Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-19-2014, 01:32 PM   #46
Veteran Member
Andi Lo's Avatar

Join Date: Jul 2008
Location: Halifax, Nova Scotia
Posts: 2,925
QuoteOriginally posted by Nicolas06 Quote
I said the same optic. I mean the same physical object. That 85mm f/1.4 you mount on your FF you can mount on your APSC.

If you do that focussing at same distance you'll have narrower field of view AND shallower deph of field as an FF.

Equivalence is just what happen when you keep same framing AND deph of field (and not focussing distance). You need to change apperture and focal lens.

From actual practical availables lenses in term of prime, FF is not that better when looking at long focal lenses. Lense are expensive on both sides:

85mm f/1.4 on APSC give 135mm f/2 on FF.
135m f/2 on APSC give 200mm f/2.8 on FF.
200 f/2.8 on APSC give 300mm f/4 on FF.
300mm f/2.8 on ASPC give 400mm f/4 on FF.

That's true an f/2.8 zoom is inexpensive on FF and so that easier to find good practical zoom on FF with shallower deph of field.

But if you are really into that shallow deph of field thing you'll want the f/1.4 prime anyway ! And then for wide and normal FF clearly win... For tele that's a draw...

And that using a tele you'll get the most blurred background and the best subject isolation (if that what you are after).
By using a longer tele I'd be too far from my client though. The 85mm is my most used lens for paid portrait / wedding work, and I shoot it mostly in 1.8 (about 80% of my shots). I can't replicate this cheaply in APSC (50mm/1.2 with AF, for $350?). As you mentioned above there's the difference in OOF falloff as well. I'm not sure if this is true scientifically, but the 85mm pictures at 1.8 (ff) look better to me than my 50mm pictures at 1.4 (apsc)

Of course everyone is different, and not everyone would be interested in shooting with 85mm at 1.8, but the 85mm (and 28-75/70-200 2.8 zooms) was the FF system seller to me.

08-19-2014, 01:57 PM   #47
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,312
QuoteOriginally posted by Nicolas06 Quote
Snip........


And, last thing for the fun (from dof master):

50mm f/1.4, focus at 2m on FF: 0.13m
same lens 50mm f/1.4, focus at 2m on APSC: 0.09m

Using the same optic, same apperture on an APSC sensor give LESS deph of field than on FF. This is because the focal lens has more influence on the deph of field than apperture. Double the focal lens, deph of field is divided by 4. Double the apperture, the deph of field is multiplyed by 2.

This just mean that if we both use an 85mm f/1.4, the guy on APSC will get less deph of field from his shoot is taken same distance. FF will remain will less deph of field if framing is the same. Funny thing is if FF guy want to find an equivalent of that 85mm f/1.4... This is 135 f/2. It exist, that good. But there is no easy to find 135mm f/1.4... The FF guy will not be able to get more.

This is on short focal lens and wide angle that this deph of field difference is really interresting from an FF point of view.
What you have discovered here is that DOF is a function of 2 things. One is the lens focused to the subject at any given aperture, and the second is that one that you have not considered correctly, that depth of field calculators all consider blowing an image up to 8" x 10". As a result, the crop sensor has more magnification at the enlargement stage. But if you are using the same lens and same enlargement ratio you do not get this benefit. You may be double counting here and the framing won't be the same shooting Ff and crop sensor from the same distance
08-19-2014, 02:09 PM   #48
Pentaxian




Join Date: Nov 2013
Posts: 4,541
QuoteOriginally posted by Lowell Goudge Quote
What you have discovered here is that DOF is a function of 2 things. One is the lens focused to the subject at any given aperture, and the second is that one that you have not considered correctly, that depth of field calculators all consider blowing an image up to 8" x 10". As a result, the crop sensor has more magnification at the enlargement stage. But if you are using the same lens and same enlargement ratio you do not get this benefit. You may be double counting here and the framing won't be the same shooting Ff and crop sensor from the same distance
Don't get your point honestly... Both image would be magnified to 8"x10" anyway. And because the 23x36 sensor is bigger, it will be magnified less. But the magnification the lens would have produced would not have been the same anyway.

If I display my image on screen full screen I see it at rougly 25"x10" while I see Pentax forum pictures I embbed or other embbed typically mostly as this 8"x10". I don't understand personnaly the interrest of an FF if I need to display it at a very small magnification. I expect to print my best photo something like 20"x30" and not far less than 8"x10".
---------- Post added 08-19-14 at 11:12 PM ----------

QuoteOriginally posted by Andi Lo Quote
By using a longer tele I'd be too far from my client though. The 85mm is my most used lens for paid portrait / wedding work, and I shoot it mostly in 1.8 (about 80% of my shots). I can't replicate this cheaply in APSC (50mm/1.2 with AF, for $350?). As you mentioned above there's the difference in OOF falloff as well. I'm not sure if this is true scientifically, but the 85mm pictures at 1.8 (ff) look better to me than my 50mm pictures at 1.4 (apsc)

Of course everyone is different, and not everyone would be interested in shooting with 85mm at 1.8, but the 85mm (and 28-75/70-200 2.8 zooms) was the FF system seller to me.
I suspect the rendering more than the deph of field... Between f/1.4 and f/1.2 there is 15% less deph of field with f/1.2. This is not much and likely not worth the price difference.

But many choose the FA ltd for the rendering. I don't remember who say that recently but looking at FF of his friend and himself with FA ltd APSC, the FA ltd + APSC looked better. And the 2 FF friend where said to be same level of photography as him.

But FA ltd are not one could call cheap, sure.

Last edited by Nicolas06; 08-19-2014 at 02:17 PM.
08-19-2014, 02:33 PM   #49
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,312
QuoteOriginally posted by Nicolas06 Quote
Don't get your point honestly... Both image would be magnified to 8"x10" anyway. And because the 23x36 sensor is bigger, it will be magnified less. But the magnification the lens would have produced would not have been the same anyway.

If I display my image on screen full screen I see it at rougly 25"x10" while I see Pentax forum pictures I embbed or other embbed typically mostly as this 8"x10". I don't understand personnaly the interrest of an FF if I need to display it at a very small magnification. I expect to print my best photo something like 20"x30" not 8"x10"

---------- Post added 08-19-14 at 11:12 PM ----------



I suspect the rendering more than the deph of field... There is not much difference between f/1.4 APSC and f/1.8 FF in term of deph of field. And both option are cheap.

The rendering through is a different problem. Some see that their photos with FA ltd on APSC will look better than many lenses on FF. But FA ltd are nowhere cheap.
Then you don't really understand DOF

You started by saying shoot using the same F1.4 lens from the same distance , and then said the Crop sensor has lower DOF than full frame. But if you print the full frame of both images on 8x10 they are NOT identical images, because while the magnification subject to sensor is the same in both, the final image magnification in the print is higher for the crop sensor, therefore your apparent loss of depth of field.

This is why you need to understand the full math of depth of field. Depth of field is a function of a whole bunch of interacting constraints,
- what I will call the primary magnification (I.e. Subject to sensor) which is a function of focal length / distance
- the lens aperture and by this, I really mean diameter not FStop
- what I call secondary magnification, which is from the sensor to printed image.

When we discuss focal length equivalents between crop sensors and FF we generally modify focal length (hence primary magnification) and secondary magnification in unison. But we fail to consider that F1.4 on (let's say a FF50) is a bigger diameter than F1.4 on a 35mm lens, which is about equivalent in terms of FOV for a crop body.

This is why you need faster lenses on a crop sensor to get the same overall effect. If you don't believe me, just look at medium format and large format cameras. I'll bet you can't find any F1.4 lenses yet they can produce images with very shallow depth of field . Why do you think most portrait shooters use them still.

But the real issue her is not just DOF. Wide open shots with really thin DOF are over rated. Most shooters don't make use of it all that often, and therefore while they make the argument all the time. It is really wasted energy

08-19-2014, 08:22 PM   #50
Veteran Member




Join Date: Nov 2010
Location: San Diego, CA
Posts: 360
QuoteOriginally posted by Nicolas06 Quote
An example with dof master:

33mm on APSC f/2.8, focus at 3 meters: deph of field 0.95m
50mm (=33 * 1.5) on FF, focus at 3 meters:

The computation give: f/4.2 (f/2.8 * 1.5 = f/4.2)
dof master give:
deph of field for f/4: 0.87
deph of field for f/4.5: 0.98.

"Oh my god, this is nearly the same deph of field !!! 0.95 us between f/4 and f/4.5 !!!"

Man there nothing special here, we have 1.5x crop factor and 1 stop difference is 1.4. For practical purpose, you can say there 1 stop difference between APSC and FF.

So yes on can say you get approx the same framing and deph of field with an 17-50 f/2.8 on APSC than an 24-70 f/4. The math doesn't match exactly. 17-70 goes a little longer and a little less wide... And the deph of field will be a bit, really a bit, bigger. But for all practical purpose, this is close enough.

Now for practical purposes if you use an f/4 zoom on FF and f/2.8 zoom on APSC:

- You don't get any benefit from deph of field by using the FF.
- Your iso will go twice as high on FF (f/4) than on APSC (f/2.8) in low light situation. You'll speak of how your 12800 iso shoot is so clean, well with APSC and an f/2.8 zoom you will shoot at 6400 isos and you'll not see the difference in term of noise between the 2 shoots.
- There no reason to have more color deph or dynamic range as sensor perform the same on that topic for both APSC & FF (compare an old K5 with best FF)

What remains in benefit of FF ?
- The optics tend to be better at f/4 in general than f/2.8. This depend of the optics. This mean a little more constrast and sharpness to expect on the FF. This negate as you get better optics. I mean 18-35 f/1.8 zoom (APSC only) is razor sharp wide open.
- You can get more sharpness from the FF (like 36MP vs 24MP).
- The in focus - out of focus transition my be better on the FF (I would use a prime if I want this kind of thing honestly)


And, last thing for the fun (from dof master):

50mm f/1.4, focus at 2m on FF: 0.13m
same lens 50mm f/1.4, focus at 2m on APSC: 0.09m

Using the same optic, same apperture on an APSC sensor give LESS deph of field than on FF. This is because the focal lens has more influence on the deph of field than apperture. Double the focal lens, deph of field is divided by 4. Double the apperture, the deph of field is multiplyed by 2.

This just mean that if we both use an 85mm f/1.4, the guy on APSC will get less deph of field from his shoot is taken same distance. FF will remain will less deph of field if framing is the same. Funny thing is if FF guy want to find an equivalent of that 85mm f/1.4... This is 135 f/2. It exist, that good. But there is no easy to find 135mm f/1.4... The FF guy will not be able to get more.

This is on short focal lens and wide angle that this deph of field difference is really interresting from an FF point of view.
since I suck at math, let a pro show you how it really works. and BTW, your ISO # on a crop isn't what it actually is either. You can thank me after you watch the video. Sorry you have to write all that stuff up, but essentially it's not correct.

and also I really like how you round 1.5X to 1... that's some serious good math to prove your point.

Last edited by clockwork247; 08-19-2014 at 08:36 PM.
08-22-2014, 12:25 PM   #51
Forum Member
brandonbpm's Avatar

Join Date: Apr 2011
Location: United States
Posts: 86
Original Poster
Just want to thank everyone for their replies to this, it definitely was helpful, and photokina is sort of making me anxious. Just to clarify, I never meant to imply that I was some big shot professional (couldn't be any further from it) or that my current gear was anything spectacular if that is how it was taken. I simply was trying to communicate that I have gotten skilled enough to make some extra bucks on the weekends and feel I am starting to outgrow my current setup, either that or I'm just bored/complacent.

As for examples, I was referring to the noise profile and colors of the 5D and 5Dmkii specifically, but I can even see part of the rendering "je ne sais quoi" in these b/w photos from this thread where a member modded a 1Ds to mount pentax lenses:

https://www.pentaxforums.com/forums/169-pentax-full-frame/130552-pentax-full-...well-sort.html

In the first two photos, it is very subtle, but they have that aforementioned slight extra "character" I have seen in FF photos with wide apertures, in the grain, shadows, negative space and bokeh transition. Like I said, it can just be placebo, but even trying that "guess the format" test, I got 78% after 50 shots so I can at least decently tell a difference (of course as said before, the photographer's experience skews this). Does anyone else possibly see what I mean and can somewhat explain it better?
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
50mm, 5d, approx, camera, canon, ccd, crop, d600, dslr, f/4, ff, field, k-3, k-5ii, lens, lenses, love, night, pentax, photography, reason, sensor, street, system, view
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Machinery My 2000 4Runner THatfield Post Your Photos! 3 03-24-2014 06:23 AM
Finalizing my decision thehiko Pentax K-30 & K-50 13 11-10-2012 05:17 PM
Need help with upgrade decision rockmaster1964 Pentax K-5 24 10-28-2012 02:57 PM
To upgrade or not?...thoughts... dwhopson Digital Processing, Software, and Printing 6 02-03-2008 08:22 PM
2000 miles and 2000 pictures later Petthefish Post Your Photos! 4 10-03-2007 03:04 PM



All times are GMT -7. The time now is 08:21 AM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top