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Thread: Actual zoom focal length when shooting.

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    Default Actual zoom focal length when shooting.

    Apart from reading the number off the side of the zoom lens, is there any way of determining the actual focal length as set with the zoom ring ?
    Perhaps on an m4/3 body ?
    I would like to be able to repeat a shoot (eg a day later) with the zoom lens re-set to exactly the same focal length.
    Any ideas, anybody ?
    Cheers,
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    My E-M10 m43 camera displays the focal length in the viewfinder and LCD screen. I think that it will do so even with a 4/3 lens, but I am not completely sure. The displayed FL seems to go in increments, so even though the zoom itself is smooth, going in very fine steps as you zoom, the display doesn't change seemingly till you reach the next level it recognizes. What I am trying to say is that it doesn't seem to be exact and there is some leeway in the FL it shows. So for your use, I guess you could set the lens at the FL when it first appears - i.e. zoom in say till the FL you want to use first appears in the display. That would probably work.

    Edit: I think that an adapted lens (like a 4/3 lens) would NOT show the FL on the display. I think it must be a m4/3 lens.
    Rich
    Olympus E-M10; Panasonic GM5
    m4/3 lenses: Oly 75-300; Oly 14-42 f3.5-5.6 II R; Oly 17 f1.8; Oly 40-150 f4.0-5.6 R; Oly WCON-P01 adapter; Rokinon f7.5 fisheye; Sigma 19 f2.8; Pan 20 f1.7; Pan 12-35 f2.8; Pan 12-32

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    Default Re: Actual zoom focal length when shooting.

    You can always look at EXIF info.

    FNumber - 5.60
    ExposureProgram - Manual control
    ISOSpeedRatings - 200
    ExifVersion - 0230
    DateTimeOriginal - 2017:01:15 13:42:01
    DateTimeDigitized - 2017:01:15 13:42:01
    ShutterSpeedValue - 1/250 seconds
    ApertureValue - F 5.60
    ExposureBiasValue - 0.00
    MaxApertureValue - F 2.00
    MeteringMode - Spot
    LightSource - Flash
    Flash -
    FocalLength - 22 mm
    UserComment - Olympus OM-D E-M1

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    Default Re: Actual zoom focal length when shooting.

    Yes, but there is no way to check it in-camera, is there? I mean, can you take a shot and then view the FL (from the EXIF) on the playback screen? If so, then you could do that; otherwise, it would be pretty cumbersome to match your FL now with shots you took yesterday, I should think.
    Rich
    Olympus E-M10; Panasonic GM5
    m4/3 lenses: Oly 75-300; Oly 14-42 f3.5-5.6 II R; Oly 17 f1.8; Oly 40-150 f4.0-5.6 R; Oly WCON-P01 adapter; Rokinon f7.5 fisheye; Sigma 19 f2.8; Pan 20 f1.7; Pan 12-35 f2.8; Pan 12-32

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    Default Re: Actual zoom focal length when shooting.

    Thanks Rich and Greg,
    EXIF data is certainly the way to see what focal length was used, after the shoot. Though I wonder how accurate that is using a zoom lens, given Rich's comments on the incremental display of focal length.
    The body has to determine the focal length some way, to set up the IS, but again how accurate is it.
    I'm thinking of astrophotography, where it's common to stack a series of star shots to improve the signal-noise ratio. Since the stars don't change much (if at all) over days or weeks, then it's perfectly acceptable to collect a series of images over the course of days or weeks. The framing doesn't even have to be identical, but I think the "zoom" factor would.
    I shall ask the stacking software designer if there is any tolerance.
    Cheers,
    Alec
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    Yeah, that sounds pretty iffy to me, unfortunately. It seems like you would have to be pretty close to the same FL each time, and I do think that the stepping of the FL display and capture to EXIF would be a problem. (I assume you know how to center on the same star each time or whatever else is necessary; sounds really HARD to me!! ).
    Rich
    Olympus E-M10; Panasonic GM5
    m4/3 lenses: Oly 75-300; Oly 14-42 f3.5-5.6 II R; Oly 17 f1.8; Oly 40-150 f4.0-5.6 R; Oly WCON-P01 adapter; Rokinon f7.5 fisheye; Sigma 19 f2.8; Pan 20 f1.7; Pan 12-35 f2.8; Pan 12-32

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    Default Re: Actual zoom focal length when shooting.

    Thanks Rich,
    Yes, framing is not a problem. Any error in shift or rotation just results in part of the frame being lost as the stacking program aligns all the stars.
    I have just asked the DeepSkyStacker forum if there is any tolerance in the "zoom" factor.
    I think your idea of rotating the zoom ring until the correct FL reading just appears may be the most accurate way of repeating that FL.
    Cheers,
    Alec
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    I have done some testing with a Sigma 150-600 S and the actual focal length is always somewhat shorter than what the lens data shows, even in the EXIF data. 600mm is actually 560, 500 about 470, etc. I think pretty much all long zooms are like that. They all fudge a bit on the long end for marketing reasons.
    The only way to really find out is to do some measurements and calculations. I my case I just compared the Sigma to my Canon 400 with and without a 1.4x TC, and to my 600mm telescope. The focal lengths on those are exact.

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    Default Re: Actual zoom focal length when shooting.

    I found a DPReview forum thread from last year on much the same subject, on the EM-5. The consensus there was that the zoom focal length was displayed under the Info button, but it was a series of about 34 discrete steps, regardless of which (m4/3) zoom lens was used.
    Presumably the EM-5 II is the same, but I can't find any data in the on-line manual. Seems like it needs someone with the EM-5 II in their hands, plus a zoom lens. There's one on eBay at present but I can't get a reply from the seller
    And I haven't got any definitive answers from the DeepSkyStacker forum yet either regarding zoom tolerance.
    Just be patient. The moon's coming up at night now anyway so the stars are not so clear.
    Cheers,
    Alec
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    I do have one question, Alec - I'm surprised you aren't thinking about a wider lens than what you have (unless, of course, you are trying to get by without spending much). From what I have read, star photography (where they don't rotate - just sharp dots) is best done with a fairly wide, FAST lens. Say a 24mm (12 in m4/3) at f2. Good article here:


    http://www.lonelyspeck.com/lenses-fo...y-photography/


    So, if you are thinking about buying an E-M5II, you could consider a prime lens like the Olympus 17mm f1.8 - it may not be quite as wide as desired, but it is fast, and seems to be the best option based on that article. Of course, bucks would need to be spent, but that might be a better way, I would think.
    Rich
    Olympus E-M10; Panasonic GM5
    m4/3 lenses: Oly 75-300; Oly 14-42 f3.5-5.6 II R; Oly 17 f1.8; Oly 40-150 f4.0-5.6 R; Oly WCON-P01 adapter; Rokinon f7.5 fisheye; Sigma 19 f2.8; Pan 20 f1.7; Pan 12-35 f2.8; Pan 12-32

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    Default Re: Actual zoom focal length when shooting.

    Thanks Rich, I have been studying the LonelySpeck articles. His favorite lenses on full frame are the Samyang 14/2.8 and 24/1.4. In Olympus terms that's 7mm and 12mm. ie much the same angle of view as the Oly MD 7-14mm PRO zoom. The Oly zoom is about $1000 US, a bit less (used) on eBay. The two Samyangs add up to almost $1000 US, and are the wrong wide angles for 4/3 anyway. I already have a 8mm/3.5 Oly ZD fisheye, so that's covered. It seemed more sense to cover the wide angles with the Oly PRO zoom, than spend as much on manual primes. Also, the Oly 7-14mm has glowing reviews for its sharpness and lack of aberrations.
    My other planned weapon is the Sky-Watcher Star Adventurer tracking mount, about $350 US, which would allow the use of slower lenses such as my f/3.5 fisheye, my OM 50/1.4 (which doesn't shine until stopped down to 2.8) and my Tokina AT-X 90/2.5.
    Does all that make any sense ?
    Cheers,
    Alec
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    Yup, that makes sense. There is a m4/3-specific Samyang 12mm f2 lens (only about $300) that the article mentions as being good (or maybe it just has a high number in his charts). But I do think that this is kind of a one-use lens, and of course an ultra-zoom like the 7-14 is much more useful. This is kind of why I suggested the Oly 17mm 1.8, which is an excellent standard walk-around lens, besides being good for astro too. You can often pick them up reconditioned on the Oly website for about $350.


    This type of photography sounds like fun! I should try it myself - I am going to Utah soon and the skies are supposed to be good while I am there (no moon!). But after trudging around the national parks all day, I don't know if I can bring myself to go out again and shoot stars. Anyway, good luck!
    Rich
    Olympus E-M10; Panasonic GM5
    m4/3 lenses: Oly 75-300; Oly 14-42 f3.5-5.6 II R; Oly 17 f1.8; Oly 40-150 f4.0-5.6 R; Oly WCON-P01 adapter; Rokinon f7.5 fisheye; Sigma 19 f2.8; Pan 20 f1.7; Pan 12-35 f2.8; Pan 12-32

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    Default Re: Actual zoom focal length when shooting.

    Quote Originally Posted by 3dpan View Post
    Apart from reading the number off the side of the zoom lens, is there any way of determining the actual focal length as set with the zoom ring ?
    Perhaps on an m4/3 body ?
    I would like to be able to repeat a shoot (eg a day later) with the zoom lens re-set to exactly the same focal length.
    Any ideas, anybody ?
    Cheers,
    Thinking outside the square, how about marking the spot on the lens with a white chinagraph pencil?
    E-M1, 12-40mm PRO, 60mm macro, MMF-3
    E-450, 50-200mm SWD, 25mm f2.8, EC-14
    FL-50R

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    Default Re: Actual zoom focal length when shooting.

    Thanks Bob, you have just introduced the next problem.
    I have just realised the zoom control ring only rotates about a quarter turn (90 degrees) from one end of the zoom range to the other. On the 7-14mm zoom it's quite easy to set 7mm, or 8mm, or 9mm etc. But on the 40-150mm you could never set 1 mm increments. But maybe that doesn't matter anyway. It needs someone with the EM-5 II (with zoom readout), and one of the PRO zoom lenses to test it in practise. Perhaps the zoom adjustment is too coarse to actually repeat a zoom setting anyway.
    And I still don't have an answer from the DeepSkyStacker forum. Lots of other suggestions but nothing positive about the zoom tolerance.
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    Hi Rich,
    It would be a shame not to take advantage of a dark sky and no moon. The sky should be dark enough by about 9pm (?). Even if you just use the fisheye lens that could give you some dramatic pics. Up to about 1 minute for relatively sharp stars, or ten minutes or so for star trails.
    Cheers,
    Alec
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    Yeah, it would be a shame to not take advantage, especially since I'll be at Bryce Canyon, which is supposed to be spectacular for such photography (being at 9,000 ft and not many cities around it). 9PM wouldn't be too bad, I guess - thanks for the tip.

    I have one other obvious suggestion for using a zoom lens with a consistent FL - use the widest FL! (just zoom out till it stops). I know this is obvious, but I think you generally want a wide FL anyway (although perhaps not as wide as 7mm, I suppose). Just a thought.
    Rich
    Olympus E-M10; Panasonic GM5
    m4/3 lenses: Oly 75-300; Oly 14-42 f3.5-5.6 II R; Oly 17 f1.8; Oly 40-150 f4.0-5.6 R; Oly WCON-P01 adapter; Rokinon f7.5 fisheye; Sigma 19 f2.8; Pan 20 f1.7; Pan 12-35 f2.8; Pan 12-32

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    Default Re: Actual zoom focal length when shooting.

    The problem with the f/2.8 zoom is that at f/2.8 it simply isn't very fast. Astrophotography is really demanding in respect to noise, and I find ISO 800 to be the reasonable limit I can shoot with. After that sharp stars are beginning to get smudged out by noise reduction and I can't push as hard in post processing.

    So while you can get by with 7mm @ f/2.8 (which allows for shutter speeds of around 30-35s before star trails appear), getting a shot at 12mm and f/2.8, which allows for only 20 second exposures, is gonna be tough. On location the shot looks really bright because of the darkness, but back home it turns out to be dark. At 12mm and f/2.0 and 20s exposure I normally have to push RAW files up to another +2EV (so that's 2 stops).

    While the 7-14mm f/2.8 is nice at 7mm, I find composition at 7mm quite hard.
    Olympus OM-D EM-5
    12-40mm f/2.8 - 12mm f/2.0 - 17mm f/1.8 - 25mm f/1.4 - 60mm f/2.8 macro - 75-300mm f/4.8-6.7
    - FL36R

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    Default Re: Actual zoom focal length when shooting.

    Thank you "Ed", I agree, getting a decent exposure at 2.8 is very difficult without star movement. I have resorted to stacking to try and improve the S/N ratio, but the potential for star movement defeats my present gear.
    That's why an essential part of my kit will be a lightweight tracking mount, and I'm thinking of the Sky-Watcher Star Adventurer, about $350 US, which is cheaper than a super fast lens. There's a very good review here, http://www.wexphotographic.com/blog/...eview-part-one, with a link to part two.
    I also found a very good review of the 7-14mm PRO lens with the E-M5 II, here, including some astro pics, https://robinwong.blogspot.co.nz/201...-pro-lens.html There's also a reference to using Live View Boost 2, for low light composition.
    Cheers,
    Alec
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    Using a tracking mount is one way to solve the problem, but it introduces another problem. You'll need to take a separate picture of the foreground and stitch together.

    I'd love to get one of those tracking mounts, just to play with it. Unfortunately I get so few starry nights here
    Olympus OM-D EM-5
    12-40mm f/2.8 - 12mm f/2.0 - 17mm f/1.8 - 25mm f/1.4 - 60mm f/2.8 macro - 75-300mm f/4.8-6.7
    - FL36R

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    Default Re: Actual zoom focal length when shooting.

    I think the work involved in stitching in a foreground would be worth not ever having to worry over elongated stars. There's a tutorial somewhere on this website, http://www.lonelyspeck.com/ .
    Those tracking mounts don't actually weigh very much, about a Kg. Easy enough to put into hand luggage and catch an airplane to a starry night somewhere.
    Cheers,
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    If you're willing to do the stitching work, it makes a lot of sense! You can probably get by with an f/2.8 lens on a lot of occasions. At 7mm, just being able to increase your shutter speed from 30s to 2 minutes will give you a huge difference.
    Olympus OM-D EM-5
    12-40mm f/2.8 - 12mm f/2.0 - 17mm f/1.8 - 25mm f/1.4 - 60mm f/2.8 macro - 75-300mm f/4.8-6.7
    - FL36R

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    Default Re: Actual zoom focal length when shooting.

    BTW, Laowa just came out with a teaser video for their new m4/3 7.5mm f/2.0 lens

    https://www.youtube.com/watch?v=1cC-j4_NtvE

    If its anywhere as good as their full frame 12mm f/2.8 supposedly is, it would be another great option in the future.
    Olympus OM-D EM-5
    12-40mm f/2.8 - 12mm f/2.0 - 17mm f/1.8 - 25mm f/1.4 - 60mm f/2.8 macro - 75-300mm f/4.8-6.7
    - FL36R

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    Default Re: Actual zoom focal length when shooting.

    Thanks, that looks a superb lens. And it's also very good to see other manufacturers producing top-class lenses for the m4/3 system. There's a good review here, with pics, including astro.
    http://3d-kraft.com/index.php?option...enses&Itemid=2
    There don't seem to be any prices yet though.
    If weight is not a problem then I think the m4/3 7-14mm PRO zoom lens is a very hard combo to beat. Even if it's just used at the ends of the zoom range, then that is two very useful focal lengths. And then there's in-camera lens corrections too.
    Twin E-620/70-300mm/14-42mm/pinhole lens, plus 8mm FE, Tokina AT-X 90mm macro, and Zeiss 500/8 mirror.

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    Default Re: Actual zoom focal length when shooting.

    The picture of the stars looks VERY promising. This would be an excellent lens for starry nightscapes.

    ISO800 + f/2.0 + 7.5mm + 30sec exposure gets you very very nice pictures
    Olympus OM-D EM-5
    12-40mm f/2.8 - 12mm f/2.0 - 17mm f/1.8 - 25mm f/1.4 - 60mm f/2.8 macro - 75-300mm f/4.8-6.7
    - FL36R

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