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Paul G Hammond
29-Jun-2020, 15:29
Hi LFPF,

This is my first post so I hope everyone is well in this strange period of time.

I own a tailboard camera and have been hitting the wet plate process hard since we have been in lockdown in the UK. My camera can shoot 14" x 14" but I mainly shoot whole plate for ease and cost. I recently purchased a FRANKE & HEIDECKE Heidosmat 1:3/ 250 as I wanted to experiment with a faster lens for portraits as my flash wasn't powerful enough with my other lens.

So my question is why would there be a discrepancy between the focus on the ground glass and the image plate?

My work flow has been:

Focus the ground glass so the eyes are tack sharp (I use a mannequin head for practising as it doesn't move). I remove the ground glass and replace with the darkslide and shoot the plate. After development and fixing the plate the image is out of focus on the eyes.
I have worked out that the focus at this point is 5mm forward (part of the neck is in focus), so it seems that I need to pull the focus back by 5mm after I have focused on the eyes to get a sharp plate.

I have tested that distance between the front of the camera to the ground glass and them the distance to the plate and they are the same.

I know that Wet Plate sees light differently so could it be this? Or is it the lens? I can't work out why the image is sharp when focusing and out of focus when shooting.

If anyone can help me understand what's going that would be great..

Thanks in advance

Paul

Two23
29-Jun-2020, 15:52
Try this: Focus on a sharp point, remove lens and then stick a rod straight back through the opening all the way to the ground glass. Mark the distance from the GG to the front edge of the lens board. Replace GG with an opened holder that has a tin (or glass plate) in it. Do the same thing--stick a rod all the way through and mark/measure the difference. It should be the same. This is called "checking the register."


Kent in SD

Bill Rolph
29-Jun-2020, 15:53
Are you stopping down after focusing? Closing the aperture can induce focus shifts, particularly with certain lens designs.

goamules
29-Jun-2020, 17:49
This is a projector lens. Have you shot any film with this lens? There is no telling how corrected this projector lens is for photography at all. I'd say that is your main problem, not wetplate, and not the registry of the film plane to the ground glass. All those things are made to be perfect for photography. Your projector lens is not.

Paul G Hammond
30-Jun-2020, 00:19
Hi thanks for the quick replies.
Yes, I knew it was a projection lens when purchased, but it was fast and cheap and I hoped would do the job for messing around with trying to reduce the amount of power needed. I've already checked the register and this is pretty much perfect.

Can you advise why the image is sharp on the ground glass, but is out by 5mm when developed? That's the confusing part for me.

Thanks for any information.

Ron_in_Alaska
30-Jun-2020, 03:52
It's all about the type of light you need to make wet plate work. UV focuses at a different point than the light used in a projector. I had to reposition my lens after it was focused to fix the problem. By measuring the distance difference you could make a special plate holder just for that lens. I never went that far.

Bill Rolph
30-Jun-2020, 10:18
If the focus shift is due to chromatic abberation, you could try focusing with a blue filter over the lens. Collodion processes, depending on the combination of halides used, are sensitive from 380 to roughly 520nm, with the maximum sensitivity at about 430nm. A #47 filter over the lens will isolate this band for focusing.

Two23
30-Jun-2020, 13:17
If the focus shift is due to chromatic abberation, you could try focusing with a blue filter over the lens. Collodion processes, depending on the combination of halides used, are sensitive from 380 to roughly 520nm, with the maximum sensitivity at about 430nm. A #47 filter over the lens will isolate this band for focusing.

Neat idea. I had also thought of figuring out how far the focus is off and making a permanent shim.


Kent in SD

michael_los_angeles_photo
30-Jun-2020, 15:04
If you have not, look up the concept of “chemical focus.” Here is something I found quickly...dealing with Daguerreotypes, but in the end the same idea. Some lenses of course suffer from it more than others — not many, I believe, especially among comparatively recent ones, but ... it could conceivably be an issue, especially with such shallow dof? (Btw, I have shot wet plate for several years now and am not at all an expert when it comes to this, but I have heard it mentioned quite a few times. I myself have never experienced it, or at least noticed it if present.)

“Light in the blue-violet wavelength range of the spectrum affected daguerreotype plates singly-sensitized with iodide more and sooner than light of other colors (wavelengths). The light rays toward the violet end of the spectrum which had this greater intensity of photographic effect were referred to as the CHEMICAL RAYS of light. The spot at which the lens focused blue-violet light was known as the point of CHEMICAL FOCUS. Light rays much closer to the red end of the spectrum exerted the greatest action on the retina of the human eye, and such rays were referred to as the LUMINOUS RAYS of light.. The point at which the lens focused them on the daguerreian plate became known as the VISUAL FOCUS or LUMINOUS FOCUS.

Most early operators, unaware of these principles, logically focused lenses by sight at the visual focus. This effectively missed the point of clearest focus for the daguerreotype which was at the chemical focus.”

(From: http://www.historybroker.com/light/web/gloss.htm)

goamules
30-Jun-2020, 16:26
That's exactly what the problem is, chemical focus. If you shot on film, it would be more in focus, but still have some "softness" from parts to the spectrum that it's not handling well. Even Petzvals were not very corrected until Lerebours optimized the formula. Wetplaters had to focus, then slightly move the focus to make a plate that was actually sharp. I'm sure a projector lens didn't worry about all that.

Mark Sawyer
30-Jun-2020, 19:03
Neat idea. I had also thought of figuring out how far the focus is off and making a permanent shim.


The amount it is off by will vary with different focusing distances.

Paul G Hammond
1-Jul-2020, 00:45
Wow, thanks Ron, Bill, Michael, Goamules & Two23.

This amount of information is amazing, I tip my hat to you all. It's great that it all layers upon itself to describe what I've been suffering and confused with.


The amount it is off by will vary with different focusing distances.

This was going to be my next question as a quick fix, but it make senses that this would change depending on focusing distances. I will look to invest in a #47 filter to focus through and see if this helps.

Wet Plate photography isn't as popular in the UK as it is in the USA so it is wonderful to reach out and receive solutions from you all.

Thanks again.

goamules
2-Jul-2020, 05:31
Talk to John Brewer in Manchester. He's a pro. Tell him Garrett sent you!

rjbuzzclick
2-Jul-2020, 09:24
Just another idea-Check to make sure that your ground glass is installed correctly, with the ground side facing the lens.

paulbarden
2-Jul-2020, 10:31
Maybe I've just been lucky, but I have not had issues like this with my Petzval lenses. WYSIWYG is how they've worked for me.

Mark Sawyer
2-Jul-2020, 11:53
Maybe I've just been lucky, but I have not had issues like this with my Petzval lenses. WYSIWYG is how they've worked for me.

Collodion is relatively close to the visible range, from well into the visible blue to the near-visible-UV. Camera lenses made after around 1850, including Petzvals, were pretty well corrected for it, but there's no reason for projector lenses to be corrected for it. Those are meant to be used only in visible light.