Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-12-2015, 03:31 AM   #1
Moderator
Loyal Site Supporter
BigMackCam's Avatar

Join Date: Mar 2010
Location: North East of England
Posts: 6,672
Perspective distortion with lenses on Q7

I have some questions regarding lenses in general on the Q7...

I understand that the small sensor size reduces the field of view, a result of the 4.7x crop factor. But - is the perspective distortion (in terms of extension / compression) the same when I use a lens on my Q7 versus my K3? And whether yes or no,why?

I assume the answer is yes because the optics are the optics, and once situated at the accurate distance from the sensor by the K to Q adapter, they will perform in just the same way. So, for portraits, I would still use a short tele for compression, but would have to back up somewhat to capture the subject within the field of view - yes?

Which leads me to another question...

Does a 25mm C-mount lens exhibit roughly the same perspective distortion characteristics as a 28mm K-mount lens on the Q7?

I'm trying to understand this so I can judge the usefulness of certain focal length lenses in relation the subject matter I want to shoot.

Thanks in advance


Last edited by BigMackCam; 09-12-2015 at 03:43 AM.
09-12-2015, 06:00 AM   #2
Forum Member




Join Date: Nov 2014
Posts: 70
QuoteOriginally posted by BigMackCam Quote
I have some questions regarding lenses in general on the Q7...

I understand that the small sensor size reduces the field of view, a result of the 4.7x crop factor. But - is the perspective distortion (in terms of extension / compression) the same when I use a lens on my Q7 versus my K3? And whether yes or no,why?
Perspective distortion and "compression" only depend on field of view, they have nothing to do with focal length. So, if you use the exact same lens one time on Q7 and one time on K3, perspective distortion will be different. Due to different crop factors the field of view is different - you have to counter this by "zooming with your feet" and presto - your image looks more compressed on the Q7 than on the K3. That is, if you use the exact same lens on both.

QuoteOriginally posted by BigMackCam Quote
I assume the answer is yes because the optics are the optics, and once situated at the accurate distance from the sensor by the K to Q adapter, they will perform in just the same way. So, for portraits, I would still use a short tele for compression, but would have to back up somewhat to capture the subject within the field of view - yes?

Which leads me to another question...

Does a 25mm C-mount lens exhibit roughly the same perspective distortion characteristics as a 28mm K-mount lens on the Q7?
If you adapt both to the Q7, then yes.
09-12-2015, 06:39 AM   #3
Senior Member




Join Date: Dec 2013
Posts: 223
25mm x 4.7 = 117.5mm in full frame equivalent
28mm x 4.7 = 131.6mm ""

c-mount is mainly used for cctv for sensors from 1/2 inch to 1 inch (16mm diagonal)
because they are used for surveillance light transmission is more important than overall resolving power (its why they have really wide apertures)

on the Q7 expect softer edges and lower overall sharpness but plenty of bokeh when using a $25 c-mount lens
09-12-2015, 06:44 AM   #4
Pentaxian




Join Date: Oct 2011
Location: Savannah, GA
Posts: 5,002
Compression being a function of the lens is actually an illusion -- the effect is entirely caused by distance to subject and the lens or camera don't matter at all as they do not "create" it. (Farther away=more "compression") In other words, if you shoot something with a long lens, and the same thing from the same distance with a wider lens, and then crop & magnify the wide shot to show the view of the long shot, they will look identical in terms of compression. So the effect is entirely determined by how far away from your subject you are standing.

09-12-2015, 07:00 AM   #5
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,686
QuoteOriginally posted by vonBaloney Quote
Compression being a function of the lens is actually an illusion -- the effect is entirely caused by distance to subject and the lens or camera don't matter at all as they do not "create" it. (Farther away=more "compression") In other words, if you shoot something with a long lens, and the same thing from the same distance with a wider lens, and then crop & magnify the wide shot to show the view of the long shot, they will look identical in terms of compression. So the effect is entirely determined by how far away from your subject you are standing.
Agree, 100%. In fact I did this a few years ago because I was skeptical. I cropped a wide angle to the same FOV as a long lens and confirmed; perspective is solely determined by subject distance.
09-12-2015, 09:24 AM   #6
Site Supporter




Join Date: Nov 2012
Location: North Wales
Photos: Gallery | Albums
Posts: 1,549
Understanding Depth of Field in Photography
09-16-2015, 01:48 AM   #7
Moderator
Loyal Site Supporter
BigMackCam's Avatar

Join Date: Mar 2010
Location: North East of England
Posts: 6,672
Original Poster
QuoteOriginally posted by vonBaloney Quote
Compression being a function of the lens is actually an illusion -- the effect is entirely caused by distance to subject and the lens or camera don't matter at all as they do not "create" it. (Farther away=more "compression") In other words, if you shoot something with a long lens, and the same thing from the same distance with a wider lens, and then crop & magnify the wide shot to show the view of the long shot, they will look identical in terms of compression. So the effect is entirely determined by how far away from your subject you are standing.
Fascinating. I'll have to try that when I get back to the UK (and my gear!). It sounds wrong, but I take your word on it

So... If I use an adapted K mount lens on my Q7 and frame the shot for the same field of view I'd see with that same lens on my K3 (meaning I'd have to stand much farther from the subject), I'd see a greater compression of perspective, as the distance from lens to subject is greater. Have I understood that correctly?
09-16-2015, 07:37 AM   #8
Pentaxian




Join Date: Nov 2014
Location: South Bend, IN, USA
Photos: Gallery | Albums
Posts: 2,983
QuoteOriginally posted by BigMackCam Quote
Fascinating. I'll have to try that when I get back to the UK (and my gear!). It sounds wrong, but I take your word on it

So... If I use an adapted K mount lens on my Q7 and frame the shot for the same field of view I'd see with that same lens on my K3 (meaning I'd have to stand much farther from the subject), I'd see a greater compression of perspective, as the distance from lens to subject is greater. Have I understood that correctly?
Yes, if I use on my Q7 the 50mm lens that was kitted with the Super Program I bought in 1984, the resulting image will look the same as one I would have taken with that Super Program using a 235mm lens.

09-16-2015, 04:41 PM   #9
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,686
QuoteOriginally posted by reh321 Quote
Yes, if I use on my Q7 the 50mm lens that was kitted with the Super Program I bought in 1984, the resulting image will look the same as one I would have taken with that Super Program using a 235mm lens.
You would also need to equalize apertures for that, to equalize DOF; e.g. f2.8 on the Q7 would need f13 on the Super Program.
09-21-2015, 07:48 AM   #10
Senior Member




Join Date: Dec 2013
Posts: 223
QuoteOriginally posted by reh321 Quote
if I use on my Q7 the 50mm lens that was kitted with the Super Program
would make a great combo to shoot kite surfers with
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!
camera, distortion, lenses, mirrorless, pentax q, pentax q10, pentax q7, perspective, q-s1, q10, q7
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
wanted: DA 15 perspective distortion examples slip Pentax SLR Lens Discussion 23 07-31-2015 06:53 AM
Comparison of the 03 fisheye on Q and Q7 and Q7 with third party raw converter Altglas Pentax Q 14 02-02-2015 10:59 PM
Perspective Distortion Example ChristianRock General Photography 8 01-28-2015 05:29 AM
Perspective: An example on focal length, subject distances and perspective correction carrrlangas Photographic Technique 4 09-26-2014 09:02 AM
How to fix RAW distortion for Q7 hongning Pentax Q 4 01-31-2014 09:43 PM



All times are GMT -7. The time now is 07:14 PM. | See also: NikonForums.com, CanonForums.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