Re: Matching lenses (was: Re: HTML help)

[Joel Alpers <joel.alpers@xxxxxxxxxxx>]

Greg Erker wrote:
> 

> 
>   That's a great method for cameras
> with interchangable lenses. For my
> TLR's I have to shoot an awful lot of
> rolls of film to do this (or attempt
> to reroll one film a bunch of times
> and load it into the next camera.)

Yes, it really is for interchangeable lenses. I have done
stuff like this with TLR's but it is a pain unloading and
loading the next one in the dark.  Now, you could load
each of them in the dark, by cutting up a 120 roll into
pieces. You don't need to advance, as one shot does it.
Then tape the sections together for developing.

Of course, you need an MF projector, as the method relies
on projection to a large image to get the required accuracy.

 >   Using two points is fine as long
> as the lenses all have the same
> amount and type of distortion.
> Suppose your first lens has zero
> distortions and is exactly 50mm FL.
> The second one might be 2% shorter
> FL and have 2% barrel distortion
> that makes the two points come into
> alignment, fooling you into thinking
> the lenses match.

Excellent point! I hadn't thought of that. For now
I'll proably just hope it isn't a problem with my
mass-produced Pentax lenses, but you're right, it
could be an issue.

>   So, I think you can use this method
> to match up Pentax 50mm f2.0's with
> each other, but wouldn't try to match
> f2.0's with f1.7's or f1.4's or other
> mfgr's lenses (due to the different
> number of elements in the Pentax lenses
> and construction differences with
> other brands).

True, but I wonldn't want to match up different
models of lens anyway. In my test of 10, I had
6 f/2 lenses and 4 f/1.7 lenses, I treated them
as two separate "groups".

>   We discussed this before, but, for
> my TLR matching I'm going to use a
> test slide at the film plane of my
> cameras and us it to project the image
> on the wall by shining a light thru
> the back. The slide will lifted off
> the camera film rails by a thick piece
> of glass so that the image is in focus
> at a reasonable distance, rather than
> infinity.

True we did mention it before, but thanks for
bringing it up again, as we have a number of
new folks since that discussion...
 
[ snip ]


One drawback I didn't mention --- I now have 3 lens
matched pairs and four lenses that don't match well.
I can't re-use the results from this time, I have to
re-shoot those four when/if I want to try matching
with future lenses. Now, I suppose if I had put marks
on the deck where the tripod legs go, and measured
the height of the tripod when I had it set up.......

Joel.