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What's the advantage with fixed lens over vari lens

Discussion in 'Lens Matters' started by Keith Jones, Jan 14, 2021.

  1. Petrochemist

    Petrochemist Well-Known Member

    It seems my memory is starting to go :(
    It was the f/1.8 zooms I was thinking of. Unfortunately I can't edit the post anymore to correct it.

    If a moderator could edit the post to correct my mistake that would stop the spread of misinformation.
  2. PeteRob

    PeteRob Well-Known Member

    Too late, I wouldn't worry, I think everyone who is vaguely interested has had a good look at the Sigma web page now :)
  3. Chester AP

    Chester AP Well-Known Member

    That's why I posted the link to the Pentax Forum website page, which as well as having the technical details, also has comments from users about the lens and saved me the task of explaining its design and use. If I ever wanted to photograph something and have a print done to 5 or 6 feet across, I would try to take the shot with this lens at F5.6 or F8. For small prints, or viewing only on a PC monitor or smaller handheld device, a kit zoom would be more than adequate.

    What I did not perhaps make clear was that my comments, and the web page links, refer to the old model 30 mm F1.4 made for half-frame (APS-C) DSLRs. I believe there is a new version made for mirrorless camera bodies, that will have a shorter lens to sensor distance and probably a revised optical design too (at a price). However, since the original query came from somebody who has an 18-55 lens already, it's safe to assume a half frame (APS-C) DSLR for which the older 30 mm F1.4 would be ideal if it was the lens that was required for a specific purpose.
  4. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    I've posted this before but it seems it needs repeating: I've seen pictures taken on 6MP cameras and cameras with 1/2.3" sensors that have been printed to 4 foot wide for exhibition. I have myself printed 35mm Tri-X negatives to 6ft for commercial use. There are numerous myths about photographic "quality" but only one thing really matters: does the "customer" like the result?

    Wildlife photography exhibition at Winslade Park DSC01097.JPG
  5. Chester AP

    Chester AP Well-Known Member

    You are correct, but I had in mind not only the sharpness of the image, but lens distortion and sharpness in the corners too. Of course, many people look at large prints from stupidly close distance, as if looking for flaws instead of appreciating it from a sensible viewing distance.
  6. ChrisNewman

    ChrisNewman Well-Known Member

    The Sigma lens designations are:

    DG indicates full frame coverage (but of course could also be used on cameras with smaller sensors).​

    DC indicates APS-C frame coverage; unsuitable for full frame.

    DN is also added if the lens is designed exclusively for cameras with a short flange distance (typically mirrorless cameras which don’t need space for a mirror box between the sensor and lens).​

    So a DC lens available with a Nikon mount would be optimized for a Nikon APS-C camera such as the D7000.

    A DG lens available with a Nikon mount could be also be used on the D7000, but for wider angles, such a lens is likely to be bigger and heavier (and thus probably more expensive) than a DC lens with a similar focal length and optical quality.

    A DN lens couldn’t be used on a DSLR.

    Yes, Sigma offer both 30mm F1.4 DC HSM and 30mm F1.4 DC DN lenses, although the 30mm F1.4 DC DN isn’t (yet) available for the Nikon Z mount.

    (I find it confusing that Sigma have retained the DG and DC codes for mirrorless lenses and added DN. I would have thought it far more straightforward to use different two-letter codes for mirrorless lenses, such as MG and MC.)

  7. Petrochemist

    Petrochemist Well-Known Member

    I don't find the Sigma codes memorable at all.
    I can easily come up with an expansion that makes sense for DC (digital cropped), but DG is less intuitive & looks all too similar - especially on a somewhat worn old lens!
    Personally I would have thought adding a third letter for mirrorless would have made more sense if keeping the old codes for size, eg DCN (Digital, Cropped, No mirror) or DMC (Digital, Mirrorless, Cropped)...

    Thinking about it though, Sigma certainly aren't the only ones whose nomenclature needs a code book...
    RogerMac likes this.
  8. GeoffR

    GeoffR Well-Known Member

    Most camera manufacturers use codes for their products, they seem to cover most of the alphabet. Some actually make some sense; Canon's EOS for example, more often they are meaningless to the uninitiated however, when they start to combine them it gets really complicated. Nikon's AI (Auto Indexing) which them moved to AI-S (Auto Indexing-Shutter) then came AF (Auto Focus) but all AF lenses were also AI-S. Then came AF-D (Auto Focus-Distance [reporting]) also AI-S, it only gets more complicated later.
  9. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    I'm just glad that the codes aren't in Kanji! :eek:
  10. Petrochemist

    Petrochemist Well-Known Member

    I think all of them only make sense to the initiated. Canon calling their system EOS (electro optical system IIRC) but then using EF (electrical focusing) for the mount, & adding in incompatible subdivisions EF-S, EF-M...

    Avoiding each others patents/trade marks must add to the complication so stabilised lenses might be 'Image stabilised', 'optical image stabilisation', 'optical stabilisation', 'vibration reduction', 'shake reduction', 'optical steady shot', 'vibration compensation', 'anti shake'... Each of which of course is abbreviated to only initials, then sometimes gets an addition as in 'Mega OIS'
  11. GeoffR

    GeoffR Well-Known Member

    I think you are right and the longer the manufacturer has been doing it the more complicated the system becomes.
  12. ChrisNewman

    ChrisNewman Well-Known Member

    Yes, like you, I find DC (digital cropped) informative, and thus easy to remember, but I’m puzzled by DG. I don’t now whether there’s any good reason why they didn’t use DF (Digital Full-frame). And I also thought DMC (Digital, Mirrorless, Cropped) and DMG or DMF would be good alternatives to MC and MG or MF.

  13. GeoffR

    GeoffR Well-Known Member

    Could the fact that there is a Nikon Df camera have anything to do with it?

    DF also refers to Direction Finding as in RDF Radio Direction Finding and ADF Automatic Direction Finding which abbreviation has been in use for 80+ years.

    MG obviously is a trade mark of MG Motors

    MF has various connotations but I know it as Medium Frequency (Medium wave to most people)

    DMC is a trade mark

    As previously mentioned, steering clear of other peoples trademarks and patents is a minefield.
    Last edited: Jan 18, 2021
  14. Petrochemist

    Petrochemist Well-Known Member

    I don't think there's any need to worry about unrelated abbreviations such as direction finding or MG motors (but the MG camera made by Pentax might be an issue). It's not uncommon to find abbreviations with multiple meanings, just take MF in photography used for both Medium Format & manual focus...

    In analytical chemistry I used to FID being flame ionisation detector (a very common usage going back to the 1950s) yet it's now also being used for something like flow injection device IIRC.
  15. GeoffR

    GeoffR Well-Known Member

    You are right about trademarks in unrelated areas but it is possible that some other photographic or imaging company in Japan or Korea uses the more relevant letter combinations.

    In aviation we have so many acronyms that we have probably used the lot at least twice! Each manufacturer will use the same letters to mean something totally different from another. Sometimes they don’t even make sense when you know what they mean, how would you abbreviate Stabilizer Trim and Elevator Asymmetry Module? I doubt you would come up with SAM but that is what Boeing did.
    Last edited: Jan 18, 2021
  16. Bipolar

    Bipolar Well-Known Member

    At my last job my employer had an acronym web page for us to look them up.
  17. Chester AP

    Chester AP Well-Known Member

    Whenever possible, if buying a lens that is not the same brand as your camera body, take your camera body to the shop and try the lens on it before purchase. If buying by mail order, ask the retailer if they could try the lens on a camera body the same as yours (or at least the same make and sensor size). I have done this, and had an email confirming success before buying the lens.

    I have purchased 4 second hand Sigma lenses and 1 second hand Tokina lens during the last 15 years, all with a Pentax fitting to use on a Pentax half-frame (APSC) DSLR, and had no problems. But I have always been very careful and done some research first, in one case telling the retailer that their website image showed one model but the text described a later version and it was priced accordingly. Once investigated, it was confirmed as the older model and the price was drastically reduced. I still have the lens - it's and older model Sigma 17-70 and I would recommend it to anybody wanting a 'general purpose' lens for a half-frame (APS-C) camera body.
  18. GeoffR

    GeoffR Well-Known Member

    We had, and I assume still have, an intranet page, half of which was incorrect.
  19. GeoffR

    GeoffR Well-Known Member

    Unfortunately, with some Sigma lenses even that doesn't work. I did just that with my first D3 but later found that the lens that appeared to be OK in the shop wasn't a week or so later. I haven't bought a used Sigma lens since.
  20. Chester AP

    Chester AP Well-Known Member

    I suspect that the camera body to lens connection may be simpler with my Pentax DSLR - none of my lenses have built-in focus motors (because the motor is in the camera body with a 'shaft drive' to the lens), and none have any built-in image stabilisation either.

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