a57 v d5100 for first DSLR

Started Apr 6, 2013 | Questions thread
Bjorn_L Veteran Member • Posts: 5,770
Re: a57 v d5100 for first DSLR

123Mike wrote:

Bjorn_L wrote:

123Mike wrote:

That is your hypothesis. I have another: the sensor is more sensitive to begin with.

Amusing theory given that they use the same sensor.  The a57 just gives up 1/3 to 1/2 stop due to their puzzling use a old technology called a Translucent Mirror.  It is possible to have an EVF without this loss (such as Olympus and Panasonic do).  I don't understand what advantage Sony thinks they get with this approach.  The viewfinder in the gh2, for example, compares favorably to the Sony ones I have seen.

End of day, the end results aren't much apart. Much less than you suggest based on your belief that it must be bad because "light is taken away". But it won't matter what anyone says. Beliefs isn't something that anyone can influence.

Again you are just wishing for stuff without checking out the facts. The above makes no more sense than your assertion that the same processer in the a57 and d5100 perform differently. The effect of the translucent mirror is well known. This is not new tech or some murky unknowable magical thing. Beliefs have nothing to do with it, except for your defense of the a57 of course. The cost of this approach is quite well documented.

You should also read a little more carefully. I said what a translucent (or pellicle) mirror does and wondered why Sony uses them since it does not seem to give any benefit that I can see worth that much of the light not hitting the sensor (in comparison to other EVF methods). Canon first used this in 1965. Nikon also used it briefly around 1978. So a well-known and well tested old technology abandoned by everyone else who tried it... presumably due cost not being worth the payoff.

You shooting off your mouth without the facts just makes you look silly.

"The a57 has a more sensitive sensor..." no, it has the same sensor

"The loss is not as bad as you believe..." no, it is tested and documented and not a matter of belief.

What next? Name calling, I'm betting. How about we skip that step and you just read up on it. Knowing the facts won't make your camera any more or any less it will just acquaint you with the facts. I'm not saying you chose a bad camera; just pointing out there is a benefit to understanding your cameras advantages and disadvantages.

Back on the translucent mirror.... I do not understand the benefit over other mirrorless designs. This is all I said above. It does have a price... loss of some light (around 1/2 stop by most accounts) as well as a trivial reduction in DR, color and image detail. So that is the cost, what is the benefit over, for example, Panasonics approach? The GH series certainly has lighting fast and accurate video focus, etc... And so would seem to have the same benefits without the same cost.

Of course this is only relevant to this thread in comparing the a57 to the d5100 which does not have these penalties but also does not have the fast video focus. Still think how much more compelling the a57 would be if it used a different EVF implementation.

If you think about it the costs make sense... it puts a semi-transparent object between the lens and the sensor, additionally this object is at an angle. There is no way this cannot have an effect. Light passing through anything is impacted.

A little info about the mirror tech (more links in the article if you want to understand it better)



From DXOMark, the defacto industry standard for raw sensor performance.  Used by a great many highly respected review sites (including this one).

Copy the entire mess and paste it in to your browser for a comparison of raw sensor performance.  Keeping in mind that despite your earlier assumption they use the same sensor but the d5100 clearly out performs the a57 at the sensor.  This is not because the a57 is bad or using an inferior version of the sensor.  It is just illustrating the cost of this translucent mirror.


The above link is probably also of interest to the OP in evaluating these two cameras.

-- hide signature --

See my plan (in my profile) for what I shoot with. See my gallery for images I find amusing.

 Bjorn_L's gear list:Bjorn_L's gear list
Canon PowerShot SX30 IS Sony Cyber-shot DSC-RX10 Nikon D700 Panasonic Lumix DMC-GH3 Nikon D750 +19 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow