I have done a search both on the forum and in Google and have a query as to the expected maximum aperture when using the front element only of a symmar covertable lens.
I realise that to get the converted value of the lens you remove the front element and use the rear element only for my 210/370mm f5.6/f12 symmar. But prior to knowing this I had removed the rear element and had a play but was surprised at the fact I was not receiving the focal length I was expecting. Since then I have been informed of the correct way to convert the lens but looking at the image on the ground glass and with an 8x lupe with just the rear element removed and it looks like a reasonably useable image (I would use for portraiture only). When focussed on infinity the length between the rear element and the ground glass is about 250mm (10"). Can I assume that the max aperture would be similar to that when using the rear element ie circa f12?