Mirror lenses (2)

anthills wrote: I've been doing some testing of the Vectis 400 and Minolta/Sony AF 50 I haven't MTF-tested a lot of comparable lenses yet, so I can't really report how this compares to any of the dozens of other 400-500-600mm mirror lenses someone interested in these two might also consider. I do other types of testing, though, and subjectively I believe these are in the top of the class.

I've tested quite a few mirror lenses, some of them with line-pairs. However I've never been able (or willing) to produce actual MTF curves, being more interested in whether a given amount of detail can be recovered, eg in birds feathers.
The biggest problem with mirror lenses is that the hole in the middle lowers the contrast at medium MTF which makes images look flat, but the resolution is often very good. The Paragon 300mm, Kenko 400, and Tamron 500mm lenses were the best I'd tested until I got a copy of the Minolta 500mm reflex, which beats them all (just) for recoverable detail (lp/mm after processing) at a given object distance (not how lenses are normally tested, I know).
I tend to use mirror lenses to photograph the moon and the Reflex is the easiest to get good results with.

I think it's well worth considering that with digital cameras it no longer makes sense to worry very much about the MTF curve of the lens itself but what you can get from it with processing, which is very heavily dependent on the camera and sensor used and a lot of other things. Go back and read MTF measurements from older lenses taken on Nikon 6 - 12Mp cameras, for example, and you'll find modern kit zooms can do a lot better! With the A7R series, even old lenses can achieve amazing detail due to the system MTF being so much higher.

Edited by Miranda F - 30 October 2022 at 20:16

Taken at Manor Park in Glossop , Derbyshire .
Taken with the Minolta Vectis on a Sony a7Riv with the new AF Monster adapter LA-VE2 .
Turned out the problems I was having with this lens and the adapter in general was partly resolved by going into the settings on the camera , ont format , and then Initialise .
The other reason I was having a problem was the rear light baffle was doing anything other than that . It had a gloss finish , so was causing flare and light scatter , reducing contrast and confusing the AF .
These were taken before I fixed this with manual focus .

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Fuchsia by Neil , on Flickr


Autumn Rose by Neil , on Flickr


Goose ? by Neil
, on Flickr

These are a couple taken today as test shots after I've changed the rear baffle .
AF is spot on now and the flares gone .
Camera used is the Sony a6600 .


Autumn Leaves #1 by Neil , on Flickr

Wow! Amazing pictures, Brownie, and thanks for sharing them!
It's certainly an inspiration - I've never thought of using the Reflex for that; I shall have to try it myself!

Thanks gents! I figured you couldn’t have much more fun than an AF Reflex. What’s weird is the distance I shot those from. I think you could use it for street photography and shoot from the next block!

@Howard_S, that second shot is definitely spooky!

neilt3 wrote: These are a couple taken today as test shots after I've changed the rear baffle . AF is spot on now and the flares gone.

neilt3, I’d be interested to hear more about how you modified the baffle on the Vectis 400. Was there a problem on your specific copy, or do you think all copies are similarly impaired?

anthills wrote: neilt3, I’d be interested to hear more about how you modified the baffle on the Vectis 400. Was there a problem on your specific copy, or do you think all copies are similarly impaired?

Erm , well , how can I put this ....
It wasn't Minolta messed my lens up , it was me !

I've had another look at the baffle , and had a look at the ones on all my other Vectis lenses ( I've got at least a couple of dozen ) and I realise what's happened .
A few years ago I had a look at altering the baffle to trim it to cut down on the cut-off / vignetting on a full frame sensor .
Turns out what I'd done ( and forgot about ) was rather than chop up the original baffle , I took one out of a 22-80mm lens that was faulty and chopped bits off that rather than cutting up the original .

The issue with the lens and baffle is that the baffle is needed to hold the electronic contacts , so has to stay . When you focus closer (IIRC) the rear lens element recedes up the barrel and as the baffles are basically a tube , this is what causes the problem .
The rear element of the 22-80mm doesn't recess anywhere near as much as the 400mm , that's why the tube isn't flocked .

Regarding a fix , I'll sand down the tube so it doesn't reflect the light and that'll sort it , though I'll still have the original baffle somewhere .

The pelican shots are amazing!