LENSE i BOUGHT A LENSE optomax 300 mm f5.5, with a sliding hood at the end...I put it on my Pentax ist DL but it seems that it's not working.. DO I have to set up the aperture. the shutter is not functioning everytim I use this lense. Pls. Help Thanks.

Make sure the aperture ring is set to the "A" position. If the lens doesn't have an auto aperture setting then I don't think the lens will work. There is a setting called "Using Aperture Ring" that you can setup using the menu and configuration that can be set to "Permitted" that will allow you to take pictures even if the aperture ring is not set on "A", but not sure how well this work for you, but should allow the shutter to work.

This is a good quality all metal/glass Japanese made Optomax 300mm f5.5 lens with M42 to Canon EF/EOS adapter. Length: 250mm, diam: 67mm, weght: approx 600g. A tripod mount is attached to this lens.
This lens is in excellent condition both cosmetically and optically. There are no marks or defects on the glass and no dust as far as I can see. The focussing is smooth and the aperture ring is nice and clicky.
It is supplied with M42 to Canon EF/EOS adapter which allows use with any current Canon DSLR camera. With adapter in place it focusses from approx 3m to infinity.
I have used this lens with a Canon 400D and the results are VERY SHARP when stopped down to f8 or f11. The procedure is very simple: focus wide open, stop down, take a speed reading on Av mode and transfer same reading to manual (M) mode and press the shutter button. Any slight over/under exposure can be dealt with using the camera software. You will get good results with this lightweight lens!
This lens will cost a tiny fraction of the latest Canon 300mm f4 L lens which has AF and IS (both of which eventually break down!!)