Petzval double take

[Charles Twist]

I have recently acquired a Petzval lens. It's a lot of fun in a LF way, and I have stumbled upon something which I haven't seen described elsewhere. In occasional pictures, I am getting a secondary image, as in:



LH pic: the problem; RH pic: the correct exposure.

Closer up of the LH pic:



It's always in part of the picture and I am wondering if it's due to the shuttering method I use - ie a piece of card moved in front of the lens. It could be that the card flexes and lifts slightly, while I am struggling to put the dark slide back. Then a significant amount of light might hit the front glass at a very wide angle to form a secondary image which is not normally visible.
Does anyone have any other explanations? Or noticed this? It would be good to be reliably consistent.
Apparently there was an article on the physics of Petzval lenses in AP not so long ago. Anyone have a copy or a reference?
Thank you,
Charles

[Marizu]

Looks like tripod wobble (forward and back) to me.
I'm guessing that you're shuttering vertically and knocking the lens which is making it shake.
I've done this on Petzvals before.

I usually shoot wet plate with mine so I don't tend to have exposure times less than 3 seconds which makes things easier.
I have recently shot some Efke IR film with it using an R72 and flash, though.

[Charles Twist]

Hello Marizu,
How would that affect only part of the image? Maybe by hitting the lens as the card travels. It would have to be a fast, large bounce. I think I would have noticed and I am careful to avoid contact. I have quite a sturdy set-up, but I don't deny I do wobble some pictures. However the amplitude of the wobble is seldom as great as in this picture and is most commonly only visible with a lupe. Do you reckon that the centre of the lens being forward of the front standard's axis of rotation would give that kind of wobble with a minor nudge?
I'll think some more about your suggestion in case it leads anywhere...
Thanks,
Charles

[timparkin]

I have recently acquired a Petzval lens. It's a lot of fun in a LF way, and I have stumbled upon something which I haven't seen described elsewhere. In occasional pictures, I am getting a secondary image, as in:

Looks like a lens has 'tilted' because the centre of the image shows no offset. I would imagine that the lens weight has caused the front standard to 'droop' which would leave the centre line alone but shift the bottom of the picture up and cause it to be out of focus.

Does that sounds possible?

Tim

[Marizu]

I hadn't noticed that it was only the bottom part of the image that was ghosted but the nature of that ghosted part is commensurate with my experiences of a rocking tripod.
From the image I can't see whether the ghosting gets bigger the further down the film you get or whether the amplitude of it remains the same but the ghosted density increases towards the bottom.

I'm curious what kind of shutter speed you are attempting. It might be worth videoing yourself to help locate any potential shutter technique issues.

Good luck!