macro lenses and reverse adaptor

two questions for you, first what measurements should i look for in a macro lens, and how do i use a reverse adaptor? i have a 50mm reverse adaptor, it isnt for screwthreads, as i have a seperate one for that.

Hi,
The purpose of a reverse adapter is to use when you are taking photos at lifesize or greater as this gives a better lightpath through the lens. You will not get this sort of magnification even with a true macro lens unless you are using rings or bellows. The 50 and 100mm Macro lenses give about half lifesize on their own. This is often referred to as 1:2.

So called zoom macro lenses will only give you about 1:4 or 1/4 life size. If you need greater than this, I wouldn't use tubes on them as they are not up to it but rather use a proper macro lens. It really depends on what you are trying to photograph!

The reverse adapter you have should either be 49mm or 52mm. This refers to the filter thread of the lens and as far as I am aware there aren't any lenses with a 50mm filter thread. If you go greater than lifesize, the adapter fits onto the rings or bellows in place of the lens and the lens is then screwed into it by the filter thread. You then have to use the lens in a stop down mode. Ifyou are going to be doing any real photography in this sort of area, I would get a decent bellows set. The Pentax auto bellows allows you to reverse the lens and still retain the ability to stop down using a double cable release. If you go to my website, www.pentax-manuals.com, you will be able to download the manual for the bellows unit and this should explain it more.

Regards
Kim

Kim

Just a minor correction to Kim's post:
The Pentax 50mm/f2.8 and 100mm/f2.8 are 1:1 (lifesize) macro lenses. That's one reason they're so expensive!
The Pentax 100mm/f3.5 (made by Cosina, I think) is 1:2.

Just to add another option - it is possible to mount a second lens back to front onto a main lens. (ie coupling two lenses together at the filter end and mounting them as one on the camera.) You can get amazing results, but often with lots of vignetting. SRB-Film (www.srbfilm.co.uk) sell the appropriate adaptors.

I've tried most macro methods: close up filters, extension tubes, zoom macro, real macro, extension tubes+macro lens, even 1.7xAF+extensions+macro lens. They all give different results and quality. However, my favourite is the genuine macro lens - doubles up as a super sharp portraiture lens

Hope that helps.
Matt

Hi,
Sorry about that, I still use the MF Macros. All the 50's and the 100/4's were (and I suppose still are) 1:2 lenses unless you used one of the extension tubes. If memory serves me correctly, you need the number 3 tube for the 50 and the 50mm tube for the 100 to get lifesize.

Kim