[virgilr]

Hey all-

Wondering if those that are using the Tamron SP 90mm f/2.5 Adaptall lens have found that using 85mm or 100mm is the best shake reduction value when using this lens?

I've been using 85mm, but wondering if through experience anybody has found one value to perform better than the other?

Thanks!

[monochrome]

Hey all-

Wondering if those that are using the Tamron SP 90mm f/2.5 Adaptall lens have found that using 85mm or 100mm is the best shake reduction value when using this lens?

I've been using 85mm, but wondering if through experience anybody has found one value to perform better than the other?

Thanks!

I have the lens and use 105. Can't see how using either estimate would ahve a material effect on image quality, but I go to the longer spot, just in case. It might take the hand a moment longer to appear would be the only effect I can imagine.

[dave sz]

from a test someone ran, use the smaller number, 85...

[Nick Siebers]

But if you are doing macro, turn it off! Or so I was told. Number needs to be recalculated based on extension, otherwise, and it gets complicated.

[monochrome]

But if you are doing macro, turn it off! Or so I was told. Number needs to be recalculated based on extension, otherwise, and it gets complicated.

If you mount to a tripod turn SR off. It seems the sensor hunts for motion to correct if it is overly still.

[hinman]

I always use the lower of the SR focal length value that is closest to the lens' focal length, and in the case of the 90mm, I use 85mm. I heard it somewhere that using the lower value will avoid over-compensation on the SR calculation, hence my norm is to use the lower value that is available in selection.

As for 1:1 macro with extension tube on the 52B or 52BB, I add 45mm to the SR focal length for 135mm. The 1/2 gain on magnification ratio comes from

magnification ratio: extension length / focal length
1/2 = 45mm/90mm

Gain of 1/2 ratio comes from the addition of 45mm from the extension tube, hence I register 135mm for SR focal length when the extension tube is mounted. But, if I am using the 2x TC, I will simply dial in 180mm. I may have the wrong assumptions, I hope others can jump in for the correction.

On tripod, SR should be turned off. And I am not sure on monopod?

Thanks,
Hin

[monochrome]

I have the lens and use 105. Can't see how using either estimate would have a material effect on image quality, but I go to the longer spot, just in case. It might take the hand a moment longer to appear would be the only effect I can imagine.

from a test someone ran, use the smaller number, 85...

I always use the lower of the SR focal length value, and in the case of the 90mm, I use 85mm. I heard it somewhere that using the lower value will avoid over-compensation on the SR calculation, hence my norm is to use the lower value that is available in selection.
Hin

You learn something new every day. I stand corrected.

Paul

[Marc Sabatella]

It is always the case that giving too *low* a value for the focal length will simply cause the SR system to not perform up to to its full potential, but giving to *large* a value can cause it overcompensate to the point of actually producing worse results than leaving it off. This becomes obvious if you think through how the SR system actually works. In practice, being off a few mm one way or another won't matter at all, though.

If you feel like a demonstration, though, take a 28mm lens and a 200mm lens, and set SR to the other's focal length. The 200mm lens set as 28mm will behave as though there were no SR at all: you'll be able to take sharp pictures with a fast enough shutter speed. The 28mm lens set as 200mm will produce nothing but garbage at shutter speeds you should have been able to hand hold easily without SR.

[virgilr]

Thanks to all- I think Marc has the right idea- jives with how the SR system functions. I may, when shooting indoors wide open try the 100mm setting to give a bit more "agressive" SR, esp. when shooting something in the close field (but not macro area) - I find this is where movement is the most apparent for me.

I don't have the extension tube, but I will keep in mind hinman's formula and setting if I ever get my hands on one. Not too concerned- not a bug shooter, me.. Don't have the patience, I guess!

[Groucho]

I have the lens and use 105. Can't see how using either estimate would ahve a material effect on image quality, but I go to the longer spot, just in case. It might take the hand a moment longer to appear would be the only effect I can imagine.

Does the K10D let you choose 105mm? The K20D jumps from 100 to a higher number, maybe 120 (I don't have mine in front of me so I can't check.)

I wish it had 105mm for my Lester Dine and my Super Tak 105s, just so the exif data would be correct right off the bat. Since I select 100, they are too tagged as 100mm.

[WerTicus]

my SR malfunctioned on my k20d and was giving me garbage all the time - sent the camera back to pentax and they fixed it... not really on topic, but an interesting bug that came up suddenly. Test report said they replaced the SR unit.