Search results for 'sensor cleaning' - page 153
I want some lenses! BUT
That being a crop sensor lens. It's easy to forget we're on Pentax User and the members here may not be au fait with Nikon and Canon terminology. So it may not be so obvious.
Posted by johnriley on 13/06/2013 - 11:05
Sigma HSM compatability
Has anyone heard or had experience of the compatability of earlier Sigma HSM lenses with the K5-ll/lls? I bought a non OS 120-400mm which works perfectly on my K-30 but will sometimes refuse to lock focus on my K5-lls. It's rather as if you've put a tcon onto a slow lens - the af just goes from one ...
Posted by greypoint on 29/06/2013 - 10:03
Manual focus zooms on dslr question
An interesting difference of opinion [which doesn't help you a great deal]. I had always assumed that the SRS needed to understand the likely degree of magnification that the sensor would need to deal with, and as a zoom will likely capture a range of focal lengths during a single use, that it was t...
Posted by GaryJohn on 14/07/2013 - 10:20
Manual focus zooms on dslr question
Gary, I know many people may disagree but I think that your premise that having a cropped sensor with respect to full frame or 35mm film cameras leads to some form of magnification is incorrect. Having a smaller sensor I my opinion simply leads to capturing a cropped image of the scene. I think it ...
Posted by jamieallan on 14/07/2013 - 10:49
Manual focus zooms on dslr question
I had always assumed that the SRS needed to understand the likely degree of magnification that the sensor would need to deal with, This is absolutely true but the SRS does its sums based on the focal length of the lens and as such it is always the real focal length you need to input and the sensor s...
Posted by gwing on 14/07/2013 - 10:52
Manual focus zooms on dslr question
Gary, I know many people may disagree but I think that your premise that having a cropped sensor with respect to full frame or 35mm film cameras leads to some form of magnification is incorrect. Having a smaller sensor I my opinion simply leads to capturing a cropped image of the scene. I think it ...
Posted by DoctorJeff on 14/07/2013 - 11:25
Manual focus zooms on dslr question
Thanks Jamie and Rob - very helpful. And hopefully this will cover 456's original question ! Jamie - I will have a proper read of those articles... thank you. I was aware of the concept of cropping resulting from the sensor being smaller than a 35mm film plane, but have misunderstood the concept o...
Posted by GaryJohn on 14/07/2013 - 11:26
Manual focus zooms on dslr question
Geoff, I used to own the Olympus 70-300mm. Here's an image of it. The 140-600mm equiv is in blue and the lettering is at least twice the size of the 70-300mm. I always felt that this was nothing other than an advertising gimmick. I've never compared 35mm and cropped sensor performance using...
Posted by jamieallan on 14/07/2013 - 11:53
Manual focus zooms on dslr question
Jamie, Any lawyer will tell you it is all in the wording. I do have to agree with you that it looks like a bit of a gimmick on that lens. Now, just out of arm's reach I have a P50, fitted with a Tamron Adaptall-2 in 17mm F2.5. When I stick that lens on my K20D it behaves like a 24mm (really, it s...
Posted by DoctorJeff on 14/07/2013 - 18:25
Manual focus zooms on dslr question
Jamie, I did find your quote from Ansel Adams interesting, in that a 1980 publication pre-dates the Sony Mavica by a year, the Nikon SVC by 6 years, and the Kodak KAF-1400 M1 (generally considered as the first usable DSLR) by 8 years. The statement about the image not being magnified is of course ...
Posted by jamieallan on 14/07/2013 - 23:05
Manual focus zooms on dslr question
Jamie wrote: I'm sorry but I don't understand your last two sentences - I can't see where magnification comes into it - it's the laws of physics and consequently the decrease in field of view seen through the smaller sensor. I guess that you are having a little problem with the "laws of physics" Ja...
Posted by DoctorJeff on 15/07/2013 - 23:40
Manual focus zooms on dslr question
Jamie wrote: I guess that you are having a little problem with the "laws of physics" Jamie. The focal length of a lens determines the acceptance angle of that lens. In lay terms, that is it's "seeing angle". Because there is a difference in the size of the sensor between 35mm and a DSLR (and i...
Posted by Cuchulainn on 16/07/2013 - 09:17
Manual focus zooms on dslr question
Geoff, Here's an illustration that hopefully sums up the discussion http://www.google.co.uk/imgres?imgurl=http://www.blogcdn.com/www.engadget.com/media/2011/12/digitalsensor-sizes.png&imgrefurl=http://www.engadget.com/2011/12/16/engadget-primed-why-your-cameras-sensor-size-matters/&h=208&w=310&s...
Posted by jamieallan on 16/07/2013 - 09:45
Fastish AF lens for portrait
Best portraits I got from Pentax gear were taken with the DA70Ltd and FA77Ltd. Both exceptional and hard to choose between them, although the DA arguably makes more sense on an APSC sensor.
Posted by JonSchick on 21/07/2013 - 16:15
Calculating depth of focus
What you are referring to is Depth of Field. Depth of Focus is something else entirely and refers to the amount of leeway available in the actual location of the sensor plane. There are depth of field tables in books and no doubt on the web, but if you want a simple "rule of thumb" for landscapes...
Posted by johnriley on 22/07/2013 - 13:19
Calculating depth of focus
Many of the older prime lenses actually show the depth of field available at each aperture such as this M50mm f2. The depth of field scales on these older lenses assume a full frame image (35x24mm on film). However, with a Pentax K-series crop frame sensor (24x16mm), the actual depth of field is o...
Posted by MrB on 22/07/2013 - 20:26
Calculating depth of focus
Many of the older prime lenses actually show the depth of field available at each aperture such as this M50mm f2. The depth of field scales on these older lenses assume a full frame image (35x24mm on film). However, with a Pentax K-series crop frame sensor (24x16mm), the actual depth of field is o...
Posted by JAK on 23/07/2013 - 11:53
Calculating depth of focus
I haven't quite grasped any specific dispute or argument here yet, as in specific opposing views. Its been informative for sure. So if we seem to be agreeing that the actual lens 'DOF' remains constant, is it the case, (as MrB has said), that lens DOF scales will only be correct when applied to a...
Posted by McGregNi on 23/07/2013 - 21:52
Calculating depth of focus
Phillip, I remember a good discussion on this subject a few years back on Digital Photography Review. To understand DOF you must understand that it originally related to a given print size enlarged from a negative. We can now refer to a print size or screen image, but the relevance is still the ...
Posted by pschlute on 24/07/2013 - 12:30
Calculating depth of focus
At best, DOF scales on lenses are notoriously inaccurate. They are good enough for a rough and ready evaluation of the hyperfocal distance, but I would always stop down one stop further than they suggest for the optimum result. Agreed - especially when using them on an APSC sensor. But for all thei...
Posted by gwing on 24/07/2013 - 13:33
