size (approximately 22.5mm diagonal, with a 2x crop factor when compared to full frame cameras) They have the mirror block removed, so the camera is full time live-view, which makes them more advantageous for video than other DSLR's. Some micro 4/3rds cameras have a viewfinder for framing/exposure either built in or available as an optional extra, so you don't have to rely on the rear LCD panel when shooting video like you do with DSLR's.

One of the big advantages of Micro 4/3rds cameras when shooting video is the adaptadility of other lenses. The shorter flange distance (between the lens mount and the sensor) of the m4/3rds system, thanks to the removal of the mirror block, means that more lenses are physically able to be used via adaptors while still achieving the correct flange distance. Given that most people here shoot manual-everything with video DSLR's, this opens up a whole world of older, almost forgotten manual lenses - your Minolta's included.
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