500c/m & CF39 - Focus & maybe Shim advice

[HenryFool]

Hi I have a relatively new to me 500/cm and CF39 (which came from B23) I had run 5 or 6 rolls of film through this the camera prior to getting the CF39 and on portraits or close up still life shots I found I was missing focus but landscape or infinity shots were perfect, I put this down to a learning curve having used a Rolleiflex TLR and rangefinders for years.

When I received the CF39 I noticed quite quickly that my close up images were back focused so I sent my 500c/m and 80mm to my local Hasselblad technician who realigned the mirrors, squared up the body, CLA'd the lens etc.

Now with the CF39 the close focus is certainly much improved but I'm still missing critical focus. e.g. if I'm shooting a portrait and I focus on the eye it still looks like I'm getting a little bit of back focusing - this is with both my 80mm and 150mm lenses, an acute matte split screen and both WLF or 45 Degree Prism.

This leads me to question whether maybe I need to shim the CF39 or the Acute Matte screen and would really appreciate some advice from anyone who has experience of this - or any other recommendations?

I should also mention that for any tests I'm using a tripod and shooting tethered - which by the way is also a new experience for me, it's amazing that you can plug a cable into a 2008 digital back on a camera made in 1982 into a 2020 MacBook, open Phocus and it just works (and syncs with Phocus mobile on the iPad!).

Sorry, I digress - has anyone shimmed a CF back back in the day or in recent memory? what did you use? did you shim the focussing screen or the CF? - I have not removed the iApdater - is this straight forward or are there any pointers here too?

Thanks 😊

[Bashir Lunat]

Hi, Iwont recommend shimming. Here are a couple of discussion threads addressing similar topics.
https://forum.luminous-landscape.com/index.php?topic=58274.0
https://www.photo.net/discuss/threads/hasselblad-digital-back-with-back-focus-problem.403311/

[HenryFool]

Thanks Bashir - why would you not recommend shimming? are there potential issues that I might be unaware of?

I'm thinking of trying a makeshift shim using some layers of 120 film under the focus screen for starters and a seeing if there is any difference... I'd be really interested in hearing if anyone has done similar?

[HenryFool]

Thanks Dicky - I have the NC2 45 degree prism which I believe has 3x magnification and I definitely prefer to use this with the CF39, I don't see any visible wear on the adapter - i actually got the CF39 refurbished from B23 so I'm also pretty confident that the IR filter is the latest... the only thing that is making me wonder is whether moving the screen or the back a few microns will make any difference 🧐

[HenryFool]

Thanks Dicky - I had seen that, I think that's what got me thinking about the shim route in the first place
I think I'll mail Jimmy in B23 and ask his advice before I do anything.

[HenryFool]

I just had the 500cm serviced and the mirror realigned so I don't think it's that, I've just put one roll of Portra through and I was pretty happy with how they came out, but I wasn't shooting scientific test shots to check focus

I'll have to try to meet up with a friend who also shoots with a 500 series and check the CF39 on his camera and that'll help narrow down a few of my questions.

[NickT]

Hi Henry
I shimmed two of my backs over the years and it worked a treat after a fair bit of trial and error.

I used stack of thin plastic, (about the weight of the plastic of say a windex bottle).

Obviously be very careful working that close to the sensor but once I got mine right (On a freshly serviced 503CW) it worked a treat.

[HenryFool]

That's really interesting Nick, tell me - where did you put the shims? I have a CF39 with the Hasselblad V iAdapter, in this case would you take off the adapter and shim between the back and the adapter?

[NickT]

That's really interesting Nick, tell me - where did you put the shims? I have a CF39 with the Hasselblad V iAdapter, in this case would you take off the adapter and shim between the back and the adapter?

Yes that's exactly it.

[Bashir Lunat]

Hi Nick, Are you able to upload a photo showing how you did it? Thanks.

[NickT]

Hi Bashir
I've since sold the back I shimmed but here's a demo using an old 384 (16MP Multishot AKA paperweight), and yes the sensor needs a clean....


You can see I'm removed the 4 Torx screws holding the adaptor plate on.

The plastic strips go between plate and body (making sure to allow for contacts and Torx screws, that's it!

[HenryFool]

UPDATE - Success story! 

OK based on what I had read I did a few tests, firstly I tried making some plastic shims for under the focus screen - this didn't work out too well and felt very trial and error so I didn't spend any more time at this. I tried to source some shims that would fit the CF39 but could not find any, so I bought 2 gauge tools on Amazon (€4 each) so I would have proper metal components to work with. I took off the iAdapter and put in the 0.50mm leaves from the gauge tool at the top and bottom, screwed the iAdapter back on and took some test photos tethered to my MacBook and now the photos were focussing in front of what I was seeing as being in focus through the viewfinder, I repeated the process with the 0.25mm leaves which for some reason are brass instead of steel like all the others, tested it again and it was 100% accurate, I took out the shims, drilled a hole at the end of both and so that I could keep them in place with the iAdapter screws and that's it - perfect focus!

I'll add a few photos in case it helps anyone else - just look at my Frankenstein camera with its new brass plates! LOL

[NickT]

Krug would have been better but I'll settle with Bolly.

[Alex]

Brilliant 👍 Henry!