Slide holding for Scanning - Ohnar and Other Options

I'm having another attempt to digitise my collection of Kodachromes. I've tried two flatbed scanners in the past and an OpticFilm scanner but have always found that the results take a lot of effort and lack the dynamic range to capture what I can see with my own eyes on the slide.

The current project will use my Canon crop frame DSLR. By googling and trial and error I have arrived at an optical setup using a BPM bellows unit and an 80mm enlarger lens. Initial tests with this setup and using bracketed exposures and HDR have been very promising.

Now I need to turn my table top lash up into something that will be easier to use for repetitive work. I fully expect some DIY design and build and creative upcycling of 35mm kit. The current question is how to hold the slides.

I think I've ruled out the BPM holder. I have two of these. One is less dirty than the other but they don't seem designed to allow cleaning of the side facing the slide. Getting the slide out after use is also awkward.

I've also ruled out the holder from the OpticFilm - I was always nervous about damaging slides when using this because the springs seem too stiff

I've also bought an Ohnar duplicator from eBay. It isn't the right model for the crop sensor but the slide holder seems less awful than the other options. At least I can get slides in and out without too much risk of damaging them or dropping them.

It does puzzle me though... why are there two slots (pic below) ? The rear one seems designed for some sort of sliding frame but mine did not come with anything to go in here. How can two slots work with fixed focus optics anyway?

Any other ideas for reasonably priced slide holding options?

Just one point: the opal plastic or glass should be about an inch (or more) behind the slide, to be sure that no dust on it is in focus.

In most holders it is much too close.

Don Cox

I use a ChromaPro, which is a slide duplicator from the film era. It has an excellent holder for the slides.

It's all painted black, so I lightened the photo considerably, which shows all the dust.

There are two metal blocks, each with a V groove which holds the slide. The left one is fixed, while the right one has two slots so it can move to let you insert the slide. The two springs hold the right hand block firmly against the slide.

The big advantage of this holder is that the slides stay in focus even with different mounts.

Perhaps if you are handy you cam make something along these lines. In the ChromaPro it sits on top of a light box, with the camera looking down.

Don Cox

Check out this post for a good way to hold the camera. I see he is using a slde carrier from a Beseler 45 enlarger.

https://discuss.pixls.us/t/diy-copy-stand-for-dslr-scanning/14833

Don

Halina3000 wrote:

Thanks Ernst. Nice setup. I don't have a history of using enlargers and therefore nothing of that sort tucked away in a cupboard so for me the bellows seemed like less 'stuff' to find a home for when not in use.

TBH a set of BPM bellows came up on eBay and it was a bit of an impulse buy but it got me started experimenting with different lenses from my old 35mm camera and figuring out what other bits I was going to need.

A BPM bellows is a very good thing to have, especially if you can build up a collection of the various lens and camera mounts. I find the M39 Leica thread ones (both male and female) the most useful. An M39 adapter on the camera is the shortest and helps you to get infinity focus. At the front end, an M39 ring accepts enlarger lenses.

The 'maker' rail systems are interesting - I was considering a setup with some longer rails covering the full length from the light source to the camera but then decided that I could go ahead and make something using bits of aluminium that I had left over from other projects. The 'stuff' already in my house does include some small machine tools so it would have been rude not to use them.

Don Cox

D Cox wrote:

Halina3000 wrote:

Thanks Ernst. Nice setup. I don't have a history of using enlargers and therefore nothing of that sort tucked away in a cupboard so for me the bellows seemed like less 'stuff' to find a home for when not in use.

TBH a set of BPM bellows came up on eBay and it was a bit of an impulse buy but it got me started experimenting with different lenses from my old 35mm camera and figuring out what other bits I was going to need.

A BPM bellows is a very good thing to have, especially if you can build up a collection of the various lens and camera mounts. I find the M39 Leica thread ones (both male and female) the most useful. An M39 adapter on the camera is the shortest and helps you to get infinity focus. At the front end, an M39 ring accepts enlarger lenses.

Don Cox

I fully agree, I find it bizarre that it's often cheaper to buy a new set of bellows for the pair of adapters than to but the adapters alone! I think I now have 3 sets of BPM bellows because of this.

Some of my other bellows take similar style end fittings, but of course they're a different size (and very rarely seen). I actually prefer my double extension bellows so have been debating making up some adapters to fit BPM ends to this.

First class work. I am much impressed.

Don Cox

Halina3000 wrote:

I've bought a bigger opal panel but at the moment I'm still using the opal screen from the Ohnar copier behind the slide. Making some less 'bodged' arrangements (than chopped up cerial boxes) to block stray light is still on the 'to do' list.

Several of the classic bellows units with slide copiers used a second bellows between the lens and slide holder for this.

very nice work with your DIY brass holder !

Sorry to be so late commenting about the lens.

There are several reasons why your old enlarger lens may produce less good results than other options.

- a basic minor issue is that the focal length of 80mm is a bit long, requiring quite a bit of bellows extension. This is slightly inconvenient. A focal length of 40-60mm would give a correspondingly shorter setup. In my dpreview tech album you can find several images from my explorations on camera slide digitizing: this or that .

- another issue may be with the sharpness of the enlarger lens.  I stems from film time, when a circle of confusion of 1/30 mm was considered sharp enough for DoF considerations. Also the f/4 enlarger lenses were typically Gauss type designs with 4 lenses in two groups, while f/2.8 were produced as higher corrected designs with 6 lenses in 4 groups.

- and an 80mm enlarger lens may be designed for a magnification range of 3-8x or similar, while slide copying is at 1x or 1:1.6x for the APS-C crop camera.

- photographic close-up lenses are typically designed to cover magnification ratios up to 1:1. Older lenses can be quite good and come very cheap. Newer lenses may be better than really needed. Do not ignore that modern, internal focus, lenses should be mounted directly on the camera. They would be outside their design specifications when mounted with about 50mm extension on a bellows.

Halina3000 wrote:

Thanks for the comments.

I did some testing with lenses from my old Minolta SLR before buying the secondhand enlarger lens. With a 50mm prime or 28mm plus a x2 teleconverter and the BPM bellows I could not get the whole of the slide onto the sensor. I think I calculated that 70mm would be somewhere near the minimum. My test with my old 80-205 zoom seemed to confirm this but that is a stupidly big lens compared to the bellows. Some articles about digitising slides suggest that enlarger lenses are a better bet so I ended up buying a secondhand 80mm. It's a Rodagon P.

I don't have anything suitable in terms of DSLR lenses BTW.

I would not be against owning something like a macro prime that can do the job but I'm not in the market (i.e. price range) for a new Canon one so I'd probably be looking at something older and manual... perhaps from Nikon that can also use a glassless adapter on the EF mount (MD lenses can't do infinity). I did look for one but nothing compelling presented itself before I bought the enlarger lens.

Resolution and sharpness-wise my results seem very similar to my OpticFilm scanner when zoomed to 1:1. Maybe there is more fine detail that I am not getting out of the slides... probably not in the older 80% because the cameras and lenses were pretty so-so (see my forum handle) but possibly so in my later films when I was getting paid and could afford a Minolta SLR. Trouble is I mostly used print film with the Minolta so there are not very many slides from it.

Getting the entire slide onto the sensor is purely a matter of the relative spacing of slide(subject), lens & sensor. With subject & sensor both two focal distances from the lens you will get 1:1 images - irrespective of what value the focal distance is. 35 mm slides on a FF sensor would fill the frame well at this magnification. If the sensor size is smaller than the slide the relative distance form slide to lens will need to increase & lens sensor distance will need to be adjusted appropriately for focus.

As a quick guide the thin lens formula can be used:

1/focal length = 1/image distance + 1/subject distance

With real lenses the position needed for these measurements are at the lenses entrance & exit principle planes. These are sadly not very obvious (and not always even within the lens dimensions) so some variation around calculated values is needed.