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11-14-2011, 07:34 AM   #1
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Input Focal Length

If I were to use my Tamron SP 500mm f/8 (Adaptall-2 model 55BB) with the Tamron SP 2X teleconverter (Adaptall-2 model 01F), the effective focal length should be 1000mm.
However the K-5 has a maximum focal length input of 800mm. If I were to use this maximum setting, what are the hidden implications for my pictures? Out of focus constantly or will there be no effects at all?

11-14-2011, 07:36 AM   #2
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Nope, the input focal length is for the Shake Reduction system...may not be 100% effective, but you'll be able to use it normally
11-14-2011, 07:41 AM   #3
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GabrielFFontes has already answered your query - it's just for the SR algorithm so if you select 800mm it will not give brilliant SR, but I guess it will be better than none.

Out of interest though, how much can you see through the viewfinder with a 1000mm f32? I'd love to see some samples too!
11-14-2011, 07:50 AM   #4
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I have not used neither such a lens, nor a teleconverter, nor K-5. So I may not know the issue properly. I think that the necessity to input focal length refers to so-called manual lenses which do not support autofocus and other features. These lenses cannot also report the data about focal length to the camera. Pentax has an in-body shake reduction which requires the data about the focal length. So camera requests to input this data to operate SR. As I understand, the input data only affects SR. You will have to use manual focus anyway. So this data will not affect the sharpness of image or similar features. If you input incorrect data, the SR might not work properly.
I suggest you to input the closest available number – 800 mm (the manual of my K-x suggest so). And check how the SR works. If it does not work properly, simply try to shoot without SR. As I understand, lenses with such focal length are usually used with tripod not hand-held. So there is necessity for SR.

11-14-2011, 08:18 AM   #5
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I sometimes mount a Rubinar Makpo 1000/10 mirror on my K20D and shoot handheld. Not easy -- it's rather heavy. I set SR to 800mm and hope for the best, which often isn't great. I haven't bothered putting my Spiratone 400/8 on a 2x TC to make it 800/16 because it's damn hard to see a subject and focus on it handheld at f/16. That's tripod territory, folks. And with a tripod, forget the SR.
11-14-2011, 09:53 AM   #6
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Thanks for all the replies and help! I guess I should spend a bit more time on that thick user manual. Guess I will use 800mm as the input, having some SR is better than none. Alberts, the 500mm can be hand-held if the weather is good. I am still having some problems getting my focus right. I have not tried it together with the 2X hand-held though. I doubt I will as it will be tough as what RioRico had mentioned. The below are thumbnails of the pictures I had placed in my album. The first is not sharp as my hands were shaking a bit but I am happy with it. I did a fair bit of PP on the last two. The last was of the 500mm with the 2X. I had always wanted to take a picture of the moon.




11-15-2011, 02:21 AM   #7
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Hi Butterfingers,

Nice pictures. If it is possible, could you post them a little bit larger, for example, with dimensions about 1000 pixels?
I also am like to shoot the moon. However, I have not shoot moon with such large focal length. A Lens with focal length 500 mm shout provides a good and detailed picture. If the lens is used together with teleconvter 2x, then the picture should even much impressive.
I agree that it is not impossible to shoot with 500 mm lens hand-held, too. The traditional 1/focal length rule requires to use shutter speed 1/750 (As I understand, your camera has cropped sensor with crop factor 1.5) or faster. If it is sunny day with EV 15, then you can shoot at shutter speed 1/750 and aperture F15 or with shutter speed 1/000 and aperture F11. Such exposure parameters should allow achieving quite a sharp picture by hand-held camera. If you widen aperture to F8, then with shutter speed 1/750 you can reach exposure value 13.5 EV that corresponds to “subjects in weak, hazy sun”. If you widen aperture to F5.6, then with shutter speed 1/750 you even can reach EV 12.5 that corresponds to “subjects in cloudy-bright light (no shadows)”. If your lens is “bright”, you can widen aperture even more and shoot in weaker light conditions. However, the wider aperture, the shallower DOF and harder it is to get well focused and sharp picture.
So, it is possible to shoot hand-held. SR allows you to use even slower shutter speed by one or may be several exposure stops. However, I think it is still better use tripod or something like to support camera.
11-16-2011, 08:28 AM   #8
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Hi Alberts, you are right, it is always preferable to have a tripod/monopod to support the camera whenever possible.
Oh yes, the link to the pictures is here

11-16-2011, 10:03 AM   #9
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Good luck hand-holding that combo

If you'll be using it on a tripod you should probably disable SR. Also, if you leave the setting at 800mm, SR will still work, but the corrections it will apply won't be as effective as they'd be at the correct 1000mm setting (I'm surprised that the menu doesn't let you select FL's up to 2000mm, as that's the longest lens available for pentax).
11-16-2011, 10:07 AM - 1 Like   #10
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Your name and the combo you are hoping to handhold gives me a little pause
11-16-2011, 11:30 AM   #11
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QuoteOriginally posted by JinDesu Quote
Your name and the combo you are hoping to handhold gives me a little pause
God one.

I was going to mention a tripod would be handy for that lens, in which case SR is off and, therefore, the input FL restriction does not really matter.
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