Absolutely agree with Matt's observations.

If you were copying documents, you might want to use a 50mm macro simply because the tripod would be getting uncomfortably high with a 100mm or longer lens.

It does really depend what you want to photograph.

Depth of field will be similar with all the lenses for a given subject, because although longer lenses will have less DOF you will be using them from further away, so the magnification will be the same.

I'm probably tempting fate mentioning DOF...

I think its safe to assume that any marque Macro lens, like the Pentax ones, will be superb. I would expect them to out-perform the Tamron or any other independent manufacturer, but in any event they are likely to match the cameras better as well.

The SMC Pentax-F would be an earlier autofocus lens.

If we are in the area, which is always possible, we will certainly call by.

Please accept our reciprocal invitation from ADAPS

www.adaps.org.uk

(Atherton & District Amateur Photographic Society - ADAPS is easier!)

The autofocus motor is in the camera body, so turning a helical thread on a huge telephoto would be unlikely to work. Instead, Internal Focusing is used, which shifts the position of a small number of lens elements - much easier.

For the pedantic, this does actually shift the focal length slightly as well.

The 85mm f1.9 was designed to be slightly soft at wide apertures for portraiture, sharpening up as it was stopped down. Some of the later versions were SMC coated. The f1.8 version is I think a slight redesign, possibly to make the lens sharp at all apertures which is the modern style for 85mm lenses.

There are various versions of the 105mm, but the Super Takumar version at least is superb, probably one of the best lenses in the range. The last examples made had SMC coatings.

The 120mm is another lens designed to be softer at open aperture, crisping up as stopped down. If it appeared at all as a screw thread version it was very late on as an SMC lens. I never liked the characteristics of this design, preferring my lenses to be as sharp as possible at all apertures.

If you have distance haze then a filter may well be necessary. Personally, I have never found the UV filter to be enough, preferring the Skylight or even an 81A with colour film. For black and white film then a red filter is the most effective, or the Infra-red one even more so if you are after special effects with IR film.

Digital is a different issue, as so much can be done post capture. What you can't do is cut through haze once it is recorded, so a filter may have a use there. Even if you eliminate the problem colours in channel mixer, the scattering of light generally will have caused some degradation, so better to eliminate it in the first place with a filter.

However, for general purposes I still think the principle of only using filters when necessary is the right one for me.

I totally agree with George - don't fit filters anless you need them photographically.

I know the arguments about protecting the lens are there, but how often have you damaged a filter? Never? Then that's how often, hopefully, you will damage a lens.

I think a lens hood is far more essential - it protects from flare and also protects to some degree from any physical damage.

Others may well disagree, and if so I'm sure they'll say why!

You would have to ensure the fill in does not overwhelm the ring flash. As these set ups are usually put together on one portable bracket arrangement, it is more usual to use a tiny pocket flash unit to add the modelling.

A ring flash allows even illumination at very close distances, essential for some subjects. However, the downside can be that the lighting will be very frontal and relatively flat, so for three dimensional subjects a small additional flash could be added to produce some modelling and a nice highlight.

The clasic example would be Dental Macro photography, where a ring flash illuminates the teeth but they look dead. The extra flash adds a nice highlight where one is expected/needed and this lifts the picture and gives a more vibrant result.

I've never seen a mirror lens with aperture settings on it, but if you have one then they must exist! You can test this by changing the setting and checking that the shutter speed varies in the way it should. I wonder if it is some sort of rotating ring with Waterhouse stops - that is, circular openings of the appropriate sizes.

As for the converter, why not just try it and see if it all fits together properly?

Have fun!