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01-12-2018, 01:30 PM   #1
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What is a "Reflex" Camera ?

I'm not asking the question as a beginner (!), but because I am surprised to see mirrorless cameras widely being described as SLRs (where the "R" surely stands for "Reflex"), for example here : Sony Digital SLR Cameras - Jessops

My understanding is that "Reflex" means "Reflection", ie a mirror is involved. A possible alternative is that it refers to the "reflex" action (as in a knee jerk) of the mirror (again) jumping out of the way when the shutter is pressed as in a traditional SLR; however the latter meaning is belied by the long-established term "Twin Lens Reflex" in which the mirror does not move.

Sony themselves on their website do not describe the A99 II (for example) as a DSLR, but as an "Interchangeable lens mirrorless" (SLT & DSLR-Like Cameras | Digital SLR-Like Cameras for Professionals | Sony UK). I understand that the mirrorless do in fact contain some sort of translucent mirror, but you can hardly say they have a mirror and call them mirrorless in the same breath (unless you are a salesman of course ).

The Wikipedia entry for "Reflex Camera" (Reflex camera - Wikipedia) is nonsense IMHO : saying, among other things, "The twin-lens reflex camera provides both a viewfinder image and the reflected image from the actual camera lens". In fact a TLR does not show the user the view through the "actual camera lens" which will take the picture.

PS : The Sony website is a mess of Javascript and the above link may not work properly, but I've done my best. I notice that the same Javascript automatically put the phase "DSLR-Like" into the link description above, although that term does not appear on that web page anywhere AFAICT.

01-12-2018, 01:43 PM   #2
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QuoteOriginally posted by Lord Lucan Quote
I'm not asking the question as a beginner (!), but because I am surprised to see mirrorless cameras widely being described as SLRs (where the "R" surely stands for "Reflex"), for example here : Sony Digital SLR Cameras - Jessops
Sony used to make SLRs, AFAIK, then they switched to SLT's (which have the mirror just for AF purposes), and then they took the mirror out entirely once they improved the on-sensor AF sufficiently. I think when anyone says "SLR like" regarding the newer Sony cameras they are talking about "big and heavy" (i.e. the A99 II as opposed to the smaller mirrorless bodies like the A7).

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01-12-2018, 01:51 PM   #3
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All reflex means here is that it allows the photographer to see the image to be photographed through the taking lens. So yes, Sonys are ‘reflex’ under this definition - but so’s my iPhone! 😜 Technology has outstripped the original definition of ‘SLR’.
01-12-2018, 02:50 PM - 1 Like   #4
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A reflex camera does indeed have a mirror that reflects the image from a lens, usually onto a ground glass for precise focusing and composition.

It doesn't have to be the taking lens (as in a Single Lens Reflex), but it can be a separate, viewing only lens, with a reflex finder, like in the Twin Lens Reflex (TLR) type - such as the famous Rolleiflex.

If a camera isn't a reflex type, then it may have a separate glass viewfinder (such as a Leica), or maybe a cheap pop-up wire frame, or an electronic screen that shows the actual image on the sensor (EVF).

I think it was Canon that first started to muck things up back in 1964 or so when they brought out their Pellix: a 35mm SLR, but with a semi-transparent mirror that didn't move out of the way at the moment of exposure. You literally shot right through the mirror. There was much less vibration, and you didn't see any blackout from the mirror going up. Unfortunately, the viewfinder only got about 1/3 of the light, and was noticeably dimmer. And the film only got 2/3 of the light, so it was less efficient.

Semi-transparent mirror cameras were often used for special high frame rate motor drive cameras.

However, Sony resurrected the concept with their SLT models, mainly for supposed AF and live view advantages, but with similar loss of light. It seemed to be more of a stop-gap between true SLR and mirrorless.

01-12-2018, 03:22 PM   #5
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QuoteOriginally posted by Lord Lucan Quote
I'm not asking the question as a beginner (!), but because I am surprised to see mirrorless cameras widely being described as SLRs (where the "R" surely stands for "Reflex"), for example here : Sony Digital SLR Cameras - Jessops
SLT = Single Lens Translucent. The mirror is a fixed pellicle type that is translucent and directs some of the light to the AF phase detect system and the rest to the sensor for the electronic viewfinder.

I think there are many reasons why they are often lumped together as SLRs, such as:
a) They look like SLRs externally.
b) Why should an optical viewfinder that uses a mirror be 'reflex' whereas an electronic viewfinder using a pellicle mirror not be a 'reflex'?
c) They sell more if they call it both a DSLR and DSLT. Most consumers don't know the difference.
d) Language evolves slowly. When videotape was common, it bothered me when people said they were filming and not taping. Now that videotape is gone, it bothers me people still say they are filming and not that they are shooting a video. We still refer to the sensor plane as the film plane.

I also wonder who actually starts these terms. Interesting to me that with film, they called them rangefinders and not sans reflex or mirrorless.

Last edited by Alex645; 01-12-2018 at 05:50 PM. Reason: Post #6 and #7.
01-12-2018, 03:35 PM - 1 Like   #6
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QuoteOriginally posted by Alex645 Quote
Sony, Olympus, Lumix, etc, are all technically SLT cameras with a Single Lens Translucent. The mirror is a fixed pellicle type that is translucent and directs some of the light to the AF phase detect system and the rest to the sensor for the electronic viewfinder.
Um. No. Only Sony had DSLT cameras, and only for a few years. Sony and Olympus have mirrorless systems that have replaced their SLRs. Panasonic has only ever had mirrorless cameras. Canon had a pellicle mirror film SLR...
01-12-2018, 05:31 PM   #7
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QuoteOriginally posted by boriscleto Quote
Um. No. Only Sony had DSLT cameras, and only for a few years. Sony and Olympus have mirrorless systems that have replaced their SLRs. Panasonic has only ever had mirrorless cameras. Canon had a pellicle mirror film SLR...
Correct: The major mirrorless cameras are in fact mirrorless as said above. The sensor is direct readout and sent to the LCD or EVF. The SLT type Sony with a translucent mirror was all but dead until the a99 II came out in 2016.
01-12-2018, 05:48 PM - 1 Like   #8
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QuoteOriginally posted by boriscleto Quote
Um. No. Only Sony had DSLT cameras, and only for a few years. Sony and Olympus have mirrorless systems that have replaced their SLRs. Panasonic has only ever had mirrorless cameras. Canon had a pellicle mirror film SLR...
Thanks for the correction! I didnʻt know that. I will edit the post.

I thought they were more common, but apparently not. I remember both Nikon and Canon high-speed film SLRs that used a pellicle and when I worked as a cinematographer, a good friend had a Mitchell with a pellicle mirror.


Last edited by Alex645; 01-12-2018 at 06:13 PM.
01-13-2018, 07:20 AM   #9
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As others have noted "reflex" generally means a mirror is used to divert light coming through a lens onto a screen that is used for framing and usually focusing as well*. The most common late-type "reflex" cameras were TLR = twin lens reflex such as Rolleiflex, and SLR = single lens reflex, the type or camera that dominated 35mm from about 1960 to the early 2000's. Micro four thirds (MFT) and full frame mirrorless cameras such as made by Sony have a design that is strongly influenced by film-era SLR's and current DSLR's that still have a mirror. Consequently they are sometimes called an SLR or DSLR even though there is no mirror to justify the word "reflex.".

*Many cameras from the bellows-folder era had little right-angle prisms that allowed waste-level framing but not focusing which was generally done by guessing the distance and setting a scale. These were called "reflex finders" or something of that sort. Some plastic "Brownie" cameras also had such right-angle reflex finders. If you've never used one, be grateful. They were generally tiny and not easy to use, definitely not for action photography. The compact twin lens reflex such as the Rolleiflex which allowed both framing and focusing, and provided a much larger viewing image was a significant improvement. It was basically a miniaturization of a twin-lens design that had existed for large format glass plate and cut film bellows cameras, but the latter were generally big and expensive and not suitable for amateur/family vacation photography.
01-13-2018, 02:42 PM   #10
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QuoteOriginally posted by boriscleto Quote
Um. No. Only Sony had DSLT cameras, and only for a few years. Sony and Olympus have mirrorless systems that have replaced their SLRs. Panasonic has only ever had mirrorless cameras. Canon had a pellicle mirror film SLR...
Actually, Panasonic did have two actual DSLR models, using the 4/3 mount (not micro 4/3). I believe they used parts sourced from Olympus, and were quickly forgotton once micro 4/3 arrived and Panasonic never looked again at a true DSLR.
01-13-2018, 04:38 PM   #11
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QuoteOriginally posted by Ontarian50 Quote
Actually, Panasonic did have two actual DSLR models, using the 4/3 mount (not micro 4/3). I believe they used parts sourced from Olympus, and were quickly forgotton once micro 4/3 arrived and Panasonic never looked again at a true DSLR.
I had to Google them. L1 & L10. 2006-07 and forgotten about by 2009. Which explains why I had never heard of them...The L1 doesn't even look like an SLR...
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