[Bertminator]

I have several manual Pentax lenses "M" Series, and was wondering what focal-length setting should I select when I put on my 80-200 mm lens? Is there a rule of thumb to follow? What difference does it make to the camera? Is there anything that I need to know other than just putting the setting? Thanks in advance.

..Bert

[MSL]

Any setting you put in other than the length you are shooting will introduce errors to the shake reduction. If you are shooting at a fast enough shutter speed it won't matter much, but at slower speeds it will. There are a lot of opinions on how to pick the optimum setting

Here are some previous discussions on the topic:
https://www.pentaxforums.com/forums/58-pentax-beginners-corner-q/58463-manual...reduction.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/34979-shake...zoon-lens.html
https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/111544-k-x-shake...om-lenses.html
https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/107323-trying-se...reduction.html

[Bertminator]

So you're basically saying that I have to chose one focal length I will use on that zoom lens? Then if I zoom in, I have to change it again to whatever I selected? This destroys the convenience of zooming, does it not?

[elliott]

You don't need SR at all if you can keep your shutter speed fast enough. Set it at the widest and keep your shutter speed up.

The shake reduction doesn't destroy the convenience of a zoom when using a manual lens, the zoom reduces the effectiveness of the SR when you have to make compromises. Setting the focal length longer than what you are going to be using is bad, setting it shorter than you will be using isn't that bad.

Most people shooting manual lenses avoid zooms anyway, so it isn't usually a problem. I've found a few zooms that I like though and my SR strategy changes with which lens and how I plan on shooting. For example I know my 60-300 is going to spend all of its time above 200 in most situations, so I just set it at 200. My 70-210 is usually used throughout the whole range, so I set it at 70. If I'm sure I'm only going to be shooting at a certain focal length I input that one, like using the 70-210 in macro mode.

Of course, on a tripod the SR should always be off.

[Bertminator]

I was actually referring to setting the Focal Length when using a manual focus zoom lens, when I meant it kind of ruins zooming in and out, not the shake reduction. Thanks for the tip anyway.

[elliott]

If the shake reduction is turned off it won't even ask when you turn the camera on, that is the only reason it cares about focal length at all.

[VisualDarkness]

As long as you keep it set at the shortest focal length there won't be any adverse effects induced by the SR, the only thing is lower effectiveness at the longer end. If you do the opposite the SR will overcompensate at the short end and therefore induce shake.

[Na Horuk]

Hey, welcome!

I was actually referring to setting the Focal Length when using a manual focus zoom lens

Yes, camera only asks you about that for SR purposes. Some say to select the most used focal length, others to use the widest (that way SR won't overcompensate and blur the image, but it won't be as effective on the longer focal lengths). You can try just disabling SR and it won't matter at all what focal length you input, except the info in the exif.

But its not that "this ruins manual zoom" - manual zoom lenses were made way before AF and SR even existed. So how can you expect your modern day digital camera to communicate with a lens that was made in the 80s, 70s? At least you still get to use it, even if with some limited functionality (like missing AF, missing A on aperture, missing focal length contacts..)

[bluenose]

From the Pentax site: Using K-30 With Older Lenses | Ricoh Imaging Support

At the very bottom of the page they suggest using the midpoint of the zoom range to set the focal length.

Regards

[Bertminator]

Thank you ALL for your replies. They are very informative.

[BenTurpin]

My KS2 asks for the focal length when shake reduction is off. I am inputting when t-mounting to my telescopes - I've not checked yet but I assume it will be recorded in exif data to help when searching and filtering the photo library.

[m42man]

If you want a compromise focal length, use the following:

2*min*max/(min+max)

This will equalise the amount of shake reduction at both ends of the zoom range. So, for an 80-200, set 120mm for the closest approximation.

Best SR results are obviously when you set the focal length to the value which you input to the camera. But don't make the mistake of inputting, say, 200mm and then forgetting and operating at the 80mm end. Because you'll end up magnifying the shake-induced blur. The other way round is fine though (i.e. telling the camera it's a 75 or 80 and operating at 200mm) - it's just that you won't get optimum shake reduction.