[rollei_list] Re: Rollei 35 mm SLR Flange focal distance
- From: Richard Urmonas <richard@xxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Tue, 9 Sep 2014 19:51:06 -0700
Hello Dirk,
The maker of your digital camera will already have positioned the
sensor at the optimum point to match the Canon lens mount. Thus you do
not have to worry about this dimension, just the additional thickness
to convert from Canon to QBM.
I think the +/- 0.15mm tolerance you specify is not a difficult one to
meet, and you could easily tighen this to +/- 0.1mm, and it would not
be hard to find someone to machine the part to better than this. It
will of course become more expensive to improve the accuracy.
The effect of such a variation can be estimated by using simple lens
formulae (as if the lens was a single element of the correct FL).
Taking +/- 0.1mm and a 28mm lens as an example. At one end
(0.1mm more too thick) infinity focus will be sharp for a target at
7.84m and at the other end (0.1mm too thin)you will need to focus at
7.84m for a target at infinity.
If you improve the tolerance to +/- 0.05mm at one end infinity focus
will be sharp for a target at 15.68m, and at the other end you will
focus to 15.68m for an object at infinity.
One idea you could consider is to machine the part to be slightly thick
(+0.1 / -0 mm) and then use very fine sandpaper on a flat surface (like
a thick piece of glass) to trim the thickness to the correct dimension.
Note that the thickness will have the most effect on focus for wide
lenses.
I hope this helps
Richard
On Tue, 9 Sep 2014 20:59:45 +0000
<Dirk-Roger.Schmitt@xxxxxx> wrote:
> Hello,
>
> thanks for all of your help.
> The reason for my inquiry is the following:
>
> I run a "research programme" to adapt all my Rolleinar and Zeiss
> lenses from the SL35 system to my Kodak DCS Pro SLR/c. This is a nice
> camera designed by Kodak with a full frame digital chip which was
> designed and made at Fillfactory in Belgium. The camera has a Canon
> mount, however the body was made by Sigma. So it is an US/Japanese
> camera with a European sensor. Very exotic.
>
> So I got an QBM to Canon adapter from Ebay.
> Available data where: Focal flange distance Canon EF mount: 44.00 mm.
> The same for QBM 44.70 mm.
> These data have been published for a long time everywhere, including
> Wikipedia. I got the China made adapter.
> I did not achieve infinity with my lenses. What was the reason?
> I measured the thickness of the adapter to 0.67 mm. So everything
> should be ok. Nevertheless it did not work. So I was working to find
> out how to adjust the camera or the flange focus distance of the
> camera. My guess was, it was too large. Just now I found out, that at
> the Wikipedia, they corrected the QBM 44.70 to 44.50, stating the
> 44.70 where wrong.
>
> What do I understand now? If this information is correct, the adapter
> is TOO thick. It has to have a thickness of max 0.50 mm to achieve
> infinity with my Zeiss lenses. I believe, the factory in China, which
> makes the QBM adapters, also did rely on the wrongly reported 44.70
> mm and manufactured the adapters accordingly wrong!
>
> Now I am going to trim the adapter to the difference, hence to say
> 0.50 mm. But what is the best thickness, to obtain best infinity
> adjustment with a digital sensor?
>
> 0,50 mm +0/-0.15 mm?
>
> Emanuel, do you think this a good value I could give to our workshop
> order?
>
> Or would digital sensors also need a certain "penetration" of the
> focal plane into the sensor?
>
>
> Best regards, and thanks a lot!
>
>
>
>
> Dirk-Roger Schmitt
>
---
Rollei List
- Post to rollei_list@xxxxxxxxxxxxx
- Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe'
in the subject field OR by logging into www.freelists.org
- Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with
'unsubscribe' in the subject field OR by logging into www.freelists.org
- Online, searchable archives are available at
//www.freelists.org/archives/rollei_list
Other related posts: