Riddle me this


Gravelrash

Link Posted 08/12/2013 - 23:54
So I put my vintage lens on my digital Pentax and the first question I get asked is to input the focal length. That's easy cos it's my trusty 50mm.

Then I get a zoom! Now things have just got complicated in my little, probably stupid, world. Do I put the lowest number, the highest number, a middle of the road number or none of the above?

If you can tell me, that would be cool. If you can tell me why the camera needs to know, that would be even cooler
Steve

Sometimes I'm serious and sometimes not, but I consider sarcasm an artform. Which is it today?

myles

Link Posted 08/12/2013 - 23:59
Ideally it would be the actual focal length you are using at the time, or the nearest offering to that.

If you can live without SR, you need to enter anything at all because that is why you are being asked for the focal length.

Hope this clarifies the mud a little!

Best,
Myles

johnriley

Link Posted 09/12/2013 - 00:03
SR is adjusted according to focal length, which is why the camera needs to know.

It's probably impractical to change the figure every time you zoom, so I'd start with a mid one. Then experiment with what works best for you. It would be equally valid to start with the longest or shortest length and go from there.
Best regards, John

Gravelrash

Link Posted 09/12/2013 - 00:07
Thanks guys...much appreciated.
Steve

Sometimes I'm serious and sometimes not, but I consider sarcasm an artform. Which is it today?

geordie01

Link Posted 09/12/2013 - 07:14
I always use a mid point no and it seems to work.

SteveEveritt

Link Posted 09/12/2013 - 14:02
I always put in the long end, my reasoning is the camera needs to approximate the physical size of the lens. Surely it is this parameter that makes the difference when stabilising the lens, the longer the lens the more the element end will move around due to breathing or heartbeat. A 200mm lens will require more adjustment than a 50mm lens will it not? So if you have a manual 50-200 it will be just as twitchy at 50mm as it is at 200mm due to its physical size. I for one would guard against this by putting in the long end measurement.
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johnriley

Link Posted 09/12/2013 - 14:24
The size of the lens doesn't come into it, it's the magnification that makes the difference.

I suppose it's easy enough to test though. Put a lens on and enter the wrong amount and see what happens.
Best regards, John

petrochemist

Link Posted 10/12/2013 - 15:12
geordie01 wrote:
I always use a mid point no and it seems to work.

Seems like the right approach to me (at least if you can't put in the actual focal length)
Using the mid point the system will under compensate at the telephoto end and over compensate at the wide end but both should be fairly minimal for most zooms.
Mike
.
Pentax:K5ii, K7, K100D, DA18-55, DA10-17, DA55-300, DA50-200, F100-300, F50, DA35 AL, 4* M50, 2* M135, Helicoid extension, Tak 300 f4 (& 6 film bodies)
3rd Party: Bigmos (Sigma 150-500mm OS HSM),2* 28mm, 100mm macro, 28-200 zoom, 35-80 zoom, 80-200 zoom, 80-210 zoom, 300mm M42, 600 mirror, 1000-4000 scope, 50mm M42, enlarger lenses, Sony & micro 4/3 cameras with various PK mounts, Zenit E...
Far to many tele-converters, adapters, project parts & extension tubes etc.

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Algernon

Link Posted 10/12/2013 - 15:35
The best way is obviously test it at a few settings and see which is best. I always use the longest setting.

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Algi

alfpics

Link Posted 10/12/2013 - 15:39
I have recently sent my DA17-70 in for repair as it had stopped reporting the focal length correctly; always giving a mid-range reading no matter what the focal length. I had noticed that shots at wider and more tele lengths were less sharp than usual, so the figure is fairly critical IMHO
Andy

Gravelrash

Link Posted 10/12/2013 - 15:50
I'll have a play soon. I'm waiting on a 75-150 and hope to work with it a little. Hopefully I should have a head start with your tips.

Thanks again
Steve

Sometimes I'm serious and sometimes not, but I consider sarcasm an artform. Which is it today?

Gamka

Link Posted 10/12/2013 - 17:22
johnriley wrote:
The size of the lens doesn't come into it, it's the magnification that makes the difference.

I suppose it's easy enough to test though. Put a lens on and enter the wrong amount and see what happens.

I depends on how much you shake!

I used a 600mm lens but had SR set at 50 ... the images were fine. So, maybe I don't shake too much.

johnriley

Link Posted 10/12/2013 - 19:40
A steady hand indeed Gamka!
Best regards, John
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