Lens diameter


stub

Link Posted 05/09/2021 - 19:53
One for the techies...! With modern lens filter diameters getting wider and wider. I was just wondering what actual difference. If any was made ? Except more expense in filter costs, of course...!
K-1Gripped K-1 ungripped K-5ii K7 Various lenses

Stuart..

johnriley

Link Posted 06/09/2021 - 07:28
Faster lenses will be wider as the elements need to be bigger. Full frame lenses will also need to be wider to cover the format. Then we add motors and electronics and plastics that might need to be thicker than metal.

I don't think the motivations will be increased filter costs as generally lens manufacturers sell lenses rather than filters. Most filters may not be needed anyway.
Best regards, John

RobL

Link Posted 06/09/2021 - 07:32
I am no techie but guessing several reasons: lenses need to incorporate electronic motors to drive focus, to help edge to edge sharpness, to facilitate wider f-stops like f1.4. Another reason could be that lenses need to match the performance of high pixel count sensors.

stub

Link Posted 06/09/2021 - 07:47
Hmmm... Except in my case my 2 fastest lenses FA 50mm and 77mm limited have the smallest diameters at 49mm. Just saying. I'm sure your right in some ways.
K-1Gripped K-1 ungripped K-5ii K7 Various lenses

Stuart..

Lubbyman

Link Posted 06/09/2021 - 08:12
It's a good question and as stub points out, it isn't just a matter of speed of lens or the need to squeeze in AF motors etc. The Pentax D-FA 100mm macro takes 49mm filters. The Sigma 105mm EX macro takes 58mm filters. Both are FF, screw-drive lenses. And then there is the Irix 150mm macro. Still FF, only manual focus, but it takes 77mm filters. And for comparison, the medium format Pentax-FA645 150mm AF macro, which of course has to cover a bigger sensor, take a 67mm filter.

My guess is that a lot depends on how far the designers want to go in reducing abberations. Less abberation typically means more (and fancier) glass. So given the current obsession with pixel peeping and sharpness, it's perhaps not surprising that lenses (and filters) are getting bigger - and more expensive .

Steve

RobL

Link Posted 06/09/2021 - 21:12
stub wrote:
Hmmm... Except in my case my 2 fastest lenses FA 50mm and 77mm limited have the smallest diameters at 49mm. Just saying. I'm sure your right in some ways.

I am with you on the 77mm Limited but I understand it is not as sharp around the edges and can get chromatic aberration; both of these were understood by the designers but as it is designed as a portrait lens then they would have no detrimental effect, itís other design features being a priority. Also of course it does not have an in-built motor.

pentaxian450

Link Posted 08/09/2021 - 02:01
Lenses today have more elements to better control chromatic aberration, edge sharpness, finer details and, especially for zoom lenses, distortion. Adding those elements make the lens longer. On those longer lenses for a given focal length, the entrance pupil is situated further back in relation to the total lens length, so to compensate for the extra length in front of the entrance pupil, the lens needs larger front elements to cover the angle of view, so they also need larger filters. That said (or written), about the only filter you really need in digital photography is the polarizer. Just about everything else can be done in post. With the latest cameras, if you expose to save the highlights, you can generally recover almost everything in the shadows, so you don't really need graduated filters anymore (thank god, those were a hassle to use). All other filters can be digitally created.
Yves (another one of those crazy Canucks)

stub

Link Posted 08/09/2021 - 05:58
Thanks that explains it very well. I'm not very technical..lol But I do use ND filters in my studio work. Sometimes my lighting can be too strong, at their lowest setting, when I need to use lenses at the wider apertures. So I restrict the light entering the lens with an ND filter. The other day I was using my 77mm limited and my DFA 24 70 which just made me ponder for a minute. On the size. The solution is simple enough to just have 82mm filters and stepping rings
K-1Gripped K-1 ungripped K-5ii K7 Various lenses

Stuart..

RobL

Link Posted 08/09/2021 - 07:31
A very lucid explanation from pentaxian450, although I would qualify his comments about filters. I agree that in most circumstances a high dynamic range can be resolved in post processing but this will often require two or three exposures; just lightening shadow areas will often result in noise and the details may not be as sharp, so for those who like to get everything right in camera or when only one shot is possible due to movement in the subject then a graduated ND filter is the answer. Also for longer exposures an ND filter is essential when reducing the aperture is not sufficient.

Chrism8

Link Posted 08/09/2021 - 13:26
stub wrote:
simple enough to just have 82mm filters and stepping rings

Exactly what I did about 8 years ago.
Chris

www.chrismillsphotography.co.uk

" A Hangover is something that occupies the Head you neglected to use the night before".

-------------------------------------------------------------
K1 - Sigma 85mm F1.4, Pentax DFA 150 -450 F4.5 / 5.6, Pentax DFA* 24 - 70 F2.8

Samyang 14mm F2.8, Pentax DFA* 70-200 F2.8

K3iii + K3ii + K5iis converted to IR, Sigma 17 - 70 F2.8, Pentax 55 - 300 F4.5 / F5.6 PLM

stub

Link Posted 08/09/2021 - 18:40
Except on a DFA 15-30 Chris.....!! Still bugs me after all these years..
K-1Gripped K-1 ungripped K-5ii K7 Various lenses

Stuart..

Chrism8

Link Posted 09/09/2021 - 11:24
stub wrote:
Except on a DFA 15-30 Chris.....!! Still bugs me after all these years..

Don't have one of those Stuart, and don't intend to either
Chris

www.chrismillsphotography.co.uk

" A Hangover is something that occupies the Head you neglected to use the night before".

-------------------------------------------------------------
K1 - Sigma 85mm F1.4, Pentax DFA 150 -450 F4.5 / 5.6, Pentax DFA* 24 - 70 F2.8

Samyang 14mm F2.8, Pentax DFA* 70-200 F2.8

K3iii + K3ii + K5iis converted to IR, Sigma 17 - 70 F2.8, Pentax 55 - 300 F4.5 / F5.6 PLM
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